High-hardness high-strength corrosion-resistant die steel and refining heat treatment process thereof

Abstract

The high-hardness, high-strength and corrosion-resistant die steel has high hardness, high strength, corrosion resistance and high mirror surface within the range of 0-400 DEG C. After external refining, electroslag remelting, heating forging and rough machining, the hardness is detected to be larger than 56 HRC and the average tensile strength is detected to be larger than 2050 N / mm < 2 > after performance heat treatment, and in component design, the hardness of the die steel is larger than 56HRC and the average tensile strength is larger than 2050 N / mm < 2 >. The high chromium content is utilized to adapt to the corrosion environment, 2.00%-2.50% of molybdenum element, 0.40%-0.60% of vanadium element and 0.08%-0.15% of nitrogen element are further added, so that the steel has the potential characteristics of corrosion resistance, high tempering resistance, ultrafine structure and high strength, after external refining, electroslag remelting, heating forging and rough machining, structure control and performance strengthening are carried out according to the designed heat treatment process, and the performance of the steel is improved. Therefore, the designed performance indexes are obtained, and the method is widely used for manufacturing the corrosion-resistant and long-service-life high-mirror-surface die steel.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material design and manufacturing, and specifically relates to a high-hardness and high-strength corrosion-resistant die steel having high hardness, high strength, corrosion resistance and high mirror surface in the range of 0°C to 400°C and a refined heat treatment process thereof. After refining outside the furnace, electroslag remelting, heating forging and rough processing, the hardness after performance heat treatment is greater than 56HRC, and the average tensile strength is greater than 2050N / mm 2 . Background Art

[0002] The mirror mold steel used in the manufacture of high-end electronic and electrical products requires not only a high degree of polishing, but also high temperature resistance (0℃~400℃), corrosion resistance, high hardness, and high strength. Usually, the material of this type of mold steel is standard stainless steel containing 13% chromium, but this type of standard mold steel is deficient in high temperature corrosion resistance, tempering stability, wear resistance, etc. The life of the mold is relatively low. In addition to being easy to deform, the surface finish of the products produced later will deteriorate after wear, and the dimensional deviation will become larger. The mold industry needs materials with upgraded performance. Therefore, it is urgent to design a material with high hardness, high tensile strength at this hardness, and good wear resistance and strong dimensional stability. This steel is Cr14Mo2VN. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a high-hardness, high-strength, corrosion-resistant mold steel and its refined heat treatment process developed by optimizing element design. This mold steel has high hardness, high strength and corrosion resistance. It is a high-mirror mold steel used in an acidic corrosive environment within the range of 0°C to 400°C.

[0004] The object of the present invention is achieved in that: A high-hardness and high-strength corrosion-resistant die steel, whose steel number is written as Cr14Mo2VN, and the components of the steel include the following according to mass percentage: C0.36-0.45%, Si0.15-0.55%, Mn0.20-0.70%, P≤0.015%, S≤0.005%, Cr13.8-14.2%, Mo2.00-2.50%, V0.40-0.60%, N0.08-0.15%, Cu≤0.15%, Al0.015-0.030%, Ti≤0.003%, Pb≤0.010%, As≤0.010%, Sn≤0.010%, Sb≤0.010%, Bi≤0.010%, and the balance is iron.

