CD3MWN（A890 7A）-Hyper Duplex Stainless
Index
CD3MWN, a duplex stainless steel, was introduced as a new steel grade under the American ASTM A890/A890M-12 standards. Its alloy composition distinguishes it from other duplex stainless-steel grades by featuring low carbon content, and high levels of chromium, nickel, tungsten, nitrogen, copper, molybdenum, boron, barium, and the rare earth element Re. With a pitting corrosion resistance index (PREN) value of at least 45, CD3MWN falls into the category of fourth-generation super duplex stainless steel. It demonstrates exceptional performance in challenging environments and serves as a cost-effective substitute for expensive nickel-based alloys, high-alloy austenitic stainless steels, and even titanium alloys.
The pitting corrosion resistance and crevice corrosion resistance of A 890 7A steel are better than those of CD3MN steel and CN7MS steel.
It is widely used in chemical processing, oil and gas production, and other applications where corrosion resistance is critical. A890 7A is often compared to other duplex stainless steels, such as 2205 and 2507, and it is generally considered to be more corrosion-resistant than these options. It is an ideal choice for applications that require high strength, resistance to corrosion, and good weldability.
Advantages and disadvantages of-27Cr-7Ni-Mo-W-N（A890 7A）
SA890 7A is a specific type of duplex stainless steel. Duplex stainless steels are characterized by their combination of austenitic and ferritic microstructures, which offer a unique set of properties. Here are the advantages and disadvantages of A890 7A
Advantages
- Corrosion Resistance: CD3MWN (A890 7A) offers excellent resistance to corrosion, especially in aggressive environments such as seawater, chloride-containing solutions, and acidic environments. This makes it suitable for applications in offshore oil and gas industries, chemical processing plants, and marine environments.
- Strength and Toughness: A890 7A exhibits high strength and toughness due to its duplex microstructure. It can withstand high pressures, making it suitable for applications where mechanical strength is crucial, such as piping systems and pressure vessels.
- Fatigue Resistance: This duplex stainless steel has good fatigue resistance, allowing it to endure cyclic loading conditions without suffering from fatigue failures. It is suitable for applications subjected to repeated stress cycles, such as structural components in offshore platforms.
- Cost-Effective: It provides a cost-effective solution compared to some other corrosion-resistant alloys like nickel-based alloys. It offers a balance between performance and cost, making it an attractive choice in various industries.
Disadvantages:
- Weldability: One of the main challenges with duplex stainless steel is its weldability. CD3MWN (A890 7A) requires careful control of welding parameters and post-weld heat treatment to avoid the formation of detrimental phases, such as the sigma phase and intermetallic compounds. Improper welding practices can lead to reduced corrosion resistance and mechanical properties.
- Sensitivity to Temperature: Like other duplex stainless steels, CD3MWN (A890 7A) can experience a loss of mechanical properties at elevated temperatures. The high-temperature embrittlement can reduce its overall performance in applications where sustained high temperatures are present.
- Design Considerations: The duplex microstructure of CD3MWN (A890 7A) requires careful consideration during the design phase. It is important to account for the potential phase separation, which can occur during cooling or exposure to certain temperature ranges. Proper design and material selection are crucial to ensure optimal performance.
- It’s worth noting that the advantages and disadvantages listed here are specific to CD3MWN (A890 7A) and duplex stainless steel in general. Different grades and alloys within the duplex stainless-steel family may have varying properties and characteristics.
Chemical composition and mechanical properties of A890 Gr 7A
Chemical composition
Carbon: 0.03% Max
Manganese: 1.00%-3.00%
Silicon: 1.00% Max
Phosphorus: 0.03% Max
Sulfur: 0.02% Max
Chromium: 26.00-28.00%
Nickel: 6.00 – 8.00%
Molybdenum: 3.00 – 3.50%
Nitrogen: 0.30 – 0.40%
Tungsten: 3.0 – 4.0%
Copper: 1.00% Max
Barium: 0.0002 – 0.0100%
Boron: 0.0010 – 0.0100%
Cerium + Lanthanum: 0.005 – 0.030%
Mechanical properties
- Yield Strength: 75 ksi Min
- Tensile Strength: 100 ksi
- Elongation at 2 in: 20% Min
J93379(A890 7A) Reference Casting Standards and others.
