Effect of Retained Austenite and Non-Metallic Inclusions on the Mechanical Properties of Resistance Spot Welding Nuggets of Low-Alloy TRIP Steels

Abstract

The combination of high strength and formability of transformation induced plasticity (TRIP) steels is interesting for the automotive industry. However, the poor weldability limits its industrial application. This paper shows the results of six low-alloy TRIP steels with different chemical composition which were studied in order to correlate retained austenite (RA) and non-metallic inclusions (NMI) with their resistance spot welded zones to their joints’ final mechanical properties. RA volume fractions were quantified by X-ray microdiffraction (µSXRD) while the magnetic saturation technique was used to quantify NMI contents. Microstructural characterization and NMI of the base metals and spot welds were assessed using scanning electron microscopy (SEM). Weld nuggets macrostructures were identified using optical microscopy (OM). The lap-shear tensile test was used to determine the final mechanical properties of the welded joints. It was found that NMI content in the fusion zone (FZ) was higher than those in the base metal and heat affected zone (HAZ). Whereas, traces of RA were found in the HAZ of highly alloyed TRIP steels. Lap-shear tensile test results showed that mechanical properties of spot welds were affected by NMI contents, but in a major way by the decomposition of RA in the FZ and HAZ.

An advanced modelling to improve the prediction of thermal distribution in friction stir welding (FSW) for difficult to weld materials

“…At higher temperature regions, free electrons with higher kinetic energy travel to lower temperature regions until it collides with an imperfection or a phonon in the material. Thus, any imperfection such as retained austenite has a direct impact on thermal conductivity and electrical resistivity that are the dominant parameters for calculation of the temperature profiles [58]. The presented model in this study consistent with experimental result at 80 and 100 rpm rotational speeds.…”

“…It is stated that higher hardness could be associated with the transformation products such as retained austenite and high dislocation density [14]. Cortes et al [58] reported the effect of retained austenite on the thermal/electrical properties of five advanced high-strength TRIP steels. The physical properties of TRIP steels are influenced by the presence and quantity of impure atoms and precipitated phases.…”

Deformation-Assisted Joining of Sheets to Tubes by Annular Sheet Squeezing

“…In recent years, there has been a growing utilization of deformation-assisted joining processes driven by an increasing demand of assembling lightweight components. Deformation-assisted joining processes are classified into three distinct groups according to their operating principles:Based on mechanical, hydraulic, and magnetic loading, such as clinching [1,2], self-pierce riveting [3], sheet-bulk compression [4], hydraulic forming [5], and electro-magnetic forming [6];Based on solid-state welding, such as friction stir welding [7], friction spot welding [8] and explosive welding [9];Based on fusion welding combined with plastic deformation, such as resistance spot and projection welding [10] and weldbonding [11]. …”

“…Based on fusion welding combined with plastic deformation, such as resistance spot and projection welding [10] and weldbonding [11].…”