CN111485091A - Pre-hardening method for oversized plastic die steel - Google Patents
Pre-hardening method for oversized plastic die steel Download PDFInfo
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- CN111485091A CN111485091A CN202010297432.9A CN202010297432A CN111485091A CN 111485091 A CN111485091 A CN 111485091A CN 202010297432 A CN202010297432 A CN 202010297432A CN 111485091 A CN111485091 A CN 111485091A
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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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
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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
- 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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- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
-
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/28—Normalising
-
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
- C21D1/60—Aqueous agents
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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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
- C21D1/613—Gases; Liquefied or solidified normally gaseous material
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
Abstract
The invention discloses a method for pre-hardening oversized plastic die steel, which adopts a water-air alternative cooling process to replace the traditional water quenching oil cooling process and is matched with a special tempering process, so that the cracking tendency of a module can be reduced, and the hardness uniformity can be improved. The invention adopts the following specific process route: normalizing → annealing → keeping head and tail and coping surface defect → heating and quenching, alternately cooling by water and air → stepped primary tempering → flaw detection, sawing head and tail, hardness inspection → secondary tempering → final flaw detection and hardness flaw detection; compared with the prior art, the invention has the advantages that: (1) the head and the tail of the module belt are pre-hardened, so that the corner cracking risk is reduced; (2) multiple times of water and air cooling are adopted for cooling, the temperature return effect is achieved, the module plasticity is improved, and the corner cracking risk is reduced; (3) the temperature return range after cooling is controlled to be 230-260 ℃, and the risk of core transverse cracking is reduced; (4) the hardness uniformity of the module is improved through a step tempering process; the investment cost of heat treatment is reduced, and the environment-friendly level is improved.
Description
Technical Field
The invention belongs to the technical field of plastic die steel heat treatment, and particularly relates to a prehardening method of extra-large plastic die steel 718HH (a large module with the thickness of 800-1200 mm, the width of 1200-2000 mm and the length of more than 2500mm, hereinafter referred to as 718 HH).
Background
The 718HH large module is mainly applied to an automobile bumper mould, the Hardness (HRC) is 32-38, along with the development of the automobile industry, the requirement of users on the polishing performance of the mould is higher and higher, the hardness uniformity is one of main factors influencing the polishing performance, the attention of the users is gradually drawn, and the integral Hardness (HRC) difference of the large module is expected to be not more than 4. The components in percentage by mass (%) are: carbon: 0.24-0.30, silicon is not more than 0.20, manganese: 1.40-1.60, phosphorus is not more than 0.025, sulfur is not more than 0.010, chromium: 1.25 to 1.45, nickel: 0.80-1.20, molybdenum: 0.45-0.60, vanadium: 0.09-0.15, and the balance of iron and inevitable impurities.
At present, the pre-hardening process route for producing 718HH large modules in China mainly comprises ' normalizing, annealing, head and tail sawing, quenching (water quenching and oil cooling) ' -two-time one-stage tempering ', according to different specifications, water cooling is generally carried out for 30-50 min, oil cooling is carried out for 360-500 min, steel is cooled to 160 ℃ and then is charged and tempered, and the tempering temperature is 540-560 ℃. In order to ensure the uniformity of hardness, the cooling depth needs to be increased as much as possible to ensure the full quenching of the module. There are two cracking risks during quenching: longitudinal corner cracks and transverse core cracks. In order to prevent hardening cracks, the cooling strength is controlled, the martensite transformation amount of the core part of the module is less than that of the other positions, and then the core surface has larger hardness difference after one-stage temperature tempering.
Disclosure of Invention
The invention discloses a method for pre-hardening oversized plastic die steel, which adopts a water-air alternative cooling process to replace the traditional water quenching oil cooling process and is matched with a special tempering process, so that the cracking tendency of a module can be reduced, and the hardness uniformity can be improved.
