Torch cutting stainless steel

diyer_miOctober 19, 2004

Can anyone tell me why I cant cut thru s.s. like regular steel. I use acetylene (sp?) and oxygen tanks and have cut a lot of steel but never had to cut s.s. until recently. I was attempting to cut thru 2x3/8 flat s.s stock but couldnt penetrate it. Thanks for any advice...

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formulaross

It's probablty the alloying elements in the ss. Stainless steel typically has high levels of chromium and/or nickel. These elements form stable oxides on the metal surface which protects the surface from rusting. When you cut with an oxy-acetylene torch, your are literally burning the iron in the steel with the extra oxygen you supply. The chromium and nickel are much more stable at high temps than iron (that's why jet engine alloys use a lot of chromium and nickel) and may be protecting the iron from making contact with the oxygen from the torch. No contact = no iron burning = no cutting.

    Bookmark   October 19, 2004 at 4:20PM
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kbeitz

Take a normal welding rod and hold it in front of your torch when cutting Stainless... Cut both at the same time... This works good...

    Bookmark   October 19, 2004 at 7:49PM
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gooseberry_guy

Stainless steel is a non-ferrous (contains no iron) material. When cutting regular carbon steel, a chemical reaction takes place because oxygen has a chemical attraction to ferrous metals(iron), when they are heated above their melting point. When excess pure oxygen is added to red hot ferrous metal, the iron oxidizes very rapidly. The force of the oxygen aids in blowing away the molten metal from the cut.

A couple of ways to cut thick stainless is with a plasma torch, or with the use of the fiberglas reinforced cut-off wheels. The website below mentions the use of a mig welder to cut stainless.

GG

Here is a link that might be useful: Metal cutting options

    Bookmark   October 19, 2004 at 10:16PM
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brickeyee

"Stainless steel is a non-ferrous (contains no iron) material."

Most stainless steel contains significant iron. Some is non-magnetic, but far from all.

    Bookmark   October 20, 2004 at 2:45PM
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blacksmithman

Staniless steels are iron-based alloys containing 10.5% or more chromuum. The elements which gives stainless steel their desired properties produce oxides which reduce the operation to a slow melting away process when the conventional oxy-acetylene cutting equipment is used. By injecting a suitable flux directly into the stream of cutting oxygen before it enteres the torch, the obstructing oxides are removed. Machinery's hand book This is why Kevin's idea would work.

    Bookmark   October 20, 2004 at 4:49PM
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gooseberry_guy

Well, that's what one of my welding books says, so that's all I can tell you. It might depend on the alloy content of the stainless, but I understand stainless doesn't rust is because it contains no iron, and so it cannot oxidize. Obviously, if there is no iron in the stainless alloy, a magnet will not stick to it. I've never seen non-magnetic iron.

GG

    Bookmark   October 20, 2004 at 4:52PM
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brickeyee

Stainless does not rust because of the alloy content forming a protective layer.
The flux trick works well by attacking the non-iron alloying elements (chiefly nickel and chromium).
The percentage of iron remaining governs the magnetc properties, since nickel is a magnetic metal also. get a stronger magnet and you can probably get most of the stainless you encounter to stick.

    Bookmark   October 20, 2004 at 4:58PM
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brickeyee

See the site below. Note the ** footnote to the table. The crystal structure of even non-magnetic stainless steels can be modified from working to make them feromagnetic.

Here is a link that might be useful: Stainless Composition

    Bookmark   October 20, 2004 at 5:03PM
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gooseberry_guy

OK, I did some additional research on why you can't cut stainless with a torch. Apparently, the previous information I found was not true. From this website, I found the following:

http://www.ulearntoday.com/magazine/physics_article1.jsp?FILE=steel

"The chromium in stainless steel has a great affinity for oxygen, and will form a film of chromium oxide on the surface of the steel at a molecular level. The film itself is about 130 Angstroms in thickness, one Angstrom being one millionth of one centimetre. This is like a tall building being protected from the rain with a roof the thickness of one sheet of ordinary copy paper. This layer is described as passive, tenacious and self-renewing. Passive means that it does not react with or influence other materials; tenacious means that it clings to the layer of steel and is not transferred elsewhere; self-renewing means that if damaged or forcibly removed, more chromium from the steel will be exposed to the air and form more chromium oxide. So, even if a stainless steel object withers away by use and reuse, it will still remain stainless".

