Hitomi Nishibata

Prediction of Post Weld Hardness of Advanced High Strength Steels for Automotive Application using a Dedicated Carbon Equivalent Number

Weldability of advanced high strength steels in automotive manufacturing is a key issue. There are two important aspects to weldability: producing the welds and the quality of the welds. Producing the welds concerns the process to be used, possible addition of filler materials, the electrodes to be used, et cetera. Weld quality concerns the performance of the welds in a construction (e.g. strength and crash). With advanced high strength steels issues arise with increasing strength levels concerning the weld-quality. Traditionally carbon equivalent numbers are used to predict weldability. These traditional carbon equivalent numbers are not sufficient to predict post weld hardness of advanced high strength steels. Sumitomo Metal Industries and Corus cooperate to research weldability of advanced high strength steels. This paper concentrates on the influence of the chemical composition on weldability, as a first step to assess weldability of advanced high strength steels. This is done in two steps. First the traditional use of carbon equivalent numbers to predict weldability is explored. Literature is reviewed and possible issues with welding of advanced high strength steels are identified. Next the application of carbon equivalent numbers to predict post weld hardness for various welding processes (e.g. laser beam welding and resistance spot welding) is discussed. A wide range of steels was evaluated experimentally to determine the relationship between chemical composition and post weld hardness. The influence of welding processes expressed in terms of the cooling rates. The results are combined into simple models to predict post weld hardness of advanced high strength steel joints.

Influence of Welding Conditions on Nugget Formation in Single-Sided Resistance Spot Welding Process

This paper describes the single-sided resistance spot welding (SSSW) process which is expected to be a productive welding technology for joining stamped sheet panels to hollow parts for auto bodies. To obtain guidelines for making a good weld with SSSW process, the influence of welding parameters and set-up conditions of the specimen upon nugget growth were investigated experimentally. In addition, a numerical study was carried out to establish the mechanism of nugget growth in the SSSW process. Since deflection of parts during welding is one of the features of the SSSW process, this report focuses on the influence of electrode force and the stiffness of the specimen upon nugget formation. In addition, the effect of electrode geometry was examined.

Performance of Resistance Spot-Welded Joints in Advanced High-Strength Steel in Static and Dynamic Tensile Tests

The performance of resistance spot-welded joints in advanced high-strength steel sheets is critical for the application of these materials in safety-critical areas. To be able to predict the performance of such joints from C available material data would be of great benefit to the automotive industry. This report starts with a review of literature about various aspects of spot weld performance in advanced high-strength steels. It then describes experimental work whereby a set of resistance spot-welded joints in various advanced high-strength steels Qwas tested in lap shear and peel-type tensile testing. Testing was done both statically and dynamically. The steel sheet materials varied in microstructural and chemical compositions, strength and thickness. The goal of the tests was to investigate possible relations between material characteristics and performance of the welded joints. Therefore, the experimental results are related to several material parameters, i.e., sheet thickly ness, base metal yield and tensile strength, carbon content and various Carbon Equivalent numbers.