Influence of austenitisation temperature on the structure and properties of weather resistant steels

The influence of austenitisation temperature on the structure and properties of three experimental weather resistant steels has been studied. All these steels contain 1% Mn, 0.3% Ni, 0.47% Cr and 0.47% Cu. In addition, steel #1 has 0.1% C, 0.1% P, steel #2 has 0.1% C, 0.05% P and 0.024% Nb while steel 3 has 0.2% C, 0.054% Nb and 0.046% V. It has been found that the hardness, yield strength and tensile strength do not change significantly with austenitisation temperature over the range 900–1200 °C for steel #1 but they increase considerably when austenitised above 1000 °C for steels 2 and 3. Similarly, the ductility decreases with increasing temperature of austenitisation. All the steels austenitised up to 1000 °C exhibit sharp yield points. None of these steels shows sharp yield point after 1200 °C. At 1100 °C, however, sharp yield points were observed in steels 1 and 2. There has been a noticeable change in optical microstructure. In steels 2 and 3 the pearlite is gradually replaced by granular bainite when austenitised above 1000 °C. The transmission electron microscopy study reveals that the granular bainite consists of acicular ferrite and martensite/austenite constituent.