A890 CD4MCuN alloy is nominally a 26Cr-6Ni alloy (C≤0.04) with the addition of molybdenum and copper. There is no corresponding deformed steel grade for this alloy. The ASTM A890 CD4MCuN has a dual-phase structure in the as-cast state, which is composed of austenite distributed in a ferrite matrix. Although carbide precipitation is limited by the low carbon content of the alloy, if it is not eliminated by solution treatment, it will also disperse in the ferrite matrix, thereby reducing corrosion resistance. The alloy is essentially ferritic, its yield strength is about twice that of the 19Cr-9Ni austenitic alloy, and it has high hardness, good tensile ductility, and satisfactory impact toughness. The alloy’s high strength and hardness combined with good corrosion resistance make it particularly suitable for use in corrosive (including abrasive and erosional) working conditions.
1. A890 CD4MCuN chemical composition:
2. Performance characteristics of CD4MCuN
It contains relatively high elements such as Cr, Mo, and N, so the pitting corrosion resistance and crevice corrosion resistance of the steel are significantly better than the general 18-8Cr-Ni austenitic stainless steel and 18-14-2,18 -14-3 Cr-Ni-Mo austenitic stainless steel; due to its α+γ dual-phase structure and excellent pitting corrosion resistance, this steel is resistant to chloride stress corrosion and has better corrosion fatigue resistance than commonly used Cr-Ni austenitic stainless steel. Tensite stainless steel; due to the excellent intrinsic corrosion resistance of this steel, higher hardness after aging and α+γ dual-phase structure, the corrosion resistance is also better than Cr-Ni austenitic stainless steel, high chromium ferritic stainless steel and non-precipitation hardening α+γ duplex stainless steels.
3. CD4MCuN heat treatment:
The solution treatment temperature is 1100°C, and the temperature is kept for at least two hours to ensure uniform temperature. Slowly cool to 1010-1065°C, hold for half an hour, and then quench. Insulation at lower temperatures is to prevent castings (especially those with thicker sections) from cracking during quenching. The structure after heat treatment is also duplex, containing 35 to 40% austenite in the ferrite matrix. After solution treatment, it can be further strengthened by precipitation hardening caused by aging at 480-510°C. The degree of aging reaction and all the properties of the alloy in the aging state, including corrosion resistance, strength, impact toughness and quenching cracking tendency are related to the rephase treatment method, that is, the level of solution treatment temperature, aging temperature and aging time related. Because the alloy has sufficient strength and good corrosion resistance in many applications after solution treatment, it is not often used in the aged condition.
4. Application field of CD4MCuN
It has better corrosion resistance than CF alloy in many corrosive media, and is widely used in strong acid working conditions of oxidation and reduction, and has special resistance to stress corrosion cracking in chlorine-containing environment.
For example：
Subsea control lines
Decanter centrifuge components
Paper rollerers
Water systems
Offshore platforms
Pump and valve industry
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