In order to achieve the purpose, the invention adopts the following specific process:
⑴ process route, normalizing → annealing → keeping head and tail and coping surface defect → heating quenching (water and air alternate cooling) → stepped primary tempering → flaw detection, head and tail sawing, hardness inspection → secondary tempering → final flaw detection and hardness inspection;
⑵, after normalizing and annealing the module, cooling to room temperature, detecting flaws to ensure that the interior of the module is free of defects, inspecting the surface of the module, and if the defects such as folding and cracks exist, polishing the module, and keeping the head and the tail of the module;
⑶ loading the module into a furnace, heating and quenching, allowing the loading temperature to be no higher than 350 ℃, heating to 650 +/-10 ℃ at a heating rate of no more than 40 ℃/h, preserving heat for 10h, heating to 920 +/-10 ℃ at a heating rate of no more than 60 ℃/h, and preserving heat for 20-35 h;
⑷, after quenching, heating and heat preservation are finished, the steel is taken out of the furnace and air-cooled to the large surface core part at 700-750 ℃, water is rapidly added, according to the specification of the module, the steel is alternately cooled by adopting a cooling process of water cooling (110-130 min) → air cooling (60min) → water cooling (60 min-70 min) → air cooling (20min) → water cooling (15 min-25 min) → air cooling (returning to the maximum temperature of 230-260 ℃, cooling to 180-200 ℃ and charging and tempering), and the water temperature is required to be not higher than 35 ℃ in the cooling process;
⑸ the primary tempering process adopts step tempering, after quenching and cooling, furnace tempering is carried out, the materials are treated for 5 h-10 h at 250 ℃ +/-10 ℃, then the temperature is raised to 610 ℃ +/-10 ℃ at a speed of not more than 60 ℃/h, the temperature is kept for 10 h-18 h, the materials are slowly cooled to 500 ℃ +/-10 ℃ along with the furnace, the temperature is kept for 50 h-80 h, and the materials are slowly cooled to room temperature along with the furnace after the temperature is kept;
⑹ performing flaw detection confirmation after primary tempering and cooling to room temperature, cutting off the head and the tail of the module, performing hardness inspection, finally performing secondary tempering, heating to 480 +/-10 ℃ at a temperature of not more than 30 ℃/h, keeping the temperature for 35-60 h, and then slowly cooling to room temperature along with the furnace;
⑺ final flaw detection test and hardness test.
The invention has the following mechanism analysis and invention points:
the traditional pre-hardening principle of the water quenching and oil cooling process is that a module is converted into a quenched structure (generally martensite or bainite) from inside to outside through quenching and cooling, and then a certain constant temperature tempering below a critical point A1 is selected according to the hardness value required by a user to convert the module into a stable tempered structure. The key point of the process is to ensure that the type and the transformation amount of the core-surface structure of the module tend to be consistent, or the closer the core-surface structure is, the better the hardness uniformity after tempering is, so that the requirement on the cooling strength of the module is higher. However, during the cooling process, there are tissue stress and thermal stress, wherein the thermal stress variation law is as follows: the surface layer is pulled in the early cooling stage, the core is pressed, the surface layer is pressed in the later cooling stage, and the core is pulled; the change rule of the tissue stress is as follows: the surface layer is pressed at the early stage of cooling, the core is pulled, the surface layer is pulled at the later stage of cooling, and the core is pressed; when two kinds of stress action directions counteract each other when opposite, the mutual superpose of action direction when the same, when stress superpose surpassed the ultimate strength of steel, will cause the fracture, especially super large specification module, the heating quenching after the head and the tail saw cuts, the module edges and corners position easily forms stress concentration and causes the bight to indulge the fracture, and the oil cooling time is longer, and the cooling depth is darker, and the drawing thermal stress that the core cooling later stage formed is big more, causes the heart to transversely split the risk and is higher. If the cooling strength is reduced, the transformation of the surface structure of the heart is different, and the larger the difference is, the worse the uniformity of hardness is.
