Resistance to Corrosion and Passivation of 316L Stainless Steel Directionally Solidified Samples

Abstract

The three main types of crystalline structure that stainless steel can be classified are Austenitic, Ferritic and Martensitic. Austenite, also known as gamma phase iron (γ-Fe), is a metallic, nonmagnetic allotrope of iron or a solid solution of iron, with an alloying element. Ferrite, also known as α-ferrite (α-Fe) or alpha iron is a materials science term for pure iron, with a body-centered cubic crystal structure. It is this crystalline structure which gives steel and cast iron their magnetic properties. Martensite most commonly refers to a very hard form of steel crystalline structure, but it can also refer to any crystal structure that is formed by displacive transformation (Lambers et. al., 2009 and Batra et al., 2003). These are alloys containing chromium and nickel (sometimes manganese and nitrogen), structured around the type 302 composition of iron, 18%Cr, and 8%Ni. Austenitic steels are not hardenable by heat treatment. The most familiar stainless steel is probably type 304, sometimes called T304 or simply 304. Type 304 surgical stainless steel is austenitic steel containing 18-20%Cr and 8-10%Ni (Kilicli & Erdogan, 2008). Primary stainless steel used in aviation construction. Chemical and steel industry applicable grades are 308, 308L, 316, 316L, 316LN Nitrogen bearing, 312, 309L, 310L L denotes carbon percentage less than 0.03%, mostly used for corrosion heat resistance have work hardening properties, welding primarily done by TIG and MMAW process. Another grade, 312 is used for dissimilar steel welding, also known as universal alloy steel as unknown composition steels can be welded. For high temperature application, above 600 °C, 309 and 310 grades are preferred.