Stainless steel powders and articles produced therefrom by powder metallurgy

An alloy powder comprising, in weight percent, chromium 20 to 28, molybdenum 2 to 3, vanadium 1.5 to 2.5, tungsten 2.5 to 3.5, silicon 0.8 to 1.5, carbon 0.555 to 2, a strong carbide forming element 0 to 5, and if present, requiring additional carbons sufficient to form carbides therewith so as to give C.sub.min =(%V.times.0.24)+(2.times.%Mo+%W).times.0.03+(%Nb.times.0.13)+(%Ti.times.0 .25)+(%Ta.times.0.066), and

• C.sub.max =C.sub.min +0.3+(%Cr-12).times.0.06, balance iron including incidental impurities, the powder being formed by rapid atomisation followed by an annealing treatment such that the powder contains at least 12% of chromium in solution and a dispersion of carbides.

A method of producing articles by a powder metallurgy process comprising forming a shape by compaction of a powder followed by sintering without the application of external pressure or deformation, in which the powder is a stainless steel alloy powder which has been produced by rapid atomisation followed by an annealing treatment, the alloy powder comprising, in weight percent, chromium 14 to 30, molybdenum 1 to 5, vanadium 0 to 5, tungsten 0 to 6, silicon 0 to 1.5, carbon according to the formula set forth below, a strong carbide forming element 0 to 5, wherein the total of Mo, V and W being at least 3, the balance being iron including incidental impurities, the alloy powder together with any addition of free graphite powder mixed therewith having a minimum and maximum carbon content according to C.sub.min =(%V.times.0.24)+(2.times.%Mo+%W).times.0.03+(%Nb.times.0. 13)+(%Ti.times.0.25)+(%Ta.times.0.066), and

• C.sub.max =C.sub.min +0.3+(%Cr-12).times.0.06, such that the powder has a sufficient carbon content to form carbides with all the Mo, V, W and other strong carbide forming elements present while leaving at least 12% chromium in solution in the matrix.

An alloy powder comprising, in weight percent, chromium 14 to 30, molybdenum 1 to 5, vanadium 0 to 5, tungsten 0 to 6, silicon 0 to 1.5, carbon C.sub.min to C.sub.max, a strong carbide forming element 0 to 5, and a balance iron including incidental impurities,

• wherein C.sub.min =(%V.times.0.24)+(2.times.%Mo+%W).times.0.03+(%Nb.times.0.13)+(%Ti.times.0 .25)+(%Ta.times.0.066) and C.sub.max =C.sub.min +0.3+(%Cr-12).times.0.06, such that the powder includes sufficient carbon to form carbides with all the Mo, V, W and strong carbide forming element present in the powder.