abpt1
09-08-2010, 07:26 AM
Here is some info I pulled off the web.
General ghetto tech heat treat for medium carbon steels (4130). This is how I do it, but no recommendations or warrantees are expressed or implied here. This is for entertainment purposes only, the post below involves high temeratures, flammable and/or explosive gasses. Proceed entirely at your own risk. You could very easily hurt yourself & others and/or damage property and/or end up with a FUBAR'd receiver. I am well know having a loose grip on reality and to play fast and loose with the truth, blame anyone but me for any misfortune that befalls you. If things work out for you though, a small gratuity would be nice
Step 1: Heat the desired area to temerature it becomes non-magnetic.
On 4130 this equates to dull orange color, approximately 1550° F. The easiest way to find the correct temperature is to heat a scrap of the material with a torch and test the attraction of a large magnet as you heat it. It will be obvious when the steel looses its attraction for a magnet. Note the color of the steel at this temperature. Color of steel is a very good indicator of temperature. With a little practice you can recognize the correct color and it will always be the same color for that particular alloy. It would be nice to post a picture of the correct color, but with uncorrected color on my cheap camera, and unknown correction on different monitors displaying the picture, it could cause errors. A big/strong magnet and a test run on scrap will leave no doubt about the correct color.
Step 2: As soon as you have heated the area to be hardened to the correct color, quickly quench it.
Medium carbon steels like 4130 do best with a water quench. Higher carbon steel alloys will overharden in a water quench and break or shatter from internal stresses, they require an oil quench. There are some high tech alloys that require an air-quench and will shatter when quenched in oil. Low carbon steel won't harden well with any type of heat treatment and require case hardening. If you don't know what alloy you are working with, you will have to test a scrap and see what gives a satisfactory quench. Heat a scrap to non-magnetic color and quench it in oil. Test with a file to see if it is hardened. A file should have a very difficult time marking a hardened, undrawn piece. If it isn't hardened, heat it back up and quench in water. See if it shatters when quenched, if so it is a oil quench alloy. Test the hardness with a file. If it hasn't hardened much with a water quench, you have a sample of low carbon steel which can be case hardened, but won't heat treat.
Quenching water should be luke warm. Transmission fluid makes very good quenching oil. When quenching in oil, be prepared for smoke and the possibility of the oil igniting.
Step 3: After quenching, the material will be very brittle and requires drawing some of the hardness. Heat the piece to the correct temperature to draw and let it air cool.
The correct temperature to draw 4130 is about 700° F. The easiest indicator for this temperature is the metal should turn a blue color under good lighting, almost looking like blued gunmetal. Once it reaches the temperature and turns blue the color will persist after cooling. The blue color can be rubbed off with a wire brush or sand paper. The way I reach this temperature is to pre-heat the whole receiver (with spot hardened points already done) in my kitchen oven. My oven only goes to 550° so I preheat the receiver to that temp for 45 minutes. When preheated, I open the oven door just enough to get a propane torch flame on the spot hardened points. I quickly heat them to the "blue" temperature, it requires good light on the receiver to see the color change well. As soon as all points are "blued" (about 15-20 secs per point direct flame), I shut the oven door and let the temperature inside stabilize. I then shut off the oven and allow to cool normally without opening the door till cool.
Various notes and observations:
Testing scraps of metal will demonstrate heat treating better than any written instuctions. A three corner file is a great "ghetto tech" testing tool that will show what happens at each step. File on an untreated scrap with the corner of the file. It will cut a notch easily. Harden the same piece by heating and quenching. Now the file has a tough time even marking the steel. Bend the hardened scrap, hit the scrap on an anvil. Cracks and breaks, doesn't it? Draw the temper in an oven. Now the file will cut, but not as easily as on an untreated scrap. Hit it with the hammer, it shouldn't break, but it should be less ductile than an untreated scrap.
There is a broad range of hardness that you can draw to by changing the drawing temperature and time, and the cooling rate. This is mostly beyond the scope of at home "ghetto tech" but it is fun to experiment. Less temperature and time spent on drawing will yield a harder and more brittle treatment.
When a receiver is spot hardened, as opposed to heat treated in its entirety, a "composite" structure is created. This composite structure can be made superior to any whole-unit heat treatment. The structure of the receiver can be made superhard at the points that require hardness, yet the hard points can be supported by unhardened areas adjacent to the hardened spots. This support allows a harder area to keep from cracking or breaking than is possible in a receiver that is heat treated all over. A receiver that is treated whole will "ring like a bell" which shows that vibrations are travelling through the receiver where they can concentrate stresses at specific areas and crack them over time. A spot hardened receiver will have a "duller" sound when struck, which shows that vibrations are damped out and absorbed throughout the receiver. In no way would I claim that a home "ghetto teched" spot hardened receiver is superior to one done at a professional heat treating shop. With a little practice it is easy to treat one at home where the heat treament won't be an issue though. It is pretty easy to do it "good enough" for a long lasting AK.
