CN102230058A - Heat treatment process of low alloy high-strength steel with yield strength of 690 MPa - Google Patents
Heat treatment process of low alloy high-strength steel with yield strength of 690 MPa Download PDFInfo
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Abstract
The invention provides a rapid heat treatment process of low alloy high-strength steel with yield strength of 690 MPa. The contents of alloy elements in the steel (percentage by weight) are as follows: the content of Mn (Manganese), Cr (Chromium), Ni (Nickel), Cu (Copper) and Mo (Molybdenum) is 2.05-2.6% while the content of Nb (Niobium) and Ti (Titanium) is 0.045-0.085 %. The heat treatment is carried out through rapid heating and quenching; and the method comprises the steps of heating the steel to 960 DEG C at a heating speed of no more than 50 DEG C/min, wherein the austenitizing heat preservation time is 3-5 minutes; and then hardening the steel to the room temperature at a cooling speed of 30-300 DEG C/s. The rapid heat treatment process of the low alloy high-strength steel with yield strength of 690 MPa, provided by the invention, has the following advantages that: the heating and heat preservation time of the heat treatment is reduced through increasing the heating speed and preserving the heat for a short time at a higher austenitizing temperature while the mechanical property of the steel is assured to the benefit of saving energy consumption and improving the production efficiency; and references can be also provided to the heat treatment of low alloy high-strength steels with other strength levels.
Description
Technical field
The invention provides a kind of yield strength is the thermal treatment process rapidly and efficiently of 690MPa level low alloy high-strength steel, belongs to metallic substance heat treatment technics field.
Background technology
Improving the steel alloy mechanical property by thermal treatment is field of metallurgy method commonly used, and thermal treatment can exert an influence to the tissue and the mechanical property of steel.
The quenching of steel is heated to critical temperature (Ac with steel exactly
3Or Ac
1) more than, after the insulation certain hour makes it austenitizing, to carry out a kind of technological process of refrigerative greater than the cooling rate of critical cooling velocity.The main purpose of quenching is to make workpiece behind the austenitizing obtain martensite as much as possible and the tempering that is equipped with differing temps obtains the performance of various needs.For quenching technology, at first steel must be heated to stagnation point (Ac for realizing quenching
3Or Ac
1) the above austenite structure that obtains, speed of cooling thereafter must be greater than critical quenching rate to obtain whole martensites (containing residual austenite) tissue.Therefore when formulating the quenching technology of steel, should reasonably select processing parameters such as rate of heating, Heating temperature, soaking time, speed of cooling.
To modified low-alloy high-strength steel, thermal treatment is one of key link in the production process.But heat treatment process also is simultaneously one of higher process of power consumption, and according to measuring and calculating, the thermal treatment energy consumption accounts for thermal treatment cost nearly 50%.Originally be divided into constant cost (fixed costs such as wage, equipment amortization) and variable cost calculating if will be heat-treated to, energy consumption almost accounts for more than 85% of variable cost so.Therefore, thermal treatment is energy-conservation very close with the relation thermal treatment economic benefit.Present stage, when iron and steel enterprise carried out modified thermal treatment to yield strength 690MPa level low alloy high-strength steel, the general technology that adopts is: the rate of heating with 10 ℃/min was heated to 900 ℃, and shrend behind the insulation 30min is then at 550～600 ℃ of tempering 25～30min.Because rate of heating is slower, soaking time is longer, and the time inside furnace of steel is about 150min when therefore carrying out modified thermal treatment, the energy consumption height, and the production cycle is long.
In the patent application (CN1974802) of " the 6CrNiSiMnMoV steel hardness gradient tempering heat treatment processing method " of Bai Yang town, Zhijiang City, Hubei Province State-owned Factory 404, relate generally to 6CrNiSiMnMoV Heat Treatment Of Steel process, comprise normalizing treatment, isothermal annealing, quench treatment, temper, double tempering, though improved the tissue and the performance of steel, but the heat treatment process complexity, soaking time is long.
The patent CN1721558 of Wanxiangqianchao Co. Ltd is a kind of carburizing quenching process of cold-extruded steel, the cold-extruded steel are heated to 920～980 ℃ with 30 ℃/minute～50 ℃/minute rate of heating, ooze insulation 3～11 hours by force, then with 30 ℃/time～60 ℃/time cooling rate be chilled to 820 ℃～880 ℃ quenchings, steel toughness, plasticity and intensity after the processing are higher.
