Metallurgical Characterization of Welded Joint of Nanostructured Bainite: Regeneration Technique versus Post Welding Heat Treatment

• Published in: Materials Vol. 13; no. 21; p. 4841
• Main Authors: Królicka, Aleksandra, Radwański, Krzysztof, Janik, Aleksandra, Kustroń, Paweł, Ambroziak, Andrzej
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 29-10-2020; MDPI
• Subjects: Annealing; Bainite; Bainitic transformations; Carbon; Chemical composition; Chemical elements; Cold; Construction materials; Cooling; Decomposition; Friction stir welding; fusion zone; Hardenability; Hardness; HAZ; Heat affected zone; Heat treating; Heat treatment; Mechanical properties; Metallurgy; Methods; Morphology; nanobainite; Nanostructure; nanostructured bainite; Pearlite; Regeneration; regeneration technique; Simulation; Solidification; Steel; Structural analysis; Temperature; Tensile strength; Welded joints; Welding
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma13214841

One of the main limitations in application of nanostructured carbide-free bainite as a construction material is the difficulty of joining. This research presents a structural characterization of welded joints of medium carbon 55Si7 grade steel after the welding process with a regeneration technique as well as post welding heat treatment (PWHT). The hardness distribution of the welded joint with regeneration exhibit an overall decrease in hardness when compared to the base material and a significant decrease in hardness was observed in the heat-affected zone (HAZ). Unfavorable hardness distribution was caused by the presence of diffusion-type transformations products (pearlite) in the HAZ and bainite degradation processes. On the other hand, welding with the PWHT promotes the achievement of a comparable level of hardness and structure as in the base material. However, a slight decrease in hardness was observed in the weld zone due to the micro-segregation of the chemical composition caused by the indissoluble solidification structure. Based on the structural analysis, it was found that steel with relatively low hardenability (55Si7) should be welded using PWHT rather than a regeneration technique.