1. The method for determining the carbide precipitation kinetics curve based on isothermal stress and phase transition is characterized by comprising the following steps of:

step 1: acquiring a true stress-strain curve of the alloy steel at different isothermal times within a set temperature, and taking the stress value of the yield stress point as an isothermal yield strength value sigma_yPlotting isothermal yield strength values σ_yDetermining carbide precipitation finishing time P according to isothermal temperature-time change relation curve_f；

Step 2: measuring the phase change starting time (T) of the alloy steel at a set temperature_s) And an end time (T)_f)；

And step 3: according to the obtained phase change starting time T_sDrawing a change curve of isothermal yield strength increment along with isothermal time before the phase change of the alloy steel sample starts at different set isothermal temperatures, and determining the carbide precipitation starting time P at different isothermal temperatures_s；

And 4, step 4: according to the precipitation start time P of the obtained carbide_sAnd an end time P_fAnd drawing a precipitation-temperature-time curve of carbide in the isothermal process of the alloy steel.

2. The method for determining the carbide precipitation kinetics curve based on isothermal stress and phase transformation according to claim 1, wherein the stress value at 2% strain compensation on the true stress-strain curve is taken as the stress value at the yield stress point.

3. The method for determining the carbide precipitation kinetics curve based on isothermal stress and phase transformation according to claim 1, wherein the steps 1 and 2 specifically comprise:

processing an alloy steel sample;

welding a thermocouple wire on an alloy steel sample;

respectively connecting a metal tantalum sheet and a graphite sheet at two ends of an alloy steel sample in sequence;

installing the alloy steel sample connected with the metal tantalum sheet and the graphite sheet in an experiment cabin of a thermal simulation testing machine, and adjusting the axial displacement of a main shaft of the thermal simulation testing machine to enable a chuck to tightly press the alloy steel sample;

clamping the alloy sample by a quartz glass chuck of a thermal expansion instrument, and enabling the quartz glass chuck and the thermocouple wire to be positioned on a cross section of the sample; the output data line of the thermal expansion instrument is connected with the sensor interface of the thermal simulation testing machine;

connecting the thermocouple wire with a temperature channel of a thermal simulation testing machine, closing a cabin door of the experiment cabin and vacuumizing;

after the vacuum degree in the experiment cabin meets the requirement, starting a thermal simulation testing machine, and testing according to a set testing process flow;

after one test process is finished, changing the process parameters of the test, and repeating the steps to perform the next test until the test is finished;

after the test is finished, according to the values of the temperature, the time, the true strain, the true stress and the thermal expansion quantity collected by the thermal simulation testing machine, the set true stress-strain curves at different isothermal temperatures and time and the thermal expansion curve changing along with the time are obtained, and further the isothermal yield strength and the phase change starting time and the phase change ending time at different isothermal temperatures are obtained.

4. The method for determining carbide precipitation kinetics curves based on isothermal stress and phase transformation according to claim 3, characterized in that: the machined alloy steel specimens were cylindrical in shape with a length to diameter ratio of no greater than 2.

5. The method for determining carbide precipitation kinetics curves based on isothermal stress and phase transformation according to claim 3, characterized in that: the thermocouple wires are K-type thermocouple wires or R-type thermocouple wires.

6. The method for determining carbide precipitation kinetics curves based on isothermal stress and phase transformation according to claim 3, characterized in that: and welding and fixing the thermocouple wire on the alloy steel sample by a thermocouple welding machine, wherein the voltage of the thermocouple welding machine is set to be between 34 and 38V.

7. The method for determining carbide precipitation kinetics curves based on isothermal stress and phase transformation according to claim 3, characterized in that: the vacuum degree for starting the Gleeble-3800 tester to run is lower than 1.5 multiplied by 10^-1Pa。

8. The method for determining carbide precipitation kinetics curves based on isothermal stress and phase transformation according to claim 3, characterized in that: the thermal expansion coefficients of different phases in the alloy steel are from large to small: martensite < bainite < pearlite < ferrite < austenite, an inflection point appears on a measured thermal expansion curve along with volume expansion when austenite transformation occurs in an isothermal process, and the starting time and the ending time of the isothermal transformation are judged by measuring the time at the inflection point.

