A method for producing 1.2311 steel plates with thickness of 250-330 mm by short process of rolling instead of forging

Abstract

The application discloses a method for producing 250-330mm-thick 1.2311 steel plates by short process of rolling instead of forging, adopts water-cooled ingots with thickness greater than or equal to 800mm, adjusts water-cooling parameters and pouring processes to ensure good original cast state organization, ensures that the internal quality and the core hardness of the steel plates meet the standard requirements through high-temperature heating, two-stage rolling and post-rolling stage quenching and cooling, adjusts the hardness through tempering heat treatment, removes stress, and obtains 250-330mm-thick 1.2311 steel plates, the surface hardness of the steel plates is 30-36HRC, the core hardness of the steel plates is 30-36HRC, the overall hardness of the steel plates is uniform, and flaw detection meets the requirement of the diameter of defects being less than or equal to 3mm in GB / T 6402-2008 4-grade forgings. The overall process flow is short, the high temperature of the steel plates after rolling is fully utilized, medium consumption is reduced, the production cost of heat treatment is reduced, the treatment progress is accelerated, the production efficiency is improved, and obvious market advantages are obtained.

Description

Technical Field

[0001] This invention belongs to the field of extra-thick plate production technology, specifically involving a method for producing 250-330mm thick 1.2311 steel plates using a short rolling process instead of forging. Background Technology

[0002] Mold steel is a crucial material in the mold manufacturing industry. Its internal quality and hardness uniformity directly affect mold processing, mold quality, and product quality. 1.2311 plastic mold steel is typically pre-heat-treated by the steel mill to achieve the required hardness for the customer before further processing. Once the mold is formed, it can be used directly without further heat treatment. This type of mold steel effectively avoids mold deformation and cracking problems caused by heat treatment, making it ideal for manufacturing large and medium-sized precision plastic molds with complex shapes.

[0003] Chinese patent CN201810969366.8 discloses an extra-thick 1.2311 mold steel plate and its production method. It uses a low-Cr, high-Mo+V composition and a quenching and tempering process. The resulting 400mm thick 1.2311 plate meets the core hardness requirements. Its advantage lies in increasing the core hardness by raising the alloy content. However, it requires reheating after initial cooling, normalizing, and tempering, which increases media consumption, results in a longer production process, and higher costs.

[0004] Chinese patent CN201110218086.1 discloses a non-modulated plastic mold steel plate production process. This process uses a 320mm continuous casting billet to roll non-modulated plastic mold steel plates with a thickness of 120mm or less. The final rolling temperature is controlled between 850 and 900℃. After rolling, the plates are water-cooled to 500℃ to regain their red color, and then air-cooled to 200℃ before being removed from the production line. The maximum thickness achieved is 120mm. The drawback is that this method has certain limitations in terms of steel plate thickness and cannot meet the requirements for large plastic molds.

[0005] Chinese patent CN200610028195.6 discloses an ultra-thick non-quenched and tempered plastic mold steel and its manufacturing method. This method overcomes the shortcomings of pre-hardened plastic mold steel, such as high manufacturing cost, high quenching crack sensitivity, and the small forming thickness of existing non-quenched and tempered plastic mold steel. It ensures that large-section plastic mold steel can achieve bainitic structure and hardness. It employs forging for hot working and controls the cooling rate after forging, achieving non-quenching and tempering of ultra-thick plastic mold steel exceeding 300mm in thickness. However, it uses a forging method, resulting in multiple production steps, low yield, and low production efficiency. Summary of the Invention

