Temper Embrittlement Characteristics of 2¹/₄Cr-1Mo Steels

Abstract

Influences of impurities, alloying elements and grain refining elements were investigated systematically in relation to high temperature strength and temper embrittlement of 2¹/₄ Cr-1Mo steel which was widely used for high temperature chemical equipments such as a desulphurization reaction vessel of heavy oil.
The following results were obtained.
1) The degree of the temper embrittlement increased remarkably with increasing the amount of impurites such as P, Sb and Sn. It was also larger with higher C content, cooling rate at quench and strength level. However, relative ratio of their degree of the embrittlement among various impurities was nearly constant.
2) Effective element for high temperature strength was generally harmful to temper embrittlement.
3) Steels with fine grain size had less susceptibility to temper embrittlement than those with coarse grain size. Accordingly, addition of grain refining elements such as Ti, Nb, Te and Al decreased the susceptibility.
4) Rare earth elements lowering the content of P on grain boundaries decreased the susceptibility.
5) Both high strength at elevated temperature and less susceptibility to temper embrittlement was obtained with steel containing a combination of Ti, B and REM.