Duplex steel forgings

I. Main types and characteristics of high temperature and corrosion resistant materials

1. Metal and alloy materials

• Stainless steel (such as 316L and 904L)
  • Features: It contains chromium, nickel and other elements, the oxidation resistance temperature can reach above 800℃, and it is resistant to acid, alkali and salt solution corrosion.
  • Typical applications: chemical reaction kettle, seawater desalination equipment, food processing pipeline.
• Titanium and titanium alloys (such as TA2 and TC4)
  • Characteristics: low density, corrosion resistance to seawater and chloride ions, high temperature up to 500℃, high strength.
  • Typical applications: ship propellers, marine engineering structural parts and aero-engine parts.
• Nickel-based alloys (such as Hastelloy and Inconel)
  • Characteristics: Excellent stability in high temperature (above 1000℃) and strong corrosive media (such as sulfuric acid and hydrochloric acid).
  • Typical applications: petroleum refining reactor, coal chemical gasifier, nuclear reactor fittings.
• zirconium alloy
  • Features: Resistant to strong alkali and hydrofluoric acid corrosion, high temperature up to 400℃, and strong nuclear radiation stability.
  • Typical applications: nuclear fuel cladding, corrosion-resistant pipeline in pharmaceutical industry.

2. Ceramic materials

• Silicon carbide (SiC), silicon nitride (Si3N4)
  • Characteristics: High temperature resistance (above 1600℃), wear resistance, acid and alkali resistance and high thermal conductivity.
  • Typical applications: high-temperature kiln lining, wafer carrier in semiconductor manufacturing, automobile exhaust gas treatment parts.
• Alumina ceramics (Al2O3)
  • Characteristics: Strong oxidation resistance, corrosion resistance of molten metal and good insulation.
  • Typical applications: high temperature thermocouple protection tube, electronic packaging substrate, wear-resistant mechanical seal.

3. Polymer materials

• Polytetrafluoroethylene (PTFE, Teflon)
  • Characteristics: high and low temperature resistance (-200℃~260℃), strong acid and alkali resistance and organic solvent resistance, low friction coefficient.
  • Typical applications: chemical pipeline seal, non-stick pan coating, corrosion-resistant lining of semiconductor equipment.
• Polyether ether ketone (PEEK)
  • Characteristics: High temperature resistance (long-term use at 260℃), radiation resistance, chemical solvent resistance and high mechanical strength.
  • Typical applications: aerospace lightweight components, medical implants, high-temperature gears.
• Fluorocarbon (FKM)
  • Characteristics: oil resistance, weather resistance, high temperature resistance (200℃~300℃), strong aging resistance.
  • Typical applications: automobile engine seals, oil pipeline O-rings.

4. Composite materials

• Metal matrix composites (such as carbon fiber reinforced aluminum alloy)
  • Characteristics: It has both the toughness of metal and the high temperature resistance of ceramics, and the corrosion resistance is improved.
  • Typical applications: turbine blades of aero-engines and brake parts of high-speed trains.
• Coating materials (such as ceramic coating and nano-composite coating)
  • Characteristics: a protective layer is formed on the metal surface by spraying or electroplating, which is resistant to high temperature corrosion.
  • Typical applications: gas turbine blade coating, inner wall anticorrosion coating of chemical equipment.

II. Typical application scenarios in the industrial field

1. Chemical Industry and Petroleum Industry

• Scene: acid-base reaction kettle, petroleum cracking furnace, seawater bromine extraction equipment.
• Material selection: Hastelloy C-276 is used to treat concentrated hydrochloric acid or chloride solution; Titanium alloy is used in seawater heat exchanger to prevent chloride ion corrosion; PTFE-lined pipeline transports hydrofluoric acid.
• Case: In the catalytic cracking unit of a petrochemical enterprise, Inconel 625, a nickel-based alloy, was used in the inner wall of the reactor, which can run stably at 850℃ and sulfide environment.

2. Energy and power industry

• Scene: Coal-fired power generation boiler, steam generator of nuclear power plant, solar thermal power generation collector.
• Material selection: silicon carbide ceramics are used for high temperature furnace support; Zirconium alloy is used for cladding of nuclear reactor fuel rods: Incoloy 800H, a high temperature alloy, is used for superheater pipes (resistant to 650℃ high temperature and oxidation).
• Case: The molten salt heat storage tank of photothermal power station adopts 316L stainless steel lined ceramic coating, which can withstand molten nitrate corrosion at 550℃.

3. Aerospace and national defense

• Scene: aero-engine combustion chamber, rocket propellant storage tank and shipboard equipment.
• Material selection: Titanium alloy Ti-6Al-4V is used for aircraft skin (salt spray corrosion resistance); Ceramic matrix composites (CMC) are used for turbine blades (resistant to high temperature above 1200℃); Polyimide film is used for insulating layer of spacecraft.
• Case: The engine tail nozzle of F-35 fighter is made of nickel-based alloy with oxidation-resistant coating, which can withstand gas erosion above 1100℃.

4. Semiconductor and Electronic Industry

• Scene: Etching equipment and thin film deposition chamber in chip manufacturing.
• Material selection: Shi Ying glass (resistant to hydrofluoric acid etching and 800℃ high temperature); SiC wafer stage (resistant to plasma corrosion and high thermal conductivity); PTFE parts are used for high purity gas pipelines.
• Case: The plasma etching machine cavity of a wafer factory is coated with silicon carbide, which can resist the long-term corrosion of fluorine-based plasma and prolong the service life of the equipment.

5. Food and pharmaceutical industry

• Scene: high temperature sterilization equipment, medicine synthesis reaction kettle, food baking machinery.
• Material selection: 316L stainless steel is used in pharmaceutical reaction kettle (strong acid and alkali resistant cleaning solution, which meets hygiene standards); PEEK is a high-temperature bearing used in food processing (non-toxic, steam sterilization resistant).
• Case: The cavity of the freeze-dryer in a pharmaceutical company is made of electrolytic polished 316L stainless steel, and the surface roughness Ra is less than 0.2μ m, which can not only clean with corrosion-resistant reagents, but also avoid drug residues.

III. Emerging Applications and Technology Trends

• Hydrogen energy industry: The electrode plate of hydrogen fuel cell stack needs to be resistant to electrolyte corrosion, and platinum plating or coating (such as TiN) on the surface of titanium metal can improve the corrosion resistance.
• Deep-sea engineering: the shell of deep-sea robot is made of titanium alloy or composite material, which is resistant to high-pressure seawater (salinity 3.5%) and microbial corrosion.
• Nanotechnology: Nano-structured ceramic coating (such as Al2O3-ZrO2 composite coating) can improve the high-temperature corrosion resistance of metal matrix and is applied to aero-engine turbine blades.

IV. Key factors of material selection

1. Environmental compatibility: Select materials according to parameters such as temperature, medium (acid/alkali/salt/gas) and pressure.
2. Cost and cost performance ratio: For example, the cost of titanium alloy is higher than that of stainless steel, but it has a longer life in marine environment and a lower comprehensive cost.
3. Processing technology: ceramic materials have high hardness but high brittleness, so molding technology (such as sintering and 3D printing) should be considered; Attention should be paid to the creep characteristics of polymer materials at high temperature.