CN111230255A - Welding method for improving low-temperature toughness of 304L austenitic stainless steel welding joint - Google Patents
Welding method for improving low-temperature toughness of 304L austenitic stainless steel welding joint Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K33/00—Specially-profiled edge portions of workpieces for making soldering or welding connections; Filling the seams formed thereby
- B23K33/004—Filling of continuous seams
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
- B23K9/16—Arc welding or cutting making use of shielding gas
- B23K9/167—Arc welding or cutting making use of shielding gas and of a non-consumable electrode
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
- B23K9/235—Preliminary treatment
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- 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
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- 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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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/02—Iron or ferrous alloys
- B23K2103/04—Steel or steel alloys
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Abstract
The invention discloses a welding method for improving low-temperature toughness of a 304L austenitic stainless steel welding joint, which comprises the following steps: after preparing a groove on the 304L base metal, assembling the 304L base metal to be welded, and performing tack welding by adopting argon tungsten-arc welding; performing backing welding by adopting double-sided tungsten argon arc welding; welding the filling layer and the cover surface layer by adopting shielded metal arc welding; the welded 304L austenitic stainless steel weld joint was heat treated. The welding method provided by the invention can greatly improve the low-temperature toughness of the 304L austenitic stainless steel welding joint, particularly the low-temperature toughness at minus 196 ℃.
Description
Technical Field
The invention relates to the technical field of welding processes, in particular to a welding method for improving low-temperature toughness of a 304L austenitic stainless steel welding joint.
Background
The 304L austenitic stainless steel has higher strength, excellent low-temperature toughness and shaping, and simultaneously has excellent corrosion resistance due to low carbon content, so the steel is often used as low-temperature steel, such as a cryogenic low-temperature liquid storage and transportation container produced in China, the service temperature is usually-196 ℃ to-183 ℃, and the main body base material is usually 18-8 type austenitic stainless steel.
At present, a pressure container product is mainly welded by shielded metal arc welding, for 304L austenitic stainless steel, an E308L-XX shielded metal matched with chemical components is usually adopted, the average impact energy of deposited metal at-196 ℃ is about 34J, and the use requirement of common civil products can be met. However, for some military products, such as large-scale low-temperature wind tunnels, the low-temperature impact energy of the welding joint reaches more than 50J or even higher at the temperature of 196 ℃ below zero after heat treatment, and the requirements cannot be met by adopting the conventional shielded metal arc welding process.
Although the 304L austenitic stainless steel shielded metal arc welding process is well-established, Cr is precipitated in grain boundaries after heat treatment of a welding joint23C6The corrosion resistance is lowered, so that the general 304L austenitic stainless steel product is not heat-treated. The military products generally adopt medium-thickness plates, the quality requirement of welding joints is high, stress-relief heat treatment is required, the low-temperature toughness of the welding joints at the temperature of-196 ℃ can be greatly reduced, if the conventional shielded metal arc welding process is adopted, the low-temperature impact energy of the welding joints at the temperature of-196 ℃ is only about 20J on average, the use requirement can not be met, and domestic research results on the aspect almost do not exist.
Disclosure of Invention
The invention mainly aims to provide a welding method for improving low-temperature toughness of a 304L austenitic stainless steel welding joint, and particularly improves the low-temperature toughness at minus 196 ℃ or below.
In order to achieve the above object, the present invention provides a welding method for improving low temperature toughness of a 304L austenitic stainless steel welded joint, comprising the steps of:
after preparing a groove on the 304L base metal, assembling the 304L base metal to be welded, and performing tack welding by adopting argon tungsten-arc welding;
performing backing welding by adopting double-sided tungsten argon arc welding;
welding the filling layer and the cover surface layer by adopting shielded metal arc welding;
the welded 304L austenitic stainless steel weld joint was heat treated.
Preferably, after the groove is formed on the 304L parent metal, the predetermined ranges on both sides of the groove of the 304L parent metal are heated by using oxyacetylene neutral flame to remove moisture.
