CN112662861A - Heat treatment process after thermite welding of bainite steel rail - Google Patents
Heat treatment process after thermite welding of bainite steel rail Download PDFInfo
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Abstract
The invention provides a post-weld heat treatment process for thermite welding of a bainite steel rail, which comprises the following steps of: (1) cooling the joint obtained by thermite welding to room temperature, heating the joint for 5-10min, and keeping the temperature for 5-10 min; then, slowly cooling the joint obtained through heat preservation treatment at a cooling speed of 0.2-0.8 ℃/s until the temperature of the joint reaches below 100 ℃; (2) and (2) heating the joint obtained by the treatment in the step (1), then preserving heat, and naturally cooling to room temperature.
Description
Technical Field
The invention relates to the technical field of steel rail welding, in particular to a heat treatment process after thermite welding of a bainite steel rail.
Background
The jointless track is an important result of the track structure progress and is also the optimal choice of the track structure of the high-speed railway and the heavy haul railway at present. Since the seamless lines are laid on the Jingmen branch (Beijing) and the Zhenxi branch (Shanghai) in 1957, the mileage of the seamless lines is greatly increased after years of continuous efforts. The comprehensive technology and economic effect of the seamless line are outstanding and are proved by railway practices of various countries in the world. The seamless track can prolong the service life of the steel rail, reduce the labor and materials for maintenance and repair, reduce the energy consumption of train operation and reduce the additional cost of laying.
Rail welding is a key technology for seamless tracks. For steel rail welding, electric arc welding is adopted at first in China, thermite welding, gas pressure welding and contact welding are adopted later, and the quality of a steel rail joint is continuously improved through improvement of a welding technology. The thermite welding of steel rail is a welding mode that thermite welding agent is ignited by high-temperature match to initiate thermite reaction and fill rail gap. The main components of the thermite welding agent for the steel rail comprise aluminum powder, ferric oxide and other alloy additives according to a certain proportion. After the welding flux is ignited, aluminum powder reduces iron oxide in the thermite reaction process, so that a large amount of heat is released, molten steel is generated, and alloy additives are melted into the molten steel; the molten steel sinks to the bottom of the crucible because its density is higher than that of the alumina produced by the reaction, and the molten slag such as the alumina produced by the reaction and impurities floats to the upper part because its density is low. At present, a disposable crucible adopted by thermite welding is provided with a self-melting plug, molten steel generated by thermite reaction can melt the self-melting plug at the bottom of the crucible, is poured into a sand mold with the same outline dimension as a steel rail, and is cooled and crystallized inside the sand mold, so that two sections of steel rails are welded into a whole. The main characteristics of the thermite welding of steel rails are: 1. the equipment is simple: the thermit welding of the steel rail utilizes the chemical reaction of raw materials to release heat, the whole reaction process only needs the heat of igniting high-temperature matches, welding materials such as a crucible, a sand mold and a welding flux are needed, matched equipment such as a beading machine, a grinding machine and an air source is needed, and the device is small and portable and is particularly suitable for field flow operation. 2. Filling and welding: in the process of thermite welding of the steel rail, the thermite molten steel is filled into the gap between the steel rails to be welded without stretching the steel rail, so that the thermite welding is suitable for on-line repair of broken rails and welding of turnouts. 3. The operation flow is efficient: the thermite welding process of a single joint can be completed in 90 minutes, and the field welding can be performed simultaneously without interference. 4. The welding occupies small space: when the rail thermit welding is used for the welding and repairing welding of turnouts, the welding can be completed in a small space.
At present, the transportation of bulk and long-distance goods in China is mainly borne by freight railways, and the freight capacity of the railways directly influences the development of national economy in China. The heavy haul railway is the most effective way for improving the freight capacity and is also an important direction for railway development in China. With the development of heavy haul railways, new steel rails with better toughness, plasticity, wear resistance and fatigue resistance need to be developed. Therefore, the development of the next generation of heavy-duty steel rail with excellent comprehensive performance is imperative. Bainite steel rail is the development direction of heavy-duty steel rail with high wear resistance and high strength and toughness.
