Production method for improving yield strength of German standard A150 crane rail

Abstract

The invention discloses a production method for improving the yield strength of a German standard A150 crane rail, and belongs to the technical field of steel rail steel smelting. The method comprises the following steps: 1) a steelmaking process; (2) rolling the steel rail after rolling a steel billet, and naturally cooling in the air after rolling: adopting 13-pass rolling in the rolling process, and limiting specific passes and rolling reduction; through multi-pass small rolling reduction rolling, grains are gradually refined, and the yield strength is improved; the crane rail comprises the following chemical components in percentage by mass: 0.8%-0.85% of C, 0.4%-0.5% of Si, 1.0%-1.3% of Mn, 0.2%-0.4% of Cr, 0.04%-0.12% of V and the balance of iron and impurities. According to the crane rail, Rm is larger than or equal to 1160 MPa, Rp0.2 is larger than or equal to 650.5 MPa, the elongation is larger than or equal to 12%, and the tread hardness is larger than or equal to 330 HB.

Description

Technical Field

[0001] The invention belongs to the technical field of rail steel smelting, and in particular relates to a production method for improving the yield strength of German standard A150 crane rails. Background Art

[0002] Demand for German standard A150 crane rails is increasing in the heavy-duty lifting sector. Due to their large cross-section, crane rails require extremely high mechanical properties such as strength, wear resistance, and toughness. While existing technologies are capable of producing this type of rail, achieving a yield strength that meets design requirements remains challenging. To further stabilize the yield strength of crane rails, this patent provides a production method for increasing the yield strength of German standard A150 crane rails. Summary of the Invention

[0003] The purpose of the present invention is to provide a production method for improving the yield strength of German standard A150 crane rail, to improve the yield strength of German standard A150 crane rail, to meet the following requirements: Rm≥1160MPa (required ≥1080MPa), R p0.2 ≥650.5MPa (requirement ≥640MPa), elongation ≥12% (requirement ≥7%), tread hardness ≥330HB (requirement ≥320HB).

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention provides a production method for improving the yield strength of German standard A150 crane rails, comprising:

[0006] 1) Steelmaking process

[0007] 1.1) Converter smelting

[0008] Before the molten iron enters the furnace, it is pre-desulfurized to reduce the sulfur content in the molten iron to below 0.01%, reducing the adverse effects of sulfur on the performance of the rails. According to the composition of the molten iron and production needs, an appropriate amount of scrap steel is added, and the proportion of scrap steel is controlled at 20%-30% to reduce production costs and optimize the composition of the molten steel. High-intensity oxygen supply and bottom-blown argon stirring are used, and the oxygen pressure is controlled at 0.8-1.0MPa. The gun position is operated alternately at high and low gun positions. In the early stage, a high gun position is used for light blowing to promote the temperature rise of the molten pool; in the middle stage, it is switched to a low gun position for strong blowing to accelerate the carbon-oxygen reaction and increase the decarburization rate; in the later stage, it is adjusted to a high gun position for light blowing again to ensure that the composition of the molten steel is uniform; when the steel output reaches 30%-40%, an aluminum-free deoxidizer is added for deoxidation and alloying operations, and 4-6kg of low-aluminum silicon calcium barium is added at the same time to perform deep and strong deoxidation of the molten steel to ensure that the molten steel is low in oxygen and aluminum, reduce inclusions, and improve purity;

[0009] 1.2) LF refining

[0010] White slag refining with slag forming material, total amount controlled at 15-20 kg / t, to ensure white slag formation speed and quality, improve slag covering effect and inclusion adsorption capacity; argon continuously blown during refining, gas flow controlled at 0.15-0.20 m 3 / (m 2 ·h), promote steel liquid uniform mixing, conducive to inclusion floating removal, while avoiding excessive oxidation of steel liquid; according to converter liquid composition and temperature, precise desulfurization, composition fine tuning and temperature rise; desulfurizer adopts CaO-SiO2-Al2O3 series, addition amount determined according to liquid sulfur content, to ensure desulfurization efficiency ≥80%; strictly control final slag basicity at 2.5-3.0, Al2O3 content ≤7wt%, white slag maintenance time not less than 40 min, to ensure stability of refining effect;

