CN113969333B - Method for inhibiting structure grain size in quenching heat treatment process of steel workpiece - Google Patents
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 189
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 118
- 239000010959 steel Substances 0.000 title claims abstract description 118
- 238000000034 method Methods 0.000 title claims abstract description 63
- 238000010791 quenching Methods 0.000 title claims abstract description 42
- 230000008569 process Effects 0.000 title claims abstract description 37
- 230000000171 quenching effect Effects 0.000 title claims abstract description 33
- 230000002401 inhibitory effect Effects 0.000 title abstract description 12
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 54
- 230000009466 transformation Effects 0.000 claims abstract description 27
- 238000001816 cooling Methods 0.000 claims abstract description 18
- 238000005496 tempering Methods 0.000 claims abstract description 13
- 238000006243 chemical reaction Methods 0.000 claims description 6
- 229910000851 Alloy steel Inorganic materials 0.000 claims description 5
- 229910000975 Carbon steel Inorganic materials 0.000 claims description 5
- 239000010962 carbon steel Substances 0.000 claims description 5
- 238000012937 correction Methods 0.000 claims description 5
- 230000007704 transition Effects 0.000 claims description 2
- 230000001131 transforming effect Effects 0.000 claims 1
- 239000013078 crystal Substances 0.000 description 19
- 230000008859 change Effects 0.000 description 10
- 230000000052 comparative effect Effects 0.000 description 8
- 229910000734 martensite Inorganic materials 0.000 description 8
- 238000004321 preservation Methods 0.000 description 7
- 239000010410 layer Substances 0.000 description 5
- 229910001562 pearlite Inorganic materials 0.000 description 5
- 229910000859 α-Fe Inorganic materials 0.000 description 5
- 238000012546 transfer Methods 0.000 description 4
- 238000009792 diffusion process Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 3
- 239000010931 gold Substances 0.000 description 3
- 229910052737 gold Inorganic materials 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 238000002407 reforming Methods 0.000 description 3
- 238000005265 energy consumption Methods 0.000 description 2
- 238000011534 incubation Methods 0.000 description 2
- 238000003754 machining Methods 0.000 description 2
- 238000010587 phase diagram Methods 0.000 description 2
- 239000002344 surface layer Substances 0.000 description 2
- 238000004227 thermal cracking Methods 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 238000002203 pretreatment Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
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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
- 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
- C21D2211/001—Austenite
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Abstract
The invention discloses a method for inhibiting the structure grain size in the quenching heat treatment process of a steel workpiece, belonging to the technical field of heat treatment. The method comprises the following steps: heating the steel part to be treated to A 1 Temperature, reaches A 1 After the temperature, keeping the temperature for a time t 1 (ii) a Continuing to heat to A 1 +50 ℃ for a heating time t 2 (ii) a Air-cooling the workpiece in the complete austenite region to the elastoplasticity transformation point of the steel piece to be treated; directly heating the steel part to a target heat treatment temperature A 3 Heating to 20-50 deg.c for 30min; and directly carrying out quenching and low-temperature tempering treatment after the target heat treatment temperature is reached. The heating method can inhibit the growth tendency of austenite grains in the heating process, compared with the initial grain size of the steel part, the grains can not grow obviously, and the steel part with overlarge initial grain size can even be reduced to a certain degree.
Description
Technical Field
The invention belongs to the technical field of heat treatment, and particularly relates to a method for inhibiting the structure grain size in the quenching heat treatment process of a steel workpiece.
Background
The mechanical property of the workpiece can be controlled by changing the microstructure on the surface or in the metal material through heat treatment, so that the application requirement of the workpiece under the service condition of the workpiece is met. Heat treatment is a process of "heating and cooling", and heating is a very important process. Generally, the heating of a steel workpiece is accompanied with the phase transformation process of austenite, and austenite grains are inevitably grown in the processes of reaching the temperature and keeping the temperature, so that the mechanical property of the workpiece is deteriorated. If the subsequent heat treatment is a quenching process, the martensite structure obtained by quenching becomes brittle due to coarsening, and in more serious cases, if the crystal grains are coarsened to a certain extent, the martensite needle crystals are cracked to cause thermal cracking.