For bainite thermite welding, iron III-50 bainite thermite welding flux was developed in 90 s of the 20 th century by the academy of iron sciences, a dry die rapid preheating thermite welding process is adopted in the welding process, the weld hardness is higher than 260HB, and the dry die rapid preheating thermite welding flux is suitable for 50kg/m U71Mn and U74 pearlite steel rails and is applied to railways in China.
Chinese patent application CN 105364299 a provides a welding material for thermite welding of bainitic steel, a preparation method thereof and a process for thermite welding of bainitic steel rails using the welding material. The thermite welding process for the bainite steel rail comprises the following steps: (4) postweld heat treatment: cooling the welding head to below 200 ℃ in the air, heating the welding head to 900-1000 ℃ again, cooling the welding head to the room temperature at a speed of less than 5 ℃, and removing residues. In addition, chinese patent application CN 105414797 a provides an aluminothermic welding material of bainite steel and pearlite steel and its application in bainite steel and pearlite steel welding.
However, joints welded using existing processes are still susceptible to damage during service, and therefore, there is still a need for improvements in existing processes that provide an improved post-weld heat treatment process to further ensure the safety of service of thermite welded structures.
Disclosure of Invention
Aiming at the defects in the prior art, the inventor of the application shows that the performance of an aluminothermic welding joint can be improved and the microstructure can be improved through postweld heat treatment through experimental research on aluminothermic welding of a bainite steel rail. The bainite steel rail thermit welding joint treated by the provided postweld heat treatment process can have good service effect.
Accordingly, it is an object of the present invention to provide a post thermite process for bainite steel rails.
It is a further object of the present invention to provide the use of the above post-weld heat treatment process in thermite welding of bainitic rails.
The technical scheme for achieving the purpose of the invention is as follows.
In the analysis and research of the Bainite steel rail aluminothermic welding joint paved on the Daqin line, the damage of the joint welded by the prior art is mainly located at a position 2: a fusion zone and a heat affected zone. The crack growth direction of the head weld zone damage is perpendicular to the weld line, the occurrence of coarse lath structure in the heat affected zone is the main cause of damage, and the coarse lath structure is a high hardness zone and rapidly grows along the crystal after the crack occurs (as shown in fig. 1).
In addition, the inventor of the application further researches the damage condition of the bainite aluminum hot welding joint, and increases the sampling position through a laboratory heat treatment simulation test, the heating temperature is 900 ℃, the heating time is 12min, and then the air cooling is carried out. Each area of the aluminothermic welding head is taken for analysis, and the results show that: the high-hardness white strip-shaped structures exist in the heat affected zone, the hardness of the white strip-shaped structures is over 520HV, the white strip-shaped structures cannot be completely eliminated through normalizing, and the white strip-shaped structures are large in size and uneven in distribution along the length direction of the steel rail (as shown in figure 2).
The inventor discovers that the bainite aluminothermic welding head damage originates from a rail head fusion area after analysis and research on the damage, the crack develops in a direction perpendicular to a fusion line, a coarse lath structure and a white lath structure appear in a heat affected area are main reasons for the damage, and the lath structure are high-hardness areas and rapidly expand along crystals after the crack appears.
Based on the research, the inventor develops a large amount of experimental research to improve the existing postweld heat treatment process, and screens a large amount of key parameters related in the process, so that the welded joint with more uniform tissue, obviously improved mechanical property and obviously enhanced tread hardness and tensile strength is obtained.
Accordingly, in one aspect, the present invention provides a post-weld heat treatment process for thermite welding of bainitic steel rails, the post-weld heat treatment process comprising the steps of:
(1) cooling the joint obtained by thermite welding to room temperature, heating the joint for 5-10min, and keeping the temperature for 5-10 min; then, slowly cooling the joint obtained through heat preservation treatment at a cooling speed of 0.2-0.8 ℃/s until the temperature of the joint reaches below 100 ℃;
(2) tempering the joint obtained by the treatment in the step (1), then preserving heat, and naturally cooling to room temperature.
