CN116536581A - Hot work die steel SD400 and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of metallurgy, and particularly discloses hot work die steel SD400 and a preparation method thereof. Wherein, the composition comprises the following components in percentage by weight: c:0.35% -0.40%, si:0.20% -0.50%, mn:0.30 to 0.80 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.005 percent, cr:4.80% -5.40%, mo:1.80% -2.40%, V:0.60% -1.00%, ni:0.30% -0.60%, co:0.30% -0.60%, and the balance of iron and unavoidable impurities. The die steel SD400 provided by the invention has higher transverse unnotched impact performance and hardness, has excellent banded segregation structure and excellent grain size, and solves the problems of poor hardenability, poor banded structure and microstructure, poor transverse unnotched impact performance and the like of large-module die steel.

Description

A kind of hot working die steel SD400 and its preparation method

technical field

The invention relates to the technical field of metallurgy, and specifically discloses a hot work die steel SD400 and a preparation method thereof.

Background technique

The development of domestic die-casting die steel started relatively late compared with foreign countries. In recent years, with the continuous progress of science and technology, and with the introduction of foreign advanced production process equipment, as well as further exploration of die steel alloy system and heat treatment, the product The quality has been greatly improved, and the stability has gradually improved.

At present, there are three types of mainstream die-casting hot work die steels in China: 4Cr5MoSiV1 (H13), 4Cr5Mo2V (DIEVAR), and 4Cr5Mo3V (1.2367). The ideal operating temperature of 4Cr5MoSiV1 (H13) and 4Cr5Mo2V (DIEVAR) is not higher than 600 ° C. When the operating temperature is higher than 600 ° C, the thermal stability of the material will be significantly reduced, resulting in softening of the material and a decrease in local hardness. Serious Shorten mold life.

The automotive industry is increasingly demanding large cross-section, high hardenability, and high strength and toughness die-casting die steels, but most of the die-casting die steels currently on the market have limited hardenability. When the cross-sectional size of the module exceeds 400mm, it is difficult to ensure the hardening of the core; in addition, band segregation and microstructure are another important index of large module die steel, and it is difficult to achieve the ideal by simply relying on high-temperature diffusion and ultra-fine treatment. state. Therefore, the development of a die steel with excellent hardenability, band structure and microstructure is of great significance for the development and application of steel grades.

Contents of the invention

Aiming at the problems of poor hardenability, poor band structure and microstructure, and poor transverse unnotched impact performance in the prior art, the present invention provides a hot work die steel SD400 and a preparation method thereof. Die steel has high transverse unnotched impact performance and hardness, excellent banded segregation structure and excellent grain size, and has extremely high application value.

In order to achieve the above object of the invention, the present invention provides the following technical solutions:

The first aspect of the present invention provides a hot work die steel SD400, which comprises the following components in terms of weight percentage: C: 0.35%-0.40%, Si: 0.20%-0.50%, Mn: 0.30%-0.80%, P≤ 0.015%, S≤0.005%, Cr: 4.80%-5.40%, Mo: 1.80%-2.40%, V: 0.60%-1.00%, Ni: 0.30%-0.60%, Co: 0.30%-0.60%, and the rest are Iron and unavoidable impurities.

Compared with the prior art, the present invention provides a hot work die steel SD400. The die steel provided by the present invention improves the hardenability of the die steel by adding a certain content of Ni element, so as to ensure the hardenability of the die steel after quenching and tempering. The uniformity of material hardness, and the die steel provided by the present invention also adds a certain content of Co element, which can suppress the coarseness of secondary carbides and refine the grains, and can reduce the overheating tendency of steel and improve the high temperature of die steel. state service life.

The second aspect of the present invention provides the preparation method of said hot work die steel SD400, at least including the following steps:

Step 1. After the consumable ingot is subjected to high-temperature calcination, upsetting forging and waste heat quenching, a waste heat quenched forging is obtained;

Step 2: raising the temperature of the waste heat quenched forging to 1000°C-1050°C, keeping it warm for 4h-6h, and then alternately cooling to 150°C-300°C through water cooling and air cooling to obtain an ultra-fine forging;

Step 3: Heat the super-fine forging to 840°C-880°C, keep it warm for 15h-20h, then cool it with the furnace to 720°C-760°C, keep it warm for 25h-30h, cool it down to below 300°C, and get hot work Die steel SD400.

