1. The preparation method of the hot-rolled section steel for the forklift mast is characterized by comprising the steps of converter smelting, LF refining and continuous casting in sequence;

wherein the LF refining is accompanied by a nitrogen blowing operation;

the hot-rolled section steel for the forklift mast meets the requirement that the carbon equivalent is less than or equal to 0.48 percent.

2. The manufacturing method according to claim 1, wherein the molten steel obtained by the converter smelting is further subjected to deoxidation alloying before being subjected to LF refining.

3. The method according to claim 1 or 2, wherein the steel obtained by continuous casting is subsequently hot rolled, air cooled and finished.

4. The method according to any one of claims 1 to 3, characterized in that said nitrogen-blowing operation comprises in particular the steps of:

(1) starting bottom blowing nitrogen and arc heating at a first flow rate, and keeping for a first time period;

(2) adjusting the bottom blowing nitrogen to a second flow rate, and keeping for a second time period;

(3) adjusting bottom-blown nitrogen to a third flow rate after the first sampling analysis, and keeping for a third time period;

(4) adding a recarburizing agent and an alloy, adjusting bottom blowing nitrogen to a fourth flow, and keeping for a fourth time period;

(5) stopping blowing the nitrogen gas from the bottom after the second sampling analysis;

wherein the absolute pressure of the bottom-blown nitrogen in the steps (1) to (5) is 1 to 1.4 MPa.

5. The method as claimed in claim 4, wherein the first flow rate in step (1) is 100-150 NL/min;

preferably, the first period of time of step (1) is 8-12 min;

preferably, the second flow rate in step (2) is 550-650 NL/min;

preferably, the second time period of step (2) is 0.8-1.2 min;

preferably, the third flow rate in the step (3) is 200-300 NL/min;

preferably, the third time period of step (3) is 7-8 min;

preferably, the fourth flow rate in the step (4) is 550-650 NL/min;

preferably, the fourth time period of step (4) is 4-8 min;

preferably, the total volume of the bottom-blown nitrogen gas in the steps (1) to (5) is 9 to 10m³。

6. The method according to claim 4 or 5, wherein the power consumption of the arc heating in step (1) is 50-80 kwh/t.

7. The production method according to any one of claims 4 to 6, wherein the recarburizing agent of step (4) comprises petroleum;

preferably, the dosage of the carburant in the step (4) is 0.2-0.3kg/t molten steel;

preferably, the alloy in the step (4) comprises any one of aluminum ingot, silicon manganese alloy, ferrovanadium alloy, medium carbon ferromanganese or high carbon ferrochrome or a combination of at least two of the above;

preferably, the alloy in the step (4) is used in an amount of 0.5-5kg/t molten steel.

8. The production method according to any one of claims 1 to 7, wherein the carbon content ratio of the hot-rolled steel section for forklift mast is 0.16 to 0.18 wt%;

preferably, the silicon element proportion of the hot-rolled steel section for the forklift mast is 0.32-0.36 wt%;

preferably, the manganese element of the hot-rolled steel section for the forklift mast accounts for 1.51-1.55 wt%;

preferably, the chromium element of the hot-rolled section steel for the forklift mast accounts for 0.06-0.1 wt%;

preferably, the vanadium content of the hot-rolled steel section for the forklift mast is 0.095-0.105 wt%.

9. The production method according to any one of claims 1 to 8, wherein the production method comprises converter smelting, deoxidation alloying, LF refining, continuous casting, hot rolling, air cooling and finishing in this order;

the LF refining is accompanied with a nitrogen blowing operation, and the nitrogen blowing operation specifically comprises the following steps:

(1) starting bottom blowing nitrogen gas and arc heating with power consumption of 50-80kwh/t at 100-150NL/min, and keeping for 8-12 min;

(2) adjusting the bottom-blown nitrogen to 550NL/min, and keeping the temperature for 0.8-1.2 min;

(3) after the first sampling analysis, bottom blowing nitrogen is adjusted to 200-300NL/min, and the time is kept for 7-8 min;

(4) adding carburant and alloy, adjusting bottom blowing nitrogen to 550-650NL/min, and keeping for 4-8 min; the recarburizing agent comprises petroleum, and the dosage of the recarburizing agent is 0.2-0.3kg/t molten steel; the alloy comprises any one or the combination of at least two of aluminum ingot, silicon-manganese alloy, ferrovanadium alloy, medium carbon ferromanganese or high carbon ferrochromium, and the dosage is 0.5-5kg/t molten steel;

