Melting steel with a backyard furnace.

[100model]

I watched this video about him trying to melt steel, no surprise that it failed. A long time ago I tried the same experiment and failed so let me give the reasons why it failed. Steel at room temperature is very unreactive but when steel is heated to close to the melting point it becomes very reactive and burns. When steel is cut with a cutting torch it does not melt but it burns because oxygen is used. Some small ball bearing races were used in my experiment which has a large carbon content for hardness and chromium. So what happened was it all turned into iron oxide slag which has a low melting point and I poured it into a sand mold. I thought it was a success until I tapped it with a hammer and it shattered. In his video he tilts the crucible and sees the same thing. So how come the steel did burn when the furnace atmosphere is carbon dioxide when burning propane? At high temperatures carbon dioxide is unstable when carbon is present so graphite in a crucible is the carbon source. Carbon dioxide breaks down to carbon monoxide and oxygen which combines with the steel to form iron oxide.

Green twin tried this experiment with thick chunks of steel with the edges burning but never melted the large diameter round bars. I would recommend this experiment to anyone to satisfy their curiosity if it can be done.

 

[timo_gross]

Too cold I would say, not the best prevention for oxidation to use nails as material, switch off the burner twice to let air inside.
Just first thoughts. I would rather choose an electric oven for such small sample sizes.

p.s. the crackling noise would make me nervous

 

[GreenTwin]

I tried to melt steel in my furnace, but did not succeed.

It is puzzling because I can easily melt gray iron, and if I leave my steel skimming tool in the molten iron for more than about 15 seconds, the end of the steel will melt off.

So it made me wonder, what if I just place some 1/2" steel rods in the crucible, and tried to melt them.

I ran my furnace for an hour, and the steel rods got red hot, but no melting at all, and not really close to melting; ie: the rods were still very solid.

I have been told that when steel is placed in molten iron, some sort of chemical reaction takes place, which lowers the melting point of the steel.
I don't know for sure, but that sounds like a reasonable explanation.

I have known of an individual who could afford an iron-temperature-rated pyrometer, and as I recall, he generally measured his molten iron at pour temperature to be somewhere in the 2,500-2,600 F range, and closer to 2,500 F if I remember correctly.
He uses the same burner/furnace arrangement as I have.

I have an optical pyrometer, but have not been able to use it successfully yet.

Generally, I can tell when iron is at pour temperature, because the end of my skimmer gets really hot really fast, and will begin to melt away if exposed for very long to the melt.
I have hear some say that the pour temperature of iron can be critical, but it seems like the iron temperature peaks at about the right pour temperature with an oil burner, and it does not really matter exactly what that temperature is.

What is important is that the iron is very fluid, so you get a complete mold fill.

I use a ceramic mold coat, so there is no danger of burn-in into the sand mold, from a superheated pour temperature.
If you superheat aluminum above 1,350 F, you can get a rough surface finish, especially when not using coated bound sand.

I have seen some get a rough surface finish with their iron when using greensand, and it is possible that they are pouring too hot.

Ironman (aka: 100model) always seems to have a very good surface finish on his iron, and it is the best I have seen of any of the backyard ironcasters.

I considered adding oxygen to the burner, but the problem is that there is a high probability of exceeding the rating of the furnace lining, and exceeding the rating of the crucible, when you add oxygen.
So you may get the steel to melt with oxygen added, and then your furnace and crucible may be ruined.

I do have some 3,800 F plastic refractory, but my furnace hot face is made from Mizzou, and I am sure Mizzou does not have a 3,800 F rating.
If I ever build another furnace, the hot face will be made from 3,800 F plastic refractory.
With plastic refractory, you don't add water, since it is like putty.
You either roll it out flat, or pound it onto the inside of a cylinder form.

And if you did get steel to melt, it is my understanding that the chemical properties must be closely controlled, else you will not have a strong casting.

I have given up on trying to cast steel.

I am working on learning the ductile iron process, and this is the best of both worlds, in that the iron melts in my furnace, but can be as strong as steel, and flexible; perhaps not quite as flexible as steel.

.

 

[GreenTwin]

Here is an optical pyrometer, and color temperature chart.

I have played around with it, but never got a good reading.

The bottom line is you really don't need a pyrometer with iron.
What matters is that you get good fluidity, and a complete mold fill.

