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

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

Low carbon steel, also known as low carbon steel, contains between 0.10% and 0.30% carbon. Low carbon steel is easy to accept forging, welding and cutting, and is often used to make chains, rivets, bolts, shafts and so on.

Carbon content below 0.25% carbon steel, because of its low strength, low hardness, low softness, so it is also called soft steel. It includes most ordinary carbon structural steel and some high quality carbon structural steel, most of which are used for engineering structural parts without heat treatment, and some are used for wear-resistant mechanical parts after carbon heat treatment.

The annealed structure of low carbon steel is ferrite and a small amount of pearlite, its strength and hardness is lower, plasticity and toughness is better. Therefore, it has good cold formability, and can be cold formed by rolling, bending, stamping and other methods. This steel fin has good weldability. Low carbon steel with very low carbon content has very low hardness and poor machinability. Quenching treatment can improve its machinability.

Low carbon steel is generally rolled into Angle steel, channel steel, I-steel, steel pipe, steel strip {steel plate, and is used to manufacture a variety of building components, containers, boxes, stoves, and agricultural machinery. High quality mild steel is rolled into sheets for deep drawing products such as car cabs and generator covers. It can also be rolled into bars, which are used to make mechanical parts with lower strength requirements. Low carbon steel is generally not heat treated before use, carbon content in 0.15% or more carburizing or cyanide treatment, used for shaft, shaft sleeve, sprocket and other surface high hardness, good wear resistance parts.

Mild steel is limited in use because of its low strength. The strength of steel can be greatly increased by increasing the content of manganese in carbon steel and adding trace alloying elements such as vanadium, titanium and niobium. If the carbon content of steel is reduced and a small amount of aluminum, a small amount of boron and carbide forming elements are added, the ultra-low carbon bainite structure with high strength, good plasticity and toughness can be obtained.

Medium carbon steel is carbon steel with carbon content of 0.25% to 0.60%. There are sedated steel, semi-sedated steel, boiling steel and other products. In addition to carbon, it may contain small amounts 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. Good hot working and cutting performance, poor welding performance. The strength and hardness are higher than low carbon steel, but the plasticity and toughness are lower than low carbon steel. Hot rolled and cold drawn materials can be used directly or after heat treatment. Medium carbon steel has good comprehensive mechanical properties after tempering treatment. The highest hardness that can be achieved is about HRC 55 (HB538), σb 600-1100M Pa. Therefore, in the medium strength grade of various uses, medium carbon steel is the most widely used. In addition to being used as building materials, it is also widely used in the manufacture of various machinery parts.

Medium carbon steel has higher carbon content, higher strength and poor weldability than low carbon steel. Commonly used are 35, 45, 55 steel. The main characteristics of arc welding and casting repair of medium carbon steel electrode are as follows:

(1) The heat-affected zone is easy to produce hardened tissue. The higher the carbon content, the thicker the steel plate, the greater the tendency. If the welding materials and process specifications are not selected properly, cold cracks are likely to occur.

(2) Due to the high carbon content of the base material and the high carbon content of the weld, it is easy to produce thermal cracks.

(3) The sensitivity to pores increases with the increase of carbon content. Therefore, more strict requirements are put forward for deoxidation of welding materials, degreasing and derusting of base materials and drying of welding materials.

High carbon steel is often called tool steel, carbon content is 0.60% to 1.70%, adjustable quality. Hammers and crowbars are made of steel with a carbon content of 0.75%. Cutting tools such as drills, taps and reamers are made of steel with carbon content ranging from 0.90% to 1.00%. Welding of high carbon steel.

High carbon steel has poor weldability due to its high carbon content. Its welding has the following characteristics:.

(1) Poor thermal conductivity, obvious temperature difference between the welding area and the unheated part. When the weld pool is cooled rapidly, the internal stress in the weld is easy to form cracks.

(2) It is sensitive to quenching and easy to form martensite in the near seam area. Due to the effect of structural stress, cold cracks occur in the near seam zone.

(3) Due to the influence of high welding temperature, the grain growth is fast, carbide is easy to gather and grow on the grain boundary, so that the weld is weak and the strength of the welded joint is reduced.

High carbon steel is more prone to heat cracking during welding than medium carbon steel.