ABSTRACT
In the last years microalloyed boron steels have been adopted in the automotive industry to achieve weight reductions. Namely, they are used as load-bearing elements such as pillars and reinforcements, in a quenched and tempered (QT) condition with tensile strength ranging from 800 to 1300 MPa. Dual-Phase (DP) steels have also been introduced in this industry given their good combination of high strength and ductility, coupled with good energy absorption characteristics. The automobile is largely a welded steel frame construction. Thus, the weldability of these advanced high strength steels is a key aspect. The Plasma Arc Welding process (PAW) presents features that make it suitable for these applications. Furthermore, the mechanical response, specifically the fatigue behavior of weldments is crucial for this kind of applications. In this manner, the purpose of this work was to study the fatigue response of PAW welded joints of 1mm high strength (900 MPa) microalloyed boron steels sheets in two microstructural conditions: quenched and tempered (QT) and dualphase (DP). Intercritical and quenching and tempering heat treatments were performed. Coupons of 100x100mm were welded by PAW and characterized. Finally, by means of pulsating 4-point bending fatigue tests, fatigue curves were obtained for both types of welded joints (PAW+TR and PAW+DP). A superior fatigue life was measured for de PAW+DP samples. This observation could be related to the different microstructural evolution experienced in the heat affected zone of this two materials.
Keywords
Weld; fatigue; microalloyed boron steels; DP
