CN111139348A - Heat treatment method for improving impact toughness of large-section low-alloy high-strength steel forging core - Google Patents
Heat treatment method for improving impact toughness of large-section low-alloy high-strength steel forging core Download PDFInfo
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- CN111139348A CN111139348A CN201911287666.9A CN201911287666A CN111139348A CN 111139348 A CN111139348 A CN 111139348A CN 201911287666 A CN201911287666 A CN 201911287666A CN 111139348 A CN111139348 A CN 111139348A
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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
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
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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
- C21D1/28—Normalising
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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
- C21D6/00—Heat treatment of ferrous alloys
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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
- C21D2211/00—Microstructure comprising significant phases
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
-
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
Abstract
The invention discloses a heat treatment method for improving impact toughness of a large-section low-alloy high-strength steel forging core, which comprises the following steps: high-temperature positive tempering → low-temperature quenching and tempering pretreatment → high-temperature quenching + sub-temperature quenching + high-temperature tempering. The method breaks through the traditional heat treatment method for realizing the core performance by hardenability, researches the characteristics of structure transformation and the relation between the structure and the performance, and achieves the purpose of improving the performance by realizing a specific metallographic structure. The advantages are that: the addition amount of alloy components is not required to be increased, so that the production cost is reduced; the requirement on production equipment is low, and equipment investment is reduced.
Description
Technical Field
The invention belongs to the technical field of alloy manufacturing, and particularly relates to a heat treatment method for improving the impact toughness of a large-section low-alloy high-strength steel forging core.
Background
The low-alloy high-strength steel forging after quenching and tempering has the processing properties of higher strength, good plasticity and toughness, lower brittle transition temperature, good thermal stability, weldability and the like, and is widely applied to the fields of petrochemical industry, energy equipment and the like. However, for some parts with large section and high performance requirement, the performance requirement can be generally achieved only near the surface layer due to the limit of hardenability, and the core performance, especially the impact toughness, is greatly different. And because of the requirement of weldability, the carbon equivalent of the material is strictly limited, and the hardenability cannot be improved by increasing the alloy components, so how to improve the impact toughness of the core part of the large forging is an important research subject for the development of the large-section forging of the low-alloy high-strength steel.
The S500Q steel is the steel type, the cake forging with the diameter more than 1m and the thickness more than 350mm is made from the steel type, the sampling position is 180mm away from the outer diameter and the thickness center (drawing can be carried out), the hardenability depth range of the steel type is completely exceeded, the impact energy of the sampling position is less than or equal to 40J on average by the conventional quenching and tempering process, and 47J which can not meet the standard requirement can not be met.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: provides a heat treatment method for improving the impact toughness of the core of a large-section low-alloy high-strength steel forging.
In order to solve the technical problems, the technical scheme provided by the invention is as follows: a heat treatment method for improving the impact toughness of a large-section low-alloy high-strength steel forging core comprises the following steps: high-temperature positive tempering → low-temperature quenching and tempering pretreatment → high-temperature quenching + sub-temperature quenching + high-temperature tempering.
The high-temperature positive tempering comprises the following temperature conditions: normalizing at 930-950 ℃ and tempering at 650-680 ℃.
The low-temperature tempering pretreatment comprises the following temperature conditions: quenching at 800-840 ℃ and tempering at 650-680 ℃.
The high-temperature quenching, the sub-temperature quenching and the high-temperature tempering have the following temperature conditions: quenching at 930-950 ℃, immediately heating to 10-20 ℃ below AC3 for quenching, and tempering at 600-650 ℃.
The heat treatment method for improving the impact toughness of the large-section low-alloy high-strength steel forging core comprises the following specific preparation steps:
1) high-temperature positive tempering: after forging, the whole is air-cooled to below 250 ℃, normalized at 930-950 ℃ and tempered at 650-680 ℃;
calculating the phase change point according to the components, and determining that the material of the low-alloy high-strength steel can keep stable and fine grains at 930-950 ℃ through a grain size growth test of a small sample;
the grain size growth test of the small sample comprises the following steps: taking a dried metallographic specimen, keeping the temperature at 880 ℃, 930 ℃, 950 ℃ and 980 ℃ for more than 8 hours, keeping the temperature, quenching and detecting the grain size.