[0005] A refinement heat treatment process for high-hardness and high-strength corrosion-resistant die steel, wherein the steel is refined outside the furnace, electroslag remelted, forged and formed, and rough-processed before being subjected to an ultra-fine treatment process, and then subjected to a performance heat treatment process, wherein the hardness after treatment is greater than 56HRC, and the average tensile strength is greater than 2050N / mm 2 ; The specific steps are as follows: Step 1), producing electrode blanks, according to the chemical composition designed by the present invention, using electric arc furnace or converter, induction furnace, VOD, AOD to smelt primary molten steel, and then refining outside the furnace, vacuum degassing, weak stirring, and then using mold casting or continuous casting to produce electrode blanks. The mold cast electrode blanks need to cut off the riser, and the electrode blanks are hot-sent or annealed; Step 2), produce electroslag ingots, use argon gas to protect electroslag remelting, remelting control melting coefficient is not more than 0.8, electroslag ingots are red sent or annealed; Step 3), forging, diffusion heating the electroslag ingot, double upsetting and double drawing forging with a hydraulic press, forging into a module, and ultrasonic flaw detection after annealing; Step 4), post-forging inspection and surface processing, use ultrasonic testing to check the internal quality, meet the JB / T5000.15-2007 standard level I requirements, then saw off the two ends and then perform surface machining; Step 5), ultra-fine organization treatment, performance heat treatment and performance testing, the ultra-fine treatment process is: the furnace temperature is not more than 500℃, heating to 650±20℃ and keeping warm for 2h, heating to 850±20℃ and keeping warm for 2h, heating to 1030±10℃, keeping warm according to 2h / 100mm thickness, cooling to 350±20℃; entering the furnace at 500±20℃ for 2h, heating to 730±10℃, keeping warm for 10h~12h, and air cooling after leaving the furnace; the heating rate of the process is not more than 80℃ / h, and the cooling rate is not more than 30℃ / h; performance heat treatment process: quenching heating temperature is 1070℃, the heating rate is not more than 80℃ / h, keeping warm for 6h~8h, tempering at 530℃ twice, each time for 3h~5h, and air cooling to room temperature; Step 6) After heat treatment, the hardness is tested at the center of the module end, and samples are taken for tensile testing to verify the strength value within the specified hardness range. The positive effects of the present invention are as follows: 1. The present invention designs a new mold steel material, and designs and develops ultra-fine processing and performance heat treatment processes. This mold steel has the characteristics of high temperature resistance, corrosion resistance, high hardness, high wear resistance, high tensile strength, good dimensional stability and long service life.

[0006] 2. The present invention improves the use effect of the mold, prolongs the service life of the mold, can reduce repeated manufacturing (mainly the smelting, electroslag, forging, machining, performance heat treatment, various quality inspections and mold manufacturing of mold steel materials), improves the utilization efficiency of resources, reduces the energy consumption and pollution emissions in the manufacturing process, is beneficial to environmental protection, and conforms to the concept of green manufacturing.

[0007] 3. The present invention provides a high-hardness, high-strength, corrosion-resistant die steel and a refined heat treatment process thereof. In the composition design, the steel contains about 14% chromium, which has good corrosion resistance and can adapt to the working environment under corrosive conditions; in addition to using high chromium content to adapt to the corrosive environment, 2.00% to 2.50% molybdenum, 0.40% to 0.60% vanadium, and 0.08% to 0.15% nitrogen are added to make the steel have the potential characteristics of corrosion resistance, high tempering resistance, ultra-fine organization, and high strength. Containing 0.4% to 0.60% vanadium can refine the organization of steel; containing 2.0% to 2.5% molybdenum, it has high tempering resistance stability; containing 0.08% to 0.15% nitrogen, it can effectively improve the strength of steel. It can not only adapt to higher working conditions, but also has good dimensional stability; refining outside the furnace, electroslag remelting, and ultra-fine treatment ensure the purity and structure of the steel, and can obtain a polishing degree of more than 10,000 mesh, meeting the use requirements of mirror mold steel; the high hardness obtained after heat treatment can ensure the wear resistance of the mold, and the high tensile strength ensures the mold's crack resistance, thereby comprehensively increasing the service life of the mold. DETAILED DESCRIPTION

[0008] The steel grade of the present invention is written as Cr14Mo2VN, and the main components of the steel are shown in Table 1.

