Cutting of SS Using Torch

More heat.

See this, about halfway down the page. The iron powder adds heat as well as producing a reducing effect. There are also specialty powder-cutting torch rigs.

Thanks, I already read the blog.

But, what I dont understand is how come iron can reduce Chromium oxide. When Chromium oxide itself is protecting iron in stainless steel.

I think that the iron powder "burns off" some of the oxygen from the flame, thereby leaving a reducing (oxygen-poor) flame.

Iron uses the oxygen making iron oxide intead of chromium using it (producing chromium oxide)

Is there a particular reason for you cutting Stainless with oxy-acetylene? So much easier with plasma, and you can hire a set for relatively cheap these days - including the argon.

I can only imagine hours of grinding and cleaning to still have discoloured stainless. What grade stainless are you cutting 304, 316, 317 super-duplex? The grade will vary the cut. Honestly though, you should not be cutting stainless with oxy-acetylene unless you have absolutely no other choice, as it is a very clumsy method for this material. For thin sheets, try a guillotine (assuming you are in a sheet shop), or a set of nibblers, but for heavy stuff use a plasma arc cutter. Very fast, neat and tidy. You can still over heat the stainless but not to the extent of the oxy-acetylene.

Lyn is correct for this method though, if you must use it, you need a more oxidising flame than a carburising one. Get a good roaring flame then slowly cranck up the oxygen until you have a very sharp blue flame.

Good luck

oxy acetyline cutting DEPENDS on oxidation to happen in order to make the cut, when cutting ,oxygen reacts with the semi molten metal and oxidation happens and more heat is produce to achieve the cut.

and since stainless steels have good corrosion resistance oxidation is not that effective to achieve the cut.

in work we have a workshops dept. and they use plasma , guillotine machine and gouging for cutting st steels - never used oxyacetylene ..

Dear PC !!

Interesting assumptions were stated,but considering this facts:

1)Oxy-acetylene torch temperature is:3,000 to 3,480 Celsius

2)Melting temperature of Chromium - 1907 Celsius and Cr-Oxide:2,435 Celsius

- " - - " - of Nickel - 1,435 Celsius and Ni-Oxide:1,955 Celsius

So energy based assumptions - are incorrect !!

As so the use of Iron powder create results not based on Higher Energy or Temperature !! please reconsider!!

oxy acetylene actually burns or oxidises the metal, in the case of mild steel, burning it and blowing it out of the way. with s/s this is negated by the chromium which raises the oxidising temperature, so all you can do is melt the stainless, very slow. adding iron powder creates an oxidising stream that burns and carries away the s/s. note that burning and melting are 2 different things. plasma operates at up to 10 times the temperature of oxy acetylene so allows the burning (oxidising) of the s/s, which is then carried away by the high pressure gas used in the process.

Quite correct the iron powder when it is burning destroys the shielding effects of the Chromium and nickle content of the stainless steel and allows it to burn the ss away.

OK.

So, this is what I understand. Please correct me if wrong.

When you are cutting MS the the oxyacetylene is not just melting it but there is vapourising effect due to the high temperature generated by the oxidation of iron with impinging Oxygen gas.

The electrode potential of chromium is lower then iron so it has more affinity for oxygen and forms oxides quicker, creating a tenacious, passive, self healing film which protects the underlying iron. While cutting the SS the same film prevents the oxygen molecules from reaching the iron and slows the heat generation. The SS only melts slowly.

When iron powder is added in the torch, the heat generation due to oxidation reaction is high enough to vapourise the chromium oxide layer also. This accelerates the cutting speed.

Dear PC

Please allow me to correct you: it is not the oxygenation itself helping cutting ,it is more the weight of the fluid jet constructed from oxyacetylene jet+iron powder. It is well known structure for penetrating Armor steel !!! (with Cu powder+hot gas jet !!)

It is the same with waterjet + Alumina/Silica Powder (a good but expensive way of cutting steels,glass ceramics etc)