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hot rolled vs cold rolled


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Hey guys. The guy I got my forge from told me to always use hot rolled steel vs cold rolled but in the excitment of my new toy I did not really understand the reason why. He said hot rolled could be worked more than cold rolled but why?
Thanks,
Ken

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There isn't really much difference, cold rolled is often ground clean of mill scale or finished rolled cold to get rid of scale and produce a more precise shape and size. If actually rolled cold it'll be work hardened and tougher. Once you heat it in the forge that's all done for though.

The main reason I buy hot rolled is price. If I need clean steel I'll buy cold rolled but not otherwise.

Frosty

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cold rolled is typically a better steel, and usually 'new' 1018 plain carbon steel, whereas hot rolled is cheaper and usually just a structural grade such as A36, which is just a minimum tensile strength. with A36 you dont always know what you're getting and could get some very hard / non homogonized steel that forges poorly relative to 1018, or you could get just fine stuff, you never really know for sure.

The latest load of a36 hot rolled 1"x3/8" that I got is MUCH harder working than any of the cold rolled in my shop (which is all 1018) and i even have a piece that i polished and etched that you can clearly see a hex bolt head in the steel (higher chromium content, etched out brighter than the surrounding steel) so you know that it's got some higher carbon spots than other spots, which makes it much riskier to use water to cool a piece while working it etc because you may crack it.

Either works fine for forging, cold rolled is usually more expensive but better controlled, hot rolled cheaper, but you dont always know what you're getting.

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Funny (as to Hot-Roll availability and price) everywhere I go, Hot-Rolled is available even down to 1/4-inch diameter rod, 1/4 x 1/4 x 1/8 angle, and thin hot-rolled sheet, and nearly always much cheaper on price.

Even my local hardware store stocks Hot-Rolled and Cold-Rolled steel, coated (galvanized), expended-metal, brass, copper, etc,... albeit that it is all a lot more expensive than going to a dedicated metals supply/service center and going through their scrap pile or even buying there "New" stock.

Hot-Rolled (typically) has a gray, "Mill-Finish," whereas Cold-Rolled steel (during processing) is "Pickled" in mixed-acids to remove the mill-scale prior to the cold-rolling process to finished-size.

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Cold rolled steel is more exact measurements than hot rolled also. For example closer to a true 1/4" size than hot rolled.

Also Cold rolled steel is a harder steel. I got a chance to test this about a month ago. I was making a bunch of sunflowers and the stems were 3/8" square, about 36" long. I would twist them cold about 5 times, then heat up a local area and back twist them in random spots. I accidentaly cut a length of cold rolled steel and could barely do the cold twist more than 1 revolution. I could have easily cold twisted the hot rolled stock at least 10 times.

Once it's in the forge though... it still works fine but is a little more expensive and rusts a little faster.

Edited by Scratch
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cold rolled steel is made to tighter/closer tolerances, and square edged, and machines better, it can also be easier to forge weld,

Usual proceedure for machining was to take a skim off each side to relieve the surface tension induced by the cold rolling process, then finish machine. it used to have a lead content to make it free cutting

The hot rolled stuff comes in made to much wider tolerances, and shapes are not always square edged or square, or even straight, or consistent. But that doesn't matter if you are going to forge it to shape.

One advantage over here in the UK is that when restoring old ironwork, you can get the cold rolled in imperial or metric sizes. Useful when trying to match sized bars or replace individual bits.

I use the cold rolled for making tools that have to be fitted together eg sliding bits like on rams/slideways or smith's helpers.

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Over here cold rolled was not leaded unless you bought it that way. ie: specifically asked for it to be leaded steel.

Now out in the scrap stream you don't know what you are getting into...


Why am I not surprised that when hot rolled steel was used you could get 10 turns before it work hardened enough to be difficult and when you use material that comes already work hardened it was difficult from the start? (smile)

Edited by ThomasPowers
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...and i even have a piece that i polished and etched that you can clearly see a hex bolt head in the steel (higher chromium content, etched out brighter than the surrounding steel)...


If you can post a picture of that, it would sure go a long way in explaining how A36 can be dramatically different than a plain carbon steel such as 1018... and also would be just plain neat to see ;)
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One of the more experienced blacksmiths that I know loves to work with cold rolled. He has influenced my work and I have found cold rolled to be more desirable as well. It is more uniform, moves easier, looks nicer, etc.. I buy all my metal at scrap prices, and don't get charged different rates for hot or cold rolled.

