1. A kind of car gear box uses the gear steel, characterized by that: the weight percentages of the chemical components are respectively as follows: c: 0.19% -0.21%, Si: 0.23% -0.28%, Mn: 0.95% -0.98%, Cr: 1.08% -1.12%, Ti: 0.05% -0.07%, S: 0.028-0.035%, P is less than or equal to 0.015%, Als: 0.008 to 0.025 percent of manganese, less than or equal to 0.0035 percent of calcium, less than or equal to 0.05 percent of nickel, less than or equal to 0.05 percent of copper, less than or equal to 0.01 percent of molybdenum, less than or equal to 0.01 percent of residual element Sn, less than or equal to 0.005 percent of lead, less than or equal to 0.02 percent of arsenic, less than or equal to 0.008 percent of bismuth (Bi), less than or equal to 0.008 percent of antimony (Sb), 13 to 20ppm of total oxygen, less than or equal to 40ppm of total nitrogen, and the balance of Fe and inevitable impurities, wherein the manganese-sulfur ratio is between 27 and 35.

2. A control method of gear steel sulfide for an automobile gearbox comprises the working procedures of converter smelting, LF + RH refining, continuous casting, heating and rolling, and is characterized in that: in the continuous casting process, the chemical components of the continuous casting billet in percentage by weight are as follows: c: 0.19% -0.21%, Si: 0.23% -0.28%, Mn: 0.95% -0.98%, Cr: 1.08% -1.12%, Ti: 0.05% -0.07%, S: 0.028-0.035%, P is less than or equal to 0.015%, Als: 0.008 to 0.025 percent of manganese, less than or equal to 0.0035 percent of calcium, less than or equal to 0.05 percent of nickel, less than or equal to 0.05 percent of copper, less than or equal to 0.01 percent of molybdenum, less than or equal to 0.01 percent of residual element Sn, less than or equal to 0.005 percent of lead, less than or equal to 0.02 percent of arsenic, less than or equal to 0.008 percent of bismuth (Bi), less than or equal to 0.008 percent of antimony (Sb), 13 to 20ppm of total oxygen, less than or equal to 40ppm of total nitrogen, and the balance of Fe and inevitable impurities, wherein the manganese-sulfur ratio is between 27 and 35.

3. The method for controlling sulfide of steel for a gear used in an automobile transmission according to claim 2, wherein: in the LF refining process, high-alkalinity slag operation with alkalinity of 5-6 is adopted in the early stage of refining, aluminum wire feeding precipitation deoxidation is adopted in the refining process, calcium carbide diffusion deoxidation process is matched, slag operation with lower alkalinity of 1.5-2.5 is adopted in the later stage of refining, and soft blowing time is guaranteed to be longer than or equal to 10 minutes after calcium pretreatment;

the RH refining process adopts high vacuum and large circulation operation, the high vacuum time is maintained to be more than 5 minutes, a sulfur wire is fed at an interval time of more than or equal to 8 minutes after final calcium treatment, and the soft blowing time is controlled to be more than or equal to 10 minutes before leaving the station;

the whole process of the continuous casting process protects casting, and the tundish adopts high SiO with alkalinity of 1.0-1.5₂Covering agent, adopting crystallizer electric stirring and end electric stirring in the whole process, adopting an intercooling mode for secondary cooling of the casting blank, controlling the specific water quantity to be 0.55-0.60 and controlling the standard drawing speed to be 0.9 +/-0.05 m/min.

4. The method for controlling sulfide of steel for a gear used in an automobile transmission according to claim 2, wherein: the converter process controls the carbon-oxygen product at the blowing end point to be 0.0024% or below, the steel ladle is strictly forbidden to slag during tapping, and meanwhile, a high-alkalinity aluminum-containing modifier with the binary alkalinity of 5-6 is added to modify the steel ladle top slag.

5. A method of controlling sulfide of steel for a gear used in an automobile transmission according to claim 2 or 3, wherein: in the LF refining process, the binary alkalinity of final slag is controlled to be 1.5-2.5 by adding quartz in the later stage of refining, the Als content in molten steel is controlled to be 0.020-0.035wt% by calcium pretreatment before station leaving soft blowing, and the Ca content is more than or equal to 0.0010 wt%;

in the RH refining process, high vacuum and large circulation mean that the ultimate vacuum degree is less than or equal to 20Pa, final calcium treatment is carried out after the circulation finishes breaking vacuum, the content of Als is controlled to be 0.010-0.025wt%, the calcium-aluminum ratio is controlled to be 0.08-0.15, and the content of S is controlled to be 0.030 wt% -0.035wt% after sulfur wire feeding.

6. A method of controlling sulfide of steel for a gear used in an automobile transmission according to claim 2 or 3, wherein: in the continuous casting process, the electric stirring parameter of the crystallizer is 350 +/-10A/3 +/-0.5 Hz, and the electric stirring parameter of the tail end is 250 +/-10A/8 +/-0.5 Hz; the continuous casting secondary cooling is divided into 4 areas, and the setting proportion of secondary cooling water distribution in the areas 1 to 4 is 35: 21: 38: mode 6.

7. The method for controlling sulfide of steel for a gear used in an automobile transmission according to claim 2, wherein: in the heating process, the temperature of the soaking section is controlled to be 1220 +/-15 ℃, high-pressure water dephosphorization is carried out on the surface of the square billet after heating, then the square billet is rolled into a bar finished product, and the temperature is controlled to be 810-.