Preferably, after spot welding is performed by argon tungsten-arc welding, a grinding wheel machine is used for grinding the back weld of the spot welding until silvery white metallic luster is exposed.
Preferably, when the filler layer and the cover layer are welded in the shielded metal arc welding process, the welding rod is E316LMn-15, other chemical components except N in the welding rod meet the GB/T983 standard, the mass content of the N is less than 0.1%, the welding rod is baked for 1-2 hours at 300-350 ℃, swing welding is adopted for welding, and the swing amplitude of the welding rod is less than or equal to 5 times of the diameter of the used welding rod.
Preferably, when the filler layer is welded, for a welding rod with the diameter of 3.2mm, the welding arc voltage is controlled to be 20-24V, the welding current is 90-100A, the welding speed is 50-85 mm/min, and the linear energy is 12.7-28.8 KJ/cm; for a welding rod with the diameter of 4.0mm, the welding arc voltage is controlled to be 20-24V, the welding current is 115-125A, the welding speed is 55-80 mm/min, and the linear energy is 17.3-32.7 KJ/cm.
Preferably, when the cover surface layer is welded, for a welding rod with the diameter of 3.2mm, the welding arc voltage is controlled to be 20-24V, the welding current is controlled to be 90-100A, the welding speed is 70-80 mm/min, and the linear energy is 13.5-20.6 KJ/cm; for a welding rod with the diameter of 4.0mm, the welding arc voltage is controlled to be 20-24V, the welding current is controlled to be 105-115A, the welding speed is 65-95 mm/min, and the linear energy is 13.3-25.5 KJ/cm.
Preferably, the step of performing heat treatment on the welded 304L austenitic stainless steel welded joint specifically comprises the following steps:
the heat treatment temperature is 550-590 ℃, the heat preservation time is 1-2 h, the temperature reduction rate is controlled to be more than or equal to 65 ℃/h within the temperature range of 400 ℃ after the heat preservation is finished, and the temperature is cooled to the room temperature in the air after being reduced to 400 ℃.
Preferably, the interlayer temperature is controlled to be less than or equal to 100 ℃ in the welding process.
Preferably, the argon tungsten-arc welding adopts a direct-current positive power supply, and the shielded metal arc welding adopts a direct-current reverse power supply.
Preferably, when double-sided argon tungsten-arc welding is adopted for backing welding, the welding wire is ER316LMn, other chemical components except N element in the welding rod all meet the GB/T983 standard, the mass content of the N element is less than 0.1%, two welders weld at the same time and at the same speed for the root of the same groove, the front groove is welded by one welder with filler wires, and the other welder performs non-filler wire remelting on the back of the groove.
Compared with the traditional welding process (adopting an E308L-XX welding rod, carbon arc air gouging back chipping, controlling the interlayer temperature within 150 ℃, directly cooling in a furnace after heat treatment and heat preservation and the like), the welding method for improving the low-temperature toughness of the 304L austenitic stainless steel welding joint greatly improves the low-temperature impact toughness of the welding joint, can meet the use requirements of military products such as large-scale low-temperature wind tunnels due to the fact that the-196 ℃ low-temperature impact energy of the welding joint subjected to stress relief heat treatment is more than 50J, and meets the requirements of pressure-bearing equipment process evaluation on tensile strength and plasticity of the welding joint. In addition, by controlling the cooling rate in the heat treatment process, the intergranular corrosion tendency is avoided, and the corrosion resistance of the welding joint is improved. In addition, the welding method is simple in operation process and can be applied to engineering.
Drawings
FIG. 1 is a microscopic gold phase diagram of a weld of comparative example 1 of the present invention after welding and heat treatment;
FIG. 2 is a microscopic metallographic image of a weld joint after welding and heat treatment according to example 1 of the present invention;
FIG. 3 is a microscopic gold phase diagram of an intergranular corrosion sample of a welded joint after heat treatment in accordance with example 1 of the present invention.
