We have a test coupon casing K55 versus K55 welded with the following at root 3/32" dia. E7016 SMAW succeeding passes 1/8" and 5/32" E10018-D2 SMAW also with preheat but no PWHT (considering K55 is below 22 HRC). The hardness of weld after cool is 30 HRC. From this we cut specimens for tensile and face and root bends the thickness of specimen for bending is 0.375" width is 1.5". We have 2 specimen for face bending one failed within welding another failed in the heat affected zone (HAZ). We also have 2 specimens for root bending both failed at the fusion line. Our 2 specimens subjected to tensile test passed since the base metal failed first and the weld remain intact except for a dotted portion observed at the fusion line at the side of one tensile specimen. As observed from the bending specimens the failure of the weld seems to be brittle because the cracked occupied the entire width while one specimen totally separated. Can you help me and tell the root cause of this failure? We reviewed ASME for a better electrode and we decided to use E10018-G instead of E10018-D2 will this solved our problem?