Background

The automobile gearbox is a core component of an automobile engine, and because the automobile gearbox gear is in service under the conditions of high rotating speed and high load and constantly alternating rotating speed and load, the surface of the gearbox gear is required to have high strength, high hardness and good wear resistance, the core part of the gear is required to have good obdurability, and meanwhile, the meshing precision of the gearbox gear is required to be high, the working noise is low, and the high precision and low noise are closely related to the cutting processing performance of gear steel, so that various gear steel production enterprises put a great deal of effort on improving the cutting performance of products.

With the increasing trend of high precision and high assembly property in the automobile industry, more rigorous requirements are correspondingly put forward on the cutting processing performance of the gear steel for the automobile. Under the large background of energy conservation and environmental protection in the world, the machining process after the direct cold forging of the hot-rolled gear round steel without hot forging is more and more emphasized, so that higher requirements are put forward on the cutting processing performance of the gear steel.

The machining performance of the gear steel is improved by adding elements such as lead, tellurium, sulfur and the like into the steel, and the sulfur is generally adopted as an easy-cutting element in China due to the environmental protection requirement and other reasons. The sulfur mainly exists in the steel in a MnS form, and the pure MnS is doped into a light black strip shape, so that the cutting processability of the steel can be improved by cutting off the continuity of a matrix; the sulfide inclusions are small in size, numerous in number and distributed in a dispersed mode, so that the sulfide inclusions can be effectively guaranteed to be in a low length-width ratio form after rolling, and the key point for improving the cutting performance of steel is realized. In addition, various calcium aluminates can be formed in the molten steel through calcium treatment, certain specific types of calcium aluminates can be used as effective nucleation cores of MnS in the solidification process, and the low deformability of the calcium aluminates is utilized to realize the low-aspect-ratio composite near-spindle-shaped MnS composite inclusions after rolling, and the composite sulfide inclusions can effectively improve the machining performance of the steel.

The control difficulty of sulfide in the gear steel for the automobile gearbox is mainly divided into two parts, namely, how to stabilize the yield of sulfur in molten steel, realize effective control of sulfur segregation in a casting blank under the condition of ensuring a proper manganese-sulfur ratio, and secondly, control of low aspect ratio and fine dispersion form of composite sulfide taking single sulfide or calcium aluminate as a core in the casting blank.

At present, much research is carried out at home and abroad on the aspects of controlling the form and the like of sulfides, and the precipitation of fine dispersion sulfides is closely related to various factors such as manganese-sulfur ratio, calcium treatment time selection, oxygen level before solidification, cooling rate in the solidification process and the like during component design. Factors influencing the form and precipitation of the sulfide are very complex, and the control difficulty of the production process is high.

Disclosure of Invention

The invention aims to solve the technical problems that the separation of sulfide in sulfur-containing gear steel is difficult to control and the cutting performance of a product is poor by improving the process.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

the gear steel for the automobile gearbox comprises the following chemical components in percentage by weight: c: 0.19% -0.21%, Si: 0.23% -0.28%, Mn: 0.95% -0.98%, Cr: 1.08% -1.12%, Ti: 0.05% -0.07%, S: 0.028-0.035%, P is less than or equal to 0.015%, Als: 0.008 to 0.025 percent of manganese, less than or equal to 0.0035 percent of calcium, less than or equal to 0.05 percent of nickel, less than or equal to 0.05 percent of copper, less than or equal to 0.01 percent of molybdenum, less than or equal to 0.01 percent of residual element Sn, less than or equal to 0.005 percent of lead, less than or equal to 0.02 percent of arsenic, less than or equal to 0.008 percent of bismuth (Bi), less than or equal to 0.008 percent of antimony (Sb), 13 to 20ppm of total oxygen, less than or equal to 40ppm of total nitrogen, and the balance of Fe and inevitable impurities, wherein the manganese-sulfur ratio is between 27 and 35.

A control method of gear steel sulfide for an automobile gearbox comprises the following working procedures of converter smelting, LF + RH refining, continuous casting, heating and rolling:

in the LF refining process, high-alkalinity slag operation with alkalinity of 5-6 is adopted in the early stage of refining, aluminum wire feeding precipitation deoxidation is adopted in the refining process, calcium carbide diffusion deoxidation process is matched, slag operation with lower alkalinity of 1.5-2.5 is adopted in the later stage of refining, and soft blowing time is guaranteed to be longer than or equal to 10 minutes after calcium pretreatment;

the RH refining process adopts high vacuum and large circulation operation, the high vacuum time is maintained to be more than 5 minutes, a sulfur wire is fed at an interval time of more than or equal to 8 minutes after final calcium treatment, and the soft blowing time is controlled to be more than or equal to 10 minutes before leaving the station;

the whole process of the continuous casting process protects casting, and the tundish adopts high SiO with alkalinity of 1.0-1.5₂Covering agent, adopting crystallizer electric stirring and end electric stirring in the whole process, adopting an intercooling mode for secondary cooling of the casting blank, controlling the specific water quantity to be 0.55-0.60 and controlling the standard drawing speed to be 0.9 +/-0.05 m/min.

According to the control method of the gear steel sulfide for the automobile gearbox, the converter process controls the carbon-oxygen deposition at the blowing end point to be 0.0024% or less, steel ladle slag tapping is strictly forbidden in the steel tapping process, and meanwhile, a high-alkalinity aluminum-containing modifier with the binary alkalinity of 5-6 is added to modify steel ladle top slag.

In the LF refining process, quartz is added in the later stage of refining to control the binary alkalinity of final slag to be 1.5-2.5, and pre-calcium treatment before station leaving soft blowing is used to control the content of Als in molten steel to be 0.020-0.035wt% and the content of Ca to be more than or equal to 0.0010 wt%.

