Residual stress is easily generated during the production of stainless steel structural parts due to processes such as welding, cutting, and heat treatment. Improper control can lead to structural deformation, cracking, or reduced corrosion resistance, directly affecting their service life and safety. Therefore, a comprehensive approach involving process design, process control, and post-treatment is necessary to effectively reduce residual stress levels.
In the welding process, residual stress mainly stems from differences in thermal expansion caused by uneven heating. To reduce this stress, welding process parameters need to be optimized. For example, controlling welding current, voltage, and speed can reduce heat input and avoid excessive temperature gradients between the weld zone and the heat-affected zone. Simultaneously, adopting a reasonable welding sequence and joint type is crucial. For instance, symmetrical welding and segmented back-welding methods can disperse concentrated heat and reduce restraint stress; while bevel design should avoid sharp corner transitions to reduce the risk of stress concentration. Furthermore, for large stainless steel structural parts, pre-setting anti-deformation amounts or using rigid clamps for fixation before welding can offset some welding deformation, thereby indirectly controlling residual stress.
During machining, intense friction between the tool and the workpiece generates localized high temperatures, leading to plastic deformation of the surface material while the inner material remains elastic, resulting in residual tensile stress. To mitigate this problem, cutting parameters need to be optimized, such as reducing the feed rate and increasing the cutting speed to minimize heat buildup. Simultaneously, using sharp tools and controlling the cutting edge radius can reduce cutting forces and the coefficient of friction. For precision stainless steel structural parts, dry cutting or micro-lubrication techniques can reduce the heat-affected zone and prevent coolant interference with surface quality. Furthermore, post-machining surface strengthening treatments, such as shot peening or roll forming, can introduce a residual compressive stress layer on the surface, effectively offsetting the original tensile stress and improving fatigue resistance and corrosion resistance.
Heat treatment is a crucial step in controlling residual stress in stainless steel structural parts. For welded parts, post-weld solution treatment can eliminate carbide segregation in the weld zone, restore material toughness, and promote residual stress relaxation through uniform heating and slow cooling. Stress-relief annealing, on the other hand, uses low-temperature holding (typically 300-450℃) to rearrange dislocations within the material, reducing stress levels. It is important to note that the annealing temperature must be strictly controlled outside the sensitization temperature range (450-850℃) to avoid the risk of intergranular corrosion. For cold-worked parts, such as stamped or drawn stainless steel structural parts, recrystallization annealing can eliminate work hardening, restore ductility, and release internal residual stress.
Vibration aging technology, with its high efficiency and energy-saving advantages, has become the preferred solution for residual stress control in large stainless steel structural parts. This technology applies mechanical vibration at a specific frequency using a vibrator, causing the workpiece to resonate and promoting micro-grain slippage and twinning, thereby homogenizing and reducing residual stress. Compared to traditional thermal aging, vibration aging eliminates the need for high-temperature heating, preventing workpiece deformation or performance degradation. Its short processing cycle (typically 1-2 hours) makes it suitable for on-site operations. For example, in the manufacture of large stainless steel structures such as ships and bridges, vibration aging is widely used for stress relief in weld areas and overall components, significantly improving structural stability.
For areas with high localized stress, targeted stress relief can be achieved through localized heat treatment or mechanical methods. For instance, residual tensile stress at welded joints can be locally annealed using induction heating or flame heating, achieving precise stress control by adjusting the heating range and cooling rate. For surface microcracks or stress concentration areas, high-frequency shock waves can be used in HOKEN localized stress relief equipment to induce surface plastic deformation, repairing surface defects and reducing stress peaks. Furthermore, for high-precision stainless steel structural parts, electropolishing or chemical passivation can remove surface machining marks, forming a dense passivation film that indirectly improves corrosion resistance and stress distribution uniformity.
Controlling residual stress in stainless steel structural parts must be integrated throughout the entire process of design, machining, and post-processing. By optimizing welding processes, cutting parameters, and heat treatment regimes, and combining vibration aging and local strengthening techniques, the residual stress can be comprehensively controlled, thereby improving the dimensional stability, fatigue resistance, and corrosion resistance of structural components, and meeting the stringent requirements of high-end equipment manufacturing.
