Cobalt-based Alloy 20

2025-07-08

CO 20) is a cobalt-based wear-resistant superalloy, which monopolizes the field of extreme working conditions by virtue of “super wear resistance × total environmental corrosion resistance × high temperature stability”. The following is a systematic analysis from six dimensions:

I. Standards and brand system

1. Implementing standards

International norms:
- Aviation/military industry: AMS 5898 (aviation material specification, defining chemical/mechanical properties of forgings and bars), SAE J467 (automotive engineering standard, specifying technical requirements for wear-resistant parts);
- General Reference: ASTM B438 (General Specification for Cobalt-based Alloy Bars, Auxiliary Test for Composition and Properties).
Domestic adaptation: there is no completely equivalent brand, and the composition of similar cobalt-based wear-resistant alloys (such as Co-based Cr30W5) is different, so it is necessary to refer to the international standard design.

II. Chemical composition (mass fraction%, typical range)

Through the design of “high carbon+Cr/W carbide strengthening”, the synergistic effect of elements is remarkable:

element	Content range	Core role
C	0.7~3.0	Forming hard phases of Cr₇C₃ and WC with Cr/W to improve wear resistance (carbon content =→ hardness =, plasticity ↓).
Co	30~70	Stabilize the matrix at high temperature to provide toughness and corrosion resistance.
Cr	25~33	Cr₂O₃ oxide film is formed, which is resistant to high temperature oxidation and acid/alkali/seawater corrosion; Cr₇C₃ carbide is also generated.
W	3~25	WC/WC hard phase (hardness HV1500+) is precipitated, which significantly improves the wear resistance.
Fe/Ni	≤3.0	Impurity elements, exceeding the limit to reduce corrosion resistance (strict control)

III. Mechanical properties (typical value, as-cast/annealed)

Co 20 properties crush conventional alloys, focusing on the core advantages of “wear resistance+high temperature”;

Performance index	typical value	Contrast 316L stainless steel.
tensile strength	700~1000 MPa	17% higher (316l ≈ 600mpa)
yield strength	300~600 MPa	100% higher （316L≈310 MPa）
extensibility（δ₅）	3~10%	75% lower（316L≈40%）
hardness	55~60 HRC	175% higher （316L≈20 HRC）
heat resistance	Long term tolerance 1000℃	150% higher （316L 长期≤400℃）

IV. Requirements for Heat Treatment and Processing

Heat treatment (optimizing structure and releasing property):
- Stress relieving after casting: heat preservation at 800~900℃ for 2~4 hours, air cooling (stabilizing carbide distribution, eliminating casting stress and preventing cracking);
- Repair after welding: preheat 300~400℃ before welding (cobalt-based alloy has poor thermal conductivity to prevent hot cracking), adopt TIG/MIG welding (ERCoCr welding wire), and anneal at 750~850℃ after welding (repair heat affected zone and restore corrosion resistance).
Machining characteristics (high hardness challenge):
- Casting: lost wax casting is preferred (precision molding of valve seats, nozzles and other complex parts);
- Machining: cubic boron nitride (CBN)/ diamond tool, low speed+high pressure cooling (to avoid tool wear, the surface roughness should be Ra ≤ 1.6μ m);
- Surfacing: it is often used for surface strengthening (such as valve sealing surface, which can improve the wear life by 5 times).

V. Main application fields (“ultimate solution” for extreme working conditions)

With the advantage of “life× performance” (the cost is 3 times that of stainless steel and the life is 10 times), CO 20 monopolizes high-value scenarios:

Energy and chemical industry:
- Valves/seals: valve seat of blowout preventer for oil drilling, plunger of chemical pump (resistant to high-pressure mud+acid and alkali corrosion, with life exceeding 3 times that of tungsten carbide);
- High-temperature components: geothermal well pipes, gas turbine combustion chamber liners (resistant to 1000℃ high temperature+corrosion, replacing nickel-based alloy to reduce cost by 40%).
Aerospace:
- Engine: turbine blade edge (anti-800℃ gas erosion, wear life is twice that of titanium alloy), landing gear hinge bushing (high impact+wear resistance);
Machinery and tools:
- Wear-resistant parts: hammer head of mine crusher, bushing of mill housing (wear-resistant, life is 5 times of ultra-high manganese steel);
- Cutting tools: tool tips made of hard-to-machine materials (dry cutting and wear resistance, life is 3 times longer than that of cemented carbide);
Medical field:
- Implants: artificial joint ball head (wear-resistant+biocompatible, life is over 20 years, replacing ceramics to reduce cost by 50%), dental implant (body fluid corrosion resistance).

Key summary

Core advantages:
- Wear-resistant ceiling: the proportion of carbide is over 30%, the hardness is ≥55 HRC, and the abrasive/adhesive wear resistance is 10 times higher than that of stainless steel;
- All-environment corrosion resistance: the corrosion rate in acid and alkali, seawater and high-temperature gas is less than 0.01 mm/year;
- No softening at high temperature: the strength is still maintained at 1000℃, which is far better than that of conventional alloys.
Limited challenges:
- Cost-sensitive (cobalt price accounts for 70%, and the price fluctuates greatly);
- Complex processing (high hardness requires special technology, and the manufacturing cost increases by 50%).

CO 20 is the “performance benchmark” of cobalt-based wear-resistant alloy. Through the synergistic strengthening of high carbon+Cr/W, it has become an irreplaceable core material in the scene of extreme wear-resistance+corrosion+high temperature, supporting the design of long-life components in high-end fields such as aviation and energy.