A method for welding stainless steel and applications thereof

Abstract

This invention provides a welding method and application for stainless steel. The method includes the following steps: S1, grinding and cleaning the weld area before welding; S2, after grinding and cleaning, assembling and fixing the steel plates to be welded, ensuring the weld root gap is no greater than 1.5mm; S3, after S2, placing a grooved copper backing plate on the back of the weld and securing it tightly; S4, welding after S3, controlling the welding heat input E to be t-2~t-0.5 kJ / cm (t is the plate thickness in cm), the interpass temperature not exceeding 85℃, and using compressed air to force-cool the weld and heat-affected zone from the front at a distance of 15~20mm behind the weld pool. Through these measures, the cooling rate of the weld and heat-affected zone is effectively accelerated, grain coarsening is suppressed, and the impact toughness of the weld heat-affected zone is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of steel production technology for saw blade backing, and more particularly to a welding method and application of stainless steel. Background Technology

[0002] T4003 is a practical ferritic stainless steel with good corrosion resistance and mechanical properties. Due to its high cost-effectiveness, it is widely used in railway transportation, coastal construction, papermaking equipment, dyeing equipment, chemical equipment, and pipelines. However, due to the compositional characteristics of T4003 stainless steel, excessive grain growth easily occurs in the heat-affected zone (HAZ) when using conventional gas-shielded welding, leading to a significant deterioration in the impact toughness of the weld joint. This problem severely restricts the further promotion and application of T4003 ferritic stainless steel in structural welding. While existing technologies can alleviate the grain coarsening problem in the HAZ to some extent by reducing welding heat input or controlling interpass temperature, they still cannot effectively solve the problem of deteriorated impact toughness in the HAZ of T4003 welds, and the overall mechanical properties of the weld joints are insufficient to meet practical engineering requirements. Summary of the Invention

[0003] The main objective of this invention is to provide a welding method and application for stainless steel. By adopting multiple measures such as strictly controlling the welding heat input and interpass temperature, and combining the back copper backing plate with the front compressed air forced cooling, the cooling rate of the weld and heat-affected zone is effectively accelerated, the formation of coarse grain zone is suppressed, and the impact toughness of the weld heat-affected zone is significantly improved.

[0004] To achieve the above objectives, the present invention provides a welding method for stainless steel, comprising the following steps: S1. Grind and clean the weld area before welding. S2. After grinding and cleaning, assemble and fix the steel plates to be welded to ensure that the gap at the root of the weld is no more than 1.5mm. S3. After the S2 group is assembled and tack-fixed, a grooved copper backing plate is placed on the back of the weld. S4. After placing the copper backing plate, proceed with welding. During the welding process, control the welding heat input E to be between t-2 and t-0.5 kJ / cm, where t is the plate thickness in cm. The interpass temperature between adjacent weld passes is controlled below 85℃. During the welding process, the weld and heat-affected zone 15-20mm behind the weld pool are forcibly cooled from the front of the weld using compressed air.

[0005] This solution addresses the technical problem of excessive grain growth and significant deterioration of impact toughness in the heat-affected zone during welding of T4003 ferritic stainless steel due to its composition. It provides a gas shielded welding process that employs a synergistic approach of strictly controlling welding heat input and interpass temperature, a copper backing plate on the back, and forced cooling with compressed air on the front. By cleaning the weld area before welding, tack welding to ensure the weld root gap is no more than 1.5mm, placing a grooved copper backing plate on the back and securing it tightly with tooling, and then controlling the welding heat input E to t-2~t-0.5 kJ / cm (t is the plate thickness in cm) during welding, and ensuring the interpass temperature between adjacent weld passes does not exceed 85℃, and by using compressed air to force-cool the weld and heat-affected zone from the front of the weld at a distance of 15~20mm behind the weld pool, the cooling rate of the weld and heat-affected zone is significantly accelerated, effectively suppressing the formation of coarse grains. As a result, the impact toughness of the weld heat-affected zone is significantly improved compared to conventional welding processes. This successfully solves the core technical problem of the deterioration of the toughness of the heat-affected zone in T4003 ferritic stainless steel welding, and provides a guarantee for its reliable application in the welding of structural components in railway transportation, coastal construction, and chemical equipment.

