Influence of silicon, aluminium, phosphorus and copper on the phase transformations of low alloyed TRIP-steels

摘要

Although silicon is very important to prevent carbide precipitation during annealing of low-alloyed TRIP-steels and thus allows the aus-tenite to be stabilized by carbon, it causes problems during processing. Therefore, other alloying elements having a similar effect as silicon have to be considered. Possible candidates to substitute or reduce silicon are aluminium, copper and/or phosphorus, which are supposed to be capable of suppressing carbide formation, too. The influence of reduced silicon contents in combination with alloying elements being capable of substituting silicon completely or partially on the phase transformations occurring during heat treatment is studied. The results of the investigations are compared with a conventional low alloyed TRIP-steel. The phase transformations are investigated by dilatometric measurements on cold rolled material. The influence of the cooling rate after the intercritical annealing on the transformation behaviour of the austenite upon cooling and isothermal holding in the bainitic range is studied. The interpretation of the phase transformations are supported by investigations of the microstruc-ture via light microscopy and measuring the content of retained austenite using a magnetic volumetric method.