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Abstract
The influence of P in the range ∼0·01 to 0·07% with high Ti and N additions on the hot ductility of 1·5%Al, boron treated twinning induced plasticity (TWIP) steels has been examined. P, even at the 0·02% level, has a small detrimental influence on the hot ductility, and ductility decreases progressively as the P content is increased. Low melting point Fe(Mn)phosphide phases were found at the austenite grain boundaries accounting for this deterioration in ductility. As it is difficult to cast these steels, without cracks forming, P levels should be as low as possible, preferably ∼0·01%. High Ti and N additions (≧0·07%Ti, 0·01%N) to these B treated, TWIP steels gave rise to good ductility throughout the straightening temperature range 800–950°C. It is suggested that the high N level results in good ductility because although there is a large volume fraction of TiN, the high Ti/N ratio encourages growth of the TiN precipitates, and the high [Ti][N] product causes the precipitation to take place at high temperatures so that it is too coarse to influence the hot ductility.
