Hardening steel

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My son enjoys making knives, crude ones for sure, not like some I've seen on here. But he's getting better each time. I think he mainly enjoys shaping the steel.  He uses steel  scraps we get at a local welding shop. Usually 3/16 x 3" or something similar. He tries to harden the steel by heating it in a coal fire and when it becomes red hot dropping it in used motor oil.What happens is that when the steel becomes red hot it appears to almost bubble which causes large pits. Almost like it's delaminating.  Pretty frustrating. Is he not doing the hardening process right or should he use a different grade of steel?  Can anyone explain a different process? I know he'll appreciate any input you guys have.
Reply:HVW,Most common grades of steel, the kind your son is likely getting as scrap from the local welding shop, are not readily hardenable.  The steel you're likely working with is low carbon steel or 'mild' steel.  It doesn't have the necessary ingredients in it to harden it by heating, quenching it in oil, and then tempering it.(tempering = re-heating to a lower temperature and allowing it to slowly cool)I'm not sure what's going on with the steel you're using; maybe it's surface contamination that the forging has driven into the surface, that's vaporizing and boiling away.  Something of that nature.  I think less heat is probably the cure.  Is the steel throwing off sparks when this bubbling happens?  If so, you're definitely too hot...  Read on, as you have other issues to resolve first...In order harden the steel, you need to start with a steel containing medium - high amounts of carbon; at a minimum.  You might try to get some 1045 or 1060 carbon steel.  45 and 60 refer to the amount of carbon in the steel; 0.045% and 0.060% respectively.  For reference the mild steel you've been using is probably equivalent to 1010 steel.  Old truck leaf springs are commonly made from this type of steel.  Try visiting a junkyard and purchasing some truck leaf springs for knife stock.The really high end knives are made from steels that are commonly referred to as 'tool' steels.  In addition to carbon, these steels contain other alloying ingredients, chromium, vanadium, molybdenum, nickel, tungsten, manganese, to name a few.  These steels are engineered to harden by the quench and temper process.  As you might guess they are harder to forge, more expensive, and prone to cracking if quenched improperly.  I suggest that you and your son stick to the leaf springs until you're confident in your skills and have done some more research on tool or alloy steels.There's a fellow named Bob Warner who posts here and makes some fantastic knives.  There are a few others as well, whose names escape me at the moment.  I'm sure if you post again in the future, they'll have detailed answers to your questions.Last thought, pictures are worth a thousand words.  If you can, post some of your son's work and what's happening when the problem occurs.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Thanks Dab. I expect you've hit it right on the head. He's not getting the right type of steel.  This is just mild steel from the welding shop. It doesn't spark when it bubbles it just looks like it's coming apart.
Reply:My guess is he has gotten the steel so hot it's starting to scale and the shock is causing the scale to flake off. I agree some old leaf springs would be a better choice for materials and yet still relatively inexpensive.Love to see some picts of his stuff. Post them up!
Reply:If he is using plain old hot roll it could be the mill scale flaking off.Tim Beeker.
Reply:For starters, I think you're overheating the steel.Yes, you would be better served with a better alloy, and mild steel isn't really hardenable, but its fine to practice on, even if the results won't be hard enough to use for a knife.Anyway, after you pass cherry heat, you can get to a point where its between yellow and white, and flux (boric acid) will kind of skate around on the surface like butter on a hot pan.  At that point, you've gotten to the temperature needed to forge weld.  VERY SHORTLY past that, and you will get the bubbling that causes craters, and ruins the surface.BUT, for hardening, you just need to pass the Curie Point temperature, which is going to be well before all this, and somewhere between a dull red and a cherry.  Unfortunately, depending on the ambient lighting, and goggle's you're wearing, using color to define heat will give widely varying results.  Instead, check the steel with a magnet.  Above the Curie Point temperature, the steel will no longer be magnetic.  Don't heat past this unless you're planning on forge welding, or making patterned steel.Keep the steel cooler, and you'll get less mill scale.  As you get hotter, the mill scale gets worse, eventually causes severe cratering, and finally, everything melts into trash.Each time you reheat, you get more mill scale as well.As for the quench, that again all depends on the alloy you are working with.Cheaper alloys probably won't harden well in motor oil, and work better in water.When hardening in water, you need to keep the piece moving quickly as it is quenched.Trial and error works well here.  I would start by quenching into water.  If that works (and doesn't destroy the piece), then a salt water brine would be my next quench to try on that alloy.Calcium chloride brine, will give about as severe a quenching as you can get.  It will cause some alloys to crack though, so be prepared to lose a piece.I would only quench in oil, if water quenching was likely to destroy the piece.Then, you still need to temper.  You need to clean the piece up to bare metal, and could probably put it in an oven for a few hours, but its faster and easier to do this in your forge.I generally temper cutting tools (lathe cutters) to a champagne color, but that will be too brittle for a knife, which will be better around blue (depending on the alloy).