[0006] To address the aforementioned technical deficiencies, the present invention aims to provide a method for producing 250-330mm thick 1.2311 steel plates using a short rolling process instead of forging. This method features a shorter overall process flow, fully utilizes the high temperature of the rolled steel plate itself, reduces media consumption, lowers heat treatment production costs, accelerates processing, and improves production efficiency, thus possessing significant market advantages.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a method for producing 250-330mm thick 1.2311 steel plates using a short rolling process instead of forging. The steel plate contains the following chemical composition by mass fraction (wt%): C: 0.35-0.42, Si: 0.20-0.40, Mn: 1.40-1.60, P≤0.015, S≤0.005, Als: 0.020-0.050, Cr: 1.80-2.0, Mo: 0.18-0.23, Ti: 0.020-0.050, B: 0.0005-0.0015, with the remainder being Fe and residual elements. The steel plate production method includes water-cooled mold casting of ingots, heating, rolling, online quenching and tempering, as detailed below: a. Water-cooled mold casting of ingots: Water-cooled molds with an inner cavity thickness of ≥800mm are used for casting. The casting temperature is 1530~1538℃, the casting time of the main body is 17~25min, the casting time of the cap is 7~10min, the initial water flow rate is 330~340m³ / h, and after 2 hours of casting, it is adjusted to 200~220m³ / h. The demolding time is controlled at 8~10 hours. b. Heating: Heating rate ≤50℃ / h, holding temperature 1290±20℃, holding time 5~10min / cm; c. Rolling: Two-stage rolling is adopted. The initial rolling temperature is ≥1030℃. The single-pass reduction in the roughing stage is controlled at 50-55mm. High-pressure water is not used during the rolling process. Vertical roller extrusion is used at the end of the roughing stage. The single-pass extrusion amount is controlled at 10mm. After roughing, the steel is dried. The drying thickness is equal to the steel plate thickness + 50mm. The steel is dried to a temperature of 860-900℃ before entering the finishing rolling process. The reduction in the finishing rolling pass is 5-15mm to control the flatness of the steel plate. The final rolling temperature is ≥820℃. d. Online quenching: The rolled steel plate is immediately placed in a water tank for two-stage water cooling. The first stage of water cooling lasts for 5 to 8 minutes, with the cooling rate controlled at 30-50℃ / min to prevent edge cracking caused by prolonged immersion time and high cooling rate. This also prepares for the second stage of water cooling, with a reddening temperature of 630-660℃. The second stage of water cooling lasts for 4 to 7 minutes, with the cooling rate controlled at 20-40℃ / min. The final reddening temperature is controlled between 450 and 550℃. After water cooling, air cooling is used to reduce the temperature to below 300℃. e. Tempering: After air cooling, the steel plate is immediately transferred to a heat treatment furnace for multi-stage tempering. First, the temperature is raised to 600±10℃ at a rate of ≤40℃ / h and held for 4min / mm to ensure that the steel plate reaches the hardness range required by the customer. Then, the burner is turned off and the plate is cooled to 550±10℃ in the furnace. The burner is turned on again and held for 1.5min / mm to ensure that the stress is fully removed and to prevent the steel plate from cracking due to high stress. After the holding period, the plate is slowly cooled to room temperature by stacking.

[0008] The steel plates obtained using this method were inspected. The surface hardness was 30-36 HRC, the hardness of the entire core section was 30-36 HRC, the overall hardness of the steel plate was uniform, and the flaw detection met the requirements of GB / T 6402-2008 Grade 4 forgings with a defect diameter ≤3mm.

[0009] Compared with existing technologies, this invention has the following advantages: By adjusting the water volume of the water-cooled mold and the casting process, a water-cooled steel ingot with excellent internal quality can be obtained. Combined with the high-temperature, high-reduction process during rolling, a steel plate with a thickness reaching 330mm can be obtained that meets the quality requirements for forgings. Compared with prior art 2, it has an advantage in thickness compared to continuous casting billet rolling. Compared with prior art 3, the production method of this invention, which replaces forging with rolling, can also meet the internal quality requirements of forgings, resulting in higher production efficiency and a greater advantage in production cost compared to forgings.

[0010] Compared to document 1, in the heat treatment process, online quenching and tempering replaces the post-cooling heating and normalizing and tempering processes. This fully utilizes the high temperature of the rolled steel plate itself, reduces media consumption, lowers heat treatment production costs, accelerates the processing progress, and improves production efficiency. Online staged quenching, by controlling the cooling rate, ensures thorough quenching of the steel plate's core while preventing edge cracking caused by prolonged immersion in water and excessive cooling rate. Subsequently, air cooling is used for weak cooling of the steel plate. Finally, a reasonable tempering temperature ensures uniform hardness and stress relief throughout the steel plate, preventing processing cracks. Detailed Implementation

[0011] The present invention will be further described in detail below with reference to implementation examples.

