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What is the difference between hot and cold rolled steel?


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cold rolling raises the price.  Hot or cold rolling are processes, not  an alloy specification.   many smiths only think of mild stuff, but when I order blade steels,  I can get 1095 in either hot or cold process.

Edited by Steve Sells
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I worked in a Steel mill for a decade right out of college.  Hot roll there was raw, un pickled steel that went through a pickle line to remove the scale.  If that's what the customer wanted, it shipped out just like that at the end of the line, as HR steel coils.  If CR was needed, those same coils went to annealing to soften the steel in huge annealing ovens over the course of many hours and days, then straight to the temper mill, where it was rolled between immense rollers which altered both its thickness and its hardness, becoming "cold rolled" steel in that process.    Both HR and CR could be slit to length, width per the customers requirements.

Edited by SpankySmith
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Wiki says

In metalworkingrolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness and to make the thickness uniform. The concept is similar to the rolling of dough. Rolling is classified according to the temperature of the metal rolled. If the temperature of the metal is above its recrystallization temperature, then the process is known ashot rolling. If the temperature of the metal is below its recrystallization temperature, the process is known as cold rolling. In terms of usage, hot rolling processes more tonnage than any other manufacturing process, and cold rolling processes the most tonnage out of allcold working processes.[1][2] Roll stands holding pairs of rolls are grouped together into rolling mills that can quickly process metal, typically steel, into products such as structural steel (I-beams, angle stock, channel stock, and so on), bar stock, and rails. Most steel millshave rolling mill divisions that convert the semi-finished casting products into finished products.

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No offence meant b4uto, and I am only speaking for myself, and also am not saying if wiki is right or wrong, but please do not give me that dribble, I apreciate acurate information, not a generalization of collected opinions, which is what wiki claims to be.

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In practical terms, there is little advantage to using the more expensive cold rolled steel for forging stock!  When the steel is to be used in fabrication without passing through the forge it could be a useful option.  Of course, if you have cold rolled stock on hand there is no reason why you couldn't forge it and the price differential is fairly modest for small amounts.

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Wiki says

In metalworkingrolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness and to make the thickness uniform. The concept is similar to the rolling of dough. Rolling is classified according to the temperature of the metal rolled. If the temperature of the metal is above its recrystallization temperature, then the process is known ashot rolling. If the temperature of the metal is below its recrystallization temperature, the process is known as cold rolling. In terms of usage, hot rolling processes more tonnage than any other manufacturing process, and cold rolling processes the most tonnage out of allcold working processes.[1][2] Roll stands holding pairs of rolls are grouped together into rolling mills that can quickly process metal, typically steel, into products such as structural steel (I-beams, angle stock, channel stock, and so on), bar stock, and rails. Most steel millshave rolling mill divisions that convert the semi-finished casting products into finished products.

​This kind of post does NOT make you look learned, just the opposite.

Frosty The Lucky.

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For solid stock it is explained, when it comes to tubes there are some differences:

A hot rolled square tube has stronger corners and generally more even distributed stress from the production.

Cold rolled tubes have weaker corners, just as you would imagine if you have ever worked hot metal ;)

There are regulations that you would have to normalize cold rolled tubes before you weld at the corners (in Germany)

 

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dislocations and pickling and oiling!  (and sometimes the alloy used)

​Exactly.

But probably not enough information for most folks to understand the actual difference, ... as it applies to them.

The term "Cold Rolled Steel" assumes a level of knowledge, of the steel making process.

It would probably be more accurate, if they called it "Work Hardened Steel".

Work hardening, also known as strain hardening or cold working, is the strengthening of a metal by plastic deformation. This strengthening occurs because of dislocation movements and dislocation generation within the crystal structure of the material.

Many non-brittle metals with a reasonably high melting point, can be strengthened in this fashion.

Alloys not amenable to heat treatment, including low-carbon steel, are often work-hardened.

 So essentially, ... "Cold Rolled Steel" is the same low-carbon alloy, as that used to make "Hot Formed Steel", ... but it has undergone additional processes, that have Work Hardened, and refined the Surface Finish of the steel.