9. The method for determining the carbide precipitation kinetics curve based on isothermal stress and phase transformation according to any one of claims 3-8, wherein the process flow parameters of the set test are as follows:

(1) heating the cylindrical sample to 1150-1280 ℃ at a speed of 1-20 ℃/s on a Gleeble-3800 thermal simulation testing machine and preserving heat for 3-10min to ensure that the sample is fully austenitized and dissolves a second phase except the N-containing compound;

(2) cooling to 1150 ℃ at the temperature of 10-100 ℃/s for 5-15s, deforming for 10-30%, cooling to 800 ℃ at the temperature of 800 ℃ for 5-20s, deforming for 10-30%, and deforming at the rate of 0.5-10.s^-1；

(3) The sample after two-pass deformation is respectively cooled to 550-750 ℃ at the temperature of 10-100 ℃/s, the sample is deformed by 10-30% after isothermal different time, and the deformation rate is 0.5-10s^-1The isothermal time is 5-10800 s.

10. The method for determining the carbide precipitation kinetics curve based on isothermal stress and phase transformation according to claim 9, wherein the process flow parameters of the set test are as follows:

(1) heating the sample to 1200 ℃ at a speed of 10 ℃/s on a Gleeble-3800 thermal simulation testing machine and preserving the temperature for 5 min;

(2) cooling to 10 deg.C/s at 20 deg.C/sDeforming 20% after isothermal 10s at 50 deg.C, cooling to 900 deg.C at 20 deg.C/s, deforming 20% after isothermal 15s at deformation rate of 1.0s^-1；

(3) After the two-stage deformation, the sample is cooled to 600-700 ℃ at the temperature of 30 ℃/s, the sample deforms 30% after isothermal different time, and the deformation rate is 1.0s^-1The isothermal time is 5-10800 s.

Background

The carbide is controlled to be precipitated in the ferrite in a nano-size and high density by adding microalloy elements and combining a controlled rolling and controlled cooling process, so that the strength of the steel can be obviously improved and good toughness can be kept. The precipitation temperature window of nano carbide in ferrite in alloy steel is narrow, the precipitation characteristic is very sensitive to heat treatment conditions (such as strain, isothermal temperature and isothermal time), and the change of a heat treatment schedule can cause remarkable difference of strength. It is generally believed that the maximum precipitation strengthening effect can be obtained by performing isothermal heat treatment at the nose tip temperature of the carbide precipitation kinetics curve. Therefore, the determination of the carbide precipitation kinetic curve of the alloy steel austenite in the isothermal process of the isothermal phase transition temperature has important significance for the guidance of production practice.

The steel alloy has a dynamic change process of austenite transformation and precipitation in an isothermal process at an isothermal transformation temperature, and the two processes are difficult to separate and directly determine the beginning and the end of the precipitation. Therefore, the research and determination of carbide precipitation kinetics curve of austenite in isothermal phase transformation process are few. Currently, most studies are to set the nucleation sites of carbides first and then calculate based on a mathematical model under equilibrium conditions. In actual production, the isothermal phase transformation process of austenite is nonequilibrium, and the position of precipitation is not unique. The method for determining the isothermal precipitation kinetics curve of the carbide (CN106018117B) of the Chinese granted patent determines the isothermal precipitation start and end of austenite by determining the difference of the compressive stress of the alloy steel after being cooled to room temperature after different isothermal treatments through experiments to determine the carbide precipitation kinetics curve in the isothermal phase change process of the alloy steel. This method considers that the difference in the room-temperature compressive stress is derived from precipitation of carbides. However, different structures generated by austenite transformation also cause differences in compression stress values, and precipitation also occurs during cooling from the isothermal transformation temperature to room temperature, which has an influence on experimental results. Therefore, a method for determining the carbide precipitation kinetic curve in the austenite isothermal phase transformation process by effectively separating phase transformation and precipitation and avoiding the interference of tissue difference is required to be found, so as to provide guidance for improving and optimizing heat treatment process parameters to obtain the optimal mechanical property.

Disclosure of Invention

In view of the above, the invention provides a method for determining a carbide precipitation kinetics curve based on isothermal stress and phase transition, the method is simple to operate, and the determined isothermal yield strength value can intuitively reflect the carbide precipitation strengthening effect in the isothermal process. In addition, the method is suitable for all steel grades with carbide precipitation in the austenitic isothermal phase transformation process.