(5) stopping blowing the nitrogen gas from the bottom after the second sampling analysis;

wherein the absolute pressure of the bottom blowing nitrogen in the steps (1) to (5) is 1 to 1.4MPa, and the total volume is 9 to 10m³；

The hot-rolled section steel for the forklift portal frame meets the requirements that the carbon equivalent is less than or equal to 0.48 percent, the carbon element accounts for 0.16-0.18wt percent, the silicon element accounts for 0.32-0.36wt percent, the manganese element accounts for 1.51-1.55wt percent, the chromium element accounts for 0.06-0.1wt percent, and the vanadium element accounts for 0.095-0.105wt percent.

10. A hot-rolled section steel for forklift gantries, prepared by the preparation method according to any one of claims 1 to 9.

Background

With the continuous upgrading of domestic forklift products and the rapid development of forklift industry, the demand of hot-rolled section steel for the forklift gantry is rapidly increased. Meanwhile, along with the improvement of the quality of the forklift, users require that the steel for the portal frame is continuously improved in the aspects of high strength, high toughness, high precision and the like. In recent years, the hot-rolled section steel for the forklift gantry is more and more widely applied to the forklift industry in China, and the improvement speed is faster and faster. The domestic forklift industry is rapidly developed, the product quality is continuously upgraded, and the production and application technology of the hot-rolled section steel for the forklift gantry is gradually mature. At present, over 80 percent of domestic hot rolled section steel for the forklift gantry is made into domestic products, and a small part of the hot rolled section steel is welded by steel plates or imported. The domestic hot rolled section steel is adopted to replace the imported hot rolled section steel, so that the manufacturing cost of the forklift can be greatly reduced, and the cost advantage of forklift enterprises is improved; in addition, the hot-rolled section steel is adopted to replace steel plate welding, so that the residual stress can be avoided while the manufacturing cost is reduced, the comprehensive performance of the steel for the portal frame is improved, the manufacturing period can be shortened, and a large amount of manpower and material resources are saved.

At present, technicians in the field of producing hot-rolled section steel for forklift gantries generally adopt alloy elements such as vanadium, niobium and the like to refine crystal grains so as to improve the strength of the steel, and increase nitrogen by means of electric furnace smelting or adding manganese nitrogen wires and the like so as to improve the mechanical property of the steel. However, the methods generally have the problems of relatively high cost, tedious operation, limited improvement range of the comprehensive performance of the steel and the like, and further optimization is urgently needed.

CN 102864279A discloses a method for adding nitrogen in LF refining process, which is mainly applied to the production of high-nitrogen steel with nitrogen element to improve the steel performance, and concretely, a nitrogen-containing alloy is added into molten steel in a refining furnace after a deoxidizer is added into the molten steel in the initial stage of LF refining or the nitrogen-containing alloy is added into the molten steel after the refining deoxidation is finished. The method can obviously improve the supersaturated solubility of nitrogen in the rolled stock, and compared with the method for alloying the nitrogen in the converter process, the method can improve the nitrogen content in the rolled stock by more than 20 percent and has high nitrogen recovery rate. However, the method adopts the nitrogen alloy to improve the manufacturing cost, and the nitrogen increasing stability is poor, so that the strength and the toughness of the steel still have a larger improving space.

Therefore, how to provide the hot-rolled section steel for the forklift mast and the preparation method thereof can ensure the nitrogen increasing stability, further reduce the manufacturing cost, obviously improve the strength and toughness of the steel, simplify the operation process and become the problem which needs to be solved urgently by technical personnel in the field at present.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide the hot-rolled section steel for the forklift gantry and the preparation method thereof.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a preparation method of hot-rolled section steel for a forklift mast, which comprises the steps of converter smelting, LF refining and continuous casting which are sequentially carried out.

Wherein the LF refining is accompanied by a nitrogen blowing operation; the hot-rolled steel section for forklift mast satisfies the carbon equivalent of 0.48% or less, and may be, for example, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or 0.48%, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.

