It is generally accepted that steel with a tensile strength of o>1470 MPa (150 kgf/mm²) that also possesses toughness is referred to as ultra-high-strength steel; today, there are also ultra-high-strength steels with tensile strengths reaching 2400 MPa.
Ultra-high-strength steel is primarily used in rocket engine casings, aircraft landing gear, fuselage frames and skins, high-pressure vessels, and certain components of conventional weapons. The scope of application for ultra-high-strength steel is continuing to expand, with many civilian components now requiring its use.
Based on differences in composition and performance characteristics, ultra-high-strength steel can be classified into the following five major categories:
1) Low-alloy ultra-high-strength steel. Primarily used in applications at room temperature or below 200°C, it evolved from low-alloy quenched and tempered steel.
2) Secondary-hardening medium-alloy ultra-high-strength steel. This type of medium-carbon alloy steel has a relatively high alloy content and excellent hardenability. After quenching, it achieves the required strength through secondary hardening caused by carbide precipitation during tempering; its tensile strength can reach
2750 MPa. At around 500°C, its specific strength is the highest among all ultra-high-strength steels. Representative grades in this category include H11 (4Cr5MoSiV) and H13 (4Cr5MoSiV1).
3) Secondary hardening-type high-alloy ultra-high-strength steels. These steels feature a high-toughness Fe-Ni-Co matrix reinforced by fine M2C-type carbides in the normal aged condition. They exhibit an excellent balance of strength and toughness, high fatigue strength, and high resistance to stress corrosion.
4) Age-hardening martensitic steel. This type of high-alloy steel achieves high strength through the age-hardening of ultra-low-carbon alloy martensite, with a tensile strength approaching 2200 MPa (megapascals).
5) Precipitation-hardening ultra-high-strength stainless steel. Under certain operating conditions, materials must not only possess ultra-high strength but also exhibit good corrosion resistance and oxidation resistance; precipitation-hardening stainless steel is designed to meet these requirements.
I haven’t worked with ultra-high-strength steel myself, and it’s unlikely to come up in my line of work, but I need to understand it—you never know when a viewer might ask about it during a live stream.
When viewers ask questions, I can’t just say, “I don’t know,” and I certainly can’t say, “Hold on a moment; I’ll look it up and get back to you.”
As the saying goes, “The usefulness of the seemingly useless is what makes it truly useful.”
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.