[0011] 1.3) VD vacuum degassing

[0012] Ensure vacuum degree in vacuum chamber within ≤0.06 KPa range for stable operation, control liquid temperature at 1620℃-1650℃ before vacuum treatment, to ensure steel liquid fluidity, conducive to gas precipitation and inclusion removal; deep vacuum time guaranteed ≥20 min, to ensure hydrogen content in liquid ≤1.0 ppm, nitrogen content ≤40 ppm, while removing other harmful gases; soft blowing time guaranteed ≥20 min, argon flow controlled at 0.05-0.10 m 3 / (m 2 ·h), to make inclusions in steel liquid fully float, while ensuring steel liquid standing time reaching 30 min or more, to avoid secondary oxidation;

[0013] 1.4) continuous casting

[0014] Set large capacity filter in tundish, filter adopts high gas permeability and high filtration efficiency material, to effectively remove large particle inclusions in liquid; at the same time, adopt protective casting technology, through long nozzle, submerged nozzle and argon sealing measures, to avoid secondary oxidation of liquid during casting, reduce oxidation atmosphere in tundish, to ensure liquid quality; apply electromagnetic braking technology, magnetic field strength controlled at 15-20 mT, to improve liquid flow state in mold, reduce slag entrapment and gas bubble defects;

[0015] 2) rail rolling

[0016] Steel billet post-rolling, after rolling, natural cooling in air; specifically including:

[0017] Steel billet heating adopts step-by-step heating furnace for heating, cast billet temperature 1200℃-1250℃, to ensure uniform heating;

[0018] The starting rolling temperature is 1050℃-1100℃, and the finishing rolling temperature is 900℃-980℃;

[0019] The rolling process adopts 13 passes, and the specific passes and reduction amounts are distributed as follows:

[0020] 1st to 3rd pass: The reduction of each pass is 10%-15%, and the cumulative reduction is 30%-40%;

[0021] Passes 4-8: Each pass has a reduction of 8%-12%, and the cumulative reduction is 60%-70%;

[0022] Passes 9-13: Each pass has a reduction of 5%-8%, and the cumulative total reduction reaches 85%-90%;

[0023] Through multiple passes of small reduction rolling, the grain size is gradually refined and the yield strength is improved;

[0024] The crane rail has the following chemical compositions by mass percentage: C 0.8%-0.85%, Si 0.4%-0.5%, Mn 1.0%-1.3%, Cr 0.3%-0.45%, V 0.04%-0.12%, and the remainder is iron and impurities.

[0025] Furthermore, the high gun position is 1.2-1.5m away from the molten pool liquid surface for gentle blowing.

[0026] Furthermore, the low gun position is 0.8-1.0m away from the molten pool liquid surface for strong blowing.

[0027] Furthermore, the aluminum-free deoxidizer is silicon calcium barium.

[0028] Furthermore, the air permeability index of the filter is ≥10 L / min·kPa.

[0029] Furthermore, it also includes: using a laser rangefinder to monitor the height of the molten steel level in the crystallizer in real time, and controlling the liquid level fluctuation within the range of ±3mm through a high-precision automatic control system to improve the quality of the casting.

[0030] Furthermore, the billet size is 280×380 mm.

[0031] Furthermore, the crane rail has the following chemical composition by mass percentage: C 0.82%, Si 0.45%, Mn 1.15%, Cr 0.30%, and V 0.08%.

[0032] Compared with the prior art, the present invention has the following beneficial technical effects:

[0033] The performance of the German standard A150 crane rail produced by the method of the present invention meets the following requirements: Rm≥1160MPa (required ≥1080MPa), Rp0.2 ≥650.5MPa (requirement ≥640MPa), elongation ≥12% (requirement ≥7%), tread hardness ≥330HB (requirement ≥320HB). DETAILED DESCRIPTION

[0034] A production method for improving the yield strength of German standard A150 crane rails, comprising:

