Carbon steel introduction and classification

Classification of carbon steel

1. According to the mass percentage of carbon: low carbon steel (C:0.25%) medium carbon steel (C:0.25%0.6%)

The higher the carbon content, the greater the hardness and strength, but the plasticity decreases.

2. According to the quality of steel (mainly the content of impurities sulfur and phosphorus): ordinary carbon steel (S<0.055%, P<0.045%) high-quality carbon steel (S<0.040%, P<0.040%) advanced high-quality carbon Steel (S<0.030%, P<0.035%)

3. By use: Carbon structural steel: Mainly used in bridges, ships, building components, mechanical carbon tool steel: Mainly used in knives, molds, measuring tools, etc.

Carbon steel grades and uses

Ordinary carbon structural steel: Q195, Q215, Q235, Q255, Q275, etc. Numbers indicate minimum yield strength. Q195, Q215, Q235 have good plasticity and can be rolled into steel plates, steel bars, steel pipes, etc. 0255, Q275 can be rolled into shaped steel, steel plates, etc. use

High-quality carbon structural steel: The steel grade is expressed in ten thousandths of the average mass of carbon, such as 20#, 45#, etc. 20# means containing C: 0.20% (20/10,000)

Mainly used for manufacturing various machine parts.

Carbon tool steel:The steel grade is expressed by the average mass of carbon, and is preceded by T such as T9, T12, etc. T9 means containing C: 0.9% (9 parts per thousand)

Mainly used for manufacturing various cutting tools, measuring tools, molds, etc.

Cast steel: The cast steel grade is prefixed with ZG before the number, and the number represents the average mass fraction in the steel (expressed in tens of thousands). For example, ZG25 means containing C: 0.25%.

Use:It is mainly used to manufacture parts with complex shapes that require certain strength, plasticity and toughness, such as gears, couplings, etc.

Conventional heat treatment of carbon steel

annealing

The steel is heated to an appropriate temperature, kept warm for a certain period of time, and then slowly cooled (furnace cooling) to obtain a heat treatment process close to the equilibrium state of the structure.

Complete annealing, isothermal annealing, spheroidizing annealing, diffusion annealing, stress relief annealing

Normalizing

The heat treatment process is to heat the steel parts to 30-50 degrees above AC3 and Acm, keep it for an appropriate time, and then cool it in the air to obtain a pearlite-like structure.

Quenching

A heat treatment process in which steel parts are heated to austenitization and then rapidly cooled to transform the structure into martensite. The morphology of the resulting martensite is closely related to the composition of the steel, the size of the original austenite grains, and the formation conditions. The smaller the austenite grains, the finer the martensite.

Tempering

After quenching the steel parts, in order to eliminate internal stress and obtain the required properties, it is heated to a certain temperature below AC1, kept for a certain period of time, and then cooled to room temperature.

alloy steel

One or more alloying elements are added to carbon steel to form a steel called alloy steel.

Alloy steel classification

According to the amount of alloying elements contained: low alloy steel (total mass fraction less than 5%), medium alloy steel (total mass fraction 5%-10%), high alloy steel (total mass fraction greater than 10%)

According to the types of main alloy elements: chromium steel, chromium-nickel steel, steel, silicon-manganese steel, etc.

By use: structural steel, tool steel, special performance steel.

Stainless steel

A type of steel that has high corrosion resistance in the atmosphere and generally corrosive media.

Use: It is mainly used to manufacture parts or structural parts that work in various corrosive media and have high corrosion resistance. Widely used in petroleum, chemical industry, atomic energy, ocean development, national defense and some cutting-edge science and technology fields.