Strength of Some Cr-Ni Austenitic Stainless Deposited Steels at High Temperatures

Abstract

Cr-Ni austenitic stainless steels are widely used for parts of power boiler and equipments of high temperature and high pressure chemical industry. These materials are employed in tubular form or sheet and are jointed together by welding in the construction of equipments. Many investigators, for the need of high temperature strength data about deposited steels, have performed creep rupture tests. However, their strength data are widely scattered even the in same kind of steel.The present work has dealt with the high temperature strength of some Cr-Ni austenitic stainless deposited steels about the effect of microstructure, composition and solution treatment on the creep rupture properties. In this investigation, the following deposited metal compositions are included.(1) Ten kinds of Cr-Ni-Mo (16∼21 Cr, 8∼13 Ni, 1∼4 Mo)(2) 20 Cr-9 Ni-CbAfter welding, some of these materials were given solution treatment for 1 hour at 1050°C and 1100°C. The specimen was prepared in such a manner as the direction of applied stress would be parallel to the direction of well-bead deposition. Tension test was carried out at room temperature and in the temperature region from 550°C to 700°C. Creep rupture test was performed at 650°C and 700°C, and rupture strength for 1000 hours was obtained by interpolation and for 10000 hours by extrapolation with log-log plotting. After creep rupture test, their microstructure were examined. The Results obtained are as follows:In general, δ ferrite in Cr-Ni deposited steel is decreased by solution-treatment and their rupture strength, rupture elongation and ductility are increased. δ ferrite in deposited metal change to σ phase during creep rupture testing and creep rupture strength decreases with increasing of δ ferrite. Otherwise, some of low Cr low Ni deposited metal, which locate the unstable austenite region near martensite in A. Schaeffler's diagram, produce martensitic ferrite after long time creep rupture test.