Compared with the prior art, the preparation of the hot work die steel SD400 provided by the present invention reduces the level of non-metallic inclusions through self-consumption remelting, improves primary carbide segregation, and can significantly reduce the degree of component segregation through high-temperature diffusion technology, making self-consumption The ingot structure tends to be uniform, which is conducive to obtaining excellent banded segregation structure die steel. Among them, the consumable ingot after the above-mentioned high-temperature diffusion treatment is subjected to 2-3 times of upsetting and drawing forging, which can effectively repair the internal defects that may occur in the forging after the above-mentioned high-temperature diffusion process is completed, and further improve the microstructure uniformity of the forging. The forged products obtained after drawing and forging are then subjected to specific heat treatment processes of waste heat quenching, high temperature tempering, ultra-fine treatment and isothermal spheroidizing annealing treatment, which can obtain both high transverse unnotched impact performance and hardness as well as excellent High-quality die steel SD400 with banded segregation structure and excellent grain size. Moreover, by controlling the temperature range of the waste heat quenching terminal blank, it is possible to avoid quenching cracks during the quenching process, and at the same time avoid the coarsening of carbides during the slow cooling process. Through the above-mentioned specific ultrafine treatment heating rate and treatment temperature, the mixed structure of martensite + bainite + pearlite that appears in the mold steel can be redissolved, and a single structure can be obtained after cooling, and the formation of mixed crystals can be avoided. Appearance, uniform and fine martensitic structure can be obtained, which improves the hardenability and hardenability of SD400 die steel, and is also conducive to the re-precipitation of dispersed and fine carbides in the subsequent heat treatment process, effectively improving the thermal fatigue resistance of die steel. Temper stability. After the ultrafine treatment, the mold steel is heated to 860°C-880°C and 720°C-760°C at a specific heating rate to perform isothermal spheroidizing annealing treatment, which can effectively avoid the aggregation and growth of carbide particles and obtain High-quality die steel SD400 with high transverse unnotched impact performance and hardness, excellent banded segregation structure and excellent grain size.

Preferably, in step one, the preparation method of the self-consumable ingot comprises the following steps:

Step a, after the raw material components are smelted in an electric furnace, LF refining and VD vacuum degassing smelting, an electrode blank of φ430mm is obtained;

Step b, electroslag remelting the electrode blank to obtain an electroslag ingot of φ590 mm;

Step c. Consumable remelting of the electroslag ingot to obtain a consumable ingot of φ660 mm.

Preferably, in step a, the electric furnace smelting temperature is 1690°C-1710°C, and the smelting time is 1h-1.5h.

Preferably, in step a, the temperature of the LF refining is 1580°C-1620°C, and the refining time is 1.5h-2h.

Preferably, in step a, the vacuum degree of the VD vacuum degassing smelting is 30Pa-40Pa, the smelting time is 15min-20min, and the smelting temperature is 1560°C-1580°C.

Preferably, in step b, the electroslag remelting is performed under an inert atmosphere at a constant melting rate, and the melting rate is 6.5kg/min-7.5kg/min.

Preferably, in step c, the consumable remelting is consumable remelting at a constant melting rate under vacuum conditions, the vacuum degree is 0.5 Pa-0.7 Pa, and the melting rate is 5.5 kg/min-6.5 kg/min.

Preferably, in step 1, the specific operation of the high-temperature calcination is: put the consumable ingot into a high-temperature diffusion furnace, and raise the temperature to 1230-1270°C at a heating rate of 80°C/h-100°C/h for 40 hours -45h, then cooled to 1180°C-1200°C, held for 2h-4h and then out of the furnace for forging, to the high-temperature diffusion state self-consumable ingot.

Preferably, in step 1, the upsetting ratio of the upsetting forging is 2-2.2.

Preferably, in step 1, the number of times of said upsetting forging is 2-3 times.

The limitation of the upsetting ratio in the present invention can further avoid the occasional structural defects and inhomogeneities in the steel ingot during the high-temperature diffusion treatment process, and can also significantly repair the porosity defects that may occur in the forgings, and can effectively change the inclusions in the forgings. The shape of the forgings can prevent defects such as cracks and looseness in the forgings during subsequent processing.

Preferably, in step 1, the specific step of the waste heat quenching is: controlling the final forging temperature of the forging to not be lower than 850°C, adding water for waste heat quenching to obtain a waste heat quenched forging at a temperature of 350°C-450°C.

Preferably, in step 2, the temperature is raised to 1000°C-1050°C at a rate of 80°C/h-100°C/h.

Preferably, in step 2, the water-air alternating cooling includes at least two times of water cooling and two times of air cooling, the time of the first water cooling is 14min-18min, after the first water cooling is completed, the air cooling is performed, and the second cooling is performed when the internal and external temperatures of the forging are consistent. Second water cooling, the time of the second water cooling is 10min-12min, air cooling after the second water cooling, control the temperature of the mold steel after air cooling to 150°C-300°C.

The invention can effectively refine the metallographic structure through the alternate cooling of water and air, so that the carbides are fine and dispersed on the matrix, and at the same time, stress cracks in the ultra-fine processed material can be avoided.

