HY30H high-alloy plastic die steel and production method thereof

Abstract

The invention discloses HY30H high-alloy plastic die steel which is prepared from the following chemical components in percentage by weight: 0.35 to 0.38 percent of C, 0.20 to 0.40 percent of Si, 1.30 to 1.50 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, 0.020 to 0.050 percent of Als, 1.80 to 2.0 percent of Cr, 0.15 to 0.18 percent of Mo, 0.020 to 0.050 percent of Ti, 0.0005 to 0.0015 percent of B, 0.030 to 0.050 percent of V and the balance of Fe and residual elements. The thickness of the obtained steel plate ranges from 200 mm to 300 mm through water cooling mold ingot casting, steel ingot heating, rolling, online quenching and tempering, the alloy cost is low, a large-compression-ratio water cooling mold is adopted for production, compared with continuous casting billet production, the finished product thickness has the advantage, through detection, flaw detection of the steel plate meets the forging GB / T 6402-2008 grade 4 standard, the defect diameter is smaller than or equal to 2 mm, the surface hardness and the core hardness of the steel plate are both 30-36 HRC, the overall hardness is uniform, and the steel plate is suitable for large-scale production. And forging quality requirements are met. The online multi-time ultrafast cooling quenching and multi-stage tempering are adopted to replace the traditional quenching and tempering process, so that the heat treatment quenching link is reduced, the production efficiency is improved, and more competitive advantages are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of extra-thick plate production, and in particular relates to a HY30H high-alloy plastic mold steel and a production method thereof. Background Art

[0002] Mold steel is a key material in the mold manufacturing industry. Its internal quality and hardness uniformity directly affect mold processing, quality and final product quality. HY30H plastic mold steel is a pre-hardened medium-carbon alloy plastic mold steel. It is pre-tempered by the steel mill to the hardness required by the customer, and then deeply processed. It can be used without heat treatment after molding. This avoids mold deformation and cracking problems caused by heat treatment, and is particularly suitable for making large and medium-sized precision plastic molds with complex shapes. In the prior art, although there are a variety of production methods for extra-thick mold steel, they all have shortcomings.

[0003] For example, Chinese patent CN2006100281956 discloses an ultra-thick non-quenched and tempered plastic mold steel and its manufacturing method, which overcomes the shortcomings of high manufacturing cost of pre-hardened plastic mold steel, high sensitivity to quenching cracks, and small forming thickness of existing non-quenched and tempered plastic mold steel, ensures that large-section plastic mold steel can obtain bainite structure and hardness, adopts forging method for hot processing, controls the cooling rate after forging, and realizes non-quenched and tempered ultra-thick plastic mold steel with a thickness of more than 300mm. However, it adopts the method of forging + air cooling + tempering, with many production links and low production efficiency.

[0004] Another example is Chinese patent CN2011102180861, which discloses a non-modulated plastic mold steel thick plate production process, which uses 320mm continuous casting billets to roll non-modulated plastic mold steel thick plates with specifications below 120mm. The final rolling temperature is controlled at 850-900℃, and after rolling, it is water-cooled to 500℃ to return to red, and then air-cooled to 200℃ before being removed from the line. However, the maximum thickness can only be 120mm, and there are certain limitations in thickness, which cannot meet the use requirements of large plastic molds.

[0005] Another example is Chinese patent CN2018109693668, which discloses a super thick die steel 1.2311 plate and its production method. It uses low Cr and high Mo+V components, and through offline quenching + tempering process, the 400mm 1.2311 produced can meet the core hardness requirements. This solution improves the core hardness by increasing the alloy content. The disadvantage is that the alloy content used in the composition design is high, and the production cost is also high; the heat treatment adopts offline quenching + tempering process. Improper execution of the quenching process can easily cause cracking of the steel plate, which is not conducive to production control.

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

[0007] In order to solve the above technical defects, the purpose of the present invention is to provide a HY30H high alloy plastic mold steel, which has low production cost, high strength after heat treatment, large thickness, and is conducive to production control.

[0008] Another object of the present invention is to provide a method for producing HY30H high alloy plastic mold steel.