In the RH refining process, high vacuum and large circulation mean that the ultimate vacuum degree is less than or equal to 20Pa, final calcium treatment is carried out after the circulation finishes breaking vacuum, the content of Als is controlled to be 0.010-0.025wt%, the calcium-aluminum ratio is controlled to be 0.08-0.15, and the content of S is controlled to be 0.030 wt% -0.035wt% after sulfur wire feeding.

In the continuous casting process, the crystallizer electric stirring parameter is 350 +/-10A/3 +/-0.5 Hz, the tail end electric stirring parameter is 250 +/-10A/8 +/-0.5 Hz, the segregation of sulfur in the continuous casting process is effectively improved, and the setting proportion of the secondary cooling water distribution in the 1-4 areas is 35: 21: 38: and in the 6 mode, the high water content is set in the 3 rd zone, so that the fine dispersion and precipitation of sulfide in the solid-liquid two-phase zone at the solidification front are effectively promoted.

In the heating process, the temperature of the soaking section is controlled to be 1220 +/-15 ℃, high-pressure water dephosphorization is carried out on the surface of the square billet after heating, then the square billet is rolled into a bar finished product, and the temperature is controlled to be 810-840 ℃ after finishing rolling.

After slow cooling, sampling and detecting sulfides, wherein the type of the sulfides is single manganese sulfide sulfides, the inner core is calcium aluminate, the outer layer is manganese sulfide composite sulfides, the length-width ratio is less than or equal to 5, the sulfides are in a dispersion distribution state, and the cutting processability of the gear steel for the automobile gearbox is effectively ensured.

According to the invention, the parameters of the refining link are set, firstly, the effective removal and control of oxygen in molten steel are ensured by high-alkalinity refining slag in the early stage of refining, quartz is added in the later stage to control the binary alkalinity of final slag to be 1.5-2.5, the sulfur content and yield in molten steel during subsequent sulfur wire feeding are stabilized under the condition of ensuring good deoxidation in the early stage, and the manganese-sulfur ratio is effectively realized within the design range; the interval between final calcium treatment and sulfur feeding line is 8 minutes, thus avoiding the generation of CaS by the combination of sulfur and calcium, further stabilizing the sulfur content in the molten steel, and controlling the calcium-aluminum ratio to be 0.08-0.15 when the refining is finished, so that the calcium aluminate in the molten steel is 3CaO. Al with low melting point₂O₃、12CaO.7Al₂O₃、CaO.Al₂O₃And the inclusions compounded by the solid phase are mainly used, and can be effectively used as nucleation cores for sulfide precipitation in the solidification process. The whole process of the continuous casting process protects the casting, and the high SiO with the alkalinity of 1.0-1.5 is adopted in the tundish₂The covering agent adopts crystallizer electric stirring and end electric stirring in the whole process, and the crystallizer adopts a weak cooling mode of 105 +/-2.5 cubic meters per hour to effectively avoid the characteristic that the titanium-containing sulfur-containing gear steel is easy to generate casting blank cracks when being solidified at a high-temperature section.

The invention relates to a gear steel for an automobile gearbox and a control method of sulfides of the gear steel, and the product standard refers to GB/T5216.

The free-cutting property of the gear steel is realized by mainly controlling the precipitation distribution and the form of sulfide, firstly, the sulfur content in a proper range and the manganese-sulfur ratio matched with the sulfur content are required to be confirmed during component design, and the precise control of the sulfur is mainly realized by low-alkalinity refining final slag, the matching degree of calcium treatment and sulfur adding time, the adding mode of the sulfur, and the adoption of a tundish low-alkalinity high-SiO₂The method is mainly characterized in that the control of manganese is achieved by stabilizing a converter loading system, adopting self-produced scrap steel to reduce the fluctuation of the steel output, perfecting an alloy weighing system, optimizing the metering precision of an LF refining process, reducing the oxygen potential of slag at the early stage of refining and the like, so that the narrow component control of the manganese content is realized, and the design requirement of the manganese-sulfur ratio is perfectly met.

Generally, the precipitation of sulfides is mainly caused byIn the process of molten steel solidification, when the equilibrium concentration product of manganese and sulfur reaches the limit requirement along with the reduction of temperature, the precipitation quantity and size of the manganese and sulfur spontaneously generate, and the precipitation quantity and size are directly related to the cooling rate, so that a higher water quantity is set at the position of a solidified mushy zone (a secondary cooling zone 3), and in consideration of the crack sensitivity of titanium-containing and sulfur-containing gear steel, a crystallizer adopts a 105 +/-2.5 cubic meter/hour weak cooling mode and a secondary cooling integral intercooling mode. The precipitation distribution is directly related to sulfur segregation among secondary dendrites, so that the improvement is carried out by adopting a double-electric stirring mode matched with electric stirring of a crystallizer and electric stirring at the tail end. Besides the single sulfide with large number of homogeneous nucleation and small size, the sulfide with low length-width ratio and fine dispersion utilizes the characteristic that calcium aluminate is not easy to deform, and the composite sulfide taking certain specific type of calcium aluminate as heterogeneous nucleation core is more beneficial to the distribution of the sulfide with low length-width ratio and fine dispersion after rolling. 3CaO. Al with low melting point as a whole₂O₃、12CaO.7Al₂O₃、CaO.Al₂O₃The inclusions compounded by the inclusions are taken as nucleation cores which can be effectively used for sulfide precipitation in the solidification process, the calcium-aluminum ratio in the molten steel is controlled to be in the range of 0.08-0.15 to be more beneficial to the precipitation of the calcium aluminate inclusions in the above types when the Als content is 0.010-0.025wt% calculated thermodynamically, in order to ensure the preferential precipitation of the calcium aluminate inclusions in the above types in the solidification stage, means such as increasing the Als content or reducing the oxygen level and the like are not deliberately adopted, on the basis of meeting the standard requirement that the GB/T5216 oxygen content is less than or equal to 20ppm, the oxygen content is controlled to be in the higher content level of 13-20ppm to be more beneficial to the effective precipitation of the calcium aluminate inclusions as sulfide heterogeneous nucleation points in the solidification process.

