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What do the element symbols and numbers in the alloy steel grade signify?

The element symbols in alloy steel grades directly represent the main alloying elements added to the steel. These symbols are usually represented using chemical element symbols, allowing people to clearly know which alloying elements have been added to the steel and the approximate range of content (represented by numbers or specific rules).

Different countries or standard systems (such as GB/T in China, AISI/SAE in the United States, JIS in Japan, DIN in Germany, etc.) have different naming rules for grades, but the principle of "using element symbols to represent alloy elements" is universally accepted.

Taking the Chinese national standard GB/T as an example, the following provides a detailed explanation of the meaning and function of element symbols in brand names:

1. Indicate the type of alloy element:

The element symbols appearing in the grade (such as Cr, Ni, Mn, Si, Mo, W, V, Ti, Al, Nb, Cu, B, RE, etc.) directly indicate the alloy elements artificially added to the steel grade that play a major role in its performance.

Example:

40Cr: Alloy structural steel containing chromium (Cr).

60Si2Mn: Alloy spring steel containing silicon (Si) and manganese (Mn) (number 2 indicates high silicon content). W18Cr4V: High speed tool steel containing tungsten (W), chromium (Cr), and vanadium (V).

1Cr18Ni9Ti: Stainless steel containing chromium (Cr), nickel (Ni), and titanium (Ti).

2. (Combined with numbers) represents the alloy element content:

The Chinese GB/T standard usually adds a number after the element symbol to indicate the average content (mass fraction) of the element.

Number meaning rules:

Elements less than 1.5%: If the average content of an element is less than 1.5%, usually only the element symbol is marked in the grade, without indicating the content number (there are exceptions, such as boron steel using B to represent trace boron). But this does not mean that the content is 0, but rather that its content is within the standard range of the steel grade and below the labeled threshold (usually 1.5%).

Example: 40Cr: The average content of chromium (Cr) is between 0.8% and 1.10% (less than 1.5%), so only the element symbol Cr is labeled without a number. The titanium (Ti) content in 20CrMnTi is usually between 0.04% and 0.10%, and only Ti is labeled.

1.5%~2.49% of elements: element symbol followed by the number 2.

Example: 60Si2Mn: The average content of silicon (Si) is between 1.50% and 2.00% (belonging to the range of 1.5% to 2.49%), so Si2 is labeled. The average content of manganese (Mn) is between 0.60% and 0.90% (less than 1.5%), so only Mn is labeled.

2.5%~3.49% of elements: element symbol followed by the number 3.

Example: 20Cr3MoWVA: The chromium (Cr) content should be between 2.5% and 3.49%, labeled as Cr3.

And so on: 3.5%~4.49% standard 4, 4.5%~5.49% standard 5... However, elements with very high content are relatively rare.

Special cases - stainless steel, heat-resistant steel, etc.: These types of steel have a high content of major elements (such as chromium, Cr, nickel, Ni), and the numbers in their grades (such as 1Cr18Ni9Ti) usually directly represent the approximate average content percentage (%) of the element.

Example: 1Cr18Ni9Ti: with an average chromium (Cr) content of about 18%, nickel (Ni) content of about 9%, and titanium (Ti) content (trace, less than 1.5%). The first 1 indicates a carbon content of approximately 0.1% (ten thousandths).

3. Indicate carbon content (number at the beginning of the brand):

In grades such as alloy structural steel, alloy spring steel, and alloy tool steel, the first digit (usually two or one) represents the average carbon content (mass fraction).

Two digit number: represents a few tens of thousands (i.e. 0.01%).

Example: 40Cr: The average carbon content is 0.40% (40 parts per ten thousand). 60Si2Mn: The average carbon content is 0.60%.

One digit: represents a thousandth (i.e. 0.1%). Usually found in high carbon content or tool steel.

Example: 8MnSi: The average carbon content is about 0.80%. CrWMn (with an average carbon content of approximately 1.0%, not numbered according to regulations). T8 (carbon tool steel, with a carbon content of approximately 0.8%).

