Reverse temper embrittlement, RTE, in low alloy steels: a substantive study concerning the influences of grain size, bulk phosphorus and accumulated service strain

摘要

This article describes a large in-service embrittlement study concerning six separate series of steam turbine casing bolts involving nearly four hundred individual bolts. The bolts, which ranged in size from 300 to 1400 mm in length, werefabricated from low alloy steels which were subjected to operating temperatures of 450℃ -490℃ for service times varying from 60000 to over 200000 h. The principal effects of grain size, d, bulk phosphorus, %P, and accumulated service strain, %ε, on the occurrence of reverse temper embrittlement. RTE, are reasonably established. Indeed, a general embrittlement threshold expression, or condition, is evolved which can be expressed as a product of these three important parameters which dictated RTE effects, viz., d× (%P) × (%ε){sup}b=α where b and α are scaling constants of value 0.64 and 0.0772 respectively. Effectively, when this product was numerically greater than the constantα bolt embrittlement was predicted; when less, no service embrittlementwas predicted.