Off Topic Massive heat treating ovens?

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tr3yanderson

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So not knife related but it is about steel. Since I got into this hobby, steel is on the mind quite often. The other day while driving to work there is an overpass being built over the freeway and I was noticing the massive I beams. I thought surely you would want those to be heat treated for added strength, but then I wondered how the heck does something like that get heat treated?

Does anyone know whether they heat treat things like that? then that gets me wondering what the biggest things that have been heat treated and how they do it? I'd like to see that process. Anyone here know anything about this?

Cheers,
 
Battleship armor. Huge slabs of steel - like a foot or more thick - used to be face hardened on the exterior side to help deflect incoming shells, but left at a lower carbon content to reduce the chance of spalling on the interior side. The armor would be kept heated and exposed to a carbon source for days in some cases. Look up "cemented armor" if you are curious about it.

I think any piece of steel that the steel companies are capable of making could be heat treated one way or another. It's just a matter of how much money you are able to spend and what you are trying to accomplish. Whether the I beams on a highway overpass are heat treated, I don't have a clue.
 
Yes there are huge ovens that could HT a giant I-beam. However, for construction purposes, I think the material is either not hardened, or it is "Q&T" (quenched and tempered) - meaning it was hardened and tempered at the mill during manufacture. Think of an armored truck - it is fabricated from pre-heat-treated steel (such as AR500). It is not re-hardened after welding.

Although hardness and strength usually go hand-in-hand, in the construction world, hardness is usually considered an undesirable side-effect of increased strength. Brittleness is an absolute no-no because it leads to unpredictable and catastrophic failure, so everything possible is done to avoid brittleness, even if that means sacrificing some strength or hardness.

You can see the mechanical properties of a typical construction grade of steel here http://www.matweb.com/search/datasheet.aspx?matguid=9ced5dc901c54bd1aef19403d0385d7f&ckck=1
 
Those big steel I-beams are not heat treated. They are, however, manufactured with a "crown", so when they're loaded to full capacity, they're almost flat. Look at an empty flatbed semi trailer as an example.

Big things that are heat treated, like massive heavy equipment parts, are usually heated with an induction coil, or case hardened using different methods (none of which require the entire giant part to be in a giant oven).
 
It's not easy to make hardened steel. There have been a lot of talk in the past of using hardened steel to make ultralight and strong cars, but today we are still stuck with cars made out of aluminum and unhardened steel. If it was easy to heat treat large steel parts, I'd imagine that they would be using it already to make cars.
 
My employer has a furnace that can heat treat 140 foot long fabrications and forgings, it's loaded with multiple train cars. It's fired with natural gas, and has around 82 burners.

I misspoke earlier, I asked the furnace operator for clarification.
 
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tr3yanderson said:
That is really cool. what is done for quenching?
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Sorry I misspoke on the size earlier I updated my post after I got clarification, I asked the furnace operator. It's 140 foot long by 16 foot wide inside, and has 82 burners. It's for stress relieving so there isn't a quench.

I had never been down there before personally, looked bigger than that from the outside.
 
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cotdt said:
It's not easy to make hardened steel. There have been a lot of talk in the past of using hardened steel to make ultralight and strong cars, but today we are still stuck with cars made out of aluminum and unhardened steel. If it was easy to heat treat large steel parts, I'd imagine that they would be using it already to make cars.
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I don t think that it is good idea to make cars from hardened steel.........
 
Most of what we stress relieve after welding are fabrications made of A36 and A572, some of the fabrications that we produce can have up to 4 inch or larger fillet welds. Needless to say that putting that much welding wire into a large bevel tends to introduce a lot of stress and warp the part. I've seen 5 inch thick plate move over a half inch from welding, so you can imagine how much stress is created.

