ボロン処理した Cr-Mo 鋼の高温焼もどし後の靱性

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Boron treatment for Cr-Mo steels has been performed to obtain the higher strength with heavy thickness. But in these steels, even under the quenched microstructure, microalloying elements affect the toughness on tempering treatment at high temperature. So, the effect of Ti, B and N on the toughness and microstructures has been investigated in B-treated Cr-Mo steels tempered at high temperature. The results are as follows : (1) In the case of Ti/N ≩ 3.42, the excess dissolved B ([B]) causes the precipitation of coarse M_<23>(C, B)_6 type boro-carbides and the formation of denuded zone along grain boundaries on tempering treatment at the temperatures higher than 600℃, and therefore the toughness decreases. But proper [B] causes no coarse boro-carbides precipitates along grain boundaries. (2) In the case of Ti/N<3.42, the precipitation of BN occurs after hot rolling. However such nonequilibrium BN precipitates partially transform to AlN at the austenitizing treatment and [B] occurs. If [B] content is excess, then M_<23> (C, B)_6 precipitates and coagulates on grain boundaries during tempering treatment at high temperature, and consequently the toughness decreases. If [B] content is proper, then microstructures are fine and BN precipitates take no effect on the toughness.
社団法人日本鉄鋼協会の論文
1986-02-01

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