CN111534681A - Heat treatment method for steel welding seam for 700 MPa-grade automobile torsion beam - Google Patents
Heat treatment method for steel welding seam for 700 MPa-grade automobile torsion beam Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
- C21D9/505—Cooling thereof
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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
- C21D1/06—Surface hardening
- C21D1/09—Surface hardening by direct application of electrical or wave energy; by particle radiation
- C21D1/10—Surface hardening by direct application of electrical or wave energy; by particle radiation by electric induction
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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
- C21D1/78—Combined heat-treatments not provided for above
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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
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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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
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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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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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/004—Dispersions; Precipitations
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
Abstract
The invention discloses a heat treatment method for a steel welding seam of a 700 MPa-grade automobile torsion beam, which comprises the following steps of welding a steel plate into a steel pipe with a welding seam; and carrying out heat treatment on the steel pipe in an area range with the welding seam distance of d by taking the welding seam as a symmetry axis, wherein the heat treatment comprises heating, primary heat preservation, primary cooling, secondary heat preservation and secondary cooling in sequence, the primary cooling is air cooling, the air cooling rate is 10-20 ℃/s, the air cooling finishing temperature is 480-600 ℃, the d is 3-5 times of the width of the welding seam, and the width of the welding seam is 1-2 mm. The local heat treatment is carried out on the welding seam of the steel pipe and the area near the welding seam, so that the formability of the steel pipe with the welding seam is improved, the problem of welding seam cracking is solved, and the fatigue performance of the torsion beam is improved.
Description
Technical Field
The invention belongs to the technical field of metal heat treatment, and particularly relates to a heat treatment method for a steel weld joint for a 700 MPa-grade automobile torsion beam.
Background
The production of the automobile torsion beam requires that a plate is welded and manufactured into a pipe, temperature gradients are generated at positions of the pipe and different distances from a welding seam in the rapid heating process of high-frequency induction welding and the rapid cooling process after welding, and welding residual stress is generated inside the pipe after the pipe is cooled to room temperature; after the welding line is cooled to room temperature, a central fusion line of the welding line is easy to form a coarse widmannstatten structure, and a heat affected zone of the welding line is easy to form non-equilibrium structures such as martensite and the like to generate structure stress.
At present, most of welded pipes for automobile torsion beams are subjected to integral high-temperature tempering after being subjected to stamping forming to eliminate weld stress and stamping residual stress, but the automobile torsion beams made of the welded pipes subjected to high-temperature tempering are prone to cracking, and the fatigue life is difficult to effectively prolong.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a heat treatment method for a steel weld joint of a 700 MPa-grade automobile torsion beam, which aims to solve the problem that the fatigue life of the finished automobile torsion beam is low because the manufactured automobile torsion beam is easy to crack after the structural stress is eliminated by adopting integral high-temperature tempering.
The invention realizes the purpose through the following technical scheme:
the invention provides a heat treatment method of a steel welding seam for a 700 MPa-grade automobile torsion beam, which comprises the following steps,
welding the steel plate into a steel pipe with a welding seam;
and carrying out heat treatment on the steel pipe in an area range with the welding seam as a symmetry axis and the welding seam distance as d, wherein the heat treatment comprises heating, primary heat preservation, primary cooling, secondary heat preservation and secondary cooling in sequence, the primary cooling is air cooling, the air cooling rate is 10-20 ℃/s, the air cooling finishing temperature is 480-600 ℃, the d is 3-5 times of the width of the welding seam, and the width of the welding seam is 1-2 mm.
Further, the welding adopts high-frequency welding, and the heating and the primary heat preservation are carried out by adopting a medium-frequency induction device.
Further, the primary heat preservation temperature is 790-820 ℃, the primary heat preservation time is 15-30 s, and the secondary heat preservation time is 20-40 s.
Further, the secondary cooling is air cooling, and the air cooling finishing temperature is 15-45 ℃.
Further, the secondary cooling is air cooling and water cooling in sequence, the air cooling time is 1-2 min, and the air cooling finishing temperature is 200-300 ℃; the water cooling rate is 30-40 ℃/s, and the water cooling finishing temperature is 15-45 ℃.
