The high-strength stainless steel adopts the method of super-carbon martensitic transformation strengthening and age strengthening effect superposition, and is the metal structural material with the best matching of strength and toughness and the best corrosion resistance. High-strength stainless steel can be divided into three grades according to strength: low strength grade is 1000~1400 MPa; medium strength grade is 1400～1700 MPa; super high strength grade is more than 1800 MPa.
one. Low strength grade, typical of 15-5PH precipitation hardened stainless steel.
This type of stainless steel alloying is characterized by the use of about 15% chromium to ensure the corrosion resistance of steel, and the nickel content of about 5% to achieve an equilibrium phase diagram, so that the steel obtains martensite structure at room temperature, while reducing the δ- in the steel. Ferrite, about 4% of copper is added to strengthen the role, a small amount of bismuth can form MC phase with carbon, which acts as a pinning grain boundary and refines the grain. After aging, a large number of face-centered cubic structures are precipitated, and a copper-rich phase that satisfies the KS-position relationship with the martensite matrix acts as a strengthening effect. 15-5PH steel is used for parts with an ambient temperature below 300 ° C or in corrosive environments to achieve weight reduction with higher material strength. Because the steel is low in cost, good in corrosion resistance, and can obtain different strengths by changing the heat treatment process, it provides a wider space for designing materials. Therefore, it is widely used in aircraft at home and abroad, such as Boeing 737-600 wing beam. , fuselage frame, Boeing 767 main landing gear front axle bracket steel pin, F-15 hatch latch, high-strength bolts, springs and other spare parts.
two. The medium strength grade is typical of PH13-8Mo precipitation hardening stainless steel.
This kind of steel adopts low-carbon alloying design, using about 13% chromium to ensure the corrosion resistance of steel, and about 8% nickel to compensate for the imbalance of phase diagram caused by low carbon and reduce δ-ferrite content. The steel is obtained from the lath martensite structure, and 2% molybdenum and 1% aluminum are added to form a NiAl phase and a Ni3Mo phase in the steel to strengthen. In the PH13-8Mo steel, lath martensite structure and a large number of dislocations are formed. The slender martensite lath can not only ensure the strength of the steel, but also toughen. There is a large amount of NiAl phase dispersed in the steel, and the dislocation line is pinned to strengthen. PH13-8Mo precipitation hardening stainless steel is a kind of precipitation hardening stainless steel with wide application range, many application parts, large dosage, high strength, fracture toughness and stress corrosion resistance. It is suitable for making high yield strength, high toughness and no Large-section members and high-stress fasteners to the opposite sex have become a must-have for foreign military and civilian aircraft. China's "Zhenlong" fighter main bearing fuselage frame and wing bearing beam are also made of this steel, and have been selected in the new generation of fighter aircraft embedded weapon ejection mechanism, rudder surface drive mechanism, engine transmission force It is used on key bearing and corrosion resistant structural parts such as pins.
three. Ultra high strength grade, typical of 6 F863 steel.
In this type of steel, C≤0.05%, the content of S, P, Si, Mn is as low as possible, reasonable chromium and nickel equivalent, and about 2% of molybdenum is added to make the steel obtain aging strengthening, and at the same time, the steel can maintain good toughness. And seawater corrosion resistance. In order to fully realize the strengthening effect of molybdenum, a certain amount of cobalt and a small amount of titanium are also added.
F863 steel is the new generation of ultra-high-strength stainless steel with the highest strength level at home and abroad. It has good corrosion resistance, welding performance and high fracture toughness. It can provide replacement for new generation weapon equipment and upgrade of parts. Stable materials have potential applications in aerospace large launch vehicle power connection devices, torpedo launchers, and submarine-launched cruise missiles.
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