ThomasPowers Posted December 20, 2020 Posted December 20, 2020 Velegski; transformation from austenite to martensite is usually a hardening step not a tempering step; however may I commend to your attention "cryo quenching" used to get retained austenite to transform to martensite---necessitating another tempering cycle afterwards of course! It, of course, is most useful for alloys that tend to retain a lot of austenite after more "normal" quenching. Quote
velegski Posted December 20, 2020 Posted December 20, 2020 Mr. Powers. Thanks, as I've stated earlier I'm still trying to wrap my head around the heat treat, temper process. Funny that you mentioned Cryo. I know of the process but never attempted it. And cold treatments are the next chapter in a book by Dr. Thomas. Thanks Quote
pnut Posted December 21, 2020 Posted December 21, 2020 This was posted by Steve sells in the heat treating knives and blades forum under the sub forum introduction to heat treating. (Tempering relaxes the thermal shock we caused during the hardening process, all hardened blade should at least get a hour or more to relieve the stress. Most take only 320F or so, and I prefer 350F two times at two hours each, with a rest period of one day between. When we harden the blade, there may be retained austenite, rather a small amount of the austenite that has not yet converted to martensite. This will convert into martensite after some time as room temperature or lower, and that is the reason for a second temper cycle, to relieve that also. This is also one reason many use a sub zero quench, for advanced steel treatment, to force the change into martensite.) This is why I asked the question about retained austenite and the need to wait between tempering cycles. Pnut Quote
Bad_Rockk Posted December 22, 2020 Author Posted December 22, 2020 Still waiting for the thermometer but already thinking about the next steps. I want to try an etch with orange juice. I know the patina won't last forever but I want to make my own long term testing with normal kitchen use. The question is can I do the etch before I epoxy the scales? Or does the etching has a negative influence on the bonding of the epoxy? Quote
Frazer Posted December 22, 2020 Posted December 22, 2020 With damascus I have not had any issues with the epoxy not bonding well after etching. Just clean the steel well with acetone or some other streak free cleaner before you glue it up. If anything I would think the rougher surface caused by etching would make the bond stronger rather than weaker, but I'm not going to say that with any certainty. Quote
ThomasPowers Posted December 22, 2020 Posted December 22, 2020 Yes; a stronger bond *if* you clean off any of the loose oxidation products first. Ever hear of etching primers for painting metal? Quote
Bad_Rockk Posted December 22, 2020 Author Posted December 22, 2020 Hi Frazer, hi Thomas, Tank you for your replies. Yes i heard of of such primers but more for painting wood/concrete. I'm new to metal working. My only practical experience is a two week basic metal working class bevor studies. So please excuse if some questions are very basic. Quote
Frazer Posted December 22, 2020 Posted December 22, 2020 Always better to ask in my opinion, no worries. Unfortunately, we aren't born knowing everything. Quote
ThomasPowers Posted December 22, 2020 Posted December 22, 2020 Not a problem; I was just truing to give an example of a similar case where it's not only a positive thing but strongly suggested! Quote
Bad_Rockk Posted December 25, 2020 Author Posted December 25, 2020 Hi, the thermometer arrived and I put it in the oven to check the temperatures during Christmas cooking. All temperatures were about 5-10 K lower than the dialed temperature. I think I used a wrong operation mode when I tempered the blade. I don't know the Englisch expression for it but there is a fan running in the oven to move the air in the oven. Thought it would result in a more even heat distribution but it didn't. Next time I use another mode for the tempering. Also worked on knife #2 witch is made out of the left over part of the farriers rasp. But this brought me to hospital this morning. I had a respirator and eye protection glasses on while working the profile with the angle grinder but somehow a metal fragment got in my eye. Kept me awake to nights... Luckily the doc could remove it without any big problems. Quote
pnut Posted December 25, 2020 Posted December 25, 2020 The metal fragment might have been in your eyebrow. I've had it happen before. It used to happen pretty frequently at the rubber refinery when I was compounding batches until I started wearing a bandana very low on my forehead. Pnut Quote
ThomasPowers Posted December 25, 2020 Posted December 25, 2020 I've had a piece lodge in my hair and fall into my eye when I took off my PPE too. I keep a disk drive magnet to pull stuff out if it's just riding on the surface. Not often mentioned but; high quality tweezers, a lighted magnifier on a base, a magnifying cosmetic mirror, and the disk drive magnet are all part of a good metalworker's first aid "kit". (Not to mention crazy glue, silvadene, and an antibiotic ointment...) Quote
Bad_Rockk Posted December 28, 2020 Author Posted December 28, 2020 Hi, I have the first aid kit ready. The tempering is done and the blade reached straw colour. With the right oven mode the temperature was pretty accurate. Unfortunately the blade bend like a banana. I will try to correct it in the vice using bolts and if that doesn't work I ordered some metal clamps to try the re-bend using coins and angle iron in a tempering cycle. Also did some vegetable cutting to get a feeling of the knife profile. Due to the thick spine the knife won't be a perfect slicer. And without the scales it is a bit heavy towards the tip. Knife #2 I will file with a thinner spine and maybe try to achieve a distal taper. Have to figure out how to achieve such a low angle with my jig. Keeping the edge thickness around 1.5-2 mm. Quote