Preferably, in the step (1), the heating temperature is 900-; more preferably 950-;
preferably, in step (1), the heating time is 10 min;
preferably, in the step (1), the incubation time is 10 min;
preferably, in the step (1), the cooling speed is 0.2-0.6 ℃/s, more preferably 0.2-0.4 ℃/s;
preferably, in the step (1), the slow cooling treatment is performed by using a heat preservation device, and further preferably, the slow cooling treatment is performed by using a heat preservation cover filled with high-temperature-resistant rock wool;
preferably, in the step (2), the temperature of the tempering is 350-; more preferably 350 ℃;
preferably, in the step (2), the tempering time is 5-15 min; more preferably 10 min;
preferably, in step (2), the incubation time is 5-15min, more preferably 15 min.
In some embodiments of the present invention, before step (1), thermite welding of the bainitic steel rail is further performed using the following process parameters:
the gap between two steel rails to be welded before welding is 26-30 mm, the pressure of preheated propane is 0.08-0.1 MPa, the pressure of oxygen is 0.25-0.3 MPa, the flame core length of preheated flame is 20-25 mm, the height of a preheater is 47-53 mm, and the preheating time is 5-7 min; removing the mold at 6min30s after the aluminothermic molten steel is poured, and pushing the knurl at 8min30 s; cooling the joint to room temperature;
in another aspect, the present invention also provides a joint treated by the above-described post-weld heat treatment process, the joint having improved microstructure, mechanical properties, tread hardness, and tensile strength.
Preferably, the tread hardness of the joint is greater than 300 HB; the tensile strength is greater than 900MPa, further preferably greater than 940 MPa.
In a further aspect, the invention provides the use of the above-described post-weld heat treatment process in thermite welding of bainitic rails.
Aiming at the problem of the thermite welding heat treatment process of the bainite steel rail, the inventor of the application carries out research and analysis, improves the existing heat treatment process through a large number of experiments, and provides a postweld heat treatment process of heating slow cooling and tempering, so that the microstructures of a fusion area and a heat affected zone of the thermite welding joint are more stable and uniform, the internal stress of the joint is reduced, and the service safety of the thermite welding joint is ensured.
Drawings
Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:
FIG. 1: wherein, the figure (a) is a schematic diagram of the damage position of the bainite steel rail aluminum hot welding joint; the figure (b) shows the appearance of the flaw of the damaged joint in the fusion area, wherein the left side is a welding line, the right side is a steel rail base material, and a white oblique line is a fusion line; FIG. (c) shows the microstructure of the crack origin in the fusion zone.
FIG. 2: showing the damage of a heat affected zone of an aluminothermic welding joint of a bainite steel rail, wherein a diagram (a) shows the strip-shaped tissue splicing of the heat affected zone, wherein a welding seam is arranged on the right side, and the direction of a steel rail base material is arranged on the left side; FIG. (b) shows a heat-affected zone banding; and (c) shows high magnification stripe-like organization.
FIG. 3: the aluminothermic weld joint CCT curve is shown.
FIG. 4: the microstructure of the bainitic aluminium hot welded joint is shown at different cooling rates.
FIG. 5: the microstructure of the joint obtained in step (3) with different tempering temperatures is shown.
FIG. 6: showing the microstructure of the various regions of the joint treated by the post-weld heat treatment process of the present invention; in the drawing, (a) shows a microstructure 500 x of a weld, in the drawing, (b) shows a microstructure 500 x of a weld zone, in the drawing, (c) shows a microstructure 500 x of a superheated zone, in the drawing, (d) shows a microstructure 500 x of a heat affected zone, and in the drawing, (e) shows a microstructure 500 x of a base material.
Detailed Description
The present invention is described in further detail below with reference to specific embodiments, which are given for the purpose of illustration only and are not intended to limit the scope of the invention.
