PNNL

Abstract

Cooling rate and temperature control is implemented in rotary friction welding in order to obtain favorable microstructures and avoid martensite and other brittle microstructures. Limits of achievable cooling rates in friction welding 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, thus decreasing the cooling rate after the weld has finished. 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, a martensite readily forms after a weld. With temperature and cooling rate control, martensitic transformations are avoided and a pearlitic microstructure is developed. Temperature control is a viable tool in designing post-weld microstructures within achievable cooling rate limitations.