1. The method for controlling sulfur in the smelting of 80-grade cord steel with a large scrap steel ratio is characterized by comprising the following steps of: the method comprises the following steps:

1) and (3) molten iron desulphurization: adding magnesium powder at one time according to 0.4-1.0 kg/ton iron; adding lime according to 0.6-1.2 kg/ton iron in the blowing process; when the slag is removed to 1/3-4/5, adding the slag-bonding agent once, wherein the addition amount of the slag-bonding agent is based on the principle that S in the molten iron at the end point is less than or equal to 0.0025%;

2) carrying out converter smelting: adding graphite carbon balls with the granularity of 10-30 mm at one time according to 7-13 kg/ton of steel while adding scrap steel, and controlling the tapping temperature to be more than or equal to 1620 ℃ and the end point carbon to be 0.08-0.15%;

3) and (3) carrying out LF refining: adding top slag when refining is carried out for 10-20min, wherein the addition amount of the top slag is based on the principle that the alkalinity R of the refining slag is 1.8-2.8; refining for not less than 20min after top slag is added, conventionally adding quartz sand and ferrosilicon, and controlling the alkalinity R at 0.7-1.3; refining for not less than 40min under the condition that the alkalinity R is 0.7-1.3; controlling the sulfur content to be less than or equal to 0.006 percent when the refining is finished, wherein the total refining time is 80-100 min;

4) the post-process is normally performed.

2. The method for controlling sulfur in smelting of high scrap steel ratio 80-grade cord steel according to claim 1, wherein the method comprises the following steps: and controlling the S in the molten iron to be less than or equal to 0.0022 percent after the slag bonding agent is added in the molten iron desulphurization period.

3. The method for controlling sulfur in smelting of high scrap steel ratio 80-grade cord steel according to claim 1, wherein the method comprises the following steps: the 80-grade cord comprises the following components in percentage by weight: c: 0.80 to 0.85 wt%, Si: 0.15 to 0.30 wt%, Mn: 0.45-0.60 wt%, P is less than or equal to 0.020 wt%, S is less than or equal to 0.010 wt%, P + S is less than or equal to 0.025 wt%, and the balance of Fe and inevitable impurities.

Background

The cord steel is the most important raw material for manufacturing the steel cord, has high requirements and great manufacturing difficulty, and is known as the bright pearl on the crown in the wire product, and the main difficulties are that: the deep processing flow of a user is long and complicated, dozens of times of drawing and intermediate heat treatment are needed, the steel wire compression rate exceeds 99 percent (the diameter is drawn from 5.5mm to the thinnest 0.10mm), and the strand twisting and breaking rate is required to be more than or equal to 6 kilometers per time.

With the development of the automobile industry, the tire has become a development direction at present, and a green tire with low noise and low fuel consumption has become a mainstream of tire design and manufacture at present. The steel cord is used as the main framework material of the tire, and the strength grade is developing from the common strength (NT) to the high strength (HT), the ultra-high Strength (ST) and the ultra-high strength (UT). In developed countries, the usage amount of HT-grade steel cords accounts for about 60% of the total usage amount of steel cords, and the usage amount of ST-grade steel cords also exceeds 20%. Taking a phi 0.20mm steel wire as an example, the strength of the NT-grade, HT-grade, ST-grade and UT-grade steel cords is 2850, 3300, 3600 and 3800MPa respectively, and the strength of the HT-grade steel cords is about 15 percent higher than that of the NT-grade products. And compared with the NT-grade steel cord, the HT-grade steel cord has the advantages that the wear resistance is improved by more than 10%, the safety (the braking distance is reduced by more than 15%) is better, and the rolling resistance of the tire can be reduced (the oil consumption is reduced by 5-12%). From this, the potential of high strength steel cords in reducing tire weight and increasing tire load capacity can be seen. However, as the strength increases, the workability and ductility of the steel wire decrease, and the requirements for the raw material cord steel are becoming more stringent in order to ensure the strand breakage rate.

80-grade cord steel for automobile tires is the most important raw material for producing tire supporting framework-high-strength steel cord (HT grade, the strength of the cord is generally required to be more than 3300 MPa). Generally, 80-grade cord steel wire rods are subjected to rough drawing after being descaled, then are subjected to heat treatment, are drawn again to be between 0.20 and 0.38mm, are subjected to copper plating treatment and are stranded. Because the drawing deformation is large, the wire rod is required to have extremely high cleanliness, and particularly the requirements on harmful elements such as phosphorus, sulfur and the like in steel are high. Particularly, the 80-grade cord steel is hypereutectoid steel, the hot brittleness of the wire rod can be caused when the sulfur content in the steel is high, in addition, the segregation is aggravated due to the high sulfur content, the plasticity of steel is reduced, the layering is caused by the non-uniform internal structure of the wire rod, and the wire rod is broken in the drawing and stranding processes. Therefore, the lower the sulfur content, the better the cord steel is required. At present, the national standard GB/T27691-: the control requirement of the sulfur content of the high-grade 80-grade cord steel is less than or equal to 0.010 percent and is far higher than the requirement of the phosphorus content of less than or equal to 0.020 percent. In actual production, in order to meet the standard requirement and reduce the breakage rate of twisted strands after wire rod drawing, the sulfur content in 80-grade cord steel needs to be controlled below 0.0055%.

