CN114737035A - Method for improving hardness uniformity of hot work die steel 56NiCrMoV7 - Google Patents
Method for improving hardness uniformity of hot work die steel 56NiCrMoV7 Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C21—METALLURGY OF IRON
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- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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Abstract
The invention relates to a method for improving the hardness uniformity of 56NiCrMoV7 hot work die steel, which consists of the following elements in percentage by mass: c: 0.52-0.55%, Si: 0.20-0.30%, Mn: 0.80-0.90%, Ni: 1.70-1.80%, Cr: 1.10-1.20%, Mo: 0.45-0.50%, V: 0.08-0.10%, B: 0.0008 to 0.0012 percent, less than or equal to 0.025 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and inevitable impurities; the heat treatment method of the die steel comprises the following steps: (1) quenching: air cooling the forged module to 350 ℃ of 300-; (2) tempering: putting the quenched module into a 300-350 ℃ furnace again, heating to 570 +/-10 ℃ at the speed of less than or equal to 60 ℃/h, preserving heat for 10-12h, heating to 610 +/-10 ℃, preserving heat for 8-10h, and cooling in the furnace; the invention solves the problems of uneven surface hardness, large difference, same-heat material hardness difference and the like of the large-scale module core of the hot work die steel 56NiCrMoV7, and avoids the quenching cracks of the module.
Description
Technical Field
The invention relates to the technical field of hot work die steel material manufacturing, in particular to a method for improving the hardness uniformity of 56NiCrMoV7 hot work die steel.
Background
1.2714 die steel (corresponding to national standard 56NiCrMoV7 die steel) has good quenching performance, toughness, polishing and heat resistance, and is often used for manufacturing various hot-work dies (large-scale pressing dies, extrusion tools and hot-forging dies). The molten steel for manufacturing the steel is generally smelted by an electric arc furnace and refined outside the furnace, and the process flow is as follows: at present, most users require that the steel is subjected to tempering, factory shipment and direct mold opening for use, the core hardness is not less than 38HRC, the surface hardness is not less than 40HRC, the hardness difference between any two points on the surface is not less than 2HRC, and any 2 pieces on the same furnace number also meet the requirements. The material thickness is mostly above 300 mm.
In the actual production process, the hardness of the material often cannot meet the requirement due to the following reasons: (1) carbon collection at a riser end of a steel ingot, carbon negative at a nozzle end and molten steel uniformity problems cause deviation of chemical components of the molten steel; (2) the temperature control precision and the loading capacity of the heat treatment furnace are large, so that the uniformity of the furnace temperature is poor, and the steel temperature is not uniform; (3) the quenching tank is small, the water temperature rises quickly under the continuous quenching condition, and the water circulation condition is poor, so that the cooling of the module is uneven.
If the hardness of the core part and the surface of the module are low, and the difference of the surface hardness is large, or the difference of the hardness of the same-heat material is large, and the hardness difference of the 56NiCrMoV7 mould steel mould is generally large, the randomness of the mould opening direction often causes the hardness difference of each point of the mould cavity to be large, or the hardness difference of the same-batch mould to be large, so that the product is damaged or the mould is scrapped early, which is unacceptable by users, and the problems are solved before the material manufacturing unit leaves a factory.
Disclosure of Invention
The invention aims to provide a method for improving the hardness uniformity of 56NiCrMoV7 of hot work die steel, and aims to solve the problems of uneven surface hardness, large difference and same-furnace material hardness difference of 56NiCrMoV7 die steel large-scale die core by adopting microalloying, improving the hardenability of the steel, narrowing chemical components, improving the tempering stability of the steel, carrying out water quenching and air cooling, carrying out self-tempering by multiple water lifting and air cooling, and the like, and simultaneously avoid quenching cracks of the die.
