Structure and properties of metal-to-metal wear resistant multilayer welds deposited by self shielded flux cored arc welding process




School of Mechanical, Materials and Mechatronic Engineering


Reclamation of worn components by arc welding is considered to be a standard costeffective industrial practice. However, gaps remain in the understanding of the solidification process and phase transformations in distinct weld zones of metal to metal wear resistant welds, deposited by self shielded flux cored arc process, as well as the interaction between thermal cycles and heat flow in the weld metal and the base metal. Improved understanding is necessary to guide alloy and process development to ensure the quality, reliability and performance of repaired components, extending service life of industrial assets and avoiding catastrophic engineering and environmental failures. Three metal-to-metal wear resistant alloys designed for deposition using self-shielded, flux cored arc welding (SSAW) have been investigated. The alloys have been designated LSMM30, MSMM40 and HSMM55; and have carbon equivalents (CE (IIW)) ranging from -0.8 to 2 and deposited hardness from 30 to 50 HRC. The objective was to investigate the effect on structure and properties of pre-heat in the range 100 degrees celsius to 300 degrees celsius, as well as a non-conventional high pre-heat temperature above the estimated martensitic start temperature, MS.

It was found that weld deposits produced for cooling rates representative of recommended pre-heats (below MS) consisted of 3 distinct macroscopic regions: Region 1 comprising the primary as solidified weld metal (WM); Region 2, a reaustenitised heat affected zone consisting of a grain coarsened heat affected zone (GCHAZ) and a grain refined heat affected zone (GRHAZ); and Region 3, a "dark etching" region extending from the intercritical heat affected zone (ICHAZ) to a subcritical tempered region developed from welded structure that had experienced a peak temperature above about 600 degrees celsius. Although two distinct weld regions (WM and HAZ) are usually identified for conventional ferritic weld deposits, the hard facing weld metals investigated in the current research showed a sub-division of the HAZ into two distinct regions. It is concluded that the "dark etching" Region 3 is a result of a strong etching response because of the presence of significant residual carbide and the occurrence of tempering via the weld thermal cycle. In contrast, Region 2 experiences complete re-austenitisation with subsequent transformation to substantially untempered martensite and/or bainite. This structure shows a comparatively lower etching response.

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