The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.
Detailed Description
It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
A welding method for improving low-temperature toughness of a 304L austenitic stainless steel welding joint comprises the following steps:
step S10, after preparing grooves on the 304L base metal, assembling the 304L base metal to be welded in an assembling way, and performing tack welding by adopting argon tungsten-arc welding;
step S20, performing backing welding by adopting double-sided argon tungsten-arc welding;
step S30, welding the filling layer and the cover layer by adopting shielded metal arc welding;
step S40, heat-treating the welded 304L austenitic stainless steel welded joint.
In step S10, after preparing the groove on the 304L parent metal, the both sides of the groove on the 304L parent metal are heated by oxyacetylene neutral flame to remove moisture (for example, 20mm on both sides of the groove on the 304L parent metal).
After spot welding is carried out by adopting argon tungsten-arc welding, a grinding wheel machine is adopted to grind the back weld of the spot welding until silvery white metallic luster is exposed. The welding material and welding process of spot welding are the same as those of argon tungsten-arc welding backing welding (front groove).
In step 20, when backing welding is performed by double-sided argon tungsten-arc welding, the welding wire is ER316LMn, two welders weld at the same time and at the same speed on the same groove root, one welder uses filler wire welding on the front groove, and the other welder performs non-filler wire remelting on the back of the groove.
The welding parameters of the double-sided argon tungsten-arc welding are as follows: the welding wire is ER316LMn with the diameter of 2.4 mm; the diameter of the tungsten electrode is 2.5 mm; the argon flow of the front groove is 15-20L/min, the argon flow of the back groove is 10-15L/min, and the argon purity is more than or equal to 99.99%; the welding arc voltage of the front groove is 10-12V, the welding current is 120-150A, the welding speed is 60-80 mm/min, and the linear energy is 9-18 KJ/cm; the back groove welding arc voltage is 10-12V, the welding current is 100-120A, the welding speed is 60-80 mm/min, and the linear energy is 7.5-14.4 KJ/cm; and welding by adopting swing welding.
In the step S30, when welding the filling layer and the covering layer by the shielded metal arc welding, E316LMn-15 with phi 3.2mm or phi 4.0mm is selected as the shielded metal, the shielded metal is baked for 1-2 h at 300-350 ℃, the shielded metal is placed in a heat-insulating cylinder for use and taken at any time in the using process, the welding is carried out by adopting swing welding, and the swing amplitude of the shielded metal is less than or equal to 5 times of the diameter of the used shielded metal.
When the filling layer is welded, for a welding rod with the diameter of 3.2mm, the welding arc voltage is controlled to be 20-24V, the welding current is 90-100A, the welding speed is 50-85 mm/min, and the linear energy is 12.7-28.8 KJ/cm; for a welding rod with the diameter of 4.0mm, the welding arc voltage is controlled to be 20-24V, the welding current is 115-125A, the welding speed is 55-80 mm/min, and the linear energy is 17.3-32.7 KJ/cm.
When the cover surface layer is welded, for a welding rod with the diameter of 3.2mm, the welding arc voltage is controlled to be 20-24V, the welding current is controlled to be 90-100A, the welding speed is 70-80 mm/min, and the linear energy is 13.5-20.6 KJ/cm; for a welding rod with the diameter of 4.0mm, the welding arc voltage is controlled to be 20-24V, the welding current is controlled to be 105-115A, the welding speed is 65-95 mm/min, and the linear energy is 13.3-25.5 KJ/cm.
Step S40 is specifically as follows:
the heat treatment temperature is 550-590 ℃, the heat preservation time is 1-2 h, the temperature reduction rate is controlled to be more than or equal to 65 ℃/h within the temperature range of 400 ℃ after the heat preservation is finished, and the temperature is cooled to the room temperature in the air after being reduced to 400 ℃.
