Studies on weldability of iron-based powder metal alloys using pulsed gas tungsten arc welding process

Abstract

The extended use of powder metal components can be improved by the use of welding joining methods. This work investigates the weldability of iron-based powder metal alloys (Fe–Ni, Fe–Ni–P alloys) using the pulsed gas tungsten arc welding process (GTAW) with three different filler metals (AWS R 70S-6, AWS R 309L, AWS R Fe–Ni). Results revealed that the Fe–Ni powder metal alloy does not present any metallurgical difficulty concerning the weldability for all types of filler metal studied. The Fe–Ni–P powder metal alloy, microstructural examinations showed that, despite its high content of phosphorus (0.25 wt%), the utilization of pulsed GTAW process with stainless steel 309L filler metal resulted in welds free of porosities and solidification cracks. Metallographics examinations suggest that the absence of solidification cracks in this alloy can be mainly attributed to the presence of delta ferrite in the stainless steel weld metal which absorbed part of the phosphorus and significantly reduced the formation of the Fe 3P low-melting eutectic in the weld pool during cooling. In contrast, solidification cracks were observed when joining the Fe–Ni–P powder metal alloy using RFe–NI and R70S-6 filler metals. Hardness tests carried out indicated a heat affected zone (HAZ) with no excessive hardening for all alloys studied. Furthermore, tensile tests showed that the fractures always occurred in the base metal with tensile strength slightly superior to the value of unwelded samples. As a result, this investigation showed the feasibility of joining iron-based powder metal alloys by the pulsed GTAW process since a rigid control of the heat input is implemented together with an adequate choice of the filler metal, especially when welding the Fe–Ni–P alloy.