Therefore, in the quenching heat treatment process of the steel workpiece, the size of austenite grains is controlled, and on the premise of obtaining good comprehensive performance, the coarsening of a martensite structure is avoided, so that the mechanical property of the steel workpiece is reduced.
Disclosure of Invention
In order to overcome the technical defects, the invention provides a method for inhibiting the structure grain size in the quenching heat treatment process of a steel workpiece, so as to solve the problems related to the background technology.
The invention provides a method for inhibiting the structure grain size in the quenching heat treatment process of a steel workpiece, which comprises the following steps:
a preheating stage: heating the steel part to be treated to A 1 Temperature, reaches A 1 After the temperature, keeping the temperature for a time t 1 ；
A heating stage: heating to A 1 +50 ℃ and a heating time t 2 ；
A pre-cooling stage: air-cooling the workpiece in the complete austenite region to the elastoplasticity transformation point of the steel piece to be treated;
and (3) a heat treatment stage: directly heating the steel part to a target heat treatment temperature A 3 Heating to 20-50 deg.c for 30min; after reaching the target heat treatment temperature, quenching and low-temperature tempering treatment are directly carried out.
Preferably or optionally, said A 1 The temperature is the phase transition temperature at which the steel piece to be treated can be transformed into austenite.
Preferably or optionally, the incubation time t 1
Wherein D is the effective thickness of the steel piece to be treated, and the unit is mm; k is a correction coefficient of the reaction charging condition, the value range of K is 1.0-1.3, and the larger the charging amount is, the larger the value is; alpha is heating coefficient, and is 0.7-0.8min/mm for carbon steel and 1.0-1.2min/mm for alloy steel.
Preferably or optionally, the heating time is t 2 And the holding time t 1 Are equal.
Preferably or alternatively, the steel piece to be treated has an elasto-plastic transformation point of 500 ℃.
Preferably or optionally, said A 3 The temperature is the final temperature at which the steel piece to be treated is transformed into austenite.
The invention also provides a method for inhibiting the structure grain size in the quenching heat treatment process of a steel workpiece, which comprises the following steps:
a preheating stage: heating the steel part to be treated to A 1 Temperature, reaches A 1 After the temperature has been reached,keeping warm for time t 1 ；
A heating stage: heating to A 1 +50 ℃ for a heating time t 2 ；
A pre-cooling stage: air-cooling the workpiece in the complete austenite region to the elastic-plastic transformation point of the steel piece to be treated;
a second pretreatment stage: repeating the preheating stage, the heating stage and the precooling stage for 1-3 times;
and (3) a heat treatment stage: directly heating the steel part to a target heat treatment temperature A 3 Plus (20-50) DEG C, and the heating time is set as 30min; after reaching the target heat treatment temperature, quenching and low-temperature tempering treatment are directly carried out.
Preferably or optionally, the second pre-treatment stage is a 2-time repetition of the pre-heating stage, the heating stage, and the pre-cooling stage.
Preferably or optionally, said A 1 The temperature is the transformation temperature at which the steel piece to be treated can be transformed into austenite.
Preferably or optionally, the holding time t 1
Wherein D is the effective thickness of the steel piece to be treated, and the unit is mm; k is a correction coefficient of the reaction charging condition, the value range of K is 1.0-1.3, and the larger the charging amount is, the larger the value is; alpha is heating coefficient, and is 0.7-0.8min/mm for carbon steel and 1.0-1.2min/mm for alloy steel.
Preferably or optionally, the heating time is t 2 And the holding time t 1 Are equal.
Preferably or alternatively, the steel piece to be treated has an elasto-plastic transformation point of 500 ℃.
Preferably or optionally, said A 3 The temperature is the final temperature at which the steel piece to be treated is transformed into austenite.
The invention relates to a method for inhibiting the structure grain size in the quenching heat treatment process of a steel workpiece, which has the following beneficial effects compared with the prior art:
1) The process is simple: the growth trend of crystal grains of the steel part in the heating process is inhibited by controlling parameters of the heating process, other processes are not needed, the workpiece can efficiently flow in furnaces with different preset temperatures, different temperature rise and fall processes are realized, and the process is simple to control;
2) The effect is remarkable: for steel with easily grown crystal grains, the growth trend of the crystal grains in the heating process can be effectively inhibited, a steel part with the crystal grains which are coarsened seriously can be saved, and the final structure and the performance of the steel part are improved;
3) High-efficiency and energy-saving: according to the heating scheme of the invention, although the workpiece is subjected to multiple phase change processes, the phase change of the workpiece occurs in a narrow temperature range above and below the phase change point, and compared with the traditional heat treatment, the heating scheme has the advantages that the energy consumption and the efficiency are improved to a certain extent.