Preferably, in step 3, the temperature is raised to 840°C-880°C at a rate of 80°C/h-100°C/h.

Preferably, in step 3, the cooling is cooling to below 300°C at a rate of ≤30°C/h.

The invention provides a hot work die steel SD400 and its preparation method, which effectively solves the problem of limited hardenability, poor band structure and microstructure, and poor transverse non-notched impact performance of large module die steel in the prior art. and other technical problems, the die steel SD400 provided by the present invention has both high transverse unnotched impact performance and hardness, excellent banded segregation structure and excellent grain size, and has extremely high application value.

Description of drawings

Fig. 1 is the band segregation structure figure of the hot work die steel SD400 that embodiment 3 provides;

Fig. 2 is a microstructure diagram of the hot work die steel SD400 provided in Example 3.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Example 1

This embodiment provides a kind of hot work die steel SD400, the specific content is as follows:

The hot work die steel SD400 includes the following components in terms of weight percentage: C: 0.36%, Si: 0.30%, Mn: 0.50%, P: 0.01%, S: 0.003%, Cr: 4.90%, Mo: 2.10% , V: 0.70%, Ni: 0.50%, Co: 0.40%, and the rest are iron and unavoidable impurities.

The preparation method of above-mentioned hot working die steel SD400:

Step 1. According to the design ratio, the raw materials were smelted in an electric furnace at 1700°C for 1 hour, then LF refined at 1590°C for 1.5 hours, and then smelted at -30Pa for 15 minutes to obtain a φ430mm electrode blank with a furnace temperature of 1560°C;

Step 2: Remelt the electrode blank with electroslag at a melting rate of 6.5kg/min under an inert atmosphere to obtain a φ590mm electroslag ingot; The melting speed of kg/min is self-consumable and remelted to obtain a φ660mm self-consumable ingot;

Step 3: Put the φ660mm consumable ingot into a high-temperature diffusion furnace, raise the temperature to 1250°C at a heating rate of 90°C/h, keep it for 40 hours, then cool it down to 1180°C with the furnace, keep it for 2.5 hours, and then take it out of the furnace for forging to obtain high-temperature diffusion State self-consumption ingot;

Step 4. The high-temperature diffusion state consumable ingot is subjected to upsetting and drawing forging three times according to the upsetting ratio of 2:1 to obtain a forging. The final forging temperature of the forging is controlled to be 860°C. After forging, it is hoisted into water for residual heat quenching , and control the temperature of the forging after quenching at 380°C to obtain a forging in the quenched state with residual heat;

Step 5. Heat the forging in the waste heat quenched state to 1020°C at a heating rate of 100°C/h, keep it warm for 5h, and then go through two water cooling and two air cooling, the first water cooling time is 15min, and the first water cooling Air cooling after completion, when the internal and external temperatures of the forging are consistent, perform a second water cooling, the time of the second water cooling is 10 minutes, air cooling after the second water cooling, control the temperature of the mold steel after air cooling to 180°C, and obtain an ultra-fine state forging;

Step 6. The ultra-fine forging is heated up to 850°C at a heating rate of 90°C/h, kept for 16 hours, then cooled to 720°C with the furnace, kept for 27 hours, and then cooled to 270°C at a rate of 25°C/h. The hot work die steel SD400 in the spheroidizing annealed state was obtained.

Example 2

This embodiment provides a kind of hot work die steel SD400, the specific content is as follows:

The hot work die steel SD400 includes the following components in terms of weight percentage: C: 0.36%, Si: 0.40%, Mn: 0.70%, P: 0.012%, S: 0.003%, Cr: 5.10%, Mo: 1.90% , V: 0.70%, Ni: 0.50%, Co: 0.50%, and the rest are iron and unavoidable impurities.

The preparation method of above-mentioned hot working die steel SD400:

Step 1. According to the design ratio, the raw materials were smelted in an electric furnace at 1690°C for 1.5h, then LF refined at 1600°C for 1.5h, and then smelted at -30Pa for 20min to obtain a φ430mm electrode blank with a furnace temperature of 1570°C ;

Step 2: Remelt the electrode blank with electroslag at a melting rate of 7.5kg/min under an inert atmosphere to obtain a φ590mm electroslag ingot; The melting speed of kg/min is self-consumable and remelted to obtain a φ660mm self-consumable ingot;

Step 3: Put the φ660mm consumable ingot into a high-temperature diffusion furnace, raise the temperature to 1270°C at a heating rate of 90°C/h, hold it for 44 hours, then cool it down to 1190°C with the furnace, keep it for 3 hours, and then take it out of the furnace for forging to obtain a high-temperature diffusion state consumable ingot;