In the following examples, the Bainite steel rail thermite welding process uses a flux prepared by alloying from the institute of iron and technology, the formula range of the flux is shown in Table 1,
TABLE 1 Bainite Steel Rail thermite welding agent alloy element content Range
In the following examples, the thermite welding described in step (1) was carried out by the following steps:
1. preparation work: and (5) checking the end condition of the steel rail, and cleaning the end face of the steel rail. And adjusting the size of the reserved rail gap to 26-30 mm of the rail bottom. And adjusting the arching amount, wherein the arching amount of each end is 1.5-2.0 mm.
2. Clamping and sand mold sealing: and (3) fixing the sand mould at the end face of the steel rail to be welded by using a sand mould clamp, checking whether a sand mould base plate is aligned with the center of the welding line, and clamping the sand mould clamp after ensuring no deviation. And filling a box sealing material into the groove on the outer side of the sand mold, and sealing the joint of the steel rail and the sand mold by using the box sealing material again.
3. Preparation of crucible and flux: confirming whether the type of the welding flux is matched with the type of the steel rail, slightly rotating the welding flux, pouring the welding flux into a crucible, preparing a high-temperature match for waiting welding, and covering a crucible cover.
4. Preheating: the distance between the bottom of a heating nozzle of the preheater and the top surface of the rail is adjusted to 47-53 mm, and meanwhile, the central line of a base of the preheater is matched with the central line of the rail, so that the preheating nozzle is centered front and back, left and right and vertically downward in a welding line. Adjusting the gas pressure to meet the process requirement: the propane pressure is 0.08-0.1 MPa, the oxygen pressure is 0.25-0.3 MPa, the preheater is ignited, the flame is adjusted, the flame core length is 20-25 mm, and the preheating time is 5-7 min. Preheating the end face of the steel rail by using the oxygen-propane mixed gas, taking out the preheater when the brightness of the whole end face of the steel rail to be welded is observed by naked eyes (700-900 ℃), and stopping heating.
5. Igniting and pouring: and after preheating is finished, removing the preheating device. A shunt plug is placed. And placing the crucible filled with the welding flux above the sand mold, and igniting the high-temperature matches to ignite the welding flux. After the flux is ignited, the crucible cover is covered. After the flux reaction is finished, molten steel is automatically injected into the cavity, and welding slag formed by the flux reaction flows into the slag receiving hopper.
6. Opening the box and pushing the knurls: and 6min30s after the pouring is finished, dismantling the sand mold clamp, removing the box sealing materials on two sides of the welding line, removing the redundant sand mold of the railhead, and pushing the built-up edge 8min30s after the pouring is finished.
7. Polishing and cleaning: after the push-up is finished, hot polishing can be immediately carried out, cold polishing is carried out after the temperature of the joint is cooled to the ambient temperature, and the rail base angle and the joint surface are cleaned, so that the joint capable of being subjected to postweld heat treatment is obtained.
Example 1
A Gleeble-1500D thermal simulation testing machine is adopted, the transformation temperature of steel is determined by the expansion or contraction of the volume of the steel during phase change, a round bar sample is taken from a welding joint, the sample is heated by the thermal simulation testing machine and cooled at a certain constant cooling speed, the temperature-expansion quantity change curve of the sample is measured, the characteristic phase change temperature point is determined by a tangent method, and a 'temperature-time (logarithm)' curve is drawn by a computer to obtain a CCT curve. Cooling a joint obtained by thermite welding to room temperature, heating a joint sample by built-in equipment of a thermal simulator at 980 ℃ for 5min, and keeping the temperature for 10 min; the transition curves obtained after successive cooling with different cooling rates are shown in fig. 3.
The microstructures of the joints obtained at different cooling rates were observed at 8 ℃/s, 4 ℃/s, 2 ℃/s, 1.5 ℃/s, 1 ℃/s, 0.8 ℃/s, 0.6 ℃/s, 0.4 ℃/s, 0.2 ℃/s, 0.1 ℃/s and 0.05 ℃/s, respectively, and the microstructures of the samples obtained at different cooling rates are shown in fig. 4.
