Cold-Rolled Steel Grades for Roll Forming

1. Definition

Cold-rolled steel grades for roll forming are a family of low-carbon and micro-alloyed steel sheet products specifically engineered for progressive bending and cold forming operations. These grades are produced by cold-reducing hot-rolled pickled strip to target thickness, followed by annealing and skin-pass temper rolling to achieve the required combination of formability, surface quality, and dimensional precision. The grade designation communicates the steel's formability level, yield strength range, and applicable standard.

In roll forming, material grade directly determines bendability, springback behavior, minimum bend radius, and required forming force. Selecting the correct grade ensures that the profile can be formed without edge cracking, excessive springback, or surface defects, while meeting structural and corrosion-resistance requirements for the intended application.

2. Grade Classification

Cold-rolled steel grades used in roll forming fall into three functional categories:

3. EN 10130: DC Series Cold-Rolled Carbon Steel

The EN 10130 standard specifies cold-rolled low-carbon steel flat products for cold forming. The DC series is classified by formability: as the grade number increases, yield strength decreases and elongation increases, enabling progressively deeper drawing operations.

3.1 Chemical Composition (max %)

3.2 Mechanical Properties (thickness 0.7–3.0 mm)

The plastic strain ratio (r90) and strain hardening exponent (n90) values indicate resistance to thinning and ability to distribute strain uniformly — both critical for deep drawing. DC06 uses interstitial-free (IF) steel chemistry with carbon content as low as 0.02%, achieving the highest formability in the series.

4. JIS G 3141: SP Series Cold-Rolled Carbon Steel

JIS G 3141 is the Japanese Industrial Standard for cold-reduced carbon steel sheet and strip. The SP series parallels the EN DC series in formability progression and is widely used in Asian manufacturing.

4.1 Chemical Composition (max %) and Mechanical Properties

SPCC is also available in temper-rolled variants: SPCC-1 (full hard, HRB ≥85), SPCC-2 (1/2 hard, HRB 74–89), SPCC-3 (1/4 hard, HRB 65–80), and SPCC-4 (1/8 hard, HRB 50–71), offering controlled hardness levels for applications requiring specific stiffness without heat treatment.

5. EN 10346: DX Series Galvanized Forming Steel

For outdoor or corrosion-sensitive roll forming applications, hot-dip galvanized steel from the EN 10346 DX series provides zinc-coated protection with varying formability levels. The coating is applied by immersing cold-rolled strip in a molten zinc bath at approximately 450°C, forming a metallurgically bonded layer that provides both barrier and sacrificial anodic protection.

5.1 Mechanical Properties

5.2 Zinc Coating Designations

The coating mass is designated by the letter Z followed by the total mass in grams per square meter for both sides combined:

6. EN 10346: SxxGD Series Structural Galvanized Steel

For load-bearing roll formed profiles such as purlins, studs, and structural decking, the SxxGD series provides guaranteed minimum yield strength combined with galvanized corrosion protection. The number in the grade designation indicates the minimum yield strength in MPa.

Chemical composition for all SxxGD grades: C ≤ 0.20%, Si ≤ 0.60%, Mn ≤ 1.70%, P ≤ 0.10%, S ≤ 0.045%. The relatively broad composition range allows manufacturers to achieve the specified yield strength through micro-alloying and controlled rolling. These steels are aluminum-killed for consistent mechanical properties and are tested longitudinally to the rolling direction.

S350GD is the most commonly specified structural grade for roll formed purlins and framing in European and international markets, offering a balance of strength, formability, and galvanized protection suitable for building construction.

7. International Grade Equivalents

Cold-rolled steel grades are specified under different national standards, but many have functional equivalents. The table below maps the most common cross-references:

When sourcing globally, engineers should verify that the equivalent grade meets the specific mechanical property requirements of the application, particularly yield strength range and elongation minimums, as tolerances vary slightly between standards.

8. Material Selection for Roll Forming

The selection of steel grade for a roll forming application depends on structural requirements, environmental exposure, forming complexity, and cost. The following table provides selection guidance for common profile types:

9. High-Strength Steel Considerations

High-strength steels (yield strength ≥ 350 MPa) are increasingly used in roll forming to reduce material thickness and structural weight. However, higher yield strength introduces specific challenges that must be addressed in roll pass design and machine configuration:

9.1 Springback

Springback is proportional to yield strength divided by elastic modulus. Since elastic modulus remains approximately constant at 210 GPa across all steel grades, increasing yield strength directly increases elastic recovery. For example, G350 steel exhibits approximately 40% more springback than G250 steel for the same bend geometry. Roll pass designs for high-strength steel require increased overbend compensation angles (typically 2°–5° versus 0.5°–2° for mild steel) and may require additional forming stations to distribute strain more gradually.

9.2 Minimum Bend Radius

Higher-strength steels have reduced ductility and are more susceptible to edge cracking at tight radii. Recommended minimum inside bend radius increases with yield strength: approximately 1× thickness for mild steel (DC01), 1.5× to 2× for S350GD, and 2× to 3× for high-strength grades above 450 MPa. Slit edge quality becomes critical — burr height and edge micro-cracks can initiate splitting during forming.

9.3 Machine and Tooling Requirements

When converting a roll forming line from mild steel to high-strength steel, the machine must be evaluated for frame rigidity, gearbox torque capacity, and shaft deflection limits. A machine designed for G250 may not achieve dimensional stability with G350 or higher grades without reinforcement.