PURPOSE: To minimize the welding defect of the valve seat of a steam control valve component member used in a power plant by providing the valve seat and a repair structure for its defective part with a buttering layer of austenitic steel having a predetermined thickness and a cobalt-containing hardfacing layer disposed thereon.

CONSTITUTION: In a valve component member 100 in which a valve seat 25 having a hardfacing layer 10 made of stellite or the like is secured to a valve body 15 by bolts 18..., if the hardfacing layer 10 has defective parts 20 showing welding defects such as cracks, slugs, or holes and they are to be repaired, the defective parts 20 are first bored to form a bored surface 30. The bored surface 30 is formed to be deeper than the thickness of the hardfacing layer 10. Then, after heating to at least about 260°C for minimization of thermal stresses during subsequent welding operations, a buttering layer 35 made of austenitic steel is welded on the bored surface 30 in a nominal thickness of about 1.59 to 3.18 mm, and a cobalt-containing hardfacing layer 50 having a nominal thickness of about 3.05 to 7.87 mm is further welded thereon.