Tailored laser pulse method to manipulate filler wire melt metallurgy from thermal cycles

Abstract

A method is introduced to simulate and study the effects of filler wire chemistry and controlled cooling conditions on the metallurgy of welds, enabling efficient mapping with prompt analysis of trends. A reduced, representative process with highly controllable conditions is proposed. Short lengths of filler wire are preplaced in a cavity drilled into a base metal sheet. Irradiation by a pulsed laser beam melts the wire to generate a sample nugget. Laser pulse shaping influences the cooling rate granting the ability to tailor weld microstructures. The method is demonstrated for S1100QL steel and undermatched filler wire, to obtain high toughness for processes like laser-arc hybrid welding. For high toughness, a controlled amount of acicular ferrite and non-metallic inclusions is desirable. This “snapshot” method has revealed a characteristic histogram of inclusion sizes, for different pulse shapes. Additional information on the thermal cycle can be acquired by employing thermocouples, a pyrometer or advanced methods like high speed imaging or modelling. The method offers a wide spectrum of variants and applications.