The invention relates to a method for improving the hardness uniformity of 56NiCrMoV7 hot work die steel, which comprises the following elements in percentage by mass: c: 0.52-0.55%, Si: 0.20-0.30%, Mn: 0.80-0.90%, Ni: 1.70-1.80%, Cr: 1.10-1.20%, Mo: 0.45-0.50%, V: 0.08-0.10%, B: 0.0008 to 0.0012 percent, less than or equal to 0.025 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and inevitable impurities;
the heat treatment method of the die steel comprises the following steps:
(1) quenching: air-cooling the forged 1.2714 module to 300-350 ℃, placing the module into a heat treatment furnace, heating to 870 +/-10 ℃ at a heating rate of less than or equal to 100 ℃/h, preserving heat for 10-12h to ensure that the module is uniform in temperature, and then quickly quenching in water;
(2) tempering: and (2) putting the module quenched in the step (1) into a 300-350 ℃ furnace again, heating to 570 +/-10 ℃ at a heating rate of less than or equal to 60 ℃/h, preserving heat for 10-12h, heating to 610 +/-10 ℃, preserving heat for 8-10h, cooling the furnace to below 250 ℃, and discharging.
Preferably, the electric furnace is adopted for heating and heat preservation in the step (1) so as to ensure that the modules can be uniformly heated and uniformly heat preserved, and the temperatures of all points of the modules and adjacent modules are consistent.
Preferably, the self-tempering mode is carried out in the step (1) by water quenching air cooling and multiple water lifting air cooling, namely, the high-temperature module is quickly put into water, water is discharged after 40-55 minutes, and air cooling is carried out for 3 minutes, and the temperature is raised to 350 ℃; adding water again, discharging water after 15-20 minutes, air cooling for 2 minutes, and returning to the temperature of 300 ℃; and repeating the operations of water inlet and water outlet until the surface temperature of the module is less than or equal to 250 ℃.
Preferably, in the step (1), the air is started to stir for 35-60 minutes when the module is put into water for the first time, and then the module is kept still and cooled, so that the nonuniform heating of the module is avoided.
Preferably, the temperature of water in the quenching bath in the step (1) is controlled to be 25-40 ℃.
Preferably, in the step (2), the tempering adopts a complete tempering process, the furnace is cross-charged, the material distribution is uniform, the nozzle end is placed inwards, and the hardness difference caused by nozzle negative carbon is reduced.
The technological principle of the heat treatment of the die steel is as follows:
(1) the micro-alloying is carried out by adding the trace element B, so that the hardenability of the steel can be improved, the thick and large modules of the 56NiCrMoV7 die steel can be fully quenched, and the hardness of the center reaches more than 39 HRC;
(2) the water quenching air cooling mode is adopted, water lifting and air cooling are carried out for multiple times for self tempering, the surface structure transformation stress can be eliminated, the full quenching of the large module is ensured, and the water quenching cracking is avoided;
(3) the chemical components are controlled in a narrow band mode, the chemical component interval is shortened, and the influence of the chemical components on the tempering stability can be reduced;
(4) the electric furnace is adopted for heat treatment, reasonable furnace charging and water cooling, so that the module is uniformly heated, uniformly insulated and uniformly cooled, and further uniform hardness is achieved.
The invention has the beneficial effects that: according to the method, the steel is subjected to microalloying, and 0.0008-0.0012% of element B is added into a 56NiCrMoV7 die steel component system, so that the hardenability of the steel is improved (the hardenability can be improved by 5 times); the chemical components are narrowed, the chemical component interval is narrowed, and the influence of the chemical components on the tempering stability is reduced; water quenching air cooling and multiple water lifting air cooling self-tempering are adopted, the surface structure transformation stress is eliminated, and the water quenching cracking of the module is avoided; by comprehensively adopting the measures, the problems of uniform surface hardness, large difference and poor hardness of the same-furnace material of the 56NiCrMoV7 die steel large-scale die block can be solved.
Detailed Description
In order to better explain the technical solution of the present invention, the technical solution of the present invention is further described below with reference to specific examples, which are only exemplary to illustrate the technical solution of the present invention and do not limit the present invention in any way.
Table 1 below is a table listing the chemical composition (wt%) values of the die steels according to various embodiments of the present invention;
table 2 below is a table of the test results of the core hardness and the surface hardness of the die according to the embodiments of the present invention.
