Effect of heat input, heat treatment on microstructure and mechanical properties of GTA welded aerospace material 15CDV6
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S. Biju Vikram Sarabhai Space Centre, ISRO, Thiruvananthapuram 695022, Kerala, India (Received 31 October 2016; accepted 8 February 2017)
In the present study, the effect of heat treatment on microstructure and mechanical properties of gas tungsten arc (GTA) welded 15CDV6 high strength low alloy steel is discussed. Experiments were carried out based on Taguchi L9 orthogonal array to weld 15CDV6 plate of thickness 3.7 mm. The input parameters considered in this work were current, voltage, and welding speed. Tensile strength, microhardness, and impact strength were measured as performance characteristics. Post weld heat treatment was carried out on the weldments to study its effect on the properties of weldments and microstructures were characterized using optical microscope and the X-ray diffraction analysis revealed the presence of MO2C and VC precipitates in the weld. Post weld heat treatment of the GTA welded samples and base metal successfully produced properties required for aerospace applications.
I. INTRODUCTION
15CDV6 steel is a high strength bainitic steel containing low concentrations of chromium, molybdenum, and vanadium as principal alloying elements. This steel has a good combination of toughness and a very good weldability.1 It is used in the manufacture of electric motors, transformers, nuclear reactors, and its contribution to the aerospace industry for the manufacture of rocket motor cases is immense.2 It can be welded easily with processes such as laser beam welding, electric arc welding, resistance welding etc. In the manufacturing sector, 90% of welding is carried out with the help of arc welding processes. One such arc welding process is gas tungsten arc welding (GTAW). Few of the works related to joining of 15CDV6 were done mostly using GTAW process. The major parameters that control the quality aspects of the GTAW weldments are welding current, welding voltage, and welding speed. Chandrasekhar et al.3 successfully welded 15 CDV6 steel using high energy beam processes, viz. electron beam welding, and laser welding. Sapthagiri et al.2 investigated the joining of 15 CDV6 using GTA welding process and concluded that copper coating present in the filler wire didn’t influence the properties of the weld and it got removed during welding process. Praveen et al.4 studied the feasibility of different manufacturing methods for pressure vessels and provided Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.70
a basis for carrying out different testing methods on 15 CDV6 weldments. Naveen Kumar et al.5 successfully welded 15CDV6 and SAE 4130 using interpass tungsten arc welding and obtained ultimate tensile strength in the range of 1384 MPa. The Microstructure of the dissimilar weld contained feathery bainite structure. Indumathi et al.6 suggested that coating 15CDV6 with a suitable material will help in achieving improved mechanical properties. 15CDV6 undergoes a secondary hardening effect at a temperature of around 650 °C. S
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