Microstructure anticipation in steel heat affected zone by the CCT diagrams

The microstructure and properties anticipation of heat affected zone (HAZ) in steel is presented. A methodology is based on continuous cooling transformation (CCT) diagrams application. Investigations are performed on the Q&T low alloy Ni-Cr-Mo steel (HY100). Two CCT diagrams are made on a weld simulator. One of them is made by shock heating to 1350degreesC for simulation of coarse grained zone (CGHAZ) in HAZ and another by slow heating to 880degreesC for simulation of grain refined zone (GRHAZ). Both diagrams are supplemented with microstructure examinations, toughness and hardness measurements. The notch impact toughness of weld simulated specimens is determined by instrumented Charpy V test with recording total fracture absorbed energy, crack initiation and crack propagation energies. Based on microstructure analysis by the optical microscope and measured propagation energy, the bainite appearance is defined. From these data, bainite morphology is classified as fine and coarse acicular or globular bainite. Verification of the suggested methodology was performed by comparison of structure and hardness with the results of investigations of GMA welded joints. The reliability and limitations of weld HAZ microstructure and properties anticipation by the methodology supported on the two CCT diagrams are discussed.