In order to achieve the above object, the present invention provides a method for determining a carbide precipitation kinetics curve based on isothermal stress and phase transformation, comprising the steps of:

(1) obtaining a true stress-strain curve of the alloy steel at different isothermal times at a set temperature through a Gleeble-3800 thermal simulation testing machine, and taking a stress value at a 2% strain position as an isothermal yield strength value sigma_yDrawing σ_yDetermining carbide precipitation finishing time P according to isothermal temperature-time change relation curve_f。

(2) Measuring the phase change starting time (T) of the alloy steel at a set temperature by using a thermal expansion instrument arranged on a Gleeble-3800 thermal simulation testing machine_s) And an end time (T)_f)。

(3) According to the obtained phase change starting time T_sDrawing a change curve of isothermal yield strength increment before the phase change of the alloy steel starts at different set temperatures along with isothermal time, and determining the carbide precipitation starting time P at different isothermal temperatures_s。

(4) According to the precipitation start time P of the obtained carbide_sAnd an end time P_fDrawing alloyPrecipitation-temperature-time (PTT) curve of steel carbides.

Further, the method for determining the phase change kinetic curve in the isothermal phase change process in the step (2) has the following principle: the thermal expansion coefficients of different phases or structures in steel are from small to large: martensite < bainite < pearlite < ferrite < austenite. When the austenite phase transformation occurs in the isothermal process, the volume is inevitably expanded, so that an inflection point appears on a thermal expansion curve measured by a thermal expansion instrument, and the starting time and the ending time of the isothermal phase transformation are judged by measuring the time at the inflection point.

2. The method for determining the carbide precipitation kinetics curve during isothermal phase transformation according to claims (1) and (2), characterized in that said steps comprise in particular:

(a) the alloy steel sample is processed into a cylindrical sample with the roughness Ra less than or equal to 0.4 mu m.

(b) And (3) welding thermocouple wires in the middle of the cylindrical sample by using a thermocouple welding machine, wherein the distance between the two thermocouple wires is controlled to be about 1 mm.

(c) And connecting the metal tantalum sheet and the graphite sheet at two ends of the cylindrical sample in sequence by using a high-temperature lubricant.

(d) And (3) mounting the cylindrical sample for connecting the tantalum sheet and the graphite sheet at two ends of a fixture at a specified position in an experiment cabin of a Gleeble-3800 thermal simulation testing machine, and finely adjusting the axial displacement of the spindle to enable the chuck to just compress the cylindrical sample.

(e) Clamping the alloy sample by a quartz glass chuck of a thermal expansion instrument, and enabling the quartz glass chuck and the thermocouple wire to be positioned on a cross section of the sample; the output data line of the thermal expansion instrument is connected with the sensor interface of the thermal simulation testing machine;

(f) the other end of the thermocouple wire is connected with a T1 temperature channel of a Gleeble-3800 thermal simulation testing machine, and then the door of the experiment cabin is closed and vacuum is pumped.

(g) The set test process flow is compiled by Quizsim software carried by a Gleeble-3800 thermal simulation testing machine.

(h) And after the vacuum degree in the experiment chamber meets the requirement, sequentially starting a RUN button on an operation panel and clicking a RUN scheme on the Quizsim software to start running the set scheme for testing.

(i) And (5) after the end of one test process, changing the test process parameters, and repeating the steps (a) to (h) to carry out the next test until the test is finished.

(j) After the test is finished, the temperature, time, true strain, true stress and thermal expansion quantity values acquired by the Gleeble-3800 thermal simulation testing machine are introduced into Origin software equipped in the testing machine, and set true stress-strain curves at different isothermal temperatures and times and thermal expansion curves changing along with time are obtained, so that isothermal yield strength values and phase change starting and ending times at different isothermal temperatures are obtained.

Further, the cylindrical test piece to be processed is required to be a cylindrical test piece having a length and diameter ratio of not more than 2, for example, 6X 10mm, 10X 15mm, 8X 12mm or the like in other dimensions.

Further, the thermocouple welder voltage was set between 34-38V.

Furthermore, the position of the thermal expansion instrument clamping cylinder sample accords with the principle of 'vertical alignment, left-right equal distance'.

Further, the vacuum degree for starting the Gleeble-3800 tester to run is lower than 1.5 multiplied by 10^-1Pa。

Further, the process flow parameters of the set test are specifically as follows:

(1) heating the cylindrical sample to 1150-1280 ℃ at the speed of 1-20 ℃/s on a Gleeble-3800 thermal simulation testing machine and preserving heat for 3-10min to ensure that the sample is fully austenitized and dissolves a second phase except the N-containing compound.

