What is this?

[Jeremy Blohm 511]

I had a good friend of mine send me this picture of a knife he had just quenched and he ended up with this green glass like substance on the very tip of his blade. He said it was very hard and he had to use a chisel to get it off. Any ideas of what it could be? The steel is scrap rebar quenched in vegetable oil.

[Zeb Camper 782]

That's what happens when you flick boogers in the quench tank. 

Did the blade have contact with sand at any point before the quench?

and just sayin, his blade probably isn't hard. I don't think rebar is high carbon. Probably the opposite. 

Merry Christmas!

Edited December 23, 2017 by Zeb Camper

[Vern Wimmer 472]

My next question would be " what type of forge is he using gas, coal, charcoal?" If coal or charcoal I'd make a SWAG that it was in the fuel. 

[Jeremy Blohm 511]

Im not sure if the blade got hard or not. It was the glass like substance that was very hard and he said the blade had no contact with sand and im waiting on a response on if there could be any kind of flux on the floor of the forge that could have gotten on the blade? 

[Jeremy Blohm 511]

45 minutes ago, Vern Wimmer said:

My next question would be " what type of forge is he using gas, coal, charcoal?" If coal or charcoal I'd make a SWAG that it was in the fuel. 

He is using a gas forge. 

[Vern Wimmer 472]

A lot of Si in the rebar (terrible material BTW) and really high heat.

Someting picked up from the forge floor

Something on the anvil

Something in the quench tank. That is least likely IMO unless the tip went through it and it bonded in the cavitation.

I'll go with "shop gremlins hid a beer bottle in the forge" for a hundred Alec.

[Alan Longmire 2,822]

Yeah, most likely something in the forge.  Looks like a Heineken bottle from here.   

Rebar comes in several grades, almost all of which is, believe it or not, carefully controlled for carbon and other elements.  That's why when you use it in construction you always tie it, never ever weld it.  A weld makes a heat affected zone that significantly weakens the rebar.  In the event of a building collapse, the rebar is one of the first things they check.  All the mills keep the certs for each and every melt.  Forever.  They do not want to be held liable for any potential disasters.  Think about it: for prestressed concrete bridge members, they lay the rebar in the mold and tension it up.  WAY up.  They they pour the concrete and let it cure, then they take the tension off the rebar.  That way the beam is already in tension, so that when it is laid as part of a bridge deck or whatever it is better able to deal with the compressive load.  Steel is strong in tension, concrete is strong in compression.  You trust your life to rebar every time you drive across a bridge.  It is not crap by any means.  It just isn't tool steel either.

It is usually a medium carbon, in the 1050-1060 range.  

[Jeremy Blohm 511]

I have never used it to make a knife but i have made a set of tongs with it and they worked out fairly well. I ended up giving them to a guy that bought a forge from me.

Heineken was my first thought! Lol

Edited December 23, 2017 by Jeremy Blohm

[Jerrod Miller 463]

On 12/23/2017 at 9:42 AM, Alan Longmire said:

Rebar comes in several grades, almost all of which is, believe it or not, carefully controlled for carbon and other elements.  That's why when you use it in construction you always tie it, never ever weld it.  A weld makes a heat affected zone that significantly weakens the rebar.  In the event of a building collapse, the rebar is one of the first things they check.  All the mills keep the certs for each and every melt.  Forever.  They do not want to be held liable for any potential disasters.  Think about it: for prestressed concrete bridge members, they lay the rebar in the mold and tension it up.  WAY up.  They they pour the concrete and let it cure, then they take the tension off the rebar.  That way the beam is already in tension, so that when it is laid as part of a bridge deck or whatever it is better able to deal with the compressive load.  Steel is strong in tension, concrete is strong in compression.  You trust your life to rebar every time you drive across a bridge.  It is not crap by any means.  It just isn't tool steel either.

It is usually a medium carbon, in the 1050-1060 range.  

I don't believe it.  

From my experience, all the grades of rebar are pretty low grades (in tensile strength, but it is pretty tough).  They control things, but still do allow pretty wide ranges on some things.  They are mainly worried about things that will directly lead to embrittlement; namely S and P.  They otherwise control C for getting the right tensile properties and Mn and Si for forgeability (it is all drawn steel).  There is a place in Spokane here that at least used to take 8640 (I think) rail car axles and draw it out to rebar.  Other plants take shredded cars (sometimes with the wiring, seats, lights, and everything) and melt it down.  As long as the mechanical tests pass, the heat is good.  It is all a cost thing.  A good clean 1030 will often meet the specs needed, but they have a lot of other random stuff that ends up in the melt because that scrap steel was cheaper.  

On a vaguely related note: I saw a technical presentation from a guy that figured out how to coat rebar with stainless steel.  Rebar corrosion is the primary factor in life expectancy in things like bridges.  Stainless rebar is just too expensive compared to standard rebar.  His proposal was to use stainless coated rebar, which was in between the two.  IIRC, the process was to run rebar through a stream of liquid stainless at just the right speed and temperature, and it would fuse just right.  Then a minor operation through a rolling mill to get the right surface finish, and BAM, rebar that lasts 5 times longer, at only about twice the price (some something like that, it was 10 years ago).  

[Joël Mercier 525]

Never thought I'd learn this much on rebar on here . 

[Alan Longmire 2,822]

Fair enough!    I was told that by an engineer who is very concerned about his bridges, and given I work for an organization that by definition is responsible for a lot of highway infrastructure I assumed he knew what he was talking about.  We do use a lot of epoxy coated grade 60 on structures, and epoxy coated grade 100 on ground anchors.I figured the grade 100 was probably the good stuff, even though, as I did say above, none of it is tool steel.

[Zeb Camper 782]

3 hours ago, Joël Mercier said:

Never thought I'd learn this much on rebar on here . 

No kidding !

[Jerrod Miller 463]

Rebar is fantastic compared to things like nails, screws, and staples.  Much like a cast iron anvil shaped object is better for moving metal than a sponge.  

[Joël Mercier 525]

All a matter of perspective, very poor perspective that is...

[Dan Bourlotos 26]

That ever so slight green tinge you see on window glass is actually due to small amounts of iron in the glass melt. Transition elements tend to make funky and unexpected colors in glass depending on the oxidation state. In the case of green-turquoise-blue  soda-lime glass, it is usually Fe(II). 

The fact that it appears as if there is no scale underneath means that it either reduced all the FeO on the surface (which isn't my first guess), or there was some sort of silicate material that was resting on the blade during heat up and as it melted it just picked up iron from the surface.  Could be sand, could be cheap ceramic blanket or low-temp fire bricks (both of which have a much higher silica percentage). 

What I find interesting though is the fact it isn't black. Normally, there is so much excess carbon floating around in a gas forge that any glass you see would turn black, just like the flux used in forge welding. I have used my forge to cast glass before and unless I ran SUPER lean on gas, it always turned black.