[0009] Table 1 (m%) C And min P S Cr Mo V N 0.36～0.45 0.15～0.55 0.20～0.70 ≤0.015 ≤0.005 13.8～14.2 2.00～2.50 0.40～0.60 0.08～0.15 With Al IT Pb Ace Sn Sat Bi ≤0.15 0.015～0.030 ≤0.003 ≤0.010 ≤0.010 ≤0.010 ≤0.010 ≤0.010 / In addition to the chemical composition design, the present invention also designs a refined heat treatment process suitable for this steel grade, and the specific steps are as follows: Step 1), producing electrode blanks, according to the chemical composition designed by the present invention, using electric arc furnace or converter, induction furnace, VOD, AOD to smelt primary molten steel, and then refining outside the furnace, vacuum degassing, weak stirring, and then using mold casting or continuous casting to produce electrode blanks. The mold casting electrode blanks need to cut off the riser, and the electrode blanks can be hot-sent or annealed; Step 2) Produce electroslag ingots, use argon gas to protect electroslag remelting, and control the melting coefficient of remelting to be no more than 0.8. The electroslag ingots can be hot-sent or annealed; Step 3), forging, diffusion heating of the electroslag ingot, double upsetting and double drawing forging with a hydraulic press (forging into a module), and ultrasonic flaw detection after annealing; Step 4), post-forging inspection and surface processing, use ultrasonic testing to check the internal quality, meet the JB / T5000.15-2007 standard level I requirements, then saw off the two ends and then perform surface machining; Step 5), ultra-fine organization treatment, performance heat treatment and performance testing, the ultra-fine treatment process is: the furnace temperature is not more than 500℃, heating to 650±20℃ and keeping for 2h, heating to 850±20℃ and keeping for 2h, heating to 1030±10℃, keeping for 2h / 100mm thickness, cooling to 350±20℃; entering the furnace at 500±20℃ for 2h, heating to 730±10℃, keeping for 10h~12h, and air cooling after leaving the furnace; the heating rate of the process is not more than 80℃ / h, and the cooling rate is not more than 30℃ / h; performance heat treatment process: quenching heating temperature 1070℃, heating rate is not more than 80℃ / h, keeping for 6h~8h, tempering at 530℃ twice, each time for 3h~5h, and air cooling to room temperature. Thus, the designed performance indicators are obtained to meet the requirements of corrosion-resistant and long-life high-mirror mold steel.

[0010] The present invention discloses a high-hardness, high-strength, corrosion-resistant die steel and its refined heat treatment process, which are essentially different from conventional standard stainless steel. The steel contains about 14% chromium, 0.4% to 0.60% vanadium, 2.0% to 2.5% molybdenum, and 0.08% to 0.15% nitrogen, and is equipped with ultra-fine processing and performance heat treatment processes. The material has high hardness and tensile strength, and can meet the requirements of high temperature resistance, corrosion resistance, wear resistance, good dimensional stability, high mirror surface, and long service life. The specific steps are as follows: Example 1: Taking the production of 305mm*860mm*2200mm~4500mm Cr14Mo2VN modules as an example Step 1), smelting electrode blank: electrode blank diameter 600mm, weight 10.6 tons; arc furnace smelting, furnace refining, vacuum degassing, die casting electrode blank, electrode blank riser cutting, electrode blank annealing, inspection, and transfer to electroslag remelting; Step 2), electroslag ingot production: the electroslag ingot has a diameter of 900 mm and a weight of 9.6 tons; 65:25:10 pre-melted slag is used, the slag amount is 380 kg, argon protection is used, and the melting coefficient is 0.78; Step 3), forging, flaw detection, blanking, surface machining: electroslag ingot heating, heating temperature 1250℃, heating and holding time 18h (including high temperature diffusion time); adopt 5000 ton hydraulic press to forge by two upsetting and two drawing, and stress relief annealing after forging; after leaving the furnace, carry out internal quality inspection by ultrasonic flaw detection according to JB / T5000.15-2007 standard, and accept according to Class I; after flaw detection, remove the excess material at both ends; finally, use milling machine to carry out surface machining, and the machining allowance is 5mm~8mm; Step 4), ultra-fine processing, performance heat treatment, performance testing: Ultrafine treatment process: put into the furnace at 450℃, heat to 650±20℃ and keep warm for 2h, heat to 850±20℃ and keep warm for 2h, heat to 1030±10℃ and keep warm for 6h, cool to 350±20℃; put into the furnace at 500±20℃ and wait for material for 2h, heat to 730±10℃ and keep warm for 12h, and air cool out of the furnace. The heating rate of the process shall not exceed 80℃ / h, and the cooling rate shall not exceed 30℃ / h; Performance heat treatment process: quenching heating temperature 1070℃, heating rate no more than 80℃ / h, insulation for 7.5h, tempering at 530℃ twice, 4h each time, air cooling to room temperature.

