Intergranular Fracture and Grain Boundary Segregation in P and Mo bearing 0.6%C Steels Tempered at Low Temperature

Abstract

The effects of P, Mo and H on the low temperature temper embrittlement of 0.6%C-Mo-P steels have been investigated for V-notched specimens by means of a slow bend test and by Auger electron spectroscopy of the intergranular fracture surfaces. The results are summarized as follows:
(1) The effect of P on temper softening is very small, but the contribution to embrittlement is very large.
(2) Most of the P, S, Mo segregations to grain boundaries occur during austenitization, but a slight enrichment of the P segregation with tempering temperature is observed.
(3) Mo additions suppress in some measure the P segregation to grain boundaries, but decrease the ductility of steel as a result of the increased resistance to temper softening.
(4) Hydrogen embrittlement enhances the contribution of P to the low temperature temper embrittlement, in the sense that hydrogen decreases the fracture strength to 1/2.5∼1/3 independently of P-content.