The invention has the beneficial effects that:

the gear steel produced by the invention has the structure of ferrite and pearlite, the product has the advantages of fine and dispersed distribution of sulfide, good cutting performance and the like, and gears for automobile gearboxes manufactured by downstream users have the characteristics of high machining precision, good matching property and the like.

Drawings

FIG. 1 is a photograph of the inclusion gold of the gear steel produced in example 1;

FIG. 2 is a photograph of the inclusion gold of the gear steel produced in example 1;

FIG. 3 is a photograph of the inclusion gold of the gear steel produced in example 1;

FIG. 4 is a photograph of the inclusion gold of the gear steel produced in example 1;

FIG. 5 is a photograph of the inclusion gold of the gear steel produced in example 1;

FIG. 6 is a photograph of the inclusion gold of the gear steel produced in example 1.

Detailed Description

The present invention will be described in further detail with reference to the following specific examples:

example 1

The specification of the gear steel bar for the automobile gearbox is phi 60mm, and the production method comprises the following steps: the process flows of converter smelting, LF + RH refining, continuous casting, heating and rolling.

The top-bottom combined blown converter adopts a bottom-blown large circular seam process, the converter process controls the carbon-oxygen deposition at the blowing end point to be 0.0024%, the steel ladle slag discharging is strictly controlled in the tapping process, meanwhile, an aluminum-containing modifier is added to modify the steel ladle top slag, and the binary alkalinity of the high-alkalinity aluminum-containing modifier is 5.

High-alkalinity slag operation is adopted in the early stage of LF process refining, binary alkalinity is controlled to be 5.3, an aluminum wire feeding precipitation deoxidation matched with a calcium carbide diffusion deoxidation process is adopted in the refining process, low-alkalinity slag operation is adopted in the later stage of refining, the final slag alkalinity is 2.2, the Als content and the Ca content in molten steel are controlled to be 0.021wt% and 0.0013wt% after calcium pretreatment, and the molten steel is discharged after soft blowing for 12 minutes.

The RH refining process adopts high vacuum large circulation operation, the ultimate vacuum degree is 16Pa, the high vacuum time is maintained at 5 minutes, the Als content is controlled at 0.016wt% after the final calcium treatment, the calcium-aluminum ratio is controlled at 0.09, the S content is controlled at 0.032 wt% after the sulfur feeding line, the sulfur feeding line is fed after the final calcium treatment interval time is 8 minutes, and the soft blowing time is controlled for 15 minutes before leaving the station, and then leaving the station.

The whole process of the continuous casting process protects casting, and the tundish adopts SiO with alkalinity of 1.5₂The 36 percent covering agent is electrically stirred and electrically stirred at the tail end of a crystallizer in the whole process, the crystallizer adopts a weak cooling mode of 105 cubic meters per hour, secondary cooling adopts an intermediate cooling mode, the specific water amount is set to be 0.60, the standard drawing speed is 0.9 meter per minute,the crystallizer electric stirring parameter is 350 +/-10A/3 +/-0.5 Hz, the end electric stirring parameter is 250 +/-10A/8 +/-0.5 Hz, the secondary cooling is divided into 4 areas, and the secondary cooling water distribution setting proportion of the 1-4 areas is 35: 21: 38: and in the 6 mode, the high cooling speed is set in the 3 region, so that the fine dispersion and precipitation of sulfide in the two-phase region at the solidification front are effectively promoted.

The size of the end surface of the casting blank after continuous casting is 200 mm-200 mm, and the chemical components and the mass percentage of the casting blank are as follows: c: 0.19%, Si: 0.28%, Mn: 0.96%, Cr: 1.08%, Ti: 0.05%, S: 0.031%, P: 0.012%, Als: 0.015%, Ca: 0.0014%, Ni: 0.01%, Cu: 0.01%, Mo: 0.005%, residual element Sn: 0.002%, Pb: 0.001%, As: 0.02%, Bi: 0.002%, Sb: 0.002%, total oxygen content 15ppm, total nitrogen content 35ppm, and the balance of Fe and inevitable impurities, wherein the manganese-sulfur ratio is 31, and the balance of Fe and inevitable impurity elements.

In the heating procedure, a 200mm square billet is placed into a heating furnace for heating, the temperature of a soaking section is controlled to be 1220 +/-15 ℃, then high-pressure water dephosphorization is carried out on the surface of the square billet, then the square billet is rolled into a bar finished product, and the temperature is controlled to be 820 plus 830 ℃ after finishing rolling.

As shown in figure 1, after slow cooling, the sample of the embodiment is taken to test sulfides, the type of the sample is single manganese sulfide, the inner core is a calcium aluminate, the outer layer is a manganese sulfide composite sulfide, the length-width ratio is 3-6 and is different, the sample is in a dispersion distribution state, and the cutting processability of the gear steel for the automobile gearbox is effectively guaranteed.

