0.6%C-1%Ni-1%Cr鋼におけるV_B族元素およびSのオーステナイト粒界偏析

抄録

Grain boundary segregations of V_B elements (N, P, As, Sb and Bi) and S in as-quenched and tempered 0.6%C-1%Ni-1%Cr steels were investigated by means of Auger electron spectroscopy and scanning electron microscopy. Results obtained are as follows:
(1) From the observation of intergranular fracture surfaces of steels quenched from 1200°C, it was concluded that Bi and S whose solubilities in γ Fe were smaller than 0.2 at%, segregated in the form of droplets, and P, Sb, Mo, and probably N and C whose solubilities in γ Fe were 0.2 to 5%, segregated in the state of atomic adsorption. The grain boundary segregation of As whose solubility is more than several atomic per cent was not so much.
(2) Apparent concentrations of P, Sb and S on the fracture surfaces were increased by about 2, 5 and 1.5 times after tempering at 500°C for 2 h.
(3) On the intergranular fracture surfaces of tempered P and Sb-bearing steels, the segregation of N as well as Ni was observed. On the other hand, the apparent concentration of C on the fracture surface was decreased by tempering.
(4) Some data suggested that the enrichment of Ni took place in the Bi-droplet/γ-matrix interface, and that the austenite grain boundary segregation of P was promoted by alloyed Ni and was restricted by alloyed Mo. Effect of P content on the apparent concentration of Mo on austenite grainboundaries was small.
(5) Apparent P concentration on the austenite grain boundaries slightly decreases with rising temperature.