Reply:I would suggest to him to explore this site and some others.  Go through the search on making knives.  I too, would like to give this a try, but one thing at a time.  There are a lot of people on here with a ton of knowledge.  Another site to look at ( not to steer anyone away from here, but...) is http://www.metalartistforum.com/ There is a lot of forging information there. Also search blacksmithing sites.Sorry, I don't have any real info to give, but hopefully these sites help.  Like I said, it is something I have been thinking about.  I am collecting parts to make a forge, and then...  I have a brake drum, and a small but powerful fan, just need to finish this that and the other to get to the next thing.Good luck to him, and post up some pics of the finished projects.
Reply:HVW, have him purchase some 1095 steel from a knife making suppy outfit such as Jantz Supply. It's dirt cheap compared to the other steels and is easy to heat treat. It is also very easy to work.After the knife is shaped, heat the steel until a magnet won't stick and quench it in light weight oil. 20 wt. motor oil and equal parts ATF works well. A gallon or so in a container deep enough to plunge the blade portion of the knife straight down works well. You can also use a pan and do an edge quench but that's something I won't go into here. You can use water instead of oil but sometime 1095 will warp or crack.  Hold the blade in the oil until it quits bubbling before you remove it. Have a lid to put on the container in case the flame doesn't go out when you remove the knife. After the blade is cool and cleaned check it with a file. A sharp file should just slide on the blade and not cut. If it bites the steel the temperature wasn't high enough when it was quenched. Just reheat to a higher temperature and quench again. If the file doesn't bite, clean it up and then draw the temper. A toaster over is ideal but the oven of your kitchen range works too. Draw it for one hour at 425 degrees. Check it with a file again like you were sharpening it. The file should cut but not easily. If you think that is too hard for your uses, draw it at a slightly higher temperature.
Reply:I'm not knife expert by any means but why not start of with steel that's already pretty hard like 1045?  Also, some/most grades of 1045 harden really well.
Reply:Thanks for the great replies folks. I can see he was going about this the wrong way. He's out of state until next week so I can't post any pics of what I'm describing until he gets back. It sounds as if he really doesn't need the coal. We have two coal trains a day pass through here going to the steam plant and bunches fall out all along the tracks so it's readily available. I think knife making is like welding...it takes a lot of practice and knowledge.
Reply:Watch out for the free coal you're picking up.  Depending on the source, it could have a lot of sulfur in it, which is really bad for steel.You're better off finding a local ABANA chapter, and asking where they buy their forge coal.  It's likely much better in quality than what you're scavenging.  You could also step up to a small propane fired furnace.  Fire brick and the other pieces are relatively cheap.  There are plans all over the internet.  Check out your local ABANA chapter as well;  my local chapter does demos, supplies coal for a low cost, teaches blacksmithing.  They have held clinics where the attendees build their own propane forges from well-tested plans.  I think they've also built pneumatic power hammers for the cost of the material.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Hvw;If your son wants to continue practicing with mild steel, he can case-harden it after shaping it. I like to use cast iron pipes for containers, even old pieces of drain pipe with discs cut and welded to the bottom and recessed to sit on and seal the top. (I got a number of Stainless cut-outs which I have used.) The steel is put in the container and the space around is packed with bits of old leather, low-temp charcoal, even sawdust---everyone used to have a 'secret formula'--and the container is heated to redness for a while depending on the depth of hardness wanted, probably 20 or 30 minutes at least. There are chemicals called "activators" which can be added to the charcoal mix to improve penetration or add other compounds; steels of certain composition, i.e. containing aluminum, will adsorb nitrogen and be hardened by that, and he can do a Google search to learn about all these variations or extra tricks once he has gotten the basic process under control. Once he gets a satisfactory result from 'just playing around', he can try to refine the process by controlling temperature, using different steels and different 'activators', etc. but this crude method should at least get him started.I should explain that this first step is just to allow carbon to diffuse into the steel, increasing the carbon content of the surface. The hardening comes from the heat treating of this higher-carbon surface as already described above. This can usually be done by just dumping the contents of the 'sealed' container directly into the first quenching medium while it is still red hot from the carbonizing step. With case-hardened steel, water is often most suitable and less a mess than using oil. Straightening and tempering, if needed, would follow.
