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Joe From NY
10-18-2010, 07:32 AM
I have a chunk of 1/2 inch steel that i am using to build a press brake. I ground the edge to a point along the length. I want to harden and temper this pointed edge. can anyone recommend a good procedure that i could do to get a good strong hard edge on the steel? (This photo was taken before i ground the edge.)

I don't know the grade. it is a piece of rail road scrap i found near the tracks.



http://i982.photobucket.com/albums/ae310/photospotxx/welding/CIMG3825Medium.jpg

http://i982.photobucket.com/albums/ae310/photospotxx/welding/CIMG3826Medium.jpg

MotorradMike
10-18-2010, 07:38 AM
You really need to know what sort of steel it is.
Some steels won't harden at all.

I don't know how to tell the type or even if it's possible to be certain.

JoeLee
10-18-2010, 08:04 AM
[quote=MotorradMike]You really need to know what sort of steel it is.
Some steels won't harden at all.

You can heat up a small piece to cherry red and dunk it in oil till it cools, then test it with a file. That will tell you if it's a steel that can be hardened.

JL.....................

Dunc
10-18-2010, 09:06 AM
Wondering if case hardening would be suitable?

Would it be possible to arc weld the surface with hard-surfacing rod as used on construction earth-moving equipment then re-grind to contour. Never done it, don't know if practical, just a thought.

gwilson
10-18-2010, 10:05 AM
Hard surfacing rod may be the best answer. Case hardening is only good for a small amount of depth,usually a few thousanths unless you can take exceptional measures. With a hunk of steel that big,i'd just use the rod.

TGTool
10-18-2010, 10:46 AM
He can use spark testing with a grinder to get an idea of high or low carbon content that would suggest whether it can be directly hardened or not. I'd suspect not but you never know till you try. Carburizing case hardening can provide a depth up to .050 or .060 which might be sufficient for his purposes. Other methods such as nitriding are usually limited to a shallower case but a harder surface.

jep24601
10-18-2010, 11:33 AM
I have made a scraper out of a reciprocating saw and the scraper blade is a piece of oil hardening ground stock. Should I temper to a blue color? or should it be harder than that for a scraper blade?

jungle_geo
10-18-2010, 12:02 PM
Using stick electrode hard-facing rod is probably your most economical solution. You could case harden it, but that would require a large enough oven at 1650F, lots of carbon (Kasenit), and the ability to quench it in a large tank. Hard-facing rod is easily obtained and not very difficult to apply; ask at your local welding supply.

camdigger
10-18-2010, 12:19 PM
Anyone recognize the part's original function?

The wear on the outside corner and the square bolt holes hint at a ground engaging tool/skid plate. If so, the material may be AR class material (aka abrasion resistant) and might be more difficult to heat treat than plain old carbon steel. The piece may be inherently harder and tougher than plain steel and might even work harden.

TGTool
10-18-2010, 12:25 PM
He'll need to regrind the edge if he's hard-faced it with welding rod so that would get him what he needs but there will be some work to do after the welding. If he's considering case hardening at all he ought to go to a commercial heat treater and just have it done there unless he already has a furnace big enough for the part. Kasenit would have the advantage that it could be applied just where he needed the hardness rather than all over, but my sense is that it doesn't give as good penetration as the atmosphere furnace or even pack hardening.

TGTool
10-18-2010, 12:29 PM
Anyone recognize the part's original function?

The wear on the outside corner and the square bolt holes hint at a ground engaging tool/skid plate. If so, the material may be AR class material (aka abrasion resistant) and might be more difficult to heat treat than plain old carbon steel. The piece may be inherently harder and tougher than plain steel and might even work harden.

So might be hard or tough enough for the OP's purposes already? That would be a nice piece of luck.

camdigger
10-18-2010, 12:40 PM
Might, maybe, perhaps.

The AR stuff is difficult to drill and difficult to weld as they need pre-heat and often post-heat as well as ductile welds to prevent cracking. That said, they stand up to the rigors of daily life for a front end loader bucket, etc.