Further, after the heat treatment is finished, the metallographic structure of the central fusion line of the welding line is ferrite and granular bainite, the volume percentage of the ferrite is 20-30%, and the volume percentage of the granular bainite is 70-80%.
Further, after the heat treatment is finished, the metallographic structure of the heat affected zone of the weld joint is ferrite and granular bainite, the volume percentage of the ferrite is 10-20%, and the volume percentage of the granular bainite is 80-90%.
Furthermore, the metallographic structure of the steel plate is granular bainite, and the volume percentage of the granular bainite is not less than 95%.
Further, the thickness of the steel plate is 2-5 mm.
Further, the steel plate comprises the following chemical components in percentage by mass: c: 0.10 to 0.20%, Si: 0.05-0.20%, Mn: 0.8-2.0%, P is less than or equal to 0.02%, S is less than or equal to 0.009%, Nb is less than or equal to 0.08%, Ti is less than or equal to 0.1%, Mo is less than or equal to 0.3%, Al is less than or equal to 0.05%, and the balance is Fe and inevitable impurities.
The beneficial effects of the invention at least comprise:
the invention provides a heat treatment method for a steel welding seam of a 700 MPa-grade automobile torsion beam, which comprises the following steps of welding a steel plate into a steel pipe with a welding seam; and carrying out heat treatment on the steel pipe in an area range with the welding seam as a symmetry axis and the welding seam distance as d, wherein the heat treatment comprises heating, primary heat preservation, primary cooling, secondary heat preservation and secondary cooling in sequence, the primary cooling is air cooling, the air cooling rate is 10-20 ℃/s, the air cooling finishing temperature is 480-600 ℃, the d is 3-5 times of the width of the welding seam, and the width of the welding seam is 1-2 mm. The weld seam of the steel pipe and the area near the weld seam are locally heated to austenitize the weld seam, and because the local heating of the weld seam is fast, the temperature of the weld seam in the wall thickness direction is uniform, the austenitized crystal grains are fine and uniform, and the whole weld seam area can obtain uniform fine crystal structures after being cooled. In the primary cooling process, by controlling the cooling rate of the welding seam and the adjacent area, the welding seam is prevented from generating pearlite transformation, and the supercooled austenite is controlled to generate bainite transformation, so that a large amount of granular bainite is obtained, the structures of the welding seam and the adjacent area tend to the granular bainite structure of the steel plate, and the hardness is close to that of the steel plate. Therefore, the fine grain structure of the welding seam and the nearby area and the base metal structure tend to be uniform, so that the formability of the steel pipe with the welding seam is improved, the problem of welding seam cracking is solved, and the fatigue performance of the torsion beam is improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a metallographic structure of a weld zone before heat treatment of a welded steel pipe according to an embodiment of the present invention;
FIG. 2 shows a metallographic structure of a base material of a welded steel pipe according to an embodiment of the present invention;
FIG. 3 shows a metallographic structure of a weld zone after heat treatment of a welded steel pipe according to an embodiment of the present invention;
FIG. 4 is a metallographic structure of a base metal after heat treatment of a welded steel pipe according to an embodiment of the present invention;
FIG. 5 is a schematic view of a horizontal closed flattening test of a weld;
FIG. 6 is a schematic view of a vertical closed crush test of a weld;
FIG. 7 is a schematic view of a 45 closed flattening test of a weld;
FIG. 8 is a schematic diagram of hardness testing numbers;
FIG. 9 is a graph showing hardness detection of a weld and a region in the vicinity of the weld before and after heat treatment in example 1;
FIG. 10 is a graph showing hardness detection of a weld and a region in the vicinity of the weld after heat treatment in examples 1 to 5 and comparative example 1;
FIG. 11 is a metallographic structure of a weld after heat treatment in comparative example 1;
FIG. 12 shows a metallographic structure of a base material after heat treatment in comparative example 1.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
In order to solve the technical problems, the technical scheme in the embodiment of the invention has the following general idea:
the embodiment of the invention provides a heat treatment method for a steel weld joint for a 700 MPa-grade automobile torsion beam, which comprises the following steps,
welding the steel plate into a steel pipe with a welding seam;
and carrying out heat treatment on the steel pipe in an area range with the welding seam distance of d by taking the welding seam as a symmetry axis, wherein the heat treatment comprises heating, primary heat preservation, primary cooling, secondary heat preservation and secondary cooling in sequence, the primary cooling is air cooling, the air cooling rate is 10-20 ℃/s, the air cooling finishing temperature is 480-600 ℃, the d is 3-5 times of the width of the welding seam, and the width of the welding seam is 1-2 mm.