Step 4. The high-temperature diffusion state consumable ingot is subjected to three times of upsetting and drawing forging according to the upsetting ratio of 2.2:1 to obtain a forging. The final forging temperature of the forging is controlled to be 850 ° C. After forging, it is hung into water for residual heat quenching , and control the temperature of the forging after quenching at 420°C to obtain a forging in the quenched state with residual heat;

Step 5. Heat the forging in the waste heat quenched state to 1040°C at a heating rate of 100°C/h, keep it warm for 5h, and then go through two water cooling and two air cooling, the first water cooling time is 17min, the first water cooling After the completion of air cooling, the second water cooling is performed when the internal and external temperatures of the forging are consistent. The time of the second water cooling is 10 minutes. After the second water cooling is completed, it is air cooled. The temperature of the mold steel after air cooling is controlled at 200 ° C to obtain an ultra-fine state forging;

Step 6. The ultra-fine forging is heated up to 850°C at a heating rate of 90°C/h, kept for 16 hours, then furnace cooled to 740°C, kept for 28 hours, and then cooled to 250°C at a rate of 25°C/h to obtain Spheroidizing annealed hot work die steel SD400.

Example 3

This embodiment provides a kind of hot work die steel SD400, the specific content is as follows:

The hot work die steel SD400 includes the following components in terms of weight percentage: C: 0.37%, Si: 0.40%, Mn: 0.60%, P: 0.013%, S: 0.004%, Cr: 5.10%, Mo: 2.10% , V: 0.70%, Ni: 0.50%, Co: 0.50%, and the rest are iron and unavoidable impurities.

The preparation method of above-mentioned hot working die steel SD400:

Step 1. According to the design ratio, the raw materials were smelted in an electric furnace at 1700°C for 1.5h, then LF refined at 1600°C for 1.5h, and then smelted at -30Pa for 18min to obtain a φ430mm electrode blank with a furnace temperature of 1570°C ;

Step 2: Remelt the electrode blank with electroslag at a melting rate of 7.0kg/min under an inert atmosphere to obtain a φ590mm electroslag ingot; The melting speed of kg/min is self-consumable and remelted to obtain a φ660mm self-consumable ingot;

Step 3: Put the φ660mm consumable ingot into a high-temperature diffusion furnace, raise the temperature to 1250°C at a heating rate of 90°C/h, hold it for 42 hours, then cool it down to 1190°C with the furnace, hold it for 3 hours, and then take it out of the furnace for forging to obtain a high-temperature diffusion state consumable ingot;

Step 4. The high-temperature diffused consumable ingot is subjected to upsetting and drawing forging three times according to the upsetting ratio of 2:1 to obtain a forging. The final forging temperature of the forging is controlled to be 850° C. After forging, it is hung into water for residual heat quenching , and control the temperature of the forging after quenching at 400°C to obtain a forging in the quenched state with residual heat;

Step 5. Heat the forging in the waste heat quenched state to 1030°C at a heating rate of 90°C/h, keep it warm for 5h, and then go through two water cooling and two air cooling, the first water cooling time is 15min, the first water cooling After the completion of air cooling, the second water cooling is carried out when the internal and external temperatures of the forging are consistent. The time of the second water cooling is 10 minutes. After the second water cooling is completed, it is air cooled.

Step 6: heating the ultrafine forging to 860°C at a heating rate of 90°C/h, keeping it for 16 hours, then furnace cooling to 740°C, keeping it for 27 hours, and then cooling to 280°C at a rate of 25°C/h to obtain Spheroidizing annealed hot work die steel SD400.

Example 4

This embodiment provides a kind of hot work die steel SD400, the specific content is as follows:

The hot work die steel SD400 includes the following components in terms of weight percentage: C: 0.36%, Si: 0.30%, Mn: 0.50%, P: 0.01%, S: 0.003%, Cr: 4.90%, Mo: 2.10% , V: 0.70%, Ni: 0.50%, Co: 0.40%, and the rest are iron and unavoidable impurities.

The preparation method of above-mentioned hot working die steel SD400:

Step 1. According to the design ratio, the raw materials were smelted in an electric furnace at 1700°C for 1 hour, then LF refined at 1590°C for 1.5 hours, and then smelted at -35Pa for 20 minutes to obtain a φ430mm electrode blank with a furnace temperature of 1565°C;

Step 2: Remelt the electrode blank with electroslag at a melting rate of 6.5kg/min under an inert atmosphere to obtain a φ590mm electroslag ingot; The melting speed of kg/min is self-consumable and remelted to obtain a φ660mm self-consumable ingot;

Step 3: Put the φ660mm self-consumable ingot into a high-temperature diffusion furnace, raise the temperature to 1250°C at a heating rate of 100°C/h, keep it for 40 hours, then cool it down to 1180°C with the furnace, hold it for 2.5 hours, and then take it out of the furnace for forging to obtain a high-temperature diffusion State self-consumption ingot;