Joe From NY
10-19-2010, 08:08 AM
I finished putting it together. It bent a an old piece of 5/8" flat like butter and it works fine for what i need, so i guess i wont do anything more to it, but i am curious about how to temper anyway. i will post another thread later on how i made it.

http://i982.photobucket.com/albums/ae310/photospotxx/welding/CIMG3837Medium.jpg

http://i982.photobucket.com/albums/ae310/photospotxx/welding/CIMG3838Medium.jpg

http://i982.photobucket.com/albums/ae310/photospotxx/welding/CIMG3839Medium.jpg

http://i982.photobucket.com/albums/ae310/photospotxx/welding/CIMG3840Medium.jpg

Joe From NY
10-19-2010, 08:08 AM
these two wouldnt fit.

http://i982.photobucket.com/albums/ae310/photospotxx/welding/CIMG3842Medium.jpg

http://i982.photobucket.com/albums/ae310/photospotxx/welding/CIMG3848Medium.jpg

camdigger
10-19-2010, 10:03 AM
Looks good Joe.


A couple minor suggestions.. Some light springs that slip over the guide rods placed on the guide rod before the upper die is put on will lift the upper die up after the bend, making repeating bends and work in general just a little easier.;) Here's mine. I never quite got to welding the guides to the upper die. I just slipped them on the guide rods as spacers so the spring would be long enough.
http://i766.photobucket.com/albums/xx301/camdigger/brakeinpress.jpg

The bottom plate looks a bit light for the job it has. In the picture it looks like the edge of the lower die lines up inside the rail of the press table which would subject it to bending. It won't be an issue for light work, but may be when you are working close to the press's capacity.

Yours looks better than mine, it has paint.

camdigger
10-19-2010, 11:14 AM
but i am curious about how to temper anyway.


As far as heat treating, there's enough variety in material and objectives to study it for one's life's work, with impressive time-temperature phase shift charts, pyrometers, and crystalline theory. For the gnat's eyelash analysis to be perfectly relevant, you need closely controlled ovens, temperature measuring apparatus,etc. You could start down that route, and it is a fascinating subject.

A quick and dirty way for carbon steels is to use a magnet, torch, a bucket of liquid (water, brine, or oil), and a kitchen oven or toaster oven.

The quick and dirty method is a two step process
1.) the quench - To get the material HARD, you need to raise it's temperature above it's transition temp (where all the crystalline structures change) and cool it fast enough that the crystalline structure doesn't have time to change back. The way the temperature is brought down that quickly is to submerge it in liquid.
An interesting phenomenon of carbon steels is that they change their reaction to magnets above their transition temperature the attractive force is markedly reduced above the transition temperature (often on the order of 1500 F or well into radiant red heat-the work glows red). So much for the theory...

In practice, it is far simpler. Heat the work with a torch. Propane is the slowest and may not be enough, depending on where you are working and how big the work is. Best is an oxy-acet torch. Heat the work and test it with the magnet. When the magnet is not attracted to the work, you're there. Continue to heat just long enough the work is heated through, then plunge into your bucket of liquid and hold it there until cool. There is so much heat energy moving around in the quench, it is the most dramatic event in the sequence. Oils can smoke and ignite.

The liquid is often called the quench media. Water is the cheapest, and least polluting. Almost any hardenable material will harden in a water quench. The issue is water sucks so much heat out of the work, some materials may crack from internal stresses and their own brittleness. These materials need an oil quench. Oils do not remove heat from the work as quickly as water does.

2.) tempering - as quenched materials are very hard, but also brittle. Tempering restores some of the materials' toughness while sacrificing some hardness by raising the temperature of the work to a lower temperature (on the order of 450 - 650F).
The next step is simple. Set the temp of the oven to 500F (or whatever you need for tempering temp) set the work on an oven rack and let it cook for 45 -60 minutes. Allow to cool.

Alternate method... Steels oxidize. The oxidation process speeds up with temperature. The amount of oxidation affects the apparent color of the surface of the steel.