By adopting the heat treatment process, about 40 percent of residual stress can be eliminated on the basis of not greatly reducing the low-temperature toughness of the welded joint at the temperature of-196 ℃. The temperature reduction rate is more than or equal to 65 ℃/h within the temperature range of 400 ℃ after the heat preservation is finished, and the intergranular corrosion tendency can be effectively prevented.
In the welding process, the interlayer temperature is controlled to be less than or equal to 100 ℃.
The argon tungsten-arc welding adopts a direct current positive power supply, and the welding rod electric arc welding adopts a direct current reverse power supply.
The 304L austenitic stainless steel belongs to the range of 18-8 section steel, but the content of alloy elements is adjusted on the basis, compared with the domestic standard, the content range of Si element is reduced, the content range of impurity element S, P is reduced, the lower limit index of austenite stable element Ni is improved, and the chemical components are as follows by weight percent: c: less than or equal to 0.03%, Si: less than or equal to 0.5 percent, Mn: less than or equal to 2.0 percent, P: less than or equal to 0.03%, S: less than or equal to 0.015 percent, Ni: 10-12%, Cr: 18-20% of Fe and the balance of other inevitable impurities.
The chemical components of other elements of the argon arc welding wire except N element meet the GB/T29713 standard, and the content of the N element can not meet the standard requirement, namely N: is less than 0.1 percent. Similarly, the welding wire for shielded metal arc welding meets the same standard, namely the chemical composition of other elements meets the GB/T29713 standard, and the content of N element can not meet the standard requirement, namely N: is less than 0.1 percent.
The groove form can be symmetrical X type, V type, symmetrical K type, and unilateral groove angle is 25~30 degrees, and the truncated edge is 1 + -1 mm, and the clearance is 3 + -1 mm.
The welding seam structure of the argon tungsten-arc welding and the shielded metal arc welding is dendritic austenite and micro ferrite which are in an A solidification mode. Among the factors affecting the-196 ℃ low temperature toughness of the welded joint, the ferrite content in the weld structure is the most important. Generally speaking, the less the ferrite content, the better the low-temperature toughness at-196 ℃, and the too less the ferrite content is easy to generate thermal cracks, and the Mn element content in the 316LMn welding material is more than or equal to 5 percent, so that the occurrence of the thermal cracks can be effectively prevented.
304L parent metal, the yield strength is more than or equal to 190MPa, the tensile strength is more than or equal to 510MPa, the elongation is more than or equal to 50 percent, and the low-temperature impact energy at minus 196 ℃ is more than or equal to 150J.
The 304L parent metal in the following examples and comparative examples is produced by Anshan iron and Steel group, Inc., and comprises the following chemical components in percentage by weight: c: 0.02%, Si: 0.33%, Mn: 1.69%, P: 0.022%, S: 0.009%, Ni: 11.10%, Cr: 18.33%, the balance being Fe and other unavoidable impurities;
the welding rod in the comparative example 1 is Berle E308L-16, the diameter is 3.2mm, and the welding rod comprises the following chemical components in percentage by weight: c: 0.02%, Si: 0.59%, Mn: 1.9%, P: 0.02%, S: 0.01%, Ni: 10.0%, Cr: 19.8%, Cu: 0.02 percent.
The argon arc welding wire in the embodiments 1, 2 and 3 is Harbin Wille ER316LMnG, the diameter is 2.4mm, and the argon arc welding wire comprises the following chemical components in percentage by weight: c: 0.017%, Si: 0.49%, Mn: 5.58%, P: 0.0084%, S: 0.0071%, Ni: 17.24%, Cr: 18.96%, Mo: 4.22%, Cu: 0.0098%.
The welding rod in the embodiment 1, 2 and 3 is Atlantic CHS027FT with the diameter of 4.0mm, and the welding rod comprises the following chemical components in percentage by weight: c: 0.037%, Si: 0.41%, Mn: 5.7%, P: 0.014%, S: 0.005%, Ni: 17.03%, Cr: 19.10%, Mo: 2.86 percent.
