Cold Rolled or Hot Rolled

[tmeric7]

Tmeric7 please correct me if I’m wrong. Elementally little difference between HR or CR steel. CR has twice the yield strength due to the shaping process. Higher dimensional tolerance and better surface finish. Also cost about double.

Take piece of CR and stick it in a forge, heat to bend or weld it anneals back to HR strength in the heated areas. Mechanical fasteners preferred attachment to maintain strength.

General rule of thumb. Exceptions because there are so many alloys. Many considerations when designing equipment and fixtures.

Worked with making and cold forming cermets. Quickly cold work harden thru a rolling mill.

Yes, I agree on everything.

CR and HR are forming processes independent of elemental composition. You can do either to many alloys. 1020 is 99.8% iron and 0.2% carbon, by weight, no matter how you form it. Although, the way you form in can change the properties.

In class we describe annealing as a "reset" button to go back to the initial properties before cold working. (Hot working does not change properties.) There are different forms or annealing, but all reasonably similar. This is done "around" 700C for various alloys. Got to hold it there a little while for the atoms to find their home again.

This all works because of small imperfection in the atomic lattice. Imagine all these iron atoms arranged in rows and columns with a few carbon atoms sprinkled in. It's mostly orderly, buy there are small imperfections here and there. Imperfections called "dislocation" allow atoms to move around under high load and this is why metals bend without breaking, but you only get so much. Eventually the dislocations get hung up on each other or run into grain boundaries. That's why the yield strength goes up... it gets to where you need more force to move the atoms around. But because the atoms cant move, you can't deform much more (more brittle). Annealing, with expansion of material, allows the atoms to move around and get past the "hang-ups" and back to a pre-deformed state.

For what it's worth, I expect that any common alloy would have worked for the OP's original question, given enough thickness in the material. This would be a good one for the students to solve out!

 

[ArlyA]

Have used some hot rolled steel in a limited fashion, its loose tolerances made the task take twice as long to complete. No more HT rolled for me.

 

[LD1]

Have used some hot rolled steel in a limited fashion, its loose tolerances made the task take twice as long to complete. No more HT rolled for me.

For a couple of stay straps on a bushhog out of 2"x1/4" flat bar with a few holes.....it wouldn't take any longer.

They each have their place. But lots of stuff is made out of HR where dimensional accuracy is of little to no concern

 

[Sberry]

Most of the worlds steel is hot roll. A little cold.

 

[BackRoad]

Along the same line as this thread on the effects of heat on metal...

One of the wheel spindles (~1" diameter by 9" long) on my 8' finish mower has a slight bend from use...maybe 5 degrees(?).

It is usable as is, but I would like to straighten it if possible.

Should heat be applied before straightening it, or is it better to just use a press on the cold spindle to straighten it?

And if Yes on the heat first, how much heat is safe before it looses long-term strength to resist future bending?

 

[LD1]

Along the same line as this thread on the effects of heat on metal...

One of the wheel spindles (~1" diameter by 9" long) on my 8' finish mower has a slight bend from use...maybe 5 degrees(?).

It is usable as is, but I would like to straighten it if possible.

Should heat be applied before straightening it, or is it better to just use a press on the cold spindle to straighten it?

And if Yes on the heat first, how much heat is safe before it looses long-term strength to resist future bending?

Its probably just mild steel. So heat will help it bend easier but have no long term effects on its strength vs bending cold.

How much heat.....enough to bend it. Dont know your press, or setup.

 

[Smokeydog]

Along the same line as this thread on the effects of heat on metal...

One of the wheel spindles (~1" diameter by 9" long) on my 8' finish mower has a slight bend from use...maybe 5 degrees(?).

It is usable as is, but I would like to straighten it if possible.

Should heat be applied before straightening it, or is it better to just use a press on the cold spindle to straighten it?

And if Yes on the heat first, how much heat is safe before it looses long-term strength to resist future bending?

The spindles on my woods finishing mower had a high failure rate. Mild steel and could straighten in press. No heat. Shaft wearing caused bending too. Replaced with 4140 tool steel. Lasted over 10 more years till the mounting bearing tubes wore out causing bending and wheel drag. Replaced with trailer bearing hubs and axles that permanently fixed a ongoing problem.