The alloying principle of low-alloy high-strength steel is mainly to improve the strength of steel by using solid capacity strengthening, fine-grained strengthening and precipitation strengthening generated by alloying elements, and at the same time, the effect of reducing the toughness-brittle conversion temperature of steel by using fine-grained strengthening is used to offset the adverse effect of carbon nitride precipitation strengthening in steel that increases the toughness-brittle conversion temperature of steel, so that steel can maintain good low-temperature performance while obtaining high strength. The performance characteristics of low-alloy high-strength steel are mainly manifested in the following two aspects.
1. High yield limit with good plasticity and toughness
The most striking feature of low-alloy high-strength steels is high strength. In the hot-rolled or normalized state, the strength of low-alloy high-strength steel is generally 30%~50% higher than that of the corresponding carbon engineering structural steel. Therefore, it can withstand large loads. The engineering structure is generally large or giant, and the weight of the component itself often becomes an important part of the load, and the strength of the structural material can be significantly reduced while the weight of the component can be significantly reduced and its ability to bear other loads can be further improved. Not only that, but this good effect also greatly improves the compactness of the engineering components, thereby further improving their reliability, while reducing the consumption of raw materials, reducing costs and saving resources.
The elongation of low-alloy high-strength steel is 15%~23%, and the impact absorption function is >34 J at room temperature, which has good plasticity and impact resistance, which can avoid brittle fracture when impacted, and at the same time makes cold bending, welding and other processes easy to carry out. In addition, low-alloy high-strength steels have a lower brittle conversion temperature, with a quality grade of E at -40°C and a value of not less than 27 J. This is of great significance for engineering components used in severe cold areas, as well as transportation vehicles such as vehicles, ships, offshore oil production platforms, containers, bridges, etc.
2. Good welding performance and atmospheric corrosion resistance
Welding is the most common method for building engineering structures, so steel used in engineering structures is required to have good welding performance. Low-alloy high-strength steel has low carbon content, low alloying element content, good plasticity, and is not easy to produce quenching structure and cracks in the weld area, and the added Ti, Nb, V, etc. can also inhibit the grain growth in the weld area, so most of this kind of steel has excellent welding performance, and heat treatment is generally no longer carried out after welding.
Most of the engineering structures are served in the atmosphere or marine environment, and a small amount of Cu, Ni, Cr, P and other elements are added to the low-alloy high-strength steel, which effectively improves the ability of the engineering structure to resist atmospheric, seawater and soil corrosion. If 0.2%~0.5% copper, 0.05%~0.1% phosphorus and aluminum are added, the corrosion resistance of steel can be significantly improved, and copper and phosphorus are added at the same time for the best effect.
