Controlling martensite and pearlite formation with cooling rate and temperature control in rotary friction welding

Abstract

A major limitation in industrial welding is the undesirable microstructures that form due to high peak temperatures and cooling rates. In particular, martensite and other brittle microstructures often form in steels during rotary friction welding (FW). In order to address this, cooling rate and temperature control is developed for FW. Limits of achievable FW cooling rates are primarily determined by thermal and geometric properties such as thermal diffusivity and length. A controller limits interface temperatures during a weld preheat, changing the thermal profile and slowing post-weld cooling.This method is demonstrated in 1045 steel. Cooling simulations, TTT diagrams, microhardness line scans, and scanning electron microscopy are used for analysis. Without temperature and cooling rate control, martensite readily forms after a weld. With temperature and cooling rate control, martensitic transformations are completely avoided and a pearlitic microstructure is developed. Temperature and cooling rate control is a viable tool in designing post-weld microstructures within achievable cooling rate limitations.