Alloys

What do… AISI 304, AISI 316, AISI 316L and AISI 316Ti mean?

• AISI 304 (1.4301) contains 18% chromium and 8% nickel. This alloy in fully annealed condition is non-magnetic and cannot be hardened, and in cold formed condition it is slightly magnetic. Less susceptible to precipitation of chromium carbides during welding.
• AISI 316 (EN 1.4401) containing 16% chromium and 10% nickel and 2% molybdenum is a more corrosion resistant but more expensive type of stainless steel. Type 316 offers higher resistance to salt corrosion and is widely used in the chemical industry.
• 316L (1.4404, "L" stands for "low carbon") is low in carbon in order to produce a more easily weldable stainless steel, and to make it less susceptible to corrosion after welding.
• Another way of making this steel more weldable is by adding titanium to the alloy, thus producing type 316Ti (1.4571). Technically speaking, this solution is virtually equivalent. It is only when considering architectural applications that one has to take into account the "typical" grinding characteristics of titanium alloy types.
• The magnetic property of stainless steel is determined by its crystal structure, i.e. by the composition of the type of SS. Stainless steel types containing 6-26% nickel (the AISI 300 series) are austenitic and are therefore non-magnetic when supplied. They offer excellent deformability (bending, deep drawing, expansion) and are also shock resistant throughout the temperature range; from very cold to very hot temperatures. Nickel ensures that the steel remains in its austenitic condition when cooling. The other elements increase the corrosion resistance and workability of the steel. However, severe cold forming will alter its crystal structure, resulting in magnetic properties in austenitic SS. In contrast, martensitic, ferritic and duplex types of stainless steel are magnetic.

What is the meaning of… 18/8 and 18/10?

Stainless steel utility products are often labelled as:

• inox 18/8. This indicates that the alloy consists of 18% chromium and 8% nickel. This alloy offers a mechanical tensile strength of 600 N/mm² and a hardness of 175–200 HB. This is a widely used steel due to its good heat resistance up to 400°C. This steel is also known as AISI 304 (1.4301) or AISI 302. It is ideal for cold forming, which produces the so-called work hardening. Cold forming makes the alloy slightly magnetic. It is highly weldable. It is an austenitic corrosion resistant chromium nickel steel.
• inox 18/10. This indicates that the alloy consists of 18% chromium and 10% nickel.