AUSTENITIC HEAT RESISTANT CAST STEEL HAVING EXCELLENT MACHINABILITY AND PART FOR EXHAUST SYSTEM WHICH COMPRISES SAME

摘要

An austenitic heat resistant cast steel having excellent machinability which comprises in mass % 0.4 to 0.55% of C 1 to 2% of Si 0.5 to 1.5% of Mn 18 to 27% of Cr 8 to 22% of Ni 1.5 to 2.5% of Nb 0.01 to 0.3% of N 0.1 to 0.2% of S 0.02 to 0.15% of Al and a remainder made up by Fe and unavoidable impurities wherein the machinability index (I value) of the cast steel which is represented by the formula I = 100×S+75×Al+0.75×Mn 10×C 2×Nb 0.25×Cr 0.15×Ni 1.2×N (wherein each atomic symbol represents the mass% of the corresponding element in the cast steel) fulfills the requirement represented by the formula 3.0 = I value = +14.0; and a part for an exhaust system which comprises the cast steel.