[0006] Specifically, 1) Welding heat input is strictly limited to E=t-2~t-0.5 kJ / cm (t is plate thickness, unit cm), which reduces the total heat input to the base material from the source, lowers the peak HAZ temperature and the high-temperature residence time of 1100~1400℃, and directly inhibits the driving force of grain growth; 2) The temperature between adjacent weld layers is controlled below 85℃, which prevents the heat from accumulating layer by layer during multi-layer and multi-pass welding, and avoids repeated heating of the HAZ to further prolong the grain growth window; 3) A grooved copper backing plate is placed on the back of the weld and the tooling is tightly fixed, and the high thermal conductivity of copper (far higher than that of stainless steel) is used to achieve forced heat conduction on the back, which significantly accelerates the heat dissipation from the root of the weld and the bottom area of ​​the HAZ; 4) Compressed air is used to force-cool the weld and heat-affected zone from the front of the weld at a distance of 15~20mm behind the weld pool, and the residual heat on the surface of the HAZ is directly removed by convection heat transfer, which further shortens the cooling time of the entire HAZ in the rapid grain growth temperature range. Low heat input and low interlayer temperature reduce heat from the input end, low interlayer temperature and the back copper pad accelerate heat dissipation from the conduction end, and front compressed air cooling achieves the most direct and fastest cooling from the convection end. The combined effect of these three factors greatly improves the cooling rate of HAZ and significantly shortens the residence time in the grain coarsening sensitive temperature range, thereby effectively avoiding the formation of coarse grain regions.

[0007] According to an embodiment of the present invention, the root gap of the weld is no greater than 1.2 mm.

[0008] According to an embodiment of the present invention, the copper backing plate and the steel plate are tightly fixed by tooling, and the contact gap between the copper backing plate and the back of the weld is no more than 0.5 mm.

[0009] According to an embodiment of the present invention, the injection pressure of the compressed air is 0.3 to 0.6 MPa.

[0010] According to an embodiment of the present invention, the welding heat input E is t-1.8 to t-0.8 kJ / cm.

[0011] According to an embodiment of the present invention, the compressed air injection position is 16-18 mm behind the weld pool.

[0012] According to an embodiment of the present invention, the welding step includes multi-layer, multi-pass welding; The multi-layer, multi-pass welding includes root pass welding, fill pass welding, and cover pass welding.

[0013] This invention also proposes the application of a stainless steel welding method in the preparation of ferritic stainless steel welded products.

[0014] According to an embodiment of the present invention, the ferritic stainless steel welded products include at least one of welded structural components, railway transportation equipment components, coastal building components, chemical equipment and pipelines, papermaking equipment, and dyeing equipment.

[0015] According to an embodiment of the present invention, the stainless steel includes ferritic stainless steel T4003. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the welded joint in Example 1; Figure 2 This is a schematic diagram of frontal jet cooling according to an embodiment of the present invention; The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0020] Example 1 Welding of 5mm thick T4003 ferritic stainless steel: A welding method for T4003 ferritic stainless steel, comprising the following steps: S1. Before welding, grind and clean the weld area to remove impurities and oxides; S2. After grinding and cleaning in S1, assemble and fix the steel plates to be welded to ensure that the gap at the root of the weld is no more than 1.5mm. S3. After the S2 assembly is fixed by tack fixing, a grooved copper backing plate is placed on the back of the weld and it is tightly fixed to the steel plate by tooling. S4. After fixing the copper backing plate in S3, welding is carried out. During the welding process, the welding heat input E is controlled to be t-2~t-0.5kJ / cm (where t is the plate thickness in cm). The interpass temperature between adjacent welds is controlled below 85℃. At the same time, the weld and heat-affected zone 15-20mm behind the weld pool are forced to cool from the front of the weld using compressed air.

[0021] In this embodiment, the plate thickness is 5mm, the welding heat input E is 3 to 4.5kJ / cm, the welding heat input for the root pass is 4kJ / cm, the welding heat input for the cover pass is 3.6kJ / cm, and the interpass temperature is controlled at 70℃.

[0022] This embodiment effectively accelerates the cooling rate of the weld and heat-affected zone by strictly controlling the welding heat input and interpass temperature, and employing multiple measures such as a copper backing plate on the back combined with forced cooling with compressed air on the front, significantly suppressing excessive grain growth in the weld heat-affected zone. Testing showed that the impact toughness of the heat-affected zone after welding in this embodiment was significantly improved compared to conventional welding processes, successfully solving the problem of deteriorated impact toughness in the heat-affected zone of T4003 ferritic stainless steel.

[0023] Figure 1 This is a schematic diagram of the structure of the T4003 ferritic stainless steel welded joint of the present invention. Figure 1As shown, the welded joint adopts a multi-layer, multi-pass welding method, mainly including a root pass (1), a filler pass (2), and a capping pass (3). The root pass (1) is located at the root of the weld, mainly ensuring root penetration and good weld formation; the filler pass (2) is used to fill the groove space; and the capping pass (3) is located at the top of the weld, mainly ensuring a smooth weld surface and good appearance quality. This figure clearly illustrates the layered structure of the welded joint of the present invention, which helps to understand the implementation of multi-layer, multi-pass welding in actual welding processes.

[0024] Figure 2 This is a schematic diagram of front-side air jet cooling during the welding process of this invention. Figure 2 As shown, during the welding process, after the weld pool is formed, a compressed air nozzle is installed 15-20 mm behind the weld pool to directly spray compressed air from the weld front onto the weld and heat-affected zone behind the weld pool for forced cooling. This cooling measure, combined with the thermal conductivity of the copper backing plate, can significantly accelerate the cooling rate of the weld heat-affected zone, effectively suppress excessive grain growth, and thus improve the impact toughness of the T4003 ferritic stainless steel welded joint.