Step 4. The high-temperature diffusion state consumable ingot is subjected to upsetting and drawing forging three times according to the upsetting ratio of 2:1 to obtain a forging. The final forging temperature of the forging is controlled to be 860°C. After forging, it is hoisted into water for residual heat quenching , and control the temperature of the forging after quenching at 380°C to obtain a forging in the quenched state with residual heat;

Step 5. Heat the forging in the waste heat quenched state to 1025°C at a heating rate of 90°C/h, keep it warm for 5h, and then go through two water cooling and two air cooling, the first water cooling time is 15min, the first water cooling After the completion of air cooling, the second water cooling is carried out when the internal and external temperatures of the forging are consistent. The time of the second water cooling is 10 minutes. After the second water cooling is completed, it is air cooled.

Step 6: heating the superfine forging to 850°C at a heating rate of 100°C/h, keeping it for 16 hours, then furnace cooling to 730°C, keeping it for 27 hours, and then cooling to 260°C at a rate of 25°C/h to obtain Spheroidizing annealed hot work die steel SD400.

Example 5

This embodiment provides a kind of hot work die steel SD400, the specific content is as follows:

The hot work die steel SD400 includes the following components in terms of weight percentage: C: 0.36%, Si: 0.30%, Mn: 0.50%, P: 0.01%, S: 0.003%, Cr: 4.90%, Mo: 2.10% , V: 0.70%, Ni: 0.50%, Co: 0.40%, and the rest are iron and unavoidable impurities.

The preparation method of above-mentioned hot working die steel SD400:

Step 1. According to the design ratio, the raw materials were smelted in an electric furnace at 1710°C for 1 hour, then LF refined at 1620°C for 1.5 hours, and then smelted at -30Pa for 15 minutes to obtain a φ430mm electrode blank with a furnace temperature of 1575°C;

Step 2: Remelt the electrode blank with electroslag at a melting rate of 6.5kg/min under an inert atmosphere to obtain a φ590mm electroslag ingot; The melting speed of kg/min is self-consumable and remelted to obtain a φ660mm self-consumable ingot;

Step 3: Put the φ660mm self-consumable ingot into a high-temperature diffusion furnace, raise the temperature to 1250°C at a heating rate of 80°C/h, keep it for 40 hours, then cool it down to 1180°C with the furnace, hold it for 3 hours, and then take it out of the furnace for forging to obtain a high-temperature diffusion state consumable ingot;

Step 4. The high-temperature diffused consumable ingot is subjected to two times of upsetting and drawing forging according to the upsetting ratio of 2.2:1 to obtain a forging. The final forging temperature of the forging is controlled to be 870°C. After forging, it is hung into water for residual heat quenching , and control the temperature of the forging after quenching at 380°C to obtain a forging in the quenched state with residual heat;

Step 5. Heat the forging in the waste heat quenched state to 1020°C at a heating rate of 100°C/h, keep it warm for 5h, and then go through two water cooling and two air cooling, the first water cooling time is 15min, and the first water cooling After the completion of air cooling, the second water cooling is performed when the internal and external temperatures of the forging are consistent. The time of the second water cooling is 10 minutes. After the second water cooling is completed, it is air cooled. The temperature of the mold steel after air cooling is controlled at 200 ° C to obtain an ultra-fine state forging;

Step 6: heating the ultra-fine forging to 850°C at a heating rate of 90°C/h, holding it for 16 hours, then furnace cooling to 720°C, holding it for 25 hours, and then cooling it to 280°C at a rate of 20°C/h to obtain Spheroidizing annealed hot work die steel SD400.

Comparative example 1

This comparative example provides a hot work die steel SD400, the difference from Example 3 is that the Co element is replaced by Cu, and other components, content and preparation process remain unchanged, the specific content is as follows:

The hot work die steel SD400 includes the following components in terms of weight percentage: C: 0.37%, Si: 0.40%, Mn: 0.60%, P: 0.013%, S: 0.004%, Cr: 5.10%, Mo: 2.10% , V: 0.70%, Ni: 0.50%, Cu: 0.50%, and the rest are iron and unavoidable impurities.