The weld seam of the steel pipe and the area near the weld seam are locally heated to austenitize the weld seam, and because the local heating of the weld seam is fast, the temperature of the weld seam in the wall thickness direction is uniform, the austenitized crystal grains are fine and uniform, and the whole weld seam area can obtain uniform fine crystal structures after being cooled. In the primary cooling process, by controlling the cooling rate of the welding seam and the adjacent area, the welding seam is prevented from generating pearlite transformation, and the supercooled austenite is controlled to generate bainite transformation, so that a large amount of granular bainite is obtained, the structures of the welding seam and the adjacent area tend to the granular bainite structure of the steel plate, and the hardness is close to that of the steel plate. Therefore, the fine grain structure of the welding seam and the nearby area and the base metal structure tend to be uniform, so that the formability of the steel pipe with the welding seam is improved, the problem of welding seam cracking is solved, and the fatigue performance of the torsion beam is improved. In the present application, the structure of the weld zone is shown in fig. 1, and the metallographic structure of the base material of the welded steel pipe is shown in fig. 2.
Because only the welding seam and the area near the welding seam are heated, the heating area is smaller, the heating power required by the heat treatment of the whole steel pipe is smaller than that of the traditional steel pipe, and the heat treatment cost of the welding seam is lower.
Further, the welding adopts high-frequency welding, and the heating and the heat preservation are carried out by adopting a medium-frequency induction device.
The skin effect and the proximity effect of high-frequency welding are utilized to quickly heat the surface layer metal at the position to be welded of a weldment to realize welding, and the high-frequency welding has the advantages of high welding speed and high production efficiency. And (3) adopting medium-frequency induction heating (the depth of a heating layer is 2-8 mm, and the requirement of the wall thickness of a welded pipe is met) to partially austenitize a weld joint tissue and control the tissue transformation by matching with a proper cooling process, so that the optimization of the weld joint region tissue is realized.
Further, the primary heat preservation temperature is 790-820 ℃, and the primary heat preservation time is 15-30 s. The welding seam and the area near the welding seam are heated and insulated for a period of time, so that the complete austenitization of the welding seam and the area near the welding seam can be promoted, and the uniform distribution of alloy elements in the austenite is promoted. The heat preservation temperature is too high, the heat preservation time is too long, the cost is high, and the efficiency is low; the heat preservation temperature is low, the heat preservation time is too short, and complete austenitization cannot be realized.
Further, the secondary heat preservation time is 20-40 s. The steel pipe is cooled by air to a temperature above the bainite transformation temperature range and is properly kept for a period of time, so that carbide in undercooled austenite can be promoted to be separated out, and the subsequent bainite transformation is accelerated.
Further, the secondary cooling is air cooling, and the air cooling finishing temperature is 15-45 ℃. And air cooling to room temperature, on one hand, the structure transformation of granular bainite is promoted, and on the other hand, the deformation of the welded pipe caused by thermal stress generated by high-temperature rapid cooling is prevented.
Further, the secondary cooling is air cooling and water cooling in sequence, the air cooling time is 1-2 min, and the air cooling finishing temperature is 200-300 ℃; the water cooling rate is 30-40 ℃/s, and the water cooling finishing temperature is 15-45 ℃. After cooling to 200-300 ℃, water cooling is carried out, so that the phenomenon that the welded pipe deforms due to thermal stress caused by rapid cooling can be avoided, and the production efficiency is improved.