Stainless steel, heat-resistant steel, etc.: The number at the beginning of the grade usually indicates a carbon content of a few ten thousandths (i.e. 0.01%).

Example: 1Cr18Ni9Ti: Carbon content ≤ 0.12% (average about 0.10% or lower, represented by 1 in the grade as ten thousandths). 0Cr18Ni9 (or new grade 06Cr19Ni10): Carbon content ≤ 0.08% (average very low, represented by 0 or 00 for ultra-low carbon).

3Cr13: Carbon content is about 0.30%.

4. Representing specific properties or uses (sometimes through specific element combinations or symbols): 

Although primarily manifested through element symbols and numerical combinations, the presence of certain elements itself implies specific properties or uses of steel:

Cr, Ni: often improve strength, toughness, hardenability, and corrosion resistance (especially stainless steel).

Mo, W, V: often improve high-temperature strength (thermal strength), wear resistance, and refine grain size.

Ti and Nb are commonly used as stabilizing elements (to prevent intergranular corrosion) and also to refine grain size.

Si, Mn: often improve strength and elastic limit (spring steel), Si enhances oxidation resistance.

B: Trace boron (B) can significantly improve hardenability (boron steel).

RE: Rare earth elements that improve performance (such as toughness and processability).

Sometimes letters are added to the brand to indicate its purpose or process, such as:

GCr15: G represents rolling bearing steel.

Y40Mn: Y represents free cutting steel.

ML30CrMnSi: ML stands for rivet steel (for cold heading).

5. Summary key points: 

Element symbol=main added alloy elements.

The number after the element symbol=the average content range of the element (according to GB rules: no number is specified below 1.5%, 2 is specified for 1.5% -2.49%, 3 is specified for 2.5% -3.49%... stainless steel/heat-resistant steel, etc. are exceptions, and the number is often directly used to approximate the percentage).

The number at the beginning of the grade (usually)=average carbon content (structural steel/spring steel/tool steel: two digit per ten thousand ratio, one digit per thousand ratio; stainless steel/heat-resistant steel: one digit per ten thousand ratio).

exceptional case:

The naming of national standard priority grades must strictly follow standards such as GB/T 5310 (boiler tubes), GB/T 3077 (structural steel), etc. 12Cr1MoVG, as a special steel for high-pressure boiler tubes, has its grade defined by GB/T 5310-2017 mandatory regulation 34. The annotation "Cr1" is an internal classification requirement of the standard, which does not conflict with the general rule (less than 1.5% without labeling) and is an exception for special application scenarios.

Understanding brand names requires combining specific national/standard system rules.

By mastering these rules, you can interpret the approximate chemical composition of alloy steel grades and infer their possible properties and uses.

Common alloy element symbols and their main functions:

The main function of element symbols and element names is

Cr chromium improves strength, hardness, wear resistance, hardenability, and corrosion resistance (core element of stainless steel)

Ni nickel improves strength, toughness (especially low-temperature toughness), hardenability, and corrosion resistance

Mn manganese improves strength, hardness, wear resistance, hardenability, deoxidizer

Si silicon improves strength, elastic limit, oxidation resistance, and deoxidizer

Mo molybdenum improves high-temperature strength (thermal strength), hardenability, wear resistance, and prevents tempering brittleness

W tungsten improves high-temperature strength, hardness, and wear resistance (core element of high-speed steel)

Vanadium refines grain size, improves strength, hardness, and wear resistance

Ti titanium refines grain size to prevent intergranular corrosion (stabilizing element for stainless steel)

Al aluminum refines grain size, deoxidizer, improves oxidation resistance (core element of nitriding steel)

Nb niobium refines grain size to prevent intergranular corrosion (stabilizing element for stainless steel)

Trace addition of boron significantly improves hardenability (boron steel)

Cu copper improves atmospheric corrosion resistance

RE rare earth improves comprehensive properties such as toughness, plasticity, hot workability, corrosion resistance, etc