The gear steel for the automobile gearbox successfully realizes the uniform dispersion distribution of sulfide in a bar finished product, and has good machinability.

The structure is ferrite and pearlite through inspection, no supercooling structure exists, and the total oxygen content is 15 ppm; the sulfur-containing gear steel for the automobile gearbox processed by the downstream user has high processing precision and good matching property.

Example 2

The specification of the hot rolled bar of the gear steel bar for the automobile gearbox is phi 50mm, and the production method comprises the following steps: the process flows of converter smelting, LF + RH refining, continuous casting, heating and rolling.

The top-bottom combined blown converter adopts a bottom-blown large circular seam process, the converter process controls the carbon-oxygen deposition at the blowing end point to be 0.0023%, the steel ladle slag discharging is strictly controlled in the tapping process, meanwhile, an aluminum-containing modifier is added to modify the steel ladle top slag, and the binary alkalinity of the high-alkalinity aluminum-containing modifier is 5.3.

High-alkalinity slag operation is adopted in the early stage of LF process refining, binary alkalinity is controlled to be 6, aluminum wire feeding precipitation deoxidation is adopted in the refining process, a calcium carbide diffusion deoxidation process is adopted, low-alkalinity slag operation is adopted in the later stage of refining, the final slag alkalinity is 1.5, the Als content in molten steel is controlled to be 0.020wt%, the Ca content is controlled to be 0.0012wt%, and soft blowing is carried out for 13 minutes.

The RH refining process adopts high vacuum large circulation operation, the ultimate vacuum degree is 18Pa, the high vacuum time is maintained at 6 minutes, the Als content is controlled at 0.010wt% after the final calcium treatment, the calcium-aluminum ratio is controlled at 0.13, the S content is controlled at 0.033 wt% after the sulfur feeding line, the sulfur feeding line is fed after the interval time of the final calcium treatment is 9 minutes, and the soft blowing time is controlled at 13 minutes before leaving the station.

The whole process of the continuous casting process protects casting, and the tundish adopts SiO with alkalinity of 1.2₂36% of covering agent, crystallizer electric stirring and end electric stirring are adopted in the whole process, the crystallizer adopts a weak cooling mode of 106 cubic meters per hour, secondary cooling adopts an inter-cooling mode, the specific water amount is set to be 0.55, the standard pulling speed is 0.9 meter per minute, the crystallizer electric stirring parameter is 350 +/-10A/3 +/-0.5 Hz, the end electric stirring parameter is 250 +/-10A/8 +/-0.5 Hz, secondary cooling is divided into 4 areas, wherein the secondary cooling water distribution setting proportion of the 1-4 areas adopts 35: 21: 38: and in the 6 mode, the high cooling speed is set in the 3 region, so that the fine dispersion and precipitation of sulfide in the two-phase region at the solidification front are effectively promoted.

The size of the end surface of the casting blank after continuous casting is 200 mm-200 mm, and the chemical components and the mass percentage of the casting blank are as follows: c: 0.21%, Si: 0.28%, Mn: 0.95%, Cr: 1.12%, Ti: 0.07%, S: 0.032%, P: 0.015%, Als: 0.008%, Ca: 0.0012%, Ni: 0.01%, Cu: 0.01%, Mo: 0.001%, residual element Sn: 0.001%, Pb: 0.001%, As: 0.008%, Bi: 0.008%, Sb: 0.001%, total oxygen content 20ppm, total nitrogen content 40ppm, and the balance of Fe and inevitable impurities, wherein the manganese-sulfur ratio is 30, and the balance of Fe and inevitable impurity elements.

In the heating process, a 200mm square billet is placed into a heating furnace for heating, the temperature of a soaking section is controlled to be 1220 +/-15 ℃, then high-pressure water dephosphorization is carried out on the surface of the square billet, then a bar finished product is rolled, and the temperature is controlled to be 810 plus 830 ℃ after finishing rolling.

As shown in figure 2, after slow cooling, the sample of the embodiment is taken to test sulfides, the type of the sample is single manganese sulfide, the inner core is a calcium aluminate, the outer layer is a manganese sulfide composite sulfide, the length-width ratio is 3-6 and is different, the sample is in a dispersion distribution state, and the cutting processability of the gear steel for the automobile gearbox is effectively guaranteed.

The gear steel for the automobile gearbox successfully realizes the uniform dispersion distribution of sulfide in a bar finished product, and has good machinability.

The structure is ferrite and pearlite through inspection, no supercooling structure exists, and the total oxygen content is 20 ppm; the sulfur-containing gear steel for the automobile gearbox processed by the downstream user has high processing precision and good matching property.

Example 3

The specification of the hot rolled bar of the gear steel bar for the automobile gearbox is phi 55mm, and the production method comprises the following steps: the process flows of converter smelting, LF + RH refining, continuous casting, heating and rolling.

The top-bottom combined blown converter adopts a bottom-blown large circular seam process, the converter process controls the carbon-oxygen deposition at the blowing end point to be 0.0022%, the steel ladle slag discharging is strictly controlled in the tapping process, meanwhile, an aluminum-containing modifier is added to modify the steel ladle top slag, and the binary alkalinity of the high-alkalinity aluminum-containing modifier is 6.