[0009] To achieve the above object, the technical solution adopted by the present invention is: a HY30H high alloy plastic mold steel, the steel plate thickness is 200-300mm, and the chemical composition by mass percentage is as follows: C: 0.35-0.38, Si: 0.20-0.40, Mn: 1.30-1.50%, P≤0.015%, S≤0.005%, Als: 0.020-0.050, Cr: 1.80-2.0, Mo: 0.15-0.18, Ti: 0.020-0.050, B: 0.0005-0.0015, V 0.030-0.050%, and the rest are Fe and residual elements;

[0010] The production method of the above HY30H high alloy plastic mold steel includes water-cooled mold casting, ingot heating, rolling, online quenching and tempering, which is specifically as follows:

[0011] a. Water-cooled mold casting: Use a water-cooled mold with an inner cavity thickness of ≥700mm for casting, ensure that the rolling reduction ratio is greater than 2.0, the mold casting temperature is 1525-1533℃, the main body casting time is 15-19 minutes, the cap pouring time is 5-8 minutes, and the water pouring volume is 340-390m 3 / h, after pouring for 2 hours, adjust to 250-300m 3 / h, demoulding after 8-10 hours;

[0012] b. Ingot heating: heating rate ≤40℃ / h, holding temperature 1280±20℃, holding time 8~12min / cm;

[0013] c. Rolling: Two-stage air-drying rolling is adopted, the starting temperature of rough rolling is ≥1010℃, the pass reduction is 55-60mm, high-pressure water is not used in the rolling process, the last pass of rough rolling adopts vertical roller extrusion, the single pass extrusion is 10-15mm, the air-drying steel thickness is equal to the steel plate thickness plus 40mm, the starting temperature of finishing rolling is 900-950℃, the pass reduction is 10-15mm to control the unevenness of the steel plate, and the final rolling temperature is ≥850℃;

[0014] d. Online quenching: After rolling, the steel plate immediately enters the ultra-fast cooling device for cooling. The period is divided into two stages of water cooling. The first stage of water cooling lasts for 3 to 5 minutes, and the cooling rate is controlled at 30 to 50 ° C / min. This can prevent the surface temperature of the steel plate from recovering too quickly, causing the surface self-tempering effect, resulting in inappropriate hardness at 15-40 mm near the surface. When the surface temperature of the steel plate is measured to be 500 ° C ± 30 ° C, it enters the second stage of cooling. The second stage of water cooling lasts for 5 to 7 minutes, and the cooling rate is controlled at 20 to 40 ° C / min. The final return temperature is controlled between 400 and 500 ° C. Compared with one quenching, two-stage quenching + full reddening can avoid excessive temperature difference between the surface and the core, resulting in excessive surface stress and cracking of the steel plate. After the water cooling is completed, air cooling is used to cool to below 300 ° C.

[0015] e. Tempering: Multi-stage tempering is adopted. The steel plate is charged into the furnace at 150-200℃ and simmered at a furnace temperature of 300-560℃ for 3-5 hours. The temperature is first raised to 570±10℃ at a heating rate of ≤40℃ / h and kept warm for 4-5min / mm. Then the burner is closed and the temperature is lowered to 300±10℃ with the furnace and kept warm for 0.8-1.2min / mm. After the insulation is completed, the steel plate stack is slowly cooled to room temperature to ensure that the stress is fully removed to prevent the steel plate from being cracked during processing due to high stress.

[0016] The 200-300mm thick HY30H high alloy plastic mold steel obtained by this scheme has less alloy usage and lower cost compared with the existing scheme. It is produced by a large compression ratio water-cooled mold. Compared with continuous casting billet production, the finished product has an advantage in thickness and can meet the quality requirements of forgings. After testing, its flaw detection meets the GB / T 6402-20084-level standard for forgings, the defect diameter is ≤2mm, the surface hardness and core hardness of the steel plate are both 30-36HRC, and the overall hardness is uniform, meeting the quality requirements of forgings. The use of online multiple ultra-fast cooling quenching + multi-stage tempering instead of the traditional quenching + tempering process reduces the heat treatment quenching link, improves production efficiency, and has more competitive advantages. DETAILED DESCRIPTION

[0017] 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.

[0018] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0019] Example 1: A HY30H steel plate with a rolling thickness of 250 mm is prepared using the chemical composition shown in Table 1 below:

[0020] Table 1 Chemical composition of 250 mm thick steel plate

[0021] C Si Mn P S Als Cr Mo Ti B V 0.35 0.3 1.38 0.012 0.003 0.035 1.85 0.16 0.025 0.0008 0.035

[0022] The production of the steel includes the following steps:

[0023] a. Water-cooled mold casting: Use a water-cooled mold with an inner cavity thickness of 720mm for casting, rolling reduction ratio of 2.8, mold casting temperature of 1528℃, body casting time of 17 minutes, cap casting time of 7 minutes, and water cooling water volume of 380m 3 / h, after pouring for 2 hours, adjust to 280m 3 / h, the removal time is controlled as 9 hours.

[0024] b. Ingot heating: heating rate 30-40℃ / h, holding temperature 1275-1290℃, holding time 8-14 minutes.

