What are the hardness levels of galvanized coils?

Of course. Here are the common hardness/strength classifications for galvanized steel coils, presented in English.

The hardness of a galvanized coil is primarily determined by the base steel’s grade and temper, as the zinc coating itself is very thin and has a negligible effect on overall hardness.

1. By Temper Designation (Most Common)
This system classifies the steel based on the degree of cold rolling and subsequent annealing before galvanizing.

Full Hard (FH)

Highest hardness/strength. Vickers Hardness (HV) typically > 180 (Rockwell B > 90).

Characteristics: Not annealed after cold reduction. Very high strength but low ductility. Poor formability, prone to cracking when bent.

Applications: Simple bend parts, blades, stiffeners, certain structural components.

Half Hard (H or 1/2H)

Medium hardness. HV ~120-150 (HRB 70-85).

Characteristics: Partially annealed. Offers a good balance of strength and limited formability.

Applications: Cabinets, chassis, framing members, parts requiring moderate strength and some forming.

Commercial Quality (CQ) / Soft

The most common grade. Low hardness, excellent formability. HV usually < 100 (HRB < 65).

Characteristics: Fully annealed after cold rolling. Soft, ductile, and easy to form.

Applications: General fabrication, HVAC ducts, electrical enclosures, appliance housings, light-duty parts.

Drawing Quality (DQ)

Better formability than CQ. Similar low hardness but with controlled metallurgy for deeper draws.

Characteristics: Emphasizes properties like plastic strain ratio (r-value) for good stretch-forming capability.

Applications: Parts requiring moderate drawing, like some automotive panels, lighting fixtures.

Deep Drawing Quality (DDQ) & Extra Deep Drawing Quality (EDDQ)

Highest formability grades. Very low hardness, superior metallurgical properties.

Characteristics: Made from specially processed steels for exceptional ductility and resistance to thinning during severe deformation.

Applications: Complex, severe stampings (e.g., automotive body panels, complex appliance parts, fuel tanks).

2. By Strength Grade (Common for Structural Use)
This system specifies minimum yield strength and is prevalent in construction and automotive structural applications (often based on standards like ASTM, EN, or JIS).

Mild Strength (e.g., DX51D, DX52D per EN 10346): Basic formability grades (similar to CQ/DQ above).

High Strength Low Alloy (HSLA): Yield strengths from 280 MPa to 550 MPa or higher. Achieved by micro-alloying (e.g., with Niobium, Titanium). Examples: S280GD, S350GD, S550GD.

Advanced High-Strength Steels (AHSS): Used primarily in automotive for lightweighting and safety. Includes grades like:

Dual Phase (DP): DP600, DP800 (numbers indicate minimum tensile strength in MPa).

Transformation Induced Plasticity (TRIP): TRIP steels.

Martensitic (MS): MS 1200, MS 1500 (very high strength).

Key Points:
Testing: Hardness is commonly measured by Vickers (HV) or Rockwell B (HRB) scales for softer grades, and Rockwell C (HRC) for very hard grades.

Specification: Always refer to the relevant material standard (e.g., ASTM A653, EN 10346, JIS G 3302) which combines the grade (chemical composition) with the temper or strength class.

Trade-off: There is a fundamental trade-off between hardness/strength and formability. Higher hardness means greater resistance to denting but lower ability to be shaped without cracking.

In summary, when specifying a galvanized coil, you would typically define it by:

Base Steel Type: Mild steel, HSLA, or AHSS.

Strength/Temper: e.g., “S350GD” (350 MPa min yield) or “DQ” (Drawing Quality temper).

Coating Weight: e.g., Z180 (180 g/m² total zinc coating).