Heat treatment effects on creep and rupture behavior of annealed 2.25 Cr-1 Mo steel

Abstract

The strength of 2 1/4 Cr-1 Mo steel depends on the microstructure, which, in turn, de-pends on the heat treatment. In the fully annealed and isothermally annealed conditions, the microstructure is primarily proeutectoid ferrite with varying amounts of bainite and pearlite. The relative amounts of the latter constituents depend on the cooling rates during the anneal. The creep and rupture properties were determined for steel plates (from a single heat) given three different annealing treatments: two were fully annealed, but cooled at different rates from the austenitizing temperature, and the third was iso-thermally annealed. Properties were determined at 454, 510, and 566°C. At 454 and 510°C, the cooling rate had a significant effect on the creep and rupture properties, with the ma-terial cooled fastest being the strongest. Although at 510°C strengths at short rupture times differed widely, the properties approached a common value at longer rupture times. The properties differed very little at 566°C, even for short rupture times. The effect of heat treatment was concluded to be the result of interaction solid solution hardening, a dislocation-drag process. This process gave rise to nonclassical creep curves (as op-posed to classical curves with single primary, secondary, and tertiary stages). By examining the creep-curve shape, it was possible to interpret the heat treatment effects on the creep-rupture properties.