In the patent of Harbin Engineering University (101831530A) " a kind of thermal treatment process that improves comprehensive mechanical property of low-alloy high-strength steel ", adopt circulating quenching to add the tempered mode steel alloy is heat-treated.Circulating quenching technology: 900 ℃～1100 ℃ * 1～10min, 3～6 circulating quenchings, the NaCl aqueous solution cooling of water-cooled or weight ratio concentration 7.5%; Tempering process: 450 ℃～650 ℃ * 1～5h, water-cooled.
In the patent of Guangzhou Research Institute of Nonferrous Metals (101555573) " a kind of steel alloy and heat treating method thereof ", the thermal treatment process that the steel alloy of its invention is adopted is: by the speed of 100 ℃/h, be warmed up to 930～950 ℃, be incubated that stove is as cold as 250 ℃ after 4 hours; By the speed of 100 ℃/h, be warmed up to 900～920 ℃ again, be incubated after 4 hours, water temperature is 20～45 ℃ of water-cooleds or air cooling; Reheat is to 250～300 ℃ of temperature, and stove is cold.
The following deficiency of above-mentioned patent (application) ubiquity: 1. complex technical process.Need repeatedly circulating quenching as 101831530A, need with the cooling of the NaCl aqueous solution, the heat treatment process of CN1974802 relates to a plurality of steps such as quench treatment, temper, double tempering.2. the heat tracing time is long in the heat treatment process, the energy consumption height, and production efficiency is low.Oozing insulation by force as CN1721558 needs 3～11 hours, and 101555573 need insulation 8 hours.So, be field of metallurgy method commonly used though improve the steel alloy mechanical property by thermal treatment, how to select the proper heat treatment condition, obtain good thermal effectiveness, be still a great problem.
Summary of the invention
The purpose of this invention is to provide the quenching-and-tempering process that a kind of yield strength is a 690MPa level low alloy high-strength steel, this technology can be in the mechanical property that improves steel, and the time inside furnace of steel can cut down the consumption of energy significantly when shortening heat was handled, and shortened the production cycle.
The invention provides a kind of thermal treatment process of yield strength 690MPa level low alloy high-strength steel, yield strength 690MPa level low alloy high-strength steel is heated to 930～960 ℃ with the rate of heating of 30～50 ℃/min, the austenitizing soaking time is 3～5 minutes, then with the cooling rate hardening of 30～300 ℃/s to room temperature.Carry out temper after the quenching, tempering temperature is 500～550 ℃, and soaking time is 15～25min.
Preferably, rate of heating is 40～50 ℃/min, is heated to 940～960 ℃.
Preferably, the austenitizing soaking time is 5min.
Preferably, described yield strength 690MPa level low alloy high-strength steel, alloying element content is (weight percent): Mn+Cr+Ni+Cu+Mo:2.05～2.6, Nb+Ti:0.045～0.085.
Steel obtains composition before quenching even, and the austenite structure that crystal grain is tiny helps improving the mechanical property of quenching the back steel.It is generally acknowledged that in heat-processed, rate of heating is fast more, the incubation period of austenitic transformation is short more, and the temperature that austenite begins to change is high more, and the initial austenite crystal of formation is also tiny more, and improve rate of heating and can significantly reduce heat-up time, also help cutting down the consumption of energy and raising the efficiency.But the selection of heat-up time and temperature is a very complicated problems, and temperature that austenite begins to change and rate of heating are not simple proportional relation, but has very complicated synergistic effect.
Because at present in the big production of Iron and Steel Enterprises in China, the actual heating capacity of quenching heating installation is the highest generally to be about 50 ℃/min, and we are increased to 50 ℃/min to rate of heating by 10 ℃ traditional/min.To yield strength 690MPa level low alloy high-strength steel, contain a certain amount of alloying element in the steel, alloying element content is (weight percent): Mn+Cr+Ni+Cu+Mo:2.05～2.6, Nb+Ti:0.045～0.085.Alloying element can influence velocity of diffusion and the solubleness of carbon in austenite, therefore can produce certain influence to austenitic forming process.