Further, after the heat treatment is finished, the metallographic structure of the central fusion line of the welding line is ferrite and granular bainite, the volume percentage of the ferrite is 20-30%, and the volume percentage of the granular bainite is 70-80%.
After two-stage cooling, the weld joint center fusion line obtains a large amount of granular bainite structures and a small amount of ferrite structures which are very close to the granular bainite structures of the base material, so that the weld joint area has the performance close to that of the base material, the fracture is not easy to occur in the deformation process, and the fatigue performance of the torsion beam is improved.
Further, after the heat treatment is finished, the metallographic structure of the heat affected zone of the weld joint is ferrite and granular bainite, the volume percentage of the ferrite is 10-20%, and the volume percentage of the granular bainite is 80-90%.
After two-stage cooling, a large amount of granular bainite structures and a small amount of ferrite structures are obtained in a heat affected zone of a welding seam, and the granular bainite structures are very close to those of the granular bainite structures of the base material, so that the welding seam area has performance close to that of the base material, the torsion beam is not easy to crack in the deformation process, and the fatigue performance of the torsion beam is improved. The heat affected zone is used as a transition area between a weld joint central fusion line and a base material, and the volume percentage of granular bainite tissues of the heat affected zone is between that of the weld joint central fusion line and that of the base material, so that the torsion beam is not easy to crack.
Furthermore, the metallographic structure of the steel plate is granular bainite, and the volume percentage of the granular bainite is not less than 95%.
Further, the thickness of the steel plate is 2-5 mm.
Further, the steel plate comprises the following chemical components in percentage by mass: c: 0.10 to 0.20%, Si: 0.05-0.20%, Mn: 0.8-2.0%, P is less than or equal to 0.02%, S is less than or equal to 0.009%, Nb is less than or equal to 0.08%, Ti is less than or equal to 0.1%, Mo is less than or equal to 0.3%, Al is less than or equal to 0.05%, and the balance is Fe and inevitable impurities.
The invention provides a heat treatment method for a steel welding seam of a 700 MPa-grade automobile torsion beam, which comprises the steps of welding a steel plate into a steel pipe through high-frequency induction welding, rapidly heating the welding seam and a region near the welding seam to a heat treatment temperature by using a medium-frequency induction heating device, and performing controlled cooling through a two-stage cooling mode after heat preservation to obtain a large amount of granular bainite structures. The structure and the hardness of the welding seam area tend to be consistent with those of the parent metal, and the micro-hardness of the welding seam is close to that of the parent metal, so that the welding seam shows excellent coordinated deformation capability, and the finished torsion beam has longer fatigue life. The method eliminates the nonequilibrium hardening structure and the welding residual stress of the welding seam heat affected zone through the medium-frequency induction heat treatment, and solves the problem of welding seam cracking in the process of producing the torsion beam by stamping the welded pipe. According to the method, the weld joint stress is eliminated by carrying out local heat treatment on the weld joint and the nearby area, and compared with the heat treatment of the whole steel pipe, the heating cost is low.
The technical solution of the present application will be further described with reference to specific examples.
TABLE 1
Example 1
Example 1 provides a heat treatment method for a 700MPa grade steel weld for an automotive torsion beam, the welded steel pipe is a 700MPa grade high frequency welded pipe, the wall thickness of the steel pipe is 2mm, the width of the weld is 2mm, the chemical components of the steel pipe are shown in table 1, and the balance is Fe and inevitable impurities. Heating to 800 ℃ within a region range which takes a welding line as a symmetry axis and is 8mm away from the welding line by adopting a medium-frequency induction heating pair, preserving heat for 20s for the first time, controlling the cooling speed to 15 ℃/s, cooling to 580 ℃ by air, preserving heat for 25s for the second time, and cooling to room temperature by air.
Observing before heat treatment, wherein the structure of a weld line center fusion line is a ferrite and lath bainite structure; the weld heat affected zone is a martensite + lath bainite structure; the matrix structure is a granular bainite structure. The weld structure is shown in FIG. 1, and the base material structure is shown in FIG. 2.
