What Does Strain-Hardened Stainless Steel Mean?
Strain-hardened stainless steel refers to the stainless steel alloys that have been plastically deformed by cold forming at low temperatures. The mechanical deformation leads to a reduced cross-sectional area, improved strength and reduced ductility. However, the strain hardening process does not alter the chemical properties and the resulting stronger stainless steel retains its high corrosion resistance properties.
Corrosionpedia Explains Strain-Hardened Stainless Steel
The strain hardening, also referred to as cold working or work-hardening, creates and tangles dislocations in the metal structure. The process makes the metal harder and stronger through the resulting plastic deformation.
Strain hardening components, such as the stainless steel bolts, are made by a cold drawing process that reduces the oversized wires or bars to the desired size. The stainless material with a larger diameter than the one desired for the finished product is drawn down through a compression system. The system puts the material under a greater tension and pressure; this strain reduces the diameter while at the same time increasing the strength of the material.
As the metal is plastically deformed, the dislocations move as more are created, and more dislocations within the metal mean more interactions, tangling or pinning of the dislocations. The process leads to a decrease in the mobility of the dislocations and subsequent strengthening of the stainless steel material.
Strain hardening must be performed at low temperatures so that the atoms cannot rearrange themselves and reduce the strengthening, otherwise any excess heat destroys the effect of strain hardening.
The austenitic stainless steel work hardens at a rapid rate as compared to the Ferritic, Martensitic stainless steel types that have limited strain hardening capabilities. The high ductility of austenitic stainless steels allows them to be heavily cold-formed into deep-drawn products with high strength levels and useful levels of toughness and ductility.
The high rate of work-hardening of the austenitic steels make them suitable for applications requiring high strength and corrosion resistance such as the springs used in corrosive environments.
The austenitic stainless steel can only be hardened by cold working; the ferric stainless steels can also be cold worked but their rates are very low and it is difficult to attain high strengths.
Strain hardening increases the strength of the stainless steel without affecting the chemical properties such as corrosion resistance; however, the process decreases the ductility and increases the chances of brittle failure.