(2) Cooling to 1150 ℃ at the temperature of between 10 and 100 ℃/s and preserving heat for 5 to 15s, deforming by 10 to 30 percent, cooling to 800 ℃ at the temperature of between 800 and 950 ℃ at the temperature of between 10 and 100 ℃/s and isothermal for 5 to 20s, and deforming by 10 to 30 percent. The deformation rate is 0.5-10.s^-1。

(3) The sample after two-pass deformation is respectively cooled to 550-750 ℃ at the temperature of 10-100 ℃/s, the sample is deformed by 10-30% after isothermal different time, and the deformation rate is 0.5-10s^-1The isothermal time is 5-10800 s.

Compared with the prior art, the invention can realize the following beneficial effects:

the method can effectively avoid the interference of the phase change and the phase change structure difference in the isothermal precipitation process of the alloy steel carbide on the measurement of the carbide precipitation starting point, and can reveal the interaction of the carbide precipitation process and the phase change. In addition, the method is simple to operate, the measured isothermal yield strength value can visually reflect the strength increase amount caused by carbide precipitation in the isothermal process, and a good guiding effect is provided for improving and optimizing the heat treatment process parameters of the alloy steel to obtain the optimal mechanical property.

Drawings

FIG. 1 is a flow chart of the measurement method of the present invention.

FIG. 2 is a schematic diagram of an experimental process according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of the isothermal thermal expansion curve of Ti-Mo alloy steel at 700 ℃ and the temperature-time-transformation (TTT) curve of austenite at 600-700 ℃ in the example.

FIG. 4 is a schematic diagram of isothermal compression true stress-strain curves of Ti-Mo alloy steel at different isothermal temperatures in the example.

The isothermal yield strength of the Ti-Mo alloy steel in the embodiment of FIG. 5 is a graph showing the change curve of the isothermal yield strength of the Ti-Mo alloy steel along with time and temperature.

The isothermal yield strength increment of the Ti-Mo alloy steel before phase change at different isothermal temperatures in the embodiment of FIG. 6 is a curve diagram along with isothermal time change.

FIG. 7 is a schematic diagram of carbide precipitation-temperature-time (PTT) curves in isothermal processes of Ti-Mo alloy steel in the example.

Detailed Description

The method of the present invention is further described with reference to the following examples and the accompanying drawings, but it should be noted that the examples are not to be construed as limiting the scope of the present invention.

The invention provides a method for determining a carbide precipitation kinetics curve based on isothermal stress and phase transition, which comprises the following steps:

step 1: acquiring a true stress-strain curve of the alloy steel at different isothermal times within a set temperature, and taking the stress value of the yield stress point as an isothermal yield strength value sigma_yPlotting isothermal yield strength values σ_yDetermining carbide precipitation finishing time P according to isothermal temperature-time change relation curve_f。

In one embodiment of the invention, the real stress-strain curves of the alloy steel at different isothermal times within a set temperature are obtained through a Gleeble-3800 thermal simulation testing machine.

In one embodiment of the present invention, materials that do not have a significant yield point typically all consider the stress value biased at 2% strain as the yield stress point.

Step 2: measuring the phase change starting time (T) of the alloy steel at a set temperature_s) And an end time (T)_f)。

In one embodiment of the invention, a thermal expansion curve of the alloy steel in the isothermal phase transition process is obtained by using a thermal expansion instrument equipped on a Gleeble-3800 thermal simulation testing machine, and the phase transition starting time (T) at a set temperature is obtained by measuring the time at an inflection point on the thermal expansion curve_s) And an end time (T)_f)。

And step 3: according to the obtained phase change starting time T_sDrawing a change curve of isothermal yield strength increment of the alloy steel sample before the phase change starts at different set isothermal temperatures along with isothermal time, and determining the carbide precipitation starting time P at different isothermal temperatures_s。

And 4, step 4: according to the precipitation start time P of the obtained carbide_sAnd an end time P_fAnd drawing a precipitation-time-temperature (PTT) curve of alloy steel carbide.

In one embodiment of the invention, the selected material is Ti-Mo-containing microalloyed steel, and the chemical components and the content thereof are as follows: 0.04-0.07 WT% of C, 0.2-0.3 WT% of Si, 1.5-1.8 WT% of Mn, 0.09-0.12 WT% of Ti, 0.18-0.24 WT% of Mo, 0.006 WT% of N, 0.01 WT% of P, 0.010 WT% of S, and the balance of Fe and inevitable impurities.