( Those "additional processes", are why it costs a bit more. )

 

For use in Forging operations, those Work Hardening and Surface Finish properties, are essentially lost, the first time the steel is heated to a "non-magnetic" state, in the Forge.

 

Of course, you'll encounter situations where one portion of a work-piece needs to be Forged, ... while it's desirable that a different portion remain true to a precise Size and/or Surface Finish.

For those situations, ... Cold Rolled is the answer, ... and for "rougher" or more "traditional" looking work, ... Hot Formed is the obvious choice.

 

They both have their virtues .....

 

 

.

Edited by SmoothBore
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Excuse me sir but what is wrong by giving a correct answer? The answer is not a collection of opinions. They are facts and since the quoter even gives the source as a wiki he is not trying to look learned he is trying to be helpful.

Cold drawn or cold rolled steel has higher tensile strength. This is why piano wire is so strong. The effect of course disappears if the material is heated so it is meaningless for a blacksmith to use it.

Cold rolled steel also has a smoother finish and better tolerances. Razor blades are made from reams of cold rolled steel. In dollars per load that a rod can pull it is cheaper to buy hot rolled and then reduce it by cold drawing (provided that the operation is big enough to pay for the equipment).

Cheers

Göte 

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in the not too distant past cold rolled tended to be a nice steel.  If you asked for hot rolled you get A36 and if you asked for cold rolled you got 1018/1020 and oft times you could tell the difference under the hammer and other processes.  Cold rolled often has "sharper" corners in Sq stock and so makes prettier twists if you will not be hammering it much.  Cold rolled is often more expensive; at my local steel dealer a 12' stick of cold rolled will often be more expensive than a 20' stick of the same cross sectional size stock in hot rolled.

 

With the cheapening of everything they are now doing cold rolled A36 I am told.

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What I don't get is the fact that some smiths harden A36 or cold rolled 1018.

Can it really be hardened??? Or are they fooling themselves??

I watch them do it and tell us they are doing it and why they are doing......................before I look stupid and call them out on it in front of an audience at nearby county fairs, I'd like to know for sure if you can harden A36 and 1018.

Even if you can.......................why harden an "S" hook????????????????? Do they wear out??????????????

 

 

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I know when I purchase steel for the society from the steel supply (Steel Equipment Corporation) I have to order exactly what I want....... i.e. Hot Rolled A36 or cold rolled 1018 which THEY refer to as a COLD FINISH (CF1018)   free delivery.......

Yep, the cold costs a small amount more. I only order that if they have no A36 in the size I desire. 20' is what I buy cuz that is the way they sell it. They charge you extra if it is to be sheared at another length.

If I desire to pay through the nose, I get steel from the local machine shop. I have had to, but it is rare. 

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Excuse me sir but what is wrong by giving a correct answer? The answer is not a collection of opinions. They are facts and since the quoter even gives the source as a wiki he is not trying to look learned he is trying to be helpful.

Cold drawn or cold rolled steel has higher tensile strength. This is why piano wire is so strong. The effect of course disappears if the material is heated so it is meaningless for a blacksmith to use it.

Cold rolled steel also has a smoother finish and better tolerances. Razor blades are made from reams of cold rolled steel. In dollars per load that a rod can pull it is cheaper to buy hot rolled and then reduce it by cold drawing (provided that the operation is big enough to pay for the equipment).

Cheers

Göte 

​There's nothing wrong with being helpful. Unfortunately simply posting a list of Wiki "fact" is all too often just a load of opinion from folk with little or no actual knowledge. When Wiki information is actually correct it's often because the "contributor" simply cut and pasted information from a reliable source. It isn't because the "contributor" actually knows what they're talking about. Sites like Wiki have actually made reliable research much harder because searches hit on Wiki instead of reliable sites. Wiki isn't as bad as all the web marketing crud that is trying to anticipate things you might buy if they bombard you hard enough but it's still more nuisance than real help.

