Scale (on steel)

[fpworks]

Is there a rule of thumb to determine what steels come with or without scale?

Such as, everytime I order 1018 CRS, it has scale. Usually, A36 HR does not come with scale (but I just talked to somebody who says that he gets A36 HR with scale)

Justin

[mxtras]

Typically, cold rolled materials have NO scale while the hot rolled materials (A-36) do have scale.

I have never seen hot rolled materials arrive from the mill without scale - plate, bar, flat - HR has scale.

Scott

[fpworks]

Scott,
Thanks for the quick reply, that is what I thought.

I have been consistently getting scaled "CR" steel from my supplier. I think I need to have it checked out.

...and maybe I'm just confused on the HR A36.

I'm not educated on the rolling processes...what is the reason for the scale? Is it by-product of hot rolling? Is it formed only on specific steel alloys?

Thanks again.

Justin

[srstol]

The scale is formed when the hot metal reacts with the atmosphere during the hot rolling process. Cold rolled steel has no appreciable heat induced during rolling thus no scale.

A36 is hot rolled, so it has scale.

If you want plate without scale you need to look for P&O (pickled and oiled) material. That is usually hot rolled A36 plate that is pickled in an acid solution and oiled to keep rust away. It can be pretty hard to find.

Rob.

[Mcgyver]

scale forms when the steel is cooled in the presence of oxygen from being red hot. obviously its a lot easier to form the metal red hot than cold so HR is much cheaper. The scale results from the process not the metallurgy (ie HR vs CR). Its possible for cold rolled to have scale if for example its been heat treated (normalizing/stress relieving). conversely, a lot (most?) coil product (sheet steel) is delivered oiled without scale is in fact hot rolled that has been pickled.

Like Scott says though, if you're just buying 1018 cold rolled bar stock and its covered in black/blue scale, something is wrong - maybe there's some communication issue, maybe they're supplying HR and charging HR because that's all they have. worst case you are being supplied HR but charged for CR....HR is a lot cheaper than CR

[mxtras]

If the material you get has scale, then it is NOT cold rolled. Your supplier is not giving you what they say. It is a simple as that.

I prefer using hot rolled materials as they do not curl up nearly as much when machined, but the scale can be an issue.

Scott

[fpworks]

Thanks for the info.

The "nonscaled" A36 HR plate that I have has a dark finish, but no scale, so that must be P&O'ed. Now I don't feel so confused.

But I definately need to confront my supplier about the "scaled" 1018CRS...obviously it is wrong. Thank goodness it was only used in house and didn't go to any of my customers.

Thanks again for clearing that up for me.

Justin

[mxtras]

A36 and 1018 are basically interchangeable - they are nearly identical in composition. They are both low carbon steels and have equivalent mechanical properties. If your customer specs 1018 and you supply a part made from A36, it is likely that he would not be able to tell the difference unless there were uncut surfaces on the part. Weldability and machinability are pretty close, but there are minor differences.

Most cost-minded engineers will not specify anything other than "LC Steel", leaving the option to the shop to use either steel. I prefer to work (machine) with A-36 despite the scale.

Scott

[fpworks]

Scott,
Good point about A36 and 1018 being nearly identical. I tend to be fairly close minded about substituting out steel alloys because there are so many subtle differences. And a good point for me to start putting "low carbon steel" on drawings instead of 1018 CRS.

You said that you prefer to machine the HR steel despite the scale. Do you have an effective way of removing the scale? On this past job, although I was cutting 0.1" below the scaled surface, I still damaged the inserts at the level of the scale.

Justin

[mxtras]

I do not process a whole lot of HR steel, but when I do I will usually just 'sacrifice' the inserts to get past the scale. I usually use insert cutters for end milling, not side milling so having the small imperfections or notches off the end of the cutter is not an issue for me.

Scale can also be removed by flame or acid. Aluminum prep acid does a good job on the scale but it adds unecessary cost and complexity in my opinion, as does breaking out the torch so I usually just mill the scale off. The surface is still hard and still will take it's toll on inserts, though.

Scott

[srstol]

I have removed scale by sand blasting, grinding, and chemical etching.

My preference is to use an acid solution to remove the scale.

Sand blasting usually imbeds abrasives into the material which sort of defeats the purpose... Grinding is noisy and dirty, but works pretty well.

For most of my hobby work I dip the material in a muriatic acid bath and let the chemicals go to town. For hobby stuff I use several large buckets. One with acid, two with water. I acid dip the part and when it stops bubbling I rinse it twice. At work we use our plating shop which has larger tanks.

Rob