This type of steel has suitable hardenability. After appropriate metal heat treatment, the microstructure is uniform troostite, bainite or extremely fine pearlite, so it has high tensile strength and yield strength ratio (generally around 0.85), high toughness and fatigue strength, and low toughness-brittle transition temperature, and can be used to manufacture machine parts with larger cross-sectional dimensions.
According to the steel type and steel quality requirements, the smelting of alloy structural steel can be carried out by oxygen top-blown converter, open hearth furnace, electric arc furnace; or electroslag remelting and vacuum degassing. Ingots can be cast by continuous casting or die casting. Ingots should be cooled slowly or hot forged and rolled. When heating the steel ingot, the temperature should be uniform and the holding time should be sufficient to improve the segregation defects and avoid uneven deformation during forging and rolling. After forging and rolling, the steel with small size, especially the carburizing steel with carbon content of about 0.2%, should be cooled quickly above 600 to avoid aggravating the banded structure. For forgings with large cross-sections, measures should be taken to eliminate internal stress and white spots. Quenched and tempered steel should be quenched into martensite structure as much as possible, and then tempered into sorbite structure. During the carburizing process of carburizing steel, the concentration gradient of the carburized layer should not be too large to avoid the appearance of continuous network carbides on the grain boundary of the carburized layer. Nitriding steel must first be heat treated to obtain the required properties, and then finally finished before nitriding. After nitriding, except for grinding and removing the brittle "white layer", no further processing is required.
steel Tubes
