high strength low alloy steel
At the end of 19, at the beginning of the development of low-alloy high-strength steel, the alloy design of steel grades only considered tensile strength. High content of silicon, manganese, nickel, chromium and other alloying elements are added to steel to improve its properties, but the main means to obtain high strength still depends on high carbon content. With the development of steel structure from riveting to welding, in order to improve the brittle fracture resistance of steel, the carbon content and composite alloying in steel are gradually changing. In 1950s, in order to save alloy elements, heat treatment was adopted to obtain a good match between strength and toughness. In 1960s, a new stage of microalloying and controlled rolling production began, and some new steel grades appeared. By 1970s, mature micro pearlite steel and pearlite-free steel, acicular ferrite steel, ultra-low carbon bainite steel, hot rolled dual-phase steel and low carbon martensite steel were widely used in oil and gas pipelines, deep well tubing, automobile steel plates and other fields. It is expected that these steel grades will play an important role in engineering structural materials in the 1980s. China began to develop low-alloy high-strength steel from 1957, and developed a series of steels such as Mn, Mn-V, Mn-Ti, Mn-Nb and Mn-Mo with yield strength of 30 ~ 70 kgf/mm2.
Low alloy high strength structural steel;
Refers to the addition of some alloying elements in the smelting process, the total amount of which does not exceed 5%. Adding alloying elements can obviously improve the strength of steel and give full play to the three main control indexes of steel structure members, especially in long-span or heavy-load structures, which generally saves about 20% steel consumption compared with carbon structural steel.
According to the national standard, it is divided into eight brands, namely Q345, Q390, Q420, Q460, Q500, Q550, Q620 and Q690. Due to the different quality, it is divided into a, b, c, d and e grades.