How are the letters and numbers in galvanized steel sheet designations determined?
The letters and numbers in galvanized steel sheet designations are not arbitrarily assigned. Instead, they are unified rules established by national standardization organizations (such as China's GB, Europe's EN, the United States' ASTM, and Japan's JIS) based on the steel's core characteristics (such as processing technology, mechanical properties, coating type, and application). The goal is to standardize product identification and facilitate information dissemination during production, distribution, and application. The logic behind this determination revolves around the following core dimensions:
1. Letter Determination: Based on "Characteristic Classification"
Letters are generally used to distinguish qualitative characteristics of steel sheets, such as process type, processing performance, coating method, and application scenarios. While the meanings of the letters vary across standards, the logic remains consistent-using concise symbols to summarize key attributes.
Letters Related to Coating Processes
Hot-dip galvanizing: China GB uses "X" (e.g., "X" in DX51D+Z), European EN uses "G" (e.g., "G" in S250GD+Z), Japanese JIS hot-dip galvanizing uses "G" (e.g., "G" in SGC400), and the US ASTM uses "SS" (abbreviation for Sheet Steel Galvanized).
Electrogalvanizing: China GB and European EN use "E" (e.g., "E" in SECC, "E" in DC01+ZE), and Japanese JIS electrogalvanizing also uses "E" (e.g., "E" in SECC).
Coating type refinement: For example, "+Z" indicates pure zinc coating, and "+ZF" indicates zinc-iron alloy coating (common to GB and EN). Suffixes clarify coating composition differences. Processing Performance-Related Letters
In Chinese GB, the suffix letters (D, E, F) represent the stamping grade: D (normal deep drawing), E (deep drawing), and F (extra deep drawing). The further the letter, the better the ductility, making it suitable for more complex forming processes.
In European EN, "D" (such as the "D" in S250GD) indicates "cold forming," indicating that the steel is suitable for cold working (such as bending and stamping) rather than direct hot rolling.
In Japanese JIS electrogalvanized steel, "CC" (SECC) indicates normal forming grade, "CD" (SECD) indicates deep drawing grade, and "CE" (SECE) indicates extra deep drawing grade, which are linked to the cold rolling performance of the base material.
In European EN, "S" (such as S250GD) indicates "structural steel," indicating that the steel is suitable for load-bearing or stress-bearing components (such as building steel structures and automobile chassis). "DC" (such as DC01+ZE) indicates "cold-rolled low-carbon steel," focusing on normal forming applications. In Japanese JIS, the initial letter "S" uniformly stands for "Steel," identifying the product type.
II. Number Determination: Based on "Quantitative Indicators"
Numbers are primarily used to reflect the mechanical properties (such as strength) or coating parameters (such as thickness) of steel plates. They directly reflect quantitative indicators and facilitate users to quickly determine the product's performance level.
Represents mechanical properties (yield strength)
In Chinese GB, the middle digit (such as "51" in DX51D) corresponds to the yield strength level: 51 represents a yield strength ≥140 MPa, 52 represents a yield strength ≥160 MPa, and 53 represents a yield strength ≥180 MPa. Each increase in the digit increases the lower limit of yield strength by approximately 20 MPa (the specific value is specified in the standard).
In European EN, the digit directly indicates the lower limit of yield strength (in MPa): For example, "250" in S250GD indicates a yield strength ≥250 MPa, and S350GD indicates a yield strength ≥350 MPa. The higher the digit, the higher the strength, making it suitable for load-bearing applications. Represents coating thickness (galvanizing weight).
In the US ASTM standard, numbers (such as SS50 and SS70) indicate the total weight of the double-sided zinc coating (unit: oz/ft², 1 oz/ft² ≈ 14.7 g/m²). SS50 corresponds to approximately 70 g/m² (50 x 1.4 ≈ 70), and SS70 corresponds to approximately 100 g/m². The larger the number, the thicker the coating and the greater the corrosion resistance.
In some standards, coating thickness may also be indicated by an additional number (for example, "DX51D+Z100" in GB indicates a double-sided zinc coating weight of 100 g/m²).
Other quantitative parameters
Some grades may include numbers that represent the cold-rolling process or hardness grade of the substrate (for example, SPCC and SPCD in Japanese JIS, where "C" and "D" are not followed by numbers, but the substrate properties correspond to a specific strength range).