Example 2
The microstructure of the samples obtained in example 1 at different cooling rates was observed at room temperature using a DM15000M metallographic microscope. Sampling is carried out from samples obtained at different cooling speeds, and the microscopic structure of each sample is observed after pre-grinding, polishing and eroding treatment. Each sample is tested by an FM-7 automatic microhardness meter, after microscopic structures are observed, microhardness is tested by an indentation method, the load is 0.2kg, and the microhardness is determined by measuring the size of an indentation. The results are shown in Table 2.
TABLE 2 microstructural analysis results and hardness test results of joint samples obtained at different cooling rates
As can be seen from Table 2, the welded joint structure is martensite at 8 ℃/s and 4 ℃/s, and the microhardness is above 500 HV; the welding joint structure is M + B under the condition of 2-1 ℃/s, and the microstructure hardness is 481-436 HV; under the condition of 0.8 ℃/s to 0.2 ℃/s, the welding joint structure is bainite, and the microhardness is 403 to 356 HV; and under the cooling condition of 0.1 ℃/s to 0.05 ℃/s, the microstructure of the welding joint is B + F.
Example 3:
1. cooling the joint obtained by thermite welding to room temperature, heating the joint to 900-1000 ℃, and preserving heat for 10 min; and then carrying out slow cooling treatment on the joint obtained by heat preservation treatment at a cooling speed of 0.2-0.8 ℃/s until the temperature of the joint reaches below 100 ℃, and then carrying out tread hardness test.
According to TB/T1632.3-2019, tread hardness test is carried out on a welded joint at room temperature, the welded joint is sawn along the longitudinal direction of a steel rail, the top surface of the rail is ground and polished, the weld hardness is detected at the transverse position of the center of a weld joint on the top surface of the rail, the Brinell hardness of 3 points is detected, the average hardness value is calculated and recorded as the tread hardness of the weld joint, and the test method of the Brinell hardness is carried out according to GB/T231.1-2009.
The results are shown in Table 3, where "no heat treatment" means that the joint naturally cooled to room temperature obtained by thermite welding was not subjected to the heating and slow cooling treatment.
TABLE 3 Tread hardness before and after heating and Slow Cooling treatment of Bainite aluminothermic welding joint sample (HBW10/3000)
| State of heat treatment | Test point 1 | Test point 2 | Test point 3 | Mean value of |
| Without heating and slowly cooling | 335 | 331 | 317 | 328 |
| By heating and slow cooling treatment (step 1) | 345 | 349 | 349 | 348 |
As can be seen from Table 3, the tread hardness of the joint which was not subjected to the heat and slow cooling treatment was 328HB, and the tread hardness of the joint which was subjected to the heat and slow cooling treatment was increased to 348HB and 20 HB. It can be seen that after the heating and slow cooling treatment, the tread hardness of the joint can be obviously improved.
Example 4:
the joint of example 3 was tested for tensile strength at room temperature with reference to TB/T1632.3-2019, the welded joint was sawn along the rail lengthwise, 9 tensile specimens were sampled with a diameter d of 10mm and l of 50mm, the tensile strength of the 9 specimens was measured and the average value was calculated and recorded as the tensile strength of the joint, and the tensile strength was tested according to the method specified in GB/T228.1-2010. The results are shown in Table 4.
TABLE 4 tensile strength of bainite aluminothermic welding joint samples before and after heat treatment
As can be seen from Table 4, the bainite aluminothermic joint meets the standard requirements before and after heating and slow cooling treatment, the tensile strength of the aluminothermic joint which is not subjected to the heating and slow cooling treatment is 801MPa, and the tensile strength of the aluminothermic joint which is subjected to the heating and slow cooling treatment is 853MPa, which is improved by 52 MPa.
From examples 1 to 4, it can be seen that the post-weld heat treatment process of the present invention employs a "heating slow cooling (step 1)" treatment method, wherein a cooling rate of 0.2 to 0.8 ℃/s is employed in the slow cooling process, so that the microstructure of the bainitic aluminum hot-welded joint is composed of carbide-free bainite and granular bainite, and no residual austenite or ferrite is found. By adopting the processing mode of heating and slow cooling, the structure of the bainite aluminum hot welding joint can be obviously more uniform, the effect of removing the residual austenite structure is obvious, and the effect of homogenizing the structure is realized by the processing mode of heating and slow cooling (step 1). The optimization of the structure also can obviously improve the mechanical property, and the uniformity of the joint structure greatly influences the tread hardness and the tensile strength of the joint.