Argon tungsten-arc welding and shielded metal arc welding adopt an argon arc manual arc dual-purpose welding machine of OrteZX 7-400 STG.
The physicochemical test standard of the embodiment of the invention is NB/T47014.
Three examples and one comparative example are specifically described below.
Comparative example 1
The welding process is as follows:
(1) preparation before welding
Preparing an X-shaped groove on a 500X 150X 40mm (2) 304L austenitic stainless steel test plate by using a beveling machine, wherein the angle of the single-side groove is 30 degrees, and polishing and cleaning the groove and the 20mm range of the two sides of the groove by using a grinding machine (adopting a stainless steel grinding wheel sheet) to remove oil stains and impurities; rapidly heating the 20mm range of two sides of the 304L parent metal groove by adopting oxyacetylene neutral flame to remove water; assembling two test plates to be welded, wherein the truncated edge is 1mm, the gap is 3mm, welding rods are adopted to perform arc welding on the two ends of the test plates for spot welding, and the welding materials and the welding process of the spot welding are the same as those of the bottoming filling cover surface welding process.
(2) Welding of
And adopting shielded metal arc welding to carry out bottoming filling cover surface welding, wherein the welding current is 105A, the welding voltage is 22V, the average welding speed is 50mm/min, and the average linear energy is 27.7 KJ/cm. The welding rod is baked for 1-2 hours at 300-350 ℃ before being used, and is placed in a heat-insulating cylinder for use and taking. And (3) welding by adopting swing welding, wherein the swing amplitude of the welding rod is less than or equal to 4 times of the diameter of the used welding rod, and back chipping is carried out by adopting a carbon arc gouging. In the welding process, the interlayer temperature is controlled to be 100-150 ℃, and the welding power supply adopts direct current reverse connection.
(3) Stress relief heat treatment
The heat treatment process at 570 ℃ for 1.5h is adopted, the furnace cooling mode is adopted for cooling, and the average cooling rate between 570 ℃ and 400 ℃ is 29 ℃/h.
Through detection, the tensile strength of the welded joint is 581MPa, the fracture position is a base material, and 4 side-bent samples are intact and have no cracks. The impact energy of the welded joint at-196 ℃ is respectively as follows: 18J of a welding line and 101J of a heat affected zone, wherein the-196 ℃ impact energy of the welding line is far less than 50J, and the requirements of military products such as large-scale low-temperature wind tunnels on the-196 ℃ impact energy of welding joints cannot be met.
Example 1
The welding method provided by the invention (the interlayer temperature is controlled within 100 ℃, and the heat treatment cooling rate is controlled to be 65 ℃/h) comprises the following steps:
(1) preparation before welding
Preparing a symmetrical X-shaped groove by adopting a beveling machine on a 500X 150X 40mm (2) 304L austenitic stainless steel test plate, wherein the angle of the single-side groove is 30 degrees, and polishing and cleaning the groove and the 20mm range of the two sides of the groove by using a grinding machine (adopting a stainless steel grinding wheel sheet) to remove oil stains and impurities; rapidly heating the 20mm range of two sides of the 304L parent metal groove by adopting oxyacetylene neutral flame to remove water; assembling two test panels to be welded, wherein the truncated edge is 0mm, the gap is 3mm, spot welding is carried out by adopting argon tungsten-arc welding, and the welding material and the welding process of the spot welding are the same as those of back welding (front groove) of the argon tungsten-arc welding. And after the tack welding is finished, polishing the back weld of the tack welding by using a grinding machine until the silvery white metallic luster is exposed.
