Advanced Characterization of HAZ Softening of AHSS for Crash Modeling

Abstract

Advanced characterization of the mechanical properties in the softened HAZ is vital for designing welded AHSS components, as it is needed to predict post-weld performance, such as during crash. The weld heat affected zone (HAZ) of advanced high strength steels (AHSS) containing significant volume fractions of martensite exhibit considerable softening because of tempering effects. HAZ softening of two AHSS; Usibor 1500 (press hardening steel) and M1500 with nominal ultimate tensile strength (UTS) of 1 500 MPa has been characterized in this study. Samples were subjected to various rapid tempering cycles using the Gleeble to simulate the microstructures found in different locations of the sub-critical HAZ. Mechanical properties of simulated weld areas have been measured with different geometries, representing different levels of stress triaxiality. Furthermore, Digital Image Correlation (DIC), to determine fracture strain of HAZ, measured the fracture strain of a spot weld and base metal for Usibor 1500. Uniaxial tensile and notch sample geometries were used to investigate the influence of different strain path. The results show fracture strain is a weak function of strain path for samples that fail in the HAZ, whereas fracture strain of the base material considerably depends on strain path.

Shear band formation at the fusion boundary and failure behaviour of resistance spot welds in ultra-high-strength hot-stamped steel

“…It is well known that martensite tempering leads to local softening, particularly for materials with high martensite content [8, 9]. Figure 4 shows the hardness profile across the weld from the centreline toward the base metal (dashed arrow).…”

“…22MnB5 [7], and MS1200 (in accordance with VDA 239-100:2016) [8]. HAZ softening is often cited to be the cause of strain localisation and failure in advanced high strength steels during crash [8-10].…”

Microstructural Evolution of a Hot-Stamped Boron Steel Automotive Part and Its Influence on Corrosion Properties and Tempering Behavior

“…Ghassemi-Armaki et al 62 have shown that Gleeble ® simulations produce results that are sufficiently representative of the HAZ of real welded joints, meaning that physical simulations constitute a powerful tool for the study of the weldability of materials and of the properties of welds. For 22MnB5 steel, minimum hardness levels of 295-300 HV were observed in the HAZ 13,63,64 .…”

Microstructure and Failure Analysis of Resistance Projection Welding of Nuts to AHSS with Capacitor Discharge Welding

“…Jiehan LUO, 1) Zhaoyao ZHOU, 1) * Xiaobing CAO, 1) Chunhua ZOU 2) and Chunya ZOU 2) 1) National Engineering Research Center of Near-Net-Shape Forming For Metallic Materials, School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou, Guangdong, 510640 China. 2) Heron Intelligent Equipment Co., Ltd, Guangzhou, Guangdong, 510900 China.…”

“…With excellent strength and good formability, hot-stamping steels-a kind of AHSS-have been applied to the fabrication of car body components, such as B-pillars, reinforcements, bumpers, roof rails, rocker rails, and tunnels. [1][2][3] Resistance projection welding (RPW), which localizes current flow and heat input by a predetermined projection on one of the parts, is a variation of resistance spot welding. The RPW of nuts to steels is widely used for the assembly of the front axles, rear axles, the seatbelt, and steering columns to reduce loose automobile components and improve the assembly quality.…”