Assessment of Resistance Spot Welds in Low Carbon and High Strength Steel Sheet

The introduction of high strength steels has highlighted the lack of knowledge regarding the properties required of resistance spot welds, particularly in the vehicle industry. The laboratory static and dynamic tests currently employed cannot be used to predict performance under service conditions, and there is a further complication because of lack of standardisation of test techniques. Specimen dimensions strongly influence the results when the properties of welds in low carbon and high strength steels are compared. The suitability of routine shop floor tests used in mass production industries has been questioned with regard to the necessity of generating plug failure. This cannot be resolved until the significance of plug failure in high strength steels is established. If plug failure is not essential, weld size can be determined by employing high speed metallurgical techniques for steels giving interface failure. Resistance welding is the most widely used technique for assembling transport vehicles and similar structures but despite this there is a lack of realistic data which adequately define the properties and likely service behaviour of such joints. This article describes the various test methods for resistance welds and summarises observations of the influence of test technique on the results obtained for welds in low carbon and high strength steels.