Stainless steel is a metal material with excellent corrosion resistance, aesthetics, and strength, widely used in various industrial and civil fields. Welding stainless steel is a technique to join stainless steel parts into a whole, playing an important role in ensuring the performance and quality of stainless steel. This article will introduce common welding methods and techniques for stainless steel, as well as considerations during the welding process.
I. Common Welding Methods for Stainless Steel
Common welding methods for stainless steel include Manual Metal Arc Welding (MMA), Metal Inert Gas (MIG) / Metal Active Gas (MAG) Welding, and Tungsten Inert Gas (TIG) Welding.
1. Manual Metal Arc Welding (MMA):
This is a widely used and easy-to-use welding method suitable for various thicknesses and shapes of stainless steel. Manual metal arc welding utilizes the heat generated by the arc between the welding rod and the workpiece to melt the welding rod and the metal of the workpiece, filling the weld joint and forming a strong connection.
Advantages of manual metal arc welding: Simple equipment, low cost, flexible operation, strong adaptability, can be performed in various environments such as indoors, outdoors, and underwater.
Disadvantages of manual metal arc welding: Slow welding speed, unstable weld quality, prone to defects such as porosity, cracks, oxidation, and deformation, requiring subsequent cleaning and repair.
2. Metal Inert Gas (MIG) / Metal Active Gas (MAG) Welding:
This is an automatic or semi-automatic gas shielded arc welding method suitable for medium to thin stainless steel plates. Metal inert gas welding utilizes continuously fed metal wire as the electrode and filler material, generating an arc between the wire and the workpiece while using inert or active gas to protect the arc and weld pool from atmospheric elements such as oxygen and nitrogen, thereby achieving high-quality welding.
Advantages of metal inert gas welding: Fast welding speed, high weld quality, minimal deformation, simple operation, wide application range.
Disadvantages of metal inert gas welding: Complex equipment, high cost, requires high wind speed and environmental conditions, not suitable for welding in outdoor or poorly ventilated areas.
3. Tungsten Inert Gas (TIG) Welding:
This is a high-quality gas shielded arc welding method suitable for thin plates and pipes of stainless steel. Tungsten inert gas welding utilizes a non-consumable tungsten electrode to generate an arc between the electrode and the workpiece, while using pure argon or argon-helium mixed gas to protect the arc and weld pool, preventing oxidation and nitriding, thereby achieving high-quality welding.
Advantages of tungsten inert gas welding: High weld quality, minimal deformation, few pores, few cracks, good welding performance, wide range of applicable materials.
Disadvantages of tungsten inert gas welding: Slow welding speed, high cost, difficulty in operation, high requirements for power source stability, not suitable for welding under high currents.
II. Welding Techniques for Stainless Steel
1）Selecting the appropriate welding method and parameters:
Based on factors such as the type, thickness, shape, structure, and application of stainless steel, choose the most suitable welding method and parameters to ensure the quality and efficiency of welding.
For stainless steel with a thickness above 3mm, manual metal arc welding or metal inert gas welding can be used;
For stainless steel with a thickness between 0.5-3mm, metal inert gas welding or tungsten inert gas welding can be used;
For stainless steel with a thickness below 0.5mm, tungsten inert gas welding or laser welding can be used.
The selection of welding parameters should be comprehensively considered based on factors such as welding method, welding power source, welding electrode, welding gas, and welding position. Generally, it should follow the principles of low current, low voltage, fast speed, and low heat input to reduce the range and degree of heat-affected zone, preventing defects such as intergranular corrosion, thermal cracking, and deformation.
2）Cleaning the welding area and welding materials:
Before welding, clean the surface of the welding area and welding materials to remove impurities such as oil, moisture, rust, and oxide scale to prevent defects such as pores, slag inclusions, oxidation, and corrosion in the weld seam. Cleaning methods can include mechanical grinding, chemical treatment, ultrasonic cleaning, etc., and the cleaning range should extend at least 25mm on both sides of the weld seam. The cleaned surface should exhibit a metallic luster without any residue of contaminants.