(2) Double-sided tungsten argon arc backing weld
And performing backing welding by adopting double-sided argon tungsten-arc welding, welding two welders at the same time and at the same speed for the root of the same groove, and performing wire filling welding on the front groove by one welder, and remelting (not filling wires) on the back of the groove by the other welder. The welding parameters of the double-sided argon tungsten-arc welding are as follows: the argon flow of the front groove is 18L/min, the argon flow of the back groove is 12L/min, and the argon purity is more than or equal to 99.99 percent; the welding arc voltage of the front groove is 12V, the welding current is 140A, the average welding speed is 70mm/min, and the average linear energy is 14.4 KJ/cm; the back groove welding arc voltage is 12V, the welding current is 120A, the average welding speed is 70mm/min, and the average linear energy is 12.3 KJ/cm; and welding by adopting swing welding.
(3) Shielded metal arc welding fill and cap weld
Baking the welding rod for 1-2 hours at 300-350 ℃ before use, and putting the welding rod in a heat-insulating cylinder for use and taking at any time during use; the swing welding is adopted for welding, the swing amplitude of the welding rod is less than or equal to 5 times of the diameter of the used welding rod, and the welding parameters of the shielded metal arc welding are as follows: filling layer: the welding voltage is 23V, the welding current is 120A, the average welding speed is 70mm/min, and the average linear energy is 23.7 KJ/cm. Covering the surface layer: the welding voltage is 22V, the welding current is 108A, the average welding speed is 70mm/min, and the average linear energy is 20.4 KJ/cm.
(4) Stress relief heat treatment
The heat treatment process of 570 ℃ multiplied by 1.5h is adopted, the temperature reduction rate is controlled to be 65 ℃/h within the temperature range of 570 ℃ to 400 ℃ after the heat preservation is finished, and the temperature is cooled to the room temperature in static air after being reduced to 400 ℃.
In the welding process, the interlayer temperature is controlled to be 70-100 ℃, a direct-current positive power supply is adopted for argon tungsten-arc welding, and a direct-current reverse power supply is adopted for arc welding of a welding rod.
The detection shows that the tensile strength of the welded joint is 567MPa, the fracture position is the base material, and 4 side-bent samples are intact and have no cracks. The impact energy of the welded joint at-196 ℃ is respectively as follows: the argon arc welding seam 127J, the argon arc welding heat affected zone 148J, the shielded metal arc welding seam 101J and the shielded metal arc welding heat affected zone 131J are far larger than 50J, and meet the requirement of military products such as large-scale low-temperature wind tunnels on the impact energy of a welding joint at the temperature of 196 ℃ below zero. The welded joint is subjected to intercrystalline corrosion test according to an E method in GB/T4334 standard, one sample is good after being bent at 180 degrees, 3 pits appear after the other sample is bent at 180 degrees, and the intercrystalline corrosion depth is not seen through a metallographic method, so that the intercrystalline corrosion tendency is avoided.
Example 2
The welding method controls the interlayer temperature to be 100-150 ℃, and the rest welding processes are consistent with those of the embodiment 1.
The tensile strength of the welded joint is 572MPa, and 4 lateral bending samples have no cracks. The impact energy of the welded joint at-196 ℃ is respectively as follows: the argon arc welding seam 110J, the argon arc welding heat affected zone 135J, the shielded metal arc welding seam 89J and the shielded metal arc welding heat affected zone 116J are far larger than 50J, and meet the requirement of military products such as large-scale low-temperature wind tunnels on the impact energy of a welding joint at the temperature of 196 ℃ below zero. The impact energy at-196 ℃ of the welded joint in example 1 was reduced in value in both the weld joint and the heat affected zone, indicating that the interlayer temperature was controlled to be within 100 ℃ and the low temperature toughness at-196 ℃ was improved relative to the impact energy at-150 ℃.
Example 3
The welding method adopts a furnace cooling mode to cool, the average cooling rate between 570 ℃ and 400 ℃ is 29 ℃/h, and other welding processes are consistent with those in the embodiment 1.
The detection shows that the tensile strength of the welding joint is 575MPa, and 4 lateral bending samples have no cracks. The impact energy of the welded joint at-196 ℃ is respectively as follows: the argon arc welding seam 124J, the argon arc welding heat affected zone 130J, the shielded metal arc welding seam 103J and the shielded metal arc welding heat affected zone 126J are far larger than 50J, and meet the requirement of military products such as large-scale low-temperature wind tunnels on the impact energy of a welding joint at the temperature of 196 ℃ below zero.
