Role of chromium in the intergranular fracture of high purity FePCr alloys with small amounts of carbon

Abstract

The role of chromium in the intergranular fracture of high purity Fe0.2%PCr alloys containing small amounts of carbon was investigated by small-scale Charpy impact tests and scanning electron microscopy on fracture surfaces. Scanning Auger electron spectroscopy, tensile tests at a low temperature and optical microscopy were performed to clarify the mechanism of the chromium effect on intergranular fracture. The experimental results show that the addition of chromium to an FeP alloy and FeP alloys containing carbon, within its solubility limit, has no effect on the segregation of phosphorus but reduces the susceptibility of the alloys to intergranular fracture. The effect of chromium is attributed to the increased grain boundary cohesion caused by chromium segregated at grain boundaries and/or to the reduced deleterious effect of phosphorus, resulting from the attractive interaction between the segregated chromium and phosphorus. However, chromium enhances intergranular fracture in FeP alloys that contain carbon above its solubility limit. The enhancement of intergranular fracture by the addition of chromium is caused by the increase in phosphorus segregation, together with the decrease in carbon and chromium segregation at grain boundaries, which result from the formation chromium-rich carbides.