FREE-MACHINING POWDER METALLURGY LEAD-FREE STEEL ARTICLES AND METHOD OF MAKING SAME

摘要

A small diameter, elongated steel article, comprising fully consolidated, prealloyed Pb-free metal powder having a superior machinability is disclosed. The consolidated metal powder has a microstructure that has substantially uniform distribution of fine grains having an ASTM grain size number of not smaller than about 9 when determined in accordance with ASTM Standard Specification E 112. The microstructure of the consolidated metal powder is further characterized by having a plurality of sulfides not larger than about 2 microns (2 µm) in major dimension and a plurality of substantially sphero?dal carbides uniformly distributed throughout the consolidated metal powder that are not greater than about 6 microns (6 µm) in major dimension, both fully geometrically compatible with the ISO Tolerance grade and surface roughness requirements to satisfy. A process for making the elongated steel article is also disclosed.