Effect of Cu Content on the Hardenability, Strength and Toughness of Ni-Cr-Mo-V Steels

Abstract

The effect of Cu content on the hardenability, strength and toughness of Ni-Cr-Mo-V steels has been investigated. The results obtained are summerized as follows:
(1) The hardenability of Ni-Cr-Mo-V steels remarkably increases with increasing Cu content. The Ms temperature and bainite transformation temperature become lower, and the each critical cooling rate to form bainite or ferrite decreases with increasing Cu content. The bainitic structure is obtained even at a cooling rate of 15 °C/h in quenching.
(2) The tensile strength of the quenched and tempered steel changes little with increasing Cu contents but the notch toughness remarkably increases. The notch toughness of 2.8% Ni-Cr-Mo-V steels containing Cu exhibits the larger value than that of 3.7% Ni-Cr-Mo-V steels containing Cu, at a slow cooling rate in quenching and after tempering. This is thought to be caused by high susceptibility to temper embrittlement in the higher Ni-containing steels. The temper embrittlement can be reduced by Cu ad dition.
(3) The improvement of hardenability and the reduction of temper embrittlement are possible by addition of Cu to 2.8% Ni-Cr-Mo-V steels. The steels containing Cu are able to have higher notch toughness than that of 3.7% Ni-Cr-Mo-V steels for large steel forgings.