The invention relates to a method for improving the hardness uniformity of 56NiCrMoV7 hot work die steel, which comprises the following elements in percentage by mass: c: 0.52-0.55%, Si: 0.20-0.30%, Mn: 0.80-0.90%, Ni: 1.70-1.80%, Cr: 1.10-1.20%, Mo: 0.45-0.50%, V: 0.08-0.10%, B: 0.0008 to 0.0012 percent, less than or equal to 0.025 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and inevitable impurities.
Table 1 value list of chemical components (wt%) of the ultra high strength steel according to each embodiment of the present invention:
example 1
The specification of the production module of the embodiment is as follows: thickness 520 × width 880 × length 3800mm, weight: 13.5t, material quality: 1.2714, the chemical composition after smelting is shown in Table 1 above.
The die block of the die steel of the embodiment after smelting and forging is subjected to heat treatment according to the following steps:
(1) quenching: air cooling the forged module to 300 ℃, placing the forged module into a heat treatment furnace, heating up to 880 ℃ at a speed of 60 ℃/h, preserving heat for 12h, then rapidly adding water, adopting water quenching, and carrying out water lifting and air cooling for 4 times, wherein the concrete steps are as follows: quickly introducing water after the module heat preservation time is up, discharging water after 58 minutes, and performing air cooling for 3 minutes until the temperature returns to 350 ℃; feeding water for the second time, discharging water after 22 minutes, and air cooling for 2 minutes, wherein the temperature is increased to 300 ℃; water is fed for the third time, water is discharged in 10 minutes, air cooling is carried out for 2 minutes, and the temperature is increased to 260 ℃; fourth water inlet, water outlet in 8 minutes, air cooling for 2 minutes, temperature returning to 230 ℃, and total water cooling time of 98 minutes; keeping the water temperature at 25-40 ℃ in the water quenching process, and starting air to stir for 58 minutes after the module is filled with water for the first time; the heat treatment furnace adopts an electric furnace;
(2) tempering: putting the module quenched in the step (1) into a 300 ℃ furnace again, heating to 580 ℃ at a speed of 60 ℃/h, preserving heat for 12h, heating to 610 ℃ again, preserving heat for 10h, cooling the furnace to below 250 ℃, and discharging; the modules are alternately arranged in the furnace, the distribution is uniform, and the water gap end faces inwards.
Example 2
The specification of the production module of the embodiment is as follows: thickness 455 × width 1000 × length 3820mm, weight: 13.6t, material quality: 1.2714, the chemical composition after smelting is shown in Table 1 above.
The die block of the die steel of the embodiment after smelting and forging is subjected to heat treatment according to the following steps:
(1) quenching: air cooling the forged module to 320 ℃, placing the forged module into a heat treatment furnace, heating to 870 ℃ at a speed of 70 ℃/h, preserving heat for 11h, then quickly adding water, adopting water quenching, and carrying out water lifting and air cooling for 4 times, wherein the concrete steps are as follows: quickly introducing water after the module is subjected to heat preservation for 55 minutes, discharging water, and performing air cooling for 3 minutes until the temperature returns to 350 ℃; feeding water for the second time, discharging water after 20 minutes, and air cooling for 2 minutes, wherein the temperature is increased to 300 ℃; water is added for the third time, water is discharged after 10 minutes, and the water is cooled in air for 2 minutes and then is warmed up to 260 ℃; fourth water inlet, water outlet in 8 minutes, air cooling for 2 minutes, temperature returning to 230 ℃, and total water cooling time of 93 minutes; in the water quenching process, the water temperature is kept at 25-40 ℃, and air is started to stir for 55 minutes after the module enters water for the first time; the heat treatment furnace adopts an electric furnace;
(2) tempering: putting the module quenched in the step (1) into a 330 ℃ furnace again, heating to 570 ℃ at a speed of 50 ℃/h, preserving heat for 11h, heating to 620 ℃ again, preserving heat for 9h, cooling the furnace to below 250 ℃, and discharging; the modules are alternately arranged in the furnace, the distribution is uniform, and the water gap end faces inwards.
Example 3
This embodiment uses the production module specification: 355 thickness 1000 width 3600mm length, weight: 9.96t, material quality: 1.2714, the chemical composition after smelting is shown in Table 1 above.