The invention adopts the module with head and tail quenching, reduces the edges and corners of the module which are easy to cause stress concentration, adopts multiple times of water and air alternate cooling, and the air cooling returns to the temperature to play a self-tempering role, thereby improving the plasticity of the module and reducing the risk of corner cracking. In addition, the surface temperature return temperature of the module is higher (230-260 ℃) in the later cooling stage of the process, the cooling strength is far lower than that of the traditional water quenching oil cooling process, the tensile thermal stress of the core of the later cooling stage is greatly reduced, the cross crack risk of the core is reduced, the quenching hardness difference of the surface of the module core is large due to the process, the hardness difference caused by stepped one-time tempering can be made up, namely, high-temperature tempering is adopted in a short time, the quenching tissue with a certain depth from the surface of the module is converted into a stable tempering tissue, the desired hardness range is obtained, the temperature is reduced to low-temperature tempering, the temperature is kept for a certain time, and the quenching hardness of the original core is basically kept not. The hardness of the near surface of the module in a certain depth range is reduced through high-temperature section tempering, the quenching hardness of the core part is reserved through low-temperature section tempering to reduce the hardness difference, and the hardness uniformity is increased.
Compared with the prior art, the invention has the advantages that:
the cracking tendency of the module can be reduced, the aim of improving the hardness uniformity is fulfilled, the investment cost of heat treatment can be reduced, and the environment-friendly level is improved;
⑴ the module belt is pre-hardened head and tail, so that the risk of corner cracking is reduced;
⑵, a multiple water and air alternate cooling process is adopted, and air cooling temperature return can play a self-tempering role, so that module plasticity is improved, and corner cracking risk is reduced;
⑶, controlling the temperature return range 230-260 ℃ after cooling, and reducing the risk of core transverse cracking;
⑷ through the step tempering process, the hardness uniformity of the module is improved.
Detailed Description
The details are described and illustrated below with reference to specific embodiments.
Example 1 and example 2
Producing steel grades: 718 HH;
execute
⑴ process route, normalizing → annealing → keeping head and tail and coping surface defect → heating quenching (water and air alternate cooling) → stepped primary tempering → flaw detection, head and tail sawing, hardness inspection → secondary tempering → final flaw detection and hardness inspection;
example 1
The production specification is as follows: 960x1310x3100 mm;
⑵ quenching and heating, charging at 200 deg.C, heating to 650 + -10 deg.C at 40 deg.C/h, maintaining for 10h, heating to 920 + -10 deg.C at 60 deg.C/h, and maintaining for 25 h;
⑶ quenching and cooling, after quenching and heating, cooling the module in air until the temperature of the large surface center is 720 ℃, cooling in water for 125min for the first time, cooling in air for 30min, cooling in water for 70min for the second time, cooling in air for 20min, cooling in water for 23min for the third time, cooling in air to return to the maximum temperature of the large surface center, 236 ℃, cooling to 190 ℃, and tempering, wherein the water temperature is not higher than 35 ℃ in the cooling process;
⑷ primary tempering, cooling the module to 190 deg.C, loading into furnace, tempering at 250 + -10 deg.C for 10h, heating to 610 + -10 deg.C at 60 deg.C/h, holding for 15h, slow cooling to 500 + -10 deg.C, holding for 60h, and slow cooling to room temperature.
⑸ secondary tempering, flaw detection after primary tempering, cutting off the head and tail of the module, hardness test, secondary tempering, heating to 480 +/-10 ℃ at 30 ℃/h, heat preservation for 40h, and furnace slow cooling to room temperature.
⑹ testing the hardness of two end faces by a portable hardness tester, wherein each end face respectively tests the four corner hardness, the four diagonal quarter hardness and the center hardness, the total hardness is 9 points, and the hardness results are shown in Table 1;
TABLE 1
The Hardness (HRC) range is 33.2-36.2, the Hardness (HRC) difference is 3, the Hardness (HRC) meeting the user requirement is not more than 4, and the flaw detection module does not crack.