Seeing as the post directly preceding by 6 hrs. (so there is no chance of it being a simultaneous post) was from a person who worked in the industry producing both hot and cold rolled steel in steel mill quantity. Who is not only posting from established industry standard definitions but has on site, hands on experience. Posting the results of a Wiki search was just grandstanding to LOOK helpful. In truth over explaining a topic more often adds confusion than being helpful. I'm not saying the poster in question didn't think he was being helpful, this is a common misconception with new comers to any craft and youngsters especially. Intentions were good and I'm not faulting the intent, unfortunately they were completely redundant and from a questionable source.

Worse than posting questionable information just look how much bandwidth the following discussion is taking up. Can we PLEASE get back to blacksmithing?

Frosty The Lucky.

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​There's nothing wrong with being helpful. Unfortunately simply posting a list of Wiki "fact" is all too often just a load of opinion from folk with little or no actual knowledge. When Wiki information is actually correct it's often because the "contributor" simply cut and pasted information from a reliable source. It isn't because the "contributor" actually knows what they're talking about. Sites like Wiki have actually made reliable research much harder because searches hit on Wiki instead of reliable sites. Wiki isn't as bad as all the web marketing crud that is trying to anticipate things you might buy if they bombard you hard enough but it's still more nuisance than real help.

Seeing as the post directly preceding by 6 hrs. (so there is no chance of it being a simultaneous post) was from a person who worked in the industry producing both hot and cold rolled steel in steel mill quantity. Who is not only posting from established industry standard definitions but has on site, hands on experience. Posting the results of a Wiki search was just grandstanding to LOOK helpful. In truth over explaining a topic more often adds confusion than being helpful. I'm not saying the poster in question didn't think he was being helpful, this is a common misconception with new comers to any craft and youngsters especially. Intentions were good and I'm not faulting the intent, unfortunately they were completely redundant and from a questionable source.

Worse than posting questionable information just look how much bandwidth the following discussion is taking up. Can we PLEASE get back to blacksmithing?

Frosty The Lucky.

​Either way Frosty you sound like a total xxx for even commenting on my wiki post. which was meant to help..not for you to make yourself look good or smarter than everyone else with your outlook on life...could of just ignored the post...just a suggestion..but sure you have a fancy retort dying to come out any how.

insulting, name calling and profanity are not tolerated here,

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No offence meant b4uto, and I am only speaking for myself, and also am not saying if wiki is right or wrong, but please do not give me that dribble, I apreciate acurate information, not a generalization of collected opinions, which is what wiki claims to be.

​Sorry Turbo7.. was tryin help.. I will consider this for the future...

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I have nephews in both high school and college and they are not permitted to site Wiki in any paper, speech or presentation, for reasons already noted here.  Wiki articles are written by whomever wants to write them.  Point of fact - I can go to a Wiki article that is GOOD, is CORRECT, and yet the way that system is built I can alter it, changing truth to my opinion which then presents itself as updated "truth."  It's insane.  

Now, as Frosty said, lets get back to blacksmithing....

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so I just picked up 14 20' Sticks of 1/2" sq solid hot rolled at US$7 a piece and the fellow then asked if I wanted around 200 22" pieces for $10  one end is even cut at an angle to make turning them into tentstakes that much easier!

He's a Maintenance guy at an apartment complex where they had to infill all the  railings on the outdoor stairs to meet the 4" rule. He laughed when I identified the source and reason.  I'm going to off load them at my new place under the OHIO rule (Only Handle It Once).

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Excuse me sir but what is wrong by giving a correct answer? The answer is not a collection of opinions. They are facts and since the quoter even gives the source as a wiki he is not trying to look learned he is trying to be helpful.

​And it would be helpful, ... it the Wiki data were completely accurate.

But it's not.

It's vague, ill-defined parameters, ... cause people to use terms like "forming", "drawing" and "rolling", ... interchangeably, ... and therefore, incorrectly.

 

The "Wiki-World" is a fine thing, for reaching a generally accepted consensus on a subject, ... but trusting it to yield definitive answers, ... is a slippery-slope, indeed.

 

.

 

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