As far as heat treating forgings, we've machined forgings that where close to 4340 in composition that came to us at around 220,000 lbs and left at around 130,000 pounds. After we machined them, they went else where for heat treating as they are shaping dies for large forging presses. I'm told from some of the truck drivers that came back to bring us more forgings that some of the prior ones had exploded during heat treatment and large sections blew out of the forging. I found out later that the forging company tried producing them in more than one pour because they where so large and that's what was causing the issues.
 
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Spent a few years in a couple of northern Indiana steel mills, mostly flat product (slabs, plate, sheet and coils, so I can't really speak for I-beams, but the flat stuff could be and was very often heat treated. The furnaces that heated the slabs for the rolling process were more than big enough to heat multiple slabs at once, though most of the heat treatment came after the slab was rolled and coiled. Depending on the application, the coils were often stacked eye side up in vertical furnaces to be annealed (Batch Anneal), or a lot of the automotive product was uncoiled and ran through large furnaces (several stories tall and 100's of feet long) to be cooled down and recoiled at the other end. This was the CHTL or Continuous Heat Treat Line. The HDCL (Hot Dip Coating Line or Galv line) had similar furnaces, though they were taylored more for making zinc stick to the sheet than necessarily heat treating the product. There was also a "temper mill" or a single stand, which didn't really use heat or a furnace, but used a cold rolling process to impart certain properties to the steel, from surface finish to tensile strength and a number of other things.

I imagine that a lot of a I-beam's properties are imparted from the rolling process, as much as the chemistry of the steel and he casting/forming process.
 
Larrin said:
The big batch furnaces don’t really do a conventional quench and temper process. Cooling those is on the order of hours, a full cycle is days.
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Yeah, batch annealing could be a 2-3 day process for some of the coil stacks, if I remember right.

Some of the old timers I used to work with told me they used to cool the hot band coils off in Lake Michigan on rare occasion. Not so much for treatment, but to get them out the door faster. Coils could take 2-3 days to cool enough to run through the pickling line in some cases.

After they got down to around 300 or 400 degrees, some guys used to bake their lunch in the coil eyes. I’m told that a guy roasted a whole turkey in one once. :D
 
I worked QA for a door company that made steel insulated doors. We bought coil from 0.017 to 0.025 or so for door skins, which were stamped with emboss patterns like you see on a typical residential steel door. Learning about the steel was fascinating. Had to self educate on tensile, yield, elongation, flatness, etc. You wouldn't think it would have been a complicated process, but when you are trying to bang out a zillion door skins as quickly as possible with the most inexpensive steel you can get away with, the material properties get pretty critical.

We had extruded aluminum, several different kinds of molded and extruded plastics, glass, wood, fiberglass, paint... Most interesting job I ever had.

GB
 
Some of the "strongest" steels are the low carbon nickel steels used for things like submarine pressure hulls.They were initially used as "structural" steel in ships for sections under 4 inches thick and called "STS" or "special treatment steel. They were kndof a modification fo the Krupp type armor steel and made by Carnegie Steel in 1910. It turned out that they were as effective as armor as the older style face hardened armor plate and better when hit from off angles. Eventually more and more of the ships were built using that type of steel. These developed into lower carbon versions which were called "high yield" steel. The stuff used during WW2 would today be classified as something like HY 42 steel (42 being how strong it was, 42,000 fr pounds or whatever) and those original HY steels were the predecessors of the more modern stuff like HY80, HY 100 and HY130 steel. HY80 was used on subs up through the improved Los Angeles. The Seawolf and Virginia classes use HY100.
 
Just a comment for readers who are new or less experienced in these metallurgical things:

Heat Treatment is not just hardening blades. ALL thermal processing - heating and cooling - done to steel are part of its heat treatment. This includes stress relief, annealing, tempering, and of course hardening. Some of these processes can be mechanically induced by rolling, like specific "tempers" of hardness on sheet stock.

The same goes for knives, heat treatment is all the thermal processes done to get the finished blade qualities. It is redundant to say, "I heat treated and tempered the blade at …."
 
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