According to the invention, nitrogen blowing operation is carried out in the LF refining process to replace the traditional feeding of manganese-nitrogen alloy wires, so that the operation process is simplified, the manufacturing cost is further reduced, the nitrogen increasing stability can be ensured, the nitrogen content of the obtained steel reaches about 110ppm, and the strength and toughness of the steel are remarkably improved by utilizing the precipitation strengthening effect of vanadium nitride. In addition, by controlling the proportion of each alloy element, the mechanical property requirement that the yield strength is more than or equal to 440MPa is met on the premise that the carbon equivalent of the hot-rolled section steel for the forklift mast is less than or equal to 0.48%.

Preferably, the molten steel obtained by smelting in the converter is further deoxidized and alloyed before LF refining.

Preferably, the steel obtained by continuous casting is further subjected to hot rolling, air cooling and finishing in sequence.

In the invention, the operations of converter smelting, deoxidation alloying, LF refining, continuous casting, hot rolling, air cooling and finishing are all conventional technical means in the field, and in view of the protection emphasis of the invention, the nitrogen blowing operation accompanied with the LF refining is performed, and the rest operations have no influence on the nitrogen increasing link, so long as the carbon equivalent of the finally obtained hot-rolled steel section for the forklift mast is less than or equal to 0.48%, the specific operation processes of converter smelting, deoxidation alloying, LF refining, continuous casting, hot rolling, air cooling and finishing are not particularly limited, for example, the conditions of example 1 in CN103469056A can be referred to.

Preferably, the nitrogen blowing operation specifically comprises the following steps:

(1) starting bottom blowing nitrogen and arc heating at a first flow rate, and keeping for a first time period;

(2) adjusting the bottom blowing nitrogen to a second flow rate, and keeping for a second time period;

(3) adjusting bottom-blown nitrogen to a third flow rate after the first sampling analysis, and keeping for a third time period;

(4) adding a recarburizing agent and an alloy, adjusting bottom blowing nitrogen to a fourth flow, and keeping for a fourth time period;

(5) and stopping blowing the nitrogen gas from the bottom after the second sampling analysis.

The absolute pressure of the bottom-blown nitrogen gas in the steps (1) to (5) is 1 to 1.4MPa, and may be, for example, 1MPa, 1.05MPa, 1.1MPa, 1.15MPa, 1.2MPa, 1.25MPa, 1.3MPa, 1.35MPa or 1.4MPa, but is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned range are also applicable.

In the invention, the specific operation of bottom blowing nitrogen in the steps (1) to (5) is to blow nitrogen into the bottom of the LF refining furnace.

Preferably, the first flow rate in step (1) is 100-150NL/min, such as 100NL/min, 105NL/min, 110NL/min, 115NL/min, 120NL/min, 125NL/min, 130NL/min, 135NL/min, 140NL/min, 145NL/min or 150NL/min, but not limited to the values listed, and other values not listed in this range of values are equally applicable.

Preferably, the first period of time in step (1) is 8-12min, such as 8min, 8.5min, 9min, 9.5min, 10min, 10.5min, 11min, 11.5min or 12min, but not limited to the recited values, and other non-recited values within the range are equally applicable.

Preferably, the second flow rate in step (2) is 550-650NL/min, such as 550NL/min, 560NL/min, 570NL/min, 580NL/min, 590NL/min, 600NL/min, 610NL/min, 620NL/min, 630NL/min, 640NL/min or 650NL/min, but is not limited to the values listed, and other values not listed in this range of values are equally applicable.

Preferably, the second time period in step (2) is 0.8-1.2min, such as 0.8min, 0.85min, 0.9min, 0.95min, 1min, 1.05min, 1.1min, 1.15min or 1.2min, but not limited to the recited values, and other non-recited values within the range are equally applicable.

In the invention, the second flow rate of the bottom-blown nitrogen in the step (2) is far higher than the first flow rate in the step (1), so that the purpose of fully stirring the molten steel is achieved, and the accuracy of the first sampling analysis in the step (3) is improved.

Preferably, the third flow rate in step (3) is 200-300NL/min, such as 200NL/min, 210NL/min, 220NL/min, 230NL/min, 240NL/min, 250NL/min, 260NL/min, 270NL/min, 280NL/min, 290NL/min or 300NL/min, but not limited to the values listed, and other values not listed in this range are equally applicable.