General ghetto tech heat treat for medium carbon steels (4130). This is how I do it, but no recommendations or warrantees are expressed or implied here. This is for entertainment purposes only, the post below involves high temeratures, flammable and/or explosive gasses. Proceed entirely at your own risk. You could very easily hurt yourself & others and/or damage property and/or end up with a FUBAR'd receiver. I am well know having a loose grip on reality and to play fast and loose with the truth, blame anyone but me for any misfortune that befalls you. If things work out for you though, a small gratuity would be nice
Step 1: Heat the desired area to temerature it becomes non-magnetic.
On 4130 this equates to dull orange color, approximately 1550° F. The easiest way to find the correct temperature is to heat a scrap of the material with a torch and test the attraction of a large magnet as you heat it. It will be obvious when the steel looses its attraction for a magnet. Note the color of the steel at this temperature. Color of steel is a very good indicator of temperature. With a little practice you can recognize the correct color and it will always be the same color for that particular alloy. It would be nice to post a picture of the correct color, but with uncorrected color on my cheap camera, and unknown correction on different monitors displaying the picture, it could cause errors. A big/strong magnet and a test run on scrap will leave no doubt about the correct color.
Step 2: As soon as you have heated the area to be hardened to the correct color, quickly quench it.
Medium carbon steels like 4130 do best with a water quench. Higher carbon steel alloys will overharden in a water quench and break or shatter from internal stresses, they require an oil quench. There are some high tech alloys that require an air-quench and will shatter when quenched in oil. Low carbon steel won't harden well with any type of heat treatment and require case hardening. If you don't know what alloy you are working with, you will have to test a scrap and see what gives a satisfactory quench. Heat a scrap to non-magnetic color and quench it in oil. Test with a file to see if it is hardened. A file should have a very difficult time marking a hardened, undrawn piece. If it isn't hardened, heat it back up and quench in water. See if it shatters when quenched, if so it is a oil quench alloy. Test the hardness with a file. If it hasn't hardened much with a water quench, you have a sample of low carbon steel which can be case hardened, but won't heat treat.
Quenching water should be luke warm. Transmission fluid makes very good quenching oil. When quenching in oil, be prepared for smoke and the possibility of the oil igniting.
Step 3: After quenching, the material will be very brittle and requires drawing some of the hardness. Heat the piece to the correct temperature to draw and let it air cool.
The correct temperature to draw 4130 is about 700° F. The easiest indicator for this temperature is the metal should turn a blue color under good lighting, almost looking like blued gunmetal. Once it reaches the temperature and turns blue the color will persist after cooling. The blue color can be rubbed off with a wire brush or sand paper. The way I reach this temperature is to pre-heat the whole receiver (with spot hardened points already done) in my kitchen oven. My oven only goes to 550° so I preheat the receiver to that temp for 45 minutes. When preheated, I open the oven door just enough to get a propane torch flame on the spot hardened points. I quickly heat them to the "blue" temperature, it requires good light on the receiver to see the color change well. As soon as all points are "blued" (about 15-20 secs per point direct flame), I shut the oven door and let the temperature inside stabilize. I then shut off the oven and allow to cool normally without opening the door till cool.
Various notes and observations:
Testing scraps of metal will demonstrate heat treating better than any written instuctions. A three corner file is a great "ghetto tech" testing tool that will show what happens at each step. File on an untreated scrap with the corner of the file. It will cut a notch easily. Harden the same piece by heating and quenching. Now the file has a tough time even marking the steel. Bend the hardened scrap, hit the scrap on an anvil. Cracks and breaks, doesn't it? Draw the temper in an oven. Now the file will cut, but not as easily as on an untreated scrap. Hit it with the hammer, it shouldn't break, but it should be less ductile than an untreated scrap.
There is a broad range of hardness that you can draw to by changing the drawing temperature and time, and the cooling rate. This is mostly beyond the scope of at home "ghetto tech" but it is fun to experiment. Less temperature and time spent on drawing will yield a harder and more brittle treatment.
When a receiver is spot hardened, as opposed to heat treated in its entirety, a "composite" structure is created. This composite structure can be made superior to any whole-unit heat treatment. The structure of the receiver can be made superhard at the points that require hardness, yet the hard points can be supported by unhardened areas adjacent to the hardened spots. This support allows a harder area to keep from cracking or breaking than is possible in a receiver that is heat treated all over. A receiver that is treated whole will "ring like a bell" which shows that vibrations are travelling through the receiver where they can concentrate stresses at specific areas and crack them over time. A spot hardened receiver will have a "duller" sound when struck, which shows that vibrations are damped out and absorbed throughout the receiver. In no way would I claim that a home "ghetto teched" spot hardened receiver is superior to one done at a professional heat treating shop. With a little practice it is easy to treat one at home where the heat treament won't be an issue though. It is pretty easy to do it "good enough" for a long lasting AK.