Drawings
FIG. 1 is a schematic view of a heating process of the present invention; wherein P is pearlite, F is ferrite, A is austenite, and M is martensite.
FIG. 2 is a schematic view of another heating process of the present invention; wherein P is pearlite, F is ferrite, A is austenite, and M is martensite.
FIG. 3 is a gold phase diagram of austenite grains before heat treatment in example 1 of the present invention.
FIG. 4 is a diagram showing the gold phase of austenite grains after heat treatment in example 1 of the present invention.
FIGS. 5a to 5f are gold phase diagrams of austenite grains after heat treatment in examples 2 to 6 of the present invention and comparative examples.
Detailed Description
In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the invention.
Summary of The Invention
Generally, the heating of the steel workpiece is accompanied by the transformation process of austenite, and the austenite grains inevitably grow up in the process of reaching the temperature and keeping the temperature, thereby causing the mechanical property of the workpiece to be deteriorated. If the subsequent heat treatment is a quenching process, the martensite structure obtained by quenching becomes brittle due to coarsening, and in more serious cases, if the crystal grains are coarsened to a certain extent, the martensite needle crystals are cracked to cause thermal cracking.
The growth process of austenite crystal grains can be considered as the diffusion transfer process of austenite crystal boundaries, and the larger the temperature difference of different parts of the steel piece is, the larger the interface energy difference is, and the more easily the diffusion transfer of the crystal boundaries occurs. When the steel part is quenched and heated, heat can be transferred from the outside to the inside, and if the heating speed is too high, the part with more heat at the external corner or the surface layer can reach A first due to faster temperature rise 1 Transformation point to austenite. In the subsequent continuous heating or heat preservation process, because the part of the steel part which firstly undergoes austenite phase transformation has sufficient time to perform intergranular fusion and growth, and forms a certain degree of interface energy gradient with the part which later undergoes austenite phase transformation, the diffusion transfer of a crystal boundary can be promoted, and the austenite crystal grains are obviously grown. Therefore, the key point for inhibiting the grain growth trend of the steel part during quenching and heating is to reduce the temperature difference of different parts of the steel part in the temperature rising process.
For steel parts with obviously coarsened crystal grains, the steel parts are heated and then cooled, and the re-refinement of the crystal grains can be realized through the reforming action of phase change. However, the conventional single-phase zone heat treatment has phase change, large heating and cooling amplitude and low heat treatment efficiency, and can aggravate the heat treatment distortion of the steel piece and increase the subsequent machining difficulty.
Based on the above theory and practical analysis, the applicant proposes the method for inhibiting the grain size in the quenching and heating process of the steel workpiece, the process route refers to the attached drawings 1 and 2, and the method comprises the following specific description:
step one, a preheating stage: namely, the steel piece to be treated is heated to A 1 Temperature, reaches A 1 After the temperature, keeping the temperature for a time t 1 ；
Step one, a heating stage: continuing to heat to A 1 +50 ℃ for a heating time t 2 ；
Step two, a pre-cooling stage: air-cooling the workpiece in the complete austenite region to the elastic-plastic transformation point of the steel piece to be treated;
step three, a second pretreatment stage: repeating the preheating stage, the heating stage and the precooling stage for 2-3 times;
step four, a heat treatment stage: directly heating the steel part to a target heat treatment temperature A 3 Heating to 20-50 deg.c for 30min; after reaching the target heat treatment temperature, quenching and low-temperature tempering treatment are directly carried out.
By adopting the heating method, the growing trend of austenite grains in the heating process can be inhibited, compared with the initial grain size of the steel part, the grains can not grow obviously, and the steel part with overlarge initial grain size can be reduced to a certain extent.