Preferably, the third time period in step (3) is 7-8min, such as 7min, 7.1min, 7.2min, 7.3min, 7.4min, 7.5min, 7.6min, 7.7min, 7.8min, 7.9min or 8min, but is not limited to the recited values, and other non-recited values within the range are equally applicable.

Preferably, the fourth flow rate in step (4) is 550-650NL/min, such as 550NL/min, 560NL/min, 570NL/min, 580NL/min, 590NL/min, 600NL/min, 610NL/min, 620NL/min, 630NL/min, 640NL/min or 650NL/min, but is not limited to the values listed, and other values not listed in this range are equally applicable.

Preferably, the fourth time period in step (4) is 4-8min, such as 4min, 4.5min, 5min, 5.5min, 6min, 6.5min, 7min, 7.5min or 8min, but not limited to the recited values, and other non-recited values in the range are also applicable.

In the invention, the fourth flow rate of the bottom-blown nitrogen in the step (4) is far higher than the third flow rate in the step (3), so that the aim of fully mixing the carburant and the alloy is fulfilled, and the accuracy of the second sampling analysis in the step (5) is improved.

Preferably, the total volume of the bottom-blown nitrogen gas in the steps (1) to (5) is 9 to 10m³For example, it may be 9m³、9.1m³、9.2m³、9.3m³、9.4m³、9.5m³、9.6m³、9.7m³、9.8m³、9.9m³Or 10m³However, the numerical values recited are not intended to be limiting, and other numerical values not recited within the numerical range may be equally applicable.

In the invention, the total volume of the bottom-blown nitrogen gas in the steps (1) to (5) affects the nitrogen content of the finally obtained steel. When the total volume of the bottom blowing nitrogen is less than 9m³When the content of nitrogen in the obtained steel is lower than 100ppm, the precipitation strengthening effect of vanadium nitride is not facilitated, and the yield strength of the steel is reduced; when the total volume of the bottom blowing nitrogen is more than 10m³In this case, the nitrogen content of the steel is not significantly increased, which leads to an unnecessary increase in production cost.

Preferably, the power consumption of the arc heating in step (1) is 50-80kwh/t, such as 50kwh/t, 55kwh/t, 60kwh/t, 65kwh/t, 70kwh/t, 75kwh/t or 80kwh/t, but not limited to the recited values, and other values not recited in the range of values are equally applicable.

Preferably, the recarburizer of step (4) comprises petroleum;

preferably, the amount of the carburant used in the step (4) is 0.2 to 0.3kg/t of molten steel, and may be, for example, 0.2kg/t of molten steel, 0.22kg/t of molten steel, 0.24kg/t of molten steel, 0.26kg/t of molten steel, 0.28kg/t of molten steel, or 0.3kg/t of molten steel, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.

Preferably, the alloy of step (4) comprises any one or a combination of at least two of an aluminum ingot, a silicomanganese alloy, a ferrovanadium alloy, a medium carbon ferromanganese or a high carbon ferrochrome, typical but non-limiting combinations include a combination of an aluminum ingot and a silicomanganese alloy, a combination of a silicomanganese alloy and a ferrovanadium alloy, a combination of a ferrovanadium alloy and a medium carbon ferromanganese, a combination of a medium carbon ferromanganese and a high carbon ferrochrome, a combination of an aluminum ingot, a silicomanganese alloy and a ferrovanadium alloy, a combination of a silicomanganese alloy, a ferrovanadium alloy and a medium carbon ferromanganese, or a combination of a ferrovanadium, a medium carbon ferromanganese and a high carbon ferrochrome.

Preferably, the alloy of step (4) is used in an amount of 0.5 to 5kg/t molten steel, for example, 0.5kg/t molten steel, 1kg/t molten steel, 1.5kg/t molten steel, 2kg/t molten steel, 2.5kg/t molten steel, 3kg/t molten steel, 3.5kg/t molten steel, 4kg/t molten steel, 4.5kg/t molten steel or 5kg/t molten steel, but not limited to the values listed, and other values not listed in the range of values are also applicable.

In the present invention, the amount of the alloy in the step (4) is related to the specific kind of the alloy, for example: the dosage of the aluminum ingot is 1-2kg/t molten steel, the dosage of the silicon-manganese alloy is 1-2kg/t molten steel, the dosage of the ferrovanadium alloy is 0.5-1.5kg/t molten steel, the dosage of the medium carbon ferromanganese is 2-5kg/t molten steel, and the dosage of the high carbon ferrochrome is 0.5-2kg/t molten steel.

