What are the differences between 300M and AerMet 100?
In aerospace and motorsport engineering, the choice of materials can either enhance performance or bring about abject failure. 300M and AerMet 100 are two high strength steels typically used for particularly difficult applications. These alloys, while appearing similar on paper, have different attributes that make each unique and suitable for specific applications.
Origins and Development
300M is a modified 4340 steel created specifically to meet aerospace needs. Its development took place in the mid-20th century. The addition of silicon and vanadium to the basic 4340 composition made 300M significantly stronger. For decades, 300M enjoyed unparalleled success as the backbone material for aircraft landing gears, rocket motor cases, and high-performance automotive parts.
Unlike 300M, AerMet 100 attempts to alleviate some existing issues and is a more recent advancement in metallurgy. This ultrahigh strength steel was developed in the 1990s by Carpenter Technology Corporation specifically to address fractures and stress corrosive resistance of existing alloys.
Molecular Structure
Alloy 300M has a molecular makeup of approximately 0.4% carbon, 1.6% silicon, 0.65% manganese, 1.8% nickel, 0.8% chromium, 0.4% molybdenum, and trace amounts of vanadium. Its distinguishing characteristic, setting it apart from 4340 steel, is the higher silicon concentration. The alloys in question differ in performance on a molecular scale.
The chemical composition of AerMet 100 is strikingly different with 0.23% carbon, 11.1% nickel, 3.1% chromium, 1.2% molybdenum, and 13.4% cobalt. The primary distinguishing factor in the alloy is the extremely high cobalt content, absent from 300M.
Physical Properties
The alloys exhibit high strength, AerMet 100 surpassing 300M, but differing on multiple fronts.
Proponents of 300M can expect a yield strength of 1520-1620 MPa and tensile strength between 1930-2000 MPa. Typical values for fracture toughness sit at 60-70 MPa.
Slightly higher values of tensile strength with AerMet 100, 1965-2050 MPa, keep yield strength unchanged. Fracture toughness, however, shows a dramatic enhancement, reaching 110-126 MPa almost doubling that of 300M.
AerMet 100’s increased fracture toughness enhances damage tolerance but also make it most useful when positioned in environments where resistance to crack propagation is key.
Corrosion Resistance
Another anomaly for stress corrosion cracking (SCC) resistance can be seen between these alloys. Because of poor SCC resistance, protective measures and careful surface treatment for corrosive environments is needed for 300M steel alloy.
This material is now more popular for aircraft and extreme environment components as it offers greater resistance to stress corrosion cracking in marine and high humidity areas.
Fabrication Considerations
From a machining point of view, 300M is in a better position than its counterparts as it has decades of processing strategies developed from its early years. The heat treatment of AerMet 100 is harder to document because of its precise temperature control needs, especially granular ageing, which impacts optimal property attainment.
Modern temperature-controlled vacuum furnaces do make achieving this precise method easier, though.
Cost and Availability
300M is easily sourced from suppliers and costs less than AerMet 100 as an older alloy. The high cobalt content AerMet 100 receives further increase lead time, costing 50 to 70 percent more than 300M.
The Definitive Difference
The difference AerMet 100 and 300M have is that the latter is an economical high strength steel for moderate fracture toughness applications, while AerMet 100 is more costly. 300M’s material profile as a metric benchmark also contrasts with AerMet 100 because of the latter’s much higher fracture toughness and stress corrosion resistance. In this case, the underlying reason for preference must stem from the intended use, which is becoming more frequently the case for AerMet 100 in critical aerospace motorsport applications.