LOW THERMAL EXPANSION CAST STEEL EXCELLENT IN 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 >=8μm 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)Mn