What are the differences between low carbon, medium carbon and high carbon steels? - Shandong Jiugang Tisco Steel Co., Ltd.

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What are the differences between low carbon, medium carbon and high carbon steels?

Low carbon steel, also known as soft steel, has a carbon content from 0.10% to 0.30%. Low carbon steel is easy to work with in a variety of processes such as forging, welding and cutting, and is commonly used in the manufacture of chains, rivets, bolts, shafts etc.

Carbon steels with a carbon content of less than 0.25% are also known as soft steels due to their low strength and softness. It includes most of the ordinary carbon structural steel and part of the quality carbon structural steel, most of them are not heat-treated for engineering structural parts, some of them are used by carbon and other heat treatment for mechanical parts that require wear resistance.

Low carbon steel annealed organization for ferrite and a small amount of pearlite, its strong and hardness is low, plasticity and toughness is good. Therefore, its cold forming properties are good and can be cold formed by rolled edges, bending, stamping and other methods. The steel fins have good weldability. The low carbon content of low carbon steel has a low hardness and poor machinability, quenching can improve its machinability.

Low carbon steel is generally rolled into angles, channels, I-beams, steel pipes, steel strips {carbon steel plates, used to make a variety of building components, containers, boxes, furnace bodies and agricultural』machinery, etc. High quality low carbon steel rolled into thin plates, making car cabs, generator covers and other deep-drawn products; also rolled into bars, used to make strength requirements not i mechanical parts. Low carbon steel in use before the general without heat treatment, carbon content { in 0.15% above by carburization or cyanide treatment, for the requirements of the surface layer { high, good wear resistance shaft, bushings, sprockets and other parts.

Low carbon steel is restricted in use due to its low strength. Properly increase the manganese content of carbon steel and add trace vanadium, titanium, niobium and other alloying elements, can greatly improve the strength of steel. If you reduce the carbon content of steel and add a small amount of aluminum, { amount of boron and carbide forming elements, you can get ultra-low carbon bainite group enough its strength is very high, and maintain good plasticity and toughness.

Medium carbon steel is the amount of carbon 0.25% to 0.60% of the carbon steel. There are a variety of products such as sedimentary steel, semi-sedimentary steel and boiling steel. In addition to carbon can also contain a small amount of manganese (0.70% to 1.20%). According to the quality of the product is divided into ordinary carbon structural steel and high quality carbon structural steel. Hot working and cutting performance is good, welding performance is poor. Strength, hardness than low carbon steel, while plasticity and toughness than low carbon steel. Can be used directly without heat treatment, hot-rolled, cold-drawn, or after heat treatment. The quenched and tempered medium carbon steel has good overall mechanical properties. So in the medium strength level of the various uses, medium carbon steel is the most widely used, in addition to as a building material, but also a large number of mechanical parts for the manufacture of a variety of.

Medium carbon steel contains higher carbon than low carbon steel, higher strength, poor weldability. Commonly used are 35, 45, 55 steel. Medium carbon steel welding electrode arc welding and its castings welding repair of the main features are as follows.

(1) the heat-affected zone is prone to hardening organization. The higher the carbon content, the greater the plate thickness, the greater this tendency. If the welding materials and process specifications are not properly selected, it is easy to produce cold cracking.

(2) Due to the high carbon content of the base metal, the carbon content of the weld is also high, which is prone to thermal cracking.

(3) Due to the increased carbon content, so the sensitivity to porosity increases. Therefore the requirements for the deoxidation of the welding material, the base metal degreasing and rust removal, the drying of the welding material, etc., are more stringent.

High-carbon steels, often called tool steels, have carbon contents ranging from 0.60% to 1.70% and can be hardened and tempered. Hammers, crowbars, etc. are made from steel with a carbon content of 0.75%; cutting tools such as drills, taps, reamers, etc. are made from steel with a carbon content of 0.90% to 1.00%. Welding of high carbon steels

High-carbon steels are poorly welded due to their high carbon content. Its welding has the following characteristics.

(1) poor thermal conductivity, a significant temperature difference between the weld zone and the unheated part, when the molten pool cools sharply, the internal stresses caused in the weld, it is easy to form cracks.

(2) More sensitive to quenching, the near seam zone is extremely susceptible to the formation of martensitic tissue. As a result of the tissue stress, the near seam zone produces cold cracks.

(3) Due to the influence of high welding temperatures, grain growth is fast, carbide is easy to accumulate on the grain boundaries, grow, making the weld fragile, welded joint strength is reduced.

(4) High-carbon steel welding is more likely to produce thermal cracking than medium-carbon steel.

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