High-alkalinity slag operation is adopted in the early stage of LF process refining, binary alkalinity is controlled to be 5.1, aluminum wire feeding precipitation deoxidation is adopted in the refining process, calcium carbide diffusion deoxidation technology is adopted, low-alkalinity slag operation is adopted in the later stage of refining, the final slag alkalinity is 1.9, the Als content and the Ca content in molten steel are controlled to be 0.020wt% and 0.0010wt% respectively after calcium pretreatment, and the molten steel is discharged after soft blowing for 12 minutes.

The RH refining process adopts high vacuum large circulation operation, the ultimate vacuum degree is 20Pa, the high vacuum time is maintained above 5 minutes, the Als content is controlled at 0.018wt% after the final calcium treatment, the calcium-aluminum ratio is controlled at 0.15, the S content is controlled at 0.031 wt% after the sulfur line is fed, the sulfur line is fed after the sulfur line is fed for 10 minutes, and the soft blowing time is controlled for 15 minutes before leaving the station.

The whole process of the continuous casting process protects casting, and the tundish adopts SiO with alkalinity of 1.2₂The covering agent with the content of 38 percent adopts crystallizer electric stirring and end electric stirring in the whole process, the crystallizer adopts a weak cooling mode of 105 cubic meters per hour, the secondary cooling adopts an inter-cooling mode, the specific water amount is set to be 0.60, the standard pulling speed is 0.9 meters per minute, the crystallizer electric stirring parameter adopts 350 +/-10A/3 +/-0.5 Hz, the end electric stirring parameter adopts 250 +/-10A/8 +/-0.5 Hz, the secondary cooling is divided into 4 areas, wherein the secondary cooling water distribution setting proportion of the 1-4 areas adopts 35: 21: 38: and in the 6 mode, the high cooling speed is set in the 3 region, so that the fine dispersion and precipitation of sulfide in the two-phase region at the solidification front are effectively promoted.

The size of the end surface of the casting blank after continuous casting is 200 mm-200 mm, and the chemical components and the mass percentage of the casting blank are as follows: c: 0.19%, Si: 0.23%, Mn: 0.98%, Cr: 1.12%, Ti: 0.05%, S: 0.031%, P: 0.012%, Als: 0.016%, Ca: 0.0025%, Ni: 0.01%, Cu: 0.01%, Mo: 0.001%, residual element Sn: 0.002%, Pb: 0.005%, As: 0.005%, Bi: 0.001%, Sb: 0.008 percent, total oxygen content of 17ppm, total nitrogen content of 33ppm, and the balance of Fe and inevitable impurities, wherein the manganese-sulfur ratio is 30, and the balance of Fe and inevitable impurity elements.

In the heating process, a 200mm square billet is heated in a heating furnace, the temperature of a soaking section is controlled to be 1220 +/-15 ℃, then high-pressure water dephosphorization is carried out on the surface of the square billet, then the square billet is rolled into a bar finished product, and the temperature is controlled to be 820 plus-material 840 ℃ after finishing rolling.

As shown in figure 3, after slow cooling, the sample of the embodiment is taken to test sulfides, the type of the sample is single manganese sulfide, the inner core is a calcium aluminate, the outer layer is a manganese sulfide composite sulfide, the length-width ratio is 3-6 and is different, the sample is in a dispersion distribution state, and the cutting processability of the gear steel for the automobile gearbox is effectively guaranteed.

The gear steel for the automobile gearbox successfully realizes the uniform dispersion distribution of sulfide in a bar finished product, and has good machinability.

The structure is ferrite and pearlite through inspection, no supercooling structure exists, and the total oxygen content is 17 ppm; the sulfur-containing gear steel for the automobile gearbox processed by the downstream user has high processing precision and good matching property.

Example 4

The specification of the hot rolled bar of the gear steel bar for the automobile gearbox is phi 45mm, and the production method comprises the following steps: the process flows of converter smelting, LF + RH refining, continuous casting, heating and rolling.

The top-bottom combined blown converter adopts a bottom-blown large circular seam process, the converter process controls the carbon-oxygen deposition at the blowing end point to be 0.0023%, the steel ladle slag discharging is strictly controlled in the tapping process, meanwhile, an aluminum-containing modifier is added to modify the steel ladle top slag, and the binary alkalinity of the high-alkalinity aluminum-containing modifier is 5.6.

High-alkalinity slag operation is adopted in the early stage of LF process refining, binary alkalinity is controlled to be 5.2, aluminum wire feeding precipitation deoxidation is adopted in the refining process, calcium carbide diffusion deoxidation technology is adopted, low-alkalinity slag operation is adopted in the later stage of refining, the final slag alkalinity is 2.5, the Als content and the Ca content in molten steel are controlled to be 0.035wt% and 0.0014wt% respectively after calcium pretreatment, and the molten steel is discharged after soft blowing for 13 minutes.

The RH refining process adopts high vacuum large circulation operation, the ultimate vacuum degree is 19Pa, the high vacuum time is maintained above 5 minutes, the Als content is controlled at 0.022wt% after the final calcium treatment, the calcium-aluminum ratio is controlled at 0.08, the S content is controlled at 0.030 wt% after the sulfur line is fed, the sulfur line is fed after the interval time of the final calcium treatment is 8 minutes, and the soft blowing time is controlled for 10 minutes before leaving the station.

