Hot Vs Cold Rolled Steel

Lienhart Fischer · Post by **Lienhart Fischer** » Thu Jun 13, 2002 9:12 am

This has been covered before i belive but is there any difference between hot and cold rolled steel besides the millscale on the hot?
-T

Mad Matt · Post by **Mad Matt** » Thu Jun 13, 2002 9:15 am

Hot is a little softer since it's rolled hot and allowed to air cool. Basically it's a little normalized.

You won't notice it very much though.

Also hot rolled sheet metal is generally lower quality. It's easier to produce then cold so much of it is made by mini-mills which have lower quality controll standards.

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The budding mid 14th century German Transitional guy.
Mad Matt's Armory

Steve S. · Post by **Steve S.** » Thu Jun 13, 2002 9:24 am

Often, hot rolled steel comes with "mill scale" on it - black iron oxide that is tough as hell to grind off.

You can, though, buy hot rolled steel that has been "pickled and oiled". This means the oxides have been eaten off with acid and they have been oiled to protect from rust.

Steve

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Forth Armoury
Highly authentic, affordable riveted maille.

Mad Matt · Post by **Mad Matt** » Thu Jun 13, 2002 9:32 am

Really? I've only seen pickeled cold rolled. Doesn't mean it doesn't exist though.

The reason the mill scale is so hard to grind off is that because of the heat and the pressure used when rolling the steel the oxide crystalizes partially making it a lot tougher then just rust.

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The budding mid 14th century German Transitional guy.
Mad Matt's Armory

wcallen · Post by **wcallen** » Thu Jun 13, 2002 10:14 am

Most of the cold rolled I have run into is actually another variation - CRA - cold rolled annealled.

That means it is even softer than hot rolled, not harder.

All very confusing in the end.

Mostly the hot rolled is a little rougher and has the nasty scale that is so hard to get off.

Wade

Guy Dawkins · Post by **Guy Dawkins** » Thu Jun 13, 2002 10:24 am

I'm going to take issue with Mad Matts comment about HR sheet being "lower quality" the CR. Remember all CR steel products start out as a HR product. CR is than run through additional rolling , at lower temp, to impart a closer gauge tollerance and finer grain structure and surface condition. HR is not necessarily of a lower quality metal. HR has a losser thickness tolerance than CR. HR with a "Temper Pass" is also available. Most HR sold in the US is pickeled and oiled, so the surface scale has been removed and rust preventive oil applied. However, ALL pickeled and oiled steel has a "shelf life". Over time and dependant on atmosheric conditions, rust will develope. So if your picking up your HR ar CR from a "secondary" source ie: scrap yard, a non-steel service center, you will probable find light to heavy rust on both.

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Guy
(mka: David Valenta )

Mad Matt · Post by **Mad Matt** » Thu Jun 13, 2002 10:53 am

Actually my point on the lower quality steel was that hot rolled sheet requires less equipment to produce then cold rolled sheet.

Meaning smaller mills generally don't produce cold rolled steel.

These smaller mills are typically the ones producing new steel from scrap as opposed to the bigger mills making new steel. The quality of recycled steel will tend to be lower and the quality controll at the smaller mills is generally lower.

Wade: Thank-you thankyou thankyou. When I went to the southern armourers gathering in Texas The cold rolled steel I used while I was there seemed a lot softer then the stuff I get. I figured that the temperature difference down there had a bit to do with it. But not that much. I thought something was wierd and didn't know what. The stuff I used in Texas was also a little shinier then the stuff I get (I'm pretty sure It's pickeled cold rolled I'm getting).

I'm gonna have to check with my suppliers and see if I can get CRA. It really was a big difference between it and the stuff I get.

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The budding mid 14th century German Transitional guy.
Mad Matt's Armory

Gundo · Post by **Gundo** » Fri Jun 14, 2002 4:08 pm

My production line at my day-job eats several tons of galvanized sheet coils every day. The galv from Thyssen Corp. is made from a cold-rolled substrate, and the crap we get when Thyssen can't keep up with our demand is hot-rolled.

In at least this case, hot-rolled is near-garbage by comparison. A coil of cold-rolled is the same thickness througout, and the same thickness as every other coil of cold-rolled [to within a thousandth, anyway]. We order .062, we get .062. With the hot-rolled, it might average .062, but probably actually won't, and it will certainly vary up and down through the coil. The finish of the steel is reflected in the finish of the coating, as well, so cold-rolled is near glass-smooth, and hot-rolled is sandpaper-ish by comparison.

YMMV.

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Gundobad,
Wise Ogre Armory

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Guy Dawkins · Post by **Guy Dawkins** » Fri Jun 14, 2002 8:08 pm

When we talk about quality we probable have to difine what we mean. If you compare the surface finish of HR to CR then yes. CR has closer tolerances and better smothness to it. But as far as chemestry... CR started its life as HR. Wheather it came from and electric arc furnace at a mini-mill ( the people who redifined the steel making industry back in the mid-70's)or a "old-line" mill who starts from iron ore and coke makes no differance to its quality. We've got HR P&O Temper Pass sheet that you would think is CR. You can't look at HR and CR and say the steel in the CR is better quality. You have to look at what the application is and detirmine if the addition cost for closser tolerances is worth it.
As far as mini-mills verses the big ole boys( Bethleham and Republic are in Chapter 11.)they bought have to produce to ASTM standards.

Hey... that reminds me...do you guys know that steel coils (the stuff sheet comes from) has about a 4 month lead time , and the cost keeps going up! At work we've gotten real picky about who we will sell to.

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Guy
(mka: David Valenta )