Alloy structural steel 30CrMnSiA with thickness of 100-200 mm and production method thereof

Abstract

The invention discloses alloy structural steel 30CrMnSiA with the thickness of 100-200 mm and a production method thereof. Ti is introduced into components to achieve the purpose of refining original crystal grains of a casting blank, and meanwhile conditions are created for further refining of the crystal grains in the rolling process. In the rolling process, high-pressure rolling is adopted, core defects are eliminated, the problem that the structure is uneven due to the fact that the compression ratio of a large-thickness steel plate is insufficient is solved, and a uniform-temperature rolling method is adopted in the finish rolling stage to ensure the uniformity of the internal structure of the steel plate; a traditional off-line quenching and off-line tempering process is replaced by an on-line quenching and stacking slow cooling mode. The structure of the steel plate obtained through the scheme comprises 70%-80% of martensite, 15%-25% of bainite and smaller than or equal to 5% of ferrite, the yield strength of the steel plate is larger than or equal to 880 MPa, the tensile strength of the steel plate is larger than or equal to 1190 MPa, the Rockwell hardness of the steel plate is 45-55 HRC, and compared with the prior art, the production period is greatly shortened, the production cost is reduced, and batch production of the steel plate is facilitated.

Description

Technical Field

[0001] The invention belongs to the field of extra-thick plate production, and specifically relates to 100-200 mm thick alloy structural steel 30CrMnSiA and a production method thereof. Background Art

[0002] 30CrMnSiA alloy structural steel is required to have good hardenability, high strength and sufficient toughness after quenching and tempering, good processability, small processing deformation, and good fatigue resistance. It is suitable for making grinding wheel shafts, gears, sprockets, piston parts, and various special wear-resistant parts for automobiles, aircraft, etc. It can also be used in aerospace.

[0003] In recent years, as the market demand for this type of special steel continues to increase, its quality requirements are also increasing. However, the currently known production methods all use die casting or forging, and require separate heat treatment to meet product quality requirements, which makes it difficult to meet the needs of continuous mass production.

[0004] Chinese patent CN118127415 discloses a production method for 100-150mm thick high-strength alloy steel 30CrMnSi. This solution can not only reduce the alloy cost, but also obtain thick steel plates that meet the use requirements. However, the production method using die casting still has certain limitations for the market application and promotion of this type of steel.

[0005] For example, Chinese patents CN102703825 and CN102660712 respectively disclose an improved preparation method of 30CrMnSi steel, which uses medium frequency melting of steel and alloy, and then casts into standard wedge-shaped and ladder-shaped test piece blanks, and completes austenitization treatment at about 840℃ for 550-600s, and then performs isothermal quenching or incomplete quenching at 180-300℃, and then quenches to room temperature after 300s-500s of heat preservation, and finally meets product requirements. Rare earth elements are required in the composition design, and the production process, especially the heat treatment process, is complicated, which is not conducive to production process control.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] In order to improve the above technical defects, the purpose of the present invention is to provide a 100-200 mm thick alloy structural steel 30CrMnSiA, which greatly shortens the production cycle and reduces the production cost compared with the prior art, and facilitates the mass production of steel plates.

[0008] Another object of the present invention is to provide a method for producing 100-200 mm thick alloy structural steel 30CrMnSiA.

[0009] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a 100-200 mm thick alloy structural steel 30CrMnSiA, comprising the following chemical components in mass percentage: C: 0.28-0.34, Si: 0.9-1.20, Mn: 0.80-1.00, P: ≤0.012, S: ≤0.005, Cr: 0.80-1.10, Ti: 0.015-0.035, Als: ≤0.050, and the rest are Fe and residual elements.

[0010] Compared with the existing technology, by adding Ti elements that refine the grains, the original cast grains can be refined during the billet casting process, while creating conditions for further refinement of the internal grains during the subsequent high-temperature rolling process of the steel plate, ultimately achieving the goal of improving the strength and impact toughness of the steel plate.

[0011] The production method of the above-mentioned 100-200 mm thick alloy structural steel 30CrMnSiA includes controlled rolling and controlled cooling, which are specifically as follows:

[0012] 1) Controlled rolling: A two-stage rolling process is adopted. The first stage rolling temperature is ≥1050℃. The steel billet is quickly put into the rolling mill for rolling by taking advantage of the high temperature and low deformation resistance of the steel billet. The single-pass reduction is controlled to be >40mm, so as to achieve the purpose of pressing defects such as looseness and shrinkage inside the ingot, and at the same time refine the grains at the 1 / 2 thickness position of the steel plate. When the thickness of the finished product is 1.5 to 2 times, the rolling is stopped and the temperature is kept. The second stage adopts uniform temperature rolling, and the rolling temperature is 910 to 940℃ to ensure that the overall temperature of the steel plate is uniform during the rolling process, which provides guarantee for the uniformity of the structure after the subsequent ultra-fast cooling (online quenching) of the steel plate. The pass reduction is 10 to 25mm, and the cumulative reduction rate is ≥50%, which creates good prerequisites for the refinement of the internal structure of the steel plate. The final rolling temperature is 850 to 900℃.

