Effect of tempering temperature on the structural properties of precipitates in Q960 steel

The morphology,distribution and components of precipitates in Q960 steel under the conditions of the same composition,rolling technology and quenching process but different tempering temperatures were systematically investigated by using transmission electron microscopy(TEM),energy dispersive X-ray spectrometry(EDX) and a multi-function internal friction device.A law was proposed for describing the effect of tempering temperature on the structure characteristics of the precipitates.It was shown that the decrease of carbon solution content in martensite was greater when the tempering temperature was less than 400℃,but it was very slow when the tempering temperature was higher than 400℃.In addition,a large number of small parallel θ-carbides dissolved and were finally replaced by Cr carbides which precipitated along martensite lath boundaries.With the tempering temperature increasing,Nb,V and Ti composite carbon and nitrogen compounds grew up and their shape evolved from a square to an oval.