In one embodiment of the invention, a sample of alloy steel is cylindrical with a length to diameter ratio of no greater than 2. Such as cylindrical samples of 6X 10mm, 10X 15mm, 8X 12mm or other dimensions.

In one embodiment of the present invention, step 1 and step 2 specifically include the following steps:

(a) machining the microalloyed steel sample into a cylindrical sample with the roughness Ra of less than or equal to 0.4 mu m and the size of phi 10 multiplied by 15 mm.

(b) And adjusting the voltage of the thermocouple welding machine to 38V, welding a thermocouple wire in the middle of the cylindrical sample, and controlling the distance between the two thermocouple wires to be about 1 mm.

In one embodiment of the present invention, the thermocouple wire is a K-type thermocouple wire or an R-type thermocouple wire.

(c) And respectively connecting the metal tantalum sheet and the graphite sheet at two ends of the cylindrical sample by using a high-temperature lubricant in sequence.

(d) The cylindrical sample connected with the metal tantalum sheet and the graphite sheet is arranged at two ends of a clamp chuck in an experimental cabin, and the axial displacement of a main shaft of the test thermal simulation testing machine is finely adjusted, so that the chuck just compresses the cylindrical sample.

(e) Clamping the alloy sample by a quartz glass chuck of a thermal expansion instrument, and enabling the quartz glass chuck and the thermocouple wire to be positioned on a cross section of the sample; the output data line of the thermal expansion instrument is connected with the sensor interface of the thermal simulation testing machine;

(f) connecting the other end of the thermocouple wire with T in the thermal simulation testing machine₁The temperature channel is connected, and then the door of the experimental cabin is closed and vacuumized.

(g) The technical process of setting the test is compiled by Quizsim software carried by a Gleeble-3800 thermal simulation testing machine.

(h) The vacuum degree in the experimental chamber is reduced to 1.5 multiplied by 10^-1After Pa, a RUN operation button on an operation panel of the Gleeble thermal simulation testing machine is started in sequence, a RUN starting machine on the Quizsim software is clicked, and a set sample scheme is operated for testing.

(i) And (5) after the end of one test process, changing the test process parameters, and repeating the steps (a) to (h) to carry out the next test until the test is finished.

(j) After the test is finished, the temperature, time, true strain, true stress and thermal expansion quantity values acquired by the Gleeble-3800 thermal simulation testing machine are introduced into Origin software equipped in the testing machine, and set true stress-strain curves at different isothermal temperatures and times and thermal expansion curves changing along with time are obtained, so that isothermal yield strength values and phase change starting and ending times at different isothermal temperatures are obtained.

In the invention, the technological process parameters are set as follows:

(1) heating the alloy steel sample to 1150-1280 ℃ at the speed of 1-20 ℃/s on a Gleeble-3800 thermal simulation testing machine and preserving heat for 3-10min to ensure that the sample is fully austenitized and dissolves second phases except the N-containing compound.

(2) Cooling to 1150 ℃ at the temperature of between 10 and 100 ℃/s and preserving heat for 5 to 15s, deforming by 10 to 30 percent, cooling to 800 ℃ at the temperature of between 800 and 950 ℃ at the temperature of between 10 and 100 ℃/s and isothermal for 5 to 20s, and deforming by 10 to 30 percent. The deformation rate is 0.5-10.s^-1。

(3) The sample after two-pass deformation is respectively cooled to 550-750 ℃ at the temperature of 10-100 ℃/s, the sample is deformed by 10-30% after isothermal different time, and the deformation rate is 0.5-10s^-1The isothermal time is 5-10800 s.

Referring to fig. 2, in a possible embodiment of the present invention, the process parameters and flow of the Ti — Mo alloy steel are as follows:

(1) the samples were heated to 1200 ℃ at 10 ℃/s and incubated for 5min on a Gleeble-3800 thermal analogue tester.

(2) Cooling to 1050 deg.C at 20 deg.C/s, keeping the temperature for 10s, deforming by 20%, cooling to 900 deg.C at 20 deg.C/s, keeping the temperature for 15s, and deforming by 20%. The deformation rate was 1.0s^-1。

(3) After the two-stage deformation, the sample is cooled to 600-700 ℃ at the temperature of 30 ℃/s, the sample deforms 30% after isothermal different time, and the deformation rate is 1.0s^-1The isothermal time is 5-10800 s.