Reply:Case hardening, good idea, wish I though of it!I've had luck with a tray of Kasenit, but in a pinch, sugar (yes, plain old sugar) will supply the carbon VERY readily.Heat until cherry red, quench in sugar.  Repeat 2 or more times.Finally harden in a water quench (or even better, brine).  You won't get decent hardness with a mild steel core, and an oil quench.If you happen to purchase 1045, that's also good to quench in brine.As you go higher in carbon though, you'll need to use an oil quench, to prevent cracking.
Reply:Originally Posted by mccolldI'm not knife expert by any means but why not start of with steel that's already pretty hard....
Reply:Back in my tool and die days when we heat treated steel we did it in an electric furnace and wrapped the item to be treated in stainless steel foil.  This kept the oxygen away and reduced the surface scale you are seeing. Some steels are air quench and others are oil quench.  Tool steel supplyers should be able to supply you with a book telling how hot to heat treat and how hot to draw the steel down to the desired rockwell poinit.   McMaster-Carr sells several kinds of tool steel in flat shapes that would be good for knife making.  If there is a tool and die shop in your area they would probably heat treat for you and they should have a rockwell tester that can tell you how hard the steel treated out.  It's good to hear about young people doing this instead of playing video games or watching TV.Dan
Reply:Case hardening + a couple of sharpings = NO case hardening.
Reply:Hello guys,If I may, I might be able to shed a bit of light on this topic.What I say here may appear to be contradicting some of the other comments but not completely so please do not be offended if your solution appears to be discounted in my response.First of all, the steel you want must be a high carbon steel. Unfortunately using lief springs and other items presents a challenge because some lief springs are 1084, others are 1095 and still others are 5160. There are still others but the point is that each one requires different heat treat methods.I would suggest buying a known steel type. The cheapest is probably 1075/1080 and can be picked up at any knife supply place. www.knifeandgun.comwww.texasknife.comwww.jantzsupply.comAnd my favorite http://www.usaknifemaker.com/ tell Tracy I sent you.Call them and ask if they carry 1075/1080 and then get a piece or two. They will send a catalog with your order. If you want the catalogs for all, just call and ask for something and they will send you a catalog.  If you just ask for a catalog, they will charge you for it. They give them free to those that appear to be potential customers and not just catalog collectors.Forges. Forges are a tricky because if you use coal, coke, charcoal or other solid fuel you need to learn to tend the fire. Propane is MUCH easier but you have to build a forge which is very easy to do. I can help anyone that wants to build a propane forge.Heat the steel to a dull cherry color for forging. If you get it so hot that it sparks, you have ruined the steel and it will never be a good knife, throw it away and start over.Lets assume you used 1075/1080 and have forged it to shape and are now ready to harden it.Get your quench ready to accept the blade. I use Automatic Transmission Fluid. You need about a gallon or more. More is always better. You heat the oil to 125 degrees. You heat it to prevent a vapor barrier forming when it is cold. You want the oil to touch the steel and cool it down. If the oil is cold it creates a vapor barrier between the steel and the oil for a second or two and that slows down the rapid cooling of the steel.You put your knife in the forge and heat it up. You need a flame that is a reducing flame. That means that the fire is coming out of the forge to get oxygen. That means there is no oxygen in the forge and you will not get scaling (or very little). You pull it out and check it with a magnet. Your goal is to check it often enough to not overheat it. You work your way up to the point the knife is non-magnetic, then you add a little more heat time. Nonmagnetic plus 100 degrees is perfect.You rapidly remove the knife and put it into the quench tank. Do not move it around or take it back out. Be prepared for the oil to catch fire. After the knife has been in the oil for 30 seconds or so you can lay it on the bottom of the oil container and put a lid on the container to put out the fire if there is one. After a minute or so you can take the blade out. It will be brittle so don't drop it.Take the knife directly to the oven and heat it to 350-425 for a minimum of two hours, then allow to cool. Do this three times. This is TEMPERING the knife and making it less brittle. If you want a skinning knife, heat to 350, if you want a tough camp knife, heat to 425. You need to play with these numbers to get the results you want. Unfortunately you will have to make some knives and destroy them to see how well your heat treat is working.Now finish the knife, any additional work on the steel must not exceed the temperature of your tempering heat or you will ruin the knife.Assemble the knife and enjoy.Remember to do all drilling BEFORE you harden the knife.
