Microstructure and Local Mechanical Properties of the Heat-Affected Zone of a Resistance Spot Welded Medium-Mn Steel

Abstract

The properties of the heat-affected zone (HAZ) are reported to have a great influence on the mechanical performance of resistance spot welded advanced high strength steels. Therefore, in the present work, the HAZ of a medium-Mn steel is characterized regarding its microstructure and its mechanical properties depending on the distance to the fusion zone (FZ). In order to obtain the local mechanical properties of the HAZ, samples were heat-treated in a joule-heating thermal simulator using different peak temperatures to physically simulate the microstructure of the HAZ. By comparing the microstructure and the hardness of these heat-treated samples and the HAZ, the local peak temperatures within the HAZ could be determined. Subsequently, tensile tests were conducted, and the austenite phase fraction was measured magnetically on the physically simulated HAZ samples in order to determine the local mechanical properties of the HAZ. As verified by energy-dispersive X-ray spectroscopy, peak temperatures above 1200 °C led to a uniform distribution of manganese, resulting in a predominantly martensitic microstructure with high strength and low total elongation after quenching. Below 1100 °C, the diffusion of manganese is restricted, and considerable fractions of austenite remain stable. The austenite fraction increases almost linearly with decreasing peak temperature, which leads to an increase of the total elongation and to a slight decrease in the strength, depending on the distance to the FZ. Temperatures below 700 °C exhibit hardly any effect on the initial microstructure and mechanical properties.

Thermal analysis of AISI 1020 low carbon steel plate agglutinated by gas tungsten arc welding technique: a computational study of weld dilution using finite element method

“…For instance, since they produce embrittlement in the heat-affected zone, quicker cooling rates may be bad for a weldment. The mechanical characteristics of weld metal and the heat-affected zone (HAZ) are directly impacted by changes in microstructure [19][20][21]. Therefore, it is crucial to manage the heat input in order to produce a solid microstructure and a weld of high quality.…”

Mechanical behavior and failure mechanism of resistance spot welded Aluminum and Copper joint used in the lightweight structures

“…The crack around the weld nugget may be subjected to biaxial stresses during propagation; see Ref. (43) When the internal tensile stresses exceed the strength of the weld joints (i.e., the weld metal, the base metal, or both), the crack has been initiated, and the specimen will be deformed (44). The formation and spread of cracks are also influenced by the residual stress distribution surrounding the weld nugget; see Refs.…”

Inspection of Spot Welded Joints with the Use of the Ultrasonic Surface Wave

“…The methods of joining steel sheet elements used in motor vehicles include: welding, butt-welding [1], laser welding [2], spot welding [3,4], adhesive bonding [5,6], and riveting [7]. Spot welding is widely used in the automotive industry and has been used for many years, but it requires quality control at the manufacturing stage as there may be around 6000 spot welds on a vehicle body [8,9]. The spot welding method is not only used for joining steel components of vehicle bodies, but also allows joining element produced by additive manufacturing technology [10] with aluminum [3,11,12], which makes the technique promising in future construction development.…”