In addition, the distribution of steel interalloy element in ferrite and carbide is uneven, and in balanced weave, carbide forming element concentrates in the carbide, but not carbide forming element concentrates in the ferrite.It is extremely uneven that austenite forms back carbon and the distribution of alloying element in austenite, therefore in steel alloy except the homogenizing of carbon, also have the homogenizing process of an alloying element.Under the same conditions, the velocity of diffusion of alloying element in austenite is little more than carbon, only is ten thousand of carbon/to thousandth.In traditional technology, the quenching temperature of yield strength 690MPa level low alloy high-strength steel is 900～920 ℃, soaking time is 30min, because the velocity of diffusion of alloying element can be accelerated greatly when temperature raise, the time that is issued to austenitic homogenizing needs at comparatively high temps can shorten greatly, therefore to yield strength 690MPa level low alloy high-strength steel, thermal treatment process in this patent has been selected at 940～960 ℃, insulation 3～5min compares traditional technology and shortened soaking time greatly when guaranteeing the alloying element homogenizing.
In steel, the velocity of diffusion of alloying element, the formation of carbide and velocity of diffusion and heat-up time and temperature are to have synergy and interactional, though can shorten greatly in the time that comparatively high temps is issued to austenitic homogenizing and needs in theory, if reasonably improve rate of heating, then heating and soaking time can shorten, but because the influencing each other and the complicacy of austenitic transformation, grain growth thermokinetics of element in the steel, the selection of heat-up time and temperature need could be determined through a large amount of experiments.
In order to obtain optimum heat treatment conditions, we are through a large amount of experiments, find with summary by in-depth analysis a large amount of experimental datas, rate of heating with 40～50 ℃/min is heated to 940～960 ℃, the austenitizing soaking time is can finish austenitic transformation in 3～5 minutes, and because rate of heating is fast, austenitic superheating temperature is big, soaking time is short, AUSTENITE GRAIN COARSENING is not obvious, and the austenite crystal of formation is tiny evenly, and the quenching temperature of higher rate of heating and Geng Gao, shorter or longer soaking time, incomplete or the austenite crystal of austenitizing problem such as excessively grow up can be caused, good thermal effectiveness can not be obtained.With the cooling rate hardening of 30～300 ℃/s to room temperature.Carry out temper after the quenching, tempering temperature is 500～550 ℃, and soaking time is 15～25min, also is the essential condition that guarantees that effect of the present invention realizes.
Heat-treat condition of the present invention can effectively shorten time inside furnace, and time inside furnace shortens to 20～30min by original 150min.The thermal treatment energy consumption reduces 60-70%, and the thermal treatment cost reduces 40-50%.
The invention has the advantages that: the heat tracing time of steel when having shortened modified thermal treatment, save energy consumption, enhance productivity.The present invention passes through to adjust heat treatment process parameter, in the mechanical property that improves steel, and the time inside furnace of steel when shortening heat is handled significantly, can save energy consumption, shorten the production cycle, reduce production costs, enhance productivity, have huge economic benefit and social benefit.
Embodiment
Following examples are to further specify of the present invention, but the present invention is not limited thereto.
Comparative Examples 1
When iron and steel enterprise carries out modified thermal treatment to yield strength 690MPa level low alloy high-strength steel, generally the rate of heating with 10 ℃/min is heated to 900～930 ℃, shrend behind the insulation 30min, then at 550～600 ℃ of tempering 25～30min, the required like this heat tracing time is about 150min.
Embodiment 1
Yield strength 690MPa level low alloy high-strength steel is heated to 900 ℃ with the rate of heating of 10 ℃/min, is incubated 5 minutes, then with the cooling rate hardening of 30 ℃/s to room temperature.Carry out temper after the quenching, tempering temperature is 500 ℃, and soaking time is 20min.R
m(R
mBe the tensile strength of metallic substance, its unit is MPa) be 818MPa, time inside furnace 95 minutes.
Embodiment 2
Yield strength 690MPa level low alloy high-strength steel is heated to 900 ℃ with the rate of heating of 30 ℃/min, is incubated 30 minutes, then with the cooling rate hardening of 35 ℃/s to room temperature.Carry out temper after the quenching, tempering temperature is 500 ℃, and soaking time is 25min.R
mBe 826MPa, time inside furnace 60 minutes.
Embodiment 3
Yield strength 690MPa level low alloy high-strength steel is heated to 940 ℃ with the rate of heating of 30 ℃/min, is incubated 5 minutes, then with the cooling rate hardening of 30 ℃/s to room temperature.Carry out temper after the quenching, tempering temperature is 500 ℃, and soaking time is 20min.R
mBe 860MPa, time inside furnace 36 minutes.
