| 摘要 |
PROBLEM TO BE SOLVED: To provide steel for machine structure that hardly causes crystal grain coarsening when carburizing treatment is performed, and is excellent in toughness.SOLUTION: The steel for machine structure includes by mass: C:0.10-0.30%, Si:0.05-2.0%, Mn:0.10-0.50%, P:0.030% or less, S:0.030% or less, Cr:1.80-3.00%, Al:0.005-0.050%, Nb:0.02-0.10%, N:0.0300% or less, and the balance consisting of Fe and inevitable impurities, wherein the structure before cold working is a ferrite and pearlite structure, and the average value of the ferrite grain size is at least 15 microns. The steel is excellent in the crystal grain coarsening-proof property and toughness in which the heat treatment shown in Figure 1 is performed. |