Example 2
The production specification is as follows: 890x1600x2800 mm;
⑵ quenching and heating, charging at 250 deg.C, heating to 650 + -10 deg.C at 40 deg.C/h, maintaining for 10h, heating to 920 + -10 deg.C at 60 deg.C/h, and maintaining for 23 h;
⑶ quenching and cooling, after quenching and heating, cooling the module in air until the temperature of the large surface center is 730 ℃, cooling in water for the first time for 120min, cooling in air for 30min, cooling in water for the second time for 75min, cooling in air for 20min, cooling in water for the third time for 21min, cooling in air to return to the maximum temperature of the large surface center of 246 ℃ and cooling to 195 ℃ for charging and tempering, wherein the water temperature is not higher than 35 ℃ in the cooling process;
⑷ primary tempering, cooling the module to 195 deg.C, loading into furnace, tempering at 250 + -10 deg.C for 10h, heating to 610 + -10 deg.C at 60 deg.C/h, holding for 14h, slow cooling to 500 + -10 deg.C, holding for 55h, and slow cooling to room temperature.
⑸ secondary tempering, flaw detection after primary tempering, cutting off the head and tail of the module, hardness test, secondary tempering, heating to 480 +/-10 ℃ at a speed of 30 ℃/h, heat preservation for 35h, and furnace slow cooling to room temperature.
⑹, finally testing the hardness of two end faces by using a portable hardness tester, wherein each end face respectively tests the four corner hardness, the four diagonal quarter hardness and the center hardness, the total hardness is 9 points, and the hardness results are shown in Table 2;
TABLE 2
The Hardness (HRC) range is 34.6-37.6, the Hardness (HRC) difference is 3, the Hardness (HRC) meeting the user requirement is not more than 4, and the flaw detection module does not crack.
Claims (3)
1. The method for pre-hardening the oversized plastic die steel is characterized by comprising the following process routes: normalizing → annealing → keeping head and tail and coping surface defect → heating and quenching, alternately cooling by water and air → stepped primary tempering → flaw detection, sawing head and tail, hardness inspection → secondary tempering → final flaw detection inspection and hardness inspection;
after the module is normalized and annealed, cooling to room temperature, detecting a flaw to ensure that the interior of the module is free of defects, inspecting the surface of the module, and if the defects such as folding and cracks exist, polishing, wherein the head and the tail of the module are reserved;
the module is charged, heated and quenched, the charging temperature is allowed to be not higher than 350 ℃, the temperature is increased to 650 +/-10 ℃ at the temperature increasing speed of not more than 40 ℃/h, the temperature is maintained for 10h, the temperature is increased to 920 +/-10 ℃ at the temperature of not more than 60 ℃/h, and the temperature is maintained for 20-35 h;
alternately cooling with water and air, after quenching, heating and heat preservation are finished, discharging from the furnace, air cooling to 700-750 ℃ of the center of the large surface, and quickly introducing water, wherein water cooling is adopted according to the specification of the module
Alternately cooling by using a cooling process of air cooling (60min) → water cooling (60 min-70 min) → air cooling (20min) → water cooling (15 min-25 min) → air cooling (returning the temperature to the maximum temperature of 230 ℃ -260 ℃, cooling to 180 ℃ -200 ℃ and charging and tempering), wherein the water temperature is required to be not higher than 35 ℃ in the cooling process;
the step type primary tempering, after quenching and cooling, furnace tempering is carried out, materials are treated for 5-10 h at 250 +/-10 ℃, then the temperature is raised to 610 +/-10 ℃ at the speed of not more than 60 ℃/h, the temperature is kept for 10-18 h, the materials are slowly cooled to 500 +/-10 ℃ along with the furnace, the temperature is kept for 50-80 h, and the materials are slowly cooled to room temperature along with the furnace after the temperature is kept;
and the secondary tempering is carried out by heating to 480 +/-10 ℃ at a temperature of not more than 30 ℃/h, keeping the temperature for 35-60 h, and then slowly cooling to room temperature along with the furnace.
