With the increasing demand for safety, energy saving and emission reduction, Advanced High Strength Steels (AHSS) have become very attractive steels for automobile makers. The usage of AHSS steels is projected to grow significantly in the next 5–10 years as new safety and fuel economy regulations are enacted. These new steels pose significant manufacturing challenges, particularly for welding and stamping. Welding of AHSS remains one of the technical challenges in the successful application of AHSS in automobile structures, especially when durability of the welded structures is required. In this paper, Gas Metal Arc Welding (GMAW) of uncoated DP 600 and boron (coated and uncoated boron) steels were investigated. In the first study, 2.0 mm DP 600 and 2.0 mm uncoated boron lap joints (Joint #1 and #2) were investigated. In the second study, 1.00 mm DP 600 and 2.0 mm USIBOR (aluminized coated boron) lap joints (Joint # 3 and #4) were investigated. Static and fatigue tests were conducted on the four joint configurations. The effects of steel stack-ups and microhardness distribution along the tensile stress flow direction of the joints on fatigue performance defined by fatigue life as well as crack initiation site and propagation path were analyzed. Metallurgical properties of the dissimilar metal lap joints were evaluated using optical microscopy. The boron steel shows a significant drop in hardness at the heat affected zone (HAZ) as compared to the DP600 steel side. It was found that for the 2.0 mm DP600 and 2.0 mm boron steel dissimilar joint, fatigue life of the joint is better when boron steel was on the top of the joint (Joint #2). However, in the case of 1.0 mm DP 600 and 2.0 mm USIBOR lap joint, the fatigue life of the joint is better when 1.0 mm DP 600 was on the top of the joint (Joint # 3). Ductility of boron steel and significant HAZ softening in boron steel are believed to be the key factors for the fatigue failure at the boron steel side (in all four joint configurations).

There has been a substantial increase in the use of advanced high strength steel in automotive structures in the last few years. The usage of these materials is projected to grow significantly in the next 5–10 years with new safety and fuel economy regulations. Advanced High Strength Steels (AHSS) are getting popular with superior mechanical properties and weight advantages compared to mild steel materials. These new materials have significant manufacturing challenges, particularly for welding and stamping. Proper understanding of the weldability of these materials is critical for successful application in future vehicle programs. Due to high strength nature of AHSS materials, higher weld forces and longer weld times are needed to weld AHSS materials. In this paper, weld lobe development for DP600, and DP780 steels are discussed. DP600 steels were joined with two different weld equipments and three different electrodes and their influence on mechanical properties are discussed. Development work on the effect of weld tips on button size, and shrinkage voids due to different welding variables is discussed. DP780 EG steel (1.0 mm) is also joined to itself. The weld lobes, mechanical properties (tensile shear and cross tension), cross-section examination, and microhardness of 1.0 mm DP780 EG to 1.0 mm DP780 EG weld joint results are discussed.

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Use of Advanced High Strength Steels in automotive applications is increasing. One of these materials is boron steel, which is commercially available in coated and uncoated sheets. Automotive manufacturers are using boron steel in body structure applications to produce light weight parts and to address safety requirements. Boron steel is available in a non heat-treated condition (also referred to as “green state”) which typically has a yield strength around 350 MPa. The yield strength for a fully temperature hardened boron steel increases to above 1000 MPa, depending on heat treatment temperature and quenching methods used. In this report, the static and fatigue properties of uncoated boron steel were evaluated. One objective was to understand whether these properties varied with respect to the material rolling direction (longitudinal, transverse and diagonal). For static strength analysis three different gages (1.0 mm, 1.5 mm and 2.0 mm) were evaluated. For fatigue evaluation, 3.0 mm thickness boron steel was evaluated. Based on the mechanical test data, ultimate tensile strength was not statistically significant in all three directions (longitudinal, transverse and diagonal) among three gages chosen. However, within the same gage, ultimate tensile strength is statistically significant in all three directions. 0.2% offset Yield strength and total elongation are uniform in all gages as well as in all three directions within each gage. However, uniform elongation (at max. load condition) was significant among the gages as well as within the same gages. A comparison of the monotonic and cyclic stress strain curves indicates boron steel is a strain-softening material.

With the increasing demand for safety, energy saving and emission reduction, Advanced High Strength Steels (AHSS) have become very attractive steels for automobile makers. The usage of AHSS steels is projected to grow significantly in the next 5–10 years with new safety and fuel economy regulations. These new steels have significant manufacturing challenges, particularly for welding and stamping. Welding of AHSS remains one of the technical challenges in the successful application of AHSS in automobile structures due to Heat affected Zones (HAZ) at the weld joint. In this study Gas Metal Arc Welding (GMAW) of a lap joint configuration consisting of 1.5 mm uncoated DP600 to itself was investigated. The objective of the study was to understand the wire feed rate and torch speed influence on lap joint strength. A two factor, two level, full factorial design of experiment (DOE) was conducted to understand the wire feed and torch speed influence on tensile strength. In order to understand the curvature effect, center point was also considered in the experiment. Based on the statistical analysis, wire feed rate was the only significant factor on static tensile strength. Metallurgical properties of the lap joints were evaluated using optical microscopy. Significant hardness drop of 40% was observed at the HAZ.