Example 5:
1. cooling the joint obtained by thermite welding to room temperature, heating the joint to 900-1000 ℃, and preserving heat for 10 min; then, slowly cooling the joint obtained through heat preservation treatment at a cooling speed of 0.2-0.8 ℃/s until the temperature of the joint reaches below 100 ℃;
2. and (3) tempering the joint obtained in the step (1), wherein different tempering temperatures are adopted for tempering treatment, the joint is heated to different temperatures by using a muffle furnace, the temperature is kept, and then the joint is naturally cooled to room temperature. The change of the microstructure after the tempering treatment was observed, wherein the temperature of the tempering and the time for which the tempering was maintained were as shown in Table 5. The microstructures of the different samples were observed and compared, and the results are shown in FIG. 5.
TABLE 5 temper test Process
| Sample number | Temperature of tempering | Time for tempering and |
| F100 | ||
| 100℃ | 15min | |
| F150 | 150 | 15min |
| F200 | ||
| 200℃ | 15min | |
| F250 | 250 | 15min |
| F300 | ||
| 300℃ | 15min | |
| F350 | 350 | 15min |
| F400 | ||
| 400℃ | 15min | |
| F450 | 450 | 15min |
| F500 | ||
| 500℃ | 15min | |
| F550 | 550 | 15min |
| F600 | ||
| 600℃ | 15min | |
| F650 | 650 | 15min |
| F700 | ||
| 700℃ | 15min | |
| F | Untreated | Untreated |
As can be seen from Table 5, different tempering temperatures have different effects on the microstructure of the steel rail, tempering at the temperature below 400 ℃ does not show significant change of the microstructure, black granular precipitates can appear in the crystal grains when tempering is carried out at the temperature of 450-600 ℃, and the microstructure changes when tempering is carried out at the temperature of 600-700 ℃.
As can be seen from the graphs in FIGS. 5 and 6, the structures of a joint welding line, a fusion area and a heat affected zone are observed by adopting the tempering temperature of 350-400 ℃ and the tempering heat preservation time of 15min, the abnormal structures of all areas of the joint are not found, the joint consists of carbide-free bainite and granular bainite, the fusion area is bainite, and the heat affected zone and a steel rail base material are a bainite-martensite complex phase structure.
Therefore, the addition of the tempering treatment can stabilize the lath tissue and the strip-shaped tissue, reduce the internal stress of the joint, improve the comprehensive mechanical property, and expect that the tempering treatment has certain influence on the hardness and the tensile strength of the tread of the welding seam.
Example 6:
the tread hardness of the samples obtained at the tempering temperatures of 350 ℃ and 400 ℃ was determined on the basis of the treatment of example 6, using the experimental method described in example 3. The results are shown in Table 6.
TABLE 6 Tread hardness of Bainite Al-heat welded joint samples after different treatments (HBW10/3000)
| State of heat treatment | Test point 1 | Test point 2 | Test point 3 | Mean value of |
| Without heating and slowly cooling | 335 | 331 | 317 | 328 |
| Heating and slowly cooling, and not tempering | 345 | 349 | 349 | 348 |
| Heating slow cooling and tempering (350 ℃ C.) | 339 | 342 | 336 | 339 |
| Heating slow cooling and tempering (400 degree) | 336 | 336 | 334 | 335 |
The hardness of the joint tread which is not subjected to heating and slow cooling treatment is 328HB, the hardness of the joint tread is increased to 348HB after the heating and slow cooling treatment, the hardness of the joint tread is increased by 20HB, and the hardness of the welding joint tread is reduced to 339HB and reduced by 9HB after the welding joint is tempered at 350 ℃. After tempering at 400 ℃, the tread hardness of the welding joint is reduced to 335HB and 13 HB.
