Gas valve and flow rate control method for propane gas

A gas valve comprising:

• a valve body including a main body having a flow path through which propane gas having a temperature of 500° C. to 800° C. flows, and a main body seat ring fixed to the main body;
• and
• a movable valve capable of opening or closing the flow path,
• the movable valve including a valve stem, a valve disc coupled to the valve stem, and a disc seat ring,
• the disc seat ring including a ring base member fixed to the valve disc using a bolt, and a first overlay layer provided on the ring base member and formed of a material having a higher hardness than the ring base member, wherein
• when the movable valve closes the flow path, the first overlay layer hermetically comes into contact with the main body seat ring,
• the valve disc is formed of a first austenitic stainless steel containing 17.0% by mass to 21.0% by mass of Cr and 8.0% by mass to 13.0% by mass of Ni, and
• the ring base member is formed of a second austenitic stainless steel containing 17.0% by mass to 20.0% by mass of Cr and 8.0% by mass to 15.0% by mass of Ni.