Influence of thin slab casting on the properties of microalloyed steel for high cold forming requirements

The grain refining influence of a TiN-precipitation during conventional continuous casting is already well established /1/. During direct hot processing of thin slabs, TiN-precipitation should occur in the liquid phase during solidification /2, 3/ and in the austenite /4/. Various experiments have been carried out in order to examine the effect of a TiN-precipitation before and during hot rolling of thin slab casted Ti- and TiNb- microalloyed high strength structural steels. The precipitation behaviour has been determined by TEM investigations. The samples show a large variety of TiN and Ti(N,C) precipitates. Number and size of the precipitates are depending on the holding and rolling-start temperatures. The impact of the individual hot rolling conditions on precipitation state, grain size as well as strength- and toughness-properties have been determined.