Transformation, Metallurgical Response and Behavior of the Weld Fusion Zone and Heat Affected Zone in Cr-Mo Steels for Fossil Energy Application: Final Technical Report for January 1985-September 1987

摘要

This research program was undertaken to provide fundamental and basic metallurgical information on the behavior of the heat affected zone (HAZ) in Cr-Mo steel welds as well as practical information on their relative weldability. The principal work was the evaluation of the post weld heat treatment (PWHT) cracking of Cr-Mo steels ranging in Cr content from 2-1/4% to 9%. Differences in observed cracking behavior were contrasted with composition, on cooling transformation behavior and HAZ microstructure. Hydrogen assisted cracking (HAC) studies using a large scale cracking test were conducted on 2-1/4 Cr and 3 Cr steels. Soft zone studies were conducted on 9 Cr NKK steel to determine the reason for the development of a low hardness region (''Soft Zone'') at the outer boundary of the HAZ. The literature review provides a concise historical review and the basis of theories for PWHT cracking and HAC in Cr-Mo steels which were employed to explain the weld cracking susceptibility of various Cr-Mo alloys. PWHT cracking susceptibility was investigated using Gleeble simulated heat affected zone (HAZ) specimens. A new test was developed at the University of Tennessee, The C-ring test, to evaluate the PWHT cracking behavior. The C-ring test was found to be an extremely useful test for PWHT cracking susceptibility and for verifying the results obtained from Gleeble tsting. An excellent correlation was obtained for the two tests. The standard Y-groove test was selected for HAC susceptibility testing. This test is very suitable for evaluating the HAC of the base metal and is defined in Japanese Industrial Standard JIS Z 3158. (ERA citation 13:022017)