[0035] 1. Optimized steelmaking process

[0036] (1) Converter smelting

[0037] Before entering the furnace, the molten iron is pre-desulfurized to reduce the sulfur content to below 0.01%, reducing the adverse effects of sulfur on rail performance. According to the molten iron composition and production requirements, an appropriate amount of scrap steel is added, and the scrap steel ratio is controlled at 20%-30% to reduce production costs and optimize the molten steel composition. High-intensity oxygen supply and bottom-blown argon stirring are used, and the oxygen pressure is controlled at 0.8-1.0MPa. The gun position is operated alternately at high and low gun positions. In the early stage, a high gun position (1.2-1.5m from the molten pool liquid surface) is used for light blowing to promote the molten pool temperature; in the middle stage, it is switched to a low gun position (0.8-1.0m from the molten pool liquid surface) for strong blowing to accelerate the carbon-oxygen reaction and increase the decarburization rate; in the later stage, it is adjusted again to a high gun position for light blowing to ensure a uniform composition of the molten steel. When the steel output reaches 30%-40%, a special aluminum-free deoxidizer (such as silicon calcium barium) is added for deoxidation and alloying operation. At the same time, 4-6 kg of low-aluminum silicon calcium barium is added to perform deep and strong deoxidation of the molten steel to ensure low oxygen and low aluminum content in the molten steel, reduce inclusions, and improve purity.

[0038] (2) LF refining

[0039] Active lime, wollastonite and other slag-forming materials are added for white slag refining, with the total amount controlled at 15-20kg / t to ensure the formation speed and quality of white slag, improve the slag covering effect and the ability to absorb inclusions. Argon is continuously blown into the refining process, and the gas flow rate is controlled at 0.15-0.20m 3 / (m 2 h) promotes uniform mixing of the molten steel, facilitates the removal of inclusions, and prevents over-oxidation. Precise desulfurization, fine-tuning of composition, and temperature increase are performed based on the converter molten steel composition and temperature. A desulfurizer series of CaO-SiO2-Al2O3 is used, with the dosage calculated based on the molten steel's sulfur content to ensure a desulfurization efficiency of ≥80%. The final slag basicity is strictly controlled between 2.5-3.0, the Al2O3 content is ≤7wt%, and the white slag is maintained for at least 40 minutes to ensure stable refining results.

[0040] (3) VD vacuum degassing

[0041] The vacuum degree in the vacuum chamber is ensured to be stable within the range of ≤0.06 KPa, the temperature of the molten steel is controlled within the range of 1620-1650 ℃ before the vacuum treatment, the fluidity of the molten steel is ensured, and the gas precipitation and inclusion removal are facilitated. The deep vacuum time is ensured to be ≥20 min, the hydrogen content in the molten steel is ensured to be ≤1.0 ppm, the nitrogen content is ensured to be ≤40 ppm, and other harmful gases are removed. The soft blowing time is ensured to be ≥20 min, the argon flow is controlled within the range of 0.05-0.10 m 3 / (m 2 ·h), the inclusions in the molten steel are fully floated, and the molten steel standing time is ensured to be ≥30 min, so that the secondary oxidation is avoided.

[0042] (IV) continuous casting

[0043] A large-capacity filter is arranged in the tundish, the filter is made of a material with high gas permeability and high filtration efficiency, so that the large-particle inclusions in the molten steel are effectively removed, and the gas permeability index of the filter is ≥10 L / min·kPa. The protective casting technology is adopted, the long nozzle, submerged nozzle and argon sealing are adopted, so that the secondary oxidation of the molten steel in the casting process is avoided, the oxidation atmosphere in the tundish is reduced, and the molten steel quality is ensured. The electromagnetic braking technology is applied, the magnetic field strength is controlled within the range of 15-20 mT, the flow state of the molten steel in the mold is improved, and the slag entrapment and gas bubble defects are reduced. The laser range finder is used to monitor the molten steel liquid level in the mold in real time, the liquid level fluctuation is controlled within the range of ±3 mm through the high-precision automatic control system, and the quality of the casting blank is improved.

[0044] II. Rail Rolling

[0045] The billets (the billet size is 280×380) are rolled after heating, and are naturally cooled in the air after rolling.

[0046] Specifically as follows:

[0047] (I) The billets are heated by using a walking beam furnace, and the billet temperature is 1200-1250 ℃, so that the uniform heating is ensured.

[0048] (II) Rolling process

[0049] 1. The opening rolling temperature is 1050-1100 ℃, and the final rolling temperature is 900-980 ℃;

[0050] 2. The rolling process adopts 13 passes, and the specific pass and reduction distribution are as follows:

[0051] 3. The first to third passes: the reduction of each pass is 10%-15%, and the cumulative reduction is 30%-40%;

[0052] 4. Passes 4-8: The reduction per pass is 8%-12%, and the cumulative reduction is 60%-70%;

[0053] 5. 9th-13th pass: The reduction of each pass is 5%-8%, and the cumulative total reduction reaches 85%-90%.