The die block of the die steel of the embodiment after smelting and forging is subjected to heat treatment according to the following steps:
(1) quenching: air cooling the forged module to 350 ℃, placing the forged module into a heat treatment furnace, heating to 860 ℃ at the speed of 60 ℃/h, preserving heat for 10h, then quickly adding water, adopting water quenching, and carrying out water lifting and air cooling for 4 times, wherein the concrete steps are as follows: quickly introducing water after the module heat preservation time is up, discharging water after 45 minutes, and performing air cooling for 3 minutes until the temperature returns to 350 ℃; water is fed for the second time, water is discharged after 15 minutes, and air cooling is carried out for 2 minutes until the temperature returns to 300 ℃; water is fed for the third time, water is discharged in 10 minutes, air cooling is carried out for 2 minutes, and the temperature is increased to 260 ℃; fourth water inlet, water outlet in 8 minutes, air cooling for 2 minutes, temperature returning to 230 ℃, and total water cooling time of 78 minutes; keeping the water temperature at 25-40 ℃ in the water quenching process, and starting air to stir for 45 minutes after the module is filled with water for the first time; the heat treatment furnace adopts an electric furnace;
(2) tempering: putting the module quenched in the step (1) into a 350 ℃ furnace again, heating to 560 ℃ at a speed of 60 ℃/h, preserving heat for 10h, heating to 600 ℃, preserving heat for 8h, cooling the furnace to below 250 ℃, and discharging; the modules are alternately arranged in the furnace, the distribution is uniform, and the water gap end faces inwards.
Example 4
The specification of the production module of the embodiment is as follows: thickness 300 × width 1000 × length 3600mm, weight: 8.5t, material quality: 1.2714, the chemical composition after smelting is shown in Table 1 above.
The die block of the die steel of the embodiment after smelting and forging is subjected to heat treatment according to the following steps:
(1) quenching: air cooling the forged module to 300 ℃, placing the forged module into a heat treatment furnace, heating up to 880 ℃ at a speed of 60 ℃/h, preserving heat for 10h, then quickly adding water, adopting water quenching, and carrying out water lifting and air cooling for 4 times, wherein the method specifically comprises the following steps: quickly introducing water after the module is subjected to heat preservation for 42 minutes, discharging water, and performing air cooling for 3 minutes to ensure that the temperature returns to 350 ℃; feeding water for the second time, discharging water after 15 minutes, and air cooling for 2 minutes, wherein the temperature is increased to 300 ℃; water is fed for the third time, water is discharged in 10 minutes, air cooling is carried out for 2 minutes, and the temperature is increased to 260 ℃; fourth water inlet, water outlet in 8 minutes, air cooling for 2 minutes, temperature returning to 230 ℃, and total water cooling time of 75 minutes; in the water quenching process, the water temperature is kept at 20-40 ℃, and air is started to stir for 42 minutes after the module enters water for the first time; the heat treatment furnace is an electric furnace.
(2) Tempering: putting the module quenched in the step (1) into a 300 ℃ furnace again, heating to 580 ℃ at a speed of 60 ℃/h, preserving heat for 10h, heating to 610 ℃ again, preserving heat for 8h, cooling the furnace to below 250 ℃, and discharging; the modules are alternately arranged in the furnace, the distribution is uniform, and the water gap end faces inwards.
Comparative example 1:
production module specification: thickness 510 × width 1000 × length 3600mm, weight: 14.3t, material quality: 1.2714, the chemical composition after smelting is shown in Table 1 above. The module after smelting and forging is subjected to heat treatment according to the following steps:
(1) quenching: and air-cooling the forged module to 300 ℃, putting the forged module into a heat treatment furnace, heating to 880 ℃ at a speed of 60 ℃/h, preserving heat for 12h, then quickly adding water, cooling the discharged water after 60 minutes, and adding the water into the furnace again until the surface temperature is 300 ℃. The water temperature is kept between 25 and 40 ℃ in the water quenching process.
(2) Tempering: and (2) putting the module quenched in the step (1) into a 300 ℃ furnace again, heating to 610 ℃ at a speed of 60 ℃/h, preserving heat for 16h, cooling the furnace to below 250 ℃, and discharging.