Observation after heat treatment: the weld seam center fusion line is composed of ferrite with the volume percentage of about 30% and granular bainite tissue with the volume percentage of about 70%; the weld heat affected zone is granular bainite with volume percentage of about 90 percent and ferrite with volume percentage of about 10 percent, and carbide is distributed; the matrix structure is a granular bainite structure. The weld structure is shown in FIG. 3, and the base material structure is shown in FIG. 4.
After the steel pipe is welded through heat treatment in the embodiment 1 of the invention, the welding seams are respectively placed on a horizontal plane passing through the axis, a vertical plane passing through the axis and 3 directions (shown in figures 5-7) at 45 degrees for a closed flattening test, no crack occurs at the welding seams, and the fatigue life of the torsion beam is 39 ten thousand times.
Example 2
Example 2 provides a heat treatment method for a 700MPa grade steel weld for an automotive torsion beam, the welded steel pipe is a 700MPa grade high frequency welded pipe, the wall thickness of the steel pipe is 3mm, the width of the weld is 1.5mm, the chemical components of the steel pipe are shown in table 1, and the balance is Fe and inevitable impurities. Heating to 820 ℃ within a region range which takes a welding line as a symmetry axis and is 6mm away from the welding line by adopting a medium-frequency induction heating pair, carrying out primary heat preservation for 27s, controlling the cooling speed to 18 ℃/s, carrying out air cooling to 560 ℃, carrying out secondary heat preservation for 30s, and carrying out air cooling to room temperature.
Observing before heat treatment, wherein the structure of a weld line center fusion line is a ferrite and lath bainite structure; the weld heat affected zone is a martensite + lath bainite structure; the matrix structure is a granular bainite structure.
Observation after heat treatment: the weld seam center fusion line is composed of ferrite with volume percentage of about 25% and granular bainite tissue with volume percentage of about 75%; the weld heat affected zone is granular bainite with volume percentage of about 85 percent and ferrite with volume percentage of about 15 percent, and carbide is distributed; the matrix structure is a granular bainite structure.
According to the welded steel pipe obtained in the embodiment 2 of the invention, the welding seams are respectively placed on the horizontal plane passing through the axis, the vertical plane passing through the axis and 3 directions (as shown in fig. 5-7) at 45 degrees for a closed flattening test, no crack occurs at the welding seams, and the fatigue life of the finished torsion beam is 36 ten thousand times.
Example 3
Example 3 provides a heat treatment method for a 700MPa grade steel weld for an automotive torsion beam, the welded steel pipe is a 700MPa grade high frequency welded pipe, the wall thickness of the steel pipe is 4mm, the width of the weld is 2mm, the chemical components of the steel pipe are shown in table 1, and the balance is Fe and inevitable impurities. Heating to 810 ℃ within a region range which takes a welding line as a symmetry axis and is 8mm away from the welding line by adopting medium-frequency induction heating, preserving heat for 17s for the first time, controlling the cooling speed to be 13 ℃/s, air-cooling to 560 ℃, preserving heat for 35s for the second time, air-cooling for 1min to 254 ℃, then cooling to 25 ℃ by water, and the water-cooling rate is 30 ℃/s.
Observing before heat treatment, wherein the structure of a weld line center fusion line is a ferrite and lath bainite structure; the weld heat affected zone is a martensite + lath bainite structure; the matrix structure is a granular bainite structure.
Observation after heat treatment: the weld seam center fusion line is composed of ferrite with volume percentage of about 28% and granular bainite tissue with volume percentage of about 72%; the weld heat affected zone is about 75 percent of granular bainite and about 25 percent of ferrite by volume percentage, and carbide is distributed; the matrix structure is a granular bainite structure.
According to the welded steel pipe obtained in the embodiment 3 of the invention, the welding seams are respectively placed on the horizontal plane passing through the axis, the vertical plane passing through the axis and 3 directions (as shown in fig. 5-7) at 45 degrees for a closed flattening test, no crack occurs at the welding seams, and the fatigue life of the finished torsion beam is 33 ten thousand times.