[0011] Ingot number, sample number, test standard and equipment, hardness and performance test results Table 2: Table 2 .

Claims

1. A high hardness and high strength corrosion resistant die steel, characterized by: The steel grade is Cr14Mo2VN, and the components of the steel in mass percentage are as follows: C0.36~0.45%, Si0.15~0.55%, Mn0.20~0.70%, P≤0.015%, S≤0.005%, Cr13.8~14.2%, Mo2.00~2.50%, V0.40~0.60%, N0.08~0.15%, Cu≤0.15%, Al0.015~0.030%, Ti≤0.003%, Pb≤0.010%, As≤0.010%, Sn≤0.010%, Sb≤0.010%, Bi≤0.010%, and the balance is iron.

2. A refinement heat treatment process for high hardness and high strength corrosion resistant die steel according to claim 1, characterized in that: After refining outside the furnace, electroslag remelting, forging and rough processing, the steel is subjected to ultra-fine treatment technology, and then to performance heat treatment technology. After treatment, the hardness is greater than 56HRC and the average tensile strength is greater than 2050N / mm 2 ; The specific steps are as follows: Step 1), producing electrode blanks, according to the chemical composition designed by the present invention, using electric arc furnace or converter, induction furnace, VOD, AOD to smelt primary molten steel, and then refining outside the furnace, vacuum degassing, weak stirring, and then using mold casting or continuous casting to produce electrode blanks. The mold cast electrode blanks need to cut off the riser, and the electrode blanks are hot-sent or annealed; Step 2), produce electroslag ingots, use argon gas to protect electroslag remelting, remelting control melting coefficient is not more than 0.8, electroslag ingots are red sent or annealed; Step 3), forging, diffusion heating the electroslag ingot, double upsetting and double drawing forging with a hydraulic press, forging into a module, and ultrasonic flaw detection after annealing; Step 4), post-forging inspection and surface processing, use ultrasonic testing to check the internal quality, meet the JB / T5000.15-2007 standard level I requirements, then saw off the two ends and then perform surface machining; Step 5), ultra-fine organization treatment, performance heat treatment and performance testing, the ultra-fine treatment process is: the furnace temperature is not more than 500℃, heating to 650±20℃ and keeping warm for 2h, heating to 850±20℃ and keeping warm for 2h, heating to 1030±10℃, keeping warm according to 2h / 100mm thickness, cooling to 350±20℃; entering the furnace at 500±20℃ for 2h, heating to 730±10℃, keeping warm for 10h~12h, and air cooling after leaving the furnace; the heating rate of the process is not more than 80℃ / h, and the cooling rate is not more than 30℃ / h; performance heat treatment process: quenching heating temperature is 1070℃, the heating rate is not more than 80℃ / h, keeping warm for 6h~8h, tempering at 530℃ twice, each time for 3h~5h, and air cooling to room temperature; Step 6) After heat treatment, the hardness is tested at the center of the module end, and samples are taken for tensile testing to verify the strength value within the specified hardness range.