고강도방탄소재 ARMOX600T FCAW 용접부 특성에 관한 연구

Abstract

ABSTRACT

A Study on Weldability Characteristics of High Strength Bulletproof Material ARMOX600T FCA Welding

Kuk Bang-Ho Advisor : Prof. Bang, Hee-Seon, Ph.D. CO-Advisor : Prof. Bang, Han-Sur, Ph.D. Department of Welding and Joining Science Engineering, Graduate School of Chosun University

Welding that can make the structure economical and reliable is widely used as a key process in the various manufacturing industries including automotive, rail, shipbuilding and aerospace. However, the welding is often faced with drawbacks relating to technical limitations on joint design, welding defects leading to critical degradation of the structural integrity and joint performance, deformation and residual stress induced by welding heat. As a result, the limitation of the process needs to be controlled for superior joint quality.

ARMOX 600T steel used in present study has been currently applied to outside panel in military automotive industry. ARMOX 600T steel, which is high-strength steel of 2 GPa, has poor weldability due to its higher carbon and alloying element contents than lower-strength steel. This makes high-strength steel more susceptible to welding thermal cycle, leading to variations of microstructures and mechanical properties of welds. Welding is needed for construction of automotive structures due to its huge potential to maintain the quality of the structures. In the present study, ultra high strength steel ARMOX 600T having excellent bulletproof performance is considered as a base material. SAAB Corporation, a material supplier, recommends ESAB's FCAW (Flux-Cored Arc Welding) wire as a recommended filler wire in welding ARMOX 600T steel. Since the price of filler wire is high, considering the economic efficiency, the applicability of domestic FCAW filler wire is examined. The automotive industries employ internationally known codes and standards to maintain the product quality. It is therefore necessary that an appropriate welding method should be required to obtain the sound joint.

Therefore, in present study, welding of ARMOX 600T steel has been performed to examine the weldability by Flux Cored Arc Welding (FCAW). Joint properties have been evaluated through non-destructive, mechanical and metallurgical test. As a result of present study, the tensile strength of joint was 594 MPa, which is approximately 95% of SW-307NS wire used. The joints produced by domestic H Company FCAW filler wire yields lower tensile strength in comparison to that of the joints made by ESAB FCAW filler wire. The weld metal hardness made by domestic H Company FCAW filler wire is almost equivalent to 216 HV. Several non-destructive inspections and quality evaluations show various defects in the weldment that do not satisfy the quality requirement criteria. Further investigations are required to resolve the current issues.