The welded joint is subjected to intercrystalline corrosion test according to the E method in the GB/T4334 standard, and two samples are bent by corrosion for 180 degrees and both have a large amount of intercrystalline corrosion cracks and fracture and inherent intercrystalline corrosion tendency. The stress-relief heat treatment of general products is carried out by adopting a furnace cooling mode, the cooling rate is basically less than or equal to 35 ℃/h, and the obvious influence on carbon steel is not caused. However, for stainless steel, if the cooling rate is too low, the retention time of the weld joint at the temperature above 500 ℃ is too long in the cooling stage, and 500 ℃ to 800 ℃ is a temperature range causing intergranular corrosion, which may cause intergranular precipitation of Cr23C6 and the generation of intergranular corrosion.
There are many factors that affect the-196 ℃ low temperature toughness, for example: uniformity of chemical components and structures in the welding seam, surface treatment of welding wires, non-metal inclusions in the welding seam, type of coating of the welding rod, content of ferrite in the welding seam and the like. The effect of the ferrite content on the low-temperature toughness is the most important and most significant. Generally, the lower the ferrite content in the weld, the better the low temperature toughness of the weld: the first is that the ferrite is of a body-centered cubic structure and has poor toughness as compared with austenite, and the second is that the ferrite is rich in Cr, a sigma phase can be separated out in the heat treatment process, a chromium-rich phase with a nominal component of FeCr is hard and brittle, and the toughness and ductility can be reduced when the volume content is high.
The weld structure of comparative example 1 is shown in FIG. 1. The weld structure consists of austenite and lath ferrite, the ferrite content is relatively high, the weld structure becomes a lath shape which grows by transversely cutting original dendrites or peritectic crystals and is in an FA solidification mode. The content of ferrite is about 8 percent through the detection of a metallographic method, and the ferrite is a factor for reducing the low-temperature toughness of a welding line at the temperature of-196 ℃.
The above comparison shows that example 1 is the best example. The weld structure of example 1 is shown in FIG. 2. The weld joint structure consists of dendritic austenite and trace ferrite, and is in an A solidification mode, and the trace ferrite exists in the crystal interior and the crystal boundary and is a white dot in the figure. The microscopic metallographic phase of the sample in which the craters occurred in example 1 is shown in fig. 3.
Compared with the traditional welding process (adopting an E308L-XX welding rod, carbon arc air gouging back chipping, controlling the interlayer temperature within 150 ℃, directly cooling in a furnace after heat treatment and heat preservation), the welding method for improving the low-temperature toughness of the 304L austenitic stainless steel welding joint greatly improves the low-temperature impact toughness of the welding joint, can meet the use requirements of military products such as large-scale low-temperature wind tunnels due to the fact that the-196 ℃ low-temperature impact energy of the welding joint subjected to stress relief heat treatment is more than 50J, and meets the requirements of pressure-bearing equipment process evaluation on tensile strength and plasticity of the welding joint. In addition, by controlling the cooling rate in the heat treatment process, the intergranular corrosion tendency is avoided, and the corrosion resistance of the welding joint is improved. In addition, the welding method is simple in operation process and can be applied to engineering.
The above description is only for the preferred embodiment of the present invention and is not intended to limit the scope of the present invention, and all equivalent structural changes made by using the contents of the present specification and the drawings, or any other related technical fields, are intended to be covered by the scope of the present invention.
Claims (10)
1. A welding method for improving low-temperature toughness of a 304L austenitic stainless steel welding joint is characterized by comprising the following steps:
after preparing a groove on the 304L base metal, assembling the 304L base metal to be welded, and performing tack welding by adopting argon tungsten-arc welding;
performing backing welding by adopting double-sided tungsten argon arc welding;
welding the filling layer and the cover surface layer by adopting shielded metal arc welding;
the welded 304L austenitic stainless steel weld joint was heat treated.