In addition, enterprises which adopt converters to produce cord steel limit the ratio of added scrap steel for controlling the sulfur content and the level of inclusions in steel, and generally require the ratio of scrap steel to be less than or equal to 15%. However, with the needs of national environmental protection and carbon neutralization, the high energy consumption processes such as sintering, coking, blast furnace and the like in the traditional long process of steel production need to be reduced, that is, as much molten steel as possible needs to be smelted by using less molten iron, which undoubtedly requires enterprises to increase the scrap steel ratio during smelting of various steel types.

At present, common converter smelting process enterprises require that the scrap ratio reaches at least 25%, but most of the common steels such as deformed steel are produced with more scrap added, and the added scrap of the varieties with high quality requirements such as cord steel is mostly controlled to be about 15%. The main reason is that when the cord steel is smelted by adopting a converter, the quality of the cord steel, particularly the sulfur content in the components, is undoubtedly greatly influenced after more scrap steel is added.

Therefore, the method has very practical significance for controlling the strictly required sulfur content in the components and simultaneously ensuring the plasticization of inclusions when 80-grade cord steel is smelted by adopting a converter with a large scrap steel ratio of more than 25 percent, and meeting the requirement of a downstream user on the strand breakage rate after drawing.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a method for controlling sulfur in 80-grade cord steel smelting, which can meet the requirement that the ratio of scrap steel is more than 25%, can control the sulfur content in the final molten steel after smelting to be less than 0.0055%, and can prolong the broken wire length from the original average length of 6.2 ten thousand meters per time to 8.4 ten thousand meters per time.

The measures for realizing the aim are as follows:

the method for controlling sulfur in the smelting of 80-grade cord steel with a large scrap steel ratio is characterized by comprising the following steps of: the method comprises the following steps:

1) and (3) molten iron desulphurization: adding magnesium powder at one time according to 0.4-1.0 kg/ton iron; adding lime according to 0.6-1.2 kg/ton iron in the blowing process; when the slag is removed to 1/3-4/5, adding the slag-bonding agent once, wherein the addition amount of the slag-bonding agent is based on the principle that S in the molten iron at the end point is less than or equal to 0.0025%;

2) carrying out converter smelting: adding graphite carbon balls with the particle size of 10-30 mm at one time according to 7-13 kg/ton of steel while adding the waste steel, controlling the tapping temperature to be not lower than 1620 ℃, and controlling the end point carbon to be 0.08-0.15%;

3) and (3) carrying out LF refining: adding top slag when refining is carried out for 10-20min, wherein the addition amount of the top slag is based on the principle that the alkalinity R of the refining slag is 1.8-2.8; refining for not less than 20min after top slag is added, conventionally adding quartz sand and ferrosilicon, and controlling the alkalinity R at 0.7-1.3; refining for not less than 40min under the condition that the alkalinity R is 0.7-1.3; controlling the sulfur content to be less than or equal to 0.0055% when refining is finished, and controlling the total refining time to be 80-100 min;

4) the post-process is normally performed.

Preferably: and controlling the S in the molten iron to be less than or equal to 0.0022 percent after the slag bonding agent is added in the molten iron desulphurization period.

Further: the 80-grade cord steel comprises the following components in percentage by weight: c: 0.80 to 0.85 wt%, Si: 0.15 to 0.30 wt%, Mn: 0.45-0.60 wt%, P is less than or equal to 0.020 wt%, S is less than or equal to 0.010 wt%, P + S is less than or equal to 0.025 wt%, and the balance of Fe and inevitable impurities.

According to the invention, the graphite carbon balls are added at one time according to 7-13 kg/ton of steel while the waste steel is added, the tapping temperature is controlled to be not less than 1620 ℃, and the end point carbon is controlled to be 0.08-0.15%, because when the waste steel ratio is increased to 25%, the heat source for smelting the converter is insufficient, and the end point tapping temperature is generally below 1600 ℃, the converter slag desulfurization efficiency can be reduced. According to the heat balance calculation, a corresponding amount of heating agent is added, so that the final tapping temperature of the converter can be ensured to be more than or equal to 1620 ℃. Meanwhile, the end point carbon is more than 0.08 percent, so that the peroxidation of molten steel can be avoided, and the generation of inclusions in the steel can be reduced.