2. The method of pre-hardening an oversized plastic die steel as claimed in claim 1, wherein the plastic die steel is 718HH, production specification: 960x1310x3100 mm;
the quenching heating is carried out, the charging temperature is 200 ℃, the temperature is raised to 650 +/-10 ℃ at 40 ℃/h, the temperature is kept for 10h, the temperature is raised to 920 +/-10 ℃ at 60 ℃/h, and the temperature is kept for 25 h;
after the quenching cooling, quenching heating and discharging, the module is cooled in air to 720 ℃ of the large surface center for primary water cooling for 125min, air cooling for 30min, secondary water cooling for 70min, air cooling for 20min, tertiary water cooling for 23min, air cooling for returning to the maximum temperature of the large surface center of 236 ℃ and cooling to 190 ℃ for charging and tempering; the water temperature is not higher than 35 ℃ in the cooling process;
performing primary tempering, cooling the module to 190 ℃ in the core of the large surface, then loading the module into a furnace for tempering, waiting for 10 hours at 250 +/-10 ℃, then heating to 610 +/-10 ℃ at 60 ℃/h, keeping the temperature for 15 hours, slowly cooling to 500 +/-10 ℃ along with the furnace, keeping the temperature for 60 hours, and slowly cooling to room temperature along with the furnace after the heat preservation is finished;
and (3) performing secondary tempering, detecting flaws after primary tempering is finished, cutting off the head and the tail of the module, performing hardness test, performing secondary tempering, heating to 480 +/-10 ℃ at a speed of 30 ℃/h, keeping the temperature for 40h, and then slowly cooling to room temperature along with the furnace.
3. The method of pre-hardening an oversized plastic die steel as claimed in claim 1, wherein the plastic die steel is 718HH, production specification: 890x1600x2800 mm;
the quenching heating is carried out, the charging temperature is 250 ℃, the temperature is raised to 650 +/-10 ℃ at 40 ℃/h, the temperature is kept for 10h, the temperature is raised to 920 +/-10 ℃ at 60 ℃/h, and the temperature is kept for 23 h;
after the quenching cooling, quenching heating and discharging, the module is cooled in air to 730 ℃ of the large surface center part, the first water inlet cooling is carried out for 120min, the air cooling is carried out for 30min, the second water inlet cooling is carried out for 75min, the air cooling is carried out for 20min, the third water inlet cooling is carried out for 21min, the air cooling is carried out for returning the temperature to 246 ℃ of the maximum temperature of the large surface center part, and the temperature is reduced to 195 ℃ for charging and tempering; the water temperature is not higher than 35 ℃ in the cooling process;
performing primary tempering, namely cooling the module to 195 ℃ of the large-surface core, then loading the module into a furnace for tempering, waiting for 10 hours at 250 +/-10 ℃, then heating to 610 +/-10 ℃ at the speed of 60 ℃/h, keeping the temperature for 14 hours, slowly cooling to 500 +/-10 ℃ along with the furnace, keeping the temperature for 55 hours, and slowly cooling to room temperature along with the furnace after the heat preservation is finished;
and (3) performing secondary tempering, detecting flaws after primary tempering is finished, cutting off the head and the tail of the module, performing hardness test, performing secondary tempering, heating to 480 +/-10 ℃ at a speed of 30 ℃/h, keeping the temperature for 35h, and then slowly cooling to room temperature along with the furnace.
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| CN114107624A (en) * | 2020-08-26 | 2022-03-01 | 中国科学院金属研究所 | Heat treatment method for thick and large-section 718H pre-hardened plastic die steel |
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