The whole process of the continuous casting process protects casting, and the tundish adopts SiO with alkalinity of 1.0₂The covering agent with the content of 38 percent adopts crystallizer electric stirring and end electric stirring in the whole process, the crystallizer adopts a weak cooling mode of 103 cubic meters per hour, the secondary cooling adopts an inter-cooling mode, the specific water amount is set to be 0.60, the standard pulling speed is 0.9 meters per minute, the crystallizer electric stirring parameter adopts 350 +/-10A/3 +/-0.5 Hz, the end electric stirring parameter adopts 250 +/-10A/8 +/-0.5 Hz, the secondary cooling is divided into 4 areas, wherein the secondary cooling water distribution setting proportion of the 1-4 areas adopts 35: 21: 38: and in the 6 mode, the high cooling speed is set in the 3 region, so that the fine dispersion and precipitation of sulfide in the two-phase region at the solidification front are effectively promoted.

The size of the end surface of the casting blank after continuous casting is 200 mm-200 mm, and the chemical components and the mass percentage of the casting blank are as follows: c: 0.20%, Si: 0.24%, Mn: 0.95%, Cr: 1.10%, Ti: 0.06%, S: 0.035%, P: 0.011%, Als: 0.018%, Ca: 0.0016%, Ni: 0.03%, Cu: 0.05%, Mo: 0.01%, residual element Sn: 0.01%, Pb: 0.001%, As: 0.003%, Bi: 0.001%, Sb: 0.001%, total oxygen content of 13ppm, total nitrogen content of 31ppm, and the balance of Fe and inevitable impurities, wherein the manganese-sulfur ratio is 27, and the balance of Fe and inevitable impurity elements.

In the heating process, a 200mm square billet is heated in a heating furnace, the temperature of a soaking section is controlled to be 1220 +/-15 ℃, then high-pressure water dephosphorization is carried out on the surface of the square billet, then the square billet is rolled into a bar finished product, and the temperature is controlled to be 820 plus-material 840 ℃ after finishing rolling.

As shown in FIG. 4, after slow cooling, the sample of the embodiment is taken to test sulfides, the type of the sample is single manganese sulfide, the inner core is a calcium aluminate, the outer layer is a manganese sulfide composite sulfide, the length-width ratio is 3-6, the length-width ratio is different, the sample is in a dispersion distribution state, and the cutting processability of the gear steel for the automobile gearbox is effectively guaranteed.

The gear steel for the automobile gearbox successfully realizes the uniform dispersion distribution of sulfide in a bar finished product, and has good machinability.

The structure is ferrite and pearlite through inspection, no supercooling structure exists, and the total oxygen content is 13 ppm; the sulfur-containing gear steel for the automobile gearbox processed by the downstream user has high processing precision and good matching property.

Example 5

The specification of the hot rolled bar of the gear steel bar for the automobile gearbox is phi 65mm, and the production method comprises the following steps: the process flows of converter smelting, LF + RH refining, continuous casting, heating and rolling.

The top-bottom combined blown converter adopts a bottom-blown large circular seam process, the converter process controls the carbon-oxygen deposition at the blowing end point to be 0.0022%, the steel ladle slag discharging is strictly controlled in the tapping process, meanwhile, an aluminum-containing modifier is added to modify the steel ladle top slag, and the binary alkalinity of the high-alkalinity aluminum-containing modifier is 5.2.

High-alkalinity slag operation is adopted in the refining early stage of the LF procedure, the binary alkalinity is controlled to be 5, an aluminum wire feeding precipitation deoxidation matched with a calcium carbide diffusion deoxidation process is adopted in the refining process, low-alkalinity slag operation is adopted in the refining later stage, the final slag alkalinity is 2.3, the Als content and the Ca content in molten steel are controlled to be 0.028wt% and 0.0025wt% respectively after calcium pretreatment, and the molten steel is discharged after soft blowing for 11 minutes.

The RH refining process adopts high vacuum and large circulation operation, the ultimate vacuum degree is 20Pa, the high vacuum time is maintained for 6 minutes, the Als content is controlled to be 0.025wt% after the final calcium treatment, the calcium-aluminum ratio is controlled to be 0.13, the S content is controlled to be 0.035wt% after the sulfur line is fed, the sulfur line is fed after the final calcium treatment interval time is 8 minutes, and the soft blowing time is controlled to be 15 minutes before leaving the station.

The whole process of the continuous casting process protects casting, and the tundish adopts SiO with alkalinity of 1.2₂The covering agent with the content of 37 percent adopts crystallizer electric stirring and end electric stirring in the whole process, the crystallizer adopts a weak cooling mode of 107 cubic meters per hour, the secondary cooling adopts an inter-cooling mode, the specific water amount is set to be 0.60, the standard pulling speed is 0.9 meters per minute, the crystallizer electric stirring parameter adopts 350 +/-10A/3 +/-0.5 Hz, the end electric stirring parameter adopts 250 +/-10A/8 +/-0.5 Hz, the secondary cooling is divided into 4 areas, wherein the secondary cooling water distribution setting proportion of the 1-4 areas adopts 35: 21: 38: and in the 6 mode, the high cooling speed is set in the 3 region, so that the fine dispersion and precipitation of sulfide in the two-phase region at the solidification front are effectively promoted.

The size of the end surface of the casting blank after continuous casting is 200 mm-200 mm, and the chemical components and the mass percentage of the casting blank are as follows: c: 0.19%, Si: 0.24%, Mn: 0.98%, Cr: 1.11%, Ti: 0.07%, S: 0.028%, P: 0.010%, Als: 0.025%, Ca: 0.0035%, Ni: 0.05%, Cu: 0.01%, Mo: 0.002%, residual element Sn: 0.001%, Pb: 0.001%, As: 0.002%, Bi: 0.002%, Sb: 0.002%, total oxygen content of 17ppm, total nitrogen content of 32ppm, and the balance of Fe and inevitable impurities, wherein the manganese-sulfur ratio is 35, and the balance of Fe and inevitable impurities.