Preferably, the carbon content ratio of the hot-rolled steel section for forklift mast is 0.16-0.18 wt%, for example, 0.16 wt%, 0.162 wt%, 0.164 wt%, 0.166 wt%, 0.168 wt%, 0.17 wt%, 0.172 wt%, 0.174 wt%, 0.176 wt%, 0.178 wt%, or 0.18 wt%, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the silicon content of the hot rolled steel section for forklift mast is 0.32-0.36 wt%, for example, 0.32 wt%, 0.325 wt%, 0.33 wt%, 0.335 wt%, 0.34 wt%, 0.345 wt%, 0.35 wt%, 0.355 wt%, or 0.36 wt%, but is not limited to the recited values, and other values not recited in the range of the recited values are also applicable.

Preferably, the manganese content of the hot-rolled steel section for forklift mast is 1.51-1.55 wt%, for example, 1.51 wt%, 1.515 wt%, 1.52 wt%, 1.525 wt%, 1.53 wt%, 1.535 wt%, 1.54 wt%, 1.545 wt%, or 1.55 wt%, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the chromium content of the hot-rolled steel section for forklift mast is 0.06-0.1 wt%, for example, 0.06 wt%, 0.065 wt%, 0.07 wt%, 0.075 wt%, 0.08 wt%, 0.085 wt%, 0.09 wt%, 0.095 wt%, or 0.1 wt%, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the vanadium content of the hot-rolled steel section for forklift mast is 0.095 to 0.105 wt%, and may be, for example, 0.095 wt%, 0.096 wt%, 0.097 wt%, 0.098 wt%, 0.099 wt%, 0.1 wt%, 0.101 wt%, 0.102 wt%, 0.103 wt%, 1.104 wt%, or 0.105 wt%, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

As a preferable technical scheme of the first aspect of the invention, the preparation method comprises the steps of converter smelting, deoxidation alloying, LF refining, continuous casting, hot rolling, air cooling and finishing which are sequentially carried out.

The LF refining is accompanied with a nitrogen blowing operation, and the nitrogen blowing operation specifically comprises the following steps:

(1) starting bottom blowing nitrogen gas and arc heating with power consumption of 50-80kwh/t at 100-150NL/min, and keeping for 8-12 min;

(2) adjusting the bottom-blown nitrogen to 550NL/min, and keeping the temperature for 0.8-1.2 min;

(3) after the first sampling analysis, bottom blowing nitrogen is adjusted to 200-300NL/min, and the time is kept for 7-8 min;

(4) adding carburant and alloy, adjusting bottom blowing nitrogen to 550-650NL/min, and keeping for 4-8 min; the recarburizing agent comprises petroleum, and the dosage of the recarburizing agent is 0.2-0.3kg/t molten steel; the alloy comprises any one or the combination of at least two of aluminum ingot, silicon-manganese alloy, ferrovanadium alloy, medium carbon ferromanganese or high carbon ferrochromium, and the dosage is 0.5-5kg/t molten steel;

(5) and stopping blowing the nitrogen gas from the bottom after the second sampling analysis.

Wherein the absolute pressure of the bottom blowing nitrogen in the steps (1) to (5) is 1 to 1.4MPa, and the total volume is 9 to 10m³。

The hot-rolled section steel for the forklift portal frame meets the requirements that the carbon equivalent is less than or equal to 0.48 percent, the carbon element accounts for 0.16-0.18wt percent, the silicon element accounts for 0.32-0.36wt percent, the manganese element accounts for 1.51-1.55wt percent, the chromium element accounts for 0.06-0.1wt percent, and the vanadium element accounts for 0.095-0.105wt percent.

In a second aspect, the invention provides the hot-rolled section steel for the forklift mast prepared by the preparation method in the first aspect.

Compared with the prior art, the invention has the beneficial effects that:

(1) according to the invention, the traditional feeding of manganese-nitrogen alloy wires is replaced by nitrogen blowing operation in the LF refining process, the operation process is simplified, the manufacturing cost is further reduced, the nitrogen increasing stability can be ensured, the nitrogen content of the obtained steel reaches about 110ppm, and the strength and toughness of the steel are obviously improved by utilizing the precipitation strengthening effect of vanadium nitride;

(2) according to the invention, by controlling the proportion of each alloy element, the mechanical property requirement that the yield strength is more than or equal to 440MPa is met on the premise that the carbon equivalent of the hot-rolled section steel for the forklift gantry is less than or equal to 0.48%.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments.