Embodiment 4
Yield strength 690MPa level low alloy high-strength steel is heated to 960 ℃ with the rate of heating of 30 ℃/min, is incubated 3 minutes, then with the cooling rate hardening of 40 ℃/s to room temperature.Carry out temper after the quenching, tempering temperature is 500 ℃, and soaking time is 20min.R
mBe 903MPa, time inside furnace 37 minutes.
Embodiment 5
Yield strength 690MPa level low alloy high-strength steel is heated to 930 ℃ with the rate of heating of 50 ℃/min, is incubated 3 minutes, then with the cooling rate hardening of 30 ℃/s to room temperature.Carry out temper after the quenching, tempering temperature is 500 ℃, and soaking time is 25min.R
mBe 855MPa, time inside furnace 14 minutes.
Embodiment 6
Yield strength 690MPa level low alloy high-strength steel is heated to 960 ℃ with the rate of heating of 50 ℃/min, is incubated 5 minutes, then with the cooling rate hardening of 30 ℃/s to room temperature.Carry out temper after the quenching, tempering temperature is 540 ℃, and soaking time is 20min.R
mBe 910MPa, time inside furnace 25 minutes.
Embodiment 7
Yield strength 690MPa level low alloy high-strength steel is heated to 960 ℃ with the rate of heating of 50 ℃/min, is incubated 5 minutes, then with the cooling rate hardening of 100 ℃/s to room temperature.Carry out temper after the quenching, tempering temperature is 540 ℃, and soaking time is 20min.R
mBe 1027MPa, time inside furnace 24 minutes.
Embodiment 8
Yield strength 690MPa level low alloy high-strength steel is heated to 960 ℃ with the rate of heating of 50 ℃/min, is incubated 5 minutes, then with the cooling rate hardening of 300 ℃/s to room temperature.Carry out temper after the quenching, tempering temperature is 540 ℃, and soaking time is 20min.R
mBe 1409MPa, time inside furnace 24 minutes.
As seen, difference quenching rate of heating according to the orthogonal experiment analysis, holding temperature and soaking time are to the influence of yield strength 690MPa level low alloy high-strength steel mechanical property, employing is heated to 960 ℃ with the rate of heating of 50 ℃/min, performance the best when being incubated 5 minutes thermal treatment process, and time inside furnace is the shortest.Compare traditional technology, in the mechanical property that improves steel, save energy consumption, shorten the production cycle greatly.
Claims (4)
1. the thermal treatment process of a yield strength 690MPa level low alloy high-strength steel, yield strength 690MPa level low alloy high-strength steel is heated to 930～960 ℃ with the rate of heating of 30～50 ℃/min, the austenitizing soaking time is 3～5 minutes, then with the cooling rate hardening of 30～300 ℃/s to room temperature.Carry out temper after the quenching, tempering temperature is 500～550 ℃, and soaking time is 15～25min.
2. the thermal treatment process of yield strength 690MPa level low alloy high-strength steel as claimed in claim 1 is characterized in that rate of heating is 40～50 ℃/min, is heated to 940～960 ℃.
3. the thermal treatment process of yield strength 690MPa level low alloy high-strength steel as claimed in claim 1 or 2 is characterized in that, the austenitizing soaking time is 5min.
4. the thermal treatment process of yield strength 690MPa level low alloy high-strength steel as claimed in claim 1, it is characterized in that, described yield strength 690MPa level low alloy high-strength steel, alloying element content is (weight percent): Mn+Cr+Ni+Cu+Mo:2.05～2.6, Nb+Ti:0.045～0.085.
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| CN1631611A (en) * | 2005-01-12 | 2005-06-29 | 钢铁研究总院 | Manufacturing method for high strength bailing band |
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| 《国外金属热处理》 20000630 张恒华等 整体淬火和感应淬火 第13-18页 1-4 , * |
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Inventor after: Zhou Ping Inventor after: Yu Hao Inventor after: Yi Zhongwen Inventor after: Duan Mingbo Inventor after: Yang Jianxun Inventor before: Zhou Ping Inventor before: Yu Hao Inventor before: Yang Jianxun Inventor before: Wang Jianjing Inventor before: Li Canming |
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Free format text: CORRECT: INVENTOR; FROM: ZHOU PING YU HAO YANG JIANXUN WANG JIANJING LI CANMING TO: ZHOU PING YU HAO YI ZHONGWEN DUAN MINGBO YANG JIANXUN |
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