| 简介 |
PROBLEM TO BE SOLVED : To provide a high strength steel product having excellent low temperature crack resistance, and to provide a method for producing the same.
SOLUTION : A steel having a composition containing, by mass, 0.02 to 0.25% C, 0.01 to 0.8% Si, 0.5 to 2.0% Mn, 0.01 to 1% Mo, 0.005 to 0.1% Al, 0.0005 to 0.008% N, ≤0.03% P and ≤0.03% S, also comprising one or more kinds selected from 0.001 to 0.1% Nb, 0.001 to 0.5% V and 0.001 to 0.1% Ti, and, if required, further comprising one or more kinds selected from Cu, Ni, Cr, W, B, Ca, rare earth metals and Mg, and the balance Fe with inevitable impurities is quenched from a temperature higher than an Ar3 transformation point to ≤500°C, and is thereafter tempered in such a manner that the average temperature rising rate at the central part of the steel from a tempering starting temperature to a prescribed tempering temperature is controlled to ≥1°C/s, and the steel contains precipitates with the average particle diameter of ≤20 nm containing Mo and one or more kinds selected from Nb, V and Ti by ≥5 pieces/250, 000 nm2.
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