In a further embodiment, said A 1 The temperature is the transformation temperature at which the steel piece to be treated can be transformed into austenite. When the steel part to be treated is at A 1 When the temperature is kept, although the austenite transformation temperature of the material is reached, the structure of the material is not completely transformed into austenite due to the existence of the internal component fluctuation and the energy fluctuation, and a certain amount of pre-transformation structure exists, namely ferrite and a small amount of pearlite structure for steel materials. When the steel piece to be processed is heated, the outer layer is heated firstly, and the primary preheating treatment is to enable the steel piece to be processed to pass through the phase change temperature relatively simultaneously inside and outside. A certain driving force, namely the degree of superheat of the temperature, is required for the growth of austenite. When the temperature reaches A 1 In the process, although the outer layer part structure is converted into an austenite structure before, the driving force for austenite growth is smaller because the heat preservation temperature is lower, so that obvious growth does not occur. Furthermore, the growth of austenite is also restricted due to the pinning effect of the non-transformed phase.
In a further embodiment, the incubation time t 1
Wherein D is the effective thickness of the steel piece to be treated, and the unit is mm; k is a correction coefficient of the reaction charging condition, the value range of K is 1.0-1.3, and the larger the charging amount is, the larger the value is; alpha is heating coefficient, and is 0.7-0.8min/mm for carbon steel and 1.0-1.2min/mm for alloy steel. Based on the above formula, the holding time t can be calculated 1 The temperature of the inner layer and the outer layer of the steel piece to be processed is ensured to be consistent, the grain size is basically kept consistent, and an ideal preparatory structure is provided for the subsequent heating procedure.
In a further embodiment, the heating time is t 2 And the holding time t 1 Are equal. When the temperature of the steel part to be treated exceeds A 1 At the point of 50 ℃, the structure of the steel part to be treated is completely transformed into austenite. As mentioned above, during heating, the growth of austenite is inevitable, the heating time is set to be the same as the heat transfer time, so that the temperature and the phase change are transferred from outside to inside at the same time, the time for the austenite to fuse and grow in the outer layer structure can be reduced as much as possible, and the inner and outer grain sizes have higher consistency when heating is finished.
In a further embodiment, the steel part to be treated has an elasto-plastic transformation point of 500 ℃. In the pre-cooling stage, austenite is transformed into ferrite and pearlite again, the prior austenite grains are reformed by utilizing phase transformation, and the nucleation rate of the next austenite phase transformation is improved, so that the aim of reducing the final grain size is fulfilled. The steel piece to be treated is cooled to the temperature, austenite can be completely decomposed into ferrite and pearlite, more severe martensite phase transformation cannot occur, on one hand, the steel piece to be treated can be always in a more uniform plastic transformation area, cracks caused by undercooling of the surface layer can be prevented, on the other hand, the heat capacity of next heating of the steel piece to be treated can be increased, the heating efficiency is improved, and the energy consumption is reduced.
In a further embodiment, the second pretreatment stage is to repeat the preheating stage, the heating stage and the pre-cooling stage 2 times. For steel parts to be treated, the grains of which have been significantly coarsened, further refinement of the original structure is therefore required. And carrying out secondary preheating, secondary heating and secondary precooling processes, so that the steel piece to be treated undergoes primary phase change to reform crystal grains, and the structure is further refined, thereby achieving the purpose of improving the performance of the steel piece to be treated after final heat treatment. Theoretically, the crystal grains of the steel piece to be processed can be continuously refined after multiple times of phase change reforming, but after the three times of phase change reforming, the degree of grain refinement is very limited, and the heat treatment deformation of the steel piece to be processed is increased, so that the difficulty of subsequent machining is increased. Experiments prove that after the preheating stage, the heating stage and the precooling stage are carried out for 2 times, the structure and the performance of the steel plate can meet the design requirements through inspection.
In a further embodiment, said A 3 The temperature is the final temperature at which the steel piece to be treated is transformed into austenite. In the heat treatment stage, the steel piece to be treated slowly and uniformly passes through the finishing temperature of the austenite transformation point inside and outside so as to achieve the purpose of inhibiting the growth of crystal grains.
The invention will now be further described with reference to the following examples, which are intended to be illustrative of the invention and are not to be construed as limiting the invention. The examples, where specific techniques and reaction conditions are not indicated, can be carried out according to the techniques or conditions or product specifications described in the literature in the field. Reagents, instruments or equipment of any manufacturer not indicated are commercially available.