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If you can post a picture of that, it would sure go a long way in explaining how A36 can be dramatically different than a plain carbon steel such as 1018... and also would be just plain neat to see ;)


I'll see if i can dig the piece out from my garage. I lose tools seconds after i put them down in there, so it may be a while till i can find it =D
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i use mostly hot rolled .. cost is main reason but some stock only comes cold rolled especially small stuff (1/8sq 3/16 sq). i have seen a difference in working especially fileing on some stuff tho.. but not enuf to change . i also use scrap and have found out what potato digger rods are made of! i was at a place in twin falls idaho (heart of potato growing) and the local supplyier informed me that some of the older ones (belt links used to dig potatoes) were 1084 but all the links they make now are 5160 ! if you get some of these they are great ! i get them with 3 ft of useable 1/2 in round rod (used and rusty). I use them to make punches and small tools .. and also make dinner triangles out of um! they ring great as long as you dont quench um!

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  • 2 weeks later...
cold rolled steel is made to tighter/closer tolerances, and square edged, and machines better, it can also be easier to forge weld,

Usual proceedure for machining was to take a skim off each side to relieve the surface tension induced by the cold rolling process, then finish machine. it used to have a lead content to make it free cutting

The hot rolled stuff comes in made to much wider tolerances, and shapes are not always square edged or square, or even straight, or consistent. But that doesn't matter if you are going to forge it to shape.

One advantage over here in the UK is that when restoring old ironwork, you can get the cold rolled in imperial or metric table. Useful when trying to match sized bars or replace individual bits.

I use the cold rolled for making tools that have to be fitted together eg sliding bits like on rams/slideways or smith's helpers.


The hot rolled stuff comes in made to much wider tolerances, and shapes are not always square edged or square, or even straight, or consistent. But that doesn't matter if you are going to forge it to shape.

I find this interesting.
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Before I started my apprenticeship as a Blacksmith I worked as a Millwright helper in a Major Steel Mill. My apprenticeship was served with this same steel company only in the shops dept.
During my time with the millwrights however I was fortunate enough to have spent time in virtually every dept of the steel Plant. This included, Coke making, Iron Making, Steel Making, Continuous Casting, Hot roll Mills, and cold roll mills.
I have seen every process of steel making from raw material to finished parts and all processes in between.
Depending on the customer needs, some of the steel making process are HIGHLY controlled right form the iron making process through to the finished product with extremely tight tolerances in everything from the chemistry , temperature of casting, hot rolling temp, cooling rates, and final finishes. These steels are very expensive and not generally sold on the open market. Most of these steels go through the cold roll process due to the customer requirement of precise finished dimensions, grain sizes,finishes, and strength.
This was the purpose of the cold roll dept. originally.
A number of processes are used to finish the steel but nearly all start out with the removal of the hot mill scale by running it through a pickling bath of hot acid. They are then either rolled in large mill stands called reduction mills that apply enough pressure on rolls to reduce the thickness down to a very precise dimension (COLD). These dimensions are measured by use of x-ray equipment, and the mills can be controlled to within hundreds of thousandths of an inch.Another process used to reduce round stock involves drawing them through a series of dies that get progressively smaller until the last one which is the precise dia. req'd.
Not all cold work steel is still work hardened either. Some of the products are sent to the annealing furnaces in the cold mill to be heated inside airtight furnaces to soften or anneal the steel. They are cooled inside the furnace so that when they are removed they still have the same bright finish.
This is the reason that cold roll products are always more expensive ,due to all the extra processing. In our trade as blacksmiths we don't need these kinds of tolerances and unless you are looking to make something without doing any forging on the steel first, and want a bright finish there is no real advantage to using it. Of course some of the smaller dimension steels such as 1/8th thick x 1/2 in wide are produce in cold mills it is just a matter of convenience for some of the steel makers. They generally have what they call slitters in the cold mill where they can take a coil of flat roll steel and cut it into multiple strips of various widths as opposed to rolling them that way in the first place. A matter of economics.

Sorry if this is long winded. I really get caught up when talking about steel.
As the wife would say " no, REALLY?" :D

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I agree with the above. I worked in an Aerospace Forge Shop (rings/forgings for jet-aircraft engines) for 10-years, then went back to college, earning a Bachelors degree.

My first job out of college, was in the Sales department at a Steel Mill. Originally the mill was fully-integrated (made steel from Iron-Ore and coal,) but had transitioned into a slab-re-rolling mill. We produced Hot-Rolled and Cold-Rolled sheet, coil and light plate, plus coated (galvanized) products.

Slabs were re-heated in a walking-beam furnace, then sent through a scale-breaker, then through a 5-stand rolling mill.

Steel-Coil (sheet-steel wound up like paper-towel rolls) was sold "as-is" (Hot-Rolled,) or sent through acid/cleaning-bath/dryer to remove scale and oil, then sold as "Hot-Roll-Pickled-and-oiled," or "H.R. Pickled-Dry" (no oil.)

To produce Cold-Rolled, pickled product was sent to the cold-mill for annealing and cold-roll processing; So, more expensive due to additional processing, producing material to closer specified tolerances and specific metallurgical properties.

Edited by DerekC
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