.

 

[timo_gross]

On this diagram the top line is showing the melting point.
Pure Iron melts at 1536°C Cast Iron will melt at a little over 1147°C that is at about 4.3% carbon.

If a steel rod is dipped into a 4.3%; 1160° C hot iron melt it will "dissolve" reduce the carbon content of the mixture a (tiny?) bit and deliver Iron to the mix.

Greetings Timo

 

[timo_gross]

Here is an optical pyrometer, and color temperature chart.

I have played around with it, but never got a good reading.

The bottom line is you really don't need a pyrometer with iron.
What matters is that you get good fluidity, and a complete mold fill.

.

View attachment 153632View attachment 153633View attachment 153634View attachment 153635View attachment 153636

Does it have a battery? There were some that looked a little like those compact super8 cameras, they would make a metal wire glow with electric power.
You crank up the power until the wire colour matches the background you are looking at.
Helpful to measure, refractory temperatures, forging temperatures and things in heat treatment.
When using it on a melt, you need to take a little care that you do not look at the slag by accident. Because the slag is usually colder on the surface than the actual metal below.

Greetings Timo

 

[GreenTwin]

It had an odd battery which was custom for that unit, but I replaced it with an equivalent number of AA batteries to get the same voltage, and it worked fine.

Yes, you adjust the incandescent filament to match the color temperature of the melt.
Works up in the steel temperature ranges too.
I think commonly used in steel mills.

I played around with my optical pyrometer before I had a good understanding of an iron furnace operation, and so I did not really know exactly what I was doing.

The time to use it would be after the final skim, and just after the ferrosilicon is added.
The surface at this point is very smooth and almost glassy, much like the photo below.

Edit:
And one problem is that the temperature would most likely need to be measured with the burner off, and perhaps measured with the crucible out of the furnace.
Once the crucible is out of the furnace, you only have about 60 seconds to complete the pour, since the melt will cool off very quickly, so there is not really any time to play around with a pyrometer with the crucible out of the furnace, and the temperature would be rapidly dropping anyway.

.

 

[timo_gross]

It had an odd battery which was custom for that unit, but I replaced it with an equivalent number of AA batteries to get the same voltage, and it worked fine.

Yes, you adjust the incandescent filament to match the color temperature of the melt.
Works up in the steel temperature ranges too.
I think commonly used in steel mills.

I played around with my optical pyrometer before I had a good understanding of an iron furnace operation, and so I did not really know exactly what I was doing.

The time to use it would be after the final skim, and just after the ferrosilicon is added.
The surface at this point is very smooth and almost glassy, much like the photo below.

Edit:
And one problem is that the temperature would most likely need to be measured with the burner off, and perhaps measured with the crucible out of the furnace.
Once the crucible is out of the furnace, you only have about 60 seconds to complete the pour, since the melt will cool off very quickly, so there is not really any time to play around with a pyrometer with the crucible out of the furnace, and the temperature would be rapidly dropping anyway.

.
View attachment 153667

Pyrometers were usually Infrared detectors a brand that I remamber was Raytek. They were in the four figure range for steel melting temperatures, but that was 15 years ago. One up to 450°C I saw in the low two figure price range two days ago.
Steel mills most times still used those paper tubes with a thermocouple inside (single use). You can also get integrated samplers to take probes.

 

[GreenTwin]

And with casting work, it is important to remember that melt temperature is quite a bit lower than pour temperature.

.

 

[100model]

The bottom line is you really don't need a pyrometer with iron.
What matters is that you get good fluidity, and a complete mold fill.

So true, although I have a platinuim tip pyrometer I found after melting iron for a long time the time taken is a very good indicator of when to pour.

 

[100model]

Pyrometers were usually Infrared detectors a brand that I remamber was Raytek.

I recently purchased a infrared pyrometer that goes to 1500C and when the hot weather goes away I will do a iron pour to test it out. Here is the link on ebay, the price has gone up a little since I purchased mine. Digital Infrared Thermometer Color LCD Non-Contact Temperature Gun Max 1500â AU | eBay

 

[timo_gross]

So true, although I have a platinuim tip pyrometer I found after melting iron for a long time the time taken is a very good indicator of when to pour.

