Post by phoenix1967 on May 18, 2009 7:23:08 GMT -5
If Life's a box of chocolates, then heat treating is baking cookies for a bake sale. There is a specific recipe to follow for best results.
Knowing what type of steel you are using is important... The chemistry of the steel will change the baking instructions just as much as changing from chocolate chip to gingerbread will in the cookies analogy.
The methodology is simple... Heat to the correct temperature, Quench, heat again to temper, and let cool.
The VARIABLES are temp, time, and what you quench in.
For the purposes of this guide, I'm going to give you a rule of thumb
recipe that will work for MOST knife steels. Keep in mind, that as with ANY "do it all" anything, it will not get the MOST out of any particular steel, but it will do passably for most simple carbon steels, and a lot of the alloy steels as well. This is intended as a beginners guide, I will go into all the techno geek chemistry and physics in a later, more advanced guidepost.
Step one: Normalizing
after you have finnished beating, twisting, bending, and grinding your steel into a roughly knife shaped object, the steel is chock full of highly stressed spots, kinda like lumps in gravy. heating and quenching with the steel in this state is likely to warp, break, or crack the blade. we want to get the steel nice and relaxed first, before we super stress it in the quench. to do this, we heat the steel to a nice even red, and let it cool back to a point that you can pick it up. straighten any warps or twists. Heat it back up to a dull red, and let it cool again. Straighten again. Continue to do this until the warping stops. Once the blade stays straight after normalizing, (that's what ya been doing, you just didnt know it), we are ready for the next step.
Step 2: Heat to critical
Here is a point of confusion among most beginners, and some even that have been doing it a while. You will hear "Heat it till a magnet wont stick to it and quench" Now this WILL harden a blade, but it will not convert most of the blade to martensite (the fandangled word for the good steel) To use our cookie analogy this is kinda like throwing all of the ingredients in a bowl and shoving it in the oven without mixing it. sure ther will be some bits of the resulting blob that will kinda resemble a Cookie...
When steel hits the critical temp (usually a color shade or two ABOVE non-magnetic) some truly interesting things happen... all of the carbon and other alloying agents begin to go into solution, like ingredients that were trapped in ice that is beginning to melt. It is important to give the steel time at that temperature to get all of the carbon and other stuff evenly distrubuted throughout.
So to recap step 2, heat to a shade or two above non-magnetic, hold at that color for 5-10 minutes, then... on to the next step
Step 3: The quench
Now that we have all of the alloying agents evenly distributed, we want to Flash Freeze them in that state. A light oil, like canola or mineral oil works well for most blade steels at a warm 120 to 130 degrees. Remove from the heat and immediately immerse the blade quickly into the quench medium, preferably point down (vertical). If you cannot go point down, go edge first. DO NOT SWISH IT AROUND. This will cause uneven cooling, making the blade warp at best, and break at worst. Once the blade has stopped boiling the oil around it, it's time for the final step.
Step 4: Temper Temper!
Temper is a word that is often misused, and poorly understood by most. Many folks believe that tempering is hardening of the blade. Older generations are likely to blame for this, as it was common in the past to call a tool or blades final hardness as it's "TEMPER" In that sense, Temper meant the entire heat treating process's final result. For our purposes, "Tempering" is used to soften the steel a little, while making it MUCH more resistant to breakage. The best overall way I have found to do this, on a beginner's budget, is to preheat a panfull of dry sand to 400 degree's in the oven (use a turkey thermometer, your oven display isn't usually too accurate)
Once you remove the blade from the quench, wipe off the oil, scuff the surface a bit with some sandpaper, and place it in the hot sand of the oven for an hour or two. Remove the blade from the sand, let cool enough that you can hold it in ungloved hands. Look at your scuff marks from the sandpaper... you should see a color anywhere from a dark straw to a brownish purple. Place the steel back in the sand, and cook it for anouther hour or two. once done, remove it and let it cool.
You have now made a blade that is hard and tough, and ready for finishing!
So, to sum up:
Normalize: heat to red, straighten, repeat till the blade stays straight when heated
Heat to critical: heat to a color shade or two above non-Magnetic, and hold for 5 to 10 minutes at that color.
Quench: Immediately fully immerse point or edge down in the quenchant till all boiling stops.
Temper: Place in 400 deg heated sand for an hour or two, let cool, then do it again.
