Welding Inspection & Metallurgy API ICP Self Study Notes

Wrought materials may consist of one or more microstructural phases that
may have different grain structures. Austenitic stainless steels, for example,
are composed of microstructural phase call austenite, which has grains of the
same crystal structure. Many nickel, aluminum, titanium and copper alloys are
also single-phase materials. Single phase materials are often strengthened
by the addition of alloying elements that lead to the formation of nonmetallic
or intermetallic precipitates. The addition of carbon to austenitic stainless
steels, for example, leads to the formation of very small iron and chromium
carbide precipitates in the grains and at grain boundaries. The effect of these
precipitates is to strengthen the alloy. In general, greater strengthening
occurs with the finer distribution of precipitates. This effect is usually
dependent on temperature; at elevated temperatures, the precipitates begin
to breakdown and the strengthening effect is lost.