CD3MWN（A890 7A） material equivalent to
A995 7A A890 7A ASTM: A890 7A ASME: SA890 7A Alloy Family:
Type: 27Cr-7Ni-Mo-W-N
ACI: CD3MWN; UNS – Cast: J93379
CD3MWN（A890 7A）) Casting Typical Application
A890 7A is a super duplex stainless steel casting material that finds applications in various industries where its unique properties are beneficial. Some typical applications of castings include:
Offshore Oil and Gas Industry: It is commonly used in offshore platforms, subsea equipment, and oil and gas production systems. Its excellent corrosion resistance, high strength, and toughness make it suitable for withstanding the harsh conditions encountered in offshore environments.
Chemical Processing Plants: The castings are used in chemical processing equipment such as reactors, pumps, valves, and piping systems. The material’s resistance to corrosive chemicals and high-pressure environments makes it ideal for handling aggressive fluids.
Desalination Plants: It is used in desalination plants where it is exposed to seawater. It’s superior corrosion resistance and high pitting resistance make it suitable for seawater intake systems, brine pipelines, and other components involved in the desalination process.
Power Generation: The castings are utilized in power plants, particularly in applications where resistance to corrosion and erosion is critical. This includes components such as pumps, valves, turbine casings, and heat exchangers.
Marine Applications: Due to its excellent resistance to corrosion in marine environments, CD3MWN (A890 7A) castings are used in marine structures, shipbuilding, and offshore renewable energy installations.
Pulp and Paper Industry: It is suitable for equipment used in the pulp and paper industry, such as digesters, bleach towers, and chemical processing vessels, where resistance to corrosive chemicals and high temperatures is required.
These are just a few examples of the typical applications of A890 7A castings. The material’s exceptional corrosion resistance, high strength, and fatigue resistance make it a valuable choice for a wide range of industries and demanding environments.
CD3MWN（A890 7A）Casting Heat treatment process.
The heat treatment process for A890 7A castings involves several steps to achieve the desired mechanical properties and microstructure. Here is an expanded explanation of the heat treatment process:
Heating to the Solution Annealing Temperature: The first step is to heat the A890 7A casting to a minimum temperature of 1130°C (2066°F). This temperature ensures that the entire casting reaches the desired heat treatment temperature uniformly. The heating process should be performed gradually to prevent thermal stress and distortion.
Holding Time for Uniform Heating: Once the casting reaches the solution annealing temperature, it is essential to hold it at that temperature for a sufficient duration. This holding time allows for the heat to penetrate the entire casting uniformly, ensuring the complete dissolution of carbides and other precipitates. The duration of the holding time depends on the casting’s size, thickness, and complexity, as well as the specific recommendations provided by the material’s manufacturer or applicable standards.
Quenching in Water or Rapid Cooling: After the required holding time, the CD3MWN (A890 7A) casting is rapidly quenched in water or cooled rapidly by other means. Quenching involves immersing the casting into a quenching medium, such as water, oil, or polymer, to rapidly cool it. This rapid cooling helps to lock in the desired microstructure and mechanical properties by preventing the formation of undesired phases or excessive precipitation.
It is crucial to follow the recommended heating and cooling rates, holding times, and quenching methods specified by the material’s manufacturer or applicable standards. The heat treatment process for CD3MWN (A890 7A) castings should be carried out with precision and care to ensure the desired mechanical properties, corrosion resistance, and microstructure are achieved. Consulting the relevant specifications, and technical data sheets, or seeking guidance from experienced heat treatment professionals is recommended to ensure the proper execution of the heat treatment process.