Newly revealed features of fracture toughness behavior of spot welded dual phase steel sheets for automotive bodies

Abstract

Fracture toughness is one of the parameters, which are used to estimate the fatigue life of resistance spot-welded (RSW) joints. A spot-welded pair is affected by the shear stress of the weld zone when it is exposed to tensile load. Repetitive loads reduce the fatigue life of the spot weld, and the material splits at the spot-welded region. This study investigates the effect of welding current, weld time and nucleus size ratios on the fracture toughness of RSW of galvanized DP450 steels having 1.0 mm thickness. The specimens were joined by spot welding at different welding currents and times. Welding processes were carried out using 3, 5, 7 and 9 kA welding current and 10, 20, 30 and 40 cycles (1 cycle = 0.02 s) weld time and the electrode pressure was fixed at 600 MPa. All series of specimens were exposed to tensile shear test in order to determine the fracture toughness. The fracture toughnesses for all series of RSW joints were calculated by using the formula given in the literature. The nugget diameters, core sizes and their heights were measured via an optical microscope. The Vickers microhardness measurement was carried out on the weld nugget, heat affected zone (HAZ) and base metal. Nucleus size ratios were calculated. The results of the study demonstrated that the fracture toughness of RSW depended not only on the nugget diameter D, but also sheet thickness t, tensile rupture force F, hardness H and nucleus size ratios hn/dn.

Deği̇şi̇k Kaynak Elektrotlari Kullanilarak Yapilan Di̇renç Nokta Kaynakli Aisi 304 Paslanmaz Çeli̇k Saclarin Kaynak İzi̇ Görüntüsü Ve Kaynak Parametreleri̇ni̇n Mekani̇k Özelli̇klere Etki̇si̇

“…Kaynaklı imalat yöntemlerinde öncelikle sorgulanan özellik kaynağın yapısal karakteristikleri olup, statik ve dinamik yüklemelerde mekanik ve yorulma dayanımının iyi olması beklenmektedir. Bunun yanında korozyon direnci, sızdırmazlık ve estetik özellikleri de ön plana çıkmaktadır (Doruk ve diğ., 2015 ve Sevim, 2015).…”

The Effect of Resistance Spot Welding Parameters on Microstructure and Strength of DP800 Steel Joints Using Response Surface Methodology

“…Kishore et al [14] studied the influcen of spot welding current on strength and nugget diameter of Zn coated DP and interstitial free steel and reported that the strength and nugget diameter of joints increases at increased levels of welding up to the evolution of expuilsion. Sevim [15] investigated fracture toughness of galvanized DP450 steel spot joints and concluded that the fracture toughness of spot joints depends on the diameter of nugget, thickness of sheet, tensile force of rupture, hardness and ratios of nucleus size. Yaghoobi et al [16] investigated RSW of DP and IF steel and reported that the TSFL of spot joints increased at increased levels of weldig current along with increase in nugget diameter.…”

The Microstructure and Mechanical Behavior of TRIP 800 and DP 1000 Steels Welded by Electron Beam Welding Method

“…There are studies in the literature reporting the weldability and post-weld strength values of DP steels and TRIP steels with welding methods such as gas metal arc welding (GMAW) [13,14], laser beam welding (LBW) [15,16] and resistance spot welding (RSW) [17,18]. There is some studies about advanced high strength steels are used at automotive industry welded by EBW [19][20][21].…”