Comparative example 2:
production module specification: thickness 320 × width 820 × length 3800mm, weight: 7.8t, material quality: 1.2714, the chemical composition after smelting is shown in Table 1 above. The module after smelting and forging is subjected to heat treatment according to the following steps:
(1) quenching: and air-cooling the forged module to 300 ℃, putting the forged module into a heat treatment furnace, heating to 880 ℃ at a speed of 60 ℃/h, preserving heat for 10h, then quickly adding water, cooling the discharged water after 40 minutes, and adding the cooled water into the furnace again until the surface temperature is 300 ℃. The water temperature is kept between 25 and 40 ℃ in the water quenching process.
(2) Tempering: and (2) putting the module quenched in the step (1) into a 300 ℃ furnace again, heating to 610 ℃ at a speed of 60 ℃/h, preserving heat for 12h, cooling the furnace to below 250 ℃, and discharging.
TABLE 2 tabulation of test results of core hardness and surface hardness of die steel of each embodiment of the present invention
As can be seen from the above table, the die steel produced by the method of the present invention, which uses the composition control and heat treatment method, has the following size specifications: the difference between the central hardness and the surface hardness is less than or equal to 2, and the difference between the surface height and the surface height is less than or equal to 1, while the difference between the large-size surface and the central hardness of the die steel produced by the conventional method is more than or equal to 3.
Claims (6)
1. The method for improving the hardness uniformity of the hot-work die steel 56NiCrMoV7 is characterized in that the die steel consists of the following elements in percentage by mass: c: 0.52-0.55%, Si: 0.20-0.30%, Mn: 0.80-0.90%, Ni: 1.70-1.80%, Cr: 1.10-1.20%, Mo: 0.45-0.50%, V: 0.08-0.10%, B: 0.0008 to 0.0012 percent, less than or equal to 0.025 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and inevitable impurities;
the heat treatment method of the die steel comprises the following steps:
(1) quenching: air-cooling the forged 1.2714 module to 300-350 ℃, placing the module into a heat treatment furnace, heating to 870 +/-10 ℃ at a heating rate of less than or equal to 100 ℃/h, preserving heat for 10-12h to ensure that the module is uniform in temperature, and then quickly quenching in water;
(2) tempering: and (2) putting the module quenched in the step (1) into a 300-350 ℃ furnace again, heating to 570 +/-10 ℃ at a heating rate of less than or equal to 60 ℃/h, preserving heat for 10-12h, heating to 610 +/-10 ℃, preserving heat for 8-10h, cooling the furnace to below 250 ℃, and discharging.
2. The method for improving the uniformity of hardness of 56NiCrMoV7 of hot work die steel according to claim 1, wherein: in the step (1), electric furnaces are adopted for heating and heat preservation, so that the modules can be uniformly heated and uniformly heat-preserved, and the temperatures of all points of the modules and adjacent modules are consistent.
3. The method for improving the uniformity of hardness of 56NiCrMoV7 of hot work die steel according to claim 1, wherein: in the step (1), water quenching air cooling and multiple water lifting air cooling are adopted for carrying out self-tempering, namely, the high-temperature module is quickly filled with water, water is discharged after 35-60 minutes, air cooling is carried out for 3 minutes, and the temperature returns to 350 ℃; adding water again, discharging water after 15-20 minutes, air cooling for 2 minutes, and returning to the temperature of 300 ℃; and repeating the operations of water inlet and water outlet until the surface temperature of the module is less than or equal to 250 ℃.
4. The method for improving the hardness uniformity of the hot work die steel 56NiCrMoV7 according to claim 1, wherein the method comprises the following steps: and (2) starting air to stir for 35-60 minutes when the module in the step (1) is put into water for the first time, and then standing and cooling to avoid uneven heating of the module.
5. The method for improving the uniformity of hardness of 56NiCrMoV7 of hot work die steel according to claim 1, wherein: and (2) controlling the water temperature in the quenching bath in the step (1) to be 25-40 ℃.
6. The method for improving the uniformity of hardness of 56NiCrMoV7 of hot work die steel according to claim 1, wherein: and (3) in the step (2), the tempering adopts a complete tempering process, the furnace is alternately charged, the material distribution is uniform, the water gap end is inwards placed, and the hardness difference caused by the negative carbon of the water gap is reduced.
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