Classification and grades of steel (part I )

I.?????????????? The composition of a steel grade accurately represents its properties, giving us confidence in working with these materials.

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1.??? Composition of steel grades

The theme code, such as using Chinese pinyin letters or international element symbols, is essential in steel classification. It provides a clear indication of the material's category. For example, "L" or "AL" signifies aluminum, while "T" or "Cu" denotes copper.

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The chemical composition can be indicated by using numbers after the subject word, combined with the product category. These numbers typically represent the content of the major alloying elements in the material, expressed as a percentage or in a specific ratio.

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Identification of characteristics or state can be done using prescribed Chinese pinyin letters to indicate specific states, processing methods, or material characteristics. For example, "R" indicates hot working, "C" indicates quenching, "B" indicates no aluminum clad, and "X" indicates fine particles.

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2. An example of alloy structural steel grade naming rules includes the average carbon content, expressed in parts per million, playing a pivotal role in the grade composition, and the alloying element content, expressed as a percentage or specific ratio, significantly influencing the steel's strength and other characteristics. Metallurgical steel quality is expressed as "A" for premium quality steel and "E" for extra premium quality steel. Product use/properties and processing methods may be used as part of a grade to identify the material's specific use or processing characteristic.

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For example, "25Cr2MoVA" alloy structural steel, where "25" indicates a carbon content of 0.22% to 0.29%, "Cr2" indicates a chromium content of 1.50% to 1.80%, and "MoV" indicates that molybdenum and vanadium are alloying elements, and "A" indicates advanced high-quality steel.

II, steel grades are denoted by a combination of numbers and letters, each with significance and meaning.

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1. Carbon structural steel

Grade: Q + number + letter

Meaning:

Q: Represents the first letter of the Chinese character "屈," indicating the yield strength.

Number: The yield strength (in MPa) is directly related to the steel's performance. For instance, Q235 indicates a yield strength of 235MPa.

Letters:

A, B, C, D: These letters represent the quality level, with A being the highest and D being the lowest, providing a clear hierarchy of steel quality.

F, b, Z, TZ: Describe boiling steel, semi-killed steel, killed steel, and special killed steel in that order. These letters describe the method of deoxidizing the steel, and these symbols may be omitted for killed steel.

Example: Q235-A.F denotes boiling steel with a yield strength of 235 MPa and an A-grade quality.

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2. Quality carbon structural steel

Grade indication: number or number + (Mn or other letters) + (deoxidation method symbols) + (symbols for specialized uses)

Meaning:

Number: Indicates the average carbon content of the steel (in units of 0.01%). For example, 45 indicates steel with an average carbon content of 0.45%.

Mn: If the steel's manganese content is high, the symbol Mn is added to the steel number.

Example: 45 indicates a high-quality carbon structural steel with an average carbon content of 0.45% and a high manganese content.

Boiling steel, semi-killed steel, and special-purpose high-quality carbon structural steel should be specially marked at the end of the steel number; for example, the average carbon content of 0.1% of the semi-killed steel is denoted by the steel number 10b.

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3. Carbon tool steels

Grade designation: T + number + letter

Meaning:

T: Represents the first letter of the word "carbon" in Hanyu Pinyin.

Number: Indicates the carbon content (in units of 0.1%). For example, T8 means carbon tool steel with an average carbon content of 0.8%.

Letters:

Mn: If the manganese content is high, add Mn after the steel number.

A: Indicates a premium quality carbon tool steel with a lower phosphorus and sulfur content than the average quality steel.

Example: T8MnA indicates that the carbon content averages 0.8%, the manganese content is also higher, and it is a premium quality carbon tool steel.