The preparation method of above-mentioned hot working die steel SD400:

Step 1. According to the design ratio, the raw materials were smelted in an electric furnace at 1700°C for 1.5h, then LF refined at 1600°C for 1.5h, and then smelted at -30Pa for 18min to obtain a φ430mm electrode blank with a furnace temperature of 1570°C ;

Step 2: Remelt the electrode blank with electroslag at a melting rate of 7.0kg/min under an inert atmosphere to obtain a φ590mm electroslag ingot; The melting speed of kg/min is self-consumable and remelted to obtain a φ660mm self-consumable ingot;

Step 3: Put the φ660mm consumable ingot into a high-temperature diffusion furnace, raise the temperature to 1250°C at a heating rate of 90°C/h, hold it for 42 hours, then cool it down to 1190°C with the furnace, hold it for 3 hours, and then take it out of the furnace for forging to obtain a high-temperature diffusion state consumable ingot;

Step 4. The high-temperature diffused consumable ingot is subjected to upsetting and drawing forging three times according to the upsetting ratio of 2:1 to obtain a forging. The final forging temperature of the forging is controlled to be 850° C. After forging, it is hung into water for residual heat quenching , and control the temperature of the forging after quenching at 400°C to obtain a forging in the quenched state with residual heat;

Step 5. Heat the forging in the waste heat quenched state to 1030°C at a heating rate of 90°C/h, keep it warm for 5h, and then go through two water cooling and two air cooling, the first water cooling time is 15min, the first water cooling After the completion of air cooling, the second water cooling is carried out when the internal and external temperatures of the forging are consistent. The time of the second water cooling is 10 minutes. After the second water cooling is completed, it is air cooled.

Step 6: heating the ultrafine forging to 860°C at a heating rate of 90°C/h, keeping it for 16 hours, then furnace cooling to 740°C, keeping it for 27 hours, and then cooling to 280°C at a rate of 25°C/h to obtain Spheroidizing annealed hot work die steel SD400.

Comparative example 2

This comparative example provides a hot work die steel SD400, the difference from Example 3 is that the Ni element content is increased to 1.40%, and other components, content and preparation process remain unchanged, the specific content is as follows:

The hot work die steel SD400 includes the following components in terms of weight percentage: C: 0.37%, Si: 0.40%, Mn: 0.60%, P: 0.013%, S: 0.004%, Cr: 5.10%, Mo: 2.10% , V: 0.70%, Ni: 1.40%, Co: 0.50%, and the rest are iron and unavoidable impurities.

The preparation method of above-mentioned hot working die steel SD400:

Step 1. According to the design ratio, the raw materials were smelted in an electric furnace at 1700°C for 1.5h, then LF refined at 1600°C for 1.5h, and then smelted at -30Pa for 18min to obtain a φ430mm electrode blank with a furnace temperature of 1570°C ;

Step 2: Remelt the electrode blank with electroslag at a melting rate of 7.0kg/min under an inert atmosphere to obtain a φ590mm electroslag ingot; The melting speed of kg/min is self-consumable and remelted to obtain a φ660mm self-consumable ingot;

Step 3: Put the φ660mm consumable ingot into a high-temperature diffusion furnace, raise the temperature to 1250°C at a heating rate of 90°C/h, hold it for 42 hours, then cool it down to 1190°C with the furnace, hold it for 3 hours, and then take it out of the furnace for forging to obtain a high-temperature diffusion state consumable ingot;

Step 4. The high-temperature diffused consumable ingot is subjected to upsetting and drawing forging three times according to the upsetting ratio of 2:1 to obtain a forging. The final forging temperature of the forging is controlled to be 850° C. After forging, it is hung into water for residual heat quenching , and control the temperature of the forging after quenching at 400°C to obtain a forging in the quenched state with residual heat;

Step 5. Heat the forging in the waste heat quenched state to 1030°C at a heating rate of 90°C/h, keep it warm for 5h, and then go through two water cooling and two air cooling, the first water cooling time is 15min, the first water cooling After the completion of air cooling, the second water cooling is carried out when the internal and external temperatures of the forging are consistent. The time of the second water cooling is 10 minutes. After the second water cooling is completed, it is air cooled.

Step 6: heating the ultrafine forging to 860°C at a heating rate of 90°C/h, keeping it for 16 hours, then furnace cooling to 740°C, keeping it for 27 hours, and then cooling to 280°C at a rate of 25°C/h to obtain Spheroidizing annealed hot work die steel SD400.

Comparative example 3

This comparative example provides a hot work die steel SD400, the difference from Example 3 is that the Ni element content is reduced to 0.20%, and other components, content and preparation process remain unchanged, the specific content is as follows:

The hot work die steel SD400 includes the following components in terms of weight percentage: C: 0.37%, Si: 0.40%, Mn: 0.60%, P: 0.013%, S: 0.004%, Cr: 5.10%, Mo: 2.10% , V: 0.70%, Ni: 0.20%, Co: 0.50%, and the rest are iron and unavoidable impurities.

