Question - What Is The Metallurgical Explanation Of Effects Of Chromium, Nickel, Molybdenum, And Carbon In Stainless Steels?
Answer -
Alloying elements in stainless steels can be divided into 2 main categories namely austenite and ferrite stabilizers. Austenite stabilizers must be present in austenitic as well as martensitic STSs (austenite at annealing temperature is the precursor phase for these two categories although for the latter group, it transforms to martensite before cooling down to room temperature). In order to stabilize austenite at annealing temperature, the ratio of austenite to ferrite stabilizers must be high.
The strongest austenite stabilizers are N, C, Ni, Mn, and Cu whereas elements like Cr, Si, Nb, Ti, and Mo are the most important ferrite stabilizers. Niequivalent to Crequivalent ratio is an effective way to quantify the austenite formation tendency of STSs. There are different expressions for Creq and Nieq, one of which looks like this:
Nieq=Ni+0.3Mn+22C+14.2N+Cu, and Creq=Cr+1.37Mo+1.5Si+2Nb+3Ti).