Development of In-Situ Weld Cooling Rate Measurement Methods

Some structural carbon steel welding applications have performance requirements that place limits on weld and heat affected zone hardness or require minimum toughness levels to reduce risk of environmental cracking, corrosion, and risk of unstable fracture for fatigue-sensitive structures.  A common approach to satisfy these performance metrics is to specify a weld cooling rate during weld fabrication that will achieve target hardness levels and promote desirable microstructures to enhance toughness and ductility.

EWI has been developing in-situ weld cooling rate measurement methods for arc fusion weld processes to enable collection of weld surface temperature profiles during arc welding and then estimating the cooling time from 800oC to 500oC for control of hardness and microstructure.  Commercially available infrared (IR) cameras are used and integrated into the welding system with data collection and analysis routines to provide cooling rate data.  This work is still in a feasibility proof of concept stage but is advancing to enable collection of real-time cooling rate data for weld process control and to ensure WPS requirements are met.  This paper will discuss the development approach, provide results from numerous welding trials, and discuss next steps to fully implement field-deployable systems for structural welding applications.