Machining Hot Rolled VS Cold Rolled Steel

A simple comparison of how 1018 Cold Rolled Steel and 1020 Hot Rolled Steel behave when machining.

[marcellemay]

I was taught very early on in my engineering classes that cold rolled steel has a lot of internal stresses because of the cold rolling process. The material is mechanically formed with no heat, hence the name. The hot rolling process relieves the internal stress as the material is formed. The internal stresses in cold rolled are throughout the material and it's pretty unpredictable and shape dependent. And can even be different at one end of the bar compared to the middle of the bar.

[preacherpdx]

As a newbie working a mill that is probably older than you, THANK YOU.
I am having so much fun making things and so much more fun watching all of the grey hairs teach me tricks on YouTube.
Again, Thank You

[Bill-wztw]

Internal stresses in metal force wise can by huge and sometimes this is actually used to an advantage for instance in the so called Roswell alien metals Nitinol also known as memory metal can be reshaped when it is cold and then when heated will return to its original dimensions which is used in automatically unfolding solar panel arrays for space craft and things like that but what is remarkable is the force per square inch of this metal is around 25000 lbs.Also in your homes thermostat there is sometimes a bi-metallic spring that is made that way so it moves with the slightest temperature variation so it can activate a mercury switch and turn on and off your heater or A/C another example of using internal stresses in metal for an advantage. I have seen a video here on Youtube of a guy cutting an oil pipeline with a torch while he was sitting on top of the pipe and once he cut it free the stored stress in the metal sent him flying up in the air like a trampoline bounce LOL We use internal stored stress in metal in our car springs and torsion bars also. That is one of the hardest parts about being a metal worker is controlling distortions from heat and internal stresses because you cannot avoid them they always will exist and you can only manipulate them to your advantage or minimize them or work towards a desired outcome while knowing what the metal is going to want to do from experience in advance and new younger engineers are only book smart and don't know these things they are used to perfect math and CAD CAM which is precise when in reality we measure with a measuring tape marked in sixteenths of an inch and mark with a soap stone that has a line width of a eight of an inch then cut with a tool that leaves a eight kerf or bigger but the blueprints are written to less than a thousandth of an inch. The old saying that fighter aircraft are designed by MIT and Embry Riddle engineering graduates then they are maintained by high school graduates once in service is similar Laughs

[thatsthewayitgoes]

As 30+ year professional gunsmith, making parts about 10% of time, tool making about 20%. So, definitely not production work; job work. This was SO informative! Usually just keep cutting & file work til have what’s needed ; definitely not running production. But have seen this when making > 3 or 5 parts. Never knew this! How do you machine HRS surface? Fly cutter? Thanks

[christopherleubner]

Cold rolled has a polarized grain to it, sorta like wood. Hot rolled can have internal inconsistancies. Hot rolled also needs to be descaled, cold rolled may not.

[patrickbeaumier]

Very interesting. Never thought there was that much of a difference.
👍👍👍

[ganjiblobflankis]

One component I make comes in 20X6mm CRS bars. Cut to about 3' and clamped to the miller bed then a 4X2.5mm cut taken out of one corner. Finally you weld the ends of these shorter bars and saw them 25mm. After milling, the short bars are going on banana shaped with even a perceptible bend the thick way. On the scale the final component is, the bend is tiny and acceptable and the overall shape and finish is important so it is cheaper to use CRS than dress HRS. It always feels shoddy, but expediency is so often king.

[MrHanky_YT]

Similar issues are present when bending tight a radius. Hot roll is more forgiving. While cold roll is susceptible to cracking.

[RoyLightle-yp]

Cold rolled has a compressed layer from the rolling process. This gives the cold rolled a higher tensil strength but it looses the extra tensil strength when the compressed layer is machined off. This surface tension is what makes the material unstable for machining

[thehobbymachinistnz]

This is very interesting. Thanks for testing this and sharing the results.

[normtheteacher]

Good information to know. I have learned to always start a project with stock that is oversized. Lately I've been milling holes in Plate steel on a rotary table for bearing races to fit snug in. Gave up scribing the circle on the stock and then trying to perfectly align the center axis of the table with the center axis of the end mill. Don't have a $100, 000 milling machine to do that with. Instead I get the two center axis close and then use the end mill to scribe a circle on the stock that is about 50 thousands smaller than what I need. I plunge cut that out and then lock my Y axis and side mill on the X axis 2 or 3 thousands per 360° rotation. After every rotation I try inserting the bearing race until it fits snug. Then I remove the stock and mill or cut or grind the stocks outer dimensions as needed. I get perfect holes and outer stock dimensions with this method. The hole is positioned perfectly in relation to the outer dimensions as need for the part. Have to start with oversized stock to do this unless one has a $100, 000 milling machine. Thanks for your video!

[jbrownson]

excellent video, I love seeing a guideline like this actually demonstrated to make it concrete

[edwardbelfiglio]

The term "Cold Rolled Steel" is completely misused! Cold Rolled Steel only applies to plate, sheet and strip!! Bar stock in rounds, squares, flats, octagons, hexagons and other bar shapes is COLD DRAWN, not sold rolled!

[mackellyman]

I wonder if Rifle barrels suffer the same when drilling? Excellent content.

[russellstanley]

That's what they make coolint for.and grab more of the block with the vice

[Zircon]

A leaded steel like 12L14 is free machining and has a higher yield strength than common hot-rolled 1014 carbon steel. StressProof® by Niagra Lasalle is also an option with 100 ksi yield strengths and stress relieve after cold rolling to provide good machinability without warping.

[piclife]

Great video. I have had problems using scrap bits of hot rolled that have been used as prybars and bent before machining. The locked in stress keeps coming out even when you turn most of the diameter away, very hard to get a straight bar.

[melgross]

I’m not fond of machining CRS either, but sometimes I have to. If you machine to a dimension, you can’t just take down one side, you have to split the amount of cut in half and take half off either side or the piece can bend to one side. Not so much of a problem in really think pieces, but on thin ones it’s a problem. But CRS is somewhat stronger because of the cold roll which compresses the metal somewhat like forging.

[cyber]

doing large long parts in cold rolled and you need to hold any flatness you bet you need to do roughing from both sides then finish both sides again seperately, cuz doing both sides once you know its gonna be bent like a banana

[JustaCommonJoe]

I'm a basic home project tinker machining hobbyist (By no means an engineer or machinist!) and noticed the discoloration of the shavings in the video. In your expert opinion do you think that running coolant or adjusting feed speeds and depth increments would change your end results at all? I appreciate your expertise in the machining/milling process and the most valuable information that you provide. I thank you, and I was wondering if my inquiry carries any pertinent merit. Please continue your beneficial tutorials, and I will be sure to continue to watch and learn from them. 👍👌