In practice, to see this color change, the steel must be clean, so a quick rub of emery cloth, etc to polish the surface of the work is needed to remove any oxidation from the heat/quench cycle. Once the work is clean, it is gently heated. Typically the heat is applied away from the cutting/working edge. As heat is conducted through the work toward the edge, the surface of the steel will change color. When the right color reaches the working edge, the work is quenched again to stop the heat transfer. In blacksmithing, this is sometimes called "running the colors".

The amount of temper is tied to the color of oxidation so you often hear of work "tempered to a light straw" etc. The oxidation colors are quite attractive and moderately durable (although thin). Some work is left as is, other work has the oxidation coloring polished off. Interestingly, there is some artwork that is colored with a torch. That is oxidation coloring.

I'll look around for a color-temp chart. I've got a good one squirreled away somewhere.

Found it! Sadly, I don't remember where I got it or who originated it. I think it came from the Anvilfire site

http://i766.photobucket.com/albums/xx301/camdigger/Temperature_guide.jpg

Hmmm, me and photobucket apparently aren't getting along.... The chart is on the anvilfire site under something like "tempering colors"...

jep24601
10-19-2010, 11:37 AM
So what color (or temp) would you suggest I temper a machinist's scraper blade to, if it is made of oil hardening ground tool steel?

camdigger
10-19-2010, 11:55 AM
So what color (or temp) would you suggest I temper a machinist's scraper blade to, if it is made of oil hardening ground tool steel?
As a cutting tool sharpened with a stone rather than with a file or by raising a burr like wood scrapers, I'd suggest straw color +/- 430F. Hardness is a bigger issue than toughness, IMHO.

That temperature is easily reached in a toaster oven or a kitchen oven as it is close to the upper limit of the temperature range where baking and roasting is commonly done.

I talked to a knife maker at the local gun show that followed the practical side of the previous post, but insisted he got more consistent results from a second 30 minute soak at temper temperature. I dunno what that might do, but it works for him.

MichaelP
10-19-2010, 12:10 PM
When the right color reaches the working edge, the work is quenched again to stop the heat transfer.
I was under an impression that you don't quench, but rather let it cool slowly during tempering. Is the method you describe any different just because the heat is not applied directly to the area that needs tempering? Won't you create more internal stress in the surrounding areas (or leave it as hard and brittle as it was right after the initial hardening stage)?

camdigger
10-19-2010, 12:25 PM
I was under an impression that you don't quench, but rather let it cool slowly during tempering. Is the method you describe any different just because the heat is not applied directly to the area that needs tempering? Won't you create more internal stress in the surrounding areas (or leave it as hard and brittle as it was right after the initial hardening stage)?

With the quick and dirty method you have to quench a second time, otherwise, the heat energy will continue to travel out to the working edge portion of the work from the heated portion and raise its' temp above the target temp making it too soft. If you look in the "Bashing about" thread, I mention heating the spine of the knife and watching for color along the cutting edge. The picture of the knife doesn't show the oxidation colors as well as one might hope, but they were left there intentionally as the girls seem to find excuses to show off the knives and describe the process to anyone who'll listen "shrug". Stresses may build up, but compromises have to be made.... If you're cooking the work in an oven, you do have the option of cooling slowly and it is the preferred method.

As an interesting side note, long work like punches can be quenched and tempered in a single heat. You have to pay attention and follow the procedure, but it can be done.
Here's how. Heat the work to quenching temp. Dip the working end into the quench for about 1/3 of the length of the work. Cool until the quench water stops sizzling on the end. Pull the work out and quickly rub it on a piece of emery cloth to make a shiny stripe on it and watch for the temper colors to run from the unquenched area to the working edge. When the right "color front" reaches the working edge, requench to stop the heat transfer by cooling the whole workpiece. Not for a beginner, but still a time saver once you learn how.

planeman
10-19-2010, 12:43 PM
If you have an oxy-acetylene torch you can "flame-harden" it. You do this by heating the edge with a carbonizing flame which is set by reducing the oxygen in the flame so all of the acetylene doesn't burn leaving pure carbon left over in the flame. This carbon infuses into the semi-molten steel of the edge of the tool and hardens the surface.

