A516-70강의 용접 입열량과 층간온도가 인성과 미세조직에 미치는 영향에 관한 연구

Abstract

Abstract

Normalized ASTM A516 Grade 70 steel is one of the most widely used material in the fabrication of low temperature pressure vessels. Steel used in the fabrication of pressure vessel steel is in two kinds, low carbon steel and alloy steel. A516/SA516 normalized products can be welded using Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW), Submerged Arc Welding (SAW) or Flux Cored Arc Welding (FCAW) processes. Among those welding processes, Flux Cored Arc Welding (FCAW) process has grown in use in recent times as a function of its characteristics of high productivity, good quality and low cast, associated with suitable mechanical properties in welded joint. When two parts of A516 steel are welded together, the properties of the metal in welded joint vary significantly. The welded joint are heterogenous structural elements composed of microstructural region, namely base metal, weld metal and heat affected zone. The properties of those regions are different due to welding high input, slag inclusions, disproportionate heat or cooling rates, or interpass temperature, and so on. This paper investigates experimentally the influences of welding heat input and interpass temperature on the fracture toughness and microstructures in normalized ASTM A516 Grade 70 (hereinafter A516-70) steel plate by Flux Cored Welding (FCAW) process. Charpy V-notch (VCN) tests were utilized to characterize the fracture toughness behavior of A516-70 FCAW weldments, and Optical light Microscopy (OLM) were used for their microstructure evaluation. The results obtained from this study are summarized as follows; The fracture toughness exhibits a tendency to decreases with increasing the welding heat input and interpass temperature. The microstructure in higher impact toughness specimens shows the larger fraction of acicular ferrite than that of the lower impact toughness specimens.