Liquid Fe-13Cr-5V-1.2C alloy and solid low carbon steel were solidified and bonded in a tube after holding at temperatures for 285sec. The effects of mutual diffusion between two alloys on the microstructural change was investigated. Primary solidified layer bonded on the low carbon steel surface was formed as planar type. Alloy contents and hardness values droped nearby the bonded interface within primary solidified layer. Reaction layer formed in the vicinity of the bonded interface within 30∼40㎛ distance had lower alloy contents than cellular type structure. It is suggested that uphill diffusion of carbon from low carbon Fe-0.2C steel into the Fe-13Cr-5V-1.2C alloy at 1200℃ had produced low Cr content austenite. The austenite was transformed to auto-tempered martensite, which were identified as reaction layer.