Sigma Formation and 475°C Embrittlement of High Chromium Steel Plates and these Weld Metals

Abstract

Sigma embrittlement was studied on two different high chromium steel plates (both 25% Cr and 24%Cr+1.5%Si+1.5%Al alloy steel) and four different weld metals deposited with 24-27%Cr+ 0.5-1.5%Si electrode. In the first place, these materials were aged to form sigma phase at 700°C for 100-1000 hours. After aging at 700°C, Charpy impact tests and tensile tests were conducted with these embrittled materials. In addition to the above experiment, Authors investigated on 475°C embrittlement in the case of 24%Cr+1.5%Si+1.5%Al steel plates and weld metals deposited with 28% Cr+1.5% Si electrode. The results of investigation concerning mechanical properties of embrittled parts were as follows :
1. 475°C embrittlement and sigma formation occurred more rapidly in weld metals than in steel plates, and tendency to embrittlement of all test materials was more intensive in the case of 475°C embrittlement than in sigma formation.
2. Sigma embrittlement was, as a rule, removed by normalizing at about 800°C.