So with that point, I checked another, more complete welding book and found a mention on Powder Cutting, a similar principle to Kevin's welding rod trick. In powder cutting, iron powder is introduced into a standard oxy-acetylene cutting torch flame. The heat of combustion of the iron powder increases the total heat of the flame. Referring to the statement about chromium oxide above, by introducing iron powder into the flame, these oxides are kept from forming, and the cut is able to occur. The high iron content particles, oxidize at the torch tip, producing a very high temperature and concentrated heat. The powder also produces a reducing action on the metal, and a high velocity gouging action. When cutting non-ferrous metal like aluminum or copper, about 10-30 percent aluminum powder can be added to the iron powder. According to my source, special powder cutting torches are available for this purpose.

GG

    Bookmark   October 20, 2004 at 11:27PM
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diyer_mi

WOW!, you guys can really get tecnical! Hopefully more people than myself learned a lot from all the responses. thanks to all for the advice, I'll just stick to the chop saw ....

    Bookmark   October 21, 2004 at 8:48AM
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gooseberry_guy

Well, it's stuff I never knew before. I never really had a need to know, but it doesn't hurt to learn about it for future reference.

GG

    Bookmark   October 21, 2004 at 10:33AM
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horseman1

Like going to skool only funner :)

    Bookmark   October 21, 2004 at 11:21PM
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Crashbob

why aint I no seed this afore? y'all probably got a circular saw for wood eh? buy a metal cutting blade, the choices are endless and hook it to the saw works like a cut off wheel... wear goggles and have a strong steady hand

    Bookmark   October 22, 2004 at 8:05PM
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JoeJ

Diyer,

Just remember "PLASMA CUTTER"
For one thing, you will get a very nice finnish cut, with a bunch of practice. And until then go with a chop or cut-off saw.

Just my $.02

Joe

    Bookmark   October 23, 2004 at 8:51AM
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Skaggydog

Posted by: Crashbob (My Page) on Fri, Oct 22, 04 at 20:05

"why aint I no seed this afore? y'all probably got a circular saw for wood eh? buy a metal cutting blade, the choices are endless and hook it to the saw works like a cut off wheel..."

Sounds like a nice way to burn up my saw.

    Bookmark   October 24, 2004 at 11:41AM
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brickeyee

There are both tootheed and abrasive metal cutting blades for circular saws. The same blade can be used in a chop saw also. they are not very good with sheet metal, but fine for larger sections. A hand nibbler tool works fine for sheets (if slow), and power nibblers can make short work of sheet metal if there is a lot to cut.

    Bookmark   October 24, 2004 at 3:11PM
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DNT1

We use a tool that looks like a grinder it is called a Metabo grinder, we only use the six inch blade model, but I know they make a four inch, it utilizes a real thin cutoff blade that will cut thru SS like a hot knife thru butter. You can also use standard grinding wheels on the tool, very versatile. Most tool places carry these, seems like the last batch I bought they were about $200.00 each and the blades are about $1.50 each, if you ever use one you will buy one, the tool has a builtin clutch that prevents burnout if it gets jammed up when cutting, and also has a variable speed adjustment. We use this where we used to use sazalls/oxy acy torch and plasmarc cutters. Its a beautiful thing.

    Bookmark   November 3, 2004 at 5:41PM
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DirtyEd

United Abrasives Inc.(SAIT) makes a 4.5 inch wheel that I use a lot of, it's only .045 inches thick and you can get them for ferrous or non ferrous metals. I keep one grinder setup with one of these all the time, another setup with a wire wheel, and for heavy grinding I use a 7 inch Metabo.
The only problem I've had with these is that they cut so good that you will try to force them to cut even faster, which can cause them to wear quicker.
DED

    Bookmark   November 4, 2004 at 8:27PM
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spambdamn_rich

By definition, a ferrous metal contains at least 50% iron. All steels commonly called stainless contain more than 50% iron, so they are all ferrous.

The non-magnetic stainless steels are generally the 300 series, of which the 18-8 type is the most common (used for flatware, etc). The non-magnetic property is due to the metal crystal structure - these are known as "austenitic". Guess what, if you heat plain carbon mild steel to over 1800F or so, it will be non-magnetic too, at least until it cools down. That's how foundries pick up the molds for white hot ingots with big magnets - the molds are magnetic but the hot steel is not, and the billets just stay on the ground as the molds are lifted away. The hot steel is in its austenitic form.

Cold-working can make austenitic stainless magnetic, but usually only mildly so. Depend on the exact alloy percentages.

The austenitic stainless steels all contain a lot of nickel... the magnetic types have no nickel or much lower amounts - but that is not the only difference, and the differences are too complex to go into more detail now.

Like the man said, a plasma cutter will handle stainless just fine. If the material is sheet and the cut is straight, a hydraulic metal shear is a good answer as well, if you have access to one.

    Bookmark   November 20, 2004 at 9:00PM
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