[0025] Example 2: 7mm thick T4003 ferritic stainless steel welding A welding method for T4003 ferritic stainless steel includes the following steps: S1. Before welding, grind and clean the weld area to remove impurities and oxides; S2. After grinding and cleaning in S1, assemble and fix the steel plates to be welded to ensure that the gap at the root of the weld is no more than 1.5mm. S3. After the S2 assembly is fixed by tack fixing, a grooved copper backing plate is placed on the back of the weld and it is tightly fixed to the steel plate by tooling. S4. After fixing the copper backing plate in S3, welding is carried out. During the welding process, the welding heat input E is controlled to be t-2~t-0.5kJ / cm (where t is the plate thickness in cm). The interpass temperature between adjacent welds is controlled below 85℃. At the same time, the weld and heat-affected zone 15-20mm behind the weld pool are forced to cool from the front of the weld using compressed air.

[0026] In this embodiment, the plate thickness is 7mm, the welding heat input E is 5-6.5kJ / cm, the welding heat input for the root pass is 6.2kJ / cm, the welding heat input for the fill pass is 5.5kJ / cm, the welding heat input for the cover pass is 5kJ / cm, and the interpass temperature is controlled at 75℃.

[0027] This embodiment effectively accelerates the cooling rate of the weld and heat-affected zone by strictly controlling the welding heat input and interpass temperature, and employing multiple measures such as a copper backing plate on the back combined with forced cooling with compressed air on the front, significantly suppressing excessive grain growth in the weld heat-affected zone. Testing showed that the impact toughness of the heat-affected zone after welding in this embodiment was significantly improved compared to conventional welding processes, successfully solving the problem of deteriorated impact toughness in the heat-affected zone of T4003 ferritic stainless steel.

[0028] Comparative Example 1 This comparative example provides a welding method for T4003 ferritic stainless steel. The welding process parameters are the same as those in Example 1, except that a copper backing plate is not set on the back, and forced cooling with compressed air on the front is not used. Natural cooling is still used instead.

[0029] Compared with the embodiments of the present invention, although Comparative Example 1 reduced the grain coarsening of the heat-affected zone to a certain extent by controlling the heat input and interlayer temperature, the cooling rate was still slow, and the improvement effect on the impact toughness of the heat-affected zone was limited, failing to reach the optimal level of the present invention.

[0030] Comparative Example 2 This comparative example provides a welding method for T4003 ferritic stainless steel. The difference from the embodiment is that it does not use front-side compressed air forced cooling, but instead uses natural cooling.

[0031] Comparative Example 2 lacks front-side forced convection cooling, resulting in limited improvement in impact toughness.

[0032] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A welding method for stainless steel, characterized in that, Includes the following steps: S1. Grind and clean the weld area before welding. S2. After grinding and cleaning, assemble and fix the steel plates to be welded to ensure that the gap at the root of the weld is no more than 1.5mm. S3. After the S2 group is assembled and tack-fixed, a grooved copper backing plate is placed on the back of the weld. S4. After placing the copper backing plate, proceed with welding. During the welding process, control the welding heat input E to be between t-2 and t-0.5 kJ / cm, where t is the plate thickness in cm. The interpass temperature between adjacent weld passes is controlled below 85℃. During the welding process, the weld and heat-affected zone 15-20mm behind the weld pool are forcibly cooled from the front of the weld using compressed air.

2. The stainless steel welding method according to claim 1, characterized in that, The root gap of the weld is no more than 1.2 mm.

3. The stainless steel welding method according to claim 1, characterized in that, The copper backing plate and the steel plate are tightly fixed by tooling, and the gap between the copper backing plate and the back of the weld is no more than 0.5 mm.

4. The stainless steel welding method according to claim 1, characterized in that, The injection pressure of the compressed air is 0.3 to 0.6 MPa.

5. The stainless steel welding method according to claim 1, characterized in that, The welding heat input E is t-1.8 to t-0.8 kJ / cm.

6. The stainless steel welding method according to claim 1, characterized in that, The compressed air is injected at a position 16-18 mm behind the weld pool.

7. The stainless steel welding method according to claim 1, characterized in that, The welding process includes multi-layer, multi-pass welding; The multi-layer, multi-pass welding includes root pass welding, fill pass welding, and cover pass welding.

8. The application of a welding method for stainless steel as described in any one of claims 1 to 7 in the preparation of ferritic stainless steel welded articles.

9. The application according to claim 8, characterized in that, The ferritic stainless steel welded products include at least one of the following: welded structural components, railway transportation equipment components, coastal building components, chemical equipment and pipelines, papermaking equipment, and dyeing equipment.

10. The application according to claim 8, characterized in that, The stainless steel includes ferritic stainless steel T4003.

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