Segregation Effects and the Toughness of High-Strength Steels.
Annual technical rept. no. 2,
CAMBRIDGE UNIV (ENGLAND) DEPT OF METALLURGY AND MATERIALS SCIENCE
Pagination or Media Count:
The tendency for Sb, P and Mn to segregate in austenite and produce embrittlement in as-quenched steels has been investigated. Sb does not appear to segregate appreciably in the austenite phase, but pure steels re-melted with 0.12P exhibit intergranular fractures after quenching from 900 and 1000C. Quench rate experiments suggest that P segregates in austenite, rather than during the quenching process. Mn does not embrittle as-quenched pure steels, but results from steels containing MnP indicate that Mn interacts with P in austenite producing more severe embrittlement than P alone. The influence of heat treatments above 1150C on the distribution of MnS particles is being studied by metallography. Fine MnS-type particles are observed on the austenite boundaries in rapidly quenched specimen. Grain boundary migration effects are considered to be responsible for the presence of the particles, however, precipitation effects cannot be eliminated as a possibility at this stage. The effects of Ni and Sb content on the susceptibility of Ni-Cr steels to temper embrittlement have been studied. Transition temperature and Auger results are presented for 0.5 and 5Ni steels containing up to 200 ppmSb. At 520C, grain boundary compositions reach equilibrium levels after approximately 100 hr. The degree of embrittlement and the extent of Sb segregation are much lower than would be expected from experiments with steels of higher Sb content. This effect is explained in terms of the Ni-Sb interaction. It is concluded that impurity content is a very important variable in systems where impurities and alloying elements interact.
- Metallurgy and Metallography