The preparation method of above-mentioned hot working die steel SD400:

Step 1. According to the design ratio, the raw materials were smelted in an electric furnace at 1700°C for 1.5h, then LF refined at 1600°C for 1.5h, and then smelted at -30Pa for 18min to obtain a φ430mm electrode blank with a furnace temperature of 1570°C ;

Step 2: Remelt the electrode blank with electroslag at a melting rate of 7.0kg/min under an inert atmosphere to obtain a φ590mm electroslag ingot; The melting speed of kg/min is self-consumable and remelted to obtain a φ660mm self-consumable ingot;

Step 3: Put the φ660mm consumable ingot into a high-temperature diffusion furnace, raise the temperature to 1250°C at a heating rate of 90°C/h, hold it for 42 hours, then cool it down to 1190°C with the furnace, hold it for 3 hours, and then take it out of the furnace for forging to obtain a high-temperature diffusion state consumable ingot;

Step 4. The high-temperature diffused consumable ingot is subjected to upsetting and drawing forging three times according to the upsetting ratio of 2:1 to obtain a forging. The final forging temperature of the forging is controlled to be 850° C. After forging, it is hung into water for residual heat quenching , and control the temperature of the forging after quenching at 400°C to obtain a forging in the quenched state with residual heat;

Step 5. Heat the forging in the waste heat quenched state to 1030°C at a heating rate of 90°C/h, keep it warm for 5h, and then go through two water cooling and two air cooling, the first water cooling time is 15min, the first water cooling After the completion of air cooling, the second water cooling is carried out when the internal and external temperatures of the forging are consistent. The time of the second water cooling is 10 minutes. After the second water cooling is completed, it is air cooled.

Step 6: heating the ultrafine forging to 860°C at a heating rate of 90°C/h, keeping it for 16 hours, then furnace cooling to 740°C, keeping it for 27 hours, and then cooling to 280°C at a rate of 25°C/h to obtain Spheroidizing annealed hot work die steel SD400.

Comparative example 4

The difference between this comparative example and Example 3 is that two water coolings and two air coolings are replaced by two water coolings in the preparation process, and other components, contents and preparation processes are unchanged, and the specific contents are as follows:

The hot work die steel SD400 includes the following components in terms of weight percentage: C: 0.37%, Si: 0.40%, Mn: 0.60%, P: 0.013%, S: 0.004%, Cr: 5.10%, Mo: 2.10% , V: 0.70%, Ni: 0.50%, Co: 0.50%, and the rest are iron and unavoidable impurities.

The preparation method of above-mentioned hot working die steel SD400:

Step 1. According to the design ratio, the raw materials were smelted in an electric furnace at 1700°C for 1.5h, then LF refined at 1600°C for 1.5h, and then smelted at -30Pa for 18min to obtain a φ430mm electrode blank with a furnace temperature of 1570°C ;

Step 2: Remelt the electrode blank with electroslag at a melting rate of 7.0kg/min under an inert atmosphere to obtain a φ590mm electroslag ingot; The melting speed of kg/min is self-consumable and remelted to obtain a φ660mm self-consumable ingot;

Step 3: Put the φ660mm consumable ingot into a high-temperature diffusion furnace, raise the temperature to 1250°C at a heating rate of 90°C/h, hold it for 42 hours, then cool it down to 1190°C with the furnace, hold it for 3 hours, and then take it out of the furnace for forging to obtain a high-temperature diffusion state consumable ingot;

Step 4. The high-temperature diffused consumable ingot is subjected to upsetting and drawing forging three times according to the upsetting ratio of 2:1 to obtain a forging. The final forging temperature of the forging is controlled to be 850° C. After forging, it is hung into water for residual heat quenching , and control the temperature of the forging after quenching at 400°C to obtain a forging in the quenched state with residual heat;

Step 5. Heat up the forging in the waste heat quenched state to 1030°C at a heating rate of 90°C/h, keep it warm for 5h, and then go through two water cooling times. The first water cooling time is 15min. After the first water cooling is completed, wait for When the internal and external temperatures of the forging are consistent, the second water cooling is performed. The second water cooling time is 10 minutes. After the second water cooling is completed, the temperature of the die steel is controlled to 260 ° C to obtain an ultra-fine forging;

Step 6: heating the ultrafine forging to 860°C at a heating rate of 90°C/h, keeping it for 16 hours, then furnace cooling to 740°C, keeping it for 27 hours, and then cooling to 280°C at a rate of 25°C/h to obtain Spheroidizing annealed hot work die steel SD400.

