Low thermal expansion cast steel with excellent machinability

摘要

PROBLEM TO BE SOLVED: To provide a low thermal expansion cast steel having a low coefficient of thermal expansion and excellent in machinability. ;SOLUTION: In the cast steel, an austenitic matrix structure has 0.5-3% graphite by area ratio, 0.02-0.3% lumpy MnS by area ratio, and (10 to 700) pieces/mm2 of ≥8 μm platelet MnS. Moreover, this cast steel has a chemical composition which contains, by mass, 0.3-0.9% C, ≤1.5% Si, ≤1.0% Mn, 0.01-0.3% S, 25-40% Ni, and 0.005-0.1% Mg and in which the contents of S and Mn satisfy a relation represented by S≤(1/4)Mn or (1/4)MnS≤(1/4)Mn+0.05. This chemical composition can contain ≤12 mass % Co and further ≤4 mass % Cr.;COPYRIGHT: (C)2001,JPO