[0025] c. Rolling: Two-stage steel drying rolling is adopted, and the starting rolling temperature is 1020℃. The single pass reduction in the rough rolling stage is 60mm, and high-pressure water is not used. The last pass of rough rolling adopts vertical roller extrusion, and the single pass extrusion is 12-15mm. The steel drying thickness is equal to the steel plate thickness of 290mm. The starting rolling temperature of finishing rolling is 920℃, and the finishing rolling pass reduction is 12mm to control the unevenness of the steel plate. The final rolling temperature is 880-910℃.

[0026] d. Online stage quenching: After rolling, the steel plate immediately enters ultra-fast cooling for cooling, which is divided into two stages of water cooling. The first stage of water cooling lasts for 4 minutes, and the cooling rate is controlled at 30-50℃ / min. When the surface temperature of the steel plate reaches 520℃, it enters the second stage of cooling. The second stage of water cooling lasts for 6 minutes, and the cooling rate is controlled at 20-40℃ / min. The final return temperature is controlled between 470-490℃. After the water cooling is completed, air cooling is used to cool to below 300℃.

[0027] e. Multi-stage tempering: The steel plate is charged with a temperature of 150-200℃ and braised at a furnace temperature of 300-560℃ for 4 hours. The temperature is first raised to 565-575℃ at a heating rate of ≤40℃ / h and kept in a temperature range of 1000 minutes. The burners are then closed and the steel plate is cooled to 295-305℃ with the furnace. Some burners are opened and kept in this temperature range for 250 minutes. After the heat preservation is completed, the steel plate is slowly cooled to room temperature by stacking.

[0028] After testing, the 250mm thick HY30H steel plate produced by this production method meets the requirements of forgings GB / T6402~2008 level 4 for defect diameter ≤2mm; the performance is shown in Table 2: surface hardness 30~36HRC, hardness of the same section in the width direction 30~36HRC, the overall hardness of the steel plate is uniform, and can meet the quality requirements of forgings.

[0029] Table 2250mm steel plate width direction same section hardness

[0030] Distance from edge 100mm 400mm 700mm 1000mm 1300mm 1600mm 1900mm Upper surface (HRC) 34.4 35.1 35.0 35.0 35.2 35.2 35.9 1 / 4 thickness (HRC) 35.8 35.1 35.7 35.7 34.7 34.1 33.8 1 / 2 thickness (HRC) 34.3 35.0 32.1 35.0 35.7 35.5 34.2 1 / 4 thickness (HRC) 34.2 35.7 35.96 35.0 35.9 34.2 35.6 Lower surface (HRC) 35.9 35.7 35.2 35.7 35.1 35.6 35.4

[0031] Embodiment 2:

[0032] The HY30H steel plate with a rolled plate thickness of 300 mm has the chemical composition shown in Table 3 below:

[0033] Table 3 Chemical composition of 300 mm thick steel plate

[0034] C Si Mn P S Als Cr Mo Ti B V 0.36 0.38 1.41 0.013 0.003 0.040 1.86 0.18 0.035 0.00132 0.045

[0035] The steel production method comprises the following steps:

[0036] a. Water-cooled mold casting: Use a water-cooled mold with an inner cavity thickness of 750mm for casting, ensure the rolling reduction ratio is 2.5, the mold casting temperature is 1532℃, the main casting time is 19 minutes, the cap casting time is 8 minutes, and the water cooling water volume is 390m 3 / h, after pouring for 2 hours, adjust to 250m 3 / h, the time of stripping is controlled as 10 hours;

[0037] b. Ingot heating: heating rate 30-40℃ / h, holding temperature 1290-1300℃, holding time 880 minutes;

[0038] c. Rolling: Two-stage steel drying rolling is adopted, and the starting rolling temperature is 1040℃. The single pass reduction in the rough rolling stage is 60mm, and high-pressure water is not used. The last pass of rough rolling adopts vertical stick extrusion, and the single pass extrusion is 12-15mm. The steel drying thickness is equal to the steel plate thickness of 340mm. The starting rolling temperature of finishing rolling is 950℃, and the finishing rolling pass reduction is 10-15mm to control the unevenness of the steel plate. The final rolling temperature is 890-910℃.

