| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide hot processed steel for surface hardening, which can reduce the coarsening of austenite crystal grains that is caused during carburization or carburization nitriding, and has cold forging property enough to eliminate softening annealing. <P>SOLUTION: The hot processed steel for surface hardening contains C: 0.10-0.30%, Si≤0.50%, Mn: 0.15-1.5%, P≤0.04%, S: 0.005-0.07%, Cr: 0.7-3.0%, Al: 0.01-0.05%, N: 0.0035-0.010%, Ti: 0.005-0.10%, Nb: 0.02-0.07%, B: 0.0005-0.0050%, H≤0.00004%, and the balance Fe and impurities. The ratio of Nb precipitated as Nb (C, N) in the Nb in the steel is 85% or more, the number density of Nb (C, N) with diameter of 100 μnm or more is 5 pieces/100 μm<SP POS="POST">2</SP>or less, and the standard deviation of ferrite crystal grain size is 0.15 or less. The steel may include one or more of Mo≤0.50% and V≤0.20%. <P>COPYRIGHT: (C)2012,JPO&INPIT |