Reply:Bob, check your PMs, please.
Reply:Does ayone know what grade old circular saw blades might be made from.I have an old 36" Dia saw blade I would like to make a few knives from.
Reply:Not sure but they are definitely stainless steel. Entirely different heat treat setup.You can however make a knife from it if you grind slow and do not let it get hot (above about 300 degrees. That means grind one pass and dunk in water. If it is too hot to touch, cool it down. If it turns blue, throw it away and start over.You are basically grinding a heat treated blade instead of making the knife first.Go for it.
Reply:Old circular saw blade body is most likely NOT made of stainlesss steel.It is most likely made of a medium carbon steel hardened up around Rc30-40 or so IIRC.  A 'prmium' blade body may be better material and be hardened up in the high Rc40's.  Freud says the use steel for their blade bodies at Rc46-48.http://www.freudtools.com/images/PDF/sb_tech_info.pdfOther than that, pretty much Bob's the man.  If you start with a KNOWN material, then you can get an idea as to how to process it (machining ,heat treating, tempering, etc).If you start with an UNKNOWN material, you are just guessing.  You may guess right, or you may guess wrong.Guess wrong and you end up with junk or broken pieces.  Try to quench an oil-hardening steel grade in water and you most likely end up with broken pieces of steel (to severe of a quench).  Etc, etc.  The best laid schemes ... Gang oft agley ...
Reply:I have an old 36" Dia saw blade I would like to make a few knives from.
Reply:Cheers Moonrise. You're right, it's deffo not SS. I know a local guy who makes some very nice blades (and commands very nice prices as well) from old Saw blades, I only met him Sept last yr, and will not see him until the same time this yr, so thanks for the advise. i think I'll make the kife and pass to him for treating
Reply:Originally Posted by Oldiron2If that saw blade is in half-decent condition, it might be worth enough to someone restoring an old 'buzz' saw that you could trade it for some known steel stock.
Reply:I've made a couple of knives out of used 10" saw blades.  They don't seem to take an edge very well.  It'll shave hair but won't pass the paper test.  I've never had a problem with any other knives I've made from different materials though.  Example:  Old tobacco knife, chainsaw bar, cross-cut saw.  I'm still trying to get a decent knife from the forge, that's a lot harder than it looks!DewayneDixieland WeldingMM350PLincoln 100Some torchesOther misc. toolsSeems like the blade from a lawn mower would make good knife steel.D
Reply:Nope on the lawnmower blade.That would typically NOT be a 'high carbon cutlery steel' material.  Medium carbon steel most likely.Lawnmower blades are not all that hard, guessing maybe around Rc30 give or take a bit.  You can usually sharpen a lawnmower blade with a plain file.To me, a knife blade is usually around Rc60 give or take a few points.  Exact hardness 'optimum' depends on specific steel alloy and desired trade-offs of hard vs tough and edge-holding versus ease of resharpening, etc, etc.If you scrounge steel, you are guessing as to the alloy.  Guessing as to the alloy means you are guessing as to the heat treatment and the possible end product material characteristics.If you start with a known material, you can have an idea of what to do, processing wise, and what you will end up with.Oh, and in case folks didn't pick up on it or know it, there are two main 'ways' of making a knife blank.  Both ways take your 'raw' steel and start to transform that into a 'blade' shaped object.  The two ways are forging (heat and beat  ) or stock-removal (lots of grinding and filing and such).  Both methods can be used to make good knives, both methods can also make junk.  And yes, even a forged knife typically involves grinding and filing and such.And the majority of the shaping of the blade is usually done before the blade is hardened, because shaping a hard blade is, well, HARD.Last edited by MoonRise; 03-10-2009 at 03:07 PM.  The best laid schemes ... Gang oft agley ...