[0013] 2) Controlled cooling: After rolling, the steel plate enters ACC for rapid cooling, the start cooling temperature is ≥830℃, and the final cooling temperature is controlled at 280~350℃. After the steel plate exits ACC for rapid straightening, it is hoisted into the slow cooling station, with 10~15 steel plates with a temperature of 500~650℃ laid below, and 10~15 steel plates with a temperature of 500~650℃ covered on top, and the stack cooling time is ≥48h; the residual heat after the steel plate is rapidly cooled is used to achieve self-tempering in the stacking slow cooling process, thereby replacing the purpose of tempering in the traditional tempering furnace.

[0014] The steel plate obtained by adopting this scheme has a metallographic structure of 70% to 80% martensite, 15% to 25% bainite, and ≤5% ferrite, a yield strength of ≥880MPa, a tensile strength of ≥1190MPa, and a Rockwell hardness of 45 to 55HRC.

[0015] The beneficial effects of the present invention include: introducing Ti into the composition to achieve the purpose of refining the original grains of the ingot, and creating conditions for further grain refinement during the rolling process; during the rolling process, large reduction rolling is adopted to eliminate core defects and solve the problem of uneven structure caused by insufficient compression ratio of thick steel plates, and the uniform temperature rolling method is adopted in the finishing rolling stage to ensure the uniformity of the internal structure of the steel plate; online quenching + stacking slow cooling is adopted to replace the traditional offline quenching + offline tempering process, which greatly shortens the production cycle, reduces production costs, and realizes mass production of steel plates. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0017] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0018] The following chemical compositions by mass percentage are used to produce 30CrMnSiA alloy structural steel with a thickness of 100-200 mm in several sizes: C: 0.28-0.34, Si: 0.9-1.20, Mn: 0.80-1.00, P: ≤0.012, S: ≤0.005, Cr: 0.80-1.10, Ti: 0.015-0.035, Als: ≤0.050, and the rest are Fe and residual elements. The compositions used in the three examples are shown in Table 1.

[0019]

[0020] The production process includes: molten iron pretreatment, top and bottom combined blowing converter, LF furnace refining, vacuum degassing, continuous casting heating, controlled rolling, and controlled cooling, as follows:

[0021] 1) Hot metal pretreatment: Ensure that the S of hot metal is ≤ 0.005% by spraying lime and stirring after desulfurization, and take insulation measures to avoid too fast temperature drop.

[0022] 2) Converter smelting: S≤0.005% and P≤0.020% of molten iron entering the furnace, molten iron temperature≥1260℃, high-quality scrap steel, slag making material, slag making basicity controlled at 3.0-4.0, steel tapping P≤0.010%, S≤0.010%, control the slag amount in the ladle during the tapping process.

[0023] 3) LF refining: Argon is blown throughout the refining process. The blowing intensity is adjusted in time according to the specific situation to ensure the blowing effect. Refining slag is added to make white slag. At the same time, the white slag retention time is guaranteed to be ≥20min. At the end of refining, calcium wire is added to calcify the molten steel to promote the denaturation of inclusions in the steel.

[0024] 4) VD refining: VD vacuum must reach below 67Pa, and the pressure must be maintained for ≥15min. After the vacuum is completed, argon is blown into the steel. The strength is based on the fact that the molten steel does not churn. After the argon blowing is completed, an appropriate amount of covering agent is added to ensure the temperature of the molten steel.

[0025] 5) Continuous casting: Before pouring steel, ensure that the casting machine equipment is in good condition, the middle bag superheat is 15±10℃, and the pulling speed is selected according to the 300-450mm thick steel billet to ensure the thick plate rolling compression ratio requirements and internal structure refinement conditions. During the casting process, electromagnetic stirring and dynamic light pressure are turned on to protect the casting throughout the process. After the steel billet is off the line, it is stacked and slowly cooled for ≥24h.

[0026] 6) Heating: Control the temperature of the preheating section at 600-800°C, the temperature of the heating section at 1200-1220°C, and the temperature of the holding section at 1180-1200°C. The billet holding time is greater than 40 minutes, and the overall heating time is controlled at 11-14 minutes / cm.

