Thermal Cycles and Peculiar Properties of Austenite Decomposition when Laser-Hybrid Welding Steel of K60 Strength Class

Abstract

Welding is an important technology of joint in engineering structures. In addition to a residual stress influence to a quality of joint, an obstacle in welding analysis are complex phenomena including phase transformation, thermal cycle and microstructure kinetics. The influence appears in microstructure development, formation of defects and in transformation of metallurgy in a welded zone. This article experimentally defines thermal cycles and shows the results in study of peculiar properties of austenite decomposition kinetics when using the technology of laser-hybrid welding in combination with multiple arc automatic sub-merged welding. There defined the rates of cooling influencing the change of properties of welded joints from tube assortment steel of K60 strength class. We found that the result of impact of laser-hybrid welding process in a heat-affected zone is that the austenite decomposition in studied steels flows in martensite area generally. The hardness of seam metal and heat-affected zone of the studied steels is of range 350-360 HV, which increases a probability of crack-like, defects formation. We revealed the normative value of hardness, which can be provided if a metal cooling rate in laser-hybrid welding is about 20 °C/s.