In the heating procedure, a 200mm square billet is placed into a heating furnace for heating, the temperature of a soaking section is controlled to be 1220 +/-15 ℃, then high-pressure water dephosphorization is carried out on the surface of the square billet, then the square billet is rolled into a bar finished product, and the temperature is controlled to be 820 plus 830 ℃ after finishing rolling.

As shown in FIG. 5, after slow cooling, the sample of the embodiment is taken to test sulfides, the type of the sample is single manganese sulfide, the inner core is a calcium aluminate, the outer layer is a manganese sulfide composite sulfide, the length-width ratio is 3-6, the length-width ratio is different, the sample is in a dispersion distribution state, and the cutting processability of the gear steel for the automobile gearbox is effectively guaranteed.

The gear steel for the automobile gearbox successfully realizes the uniform dispersion distribution of sulfide in a bar finished product, and has good machinability.

The structure is ferrite and pearlite through inspection, no supercooling structure exists, and the total oxygen content is 17 ppm; the sulfur-containing gear steel for the automobile gearbox processed by the downstream user has high processing precision and good matching property.

Example 6

The specification of the hot rolled bar of the gear steel bar for the automobile gearbox is phi 70mm, and the production method comprises the following steps: the process flows of converter smelting, LF + RH refining, continuous casting, heating and rolling.

The top-bottom combined blown converter adopts a bottom-blown large circular seam process, the converter process controls the carbon-oxygen deposition at the blowing end point to be 0.0022%, the steel ladle slag discharging is strictly controlled in the tapping process, meanwhile, an aluminum-containing modifier is added to modify the steel ladle top slag, and the binary alkalinity of the high-alkalinity aluminum-containing modifier is 5.1.

High-alkalinity slag operation is adopted in the early stage of LF process refining, binary alkalinity is controlled to be 5.2, aluminum wire feeding precipitation deoxidation is adopted in the refining process, calcium carbide diffusion deoxidation technology is adopted, low-alkalinity slag operation is adopted in the later stage of refining, the final slag alkalinity is 1.5, the Als content in molten steel is controlled to be 0.020wt%, the Ca content is controlled to be 0.0015% after calcium pretreatment, and the molten steel is discharged after soft blowing for 10 minutes.

The RH refining process adopts high vacuum and large circulation operation, the ultimate vacuum degree is 19Pa, the high vacuum time is maintained for 5 minutes, the Als content is controlled to be 0.016wt% after final calcium treatment, the calcium-aluminum ratio is controlled to be 0.10, the S content is controlled to be 0.032 wt% after a sulfur feeding line, the sulfur feeding line is fed after the final calcium treatment interval time is 10 minutes, and the soft blowing time is controlled to be 16 minutes before leaving the station.

The whole process of the continuous casting process protects casting, and the tundish adopts SiO with alkalinity of 1.5₂The whole process of the covering agent with the content of 32 percent adopts crystallizer electric stirring and end electric stirring, the crystallizer adopts a weak cooling mode of 105 cubic meters per hour, the secondary cooling adopts an inter-cooling mode, the specific water amount is set to be 0.55, the standard drawing speed is 0.9 meters per minute, and the mixture is solidifiedThe electric stirring parameter of the crystal device is 350 +/-10A/3 +/-0.5 Hz, the electric stirring parameter of the tail end is 250 +/-10A/8 +/-0.5 Hz, the secondary cooling is divided into 4 areas, and the setting proportion of the secondary cooling water distribution in the 1-4 areas is 35: 21: 38: and in the 6 mode, the high cooling speed is set in the 3 region, so that the fine dispersion and precipitation of sulfide in the two-phase region at the solidification front are effectively promoted.

The size of the end surface of the casting blank after continuous casting is 200 mm-200 mm, and the chemical components and the mass percentage of the casting blank are as follows: c: 0.21%, Si: 0.23%, Mn: 0.97%, Cr: 1.10%, Ti: 0.06%, S: 0.031%, P: 0.013%, Als: 0.015%, Ca: 0.0014%, Ni: 0.05%, Cu: 0.05%, Mo: 0.006%, residual element Sn: 0.001%, Pb: 0.001%, As: 0.005%, Bi: 0.002%, Sb: 0.002%, total oxygen content 15ppm, total nitrogen content 31ppm, and the balance of Fe and inevitable impurities, wherein the manganese-sulfur ratio is 31, and the balance of Fe and inevitable impurity elements.

In the heating process, a 200mm square billet is heated in a heating furnace, the temperature of a soaking section is controlled to be 1220 +/-15 ℃, then high-pressure water dephosphorization is carried out on the surface of the square billet, then the square billet is rolled into a bar finished product, and the temperature is controlled to be 820 plus-material 840 ℃ after finishing rolling.

As shown in FIG. 6, after slow cooling, the sample of the embodiment is taken to test sulfides, the type is mainly composite sulfides with single manganese sulfide, the inner core is calcium aluminate, the outer layer is manganese sulfide, the length-width ratio is 3-6 and is unequal, the sample is in a dispersion distribution state, and the cutting processability of the gear steel for the automobile gearbox is effectively guaranteed.

The gear steel for the automobile gearbox successfully realizes the uniform dispersion distribution of sulfide in a bar finished product, and has good machinability.

The structure is ferrite and pearlite through inspection, no supercooling structure exists, and the total oxygen content is 15 ppm; the sulfur-containing gear steel for the automobile gearbox processed by the downstream user has high processing precision and good matching property.