Example 1

The embodiment provides a preparation method of hot-rolled section steel for a forklift mast, which comprises converter smelting, deoxidation alloying, LF refining, continuous casting, hot rolling, air cooling and finishing which are sequentially performed, and the specific operation process refers to the conditions of embodiment 1 in CN103469056A, so that details are not repeated herein.

In this embodiment, the LF refining is accompanied by a nitrogen blowing operation, and the nitrogen blowing operation specifically includes the following steps:

(1) starting bottom blowing nitrogen at 200NL/min and arc heating with power consumption of 65kwh/t, and keeping for 10-15 min;

(2) adjusting bottom-blown nitrogen to 600NL/min, and keeping for 4-5 min;

(3) adjusting bottom-blown nitrogen to 250NL/min after the first sampling analysis, and keeping for 7-8 min;

(4) adding 0.25kg/t of petroleum coke recarburizer of molten steel and 1.5kg/t of aluminum ingot of molten steel, adjusting bottom blowing nitrogen to 600NL/min, and keeping for 5-6 min;

(5) and stopping blowing the nitrogen gas from the bottom after the second sampling analysis.

Wherein the absolute pressure of the bottom-blown nitrogen in the steps (1) to (5) is 1.2MPa, and the total volume is 11m³。

Through detection, the hot-rolled section steel for the forklift gantry, obtained in the embodiment, has the carbon equivalent of 0.46%, the carbon element proportion of 0.17 wt%, the silicon element proportion of 0.34 wt%, the manganese element proportion of 1.53 wt%, the chromium element proportion of 0.08 wt%, and the vanadium element proportion of 0.1 wt%; the nitrogen content was 108ppm and the yield strength was 460 MPa.

Example 2

The embodiment provides a preparation method of hot-rolled section steel for a forklift mast, which comprises converter smelting, deoxidation alloying, LF refining, continuous casting, hot rolling, air cooling and finishing which are sequentially performed, and the specific operation process refers to the conditions of embodiment 1 in CN103469056A, so that details are not repeated herein.

In this embodiment, the LF refining is accompanied by a nitrogen blowing operation, and the nitrogen blowing operation specifically includes the following steps:

(1) starting bottom blowing nitrogen at 100NL/min and arc heating with power consumption of 50kwh/t, and keeping for 12 min;

(2) adjusting bottom-blown nitrogen to 550NL/min, and keeping for 1.2 min;

(3) adjusting bottom-blown nitrogen to 200NL/min after the first sampling analysis, and keeping for 8 min;

(4) adding 0.2kg/t of petroleum coke recarburizer of molten steel and 0.5kg/t of ferrovanadium alloy of the molten steel, adjusting bottom blowing nitrogen to 550NL/min, and keeping for 8 min;

(5) and stopping blowing the nitrogen gas from the bottom after the second sampling analysis.

Wherein the absolute pressure of the bottom blowing nitrogen in the steps (1) to (5) is 1MPa, and the total volume is 9m³。

Through detection, the hot-rolled section steel for the forklift gantry, obtained in the embodiment, has the carbon equivalent of 0.44%, the carbon element proportion of 0.16 wt%, the silicon element proportion of 0.32 wt%, the manganese element proportion of 1.51 wt%, the chromium element proportion of 0.06 wt%, and the vanadium element proportion of 0.095 wt%; the nitrogen content is 100ppm and the yield strength is 450 MPa.

Example 3

The embodiment provides a preparation method of hot-rolled section steel for a forklift mast, which comprises converter smelting, deoxidation alloying, LF refining, continuous casting, hot rolling, air cooling and finishing which are sequentially performed, and the specific operation process refers to the conditions of embodiment 1 in CN103469056A, so that details are not repeated herein.