I watched this being done on a huge steel gear about three feet in diameter at a LeTerneau-Westinghouse plant that made earth moving equipment many years ago. A fellow sat on a stool with the huge gear mounted on a shaft in front of him. He played the flame over each gear tooth one at a time slowly hardening each gear face.

Planeman

camdigger
10-19-2010, 12:45 PM
Rough and ready heat treating is more forgiving than other stuff we all do. Barring a catastrophic event like the work shattering from being too brittle, the whole heat treat sequence can be repeated if the final hardness is not to spec. Too many heats can lead to superficial chemistry changes - less cycles are better, but if the work is too soft or hard, the work can be salvaged instead of scrapped.

camdigger
10-19-2010, 12:51 PM
If you have an oxy-acetylene torch you can "flame-harden" it. You do this by heating the edge with a carbonizing flame which is set by reducing the oxygen in the flame so all of the acetylene doesn't burn leaving pure carbon left over in the flame. This carbon infuses into the semi-molten steel of the edge of the tool and hardens the surface.

I watched this being done on a huge steel gear about three feet in diameter at a LeTerneau-Westinghouse plant that made earth moving equipment many years ago. A fellow sat on a stool with the huge gear mounted on a shaft in front of him. He played the flame over each gear tooth one at a time slowly hardening each gear face.

Planeman


It is possible. I think it is most practical for large work where the heated zone is quite small compared to the size of the work. The torch heats a small area past the transition temperature simultaneously exposing the heated area to a carbon rich atmosphere while, by happy coincidence, the material is highly chemically reactive (willing to absorb more carbon). As the heated area moves away, the thermal mass of the work effectively quenches the treated area by conducting the heat away.

FWIW, the bed of my lathe was flame hardened. I'd be surprised if it was done by hand though.

MichaelP
10-19-2010, 01:12 PM
Camdigger, thank you.

Planeman, this is a slick way to combine regular flame hardening with case hardening. I read about it a few times in the past, but keep forgeting it for some reason. Thank you.

Evan
10-19-2010, 01:47 PM
One thing that wasn't mentioned is that even low carbon steels like mild 1018 steel can be hardened to some extent. The plain carbon steels also contain up to .9 percent manganese which provides some hardenability. Also, when quenching the rate of temperature change affects the final hardness. The fastest possible quench makes for higher hardness. When water quenching a brine solution will quench much faster than plain water. Using a brine quench with 1018 it is possible to bring sections below 2" to near RC38. Even better is if there is considerable agitation during the quench. For round bar items like punches, taps and hobs I chuck the item in a drill if possible and heat only the business end. Then plunge it into the brine while spinning it. This minimizes distortion and maximizes initial hardness. It isn't likely to crack with steels up to around 1040 or so.

Here is a colour chart.

http://ixian.ca/pics7/colortemp.jpg

camdigger
10-19-2010, 02:48 PM
I have no idea what photobucket's hissy fit was earlier, but here is another neat chart that shows hardness as related to temper colors. I've seen further references from assorted sources that recommend temper color by application, eg: straw/yellow for cutting tools, brown for forged carbon steel lathe tools, dark purple for springs, etc. Older Machinery's handbook maybe? "Farm Blacksmithing" by J.M. Drew reprinted by Algrove publishing for sure.

http://i766.photobucket.com/albums/xx301/camdigger/temper_colors_hardness_Page_1.jpg


As a note, the right hand column illustrates oxidation colors that are not reversible. The color exhibited by the work will be that corresponding to the maximum temperature reached in that heat cycle.

The left hand column represents radiant color - the work literally glows that color. The color changes with temperature (wavelength is a 4th order function of the absolute temp, IIRC) and is fully reversible. Radiant colors are difficult to see in direct sunlight. They are most obvious in low light conditions. This phenonmenon is used elsewhere like astronomy among other places. If we know the relationship between color(wavelength) and temperature, we can look at an object (or measure the wavelength of the light it emits) and work backwards to determine the object's temperature.