Properties and processes of high carbon steel

Keywords: high carbon steel, carbon steel tube
High carbon steel (carbon steel tube), often called tool steel, contains from 0.60% to 1.70% carbon and can be quenched and tempered. Hammers, crowbars, etc. are made of steel with a carbon content of 0.75%; cutting tools such as drills, taps, reamers, etc. are made of steel with a carbon content of 0.90% to 1.00%.

After proper heat treatment or cold drawing hardening, high carbon steel has high strength and hardness, high elastic limit and fatigue limit, and the cutting performance is acceptable, but the welding performance and cold plastic deformation ability are poor. Due to the high carbon content, cracks are prone to occur during water quenching, so double-liquid quenching is mostly used, and oil quenching is mostly used for small-section parts. This type of steel is generally tempered or normalized at medium temperature after quenching or used in a surface quenched state. Mainly used in the manufacture of springs and wear-resistant parts. Carbon tool steel is a high carbon steel that basically does not add alloying elements, and it is also a steel with low cost, good cold and hot workability, and a wide range of use among tool steels. Its carbon content is 0.65 to 1.35%, and it is a steel specially used for making tools. The density of high carbon steel is 7.81g/cm³. Can be used for the production of fishing gear.

Advantage:
1. High hardness (HRC60-65) and good wear resistance can be obtained after heat treatment.
2. The hardness is moderate in the annealed state and has good machinability.
3. The raw materials are easily available and the production cost is low.

Disadvantages:
1. Poor thermal hardness. When the working temperature of the tool is greater than 200 °C, its hardness and wear resistance drop sharply.
2. Low hardenability. When water quenching, the diameter of fully hardened is generally only 15-18mm; when oil quenched, the maximum diameter or thickness of fully hardened is only about 6mm, and it is easy to deform and crack.

The hardness and strength of high carbon steel mainly depend on the amount of solid solution carbon in the steel, and increase with the increase of the amount of solid solution carbon. When the solid solution carbon content exceeds 0.6%, the hardness does not increase after quenching, but the amount of excess carbides increases, the wear resistance of the steel increases slightly, while the plasticity, toughness and elasticity decrease. For this reason, different steel grades are often selected according to the use conditions and the strength and toughness of the steel. For example, to manufacture less stressed springs or spring-loaded parts, 65 steel with a lower carbon content can be selected. Generally, high carbon steel can be produced by electric furnace, open hearth and oxygen converter. When high quality or special quality is required, electric furnace smelting plus vacuum self-consumption or electroslag remelting can be used. When smelting, strictly control the chemical composition, especially the content of sulfur and phosphorus. In order to reduce segregation and improve isotropic properties, ingots can be subjected to high temperature diffusion annealing (especially important for tool steels). During hot working, the stop forging (rolling) temperature of hypereutectoid steel is required to be low (about 800°C). After forging and rolling, the precipitation of coarse network carbides should be avoided, and attention should be paid to slow cooling below 700°C to prevent thermal stress. cause cracks. Prevent surface decarburization during heat treatment or hot working (especially important for spring steel). There should be enough compression ratio during hot working to ensure the quality and performance of the steel.

Welding process:

1. When the carbon mass fraction of high carbon steel is greater than 0.60%, the hardening and crack susceptibility after welding are greater, so the weldability is extremely poor and cannot be used to manufacture welded structures. It is often used to manufacture components and parts that require more hardness or wear resistance, and its welding work is mainly welding repair.

2. Since the tensile strength of high carbon steel is mostly above 675MPa, the commonly used electrode types are E7015 and E6015. When the requirements for component structure are not high, E5016 and E5015 electrodes can be used. In addition, chromium-nickel austenitic steel electrodes can also be used for welding.

3. Welding process: (1) In order to obtain high hardness and wear resistance of high carbon steel parts, the material itself needs to be heat treated, so it should be annealed before welding before welding. (2) The weldment should be preheated before welding. The preheating temperature is generally above 250~350℃, and the interlayer temperature must be kept not lower than the preheating temperature during the welding process. (3) After welding, the weldment must be kept warm and slowly cooled, and immediately sent to the furnace for stress relief heat treatment at 650 °C.

4. The carbon content of high carbon steel is relatively high, and the weldability is relatively poor. It should be preheated during welding, and should be slowly cooled or tempered at 350 degrees after welding. The specific heat treatment time depends on the thickness of the workpiece. decided. If preheating is not possible, then we have to use welding materials with good welding performance and good crack resistance, but the welding speed must be reduced.
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