[0027] 7) Controlled rolling: A two-stage controlled rolling process is adopted: ① The first stage rolling temperature is ≥1050℃. Taking advantage of the high temperature and low deformation resistance of the steel billet, the steel billet is quickly put into the rolling mill for rolling, and the single-pass reduction is controlled to be >40mm, so as to achieve the purpose of pressing the internal looseness, shrinkage and other defects of the ingot. When the thickness of the intermediate billet reaches 1.5 to 2 times the thickness of the finished product, the rolling is stopped and the temperature is kept; ② When the temperature of the intermediate billet reaches 910 to 940℃, the second-stage rolling is started. The process adopts the method of uniform temperature rolling to ensure the uniform temperature of the entire rolling process, so as to provide guarantee for the uniformity of the structure of the subsequent steel plate after ultra-fast cooling (online quenching). The pass reduction is controlled at 10 to 25mm to ensure that the cumulative pass reduction rate is ≥50%, creating good prerequisites for the refinement of the internal structure of the steel plate. The final rolling temperature is 850 to 900℃.

[0028] 8) Controlled cooling: After the steel plate is rolled, the cooling temperature is controlled at ≥830℃, and the steel plate is rapidly cooled by ACC. The final cooling temperature is controlled at 280-350℃. After the steel plate is rapidly straightened by ACC, it is hoisted into the slow cooling station, with 10-15 steel plates with a temperature of 500-650℃ laid below, and then covered with 10-15 steel plates with a temperature of 500-650℃. The stack cooling time is ≥48h.

[0029] Samples were cut from the steel plates obtained in Examples 1-3 and the mechanical properties of the samples were tested. The test results are shown in Table 2.

[0030] Table 2 Mechanical properties of 30CrMnSiA steel plate

[0031]

[0032] A total of 30 batches of 30CrMnSiA with a thickness of 100-200mm were produced in this trial production. The average Rockwell hardness of the steel plates after rolling and stack cooling was 51HRC. No shrinkage cavities, inclusions, delamination, cracks, bubbles or white spot defects were found in the low-power acid immersion test of the steel. The central porosity level was 0.5, and its metallographic structure was 70% to 80% martensite, 15% to 25% bainite, and ≤5% ferrite, which fully met the use requirements.

[0033] External inspection and flaw detection: The developed steel plates were inspected strictly in accordance with the standards and the genuine rate was 100%, with no surface cracks or bursts. The flaw detection was carried out according to GB / T2970, of which 90% reached the first-level standard and 100% reached the third-level standard, achieving the expected effect.

[0034] The above description is only a preferred embodiment of the present invention. The above specific embodiments are not limitations of the present invention. Any modifications, changes or equivalent substitutions made by ordinary technicians in the field based on the above description shall fall within the protection scope of the present invention.

Claims

1. A 100-200 mm thick alloy structural steel 30CrMnSiA, characterized in that: The chemical composition comprises the following mass percentages: C: 0.28-0.34, Si: 0.9-1.20, Mn: 0.80-1.00, P: ≤0.012, S: ≤0.005, Cr: 0.80-1.10, Ti: 0.015-0.035, Als: ≤0.050, and the rest are Fe and residual elements; The structure of the steel comprises 70% to 80% of martensite, 15% to 25% of bainite and ≤5% of ferrite, and its yield strength is ≥880MPa, tensile strength is ≥1190MPa, and Rockwell hardness is 45 to 55HRC.

2. The method for producing 100-200 mm thick alloy structural steel 30CrMnSiA according to claim 1, comprising controlled rolling and controlled cooling, characterized in that: 1) Controlled rolling: adopt two-stage rolling process, the first stage rolling temperature is ≥1050℃, the pass reduction is >40mm, and the rolling is stopped and kept warm when the thickness of the finished product is 1.5 to 2 times; the second stage adopts uniform temperature rolling, the starting rolling temperature is 910 to 940℃, the pass reduction is 10 to 25mm, the cumulative reduction rate is ≥50%, and the final rolling temperature is 850 to 900℃; 2) Controlled cooling: After rolling, the steel plate enters ACC for rapid cooling, the start cooling temperature is ≥830℃, and the final cooling temperature is controlled at 280~350℃. After the steel plate exits ACC for rapid straightening, it is hoisted into the slow cooling station, with 10~15 steel plates with a temperature of 500~650℃ laid below, and 10~15 steel plates with a temperature of 500~650℃ covered on top, and the stack cooling time is ≥48h.

Images