SOME INVESTIGATIONS ON THE FORMING BEHAVIOR OF AN INDIGENOUS EXTRA-DEEP DRAWING LOW-CARBON STEEL .1. EXPERIMENTAL RESULTS

Aluminium killed, extra-deep drawing (EDD) low carbon steels are widely used in the automotive industry because of their low cost and excellent properties. The results of an extensive study on the forming behaviour of six randomly selected heats of an indigenous EDD steel (to specification SS 4011) are reported. The investigation revealed that the indigenous steel exhibits a high degree of consistency in its formability, which is comparable to that of an equivalent foreign grade. The effects of stress state, sheet thickness and lubrication on the formability are discussed. Strain distribution profiles obtained after punch-stretching were analysed in terms of the severity of clamping of the blank. A meaningful correlation could be obtained among the formability parameters (like the average strain hardening coefficient nBAR, average plastic strain ratio rBAR etc.), the texture results and the experimentally evaluated Forming Limit Diagrams (FLDs). Inferior formability of one of the six heats was traced, through a fractographic study using a scanning electron microscope, to the detrimental alignment of sulphide stringers, oxide inclusions etc. along the rolling direction, which emphasized the importance of high metallurgical quality for sound forming behaviour. The suitability of the indigenous steel for the industrial production of an automobile component that involves severe stretch-draw, viz., a starter end cover, was ascertained. In view of the encouraging results, the indigenously produced SS 4011 steel is being regularly used in the commercial production of automotive components.