2. The welding method for improving the low-temperature toughness of the 304L austenitic stainless steel welded joint according to claim 1, wherein after the groove is formed on the 304L parent metal, the predetermined ranges on both sides of the groove on the 304L parent metal are heated by oxyacetylene neutral flame to remove moisture.
3. The welding method for improving the low-temperature toughness of the 304L austenitic stainless steel welded joint as claimed in claim 1, wherein after tack welding is performed by argon tungsten arc welding, a back weld of the tack welding is ground by a grinder until silvery white metallic luster is exposed.
4. The welding method for improving the low-temperature toughness of the 304L austenitic stainless steel welding joint as claimed in claim 1, wherein when the welding rod is used for arc welding to weld the filling layer and the covering layer, the welding rod is E316LMn-15, other chemical components except N element in the welding rod all meet GB/T983 standard, the mass content of the N element is less than 0.1%, the welding rod is baked for 1-2 h at 300-350 ℃, the welding rod is welded by adopting swing welding, and the swing amplitude of the welding rod is less than or equal to 5 times of the diameter of the used welding rod.
5. The welding method for improving the low-temperature toughness of a 304L austenitic stainless steel welding joint as claimed in claim 4, wherein, when performing the filler layer welding, for a welding rod with a diameter of 3.2mm, the welding arc voltage is controlled to be 20-24V, the welding current is controlled to be 90-100A, the welding speed is 50-85 mm/min, and the linear energy is 12.7-28.8 KJ/cm; for a welding rod with the diameter of 4.0mm, the welding arc voltage is controlled to be 20-24V, the welding current is 115-125A, the welding speed is 55-80 mm/min, and the linear energy is 17.3-32.7 KJ/cm.
6. The welding method for improving the low-temperature toughness of a 304L austenitic stainless steel welding joint as claimed in claim 4, wherein, when the facing layer welding is performed, for a welding rod with a diameter of 3.2mm, the welding arc voltage is controlled to be 20-24V, the welding current is controlled to be 90-100A, the welding speed is 70-80 mm/min, and the linear energy is 13.5-20.6 KJ/cm; for a welding rod with the diameter of 4.0mm, the welding arc voltage is controlled to be 20-24V, the welding current is controlled to be 105-115A, the welding speed is 65-95 mm/min, and the linear energy is 13.3-25.5 KJ/cm.
7. The welding method for improving the low-temperature toughness of the 304L austenitic stainless steel welding joint according to claim 1, wherein the step of performing heat treatment on the welded 304L austenitic stainless steel welding joint specifically comprises the following steps:
the heat treatment temperature is 550-590 ℃, the heat preservation time is 1-2 h, the temperature reduction rate is controlled to be more than or equal to 65 ℃/h within the temperature range of 400 ℃ after the heat preservation is finished, and the temperature is cooled to the room temperature in the air after being reduced to 400 ℃.
8. The welding method for improving the low temperature toughness of a 304L austenitic stainless steel weld joint according to claim 1, wherein the interlayer temperature is controlled to be less than or equal to 100 ℃ during the welding process.
9. The welding method for improving the low temperature toughness of a 304L austenitic stainless steel weld joint as claimed in claim 1, wherein the argon tungsten arc welding uses a direct current forward power supply, and the shielded metal arc welding uses a direct current reverse power supply.
10. The welding method for improving the low-temperature toughness of the 304L austenitic stainless steel welding joint according to any one of claims 1 to 9, characterized in that when double-sided argon tungsten-arc welding is adopted for backing welding, the welding wire is ER316LMn, other chemical components except N element in the welding rod meet GB/T983 standard, the mass content of the N element is less than 0.1%, two welders weld at the same time and at the same speed at the root of the same groove, the front groove is welded by one welder with filler metal, and the other welder performs non-filler metal remelting on the back of the groove.
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