[0012] Example 1: 1.2311 steel plate with a rolling thickness of 250mm.

[0013] a. The steel smelting composition is as follows: C: 0.38, Si: 0.31, Mn: 1.46, P: 0.012, S: 0.004, Als: 0.038, Cr: 1.86, Mo: 0.21, Ti: 0.041, B: 0.0008, with the remainder being Fe and residual elements; b. Water-cooled mold casting: Water-cooled mold with an inner cavity thickness of 850mm is used for casting, ensuring a rolling reduction ratio of 3.4, a casting temperature of 1534℃, a casting time of 22 minutes for the main body, a casting time of 10 minutes for the cap, a water cooling water flow rate of 340m³ / h at the beginning of casting, and an adjustment to 220m³ / h after 2 hours of casting, and a demolding time controlled at 10 hours. c. Steel ingot heating: heating rate 30~40℃ / h, holding temperature 1285~1300℃, holding time 680 minutes; d. Rolling: Two-stage rolling is adopted. The initial rolling temperature is 1080℃. The reduction per pass in the roughing stage is controlled at 55mm. High-pressure water is not used during the rolling process. Vertical roller extrusion is used at the end of the roughing stage. The extrusion amount per pass is controlled at 10mm. The thickness of the steel is 300mm. The initial rolling temperature of the finishing stage is 880℃. The reduction per pass in the finishing stage is 5-10mm to control the flatness of the steel plate. The final rolling temperature is 830-840℃. e. Online stage quenching: The temperature of the rolled steel plate is controlled between 830 and 840℃. It is immediately put into a water tank for water cooling after rolling. The water cooling is divided into two stages. The first stage water cooling time is 5 minutes, and the red temperature is controlled at 653℃. The second stage water cooling time is 4 minutes, and the final red temperature is controlled at 490℃. After the water cooling is completed, air cooling is used to cool it to below 300℃. f. Multi-stage tempering: After air cooling, the steel plate is immediately transferred to a heat treatment furnace for multi-stage tempering. First, the temperature is raised to 615℃ at a rate of 30-40℃ / h and held for 1000 minutes. After the holding time is up, the burner is turned off and the furnace is allowed to cool naturally. Then, the temperature is raised to 553℃ and held for 375 minutes. After the holding time is up, the plate is slowly cooled to room temperature by stacking.

[0014] Testing revealed that the 250mm thick 1.2311 steel plate produced using this method met the requirements for defect diameter ≤3mm in Grade 4 of GB / T 6402~2008 forgings. In terms of performance, the surface hardness was 30~34HRC, the core cross-section hardness was 30~34HRC, the overall hardness of the steel plate was uniform, and it met the quality requirements for forgings. The hardness of different parts of the steel plate's width cross-section is shown in Table 1. Example 2: 1.2311 steel plate with a rolling thickness of 330mm.

[0015] a. The steel smelting composition is as follows: C: 0.41, Si: 0.36, Mn: 1.52, P: 0.014, S: 0.004, Als: 0.044, Cr: 1.96, Mo: 0.21, Ti: 0.043, B: 0.0013, with the remainder being Fe and residual elements; b. Water-cooled mold casting: A water-cooled mold with an inner cavity thickness of 900mm is used for casting, ensuring a rolling reduction ratio of 2.73, a casting temperature of 1538℃, a casting time of 19 minutes for the main body, a casting time of 8 minutes for the cap, a water cooling water flow rate of 333m³ / h at the beginning of casting, and an adjustment to 210m³ / h after 2 hours of casting, and a demolding time controlled at 8 hours. c. Steel ingot heating: heating rate 30~40℃ / h, holding temperature 1290~1305℃, holding time 900 minutes; d. Rolling: Two-stage steel drying and rolling is adopted. The initial rolling temperature is 1100℃. The single-pass reduction in the roughing stage is controlled at 55mm. High-pressure water is not used during the rolling process. Vertical roller extrusion is used at the end of the roughing stage. The single-pass extrusion amount is controlled at 10mm. The steel drying thickness is 380mm. The initial rolling temperature of the finishing stage is 895℃. The single-pass reduction in the finishing stage is 5-10mm to control the flatness of the steel plate. The final rolling temperature is 850-860℃. e. Online stage quenching: The rolled steel plate is immediately put into a water tank for water cooling. The process is divided into two stages of water cooling. The first stage of water cooling lasts for 8 minutes, and the return temperature is controlled at 660℃. The second stage of water cooling lasts for 7 minutes, and the final return temperature is controlled at 542℃. After water cooling, air cooling is used to cool the plate to below 300℃. f. Multi-stage tempering: After air cooling, the steel plate is immediately transferred to a heat treatment furnace for multi-stage tempering. First, the temperature is raised to 605℃ at a heating rate of 30-40℃ / h and held for 1320 minutes. After the holding time is up, the burner is turned off and the furnace is allowed to cool naturally. Then, the temperature is raised to 560℃ and held for 495 minutes. After the holding time is up, the plate is slowly cooled to room temperature by stacking.

