Q550C steel belongs to low alloy high strength steel. Chemical composition of Q550C steel: C ≤ 0.18, Si ≤ 0.60, Mn ≤ 2.0, P ≤ 0.030, S ≤ 0.030, Nb ≤ 0.11, V ≤ 0.12, Ti ≤ 0.20, Cr ≤ 0.80, Ni ≤ 0.80, Cu ≤ 0.80, N ≤ 0.015, Mo ≤ 0.30, B ≤ 0.004, Al ≤ 0.015. Mechanical properties of Q550C steel: yield strength ≥ 550 MPa, tensile strength 600-780 MPa, elongation after fracture ≥ 16%, impact energy ≥ 55J. A514 grade E quenched and tempered steel, Q550C steel is mainly used for manufacturing various large-scale engineering structural components and construction machinery. Due to its high strength, Q550C steel can meet the requirements of large-scale and lightweight construction machinery.
The toughness of steel such as A514 grade E quenched and tempered steel is the ability of steel to absorb energy in the process of plastic deformation and fracture, and also the ability of steel to resist impact load. It is related to and different from the plasticity of steel. It is the comprehensive performance of strength and plasticity. The strength plasticity index of steel is obtained by static tensile test. When these indexes are used to bear the dynamic load structure, there are obvious limitations.
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Chromium element (Cr element) can improve the strength and hardness of A514 grade E quenched and tempered steel, carbon steel in rolling state, reduce elongation and area reduction. When the chromium content is more than 15%, the strength and hardness will decrease, while the elongation and reduction of area will increase correspondingly. It is easy to obtain high surface processing quality for steel parts containing chromium after grinding. The main function of chromium element (Cr element) in quenched and tempered steel structure is to improve hardenability, so that the steel has better comprehensive mechanical properties after quenching and tempering.