These colour cards, when referenced (confirming the guess with a measurement) from time to time, you can get you surprisingly close with rough "guessing" based on colour. Experience plays a big role and iron makers did not have Electronic measurement devices for quite some time.
Contemporary mass production is a different story. Telling slag from Iron? An infrared camera with a computer shows steel in yellow and slag in green (suddenly it becomes easy even for me)

p.s. the blue thingy is still quite a bit cheaper than a Raytek form 2003

 

[timo_gross]

I recently purchased a infrared pyrometer that goes to 1500C and when the hot weather goes away I will do a iron pour to test it out. Here is the link on ebay, the price has gone up a little since I purchased mine. Digital Infrared Thermometer Color LCD Non-Contact Temperature Gun Max 1500â AU | eBay

That thing looks interesting, I hope they deliver what they claim 30:1 is quite nice for a home foundry.

The laser just shows what you are roughly pointing at (red dot in the pic). The laser has no business in the measurement it is just an aiming aid.
The IR detector reads everything that is within the imaginary circle (red circle). In the example picture the device would average over everything within the red circle. ( cold rim, medium temp side wall,relatively cold outside and the small area of melt) The laser is pointing at the melt, so a lot of people get total wrong readings when they are not aware that the laser is not measuring.
For some of the cheaper devices the ratio is 9:1 which is useless for high temp, because you have to put the device very close to the measured item.

Have fun with the new toy, I would be very interested in some report how it works.

p.s. for the picture above from GreenTwin were the molten metal is in the ingot molds you have not much chance that your complete area is within the melt and not "seeing" the molds or the table.

 

[GreenTwin]

And another problem is that the IR is very intense from the indice of the furnace, from the lid if your lid opens upwards facing you (don't build your iron furnace this way), and from the crucible.

Shaded glasses must be worn, else the eyes will get burned quickly, and it is like sunburn in the eyes.

I had someone taking a video of me removing the crucible from the furnace, and the camera was 10 feet away, with video camera that had a black body.
The camera started to smell like burning plastic, and the IR was overheating it.

So if you put a plastic object in the vicinity of a hot crucible or furnace, it may not last very long.

A simple reflective heat sheild works wonders to keep things cool.
Heat shields in strategic places is a must when working at iron temperatures.

.

 

[GreenTwin]

Another way to judge iron temperature is that the melt begins to expel small sparks out the furnace lid and into the air when the melt is on the high side of what on oil burner is capable of doing as far as heating the iron.

Sparkling iron is very hot.

Hot iron will pour about like pouring ice tea; it is very fluid.
The ferrosilicon additive increases the fluidity of the melt considerably, but using more than a tiny amount causes excessive shrinkage and hot tears.

.

 

[Fidlstyks]

When cutting scrap steel with an acetylene torch, I start a cut, and shut off the acetylene and cut on pure oxygen, the carbon in the steel provides the fuel.
People have melted steel in clay graphite crucibles, never carbide carbon bonded, that changes metalurgy.
I melted some, but stuck to cast iron. When I lived in Indianapolis, we melted around 800# of a mix, making ductile in an induction furnace.
It is odd how iron is. I watch alot of videos and read, in the FB group Bloomerie iron is melted by charcoal, the Bloom is steel and may be forged. If over heated, it flows out, and is cast iron. Then they no blow air through the cast iron, burning out the carbon as flakes, to make steel, then reintroducing carbon as rolls.
In the local foundry, they buy clean punching steel and melt it, turning it back into cast iron.

 

[timo_gross]

When cutting scrap steel with an acetylene torch, I start a cut, and shut off the acetylene and cut on pure oxygen, the carbon in the steel provides the fuel.
People have melted steel in clay graphite crucibles, never carbide carbon bonded, that changes metalurgy.
I melted some, but stuck to cast iron. When I lived in Indianapolis, we melted around 800# of a mix, making ductile in an induction furnace.
It is odd how iron is. I watch alot of videos and read, in the FB group Bloomerie iron is melted by charcoal, the Bloom is steel and may be forged. If over heated, it flows out, and is cast iron. Then they no blow air through the cast iron, burning out the carbon as flakes, to make steel, then reintroducing carbon as rolls.
In the local foundry, they buy clean punching steel and melt it, turning it back into cast iron.

When cutting steel with the Oxygentorch the iron burns not (only) the carbon. It still works on mild steel, e.g. deep drawing steel with 0.03% C.