Key Features:
A heat-treatable, medium-to-high carbon, high-chromium martensitic stainless steel that achieves an excellent balance between hardness, wear resistance, corrosion resistance, and cost.
Simply put, 440A is an "entry-level knife stainless steel" or a "practical high-hardness stainless steel."
Chemical Composition and Metallurgical Principles:
High Chromium: Content approximately 16-18%.
This provides two key functions:
Ensuring sufficient chromium dissolves in the matrix, giving the material the fundamental properties of stainless steel (corrosion resistance).
Forming hard, wear-resistant chromium carbide particles with carbon.
Medium-to-High Carbon: Content approximately 0.60-0.75%. This is crucial for its hardenability. Carbon forms carbides with chromium, resulting in a hard martensitic structure after heat treatment.
Microstructure Transformation: This involves transforming the austenitic structure at high temperatures into a hard but brittle martensitic structure through quenching (rapid cooling), followed by tempering to adjust toughness, thus achieving the final properties.
Key Performance Characteristics:
High Hardness and Wear Resistance: After proper quenching and low-temperature tempering, its hardness typically reaches HRC 54-57. This gives it good edge retention and wear resistance.
Moderate Corrosion Resistance: Due to its high chromium content, its corrosion resistance is far superior to carbon steel and most tool steels. Under normal use and maintenance, it resists the erosion of water, sweat, and mild acids and alkalis. However, it is not rust-free and will still rust in humid, salt spray, or harsh environments, requiring more meticulous maintenance than austenitic stainless steels such as 304.
Magnetic Properties: It possesses strong magnetism.
Toughness: Among the 440 series (A/B/C), 440A has the lowest carbon content, therefore its toughness is relatively the best, and it is less prone to chipping, but this also means that its ultimate hardness is slightly lower.
Machinability: It can be machined, stamped, etc., in the annealed state (soft state), and then high hardness can be obtained through heat treatment.
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