Corrosion and wear resistant overlay, method for forming corrosion and wear resistant overlay, and corrosion and wear resistant valve

A method for producing a valve, wherein the valve comprises:

• a pipe section as a conduit for a fluid;
• a valve body that opens and closes the pipe section;
• a plurality of first valve seats provided in the valve body and a plurality of second valve seats provided in the pipe section in portions that come into contact with each other when the pipe section is closed;
• and
• a plurality of valve body-side valve seat overlays disposed on an outer surface of the plurality of first valve seats;
• and
• a plurality of valve casing-side valve seat overlays disposed on an inner surface of the plurality of second valve seats between the plurality of valve body-side valve seat overlays and the plurality of second valve seats;
• wherein the plurality of valve body-side valve seat overlays and the plurality of valve casing-side valve seat overlays come into contact with each other when the pipe section is closed;
• and
• wherein each of the plurality of first valve seats, the plurality of second valve seats, the plurality of valve body-side valve seat overlays and the plurality of valve casing-side valve seat overlays is formed by:
• a first step of heating and melting a Co-base alloy powder to form a first Co-base alloy layer on a base;
• and
• a second step of forming a plurality of other Co-base alloy layers, each of which is formed on a surface of a previously formed Co-base alloy layer starting with the first Co-base alloy layer, by repeating the first step a plurality of times;
• wherein an amount of heat input to heat and melt the Co-base alloy powder is reduced each time one of the other Co-base alloy layers is formed in the second step;
• wherein the first Co-base alloy layer and each of the other Co-base layers is formed by heating and melting the Co-base alloy powder deposited beforehand;
• wherein each of the first Co-base alloy layer and the other Co-base alloy layers is formed such that a carbide eutectic that precipitates at a boundary between crystals of a dendrite structure of a Co-base alloy in at least an outermost Co-base alloy layer has a maximum thickness of 10 μm or less in the first step and the second step;
• and
• wherein each of the first Co-base alloy layer and the other Co-base alloy layers is formed by using an arc discharge or a charged-particle beam in a vacuum.