Manufacture and stress rupture properties of hipped austenitic-ferritic transition joints

Diffusion welding by hot isostatic pressing (HIP) has been used to produce dissimilar metal weldments between martensitic 9% chromium steel P92 and au stenitic steel 1.4910 (Fe17Cr13Ni3MoN). Considering the results of optical metallography of the joints, it was found that the optimum HIP conditions f or good bonding were 1200 degrees C at 150 MPa pressure for a duration of 1 h. Stress rupture tests were carried at 600 and 650 degrees C, which showe d thar good;bonding could be achieved, and that the stress rupture strength s were close to those of the P92 parent material. Some joints were produced using a nickel ahoy insert between the two steels. It was found that the n ickel alloy insert had a deleterious effect on the rupture strength due to the formation of continuous carbide layers at the interface between the nic kel alloy and the martensitic steel. This led to early failure of the joint s in stress rupture tests. Further work was carried out to assess the effec t of thermal cycling on the integrity of the joints. The HIP diffusion weld ments withstood 180 thermal cycles between 650 and 20 degrees C without fai lure. (C) 1999 Elsevier Science S.A. All rights reserved.