Example 1
A steel part made of 18CrNiMo7-6 steel is heated to 738 ℃ (A of 18CrNiMo7-6 steel 1 The temperature is 738 ℃), because the embodiment adopts a hanging mode, the temperature is loose, the furnace charging coefficient is 1.0, and the heating coefficient is 1.0, the heat preservation time t is selected from Wen Houxuan 1 Is 30min; then, continuously heating to 788 ℃, and setting the heating time to be 30min; the workpiece, which is already in the fully austenitic range, is then air cooled to 500 ℃.
And repeating the steps, namely performing secondary preheating, secondary heating and secondary precooling procedures.
After secondary precooling, the steel piece is directly heated to the target heat treatment temperature of 830 ℃, the heating time is set to be 30min, after the target heat treatment temperature is reached, quenching and low-temperature tempering treatment are directly carried out, and the mechanical properties after heat treatment are shown in table 2.
Example 2
A steel part made of 18CrNiMo7-6 steel is heated to 738 ℃ (A of 18CrNiMo7-6 steel 1 The temperature is 738 ℃), because the embodiment adopts a hanging mode, the temperature is loose, the furnace charging coefficient is 1.0, and the heating coefficient is 1.0, the heat preservation time t is selected from Wen Houxuan 1 Is 30min; then, continuously heating to 788 ℃, and setting the heating time to be 30min; the workpiece, which is already in the fully austenitic range, is then air cooled to 500 ℃.
After primary precooling, the steel piece is directly heated to the target heat treatment temperature of 830 ℃, the heating time is set to be 30min, after the target heat treatment temperature is reached, quenching and low-temperature tempering treatment are directly carried out, and the mechanical properties after heat treatment are shown in table 2.
Example 3
A steel part made of 18CrNiMo7-6 steel is heated to 738 ℃ (A of 18CrNiMo7-6 steel 1 The temperature is 738 ℃), because the embodiment adopts a hanging mode, the temperature is loose, the furnace charging coefficient is 1.0, and the heating coefficient is 1.0, the heat preservation time t is selected from Wen Houxuan 1 Is 30min; then, continuously heating to 788 ℃, and setting the heating time to be 30min; the workpiece, which is already in the fully austenitic range, is then air cooled to 500 ℃.
And repeating the steps for 2 times, namely performing secondary preheating, secondary heating and secondary precooling, and performing tertiary preheating, tertiary heating and tertiary precooling.
After three times of precooling, the steel piece is directly heated to the target heat treatment temperature of 830 ℃, the heating time is set to be 30min, after the target heat treatment temperature is reached, quenching and low-temperature tempering treatment are directly carried out, and the mechanical properties after the heat treatment are shown in table 2.
Example 4
Steel part made of 18CrNiMo7-6 steelHeating to 788 deg.C (A of 18CrNiMo7-6 steel) 1 The temperature is 738 ℃), as the hanging mode is adopted in the embodiment, the operation is loose, the furnace charging coefficient is 1.0, and the heating coefficient is 1.0, the heating time is set to be 30min; the workpiece, which is already in the fully austenitic range, is then air cooled to 500 ℃.
After primary precooling, the steel piece is directly heated to the target heat treatment temperature of 830 ℃, the heating time is set to be 30min, after the target heat treatment temperature is reached, quenching and low-temperature tempering treatment are directly carried out, and the mechanical properties after heat treatment are shown in table 2.
Example 5
A steel part made of 18CrNiMo7-6 steel is heated to 738 ℃ (A of 18CrNiMo7-6 steel 1 The temperature is 738 ℃), because the embodiment adopts a hanging mode, the temperature is loose, the furnace charging coefficient is 1.0, and the heating coefficient is 1.0, the heat preservation time t is selected to Wen Houxuan 1 Is 30min; the workpiece, which is already in the fully austenitic range, is then air cooled to 500 ℃.
After primary precooling, the steel piece is directly heated to the target heat treatment temperature of 830 ℃, the heating time is set to be 30min, after the target heat treatment temperature is reached, quenching and low-temperature tempering treatment are directly carried out, and the mechanical properties after heat treatment are shown in table 2.
