Effect of normalizing temperature on the strength of 9Cr-3W-3Co martensitic heat resistant steel

Microstructure and room temperature strength of 9Cr-3W-3Co martensitic heat resistant steel after normalizing at 900-1200 degrees C for 1 h and then tempering at 750 degrees C for 1 h have been experimentally investigated using optical microscope (OM), field emission scanning electron microscope (FESEM), electron back-scattered diffraction (EBSD), field emission transmission electron microscope (FETEM) and tensile tests. The results show that with increasing normalizing temperature, the strength of the 9Cr-3W-3Co steel increases from 900 degrees C to 1000 degrees C, then keeps almost the same from 1000 degrees C to 1100 degrees C and finally increases again from 1100 degrees C to 1200 degrees C. The change in the room temperature strength can mainly be attributed to the change in precipitation strengthening. The size and the amount of particles after tempering are mainly due to the re-dissolution of particles during normalization. The higher the normalizing temperature is, the more the coarse particles formed during manufacturing will be re-dissolved, and then the larger the amount of fine particles precipitated during tempering is. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.