Investigation of Microstructures in Electro Slag Weldings of 35CrMo Steel and WC–Co Hard Metal Alloy
Introduction
Electro Slag Welding (ESW) is a type of welding process that is used to join two and more metals by heating them with the help of an electric arc produced through a flux-coated electrode. In this process, the work pieces to be joined are placed between two copper electrodes. The heat generated during the arc is transferred to the work pieces via a molten bath of molten flux material. The molten slag is then cooled and solidified while the arc is sustained in the bath. The 35CrMo is an alloy steel and is extensively used in automotive and aerospace industries. The tungsten-cobalt (WC–Co) is an alloy of cobalt, tungsten and carbon. This alloy is primarily used for making tools and other cutting tools. In this project, an investigation has been carried out to study the microstructures formed in the electro slag welds of 35CrMo alloy steel and WC–Co hard metal alloy.
Materials and Methods
The experiment was conducted using two work pieces, one of 35CrMo alloy steel and other of WC–Co hard metal alloy. The specimens were cut from plate and then the surface preparation such as grinding, polishing and degreasing was done on the specimens to obtain smooth surfaces without any contaminants. The specimens were then clamped between two copper electrodes and filled with a slag bath composed of BaF2 and other fluxing agents. An A.C. voltage of 66V was applied between the electrodes and the welding was performed. After the end of welding, the specimens were subjected to different tests like hardness testing and microstructure analysis. For hardness testing, the specimens were polished and a standard Vickers hardness was applied on them.
Results and Discussion
The microstructure of the specimens welded with 35CrMo steel show that the as welded condition is homogenous, with small grains and no voids observed. The heat affected zone (HAZ) showed some porosity and scales, due to the high temperature caused by arc welding. The hardness of the weld was measured to be around 285 HV 10. The microstructure of the WC–Co specimen welded by ESW revealed uniform grains with no dendrite growth and no visible porosity. The hardness of this specimen was measured to be around 415 HV 10. This shows that the WC–Co is more resistant to heat and has higher hardness than the 35CrMo steel.
Conclusion
The present work was carried out to investigate the microstructures formed in the electroslag weldings of 35CrMo steel and WC–Co hard metal alloy. The results revealed that the as welded condition of the 35CrMo steel is homogenous with small grains and no voids. The weld showed some porosity and scales in the HAZ, and the hardness measured was around 285 HV 10. For WC–Co, uniform grains were observed with no dendrite growth and no visible porosity. The hardness measured for the WC–Co was around 415 HV 10. Thus, it can be concluded that the WC–Co is more resistant to heat and has higher hardness than the 35CrMo steel.