Bad_Rockk Posted December 29, 2020 Author Posted December 29, 2020 Finished the sanding of knife #1 today. It's not perfect but ok. Next will be the scales and I'm looking forward on this. Also worked on knife #2 and became impatient... Hand filing the bevels take hours so I tried the 3x20 belt grinder again. Its not made for knifes but it removes metal faster than hand filing. And I learned that I have to work with a guide for the plunge lines. It takes just one moment and a crisp line is gone... Got an old 3 HP motor and I want to build a very basic 2x72 belt grinder. Nothing fancy just enough to speed up the bevel grinding. Quote
Bad_Rockk Posted November 4, 2022 Author Posted November 4, 2022 After almost 2 years I finished my first knife this week. It's not perfect but I'm proud of it. I sharpens it on my water stones and now it has to proof it's functionality in every day kitchen usage. Quote
Frosty Posted November 5, 2022 Posted November 5, 2022 Please be aware that the rasp teeth "texture" you left on the blade will make it very hard to sterilize for safe food contact. Frosty The Lucky. Quote
Bad_Rockk Posted November 7, 2022 Author Posted November 7, 2022 Hi Frosty, yes that's true. I recognized that issue while using the knife, too. But for veggies it is not a big problem. I keep that in mind for the next one. Quote
Frosty Posted November 7, 2022 Posted November 7, 2022 It looks cool though it's a problem. I suggest a little Chlorine laundry bleach in the wash. You'll want to rinse immediately and oil it or the chlorine will rust it quickly. IIRC something like 5% if you let it soak a minute or so. I'm not sure about time or concentration though. Frosty The Lucky. Quote
Bad_Rockk Posted November 8, 2022 Author Posted November 8, 2022 Hi Frosty, why do you suggest such a sterilization when only vegetables will be cut with this knife? I never worried about sterilization my other stainless knifes (no such texture) after cutting vegetables. Normally I rinse them with clear water and dry them. After cutting meat I use regular dish soap. Quote
JHCC Posted November 8, 2022 Posted November 8, 2022 Basic food safety requires elimination of all bacteria from any surface that comes in contact with food. While a smooth knife is easily washed, any knife with a textured blade provides lots of places for bacteria to hide and thus requires additional precautions. It's true that vegetables aren't generally as much a problem as animal products (meat, fish, dairy), but you should still be careful. Cross-contamination is a thing, and if listeria monocytogenes finds a way to make a home in the recesses of a knife that isn't getting fully cleaned, things can get messy. Quote
gewoon ik Posted November 8, 2022 Posted November 8, 2022 Pour boiling water over the knife. Does not need to be all that complex. Quote
Bad_Rockk Posted November 8, 2022 Author Posted November 8, 2022 Hi guys, thanks for the explanation. I think I'll rework the textured area to achiev a smooth surface. I'll try to grind carefully and reduce the spine thickness as much as possible without overheating. Here is knife No. 2: I started this before the workrest of the 2x72 was finished. So free hand grinding. Because of that the edge already got too thin and I lost some blade height. For the next one I made a simple Bevel jig to avoid that. I already removed the texture. When I came back from the shop my wife told me: Everytime you come back from working in the shed, you're happy! And I have to admit that it's true. It's satisfying to create something on your own. And with the 2x72 it's much easier and faster than filing. Quote
ThomasPowers Posted November 8, 2022 Posted November 8, 2022 My wife claims working in my smithy cures "constipation of the soul"! Quote
Frosty Posted November 8, 2022 Posted November 8, 2022 Sorry, pouring boiling water over something won't kill "all" microorganisms. The blade would need to be boiled for up to 5 minutes. Even then many organisms go dormant and the spores can be very hard to kill by denaturing the proteins. 5 minutes in boiling water gets most of them but not all. That is why autoclaves use pressurized steam, Steam can be much hotter than 100c. Just googled it for good #s. Typical autoclave temp and pressure for unwrapped items. 121c / 250f @ 15psi for 15 minutes. Lightly wrapped items get 132c / 270f. @ 30psi for 8 minutes, Tightly wrapped items . . . Heck here's a chart. https://sterilizers.com/autoclave-time-temperature-pressure-chart.html Yes, I searched and refreshed my memory about this stuff, I lost a bet years ago about what can survive boiling water. Some like yeasts benefit from a little boiling and no, not all yeast is good stuff. A little chlorine bleach kills almost anything, some molds need more serious toxins and I'm sure there are others. It doesn't take much % or time but it MUST come in contact with the organism to kill it so not even a silly strong chlorine dilution will sterilize things with cavities it can't "wet." A little dish soap emulsifies fats so water can carry it away, it "wets" fats and fat covered stuff. Products like "Jet dry" for the dishwasher, prevents water spots by breaking surface tension so water forms an even sheet. It is a strong wetting agent. Sorry, I did a lot of reading researching a story I wanted to write but there were too many much better ones already published so all I got out of it was near germophobia, AKA mysophobia. Frosty The Lucky. Quote
ThomasPowers Posted November 8, 2022 Posted November 8, 2022 And then their are Prions, (BSE) that need a toasty 700+ degF to be rendered harmless. I've made a bunch of SCA eating knives from used sewer snake but remind folks that GLOWING is above even Prion survivable temps! Quote
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