In this embodiment, the LF refining is accompanied by a nitrogen blowing operation, and the nitrogen blowing operation specifically includes the following steps:

(1) starting bottom blowing nitrogen at 150NL/min and arc heating with power consumption of 80kwh/t, and keeping for 8 min;

(2) adjusting bottom-blown nitrogen to 650NL/min, and keeping for 0.8 min;

(3) adjusting bottom-blown nitrogen to 300NL/min after the first sampling analysis, and keeping for 7 min;

(4) adding 0.3kg/t of petroleum coke recarburizer of molten steel and 5kg/t of medium carbon ferromanganese of molten steel, adjusting bottom blowing nitrogen to 650NL/min, and keeping for 4 min;

(5) and stopping blowing the nitrogen gas from the bottom after the second sampling analysis.

Wherein the absolute pressure of the bottom-blown nitrogen in the steps (1) to (5) is 1.4MPa, and the total volume is 10m³。

Through detection, the hot-rolled section steel for the forklift gantry, obtained in the embodiment, has the carbon equivalent of 0.48%, the carbon element proportion of 0.18 wt%, the silicon element proportion of 0.36 wt%, the manganese element proportion of 1.55 wt%, the chromium element proportion of 0.1 wt%, and the vanadium element proportion of 0.105 wt%; the nitrogen content was 112ppm and the yield strength was 480 MPa.

Example 4

The present embodiment providesA preparation method of hot-rolled section steel for a forklift mast comprises the steps of converter smelting, deoxidation alloying, LF refining, continuous casting, hot rolling, air cooling and finishing which are sequentially carried out, wherein the specific operation process refers to the conditions in embodiment 1 in CN 103469056A; the LF refining is accompanied with a nitrogen blowing operation except that the total volume of the bottom-blown nitrogen gas in the steps (1) to (5) is changed to 8m³The rest of the conditions are the same as those in example 1, and therefore, the description thereof is omitted.

Through detection, the nitrogen content of the hot-rolled section steel for the forklift mast obtained in the embodiment is 98ppm, and the yield strength is 440 MPa.

Compared with the embodiment 1, the nitrogen content of the steel obtained by the embodiment is lower than 100ppm due to the reduction of the total volume of the bottom-blown nitrogen, which is not beneficial to the precipitation strengthening effect of vanadium nitride and reduces the yield strength of the steel.

Example 5

The embodiment provides a preparation method of hot-rolled section steel for a forklift mast, which comprises the steps of converter smelting, deoxidation alloying, LF refining, continuous casting, hot rolling, air cooling and finishing which are sequentially carried out, wherein the specific operation process refers to the conditions in embodiment 1 in CN 103469056A; the LF refining is accompanied with a nitrogen blowing operation except that the total volume of the bottom-blown nitrogen gas in the steps (1) to (5) is changed to 11m³The rest of the conditions are the same as those in example 1, and therefore, the description thereof is omitted.

Through detection, the nitrogen content of the hot-rolled section steel for the forklift mast obtained in the embodiment is 109ppm, and the yield strength is 465 MPa.

Compared with the embodiment 1, although the total volume of the bottom-blown nitrogen gas is obviously increased, the increase of the nitrogen content of the obtained steel is not significant, and the production cost is unnecessarily increased.

Comparative example 1

The preparation method comprises converter smelting, deoxidation alloying, LF refining, continuous casting, hot rolling, air cooling and finishing which are sequentially carried out, and the specific operation process refers to the conditions of embodiment 1 in CN103469056A, so that details are not repeated.

In the comparative example, the LF refining is accompanied by feeding of the manganese-nitrogen alloy wire, and the specific process of feeding the manganese-nitrogen alloy wire is as follows: the manganese-nitrogen alloy wire is vertically inserted into the molten steel by using a wire feeding machine, so that the molten steel contains 1.53 wt% of manganese and 108ppm of nitrogen.

Through detection, the yield strength of the hot-rolled section steel for the forklift mast obtained in the comparative example is 430MPa, which is far lower than that of the steel obtained in the example 1.

Therefore, the nitrogen blowing operation is carried out in the LF refining process to replace the traditional feeding of manganese-nitrogen alloy wires, the operation process is simplified, the manufacturing cost is further reduced, the nitrogen increasing stability can be ensured, the nitrogen content of the obtained steel reaches about 110ppm, and the strength and the toughness of the steel are obviously improved by utilizing the precipitation strengthening effect of vanadium nitride; in addition, by controlling the proportion of each alloy element, the mechanical property requirement that the yield strength is more than or equal to 440MPa is met on the premise that the carbon equivalent of the hot-rolled section steel for the forklift mast is less than or equal to 0.48%.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.