The good comprehensive mechanical properties of 300M high strength steel are related to the silicon element in the composition, so it can be considered that the successful design of 300M steel composition can not be separated from the addition of silicon element. Silicon will hinder the transformation from carbide to cementite in steel. The tempering temperature of steel is increased to 320℃, which is very beneficial to stress relief and hydrogen removal. Silicon can also significantly improve the stress corrosion characteristics, especially the crack propagation characteristics in the medium.
Chemical composition of 300M high strength steel;
Mechanical properties of 300M high strength steel;
First, high strength
After standard heat treatment and oil quenching tempering, the tensile strength of this steel can reach more than 1860MPa, and it is the low alloy ultra-high strength steel with the highest working strength at present. High strength can reduce the weight of parts, and improving strength has always been one of the main goals pursued by landing gear parts design. The important load-bearing parts of American aircraft wings are also made of 300M steel, and the highest strength grade is used.
Second, the transverse plasticity is high.
In the material standard, the cross-sectional shrinkage is the main mechanical property index, which is the characteristic of 300M steel and is put forward according to the characteristics of landing gear parts.
Third, the fracture toughness is high.
High fracture toughness indicates strong resistance to crack propagation. When selecting materials, we should pay attention to both sharp notch toughness and blunt notch toughness. They represent different physical meanings, so they cannot be substituted for each other.
Fourth, excellent fatigue performance.
The fatigue resistance of 300M steel is obviously better than that of 4340 steel. This is extremely beneficial to the long-life use of aircraft parts such as landing gear, and is also the main reason why 300M steel is widely used in aircraft.
5. Good corrosion resistance.
The composition of 1.5% silicon improves the stress corrosion resistance of 300M steel, and its stress corrosion resistance is better than that of similar steel.