How to prevent stress corrosion cracking of stainless steel torsion springs during production

Stainless steel torsion springs are widely used in industries such as machinery, aviation, medical, and marine. Springs are subject to repeated torsion and external loads during use. Improper materials or production processes can easily lead to stress corrosion cracking, which can affect the spring's lifespan and equipment safety. Preventing stress corrosion cracking is a crucial step in producing high-quality stainless steel torsion springs.

Choosing the Right Stainless Steel Material
Material selection is the first step in preventing stress corrosion cracking. Common austenitic stainless steels such as 304 and 316L offer excellent corrosion resistance and toughness, making them suitable for most environments. For high-strength springs, low-carbon austenitic stainless steel or precipitation-hardening stainless steel can be selected to reduce the risk of intergranular corrosion and stress concentration. Impurity levels in the material should be strictly controlled to avoid localized corrosion and crack formation caused by elements such as sulfur and phosphorus.

Optimizing Heat Treatment Processes
Heat treatment can eliminate residual stresses generated during the manufacturing process and improve the spring's stress corrosion resistance. Annealing evens out the grain size, reduces internal stress concentrations, and improves the spring's toughness. For high-strength stainless steel torsion springs, low-temperature aging can stabilize mechanical properties and prevent brittleness caused by excessive hardening. During heat treatment, the temperature, holding time, and cooling rate should be strictly controlled to avoid thermal stress causing crack sources.

Controlling Cold Working Stress
Bending and coiling during torsion spring forming introduce internal stresses. A moderate amount of cold working and a reasonable coiling radius should be used to avoid excessive localized stresses. If necessary, intermediate annealing or stress relief treatment can be performed to reduce the impact of residual stress on corrosion-sensitive areas. Bending and coiling operations should be performed evenly and smoothly to prevent microcracks on the material surface.

Surface Finishing
Surface defects are a major cause of stress corrosion cracking. Polishing, grinding, and fine deburring can reduce surface microcracks and stress concentration points. Electrochemical polishing further removes surface oxides and impurities, improving corrosion resistance. A high-quality surface finish not only reduces the risk of stress corrosion cracking but also reduces friction and wear, thereby increasing spring life.

Surface Protection and Passivation
Passivation is a crucial process for preventing stress corrosion cracking. It chemically forms a dense oxide film on the stainless steel surface, enhancing resistance to pitting and crevice corrosion. Passivation solutions typically contain nitric acid or nitrous acid, which remove residual iron ions from the surface and stabilize the chromium oxide film. If necessary, they can be combined with plating or spraying to enhance the corrosion barrier, making them particularly suitable for marine or chemically corrosive environments.

Strictly Control the Production Environment
Environmental factors during the production process significantly impact stress corrosion cracking. High chloride ion environments and contact with strong acids and bases should be avoided. Processing, cleaning, and storage should be kept dry and contamination-free to reduce surface corrosion sources. Deionized water should be used for aqueous solutions or cleaning agents to prevent residual chloride ions from inducing localized corrosion.