The ferrite predicting diagrams are developed by calculations that use chemical analyses and measured ferrite content, then correlating composition and ferrite content. Since both composition and ferrite content are measured, each input data point used in developing the correlation has a degree of uncertainty associated with it. The uncertainty in ferrite measurement and approaches to make it as reproducible as possible were considered in great detail in WRC Bulletin 318. A series of predicting diagrams have been developed using chemical composition and measured ferrite content, including the Schaeffler Diagram (1949), the DeLong Diagram (1973) and the WRC-1988 Diagram. The latter was first published in the Welding Journal in December, 1988 (hence the name "WRC-1988 Diagram") and then was more completely described, with its supporting data, in WRC Bulletin 342. Each successive diagram was considered to be an improvement on the preceding diagram, but the degree of uncertainty in each diagram remained somewhat unknown.

The first purpose of this new WRC Bulletin is to provide a single source for information about prediction of ferrite in austenitic and duplex stainless steel weld metals that has been developed since the WRC-1988 Diagram was published. It is also noted that the WRC-1988 Diagram did not make predictions concerning the appearance of martensite in stainless steel weld metals. The second purpose is to provide a single source for information developed since 1988 about martensite prediction in stainless steel weld metals.