carbon steel
1. Definition
Mainly refers to the steel whose mass fraction of carbon is less than 2.11% and does not contain intentionally added alloying elements. Sometimes also called plain carbon steel or carbon steel.
Carbon steel is also called carbon steel, which refers to an iron-carbon alloy with a carbon content Wc of less than 2.11%.
In addition to carbon, carbon steel generally contains a small amount of silicon, manganese, sulfur, and phosphorus.
2. Classification
(1) According to the purpose, carbon steel can be divided into three categories: carbon structural steel, carbon tool steel and free-cutting structural steel. Carbon structural steel is further divided into engineering construction steel and machine manufacturing structural steel;
(2) According to the smelting method, it can be divided into open hearth steel and converter steel;
(3) According to the deoxidation method, it can be divided into boiling steel (F), killed steel (Z), semi-killed steel (b) and special killed steel (TZ);
(4) According to the carbon content, carbon steel can be divided into low carbon steel (WC ≤ 0.25%), medium carbon steel (WC0.25%-0.6%) and high carbon steel (WC>0.6%);
(5) According to the quality of steel, carbon steel can be divided into ordinary carbon steel (higher phosphorus and sulfur content), high-quality carbon steel (lower phosphorus and sulfur content) and advanced high-quality steel (lower phosphorus and sulfur content) ) and extra high-quality steel.
Description: Generally, the higher the carbon content in carbon steel, the greater the hardness and the higher the strength, but the lower the plasticity.
Three, common carbon steel
1. Carbon structural steel
Brand: Example Q235-A·F, means σs≥235MPa
Note on the grade: Q is the yield strength, A quality grade (with ABCD four grades), F boiling steel
Features: low price, excellent process performance (such as weldability and cold formability).
Application: General engineering structure and general mechanical parts. For example, Q235 can be used to make bolts, nuts, pins, hooks and less important mechanical parts, as well as rebar, section steel, steel bars, etc. in building structures
2. High quality carbon structural steel
Grade: Example 45, 65Mn, 08F
Note on the grade: it directly represents the ten thousandth of the carbon content of the metal
Application: Non-alloy steel for manufacturing important mechanical parts is generally used after heat treatment.
Common steel grades and uses:
08F, low mass fraction of carbon, good plasticity and low strength, used for stamping parts such as automobile and instrument housing;
20. Good plasticity and weldability, used for parts with low strength requirements and carburized parts, such as hoods, welding containers, small shafts, nuts, washers and carburized gears, etc.;
45, 40Mn, after quenching and tempering, have good comprehensive mechanical properties, and are used for mechanical parts with large force, such as gears, connecting rods, machine tool spindles, etc.;
60, 65Mn steel has high strength; it is used to manufacture various springs, locomotive rims, and low-speed wheels.
3. Carbon Tool Steel
Grade: For example, T12 steel means carbon tool steel with Wc=1.2%.
Note on the grade: T plus the thousandth of the carbon content of the metal
Features: It belongs to eutectoid steel and hypereutectoid steel, with high strength, hardness and good wear resistance. It is suitable for manufacturing various low-speed cutting tools.
Common steel grades and uses:
T7, T8: Make parts that require toughness to withstand a certain impact. such as sledgehammers, punches, chisels, woodworking tools, scissors
T9, T10, T11: Manufacturing tools that require high hardness and high wear resistance with low impact. Such as taps, small drills, dies, hand saw blades
T12, T13: Make tools that are not impacted. such as files, scrapers, razors, measuring tools
4. cast steel
Grade: For example, ZG200-400, which means cast steel with σs≥200MPa and σb≥400MPa.
Performance: The casting performance is worse than that of cast iron, but the mechanical performance is better than that of cast iron;
Application: It is mainly used to manufacture relatively important mechanical parts with complex shapes and high mechanical performance requirements, but it is difficult to form by forging and other methods in the process, such as automobile gearbox casings, locomotive couplers and couplings, etc. Fourth, the influence of impurity elements on the properties of carbon steel
1. Manganese
About 0.25%~0.80%. Solid solution strengthening; removing FeO to reduce the brittleness of steel; synthesizing MnS with vulcanization, which can reduce the harmful effects of sulfur. beneficial.
2. Silicon
It is about 0.10%~0.40%, solid solution strengthening; in addition to the adverse effect of FeO on steel quality, it is beneficial.
3. Sulfur
FeS and Fe form a low-melting eutectic (melting point is 985°C), which causes the steel to become brittle and crack during hot working at 1000~1250°C, “hot brittleness”. harmful.
4. Phosphorus
The strength and hardness are increased, but the plasticity and toughness are reduced, and it is “cold and brittle”. harmful.
