The piston crowns for marine diesel engines are manufactured by the following procedure; forging->rough machining->quenching & tempering->groove machining->induction hardening on groove face->Cr plating on induction hardened groove face->dehydrogen heat treatment->final machining using a 1Cr-0.4Mo alloy steel. Of them Induction hardening is required to achieve the hardness of minimum 400HV from 170HV for strengthening the matrix in order to prevent deformation of ring land. But, a number of cracking failures have been reported in the piston crown ring land during manufacturing and in service. Based on the fractured surface with intergranular cracking mode, it was found that the cracking of piston crown ring land was related to the infiltration of hydrogen generated during Cr plating into the induction hardened layer. Susceptibility to hydrogen embrittlement is strongly influenced by the strength level of the material and untempered martensite is the most susceptible phase to hydrogen embrittlement. Therefore, most alloys are generally restricted to a maximum hardness of 350 HV. These facts inform that the cracking of piston crown is caused obviously by hydrogen and maybe inevitable thing under the present manufacturing procedure. To solve this, a simple method just applied the hardenability of base material itself is proposed as a substitute of induction hardening. It is to process the shape of ring groove in advance prior to quenching & tempering instead of after quenching & tempering. As a result of applying this method the hardness of the ring groove face was able to increase from 170HV to 230HV due to formation of bainitic structure. Any kinds of failures such as cracking and deformation of the piston ring land have not been reported yet after both the final production of piston crowns and the shop test even though the achieved hardness is lower than the case of induction hardened one.