Reply:Originally Posted by MoonRiseNope on the lawnmower blade.That would typically NOT be a 'high carbon cutlery steel' material.  Medium carbon steel most likely.Lawnmower blades are not all that hard, guessing maybe around Rc30 give or take a bit.  You can usually sharpen a lawnmower blade with a plain file.To me, a knife blade is usually around Rc60 give or take a few points.  Exact hardness 'optimum' depends on specific steel alloy and desired trade-offs of hard vs tough and edge-holding versus ease of resharpening, etc, etc.If you scrounge steel, you are guessing as to the alloy.  Guessing as to the alloy means you are guessing as to the heat treatment and the possible end product material characteristics.If you start with a known material, you can have an idea of what to do, processing wise, and what you will end up with.Oh, and in case folks didn't pick up on it or know it, there are two main 'ways' of making a knife blank.  Both ways take your 'raw' steel and start to transform that into a 'blade' shaped object.  The two ways are forging (heat and beat  ) or stock-removal (lots of grinding and filing and such).  Both methods can be used to make good knives, both methods can also make junk.  And yes, even a forged knife typically involves grinding and filing and such.And the majority of the shaping of the blade is usually done before the blade is hardened, because shaping a hard blade is, well, HARD.
Reply:Originally Posted by Bob WarnerNot sure but they are definitely stainless steel. Entirely different heat treat setup.You can however make a knife from it if you grind slow and do not let it get hot (above about 300 degrees. That means grind one pass and dunk in water. If it is too hot to touch, cool it down. If it turns blue, throw it away and start over.You are basically grinding a heat treated blade instead of making the knife first.Go for it.
Reply:It's nice and fine to always have the best tools, the best materials and the best knowledge beforehand but remember that it was all learned through experience, through trial and error and through testing. While it is appropriate to start out with these if you need to have an excellent finished product, even that won't insure it because the skills need to be refined.There is still a place for starting out with what is available, using crude methods and trying different tricks, just for the enjoyment of doing it or learning from the results. It may be better to have gotten to try something, using what is at hand, rather than to never get the chance to do it right 'cause something is always in the way or it just doesn't get arranged.One can always move upward, but he needs to take the first step first.....And, so far as developing skills, that can be done using less than optimal conditions and materials, to at least some degree. I know, it can also develop bad habits too.BTW, case hardening can actually be quite deep if suitable time and good methods are employed. I have left a stainless steel 'carbonizing' container in the fireplace all day, on occasion.
Reply:Well it seems there is the beginnings of a knife making group here. I am glad to see it. You will not believe the looks you will get when you tell people you make knives. They look at you like they can't believe it. They always ask, where do you get the blades and after you tell them that you made it they always ask, How long does it take. But they are always dumbfounded.For all they guys that are considering this and maybe even for some that have made a few, I suggest goinig to ebay or Amazon and buying the book, The $50 knife shop by Wayne Goddard. There is a heck of a lot of how to stuff for the guy with little cash or knowledge. A lot of people used this book to get them started.  I bought it last year and wish I had known about it 14 years ago when I taught myself everything by trial and error. Would have saved me a LOT of time and material.To keep it on the WELDING side of things we have damascus to talk about.
Reply:I purchased "Step By Step Knife Making" by David Boye years ago. It is an excellent book and has quite a few points on steels. Old saw blades are discussed. Bought the "50 Dollar Knife Shop" a few months ago. I'm thinking about building a somewhat modified version of "The Big Red Grinder" just to be building something.
Reply:Well Bob, to be -picky- it's not Damascus steel.  It's more properly "pattern welded steel".  http://en.wikipedia.org/wiki/Damascus_steelLet the folks get up to speed first on plain high-carbon steel blades, either forged or stock removal.  Then maybe move up to alloy/tool steels (hand forge some D2 maybe  ) and then maybe stainless.Then hit them with pattern welding.  Different patterns, making designs in the pattern and not just cool swirls and ladders and such, etc, etc.btw, cool knives and nice work you do.  Starting with known 'good' materials is not a guarantee of 'good' results, I said as much.  It just takes out some of the uncertainty and hopefully gets you started in the right general direction.Especially for a newbie, they have enough going on with trying to 'do' it right without having no or wrong information about the basic START of the knife, the blade steel.Trial and error sure is one way to learn.  It's nicer if you can get a head-start toward the goal by learning at least some from someone else's trials and errors.    The best laid schemes ... Gang oft agley ...
Reply:I get hit with the pattern welded thing all the time.Modern day damascus is pattern welded steel. However since the recipes of the original damascus creation is lost, modern day descriptions are acceptable to me.Also, most people would look at you like you were a space alien if you started talking about pattern welded steel and only about half of those would look at you that way if you talked about damascus.Using the known term is more profitable because correcting customers turns them off so I speak their language unless they ask for clarification. If you read any of the knife magazines you will see that a lot of others talk about damascus instead of pattern welded steel.If I can sell a $1500 DAMASCUS knife or make the customer mad by correcting him and sell nothing, guess what I am going to call it.