Example 4
Example 4 provides a heat treatment method for a 700MPa grade steel weld for an automotive torsion beam, the welded steel pipe is a 700MPa grade high frequency welded pipe, the wall thickness of the steel pipe is 4mm, the width of the weld is 2mm, the chemical components of the steel pipe are shown in table 1, and the balance is Fe and inevitable impurities. Heating to 820 ℃ within a region range which takes a welding line as a symmetry axis and is 8mm away from the welding line by adopting a medium-frequency induction heating pair, preserving heat for 28s for the first time, controlling the cooling speed to be 13 ℃/s, air-cooling to 490 ℃, preserving heat for 25s for the second time, air-cooling for 2min to 230 ℃, then cooling to 25 ℃ by water, and controlling the water-cooling rate to be 35 ℃/s.
Observing before heat treatment, wherein the structure of a weld line center fusion line is a ferrite and lath bainite structure; the weld heat affected zone is a martensite + lath bainite structure; the matrix structure is a granular bainite structure.
Observation after heat treatment: the weld seam center fusion line is composed of ferrite with the volume percentage of about 30% and granular bainite tissue with the volume percentage of about 70%; the weld heat affected zone is composed of granular bainite with volume percentage of about 80% and ferrite with volume percentage of about 20%, and carbide is distributed; the matrix structure is a granular bainite structure.
According to the welded steel pipe obtained in the embodiment 3 of the invention, the welding seams are respectively placed on the horizontal plane passing through the axis, the vertical plane passing through the axis and 3 directions (as shown in fig. 5-7) at 45 degrees for a closed flattening test, no crack occurs at the welding seams, and the fatigue life of the finished torsion beam is 35 ten thousand times.
Example 5
Example 3 provides a heat treatment method for a 700MPa grade steel weld for an automotive torsion beam, the welded steel pipe is a 700MPa grade high frequency welded pipe, the wall thickness of the steel pipe is 4mm, the width of the weld is 2mm, the chemical components of the steel pipe are shown in table 1, and the balance is Fe and inevitable impurities. Heating to 790 ℃ within a region range which takes a welding line as a symmetry axis and is 8mm away from the welding line by adopting a medium-frequency induction heating pair, preserving heat for 22s for the first time, controlling the cooling speed to 11 ℃/s, air-cooling to 580 ℃, preserving heat for 28s for the second time, cooling to 265 ℃ after air-cooling for 1.5min, and then cooling to 25 ℃ by water, wherein the water-cooling rate is 38 ℃/s.
Observing before heat treatment, wherein the structure of a weld line center fusion line is a ferrite and lath bainite structure; the weld heat affected zone is a martensite + lath bainite structure; the matrix structure is a granular bainite structure.
Observation after heat treatment: the weld seam center fusion line is composed of ferrite with volume percentage of about 25% and granular bainite tissue with volume percentage of about 75%; the weld heat affected zone is granular bainite with volume percentage of about 83 percent and ferrite with volume percentage of about 17 percent, and carbide is distributed; the matrix structure is a granular bainite structure.
According to the welded steel pipe obtained in the embodiment 3 of the invention, the welding seams are respectively placed on the horizontal plane passing through the axis, the vertical plane passing through the axis and 3 directions (as shown in fig. 5-7) at 45 degrees for a closed flattening test, no crack occurs at the welding seams, and the fatigue life of the finished torsion beam is 34 ten thousand times.
Comparative example 1
Comparative example 1 provides a heat treatment method for a 700MPa grade steel weld for an automotive torsion beam, the welded steel pipe is a 700MPa grade high frequency welded pipe, the wall thickness of the steel pipe is 2mm, the chemical components of the steel pipe are shown in table 1, and the balance is Fe and inevitable impurities. And (3) tempering the whole steel pipe at high temperature, heating the steel pipe to 500 ℃ at room temperature, preserving heat for 0.5h, then heating the steel pipe to 570 ℃, preserving heat for 2h, and then cooling the steel pipe to room temperature along with the furnace.
