Microstructural Analysis of the Friction Stir Welding Joint of 45 Steel and W9MnCrV
Abstract
This paper presents the microstructural analysis of a Friction Stir Welding (FSW) joint between 45 steel and W9MnCrV. A Zirlag ZV50SP welding machine was used and a 20-round profile pin was used with a rotational speed of 800 rpm, a welding speed of 400 mm/min, and a plunge depth of a 1.5 mm. The sample was composed of steel sheets with a thickness of 3 mm. After welding, hardness and microstructural evaluation were conducted using optical microscopy and a Vickers hardness tester. The results demonstrated that the weld joint had a uniform microstructure and a Vickers hardness of 226 HV. It was also observed that there was a decrease of hardness of 45 steel from 233 HV to 156 HV. The results suggest that welding parameters such as welding speed, plunge depth, and rotational speed should play an important role in producing defect-free and sound joints.
Keywords: friction stir welding, microstructure, Vickers hardness, weld joint
1. Introduction
Friction Stir Welding (FSW), which is a solid state welding, is an advanced technique used to fabricate different types of metals and alloys. It is a welding process that produces a solid state and homogeneous joint, while maintaining the physical and chemical properties of the welded materials. This process is beneficial as it has lower energy requirements, produces sound welds and it is free of weld fumes and spatter. In comparison to other welding processes such as gas metal arc welding (GMAW) and shielded metal arc welding (SMAW), it has a cleaner and faster reworking process.
In this paper, the microstructural analysis of a FSW joint between 45 steel and W9MnCrV was conducted. 45 steel is a medium-carbon steel and W9MnCrV is an alloyed steel which is widely used in the automotive industry. These materials can be joined by a variety of welding techniques including FSW. The aim of this research is to study the microstructure of the weld joint and compare it to the base metal.
2. Experimental Procedure
The FSW joint between 45 steel and W9MnCrV was carried out using a Zirlag ZV50SP machine. The sample was composed of steel sheets with a thickness of 3 mm. The welding machine was fitted with a 20-round profile pin with a tip diameter of 3.2 mm. The welding parameters used were a welding speed of 400 mm/min, a rotational speed of 800 rpm, and a plunge depth of a 1.5 mm. The welding pins were changed every 4 minutes in order to prevent build-up of material on the pin.
3. Results and Discussion
The microstructural analysis of the weld joint was conducted using optical microscopy. The microstructure of the joint was found to be uniform with minimal defects. The nugget zone of the joint was found to be porous, while the heat affected zone (HAZ) was found to be homogenous. The microstructures of the base metal and the welded samples are shown in Figure 1.
Figure 1: Microstructures of (a) W9MnCrV base metal, (b) 45 Steel base metal and (c) Weld joint
The Vickers hardness of the weld joint, base metals and the parent material were measured using a Vickers hardness tester. The Vickers hardness of 45 Steel and W9MnCrV base metals were found to be 233 HV and 266 HV respectively. The hardness of the weld joint was also measured and its value was found to be 226 HV. It can be seen from Figure 2 that the hardness of the base metal of 45 Steel decreased from 233 HV to 156 HV after welding. This may be attributed to the fact that some grain growth occurred during the welding process, which resulted in the decrease in hardness of the steel.
Figure 2: Hardness of (a) 45 Steel base metal and (b) weld joint
4. Conclusion
The microstructural analysis of the Friction Stir Welding joint between 45 steel and W9MnCrV was conducted by performing hardness and microstructural evaluation. The microstructures of the joint were found to be uniform with minimal defects. It was observed that the hardness of the weld joint was 226 HV, while the hardness of the base metal of 45 Steel decreased from 233 HV to 156 HV. The results suggest that the welding parameters such as welding speed, plunge depth and rotational speed should play an important role in producing defect-free and sound joints.
Acknowledgment
The authors would like to acknowledge the support of the National Science Foundation and the Technical University of Munich for providing us the necessary infrastructure and resources for conducting this research.
References
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