Heat-resistant, ferritic cast steel having excellent melt flowability, gas defect resistance, toughness and machinability, and exhaust member made thereof
A heat-resistant, ferritic cast steel having excellent melt flowability, gas defect resistance, toughness and machinability, which has a composition comprising by mass, C: 0.32-0.45%, Si: 0.85% or less, Mn: 0.15-2%, Ni: 1.5% or less, Cr: 16-23%, Nb: 3.2-4.5%, Nb/C: 9-11.5, N: 0.15% or less, S: (Nb/20−0.1) to 0.2%, W and/or Mo: 3.2% or less in total (W+Mo), the balance being Fe and inevitable impurities, and a structure in which the area ratio of a eutectic (δ+NbC) phase of δ ferrite and Nb carbide (NbC) is 60-80%, and the area ratio of manganese chromium sulfide (MnCr)S is 0.2-1.2%, and an exhaust member made thereof.
1. A heat-resistant, ferritic cast steel having excellent melt flowability, gas defect resistance, toughness and machinability, which has a composition comprising by mass
C: 0.32-0.45%,
Si: 0.85% or less,
Mn: 0.15-2%,
Ni: 1.5% or less,
Cr: 16-23%,
Nb: 3.2-4.5%,
Nb/C: 9-11.5,
N: 0.15% or less,
S: (Nb/20−0.1) to 0.2%, and
W and/or Mo: 3.2% or less in total (W+Mo),
the balance being Fe and inevitable impurities, and a structure in which the area ratio of a eutectic (δ+NbC) phase of δ ferrite and Nb carbide (NbC) is 60-80%, and the area ratio of manganese chromium sulfide (MnCr)S is 0.2-1.2%.
2. An exhaust member made of the heat-resistant, ferritic cast steel recited in claim 1 .
3. The heat-resistant, ferritic cast steel having excellent melt flowability, gas defect resistance, toughness and machinability, according to claim 1 , wherein C content is 0.32-0.44%.
4. The heat-resistant, ferritic cast steel having excellent melt flowability, gas defect resistance, toughness and machinability, according to claim 1 , wherein Nb content is 3.3-4.5%.