Study On Microstructure And Property Of Laser Welded Joint Between Cemented Carbide And Steel

The welding of cemented carbide to 45# carbon steel in current research was carried out using YLS-5000 fiber laser manufactured by Apache Corp(IPG, USA). The specimens were prepared using Φ50mm×2mm(3mm, 4mm) base materials without groove and filler metal under argon atmosphere at the rate of 15-25L/min. Optical microscopy, scanning electronic microscopy, X-rays diffraction, and three point bend strength were used to investigate the weld formation, microstructure distribution, and mechnical properties.The results indicate: the welded joint of 2mm thickness and 3mm thickness can be reached using the optimum parameters. For 2mm specimens, Under the preheating condition, the well welded joint can be reached with the parameters of defocusing amount-8mm, laser power 2k W, laser scanning speed 2.40m/min; for 2mm specimens without preheating, the well welded joint can be reached with the parameters of defocusing amount-8mm, laser power 1.8k W, scanning speed 1.20m/min; the well welded joint without defects can be reached if the welding energy input were controlled between 190J/mm~210J/mm and the laser power were controlled among 2.5k W~2.7k W.The defects analysis of joint indicated that the main defects of joints were cracks and air holes. The cracks were often occurred at the interface between cemented carbide and welds. Generally speaking, two growth mechanism on cracks propogation were observed in the experiments: some cracks propogated from the interface of cemented carbide and welds to the cemented carbide base metal; others grew from the welds near cemented carbide to the cemented carbide base metal. The air holes were often formed at the upper of the welds. In addition, the appearance of brittle eta phase(Co2W4C) and tungsten carbide with deficient carbon tends to causing a stress concentration or micro crack which will increase the brittle damage of the products.At the cemented carbide/welds interface, WC aggregation was owed to the unmelting WC/WC migration. The aggregated WC particles led to the WC abnormal grain growth with large concentration of stesses, which might be the sources for cracks initiation.The bending test results indicated that the fracture were often occurred at the interface between cemented carbide and welds which characterized with fracture mechanism and quasi-cleavage fracture mechanism. Among them, The AGG phenomenon can be observed along the fractured interface for the brittle fracture mechanism. The interface of cemented carbide and welds was the weakest part in the as-welded microstructure. It characterized with quasi-cleavage fracture like quasi-cleavage facet, short torn edges and so on.