Off Topic Smelting steels?

[A.McPherson]

So this one is out there a bit and doesn’t have much to do about knife making but some of you folks here probably have the knowledge to answer so here it goes...

Say you have a bunch of steels of various types. Is there a way to melt them down and get all the alloying ingredients out? So you can get down to pure iron?

I know this isn’t something that can be done at home. I’m just curious.

 

[Stacy E. Apelt - Bladesmith]

From what I know about it, not really.

You start from raw iron to get an iron billet. Once alloying is added, it is there to stay. The industry melts known assay steel scrap and adds more alloying to get a desired new alloy, but they can't easily make one with less alloying.

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[skillgannon]

There are many ways to smelt steel. I had a breakdown from one company is that they use basically a updated version of the bessemer process called something like a "base slang smelt" first the steel has to be heated enough for the exothermic reaction to start and that can be done in a furnace. Then the steel is transferred to a vessel and a jet of usually pure O2 is injected to start the exothermic process. At times they may inject some nitrogen as well. The steel is protected by a base slag (I assume since a base is specifically mentioned that a acid might be used in another process. ). So with the O2 jet there is a order to how the elements burn off. Al, Mg, Ti, Cr are some of the first to go but they can keep the jet going until most of the trace alloy is burned off. Once they get what they want they add graded scrap or alloy back into the melt for the exact chemistry. If it isn't hot enough when everything is burned off the can add a measured chunk of aluminum to the melt to bring the temp up. I guess one of the advantages of the basic slag is that it picks up most of the burned off alloy and can be chemically manipulated to release certain elements back into melt so that the burned off alloy isn't waisted.

Its been like 7 years since I took the seminar so I'm sure I have some stuff mixed up. From what one of the other reps said that's not the purest or highest tech way of refining.

 

[kuraki]

When they melt a lot of scrap with little attention to the analysis, they get the standard A36 structural steel. Alloying can vary a lot, but as long as it meets the strength standards, it is OK.

This is nonsense and should not be repeated as it is on various forums. A36 has a specific formula like anything else. The tolerances of the alloy content may be greater than some other alloys but to say anything that meets a 36 ksi yield is A36 is just false. There are a number of applications including pressure vessels that demand A36, not dual A36/Gr50 or anything in between, because of weldability.

 

[Stacy E. Apelt - Bladesmith]

I stand corrected. I was told that by many people in the scrap industry as well as my Crucible rep.

 

[Larrin]

For small scale steel production (meaning laboratory or pilot size), it is almost always with induction, either in air or vacuum. Scrap steel through high purity iron can be used along with various alloying additions, of course.

 

[skillgannon]

A36 does have a looser chemistry than say some 1018's. Steel certs and chemistry is complicated and comes from a lot of different places. Eneenering perspectives can very widely and are often very conservative. For example I am inspecting a 36" pipeline running through NYC right now. The welding is done with a 6010 root 7010 fill and a 6010 cap all welded down hand. There ar many reasons why it is done this way but none of them have anything to do with the quality of the weld. In a structural setting it would be extremely rare for these techniques to be approved. Out of all of the reasons to argue one we don't often think of is historical president. With some things if a change is not truly needed its better not to mess with the system. Maybe it says something for how good modern steel is that A36 is no longer our best effort and is considered a very easy to make. Here in NYC we still run into old Carnagie Steel. From what the welders tell me some of it is almost unweldible. As knife makers we know how important for us it is to have clean steel but for industry flaws can be rather large and still be acceptable.

 

[A.McPherson]

Thanks for the info guys. So basically they burn off the impurities at with high temps and O2?