Introduction: Heat Treating a Knife Made From 01 Steel
First of all, can I please ask people not to argue with me. I am merely sharing my findings. This is the best method I can do with my limited equipment. It worked well for me. If you have a better way to do it, that's great. If you write an instructable on the method I shall read it with interest.
I'm making a chef's knife for my wife and ordered some 01 steel as it seemed like a very good steel for the purpose.
Having ordered the steel I read the instructions. It seems like it has VERY specific heat treating to get the best results. Oops!
Previously most of my knives have been made from 1075 and the like. These were easy peasy lemon squeezy and just had to be hot, plunged into oil and tempered. Not 01. Oh no! It appears that 01 contains elements that need to be heated correctly to disperse through the steel.
There is a ton of often conflicting information online, but I'm going with the information from the people who actually make the steel, as they ought to know. I'm just adapting it for my limited equipment and limited skills.
Step 1: Short Outline
Coat the knife with anti-scale (ATP-641 in my case).
Heat the steel to between 802-816c for at least 10 minutes (longer for thick pieces)
Quench the steel in oil pre-heated to 149-204c.
Immediately straighten any warps while hot. Use gloves, wood, vice, clamps, whatever. Be quick and be careful.
Immediately (before the knife drops below 51c) temper at 200c for 2 hours
Phew! That's quite an ask seeing as how I have a gas forge and no fancy kilns etc.
Step 2: Tools and Materials
01 Knife blank (I'll give a quick summary of making this)
Anti-scale. I've used ATP-641, but people use various things including borax and refractory cement. I haven't tried this so can't comment as to their effectiveness. The anti-scale not only makes your life easier in removing the scale, it is also meant to prevent carbon migration from the steel.
Steel box section or pipe. This is to equalise as well as lower the temperature in the forge. I welded one up. Some scrap to put on the box to help regulate and lower the temp.
Thermocouple thermometer to accurately measure the temperature in your forge. Mine was only £15 on Amazon and does the job well.
Oil for quench. Mine is cooking oil and works well. Any oil should work.
Metal container for quench oil. I made mine from an old scuba tank I bought on eBay for £10.
Big chunk of steel to heat in the forge then put in the quench oil to get it up to temp.
Method of correcting any warps. I use a vice and also a big chunk of straight steel that I clamp the knife to when tempering.
Oven for tempering. I use my kitchen oven and do it when my wife is out...
Step 3: Blankety Blank
This is a very quick summary of making a knife blank by stock removal.
Draw out your design on cardboard.
Trace the design onto steel of suitable thickness (mine is 2mm thick, this is thin but appropriate for the knife my wife wanted).
Cut it out. I used an angle grinder to get the rough shape and files to finish it off.
Drill the holes for the handle pins. If you leave this until after hardening you and your drill bits will regret it.
Boom. Yes, 'boom'.
Step 4: Preparation Is Everything. EVERYTHING.
To get the best from 01 steel you cannot just wing it. You need to prep properly.
Coat the blank in anti-scale. You can dip it or paint it on. Make sure you have a good coating. The first coat may have trouble sticking, but subsequent coats should go on okay. You can use a hairdryer to dry it between coats.
Put the steel pipe/tube in the forge, along with the scrap steel for heating the quench oil. Wait until it is up to temp then use the thermocouple to measure the temperature inside the pipe/tube. If it is too hot, try putting some scrap steel on top of the box/pipe. Make adjustments until you can hold the temp between 802-816c.
Put the large heated scrap steel (mine is one inch square bar) in the quench oil and take the temp. Adjust until you can get it to 149-204°c. My quench/scuba tank is large so it took a few heats of scrap to get it hot enough.
Lay out your chosen method of correcting warps.
Once you are happy you can achieve the temperatures, put your oven on at 200c, ready for the tempering.
Step 5: Go!
The pipe/tube/ box is up to temp. The scrap steel is hot and ready to heat the oil. The blank is coated with anti scale. Your oven is on. Your method of correcting warps is to hand. Go!
Put the blank in the tube. Being thin steel it will heat quickly. It will be non magnetic, but trust your thermocouple more than this. The hardness of the handle is not important, so if some of the blank won't heat up properly make sure this is the handle part. You can see in the photo that the blade part is red, the tang of the handle isn't. This is the best I can do with my kit and is good enough.
Keep it there for at least 10 minutes (this is called 'soaking'). Meanwhile bring your oil up to temp. Oil holds heat pretty well.
When your 10 mins are up get your tongs and immediately plunge it into the oil. Hopefully you will have the fun and drama of flames. This is my favourite part of knife making. I usually hold it in the quench for about 20 seconds. It needs to cool, but not so much that you can't straighten any warps.
There are no photos of the quench I was too busy doing it to photograph it!
If the blade is warped act quickly and straighten it while it is still hot. One of my three knifes had a warp, so I immediately straightened it in the vice and clamped it to some heavy steel
File test it to make sure it has hardened. The file should skate and not bite. If it hasn't hardened you need to repeat. You should probably anneal it first (for 01 steel use the pipe/box, heat it to 740-760c and allow to air cool).
Get it straight into the oven and temper it for 2 hours. If you are using clamps in the oven make sure yours doesn't have a plastic quick release button or it will melt like mine has. Oops.
Clean the crud off. You can see mine after a light sanding.
It just now needs sanding, polishing, sharpening and the handle to be glued and pinned on and sanded to shape.