(1) low-carbon steel, also known as mild steel, carbon content of from 0.10 to 0.25 percent of low-carbon steel is easy to accept all kinds of processing such as forging, welding and cutting, commonly used in the manufacturing chain, rivets, bolts, shaft. (2) the amount of carbon in the steel of 0.25% to 0.60% carbon steel. It has killed steel, semi-killed steel, rimmed steel and other products. In addition to carbon also contain minor amounts of manganese (0.70% to 1.20%). By product quality is divided into ordinary carbon steel and quality carbon structural steel. Thermal processing and cutting good, poor welding performance. Strength, hardness higher than the low-carbon steel, while ductility and toughness lower than low carbon steel. Do not heat treated, the direct use of hot-rolled sheet, cold-drawn materials, may also be used after heat treatment. Quenching and tempering of steel has good mechanical properties. The highest attainable hardness of about HRC55 (HB538), σb is 600 ~ 1100MPa. So moderate intensity levels for various applications, carbon steel the most widely used, except as a building material, but also used extensively for the manufacture of mechanical parts. (3) high-carbon steel often called tool steel, carbon content from 0.60 to 1.70%, can be hardened and tempered. Hammers, crowbars, etc. by the carbon content of steel 0.75%; cutting tools such as drills, wire-tapping, reamers by the carbon content of steel from 0.90 to 1.00% of. Most of the carbon steel processing performance using oxygen converter peace smelting furnace, high-quality carbon steel is also used electric arc furnace production. Depending on the extent of the steelmaking process deoxy, carbon steel can be divided into killed steel rimmed steel and semi-killed steel ranged between. Influence of steel smelting method performance, primarily through the purity of steel and works. People by vacuum processing, refining and injection technology, are available to the higher purity of the steel, thus significantly improving the quality of carbon steel. Plastic processing carbon steel is usually divided hot and cold. After thermal processing, the ingot small bubbles, porosity and other defects are welded together, enabling organizations to dense steel. Meanwhile, heat processing can destroy cast structure, grain refinement. So wrought than cast steel has better mechanical properties. Cold-worked steel, with the degree of cold plastic deformation increases the strength and hardness increase, lower ductility and toughness. In order to improve the finished product rate, widely used in continuous casting processes. Aging heat treatment of low carbon steel is usually two aging hardening and strain aging, are caused by the effect of interstitial elements, primarily due to carbon, nitrogen, oxygen caused by redistribution. I.e. steel after quenching and aging rapid cooling from a high temperature performance with time varying phenomenon. Carbon content in steel deoxidation extent and nitrogen content of the quench aging has a significant impact. Low-carbon steel, high boiling insufficient deoxidation steel and nitrogen content of steel was the most significant hardening aging. About 0.3% of the carbon steel, performance changes caused by the hardening aging has been greatly weakened. About 0.6% of the carbon-containing high-carbon steel, actually can not afford to age hardening effect (see metal heat treatment). After strain aging performance after cold deformation changes over time phenomenon. Effect of carbon and nitrogen similar to strain aging, and aging effect on hardening of phosphorus also promote strain aging. Low carbon steel due to cold deformation disappears yield point, with time and gradually restored. Strain aging is more complicated than quenching aging. Such as steel and then hardened by cold working, whether at room temperature or slightly elevated temperature, are to accelerate the strain aging. Aging often carbon steel to industrial production has brought great harm, such as boiling steel welding, due to the aging of the welding joint HAZ hairline cracks, seriously affect the safety of welded structures. However, due to the development of modern metallurgy techniques, and applications in industrial production, especially oxygen steelmaking get lower nitrogen, oxygen content, so the aging problem has been reduced.