A Comparison Study of the Austenite Grain Growth and Its Transformation Behavior during Uniform Continuous Cooling of a Wrought and Selective Laser Melting 4340 Steels

Abstract

This study compares austenite grain growth and its continuous cooling transformation (CCT) behavior between selective laser melting (SLM) 4340 and conventional wrought 4340 steels. Standard dilatometry tests were used to determine the austenite decomposition behavior at different cooling rates. The analysis of the data from the controlled cooling paths was used to generate CCT diagrams for the two steels investigated in this study. Advanced microstructural characterization techniques, Scanning Electron Microscopy and Orientation Imaging Microscopy, were employed to support the CCT diagrams. Electron Backscatter Diffraction (EBSD) and a special EBSD-Image Quality characterization technique were used to assess the percentage of the microstructural components observed. Three important observations were made: (1) the hardenability of the wrought 4340 steel was higher than the SLM 4340 steel; (2) the presence of granular bainite was observed after slow cooling conditions in both steels; (3) the SLM steel exhibited finer austenite grain size distribution than the wrought steel in the temperature range studied. MTEX, a MatLab program, was used to reconstruct the prior austenite grains. The SLM steel exhibited finer austenite grain size distribution than the wrought steel in the temperature range studied.

Research Plan and Preliminary Results in Developing the Fabrication Parameters for Alloy 709 in Different Product Forms―Grain Coarsening Temperature Evaluation

“…in the alloy that can pin grain boundaries. Research in this area has been important in the development of optimized thermomechanical processing of microalloyed steels in which precipitation during processing is highly controlled to develop a consistently uniform, fine-grained microstructure (Palmiere et al, 1996;Wang et al, 2006;Solis-Bravo et al, 2020, Wang et al, 2021. The T GC determination will be used for the subsequent CCP study to ensure maximum dissolution of pre-existing precipitates.…”