2) Low-temperature tempering pretreatment: quenching at 800-840 ℃, tempering at 650-680 ℃, carrying out low-temperature tempering pretreatment, and further refining grains to obtain a tempered sorbite prepared structure;
3) high-temperature quenching, sub-temperature quenching and high-temperature tempering: and (3) quenching at 930-950 ℃, immediately heating to 10-20 ℃ below AC3 (the final temperature of all free ferrite transformed into austenite during heating), quenching at 600-650 ℃, and performing high-temperature quenching, sub-temperature quenching and high-temperature tempering to obtain a tempered sorbite and undissolved ferrite mixed structure with a dislocation structure.
Has the advantages that:
1) high-temperature positive tempering: the normalizing temperature of the general material is 50-60 ℃ above AC 3; according to the technical scheme, the method has the advantages that the 930-950 ℃ normalizing is adopted, and then the 650-680 ℃ tempering is carried out, so that the related defects of segregation, coarse crystals and the like caused by forging are eliminated, elements and carbon and nitrogen compounds for refining the grains are fully dissolved and uniformly distributed, and a foundation is laid for later performance heat treatment;
2) low-temperature tempering pretreatment: quenching at 800-840 ℃ (the temperature near AC 3), tempering at 650-680 ℃, incomplete austenitizing to refine the intra-grain substructure, taking the tempered sorbite as a preparation structure, increasing the nucleation probability when re-austenitizing, and simultaneously better playing the role of crystal boundary pinning of compounds such as AlN and the like; the grain size after pretreatment is one grade finer than that in a positive tempering state;
3) high-temperature quenching, sub-temperature quenching and high-temperature tempering: the highest temperature which is confirmed by a grain size growth test and can keep fine grains is adopted for carrying out primary quenching, the quenching is carried out to a lower temperature, the temperature is quickly raised to the AC3 critical temperature, the temperature is kept for a certain time according to the size of the section, secondary quenching is carried out, and then high-temperature tempering is carried out. The obtained final structure is tempered sorbite and ferrite which retain martensite and bainite dislocation structures after high-temperature quenching, higher strength can be obtained due to the retention of dislocation, and meanwhile, the impact toughness is improved due to the uniformly distributed undissolved ferrite.
The technical scheme disclosed by the application breaks through the traditional heat treatment method for realizing the performance of the core part by hardenability, researches the characteristics of structure transformation and the relation between the structure and the performance, and achieves the purpose of improving the performance by realizing a specific metallographic structure. The advantages are that: the addition amount of alloy components is not required to be increased, so that the production cost is reduced; the requirement on production equipment is low, and equipment investment is reduced.
Detailed Description
The process of the present invention is further illustrated below with reference to examples, but the invention is not limited thereto.
The heat treatment method for improving the impact toughness of the large-section low-alloy high-strength steel forging core comprises the following specific preparation steps:
1) high-temperature positive tempering: S500Q low-alloy high-strength steel is forged, the whole is air-cooled to below 250 ℃, normalized at 930-950 ℃, tempered at 650-680 ℃, and the treatment is finished, wherein the grain size is superior to grade 6 according to a steel grain size determination method specified in GB/T6394-2017;
calculating the phase change point according to the components (calculated by using JmatPro software), and confirming that the material of the low-alloy high-strength steel can keep stable and fine grains at 930-950 ℃ through a grain size growth test of a small sample;
the grain size growth test of the small sample comprises the following steps: taking a dried metallographic specimen, keeping the temperature at 880 ℃, 930 ℃, 950 ℃ and 980 ℃ for more than 8 hours, keeping the temperature, quenching and detecting the grain size.
2) Low-temperature tempering pretreatment: quenching at 800-840 ℃, tempering at 650-680 ℃, carrying out low-temperature tempering pretreatment, and further refining grains to obtain a tempered sorbite prepared structure;
3) high-temperature quenching, sub-temperature quenching and high-temperature tempering: and (3) quenching at 930-950 ℃, immediately heating to 10-20 ℃ below AC3 for quenching, tempering at 600-650 ℃, and performing high-temperature quenching, sub-temperature quenching and high-temperature tempering to obtain a tempered sorbite and undissolved ferrite mixed structure with a dislocation structure.
The heat treatment contrast verification data for improving the impact toughness of the S500Q low-alloy high-strength steel forging is as follows:
Claims (7)
1. a heat treatment method for improving the impact toughness of a large-section low-alloy high-strength steel forging core comprises the following steps: high-temperature positive tempering → low-temperature quenching and tempering pretreatment → high-temperature quenching + sub-temperature quenching + high-temperature tempering.
2. The heat treatment method for improving the impact toughness of the core of the large-section low-alloy high-strength steel forging according to claim 1, characterized by comprising the following steps: the high-temperature positive tempering comprises the following temperature conditions: normalizing at 930-950 ℃ and tempering at 650-680 ℃.