Observing before heat treatment, wherein the structure of a weld line center fusion line is a ferrite and lath bainite structure; the weld heat affected zone is a martensite + lath bainite structure; the matrix structure is a granular bainite structure.
Observation after heat treatment: the weld seam center fusion line is a lath bainite and granular bainite structure; the weld heat affected zone is lath bainite, and carbides are distributed in the weld heat affected zone; the parent material structure is granular bainite structure with distributed carbide. The weld structure is shown in FIG. 11, and the base material structure is shown in FIG. 12.
Through the welded steel pipe obtained in the comparative example 1, the weld joints are respectively placed on the horizontal plane passing through the axis, the vertical plane passing through the axis and 3 directions (as shown in fig. 5-7) at 45 degrees for a closed flattening test, no crack occurs at the weld joints, and the fatigue life of the finished torsion beam is 30 ten thousand times.
And (3) hardness detection: the hardness of the welded seam and the steel pipe after heat treatment in the area near the welded seam are detected, the detected positions are symmetrical by the center of the welded seam, and the detected positions penetrate through a heat affected zone (the position II) and a weld seam center fusion line (the position III) from a base material (the position I) on one side to a base material on the other side, as shown in fig. 8. 15 hardness detection points of a single-side base material and a heat affected zone, 1 welding line detection point at the center of a welding line, 31 hardness detection points, a distance between every two adjacent points is 100 mu m, the pressure head loading force for hardness measurement is 100kgf, and the loading retention time is 10 s.
Detecting a sample: the test samples were welded steel pipes before heat treatment of the welded steel pipes used in example 1 of the present invention, welded steel pipes after heat treatment of examples 1 to 5, and welded steel pipes after heat treatment of comparative example 1, respectively, and the test results are shown in table 2. The hardness after heat treatment was plotted with the hardness test position number as the abscissa and the hardness as the ordinate, as shown in fig. 9 and 10.
TABLE 2
The fatigue life of the welded pipe after the local heat treatment in the examples 1 to 5 is 33-39 ten thousand times, the fatigue life of the whole welded pipe adopted in the comparative example 1 is 30 ten thousand times, and the fatigue life of the welded pipe is at least 10% higher than that of the welded pipe in the comparative document 1.
Fig. 9 is a graph showing hardness detection of the weld and the weld vicinity region before and after the heat treatment in example 1, and it can be seen from fig. 9 that the hardness of the weld and the weld vicinity region before the local heat treatment is high (see fig. 9 that the middle projection of the curve is high, similar to a parabola), and the hardness of the weld and the weld vicinity region after the heat treatment method of the present application is used is greatly reduced. Fig. 10 is a graph showing hardness detection of the weld and the weld vicinity region after the heat treatment in examples 1 to 5 and comparative example 1, and it can be seen from fig. 10 that the local heat treatment method of the present application has a more uniform hardness distribution, and the weld vicinity region have lower hardness and are closer to the hardness of the base material at a position far from the weld, as compared with comparative example 1 of the entire heat treatment method.
Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (10)
1. A heat treatment method for a steel weld of a 700 MPa-grade automobile torsion beam is characterized by comprising the following steps,
welding the steel plate into a steel pipe with a welding seam;
and carrying out heat treatment on the steel pipe in an area range with the welding seam as a symmetry axis and the welding seam distance as d, wherein the heat treatment sequentially comprises heating, primary heat preservation, primary cooling, secondary heat preservation and secondary cooling, the primary cooling is air cooling, the air cooling rate is 10-20 ℃/s, the air cooling finishing temperature is 480-600 ℃, the d is 3-5 times of the width of the welding seam, and the width of the welding seam is 1-2 mm.
2. The heat treatment method for the steel weld of the 700 MPa-grade automobile torsion beam according to claim 1, characterized in that the welding is high-frequency welding, and the heating and the primary heat preservation are performed by using a medium-frequency induction device.
3. The heat treatment method for the steel weld of the 700 MPa-grade automobile torsion beam according to claim 1, characterized in that the primary heat preservation temperature is 790-820 ℃, the primary heat preservation time is 15-30 s, and the secondary heat preservation time is 20-40 s.
