Existing form of iron, carbon in alloy chromium carbide overlay plate

If we add alloy elements in the steel plate, they will exist in solid solution (combine with iron) and carbide (combine with carbon) forms:

1.Soluble in iron
Almost all of the alloy elements (except Pb) can be dissolved in iron and being alloy fer-rite or alloy austenitic, according to their act to α-Fe or γ-Fe, the alloy can be divided into expanded austenite phase region and narrowing austenite phase region two categories.

Expanding γ phase region: also known as austenite stabilizing elements, mainly are Mn, Ni, Co, C, N, Cu, etc. They make the point A3 (transition point γ-Fe α-Fe ) decreased, point A4 (transition point γ-Fe) rise, thus expanding the existence range of γ phase region, and γ phase region will extend to room temperature when we add a certain amount of Ni, Mn, even other elements (such as C、N、Cu ) can expand γ phase region, but cannot expand to room temperature.

Narrowing austenite phase region: also known as fer-rite stabilizing elements, mainly are Cr, Mo, W, V, Ti, Al, Si, B, Nb, Zr etc. They make the point A3 decreased and point A4 rise (except for chromium, A3 point decline if chromium content is less than 7%, but will has a rapid rise if it is more than 7% ).

2.Formation of carbides
Alloy elements can be divided into carbide forming elements and non carbide forming elements. Common non carbide forming elements are: Ni, Co, Cu, Si, Al, N, B etc, and dissolved in fer-rite and austenite. Common carbide forming elements are: Mn, Cr, W, V, Nb, Zr, Ti etc., some of them will soluble in the matrix phase, others will become alloy cementite.