3. The heat treatment method for improving the impact toughness of the core of the large-section low-alloy high-strength steel forging according to claim 1, characterized by comprising the following steps: the low-temperature tempering pretreatment comprises the following temperature conditions: quenching at 800-840 ℃ and tempering at 650-680 ℃.
4. The heat treatment method for improving the impact toughness of the core of the large-section low-alloy high-strength steel forging according to claim 1, characterized by comprising the following steps: the high-temperature quenching, the sub-temperature quenching and the high-temperature tempering have the following temperature conditions: quenching at 930-950 ℃, immediately heating to 10-20 ℃ below AC3 for quenching, and tempering at 600-650 ℃.
5. The heat treatment method for improving the impact toughness of the core of the large-section low-alloy high-strength steel forging according to any one of claims 1 to 4, wherein the heat treatment method comprises the following steps: the heat treatment method for improving the impact toughness of the large-section low-alloy high-strength steel forging core comprises the following specific steps:
1) high-temperature positive tempering: after forging, the whole body is air-cooled to below 250 ℃, normalized at 930-950 ℃ and tempered at 650-680 ℃;
2) low-temperature tempering pretreatment: quenching at 800-840 ℃, and tempering at 650-680 ℃;
3) high-temperature quenching, sub-temperature quenching and high-temperature tempering: quenching at 930-950 ℃, immediately heating to 10-20 ℃ below AC3 for quenching, and tempering at 600-650 ℃.
6. The heat treatment method for improving the impact toughness of the core of the large-section low-alloy high-strength steel forging according to claim 5, characterized by comprising the following steps: the high-temperature positive tempering is carried out in the step 1), the normalizing temperature is 930-950 ℃, and the high-temperature positive tempering is obtained through a grain size growth test of a small sample.
7. The heat treatment method for improving the impact toughness of the core of the large-section low-alloy high-strength steel forging according to claim 1, characterized by comprising the following steps: the grain size growth test of the small sample comprises the following steps: taking a dried metallographic specimen, keeping the temperature at 880 ℃, 930 ℃, 950 ℃ and 980 ℃ for more than 8 hours, keeping the temperature, quenching and detecting the grain size.
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| CN111778381A (en) * | 2020-07-01 | 2020-10-16 | 锦州捷通铁路机械股份有限公司 | Heat treatment method for improving plasticity and low-temperature impact toughness of C-grade steel |
| CN112756525A (en) * | 2020-12-09 | 2021-05-07 | 上海电气上重铸锻有限公司 | Manufacturing method of 9% Ni steel oversized cake-shaped forging for ultralow temperature engineering |
| CN114262802A (en) * | 2022-01-04 | 2022-04-01 | 张家港广大特材股份有限公司 | Manufacturing method of high-strength flywheel energy storage rotor |
| CN114317893A (en) * | 2021-12-29 | 2022-04-12 | 张家港广大特材股份有限公司 | Manufacturing method of magnetic yoke ring forging |
| CN114622073A (en) * | 2022-03-09 | 2022-06-14 | 包头钢铁（集团）有限责任公司 | Method for improving low-temperature impact toughness of boron-containing steel by using sub-temperature quenching |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111778381A (en) * | 2020-07-01 | 2020-10-16 | 锦州捷通铁路机械股份有限公司 | Heat treatment method for improving plasticity and low-temperature impact toughness of C-grade steel |
| CN112756525A (en) * | 2020-12-09 | 2021-05-07 | 上海电气上重铸锻有限公司 | Manufacturing method of 9% Ni steel oversized cake-shaped forging for ultralow temperature engineering |
| CN114317893A (en) * | 2021-12-29 | 2022-04-12 | 张家港广大特材股份有限公司 | Manufacturing method of magnetic yoke ring forging |
| CN114262802A (en) * | 2022-01-04 | 2022-04-01 | 张家港广大特材股份有限公司 | Manufacturing method of high-strength flywheel energy storage rotor |
| CN114622073A (en) * | 2022-03-09 | 2022-06-14 | 包头钢铁（集团）有限责任公司 | Method for improving low-temperature impact toughness of boron-containing steel by using sub-temperature quenching |
| CN114622073B (en) * | 2022-03-09 | 2024-02-23 | 包头钢铁（集团）有限责任公司 | Method for improving low-temperature impact toughness of boron-containing steel by utilizing sub-temperature quenching |
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