Coil Temper & Hardness Explained — Full Hard vs Half Hard Steel

Learn about coil temper & hardness explained in roll forming machines. Coil Guide guide covering technical details, specifications, and maintenance.

Many coil buyers focus only on:

Thickness
Yield strength
Coating

But ignore another critical property:

Temper (hardness condition).

Two coils with the same thickness and yield strength can behave completely differently in roll forming depending on temper.

Understanding temper prevents:

Edge cracking
Excessive springback
Roll marking
Tool overload
Surface damage

This page explains what temper really means and how it affects forming.

1. What Is Coil Temper?

Temper describes the hardness condition of steel after cold rolling and heat treatment.

It is influenced by:

Degree of cold reduction
Annealing process
Skin passing
Work hardening

Temper determines:

Ductility
Bendability
Surface hardness
Forming behaviour

It is closely related to hardness measurements such as Rockwell.

2. Why Temper Matters in Roll Forming

Harder steel:

Requires more forming force
Increases springback
Wears rolls faster
Cracks more easily in tight bends

Softer steel:

Forms more easily
Has less springback
Reduces machine stress
May dent more easily

Temper directly affects production stability.

3. Common Temper Classifications

Steel temper is often described as:

Full Hard
Half Hard
Quarter Hard
Skin Passed
Annealed

These terms describe the level of work hardening.

4. Full Hard Steel

Full hard steel:

Has been cold reduced
Has not been annealed
Has high hardness
Has low ductility

Characteristics:

High yield strength
High springback
Low elongation
Higher cracking risk

Typical use:

Structural decking
Some high-strength roofing
Applications where strength is priority over bendability

Full hard is not forgiving in tight radii.

5. Half Hard Steel

Half hard steel:

Moderately cold worked
Improved ductility compared to full hard
Balanced strength and formability

Characteristics:

Moderate springback
Better bend performance
Lower cracking risk

Often suitable for:

Roofing panels
Flashing
Moderate forming profiles

Half hard is often a safer forming choice.

6. Annealed Steel

Annealed steel:

Fully heat treated
Softest condition
Maximum ductility

Characteristics:

Very good bendability
Minimal cracking risk
Lower yield strength

Used when:

Deep forming required
Tight radii needed
High surface finish critical

Annealed steel forms easily but may not meet structural strength needs.

7. Skin Passed Steel

Skin passing is a light rolling process after annealing.

Purpose:

Improve flatness
Improve surface finish
Control yield point behaviour

Skin passed steel:

Slightly hardened
Better dimensional stability
Reduced stretcher strain

Common in coated products.

8. Hardness Measurement (Rockwell Scale)

Hardness is typically measured using:

Rockwell B scale (HRB)
Rockwell C scale (HRC)

Most thin-gauge steel is measured on HRB.

Higher HRB number = harder material.

Hardness correlates with:

Yield strength
Wear resistance
Forming resistance

Hardness is not the same as strength — but closely related.

9. Temper vs Yield Strength

Temper and yield strength are related but not identical.

Cold working increases:

Hardness
Yield strength

But two steels with similar yield strength may have:

Different ductility
Different surface hardness
Different forming response

Temper condition affects real-world forming behaviour beyond simple MPa rating.

10. Why Full Hard Steel Cracks More Easily

Full hard steel:

Has limited plastic range
Has reduced elongation
Reaches strain limit quickly

When bent in roll forming:

Outer fibers stretch
Limited elongation causes edge splits

Tight flange profiles in full hard steel often crack first.

11. Temper Impact on Springback

Harder steel:

Has higher elastic recovery
Increases springback angle

This affects:

Rib height
Flange angle
Snap-lock engagement
Standing seam performance

Temper must match tooling compensation.

12. Surface Effects

Harder temper:

Increases roll marking risk
Increases friction
May scratch coatings more easily

Softer temper:

Reduces roll pressure
Improves finish
May dent during stacking

Surface finish quality depends partly on temper.

13. Coated Coil & Temper

Most galvanized and prepainted coils:

Use skin passed temper
Balanced for forming

Very high-strength coated steel:

May be full hard
Higher cracking risk in trim profiles

Always check temper on MTC.

14. Matching Temper to Application

Roofing Panels:
Medium temper / skin passed preferred.

Purlins:
Higher strength temper acceptable.

Decking:
Often higher temper required for load performance.

Flashing:
Lower temper improves bend quality.

Matching temper prevents production instability.

15. Common Buyer Mistakes

Ignoring temper condition
Ordering full hard unintentionally
Focusing only on yield strength
Not checking elongation
Assuming all G350 behaves the same

Temper variation explains many “same grade, different behaviour” complaints.

16. How to Specify Temper

Professional RFQ should include:

Thickness
Yield strength
Elongation
Temper condition
Coating mass

Example:

0.60 mm
G350
Minimum elongation 16%
Skin passed temper

Clear temper specification reduces surprises.

17. FAQ Section

What is full hard steel?

Steel that has been cold worked and not annealed, resulting in high hardness and lower ductility.

Is full hard stronger?

It has higher yield strength but lower ductility.

Why does full hard crack more?

Reduced elongation limits bend capacity.

What is half hard steel?

Moderately cold worked steel with balanced strength and ductility.

What is skin passed?

Light rolling after annealing to improve flatness and surface quality.

Does temper affect springback?

Yes. Harder tempers increase springback.

Is hardness the same as strength?

Not exactly, but they are closely related.

Should roofing use full hard?

Only if tooling is designed for it.

Can temper vary within same grade?

Yes.

Is temper listed on MTC?

Often, but not always clearly labeled.

18. Conclusion

Temper controls how steel behaves in forming — not just how strong it is.

Full hard:

Higher strength
Lower ductility
More cracking risk

Softer temper:

Easier forming
Lower springback
Better bend performance

For roll forming stability, temper must be matched to:

Profile geometry
Thickness
Strength grade
Machine capability

Ignoring temper leads to avoidable production failures.