[0054] Through multiple passes of small reduction rolling, the grains are gradually refined and the yield strength is improved.

[0055] Example 1 (yield strength 650.5 MPa)

[0056] Rails produced using the aforementioned composition and process have the following specific composition (by mass): C 0.82%, Si 0.45%, Mn 1.15%, Cr 0.30%, and V 0.08%. Billets measuring 280 x 380 mm are used, rolled through 13 passes, and then naturally cooled in air. Testing has shown that the yield strength reaches 650.5 MPa, the tensile strength ≥1160 MPa, the elongation ≥12%, and the average Brinell hardness ≥330 HB. These excellent properties meet the requirements of crane rails.

[0057] Comparative Example 1 (yield strength 600 MPa)

[0058] Rails produced using the aforementioned composition and process have the following composition (by mass): C 0.79%, Si 0.45%, Mn 0.95%, Cr 0.35%, and V 0.1%. Billets measuring 280 x 380 mm were used, rolled through 13 passes, and then naturally cooled in air. Testing revealed a yield strength of 600 MPa, a tensile strength ≥1150 MPa, an elongation ≥11%, and an average Brinell hardness ≥334 HB, which did not meet the design requirements for crane rails.

[0059] It can be seen that the carbon content and Mn content in the rail have a greater impact on the yield of the rail, among which the C content is not easy to be lower than 0.8%, and the Mn content is not easy to be lower than 1.0%.

[0060] Comparative Example 2 (yield strength 550 MPa)

[0061] Rails were produced using the aforementioned composition and process. The specific composition (by mass percentage) is: C 0.8%, Si 0.45%, Mn 1.1%, Cr 0.25%, and V 0.08%. Billets measuring 280 x 380 mm were used, rolled through 13 passes, and then naturally cooled in air. Testing revealed a yield strength of 550 MPa, a tensile strength ≥1105 MPa, an elongation ≥10.5%, and an average Brinell hardness ≥321 HB, which did not meet the design requirements for crane rails.

[0062] The Cr content in the steel rail has a relatively significant influence on the yield value, and when the Cr content in the steel is below 0.3%, the yield value of the steel rail is affected.

[0063] The above examples and comparative examples adopt the same process and parameter control, and the influence of the above-mentioned components on the performance of the steel rail is mutually synergistic. Only when the content of each element reaches the target component can the performance index of the steel rail meet the design requirements.

[0064] By optimizing the component design and process, the yield strength of the German standard A150 crane rail is significantly improved, while the toughness and hardness are maintained, so that it is more suitable for heavy lifting operation requirements, prolongs the service life, and improves the market competitiveness.

