The effects of filler metal and butter layer on the microstructure and mechanical properties of API 5L X65/AISI 304L joint

Abstract

The effects of different filler metals on the microstructure and mechanical properties of buttered API X65/AISI 304L stainless steel dissimilar joint have been investigated. The use of a butter layer and a suitable filler metal have major implications for the properties of dissimilar joints. In this study, API X65 high-strength low-alloy (HSLA) steel was first buttered with an austenitic Ni-based ERNiCr3 layer, followed by a post-weld heat treatment (PWHT) at 650 °C. ER308L (W308), ER309L (W309), and ERNiCr3 (WNiCr3) filler metals were then used to join the buttered API X65 side to AISI 304L stainless steel. All joints were first evaluated by radiographic testing to make sure that a flawless weldment has been attained. A scanning electron microscope (SEM), an optical microscope (OM), and energy-dispersive X-ray spectroscopy (EDS) were used to study microstructures of joints. Standard-sized and sub-sized tensile and impact tests were carried out. Microhardness profilometry was also conducted across the joint. Results showed that the finest grain structure was attained in the heat affected zone (HAZ) at the AISI 304L side and the lowest δ ferrite content was achieved in samples with the filler metal ERNiCr3 (WNiCr3). It appears that the heat input, generated by WNiCr3 filler metal, is comparatively lower than those generated in W308 and W309 samples. WNiCr3 weldment showed the highest hardness due to the formation of fine carbide particles such as NbC and TiC. Results of sub-sized impact tests showed that the highest impact energy was attained in the HAZ of the WNiCr3 sample.