การเชื่อมพอกแข็งเหล็กกล้า 3.5 % โครเมียม โดยการเชื่อมแบบลวดไส้ฟลักซ์

Abstract

Hardfacing weld is a technique which mainly extends the service life of engineering components. The purpose of this research is to study wear behavior of hardfacing welded on 3.5% chromium cast steel by Flux Cored Wire Arc Welding (FCAW) process. Preheating was also done in this study. Automatic and semiautomatic welding processes were conducted in the present research. Macrostructure, microstructure, micro-hardness and abrasive wear resistance of the welded sample were studied. Austenitic stainless steel and martensitic hardfacing wire electrodes were chosen to deposit as the buffer and hardfacing layer respectively. Sixteen parameters in welding procedure were investigated. Single layer and three layer hardfacing were deposited. Four different kinds of preheating temperature included without preheating (room temperature), 250 °C, 300 °C and 350 °C were applied. Optical microscope (OM) and scanning electron microscope (SEM) were used to characterize the microstructure of hardfacing. These results showed that there was no defect in the Heat Affected Zone (HAZ) and welded layers. HAZ of the base metal sevealed needle shape martensite microstructure. Preheating of the base metal reduce quantity of martensite phase in HAZ. Buffer layer showed the austenitic microstructure with grain boundaries. Martensitic steel type electrode was used to weld all hardfacing layers because of its high hardness and good abrasive wear resistance. The abrasive wear resistance of hardfacing deposits was determined by dry sand rubber wheel machine according to procedure A of ASTM G65 standard. Comparing semi-automatic process to automatic process, abrasive wear resistance of the sample welded using semi-automatic process was higher than that of the sample welded using automatic process due to martensite content and hardness of hardfacing. Moreover, the abrasive wear resistance of three layers hardfacing was totally better than that of single layer hardfacing because single layer hardfacing was more diluted with buffer layer than three layers hardfacing. Eventually, the best condition in this research is semiautomatic process with three layers hardfacing.