[0039] d. Online stage quenching: After rolling, the steel plate immediately enters ultra-fast cooling for cooling, which is divided into two stages of water cooling. The first stage of water cooling lasts for 5 minutes, and the cooling rate is controlled at 30-50℃ / min. When the surface temperature of the steel plate reaches 490℃, it enters the second stage of cooling. The second stage of water cooling lasts for 7 minutes, and the cooling rate is controlled at 20-40℃ / min. The final return temperature is controlled between 440 and 460℃. After the water cooling is completed, air cooling is used to cool to below 300℃;

[0040] e. Multi-stage tempering: The steel plate is charged into the furnace at 150-200℃, and is braised at a furnace temperature of 300-560℃ for 3-5 hours. First, the temperature is raised to 565-575℃ at a heating rate of 30-40℃ / h for insulation. The insulation time is controlled at 1350 minutes. After the insulation time is up, the burner is turned off, and the steel plate is cooled to 300-310℃ with the furnace. Some burners are turned on and the steel plate is kept warm in this temperature range. The insulation time is controlled at 300 minutes. After the insulation is completed, the steel plate is slowly cooled to room temperature by stacking.

[0041] After testing, the 300mm thick HY30H steel plate produced by this production method meets the requirements of forgings GB / T6402~2008 level 4 for defect diameter ≤2mm.

[0042] Table 4 Hardness of 300mm steel plate in the same section along the width direction

[0043] Distance from edge 100mm 400mm 700mm 1000mm 1300mm 1600mm 1900mm Upper surface (HRC) 34.2 35.8 35.1 35.2 35.6 35.2 35.9 1 / 4 thickness (HRC) 35.1 35.6 35.1 35.7 34.2 34.8 34.2 1 / 2 thickness (HRC) 34.6 35.3 34.8 35.1 35.2 35.5 34.2 1 / 4 thickness (HRC) 34.9 35.2 35.9 35.3 35.5 34.9 35.6 Lower surface (HRC) 35.3 35.0 35.4 35.2 35.4 35.8 35.4

[0044] The performance is shown in Table 4: the surface hardness is 30-36HRC, the hardness of the same section in the width direction is 30-36HRC, the overall hardness of the steel plate is uniform, and can meet the quality requirements of forgings.

Claims

1. A HY30H high alloy plastic mold steel, characterized in that: The steel plate has a thickness of 200 to 300 mm and contains the following chemical compositions in mass percentage (unit: wt%): C: 0.35 to 0.38, Si: 0.20 to 0.40, Mn: 1.30 to 1.50%, P≤0.015%, S≤0.005%, Als: 0.020 to 0.050, Cr: 1.80 to 2.0, Mo: 0.15 to 0.18, Ti: 0.020 to 0.050, B: 0.0005 to 0.0015, V 0.030 to 0.050%, and the rest are Fe and residual elements.

2. The HY30H high alloy plastic mold steel according to claim 1, characterized in that Including water-cooled mold casting ingots, ingot heating, rolling, online quenching and tempering, as follows: a. Water-cooled mold casting ingot: Use a water-cooled mold with an inner cavity thickness of ≥700mm for casting, ensure that the rolling reduction ratio is greater than 2.0, the mold casting temperature is 1525-1533℃, the body casting time is 15-19 minutes, the cap casting time is 5-8min, the water pouring volume is 340-390m³ / h, and after pouring for 2 hours, adjust to 250-300m³ / h, and demould after 8-10 hours; b. Ingot heating: heating rate ≤40℃ / h, holding temperature 1280±20℃, holding time 8~12min / cm; c. Rolling: Two-stage air-drying rolling is adopted, the starting temperature of rough rolling is ≥1010℃, the pass reduction is 55-60mm, high-pressure water is not used in the rolling process, the last pass of rough rolling adopts vertical roller extrusion, the single pass extrusion is 10-15mm, the air-drying steel thickness is equal to the steel plate thickness plus 40mm, the starting temperature of finishing rolling is 900-950℃, the pass reduction is 10-15mm to control the unevenness of the steel plate, and the final rolling temperature is ≥850℃; d. Online quenching: After rolling, the steel plate immediately enters the ultra-fast cooling device for cooling. The cooling period is divided into two stages. The first stage of water cooling lasts for 3 to 5 minutes, and the cooling rate is controlled at 30 to 50 ° C / min. When the surface temperature of the steel plate is measured to be 500 ° C ± 30 ° C, it enters the second stage of cooling. The second stage of water cooling lasts for 5 to 7 minutes, and the cooling rate is controlled at 20 to 40 ° C / min. The final return temperature is controlled between 400 and 500 ° C. After the water cooling is completed, air cooling is used to cool to below 300 ° C; e. Tempering: Multi-stage tempering is adopted. The steel plate is charged into the furnace at 150-200℃ and simmered in a furnace temperature environment of 300-560℃ for 3-5 hours. The temperature is first raised to 570±10℃ at a heating rate of ≤40℃ / h and kept warm for 4-5min / mm. Then the burner is closed and the temperature is lowered to 300±10℃ with the furnace and kept warm for 0.8-1.2min / mm. After the insulation is completed, the steel plate stack is slowly cooled to room temperature.