Hot Rolled vs Cold Drawn Bar: Properties, Surface and Cost

Two different products from the same steel

Both start as hot-rolled bar. A hot rolled bar is sold as it leaves the mill. A cold drawn bar takes that hot-rolled feedstock, pickles off the scale, and pulls it through a die at room temperature, reducing the diameter by a controlled amount. That single extra step changes almost every property that matters.

Property comparison

	Hot rolled	Cold drawn
Diameter tolerance	Loose (EN 10060), roughly ±1–2%	Close (EN 10278, typically h11–h9)
Surface	Grey mill scale, possible decarburization	Bright, smooth, scale-free
Yield strength	As-rolled value for the grade	Raised, typically by on the order of 10–25% depending on reduction and grade
Ductility	Full	Reduced by strain hardening
Straightness	Mill standard	Good, on the order of 0.5–1 mm per metre
Price per tonne	Lower	Higher (extra processing)

The strength effect is real — and conditional

Cold drawing strain-hardens the steel: yield strength climbs while elongation and reduction of area fall. Design codes and grade standards (EN 10278 lists the delivery conditions, including "+C" for cold drawn) define the guaranteed properties in the drawn condition. If the bar is subsequently annealed or quenched and tempered, the drawing benefit disappears and hot-rolled feedstock would have done the same job.

Residual stress: the hidden difference

Drawing leaves a pattern of residual stresses in the bar, locked in by the die work. The bar is straight and stable — until you machine it asymmetrically. Milling a flat or a keyway on one side removes stressed material unevenly, and the bar can bow or twist after machining. The remedies are well established:

• Specify stress-relieved drawn bar (drawn and stress relieved, "+C+SR") for asymmetric parts.
• Machine symmetrically where possible, roughing both sides alternately.
• For long slender parts, consider peeled-and-ground bar instead, which carries far less locked-in stress.

Machinability and use cases

Cold drawn bars centre and feed better in automatic lathes and bar-fed CNC machines: consistent diameter means consistent cutting conditions and fewer adjustments. Free-cutting grades are most often supplied drawn for exactly this reason. Hot rolled bar remains the rational choice when the part is machined all over, when it will be heat treated to final properties, when it is forged, or when diameter exceeds the practical drawing range — very large bars are simply not cold drawn.

Rule of thumb

Buy the finished condition the part actually needs: hot rolled for stock that will be transformed anyway, cold drawn for size, surface and strength as delivered — with stress relief when the machining is one-sided.