In case anyone was wondering, rebar is indeed any composition. Tonight I was forging on some and out of curiosity, cheezily heat treated one end (brought it to orange heat, quenched, reheated for a little longer than it took the water to boil off to sorta temper). Took a strike with the hammer and sure enough it broke. Spark test reveals something like 1040 but it must have some other alloying elements since it bears some resemblence to higher alloy steel (wrench stock for instance).
So yes, it's real crappy material. On the other hand. It can be hardened. What a scary thought, toolbits forged from rebar. Hmmmm. But still........
Tim
-- "I have misplaced my pants." - Homer Simpson | Electronics,
Not necessarily true, Tim. Rebar is available in heat treatable grades, so you may have landed on a piece of it. I recently had to weld some #5 bars to the top of a support beam, upon which I would place the blocks we're using to build our house. Before welding the rebar, I heated one to red heat and plunged it in water to be certain it wasn't medium carbon. It was just as soft after heating and quenching as it was before hand. The welding went well.
Normally rebar is not considered weldable. Weldable rebar actually has "weldable " imprinted on it along with the ribs. I have made crude chisels and centerpunches using this material. It must be remembered that structural grades of steel do not specify composition like SAE alloy numbers. There are ranges and limits on certain components but what is more important is the strength and yield points. How you get to that specification is the manufacturer's choice. For example a heavy thick section of beam will have more carbon in it that an small two inch angle iron. After coming off the rolling line one will cool to black in seconds while the other will take hours. Randy
I talked to the metalugist at North Star Steel in St. Paul about the issue. When they run the common Grade 40 and Grade 60 rebar, the only thing they have to hit is 40,000psi and 60,000psi respectively. Easiest way to get the 60,000 number is to let the carbon content float up to the .4 to .6% range. And this stuff will be unweldable, might be good for jackhammer bits!
You can buy weldable rebar, it should have 'weldable' impressed in the side every few feet. Keep in mind that SOME of the common rebar is weldable, just that you cannot be sure when you buy a bundle. And just because you get it from a commercial supplier does not mean you will be getting different stock than Home Depot.
BTW: The steel process is something to watch! 30 cars in, 60,000 pounds of molten steel out 4 hours later. Alloy ingredients show up in a wheelbarrow. Pour steel into continuous molds (copper with water cooling) 60' high. Cut the 4-1/2" square stock into
20' billets, send to the roll> In case anyone was wondering, rebar is indeed any composition. Tonight I
The question that begs to be asked is, what grade of rebar are you talking about? A-615, A-616, A-617, A-706, multi grade A706/A616? ASTM would probably dissagree with your conclusions that "rebar" (of unspecified type) is crappy material, as it has performed it's intended task for decades with very few failures. I have a very nice Sand's aluminum level on my truck that I bought as an apprentice and it has served me well for years. If you were to heat it and beat it into a chisel, you would be sorely dissapointed, and maybe call it junk, but as a level it's a real doozie.So that's what I use it for, mostly . All of the rebar grades are weldable using the proper procedure, A709 or multi grade is normally specified when a lot of welding is to be done. It will have a W stamped on it, or a W and a S if it's multi grade. These two types are easily welded with little or no preheat, depending on the size of the bar and ambient temp. The others take more time and trouble, but are weldable nonetheless. AWS D1.4 welding code addresses this pretty well.
Huh...didn't know rebar came in different grades, nor that it's *meant* to have carbon and hardness in it... All I knew was pretty much from a past thread here including similarly disparaging comments about A36. ;-)
Tim
-- "I have misplaced my pants." - Homer Simpson | Electronics,
When I was a construction engineer in El Paso 50 years ago, a friend of mine helped some Mexicans in Juarez with their re-bar mfg.plant---they'd take a sample bar from a heat and try to bend it---if it snapped-(usually after a much harder pull to bend) --he'd tell 'em " too many crankshafts in that batch "--
Rebar has to be able to be bent--so it can be placed > In case anyone was wondering, rebar is indeed any composition. Tonight I
I have been hauling scrap to a steel company in Cincinnati. They cast the long square bars and stockpile them for rolling, but they also have mountains of railroad axles which they put into the rolling mill with no alteration. I've seen truckloads of rebar leaving with heat mirage coming from them. I wonder what specific grade of rebar they get from the axles? Paul
On Wed, 3 Mar 2004 00:40:24 -0600, "Tim Williams" vaguely proposed a theory ......and in reply I say!:
I have _specs_ from BHP mregarding rebar. I get the impression it's case-hardened, with an underlying medium-carbon steel
They are this specific.
Locational Tack Welds Electrode Type Under-matching strength electrodes are preferred but matching strength may be used. Weld Length Not less than the size of the smaller bar. General Notes These are usually used for positioning and holding purposes, and in prefabricated elements. They must not be used for lifting purposes unless prior approval has been obtained from the design engineer (see AS/NZS 1554.3). They do not affect the strength of 500PLUS. Double Sided Lap Welds Electrode Type
500PLUS Rebar produced by the TEMPCORE process has a carbon equivalent (CE) limit of 0.39 max and, as such, requires no pre-heating prior to welding. Microalloyed 500PLUS coiled rebar has a carbon equivalent limit of
0.44 max, however, will still not require pre-heating when welded in accordance with the revised Welding Standard AS/NZS1554 part 3.
**** Other manufacturers? 500 MPa reinforcing steel may be made to higher CE limits and pre-heating may then be required in certain circumstances e.g. for tack & lap welding of larger bars.****
Users should also be aware that hydrogen controlled electrodes will be required for all weld types, and matching strength electrodes will be required for butt welds.
Welding is not allowed except for non structural rebar. It is mostly used as a grounding source in buildings, or to support rebar hoops in beams or the like. It is always tied using a tie wire. This method doesn't vary at all. I do see structural drawings where the engineer will specify grade 40 rebar to be welded. But, it is usually for electrical grounding purposes. Either a semiconductor plant being built, or overhead crane haunches as examples. Rebar is normally specified as grade 40, 60, or 75. There are other designations like A706 that are used too. but, each grade has a specified tensile strength. Grade 40 is 40,000. Grade 60 is 60,000 and grade 75 is
75,000 tensile strength. The markings you find on the side of the rebar tell you the grade of rebar, size, and the mill it was rolled from if it is domestic steel.
It changes the properties (resistance to bending, brittleness, etc) in a localized area, thereby creating a variable that won't work with the engineering formulae.
Torch cutting and torch bending are also verboten.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing. . . . DanG
Most rebar isn't suitable for welding. It'll crack at the welds due to the high carbon content. There is rebar available which is specifically alloyed for welding, and permanently marked to that effect, but most isn't, so the rules say don't weld it.
Realize that rebar is intended to be used only in tension, so there's no structural reason to weld it anyway.
actually, torch cutting is allowed. the amount of rebar that is affected by the torch is probably about half an inch and that is on the very end of the rebar. Not a very critical area. It is more common to torch cut slab steel and to field repair mis-fabricated rebar in beams and such. And slab steel is usually shipped in 40 foot and 60 foot stock lengths so the contractor can cut the bars to length instead of having to find one bar in 600 that is a certain length. That speeds up the time it takes to place a bar.
torch bending is definitely a no-no. But a good contractor will have the tool to bend up to a #7 (7/8 diameter) rebar.
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