Heat-resistant, cast ferritic steel having excellent machinability and exhaust member made thereof
A heat-resistant, cast ferritic steel having excellent machinability comprising by mass 0.32-0.48% of C, 0.85% or less of Si, 0.1-2% of Mn, 1.5% or less of Ni, 16-23% of Cr, 3.2-5% of Nb, Nb/C being 9-11.5, 0.15% or less of N, 0.05-0.2% of S, and 0.01-0.08% of Al, the balance being Fe and inevitable impurities, and an exhaust member made thereof.
1. A heat-resistant, cast ferritic steel having excellent machinability comprising by mass
0.32-0.48% of C,
0.85% or less of Si,
0.1-2% of Mn,
1.5% or less of Ni,
16-23% of Cr,
3.2-5% of Nb,
Nb/C being 9-11.5,
0.15% or less of N,
0.05-0.2% of S, and
0.01-0.08% of Al,
the balance being Fe and inevitable impurities.
2. The heat-resistant, cast ferritic steel having excellent machinability according to claim 1 , which further comprises 0.8-3.2% by mass in total of W and/or Mo.
3. The heat-resistant, cast ferritic steel according to claim 1 , wherein Nb and Al meet the following formula:
0.35≦0.1Nb+Al≦0.53 (1),
wherein each element symbol represents its content (% by mass).
4. The heat-resistant, cast ferritic steel according to claim 1 , which has a structure in which the number of sulfide particles per a field area of 14000 μm 2 is 20 or more.
5. An exhaust member formed by the heat-resistant, cast ferritic steel recited in claim 1 .