Performance Testing

In order to further illustrate the technical effects of the present invention, the present invention observes and mechanically tests the banded segregation structure and microstructure of the mold steel SD400 obtained in Examples 1-5 and Comparative Examples 1-3, and the observed banded The results of segregation microstructure (according to SEP1614 standard) and 500 times microstructure (according to NADCA#207 standard) and grain size test, transverse unnotched impact performance and hardness test results of die steel SD400 are shown in Table 1 :

Table 1

According to Table 1, it can be seen that the mold steel SD400 provided by Examples 1-5 of the present invention has higher sample hardness, can withstand higher transverse unnotched impact force, and the sample grain size is larger, and has excellent The banded segregation structure and microstructure.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Any modification, equivalent replacement or improvement made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (10)

1. A hot work die steel SD400, characterized in that: the coating comprises the following components in percentage by weight: c:0.35% -0.40%, si:0.20% -0.50%, mn:0.30 to 0.80 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.005 percent, cr:4.80% -5.40%, mo:1.80% -2.40%, V:0.60% -1.00%, ni:0.30% -0.60%, co:0.30% -0.60%, and the balance of iron and unavoidable impurities.

2. The method for preparing hot work die steel SD400 according to claim 1, wherein: at least comprises the following steps:

step one, performing high-temperature calcination, upsetting forging and waste heat quenching on a consumable ingot to obtain a waste heat quenching forging;

step two, heating the waste heat quenching forging to 1000-1050 ℃, preserving heat for 4-6 hours, and cooling to 150-300 ℃ alternately by water cooling and air cooling to obtain an ultrafine forging;

and thirdly, heating the ultra-fine forging to 840-880 ℃, preserving heat for 15-20 h, cooling to 720-760 ℃ along with a furnace, preserving heat for 25-30 h, and cooling to below 300 ℃ to obtain the hot work die steel SD400.

3. The method for producing hot work die steel SD400 as claimed in claim 2, wherein: in the first step, the preparation method of the consumable ingot comprises the following steps:

step a, smelting raw material components by an electric furnace, LF refining and VD vacuum degassing smelting to obtain an electrode blank with phi 430 mm;

step b, electroslag remelting the electrode blank to obtain an electroslag ingot with phi 590 mm;

and c, remelting the electroslag ingot in a consumable way to obtain a consumable ingot with phi 660 mm.

4. A method for producing hot work die steel SD400 as claimed in claim 3, characterized in that: in the step a, the smelting temperature of the electric furnace is 1690-1710 ℃, and the smelting time is 1-1.5 h; and/or

In the step a, the LF refining temperature is 1580-1620 ℃, and the refining time is 1.5-2 h; and/or

In the step a, the vacuum degree of the VD vacuum degassing smelting is 30Pa-40Pa, the smelting time is 15min-20min, and the smelting tapping temperature is 1560-1580 ℃; and/or

In the step b, under the inert atmosphere, the electroslag remelting is carried out at a constant melting speed, and the melting speed is 6.5kg/min-7.5kg/min; and/or

In the step c, the consumable remelting is constant-melting-speed consumable remelting under the vacuum condition, the vacuum degree is 0.5Pa-0.7Pa, and the melting speed is 5.5kg/min-6.5kg/min.

5. The method for producing hot work die steel SD400 as claimed in claim 2, wherein: in the first step, the specific operation of high-temperature calcination is as follows: and (3) loading the consumable ingot into a high-temperature diffusion furnace, heating to 1230-1270 ℃ at a heating rate of 80-100 ℃ per hour, preserving heat for 40-45 h, cooling to 1180-1200 ℃, preserving heat for 2-4 h, and discharging and forging to obtain the consumable ingot in a high-temperature diffusion state.

6. The method for producing hot work die steel SD400 as claimed in claim 2, wherein: in the first step, the upsetting ratio of upsetting-drawing forging is 2-2.2; and/or

In the first step, the forging times are 2-3 times.

7. The method for producing hot work die steel SD400 as claimed in claim 2, wherein: in the first step, the specific steps of the waste heat quenching are as follows: and controlling the final forging temperature of the forging to be not lower than 850 ℃, adding the forging into water, and performing waste heat quenching to obtain a waste heat quenching state forging with the temperature of 350-450 ℃.

8. The method for producing hot work die steel SD400 as claimed in claim 2, wherein: in the second step, the temperature is raised to 1000-1050 ℃ at a rate of 80-100 ℃/h.

9. The method for producing hot work die steel SD400 as claimed in claim 2, wherein: in the second step, the water-air alternate cooling comprises at least two water cooling and two air cooling, wherein the time of the first water cooling is 14-18 min, the air cooling is carried out after the first water cooling is finished, the second water cooling is carried out when the internal temperature and the external temperature of the forge piece are consistent, the time of the second water cooling is 10-12 min, the air cooling is carried out after the second water cooling is finished, and the temperature of the die steel after the air cooling is controlled to be 150-300 ℃.

10. The method for producing hot work die steel SD400 as claimed in claim 2, wherein: in the third step, the temperature is raised to 840-880 ℃ at a speed of 80-100 ℃/h; and/or

In the third step, the cooling is to cool to below 300 ℃ at a speed of less than or equal to 30 ℃/h.