Hope this helps. I'm leaving this thread open to questions and answers, as I believe the questions can be more informative than the text
Knowing what type of steel you are using is important... The chemistry of the steel will change the baking instructions just as much as changing from chocolate chip to gingerbread will in the cookies analogy.
The methodology is simple... Heat to the correct temperature, Quench, heat again to temper, and let cool.
The VARIABLES are temp, time, and what you quench in.
For the purposes of this guide, I'm going to give you a rule of thumb
recipe that will work for MOST knife steels. Keep in mind, that as with ANY "do it all" anything, it will not get the MOST out of any particular steel, but it will do passably for most simple carbon steels, and a lot of the alloy steels as well. This is intended as a beginners guide, I will go into all the techno geek chemistry and physics in a later, more advanced guidepost.
Step one: Normalizing
after you have finnished beating, twisting, bending, and grinding your steel into a roughly knife shaped object, the steel is chock full of highly stressed spots, kinda like lumps in gravy. heating and quenching with the steel in this state is likely to warp, break, or crack the blade. we want to get the steel nice and relaxed first, before we super stress it in the quench. to do this, we heat the steel to a nice even red, and let it cool back to a point that you can pick it up. straighten any warps or twists. Heat it back up to a dull red, and let it cool again. Straighten again. Continue to do this until the warping stops. Once the blade stays straight after normalizing, (that's what ya been doing, you just didnt know it), we are ready for the next step.
Step 2: Heat to critical
Here is a point of confusion among most beginners, and some even that have been doing it a while. You will hear "Heat it till a magnet wont stick to it and quench" Now this WILL harden a blade, but it will not convert most of the blade to martensite (the fandangled word for the good steel) To use our cookie analogy this is kinda like throwing all of the ingredients in a bowl and shoving it in the oven without mixing it. sure ther will be some bits of the resulting blob that will kinda resemble a Cookie...
When steel hits the critical temp (usually a color shade or two ABOVE non-magnetic) some truly interesting things happen... all of the carbon and other alloying agents begin to go into solution, like ingredients that were trapped in ice that is beginning to melt. It is important to give the steel time at that temperature to get all of the carbon and other stuff evenly distrubuted throughout.
So to recap step 2, heat to a shade or two above non-magnetic, hold at that color for 5-10 minutes, then... on to the next step
Step 3: The quench
Now that we have all of the alloying agents evenly distributed, we want to Flash Freeze them in that state. A light oil, like canola or mineral oil works well for most blade steels at a warm 120 to 130 degrees. Remove from the heat and immediately immerse the blade quickly into the quench medium, preferably point down (vertical). If you cannot go point down, go edge first. DO NOT SWISH IT AROUND. This will cause uneven cooling, making the blade warp at best, and break at worst. Once the blade has stopped boiling the oil around it, it's time for the final step.
Step 4: Temper Temper!
Temper is a word that is often misused, and poorly understood by most. Many folks believe that tempering is hardening of the blade. Older generations are likely to blame for this, as it was common in the past to call a tool or blades final hardness as it's "TEMPER" In that sense, Temper meant the entire heat treating process's final result. For our purposes, "Tempering" is used to soften the steel a little, while making it MUCH more resistant to breakage. The best overall way I have found to do this, on a beginner's budget, is to preheat a panfull of dry sand to 400 degree's in the oven (use a turkey thermometer, your oven display isn't usually too accurate)
Once you remove the blade from the quench, wipe off the oil, scuff the surface a bit with some sandpaper, and place it in the hot sand of the oven for an hour or two. Remove the blade from the sand, let cool enough that you can hold it in ungloved hands. Look at your scuff marks from the sandpaper... you should see a color anywhere from a dark straw to a brownish purple. Place the steel back in the sand, and cook it for anouther hour or two. once done, remove it and let it cool.
You have now made a blade that is hard and tough, and ready for finishing!
So, to sum up:
Normalize: heat to red, straighten, repeat till the blade stays straight when heated
Heat to critical: heat to a color shade or two above non-Magnetic, and hold for 5 to 10 minutes at that color.
Quench: Immediately fully immerse point or edge down in the quenchant till all boiling stops.
Temper: Place in 400 deg heated sand for an hour or two, let cool, then do it again.
Hope this helps. I'm leaving this thread open to questions and answers, as I believe the questions can be more informative than the text