Example 7:
the tensile strength of the samples obtained at the tempering temperatures of 350 ℃ and 400 ℃ was determined on the basis of the treatment of example 6, using the experimental method described in example 3. The results are shown in Table 7.
TABLE 7 tensile Strength of Bainite Al-heat welded joint samples after different treatments
As can be seen from Table 7, the bainite aluminothermic welding joint meets the standard requirements before and after heat treatment, the tensile strength of the aluminothermic welding joint without heat treatment is 801MPa, and the tensile strength of the aluminothermic welding joint after heating and slow cooling treatment is 853MPa, which is improved by 52 MPa; the tensile strength of the aluminothermic welding joint after the tempering treatment at 350 ℃ is 941MPa, and is increased by 88 MPa. The tensile strength of the aluminothermic welding joint after the tempering treatment at 400 ℃ is 929MPa, and is improved by 76 MPa.
Claims (9)
1. A bainite steel rail thermite welding post-weld heat treatment process comprises the following steps:
(1) cooling the joint obtained by thermite welding to room temperature, heating the joint for 5-10min, and keeping the temperature for 5-10 min; then, slowly cooling the joint obtained through heat preservation treatment at a cooling speed of 0.2-0.8 ℃/s until the temperature of the joint reaches below 100 ℃;
(2) tempering the joint obtained by the treatment in the step (1), then preserving heat, and naturally cooling to room temperature.
2. The post weld heat treatment process according to claim 1, wherein, in step (1), the heating temperature is 900-1000 ℃; preferably 950-;
preferably, in step (1), the heating time is 10 min;
preferably, in step (1), the incubation time is 10 min.
3. The post-weld heat treatment process according to claim 1 or 2, wherein, in step (1), the cooling rate is 0.2-0.6 ℃/s, preferably 0.2-0.4 ℃/s.
4. The postweld heat treatment process according to any one of claims 1 to 3, wherein, in step (1), the slow cooling treatment is performed using a heat-insulating device, preferably, a heat-insulating cover filled with high-temperature-resistant rock wool inside.
5. The post weld heat treatment process according to any one of claims 1 to 4, wherein, in step (2), the tempering temperature is 350-400 ℃; preferably 350 ℃;
preferably, in the step (2), the tempering time is 5-15 min; more preferably 10 min.
6. The post weld heat treatment process according to any one of claims 1 to 5, wherein in step (2) the holding time is 5-15min, preferably 15 min.
7. A joint treated by the post weld heat treatment process of any one of claims 1-6, the joint having improved microstructure, mechanical properties, tread hardness, and tensile strength.
8. The joint of claim 7, wherein the joint has a tread hardness of greater than 300 HB; the tensile strength is greater than 900MPa, and more preferably the tensile strength is greater than 940 MPa.
9. Use of the post-weld heat treatment process according to any one of claims 1 to 6 in thermite welding of bainitic rails.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115121907A (en) * | 2022-07-26 | 2022-09-30 | 南京工程学院 | Method for improving austenite content in duplex stainless steel weld joint |
| CN115404333A (en) * | 2022-08-01 | 2022-11-29 | 包头钢铁（集团）有限责任公司 | Heat treatment process for high-strength and high-toughness bainite steel rail thermite welding joint for heavy haul railway |
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| CN115121907A (en) * | 2022-07-26 | 2022-09-30 | 南京工程学院 | Method for improving austenite content in duplex stainless steel weld joint |
| CN115121907B (en) * | 2022-07-26 | 2023-12-22 | 南京工程学院 | Method for improving austenite content in duplex stainless steel welding line |
| CN115404333A (en) * | 2022-08-01 | 2022-11-29 | 包头钢铁（集团）有限责任公司 | Heat treatment process for high-strength and high-toughness bainite steel rail thermite welding joint for heavy haul railway |
| CN115404333B (en) * | 2022-08-01 | 2024-04-30 | 包头钢铁（集团）有限责任公司 | High-strength and high-toughness bainitic steel rail aluminum thermal welding head heat treatment process for heavy haul railway |
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