T91 dissimilar steel and 12Cr1MoVG were welded by automatic tungsten argon arc welding. The effect of different process conditions on the hardness of dissimilar steel welded joint was studied. The results show that the weld morphology of dissimilar steel welded joints is basically the same under different technological conditions

and the weld presents inverted trapezoidal upper and lower layers structure. After heat treatment

the hardness of the weld center of dissimilar steel is about250

while that of the weld center of dissimilar steel without heat treatment is about 300

the highest is 390

and the hardness of dissimilar steel weld joint increases abruptly near T91.