4. The heat treatment method for the steel weld of the 700 MPa-grade automobile torsion beam according to claim 1, characterized in that the secondary cooling is air cooling, and the air cooling finishing temperature is 15-45 ℃.
5. The heat treatment method for the steel weld joint for the 700 MPa-grade automobile torsion beam according to claim 1, characterized in that the secondary cooling is air cooling and water cooling in sequence, wherein the air cooling time is 1-2 min, and the air cooling finishing temperature is 200-300 ℃; the water cooling rate is 30-40 ℃/s, and the water cooling finishing temperature is 15-45 ℃.
6. The heat treatment method of the steel welding seam for the 700 MPa-grade automobile torsion beam is characterized in that after the heat treatment is finished, the metallographic structure of the central fusion line of the welding seam is ferrite and granular bainite, the volume percentage of the ferrite is 20-30%, and the volume percentage of the granular bainite is 70-80%.
7. The heat treatment method of the steel welding seam for the 700 MPa-grade automobile torsion beam is characterized in that after the heat treatment is finished, the metallographic structure of the heat affected zone of the welding seam is ferrite and granular bainite, the volume percentage of the ferrite is 10-20%, and the volume percentage of the granular bainite is 80-90%.
8. The heat treatment method for the steel weld of the 700 MPa-grade automobile torsion beam according to claim 1, characterized in that the metallographic structure of the steel plate is granular bainite, and the volume percentage of the granular bainite is not less than 95%.
9. The heat treatment method for the steel weld of the 700 MPa-grade automobile torsion beam according to claim 1, characterized in that the thickness of the steel plate is 2-5 mm.
10. The heat treatment method for the steel weld of the 700 MPa-grade automobile torsion beam according to claim 1, characterized in that the steel plate comprises the following chemical components in percentage by mass: c: 0.10 to 0.20%, Si: 0.05-0.20%, Mn: 0.8-2.0%, P is less than or equal to 0.02%, S is less than or equal to 0.009%, Nb is less than or equal to 0.08%, Ti is less than or equal to 0.1%, Mo is less than or equal to 0.3%, Al is less than or equal to 0.05%, and the balance is Fe and inevitable impurities.
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| CN116694989A (en) * | 2023-05-24 | 2023-09-05 | 邯郸钢铁集团有限责任公司 | 700 Mpa-level thin-specification easy-to-weld suspension arm steel and production method thereof |
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| CN1204564A (en) * | 1997-07-09 | 1999-01-13 | 上海鼎鑫商业发展有限公司 | Technology and technique for low alloy (alloy) structural steel welding steel pipe |
| CA2711795A1 (en) * | 2007-01-10 | 2008-07-17 | Kva, Inc. | Method for controlling weld metal microstructure using localized controlled cooling of seam-welded joints |
| CN110042218A (en) * | 2019-05-28 | 2019-07-23 | 攀钢集团攀枝花钢铁研究院有限公司 | Construction method for the heat treatment of bainite rail postwelding connector |
| CN110453154A (en) * | 2019-09-05 | 2019-11-15 | 首钢集团有限公司 | A kind of 700MPa grades of torsion beam of automobile steel and preparation method thereof |
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| CN1204564A (en) * | 1997-07-09 | 1999-01-13 | 上海鼎鑫商业发展有限公司 | Technology and technique for low alloy (alloy) structural steel welding steel pipe |
| CA2711795A1 (en) * | 2007-01-10 | 2008-07-17 | Kva, Inc. | Method for controlling weld metal microstructure using localized controlled cooling of seam-welded joints |
| CN110042218A (en) * | 2019-05-28 | 2019-07-23 | 攀钢集团攀枝花钢铁研究院有限公司 | Construction method for the heat treatment of bainite rail postwelding connector |
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| CN116694989A (en) * | 2023-05-24 | 2023-09-05 | 邯郸钢铁集团有限责任公司 | 700 Mpa-level thin-specification easy-to-weld suspension arm steel and production method thereof |
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