The microstructure

hardness and corrosion resistance of mold steel U338ESR for plastics treated at various solution and aging temperatures

were investigated by means of optical microscope (OM)

scanning electron microscope (SEM)

transmission electron microscope (TEM)

hardness tester and electrochemical analyzer. The results showed that with the increase of solution temperatures

which were at the range of 1 000 ~ 1 090 °C

alloying elements and NbC dissolved more into matrix

the uniformity of microstructures and the amount of martensite increased after water cooling

leading to the increase of hardness and the enhancement of corrosion resistance. When the aging temperatures were at the range of 300 -450 °C ，with the increase of temperatures

small Cu-rich phases nucleated and formed coherent bcc structure with the matrix and the coherent strain energy increased gradually

resulting in the increase of hardness and the decrease of corrosion resistance ； when the aging temperatures were at the range of 450 〜600°C

with the increase of temperatures

the Cu-rich phases transferred from coherent to incoherent state gradually

the coherent strain energy decreased

resulting in the decrease of hardness and the enhancement of the corrosion resistance. Reversed austenite formed at 600 °C

enhanced corrosion resistance further.