[0065] The above-described examples only describe the preferred modes of the present application and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A production method for improving the yield strength of German standard A150 crane rail, characterized in that: include: 1) Steelmaking process 1.1) Converter smelting The molten iron is pre-desulfurized before entering the furnace to reduce the sulfur content in the molten iron to below 0.01%, thereby reducing the adverse effects of sulfur on rail performance. According to the composition of the molten iron and production needs, an appropriate amount of scrap steel is added, and the scrap steel ratio is controlled at 20%-30% to reduce production costs and optimize the molten steel composition. High-intensity oxygen supply and bottom-blown argon stirring are used, and the oxygen pressure is controlled at 0.8-1.0MPa. The lance position is operated alternately at high and low positions. In the early stage, a high lance position is used for gentle blowing to promote the temperature rise of the molten pool; in the middle stage, it is switched to a low lance position for strong blowing to accelerate the carbon-oxygen reaction and increase the decarburization rate. Later, the process is adjusted to a high gun position with gentle blowing to ensure uniform composition of the molten steel. When the tapping volume reaches 30%-40%, aluminum-free deoxidizer is added for deoxidation and alloying. At the same time, 4-6 kg of low-aluminum silicon calcium barium is added to perform deep and strong deoxidation of the molten steel, ensuring low oxygen and aluminum content in the molten steel, reducing inclusions and improving purity. 1.2) LF refining Add slag-forming materials for white slag refining, and control the total amount at 15-20kg / t to ensure the formation speed and quality of white slag, improve the slag coverage effect and the ability to absorb inclusions; continuously blow argon during the refining process, and control the gas flow at 0.15-0.20m 3 / (m 2 h) promotes uniform mixing of the molten steel, facilitates the removal of inclusions by floating, and prevents excessive oxidation of the molten steel; precise desulfurization, composition fine-tuning, and temperature increase are performed according to the molten steel composition and temperature in the converter; the desulfurizer uses the CaO-SiO2-Al2O3 series, and the addition amount is determined based on the sulfur content of the molten steel to ensure a desulfurization efficiency of ≥80%; the final slag basicity is strictly controlled between 2.5-3.0, the Al2O3 content is ≤7wt%, and the white slag is maintained for no less than 40 minutes to ensure the stability of the refining effect; 1.3) VD vacuum degassing Ensure that the vacuum degree in the vacuum chamber is stable within the range of ≤0.06KPa. Before vacuum treatment, control the molten steel temperature within the range of 1620℃-1650℃ to ensure the fluidity of the molten steel, which is conducive to the precipitation of gas and the removal of inclusions. Ensure that the deep vacuum time is ≥20min, ensure that the hydrogen content in the molten steel is ≤1.0ppm, the nitrogen content is ≤40ppm, and other harmful gases are removed at the same time. Ensure that the soft blowing time is ≥20min, and the argon flow rate is controlled at 0.05-0.10m 3 / (m 2 h), so that the inclusions in the molten steel can fully float up, and at the same time ensure that the molten steel is left to stand for more than 30 minutes to avoid secondary oxidation; 1.4) Continuous Casting A large-capacity filter is installed in the tundish. The filter is made of a material with high air permeability and high filtration efficiency to effectively remove large particle inclusions in the molten steel. At the same time, protective casting technology is adopted, using measures such as long nozzles, submerged nozzles, and argon seals to prevent secondary oxidation of the molten steel during the casting process, reduce the oxidizing atmosphere in the tundish, and ensure the quality of the molten steel. Electromagnetic braking technology is applied, and the magnetic field strength is controlled at 15-20mT to improve the flow state of the molten steel in the crystallizer and reduce slag entanglement and bubble defects. 2) Rail rolling The steel billet is then rolled and cooled naturally in the air after rolling; specifically, the following steps are involved: The billet is heated by a walking beam furnace, with the billet temperature at 1200℃-1250℃ to ensure uniform heating; The starting rolling temperature is 1050℃-1100℃, and the finishing rolling temperature is 900℃-980℃; The rolling process adopts 13 passes, and the specific passes and reduction amounts are distributed as follows: 1st to 3rd pass: The reduction of each pass is 10%-15%, and the cumulative reduction is 30%-40%; Passes 4-8: Each pass has a reduction of 8%-12%, and the cumulative reduction is 60%-70%; 9th-13th passes: Each pass has a reduction of 5%-8%, and the cumulative total reduction reaches 85%-90%; Through multiple passes of small reduction rolling, the grain size is gradually refined and the yield strength is improved; The crane rail has the following chemical compositions by mass percentage: C 0.8%-0.85%, Si 0.4%-0.5%, Mn 1.0%-1.3%, Cr 0.2%-0.4%, V 0.04%-0.12%, and the remainder is iron and impurities.

2. The method for increasing the yield strength of German standard A150 crane rail according to claim 1, characterized in that: The high gun position is 1.2-1.5m away from the molten pool liquid surface for gentle blowing.

3. The method for increasing the yield strength of German standard A150 crane rail according to claim 1, characterized in that: The low gun position is 0.8-1.0m away from the molten pool liquid surface for strong blowing.

4. The method for increasing the yield strength of German standard A150 crane rail according to claim 1, characterized in that: The aluminum-free deoxidizer is silicon calcium barium.

5. The method for increasing the yield strength of German standard A150 crane rail according to claim 1, characterized in that: The air permeability index of the filter is ≥10L / min·kPa.

6. The method for increasing the yield strength of German standard A150 crane rail according to claim 1, characterized in that: Also includes: A laser rangefinder is used to monitor the steel liquid level in the crystallizer in real time. Through a high-precision automatic control system, the liquid level fluctuation is controlled within the range of ±3mm, thereby improving the quality of the casting.

7. The method for increasing the yield strength of German standard A150 crane rail according to claim 1, characterized in that: The billet size is 280×380 mm.

8. The method for increasing the yield strength of German standard A150 crane rail according to claim 1, characterized in that: The crane rail has the following chemical compositions by mass percentage: C 0.82%, Si 0.45%, Mn 1.15%, Cr 0.30%, and V 0.08%.