Example 6
A steel part made of 18CrNiMo7-6 steel is heated to 738 ℃ (A of 18CrNiMo7-6 steel 1 The temperature is 738 ℃), because the embodiment adopts a hanging mode, the temperature is loose, the furnace charging coefficient is 1.0, and the heating coefficient is 1.0, the heat preservation time t is selected from Wen Houxuan 1 Is 30min; then, the heating was continued to 788 ℃ for 30min.
Directly heating the workpiece in the complete austenite region to a target heat treatment temperature of 830 ℃, setting the heating time to be 30min, directly carrying out quenching and low-temperature tempering treatment after the target heat treatment temperature is reached, wherein the mechanical properties after the heat treatment are shown in Table 2.
Comparative example 1
Conventional heat treatment: directly heating a steel part made of 18CrNiMo7-6 steel to a target heat treatment temperature of 830 ℃, setting the heating time as 30min, directly carrying out quenching and low-temperature tempering treatment after the target heat treatment temperature is reached, wherein the mechanical properties after the heat treatment are shown in Table 2.
Example of detection
For the convenience of the reader to understand the protocol further, the specific numerical mechanical properties of each of examples 1 to 6, comparative examples are summarized in tables 1, 2.
Table 1, examples 1 to 6 and comparative example the main process parameters for the heat treatment
| Examples | Preheating temperature/time | Heating temperature/time | Precooling temperature | Number of repetitions | Heat treatment process |
| Example 1 | 738℃/30min | 788℃/30min | 500℃ | 2 | 830 deg.C/quench + Low Return |
| Example 2 | 738℃/30min | 788℃/30min | 500℃ | 1 | 830 deg.C/quench + Low Return |
| Example 3 | 738℃/30min | 788℃/30min | 500℃ | 3 | 830 deg.C/quench + Low Return |
| Example 4 | Is free of | 788℃/30min | 500℃ | 1 | 830 deg.C/quench + Low Return |
| Example 5 | 738℃/30min | Is free of | 500℃ | 1 | 830 deg.C/quench + Low Return |
| Example 6 | 738℃/30min | 788℃/30min | Is free of | 1 | 830 deg.C/quench + Low Return |
| Comparative example | Is free of | Is composed of | Is free of | 0 | 830 deg.C/quench + Low Return |
Mechanical Properties of Heat treatment of Table 2, examples 1 to 6 and comparative example
| Examples | Tensile strength | Defining the plastic elongation strength Rm | Elongation after fracture | Reduction of area | Energy absorption by impact | Metallographic phase of austenite |
| Example 1 | 1298MPa | 998MPa | 15.0% | 63% | 73 86 86J | FIG. 4 |
| Example 2 | 1296MPa | 980MPa | 14.5% | 61% | 74 66 62J | FIG. 5 (a) |
| Example 3 | 1268MPa | 1012MPa | 15.5% | 60% | 86 80 86J | FIG. 5 (b) |
| Example 4 | 1358MPa | 1035MPa | 14.0% | 57% | 56 70 56J | FIG. 5 (c) |
| Example 5 | 1377MPa | 1066MPa | 12.0% | 54% | 46 44 44J | FIG. 5 (d) |
| Example 6 | 1293MPa | 974MPa | 13.0% | 52% | 50 50 50J | FIG. 5 (e) |
| Comparative example | 1364MPa | 1136MPa | 11.5% | 54% | 42 44 42J | FIG. 5 (f) |
Discussion of the related Art
Comparing the embodiment 2, the embodiment 3 and the comparative example, it can be seen that the austenite crystal grain growth process in the heating process can be effectively inhibited through the preheating, heating and precooling processes, and the comprehensive mechanical property of the steel part is improved; comparing the embodiment 2 with the embodiment 3, it can be seen that the repeated preheating, heating and precooling processes have a certain refining effect on the structure with coarsened grain size, and can improve the mechanical property of the comprehensive steel piece to a greater extent; comparing example 2 with example 4, it can be seen that in the process without preheating, the austenite grains have a relatively large growth tendency by directly heating to a two-phase region for precooling and then carrying out formal heat treatment, but the grain growth degree can be neutralized through a subsequent precooling process, but the final austenite grains are still larger than those in example 2; comparing example 2 with example 5, it can be seen that there is no intermediate heating process, the pre-heated steel is directly pre-cooled, and then formal heat treatment is performed, and the amount of inhibiting the grain size is limited because the austenite transformation amount is limited at high temperature; comparing example 2 with example 6, it can be seen that pre-cooling is not performed, pre-heating and intermediate heating are performed, and then formal heat treatment is performed, only the grain growth tendency in the heating process is reduced, and the influence degree on the performance is limited.
