When stainless steel welding joints are subjected to alternating loads, their resistance to fatigue failure directly affects the structural safety and service life. Improving this resistance requires a comprehensive, systematic solution encompassing material selection, welding process optimization, structural design improvement, heat treatment control, surface strengthening, defect control, and environmental management.
Material selection is fundamental to enhancing fatigue resistance. Different types of stainless steel (such as austenitic, martensitic, ferritic, or duplex stainless steel) have different crystal structures and mechanical properties, necessitating the selection of appropriate materials based on specific operating conditions. For example, austenitic stainless steel is widely used due to its excellent toughness and corrosion resistance, but its stainless steel welding joints are prone to hot cracking at high temperatures, requiring the addition of stabilizing elements (such as titanium and niobium) or the use of low-hydrogen welding materials to suppress this cracking. Simultaneously, the chemical composition of the base metal and welding materials should be as compatible as possible to avoid the formation of brittle phases in the weld area due to compositional differences, which would reduce fatigue strength.
Welding process optimization is a crucial step. During welding, parameters such as heat input, welding speed, and interpass temperature directly affect the weld microstructure and residual stress distribution. For example, excessive heat input can lead to coarse weld grains, reducing fatigue resistance; while insufficient heat input may cause defects such as incomplete fusion and porosity. Therefore, it is necessary to determine the optimal parameter range through process experiments and employ advanced technologies such as multi-layer multi-pass welding and pulse welding to refine the grains and reduce welding defects. Furthermore, a reasonable arrangement of the welding sequence (such as symmetrical welding and segmented back-welding) can effectively reduce residual stress and avoid stress concentration.
Structural design improvements can significantly enhance fatigue resistance. The geometry of stainless steel welding joints (such as weld reinforcement and transition fillets) has a significant impact on fatigue life. For example, excessive weld reinforcement can create stress concentration points, becoming the initiation point of fatigue cracks; it needs to be controlled within a reasonable range through grinding or machining. Simultaneously, sharp corners or abrupt cross-sections should be avoided as much as possible in structural design; stress should be dispersed and localized stress levels reduced by using rounded transitions or adding reinforcing ribs. Furthermore, for joints subjected to complex loads, the amplitude of alternating stress can be reduced by optimizing the structural layout (e.g., increasing support points).
Heat treatment control is an important means of improving joint performance. After welding, the joint area may develop brittle structures such as martensite due to rapid cooling, or cracking may occur due to residual stress. Post-weld heat treatment (such as solution treatment, aging treatment, or stress-relieving annealing) can eliminate residual stress, refine grains, and improve microstructure uniformity. For example, after solution treatment, austenitic stainless steel welding joints exhibit fully dissolved carbides, reduced intergranular corrosion tendency, increased toughness, and significantly improved fatigue resistance. The heat treatment process must be precisely tailored to the material type and joint form to avoid performance deterioration due to excessively high temperatures or prolonged holding times.
Surface strengthening treatment can further enhance the fatigue strength of the joint. Surface treatment techniques such as shot peening, rolling, and laser impact can introduce a residual compressive stress layer on the joint surface, offsetting some of the tensile stress generated by alternating loads and delaying the initiation of fatigue cracks. For example, shot peening uses high-speed shot to impact the surface, causing plastic deformation of the surface metal, creating a compressive stress zone, and simultaneously refining the surface grains, improving surface hardness and wear resistance. Surface strengthening treatments require control over the intensity and coverage to avoid surface damage or uneven stress distribution due to overtreatment. Defect control is a prerequisite for ensuring fatigue resistance. Defects such as porosity, slag inclusions, and cracks generated during welding can become the initiation points of fatigue cracks, requiring timely detection and repair through rigorous non-destructive testing (such as radiographic testing and ultrasonic testing). For example, for joints in critical areas, multi-layer inspection (such as initial inspection after welding and re-inspection after heat treatment) can be used to ensure no defects are missed. Simultaneously, the welding environment (such as humidity and wind speed) and operating procedures (such as electrode drying and beveling) must be strictly controlled to prevent defects caused by environmental factors.
Environmental management is equally important. Stainless steel welding joints are prone to stress corrosion cracking in corrosive media (such as chloride ions and acidic environments). The risk of corrosion needs to be reduced through material selection (such as using more corrosion-resistant duplex stainless steel) or surface protection (such as coatings or electroplating). Furthermore, prolonged exposure of the joint to high or low temperatures should be avoided to prevent material degradation or residual stress release due to temperature changes. Regular maintenance and inspection can promptly identify potential problems and extend the service life of the joint.
