[CuttersCov]

What's the difference between these two? (I tried a search but didn't have any luck)

-Matt

[Geof]

What's the difference between these two? (I tried a search but didn't have any luck) -Matt

Cold rolled steel (CRS) and Hot rolled steel (HRS) are both low carbon steels.

Most obvious difference is appearance; HRS has a dark scaled rough finish with the corners often quite rounded, CRS has a smooth somewhat shiny finish with square corners.

Size tolerance is also different; HRS sizes are plus or minus 0.01" or even more, CRS sizes are less than plus or minus 0.005" at least for the smaller sizes. Straightness is often better with CRS.

Strength, stiffness and hardness are both practically the same; the carbon content is too low to heat treat and harden.

Machinability is practically the same although the scale on the HRS can have an effect on tool life if very light skim cuts are done.

However, when welding or machining them a big difference can be uncovered. CRS has considerable stress present from the cold working, particularly tensile stresses near the surface. If a CRS bar has the surface machine off along one edge it will warp many hundredths of an inch per foot; a HRS bar will hardly warp at all. Welding will also create more warpage in CRS than HRS because the heat relaxes the stresses.

[ANorwood]

Cold rolled steel (CRS) and Hot rolled steel (HRS) are both low carbon steels.

Most obvious difference is appearance; HRS has a dark scaled rough finish with the corners often quite rounded, CRS has a smooth somewhat shiny finish with square corners.

Size tolerance is also different; HRS sizes are plus or minus 0.01" or even more, CRS sizes are less than plus or minus 0.005" at least for the smaller sizes. Straightness is often better with CRS.

Strength, stiffness and hardness are both practically the same; the carbon content is too low to heat treat and harden.

Machinability is practically the same although the scale on the HRS can have an effect on tool life if very light skim cuts are done.

However, when welding or machining them a big difference can be uncovered. CRS has considerable stress present from the cold working, particularly tensile stresses near the surface. If a CRS bar has the surface machine off along one edge it will warp many hundredths of an inch per foot; a HRS bar will hardly warp at all. Welding will also create more warpage in CRS than HRS because the heat relaxes the stresses.

Very well put, the stress in CRS is a big factor in parts that matter. Most of the work we do here are with hot roll due to the fact it doesn't move all around when cutting on it. Also the scale can be removed if pickled in a hydrochloric acid solution to save on tool life.