Classification and grades of steel (part II)

4. Alloy structural steel

Grade designation: (special-purpose symbol) + number (carbon content) + major alloying element symbol and number + trace alloying element symbol + (quality grade symbol) + (special-purpose symbol)

Carbon content:

The numerical portion of a grade usually indicates the carbon content. Depending on the specific classification of the alloy steel, the meaning of the numbers may vary:

For alloy structural steels, the first two digits represent ten thousand times the average carbon mass fraction in the steel. For example, "40" in 40Cr indicates an average carbon mass fraction of 0.4%.

Alloying element:

The first letter (or the first few letters) in the grade usually represents the alloying elements in the alloy steel. For example, W for tungsten, Cr for chromium, and Mn for manganese. Adding these alloying elements can significantly improve the steel's strength, hardness, wear resistance, corrosion resistance, and other properties.

For alloy tool steels, when Wc < 1%, one digit indicates the mass fraction of carbon in thousands; when it is ≥ 1%, it is not labeled.

Alloying element content:

The number following the element symbol indicates the percent content of that alloying element. However, it should be noted that when the average mass fraction of the alloying component <1.5%, generally only the element is labeled without a numerical value; when the average mass fraction ≥1.5%,≥2.5%, ≥3.5%, etc., the alloying element is labeled accordingly after 2, 3, 4, etc.

Micro-alloying element symbols titanium Ti, aluminum AL, vanadium V, boron B, rare earth RE, and other alloying elements are micro-alloying elements. The content is shallow but should still be marked in the steel number. For example, in 20MnVB steel: vanadium 0.07-0.12%, boron 0.001-0.005%

Quality grade:

Letters in the grade number may also indicate quality grades, e.g., A, B, C, D, etc., distinguishing between alloy steels with different quality requirements.

Other Information:

The letter at the end of the grade may also indicate the degree of deoxidation (e.g., b for semi-sedated steel, F for boiling steel, Z for sedated steel, TZ for special sedated steel) or use (e.g., G for boiler steel, R for pressure vessel steel, etc.).

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5, particular types of alloy steel:

The sign in front of the "G," followed by a number indicating the chromium mass fraction of thousands of times the carbon mass fraction, is not labeled for rolling bearing steel.

5, stainless steel or heat-resistant steel

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The carbon content in steel is typically shallow, often just a few thousandths. For example, the steel "2Cr13" has an average carbon content of 0.2%. If the carbon content of steel is less than or equal to 0.03% or 0.08%, the steel number is modified to add "00" or "0," respectively, in front of the original number. For instance, 00Cr17Ni14Mo2 and 0Cr18Ni9 reflect these changes. Steel also contains various other alloying elements, such as niobium, titanium, and nitrogen, each typically making up a small percentage of the overall composition. Specific details should be considered when it comes to the labeling method for micro-alloying elements in structural steel.

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6. Additionally, alloy and high-speed tool steel are two essential types of steel to consider.

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The average carbon content is a key factor in distinguishing between different steel grades. When the average carbon content of an alloy tool steel grade is ≥ 1.0%, there is no need to mark the carbon content. However, when the average carbon content is <1.0%, it is expressed in thousands. For example, Cr12, 9SiCr, 3Cr2W8V. Alloying elements in the steel content of the method of expression and alloy structural steel are almost the same. However, the chromium content of lower alloy tool steel number, the chromium content of a few thousandths of the said content, and expressed the content of the number before the addition of "0", to distinguish it from the general elemental content of a few percent of the said method—for example, Cr06. High-speed tool steel grade is usually not marked out of carbon content; it just marks out the average content of various alloying elements of a few percent. For example, "W18Cr4V" indicates tungsten high-speed steel grade. Grade to the letter "C" at the beginning, that its carbon content is higher than not to "C" at the start of the general steel grade.

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?????The grade composition of metallic materials is essential for selection, processing, and use. It provides clear and accurate information about the material's chemical composition, quality level, use, and processing characteristics. The material grade is a unique and easily recognizable combination of subject code, chemical composition indication, and property or state identification. It's important to note that different countries and regions may follow different naming rules and standards, so practical applications must distinguish between them.