Relationship Between Degree of Homogeneity and Physical and Mechanical Properties of a Sintered Nickel Steel

Abstract

Commercial production of low-alloy steel components from blended mixtures of the constituents in powder form involves the use of sintering times which are too short to allow the production of a chemically homogeneous material. This has prompted an investigation into the relationships between the degree of homogeneity, microstructure, and mechanical properties in a sintered and heat-treated low-alloy steel, prepared in this way. A quantitative assessment has been made of the degree of homogeneity by measuring the nickel content of a large number of small areas within a complete cross-section of the specimen and this has been compared with plated and pre-alloyed material with the same overall composition but greater homogeneity prior to sintering. Provided the degree of homogenization was greater than a certain critical value the relationship between tensile strength and porosity fitted well with previously published work. The production of small quantities of non-martensitic phases from austenite during quenching was not detrimental in such alloys but, in quenched specimens of less homogenous alloys, residual austenite had a very detrimental effect on tensile strength, particularly when the austenite was distributed as a thin interparticle network. The relationship between tensile strength and porosity in these heterogeneous alloys did not agree with any of the accepted equations that represent this relationship.