Direct injection fuel injection valve

A direct injection fuel injection valve comprising a valve casing fitted into an engine main body of an internal combustion engine, the valve casing housing therein a valve member, the valve casing including a valve seat member and a tubular case member, the valve seat member having a valve seat and a fuel injection hole, the valve seat member being joined to one of opposite end parts of the case member, the valve member being capable of being in contact with and being detached from the valve seat, the fuel injection hole being opened and closed by cooperation between the valve seat and the valve member, at least part of the valve seat member and the case member being exposed to a combustion chamber of the engine main body, and fuel being capable of being injected into the combustion chamber via the fuel injection hole,

• wherein the valve seat member is formed from a martensitic stainless steel having a PI value of at least 19, containing at least N, and having a C content of no greater than 0.3%,
• the case member integrally has, at an outer peripheral portion of the other of the opposite end parts thereof, an outward flange-shaped annular collar portion functioning as a yoke, the case member being formed from a ferritic stainless steel containing at least one of Nb, Ti, and Zr, and
• the valve seat member is, at a cylindrical outer peripheral wall thereof, directly welded to the one end part of the case member from an outer peripheral wall side of the case member.