The Hardening Properties of AISI 321 Stainless Steel
AISI 321 stainless steel is an austenitic stainless steel offering higher levels of oxidation resistance, strength and corrosion resistance than conventional 304 stainless steel. This alloy is specially formulated to show improved characteristics when exposed to high temperatures. Due to a higher degree of chromium and nickel content, AISI 321 stainless steel is able to demonstrate a particularly high level of resistance to oxidation in comparison to many other metals. It is for this reason that it is often found in applications where high temperatures or strenuous environmental conditions are present. As a result, it has become a popular choice in many industries, from building and construction to aircraft, automotive and food processing.
When looking to fabricate components with AISI 321 stainless steel, it is important to consider the hardening properties at play. Other stainless steels can harden dramatically when subjected to cold working, but AISI 321 tends to stay relatively soft, thereby making it a more suitable choice for forming and shaping operations. This does not necessarily mean that it cannot be successfully put through a process of hardening. In fact, AISI 321 can be hardened in a variety of ways to suit the specific purpose and needs of the application in question.
Induction hardening is often used on AISI 321 components, due to the fact that it is fast and effective while still enabling a reasonable degree of control. This method works by using a coil to generate an oscillating magnetic field above the steel, inducing a strong eddy current through the AISI 321 part and in turn generating a sizeable amount of heat energy. It is essential that the part remains stable during this process and appropriate holding fixtures should be employed.
Martensitic treatments can also be applied, as AISI 321 stainless steel can be heated and rapidly cooled (quenched) in order to harden the surface of the part. This is a cost-effective and simple hardening process and whilst it tends to result in surface hardening only, it can be beneficial from a fatigue and stress perspective.
Another method of hardening AISI 321 is with passivation, a chemical treatment involving the application of nitric or citric acid. This can be used to remove contaminants from the surface of AISI 321 parts, particularly after processes like grinding or machining, and can therefore enhance the corrosion resistance properties of the steel and protect the part against accidental damage.
Since AISI 321 stainless steel is so versatile, it can be hardened in multiple ways, allowing the fabricator to achieve the desired performance characteristics while staying within the time and cost constraints of the application in question. Ultimately, understanding the hardening properties of AISI 321 will provide the best possible outcome.