FIG. 3 is a thermal expansion curve of Ti-Mo alloy steel at 700 ℃ and an isothermal phase transition curve of Ti-Mo alloy steel at 600 ℃ and 700 ℃ measured based on the inflection point of the thermal expansion curve. The phase transition is terminated substantially within 10min by measuring the time at the inflection points (points A and B) of the thermal expansion curve during isothermal phase transition, wherein the induction period of the phase transition is longest at 625 ℃ isothermal temperature, about 33 s.

FIG. 4 is a true stress-strain curve of Ti-Mo alloy steel after isothermal temperature of 600-700 ℃ for 5-10800 s. The isothermal yield strength as a function of temperature and time as shown in FIG. 5 can be obtained by measuring the stress value at 2% strain of the true stress-strain curveAnd (c) forming curves, wherein the two arrow positions on each curve represent the start and end times of the phase change respectively. The isothermal yield strength at each isothermal temperature increased rapidly with increasing isothermal time during the phase transformation, indicating that the phase transformation promoted precipitation of carbides. After the phase transformation is finished, the isothermal time is continuously prolonged, the isothermal yield strength is continuously increased, and after the peak strength is reached, the isothermal yield strength begins to decline along with the increase of the isothermal time. It is clear that the continued increase in isothermal yield strength with increasing isothermal time after the end of transformation is due to precipitation strengthening by carbides precipitated during isothermal process. In the isothermal process, the appearance of the peak stress indicates that the strength of the steel reaches the maximum value under the coordination effect of precipitation strengthening effect generated by carbides and strength softening caused by grain growth and dislocation density reduction in the steel, so that the isothermal time for reaching the peak stress can be defined as the 'effective precipitation' end time of the carbides in the isothermal process, namely the carbide precipitation end time P_f. Notably, P_fNot representing the complete end of the carbide precipitation but the precipitation time at which the steel strength reaches a maximum, and this time P_fAs well as required for production.

FIG. 6 is a graph of isothermal yield strength increase versus time before phase change at different isothermal temperatures, and additionally, for convenience of viewing the isothermal yield strength increase versus time before isothermal phase change, the start time of phase change at each isothermal temperature is indicated by the arrow on each graph. Generally, in the isothermal process before the phase transformation, the increase of the isothermal yield strength of the steel with time is basically kept unchanged, and if the increase of the isothermal yield strength is more than 0, the precipitation of carbides is indicated and a strengthening effect is generated. Further, since the precipitation strengthening effect is in a positive correlation with the precipitation volume fraction of carbides and the precipitation volume fraction increases with time, it is considered that the carbides start to precipitate when the increase in isothermal yield strength exceeds 0, and the precipitation of the carbides is accelerated as the increase in isothermal yield strength increases in the same time. As can be seen from FIG. 6, the isothermal yield strength increase at 625 deg.C and 600 deg.C was greater than 0 within 5-10s of isothermal time, and the isothermal yield strength at 625 deg.C was 5-10s isothermalThe degree increment is larger. Therefore, it is considered that carbide precipitates were generated in 5 to 10 seconds of isothermal temperature at these two temperatures, and the carbide precipitates at 625 ℃ in an earlier time. So as to obtain the starting time P of carbide precipitation in the isothermal process_s. The time and order of carbide precipitation at isothermal temperatures of 650 deg.C, 675 deg.C and 700 deg.C can be determined by the same method.

According to the obtained carbide precipitation starting time P_sAnd effective precipitation end time P_fThe carbide precipitation-temperature-time (PTT) curve of the Ti-Mo alloy steel in the isothermal process of 600-700 ℃ is plotted, as shown in FIG. 7. It can be seen that the precipitation onset curve of the carbides is a typical "C" curve, with the fastest precipitation nose temperature at 625 deg.C for about 5-10 s. Thereafter, 600 ℃, 650 ℃, 675 ℃ and 700 ℃ were successively performed. Wherein the precipitation start time at 650 ℃, 675 ℃ and 650 ℃ is within 10-20 s.

The isothermal yield strength increment method of the method is combined with the measured isothermal phase change time, so that the interference of phase change in the isothermal precipitation process of alloy steel carbide on the measurement of the carbide precipitation starting point can be effectively avoided, and the interaction of the carbide precipitation process and the phase change can be revealed. The representation of the isothermal yield strength can more intuitively reflect the strengthening effect amount of carbide precipitation on steel in the isothermal process, systematically reflect the mutual coordination mechanism of isothermal temperature, phase change, time and carbide precipitation, and contribute to research and enrichment of the precipitation mechanism of carbide. In addition, the method is simple to operate and high in practicability.

The above examples of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.