According to the invention, the top slag is added when refining is carried out for 10-20min, the addition amount of the top slag is based on the principle that the alkalinity R of the refining slag is 1.8-2.8, and the refining slag has high activity after heating and temperature rising for 10-20min, so that the top slag is added to produce the high-alkalinity slag, the sulfur in steel can be effectively removed, and the refining inclusion can be favorably and fully floated.

According to the invention, after the top slag is added and when the alkalinity R of the refining slag is 1.8-2.8, the refining is carried out for not less than 20min, quartz sand and ferrosilicon are added conventionally, and the alkalinity R is controlled to be 0.7-1.3; refining for not less than 40min under the condition that the alkalinity R is 0.7-1.3, wherein the total refining time is 80-100min, because the cord steel needs low-alkalinity acid slag to plasticize the inclusion, and meanwhile, sufficient soft blowing time is ensured, which is beneficial to floating of the inclusion.

Compared with the prior art, the method has the advantages that the graphite carbon balls are added in smelting, the tapping temperature is controlled, the method of changing the alkalinity of the refining slag is adopted during refining, and the like, so that when 80-grade cord steel is smelted in a converter with a large scrap steel ratio of more than 25%, the requirement that the scrap steel ratio is more than 25% can be met, the sulfur content in the final smelted molten steel is controlled to be less than 0.0055%, and the requirement that a user draws 80-grade cord steel wire rods to 0.20-0.38mm on strand twisting and wire breaking rate is better met. Through statistics of a stranding test, the broken yarn rate is remarkably reduced, and the broken yarn length is prolonged to 8.4 kilometers per time from the original average 6.2 kilometers per time; it is known that for steel cords with smaller diameter and higher strength, the breakage is easier, for example for steel cords with a diameter of 0.2mm of this strength class, the original strand breakage length is typically around 5 km/s, while the invention extends to at least 7 km/s.

Detailed Description

The present invention is described in detail below:

table 1 is a list of values of the molten iron desulfurization process parameters of each example and comparative example of the present invention;

table 2 shows the value lists of the main process parameters of the converter smelting in each embodiment and comparative example of the invention;

table 3 shows the values of the refining process parameters in the LF furnace in each of the examples and comparative examples of the present invention;

table 4 shows a list of the composition of molten steel after refining in an LF furnace in each of examples and comparative examples of the present invention.

The embodiments of the invention are as follows: 0.80 to 0.85 wt%, Si: 0.15 to 0.30 wt%, Mn: 0.45-0.60 wt%, P not more than 0.020 wt%, S not more than 0.010 wt%, P + S not more than 0.025 wt%.

The smelting is carried out according to the following steps in each embodiment of the invention:

1) and (3) molten iron desulphurization: adding magnesium powder at one time according to 0.4-1.0 kg/ton iron; adding lime according to 0.6-1.2 kg/ton iron in the blowing process; when the slag is removed to 1/3-4/5, adding the slag-bonding agent once, wherein the addition amount of the slag-bonding agent is based on the principle that S in the molten iron at the end point is less than or equal to 0.0025%;

2) carrying out converter smelting: adding graphite carbon balls with the particle size of 10-30 mm at one time according to 7-13 kg/ton of steel while adding the waste steel, controlling the tapping temperature to be not lower than 1620 ℃, and controlling the end point carbon to be 0.08-0.15%;

3) and (3) carrying out LF refining: adding top slag when refining is carried out for 10-20min, wherein the addition amount of the top slag is based on the principle that the alkalinity R of the refining slag is 1.8-2.8; refining for not less than 20min after top slag is added, conventionally adding quartz sand and ferrosilicon, and controlling the alkalinity R at 0.7-1.3; refining for not less than 40min under the condition that the alkalinity R is 0.7-1.3; controlling the sulfur content to be less than or equal to 0.006 percent when the refining is finished, wherein the total refining time is 80-100 min;

4) the post-process is normally performed.

Description of the drawings:

the steel scrap ratios added in the following examples are not less than 25%.

TABLE 1 process parameters related to desulfurization of molten iron in examples of the present invention and comparative examples

TABLE 2 Main process parameters for converter smelting in the examples and comparative examples of the present invention

TABLE 3 refining process parameter value list of each example and comparative example of the invention in LF furnace

TABLE 4 list of molten steel composition after refining in LF furnace for inventive and comparative examples

As can be seen from Table 4, the S content in the molten steel is controlled to be below 0.0055% in the invention; when the yarn is twisted into strands with the specification of 0.20mm-0.38mm, the yarn breakage rate is obviously reduced, and the yarn breakage rate is prolonged to 8.4 kilometers per time from the original average 6.2 kilometers per time.

The above examples are merely preferred examples and are not intended to limit the technical scope of the present invention.