The Effect of Arc Current on the Microstructure and Wear Characteristics of Stellite12 Coatings Deposited by PTA on Duplex Stainless Steel Dewei Deng + , Jun Lu and Xiaona Li School of Materials Science and Engineering, Dalian University of Technology, 116024, Dalian, China Plasma transferred arc welding (PTAW) is widely employed to improve the quality of components whose surface is subjected to severe wear conditions. However, the wear properties of these coatings is significantly affected by the welding process adopted during the deposition of the coatings. This paper details an investigation of the microstructure, composition, hardness and wear characteristics of Stellite12 Co-based coatings with different welding currents. Optical microscopy (OP), scanning electron microscopy/energy dispersive spectrum analysis (SEM/ EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the microstructure. An increase in the arc current increased the dilution of the DSS and changed the composition as well as the dendritic arms coarsening of the Co-based coatings. Increasing the arc current gives rise to a reduction in the hardness of the coatings, whereas reduction in the hardness of the coatings is accompanied by a reduction in their wear resistance with the exception of the lowest current sample. Additionally, the microstructure of the welding heat affected zone (HAZ) during PTAW was also studied. The heat affected zone was decorated with some needle-type austenites nucleated from grain boundary austenite, but without ·-phase. Moreover, some chromium-rich precipitates were also detected in the welding heat affected zone of the specimens during PTAW. [doi:10.2320/matertrans.M2013103] (Received March 18, 2013; Accepted June 28, 2013; Published August 9, 2013) Keywords: plasma transferred arc, Stellite12 cobalt-based alloy, 2507 duplex stainless steel, current intensity 1. Introduction In recent years, Plasma transferred arc welding (PTAW) has been widely employed to improve the quality of components whose surface is subjected to severe wear conditions. It represents quite an applicable alternative to other surface welding processes such as conventional techniques or more recent ones like laser cladding. 1) Normally, the PTA process produces thicker deposits with an extremely high quality, provides optimal protection with minimal thermal distortion of the parts, low environmental impact and high deposition rates in single layer deposits. 2) While the characteristics of coatings are significantly affected by the primary hardfacing alloys 3) and the different PTA process parameters. Y. Birol 3) investigated the high tem- perature sliding wear resistance of Stellite6 and Inconel617 alloys and rated their performance against that of the conventional hot work tool steel employed in hot forging of steel components. In this work, Stellite12 Co-based alloys will be used as the harding alloys because of its high wear resistance and stability of properties at high temperature. Fernandes et al. 2) and Takano et al. 4) suggested that welding techniques and relevant process parameters (transferred arc current, plasma gas flow) significantly affected the character- istics of the Ni-based or Co-based coatings. Some components made of gray cast iron or X45CrSi93 steel with special superior behaviors, such as engine valves and molds which are sensitive to wear in heavy duty cycles, need to be coated with materials that are more resistant to high temperature and wear. 2,5) Duplex (austenitic-ferritic) stainless steel, a class of stainless steels that combines good mechanical and corrosion properties as well as good weldability, 6) is used extensively in chemicals and petro- chemicals, oil and gas, pulp and paper, as well as power generation industries. 7) However, the shortage of wear properties has limited its application to fields where adequate wear resistance is required, similar to gray cast iron or X45CrSi93 steel. Thus, the enhancement of wear properties of DSSs becomes a worthy field of research. 6) This work concerns the characteristics of a Co-based Stellite12 alloy deposited by PTAW on SAF2507 Duplex Stainless Steel. In addition, it details an investigation of the microstructure, composition, hardness and wear character- istics of Stellite12 coatings with different welding currents, then determines the optimum process current for the PTAW of Stellite2 Co-based coating. 2. Experimental Procedures An atomized cobalt-based alloy, Stellite12, was deposited by plasma transferred arc hardfacing process on SAF2507 Duplex Stainless Steel plates with the thickness of 25.00 mm (as shown in Table 3). As received (the resulting?) chemical composition (mass%) of substrate and coating material is presented in Table 1. The same process parameters were used for each deposition with the exception of the arc current, which was 140 A for specimen 1, 160 A for specimen 2, 180 A for specimen 3 and 200 A for specimen 4. Table 2 lists the welding parameters used in this test. According to the excellent welding performance, the DSS base material was not pre-heated to reduce the thermal shock before coating. 8) After being coated, the plates were left to cool to room temperature in the vermiculite. Samples containing coating and base material were removed from each plate for further analysis. The samples for microstructural analysis were polished and etched following conventional procedures. Etching was performed by using electrolytic etching in 20 N NaOH solution to reveal the microstructure of the transverse section of specimens. While oxalic etchant (100 ml H 2 O, 10 g oxalic acid, electrolytic 6 V) was used to identify the possible presence of precipitates in welding HAZ of SAF2507 DSS. 7) + Corresponding author, E-mail: deng@dlut.edu.cn Materials Transactions, Vol. 54, No. 9 (2013) pp. 1851 to 1856 © 2013 The Japan Institute of Metals and Materials EXPRESS REGULAR ARTICLE