Investigation of microstructure and mechanical properties of AISI 430/AISI 1040 steel couple welded by keyhole plasma welding tecnique

SUMMARYInvestigation of Microstructure and Mechanical Properties of AISI 1040/AISI 430 Steel Couple Welded by Keyhole Plasma Welding TecniqueStainless steels which are difficult to join by conventional fusion welding techniques and increasingly employed in many important manufacturing areas, such as aircraft, space and defense industries have great importance especially in the frame of industrial investigations of joining conditions with plasma transfer arc (PTAW) welding process which is a new and modern welding technique.Plasma transfer arc weldıng (PTAW) can be defined as a gas-shielded arc welding process where the joining of metals is achieved via the heat transferred by an arc that is created between a tungsten electrode and a workpiece. The arc is constricted by a copper alloy nozzle orifice to form a highly collimated arc column. The plasma is formed through the ionization of a portion of the plasma (orifice) gas. The process can be operated with without a filler wire addition. The PTAW process is commonly used to weld stainless steels in different thicknesses. The process can also be used with carbon and alloy steels, aluminum alloys, titanium alloys, copper and nickel alloys, and more specialized materials, such as zirconium and tantalum.The PTAW process uses three current modes. These, are microplasma, medium current plasma (melt-in mode), and keyhole plasma.In this study, AISI 430 ferritic stainless steel and AISI 1040 steel couple were welded by keyhole plasma arc welding without a filler wire addition and pretreatment of welding using different process parameters (welding current, plasma gas flow, traverse speed and nozzle diameter). Additionally, effects of process parameters on the microstructure and mechanical properties have been investigated.After the plasma arc welding, microstructures and mechanical properties of the specimens were examined with tensile test, notch charpy test, optical microscopy and SEM respectively. Hardness distributions were determined by Vickers hardness scale across the welding interface. The special structures occurenced in the weld region were analysed with EDAX and X-RD. In addition, fracture types in the notch and tensile test of specimens were determined from the fractographic examinatons by using SEM.It was shown that the welding parameters played an important role on the welding quality. AISI 430 and AISI 1040 steel couple having different chemical composition were welded by plasma transfer arc welding process. It is possible to increase the weld quality of keyhole plasma arc welded joints by using appropriate parameters of welding such as current, flow rate of plasma gas and traverse speed.In the first chapter of this study, subject importance are introduced. In the second chapter, the stainless steels and its properties, the welding methods used for stainless steels and the plasma arc welding processes were presented extensively. In this chapter, also the place of this study in the literature was discussed. In the third chapter, the method of experimental study and the phases of the occured experiments were presented. In the fourth chapter, the experimental results were given and discussed in details. In the fifth and final chapter, the general results were given.Key Words: Keyhole Plasma Arc Welding, AISI 430 Ferritic Stainless Steel, AISI 1040 Steel.