Bainitic as well as quenched & tempered steels typically suffer from temper embrittlement in the temperature range between 400 and 600°C. As a consequence excellent initial toughness properties get lost in nitriding or carbonitriding processes. However, by applying innovative industrial technologies austenite grain sizes are refined significantly, not only in flat products but also in long products which improves impacts properties as such and at the same time temper embrittlement can be shifted to low temperatures. In combination with microalloying new strategies for robust high-strength long products now can be thought of.
The paper presents very first results using a new production technology called XTP, which was recently implemented at Steeltec. To demonstrate its potential properties of low carbon microalloyed bainitic steels like 7MnB8 and 13MnSiCr7 grades are shown. For rods produced with this XTP process, very detailed microstructural characterisation was performed with Field Emission Gun Electron Scanning Microscopy combined with EBSD analysis and High Resolution Transmission Microscopy. Also, light optical microscopy and X-ray diffraction technique was used, the last one for the measurement of retained austenite volume fraction. TRIP assisted bainitic steels with unique combinations of strength and toughness were obtained opening new perspectives in challenging applications.