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

This article describes a large in-service embrittlement study concerning si x separate series of steam turbine casing bolts involving nearly four hundr ed individual bolts. The bolts, which ranged in size from 300 to 1400 mm in length, were fabricated from low alloy steels which were subjected to oper ating temperatures of 450 degrees C-490 degrees C for service times varying from 60 000 to over 200 000 h. The principal effects of grain size, d, bul k phosphorus, %P, and accumulated service strain, %epsilon. On the occurren ce of reverse temper embrittlement, RTE, are reasonably established. Indeed , a general embrittlement threshold expression, or condition, is evolved wh ich can be expressed as a product of these three important parameters which dictated RTE effects, viz., d x (%P) x (%epsilon)(b) = alpha where b and a lpha are scaling constants of value 0.64 and 0.0772 respectively. Effective ly, when this product was numerically greater than the constant alpha bolt embrittlement was predicted; when less, no service embrittlement was predic ted. (C) 1999 Elsevier Science Ltd. All rights reserved.