3）Protecting the welding area and weld seam:
During the welding process, ensure that the welding area and weld seam are not invaded by elements such as oxygen and nitrogen in the air to prevent defects such as oxidation and nitriding in the weld seam. Protection methods can include gas shielding, coating protection, vacuum protection, etc., covering the arc zone, weld pool zone, and heat-affected zone. The protection should last until the weld seam is completely cooled. The selection of shielding gas should be based on the type of stainless steel and welding method, generally using pure argon or argon-helium mixed gas. The flow rate and pressure of the gas should be appropriately adjusted to ensure stability and uniformity, preventing gas leakage and disorder.
4）Controlling welding temperature and deformation:
During the welding process, control the welding temperature and deformation to prevent defects such as intergranular corrosion, thermal cracking, and stress corrosion cracking in the weld seam. Control methods can include preheating, interlayer temperature control, post-heating, forced cooling, alignment, symmetry, segmentation, etc., aiming to maintain uniform and moderate temperatures at the welding area, reduce welding stress and strain, and prevent welding deformation and residual stress.
For austenitic stainless steel, welding temperature should be controlled below 350 degrees Celsius, and interlayer temperature should be controlled between 150-250 degrees Celsius, without the need for preheating and post-heating;
For ferritic stainless steel, welding temperature should be controlled between 200-300 degrees Celsius, and interlayer temperature should be controlled between 100-200 degrees Celsius, requiring appropriate preheating and post-heating;
For duplex stainless steel, welding temperature should be controlled between 250-350 degrees Celsius, and interlayer temperature should be controlled between 150-250 degrees Celsius, requiring appropriate preheating and post-heating.
5）Selecting appropriate welding materials and welding processes:
Based on factors such as the type, composition, and performance of stainless steel, choose matching welding materials and welding processes to ensure the mechanical properties and corrosion resistance of the weld seam.
For austenitic stainless steel, matching or similar austenitic stainless steel welding wire or electrode can be used, or austenitic stainless steel welding wire or electrode with higher nickel content can be used to improve weld seam plasticity and toughness, preventing cold cracking;
For ferritic stainless steel, matching or similar ferritic stainless steel welding wire or electrode can be used, or austenitic stainless steel welding wire or electrode with higher nickel content can be used to improve weld seam toughness and corrosion resistance, preventing hot cracking;
For duplex stainless steel, matching or similar duplex stainless steel welding wire or electrode can be used, or austenitic stainless steel welding wire or electrode with higher nickel content can be used to maintain the dual-phase structure and balanced performance of the weld seam, preventing phase transformation and embrittlement.
The selection of welding processes should be comprehensively considered based on factors such as welding method, welding position, welding direction, and welding joint form. Generally, it should follow the principles of short weld seams, small gaps, minimal overlap, and moderate angles to reduce welding deformation and residual stress.
6）Inspecting and evaluating welding quality:
After welding, inspect and evaluate the weld seam to determine whether the welding quality meets the requirements and whether there are defects and non-conformities. Inspection and evaluation methods can include visual inspection, tactile inspection, percussion inspection, measurement, shearing, bending, tensile testing, impact testing, hardness testing, metallography, non-destructive testing, etc. The inspection and evaluation should cover the appearance, dimensions, shape, position, angle, alignment, symmetry, integrity, uniformity, smoothness, absence of pores, slag inclusions, cracks, oxidation, corrosion, deformation, stress, etc., of the weld seam.
The standards for inspection and evaluation should be determined based on factors such as the type, application, and performance of stainless steel, generally complying with relevant national standards, industry standards, enterprise standards, or contract specifications. If defects or non-conformities are found in the weld seam, timely repairs or rework should be carried out to ensure welding quality and safety.
III. Conclusion
Stainless steel is an excellent metal material with extensive application value and development prospects. Welding stainless steel is an important joining technology, playing a significant role in ensuring the performance and quality of stainless steel. Welding stainless steel requires mastering correct welding methods, welding techniques, and methods for inspecting welding quality to prevent various defects and non-conformities in the weld seam, improving the effectiveness and safety of welding. This article provides a detailed introduction and analysis of stainless steel welding from three aspects: common welding methods, welding techniques, and methods for inspecting welding quality, hoping to provide assistance and reference for relevant personnel engaged in stainless steel welding.
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