Remark; The above hardness test result shown in the table, hardness data of cracking area (NG side) are softer than OK side that correspond to micro structure (High Ferrite). However, the hardness were tested by Micro Vicker scale because the part too small for testing with Brinell Hardness.
P.S. it must be developed by controlling structure during casting process and may make a heat treatment process after casting to balance and homogeneous mechanical properties.