D4McuN duplex stainless steel is classified according to its chemical composition and can be divided into four types: Cr18 type, Cr23 (excluding Mo) type, Cr22 type and Cr25 type. For Cr25 duplex stainless steel, it can be divided into common type and duplex stainless steel, among which Cr22 type and Cr25 type are more widely used. Most of the duplex stainless steels used in my country are produced in Sweden, and the specific grades are: 3RE60 (Cr18 type), SAF2304 (Cr23 type), SAF2205 (Cr22 type), SAF2507 (Cr25 type). Alloy CD4MCu is nominally a 26Cr-6Ni alloy (C≤0.04) with additions of molybdenum and copper. There is no corresponding wrought steel grade for this alloy. Alloy CD4MCu has a dual-phase structure in the as-cast state, which is composed of austenite distributed in a ferrite matrix. Although the carbide precipitation is limited by the carbon content of the alloy, if it is not eliminated by solution treatment, it will also be dispersed in the ferrite matrix, thereby reducing corrosion resistance. The solution treatment temperature of CD4MCu is 1120 ° C, and it should be kept for at least two hours , to ensure uniform temperature, slowly cool to 1010 ~ 1065 ℃, keep warm for half an hour, and then quench. Keeping warm at a lower temperature is to avoid cracking of castings (especially castings with thicker sections) during quenching. The structure after heat treatment is also duplex, containing 35 to 40% austenite in the ferrite matrix.