Carbon content classification of seamless carbon steel pipes

Seamless carbon steel pipes are made of steel ingots or solid billets that are perforated into capillaries, and then hot-rolled, cold-rolled or cold-drawn.

Hot rolled carbon seamless steel pipes are divided into ordinary steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological steel pipes and other steel pipes.

In addition to general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes and other steel pipes, cold-rolled (drawn) carbon steel seamless pipes also include carbon thin-walled steel pipes, alloy thin-walled steel pipes, Stainless steel thin-walled steel pipes, special-shaped steel pipes. The outer diameter of the hot-rolled seamless pipe is generally greater than 32mm, and the wall thickness is 2.5-75mm. The outer diameter of cold-rolled seamless pipe can reach 6mm, and the wall thickness can reach 0.25mm. The outer diameter of the thin-walled tube can reach 5mm, and the wall thickness is less than 0.25mm. Cold rolling has higher dimensional accuracy than hot rolling.

Seamless pipes are classified by carbon content

1) General carbon content precision seamless pipe
Generally, steel with a carbon content of ≤0.25% is called high carbon steel. The quenching mechanism of high carbon steel is metallographic structure and a small amount of ferrite. Its compressive strength and strength are low, but its plastic deformation and ductility are good. It is convenient for stretching, punching dies, extrusion molding, forging and electric welding, among which 20Cr steel is mainly used. Steel has a certain compressive strength. After heat treatment and ultra-low temperature quenching, this type of steel has excellent comprehensive physical properties, excellent ultra-low temperature fracture toughness and weak quenching plasticity.

Main application: It is suitable for the manufacture of electric welding parts and forging, hot stamping dies and machining parts that do not bear high ground stress in the machining industry. Turbogenerator and heating furnace processing industry; also suitable for the production of small, medium and small nitriding and carbonitriding parts in small cars, large tractors and general machining industries, such as automobile brake shoes, lever shafts, inner, Balancer outer shaft sleeve, etc.; Small and medium-sized machining industries, such as forging or restraint support rods, shackles, levers, sleeve specifications, tooling fixtures, etc.

2) High carbon steel precision seamless pipe
Nitriding of high-carbon steel: After carburizing and ultra-low temperature quenching, high-carbon steel with a carbon water content of about 0.15% is used for specified parts, such as shafts, bushings, sprocket chains, and some injection molds. Good abrasiveness. After carburizing and quenching and ultra-low temperature quenching, high-carbon steel has obtained a structure with high-carbon steel austenite on the surface and low-carbon environmentally friendly austenite in the core. This ensures high toughness and wear resistance in the skin and very good compressive strength and ductility in the core. It is suitable for the production of brake shoes, lever shafts, transmission shift forks, transmission gears, engine camshafts on large tractors, suspension balancer shafts, balancer inner and outer bushes, sleeve specifications, tooling fixtures and other parts.

3) Low carbon steel precision seamless pipe
Low-carbon steel: carbon structural steel with a carbon content of 0.25% to 0.60%. Models 30, 35, 40, 45, 50, and 55 are low-carbon steels. Due to the increase in ferrite water content in steel, its compressive strength and The strength has been improved compared with before, and the strength can be significantly improved after heat treatment. Among them, 45 steel is more typical. 45 steel is a high-toughness medium-carbon quenched and tempered steel with certain plastic deformation and ductility, and excellent machinability. Used in the manufacture of parts with high compressive strength and moderate ductility. Generally used for heat treatment or quenching conditions. In order to make the steel have the necessary ductility and relieve its internal stress, the steel should be quenched into sorbite after heat treatment.

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