The effects of Al content on the microstructure and mechanical properties of Cr5 Mo1 V die steel were investigated by means of optical microscope

scanning electron microscope

transmission electron microscope and X-ray diffractometer

and the action mechanism of Al element was analyzed. The results indicate that the main phases of as-cast Cr5 Mo1 V-xAl die steel are composed of α-Fe

γ-Fe and M

7

C

3

carbide

and the area fraction of pearlite in the die steel is firstly increased and then decreased with the increase of Al content. As the Al content increases to 1.2%

the pearlite appears in the die steel. Lath martensite and secondary carbide can be observed in tempered Cr5 Mo1 V die steel without Al addition. When Al content is 1.2% or 1.5%

local fine twins and coarse carbides are generated. With the increase of Al content in tempered Cr5 Mo1 V-xAl die steel from 0 to 1.5%

the tensile strength

elongation

impact toughness and hardness of die steel are firstly increased and then decreased with the appropriate Al content of 1.2%

which is mainly attributed to the formation of nano twins

major secondary carbides and dispersed distribution of δ-Fe phase in die steel.