[0016] Testing revealed that the 330mm thick 1.2311 steel plate produced using this method met the requirements of GB / T 6402~2008 Grade 4 for forgings with a defect diameter ≤3mm. In terms of performance, the surface hardness was 30~34HRC, the core cross-section hardness was 31~35HRC, the overall hardness of the steel plate was uniform, and it could meet the quality requirements of forgings.

[0017] The hardness of different parts of the steel plate width section is shown in Table 2.

Claims

1. A method for producing 250-330mm thick 1.2311 steel plates using a short-process rolling method instead of forging, characterized in that: The steel plate contains the following chemical composition by mass fraction: C: 0.35–0.42%, Si: 0.20–0.40%, Mn: 1.40–1.60%, P≤0.015%, S≤0.005%, Als: 0.020–0.050%, Cr: 1.80–2.0%, Mo: 0.18–0.23%, Ti: 0.020–0.050%, B: 0.0005–0.0015%, with the remainder being Fe and residual elements; The production of the steel plate includes water-cooled mold casting of ingots, heating, rolling, online quenching and tempering, as detailed below: a. Water-cooled mold casting of ingots: Water-cooled molds with an inner cavity thickness of ≥800mm are used for casting. The casting temperature is 1530~1538℃, the casting time of the main body is 17~25min, the casting time of the cap is 7~10min, the initial water flow rate is 330~340m³ / h, and after 2 hours of casting, it is adjusted to 200~220m³ / h. The demolding time is controlled at 8~10 hours. b. Heating: Heating rate ≤50℃ / h, holding temperature 1290±20℃, holding time 5~10min / cm; c. Rolling: Two-stage rolling is adopted. The initial rolling temperature is ≥1030℃. The single-pass reduction in the roughing stage is controlled at 50-55mm. High-pressure water is not used during the rolling process. Vertical roller extrusion is used at the end of the roughing stage. The single-pass extrusion amount is controlled at 10mm. After roughing, the steel is dried. The drying thickness is equal to the steel plate thickness + 50mm. The steel is dried to a temperature of 860-900℃ before entering the finishing rolling process. The reduction in the finishing rolling pass is 5-15mm to control the flatness of the steel plate. The final rolling temperature is ≥820℃. d. Online quenching: The rolled steel plate is immediately placed in a water tank for two-stage water cooling. The first stage water cooling time is 5-8 minutes, the cooling rate is controlled at 30-50℃ / min, and the reddening temperature is 630-660℃. The second stage water cooling time is 4-7 minutes, the cooling rate is controlled at 20-40℃ / min, and the final reddening temperature is controlled between 450-550℃. After water cooling, air cooling is used to cool to below 300℃. e. Tempering: After air cooling, the steel plate is immediately transferred to a heat treatment furnace for multi-stage tempering. First, the temperature is raised to 600±10℃ at a rate of ≤40℃ / h and held for 4min / mm. Then, the burner is turned off and the plate is cooled to 550±10℃ with the furnace. The burner is turned on again and held for 1.5min / mm. After the holding period, the plate is slowly cooled to room temperature by stacking.

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