It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition.
Claims (7)
1. A method of suppressing the grain size of a structure during a quench heat treatment of a steel workpiece, the method comprising:
a preheating stage: heating the steel part to be treated to A 1 Temperature, reaches A 1 After the temperature, keeping the temperature for a time t 1 ；
A heating stage: heating to A 1 +50 ℃ for a heating time t 2 ；
A pre-cooling stage: air-cooling the workpiece in the complete austenite region to the elastic-plastic transformation point of the steel piece to be treated;
and (3) a heat treatment stage: directly heating the steel part to a target heat treatment temperature A 3 Plus (20-50) DEG C, and the heating time is set as 30min; after reaching the target heat treatment temperature, directly carrying out quenching and low-temperature tempering treatment;
the holding time t 1
Wherein D is the effective thickness of the steel piece to be treated, and the unit is mm; k is a correction coefficient of the reaction charging condition, the value range of K is 1.0-1.3, and the larger the charging amount is, the larger the value is; alpha is heating coefficient, for carbon steel, 0.7-0.8min/mm is taken, and for alloy steel, 1.0-1.2min/mm is taken;
the heating time is t 2 And the holding time t 1 Equal;
the steel member to be treated has an elastic-plastic transformation point of 500 ℃.
2. The method for suppressing the grain size of a structure during a quenching heat treatment of a steel workpiece as claimed in claim 1, wherein A is 1 The temperature is the energy of the steel part to be treatedA transformation temperature capable of transforming into austenite.
3. The method of suppressing the grain size of a structure during a quenching heat treatment of a steel workpiece as claimed in claim 1, wherein A is a 3 The temperature is the final temperature at which the steel piece to be treated is transformed into austenite.
4. A method of suppressing the grain size of a structure during a quench heat treatment of a steel workpiece, the method comprising:
a preheating stage: heating the steel part to be treated to A 1 Temperature, reaches A 1 After the temperature, keeping the temperature for t 1 ；
A heating stage: heating to A 1 +50 ℃ and a heating time t 2 ；
A pre-cooling stage: air-cooling the workpiece in the complete austenite region to the elastic-plastic transformation point of the steel piece to be treated;
a second pretreatment stage: repeating the preheating stage, the heating stage and the precooling stage for 1-3 times;
and (3) a heat treatment stage: directly heating the steel part to a target heat treatment temperature A 3 Heating to 20-50 deg.c for 30min; after reaching the target heat treatment temperature, directly carrying out quenching and low-temperature tempering treatment;
the holding time t 1
Wherein D is the effective thickness of the steel piece to be treated, and the unit is mm; k is a correction coefficient of the reaction charging condition, the value range of K is 1.0-1.3, and the larger the charging amount is, the larger the value is; alpha is heating coefficient, for carbon steel, 0.7-0.8min/mm is taken, and for alloy steel, 1.0-1.2min/mm is taken;
the heating time is t 2 And the holding time t 1 Equal;
the steel member to be treated has an elastic-plastic transformation point of 500 ℃.
5. The method for suppressing the structure grain size during the quenching heat treatment process of the steel workpiece as recited in claim 4, wherein the second pretreatment stage is a 2-time repetition of the preheating stage, the heating stage and the pre-cooling stage.
6. The method for suppressing the grain size of a structure during quenching heat treatment of a steel workpiece as claimed in claim 4, wherein A is 1 The temperature is the phase transition temperature at which the steel piece to be treated can be transformed into austenite.
7. The method of suppressing the grain size of a structure during a quenching heat treatment of a steel workpiece as set forth in claim 4, wherein A is a 3 The temperature is the final temperature at which the steel piece to be treated is transformed into austenite.
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