Heat Treatments and Metal Hardening

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as a continuation/slight change in course from my previous topic relating to center punches, i have decided to take the advice given and buy one. as far as my original intent goes, i guess i can't really do too much with a panzy-assed propane torch, so i plan on getting an O/A rig within the next year, probably this summer.Now to the question. what kinds of ways are best suited for case hardening, heat treating, normailzing, and annealing metals and weld joints? i understand the chemistry of what is occuring with the carbon atoms and the crystaline structure that is formed when the metal is hardened. i also understand that there are differences in how each process will affect the metal, i.e. case hardending will not completely harden the core of the metal, thus making it not well suited for knives or other items that are wear-and-tear that require a constant hardness thu-out the piece. please try and get some good details about WHY things are working like they do during these processes. i find that it is very beneficial to understand the chemistry and molecular physics of the metal and it's composition(s).Thanks in advance!Later,Andy
Reply:Go here - http://www.anvilfire.com/Click the drop-down menu and go to FAQ'sYou will find tons of detailed, specific information on case hardening and heat treating. You don't need an OA torch. A charcoal fire and a hair dryer will do a much better job of giving you an even heat. You need to let the piece soak at red heat for awhile too. It's alot easier in a forge, even an improvised one, than with a torch. Tempering is better done in an oven than with a torch. The temperatures are low, and for a good temper the steel needs to soak at heat for at least an hour. I use a toaster oven.Miller EconotigCutmaster 38Yes ma'am, that IS a screwdriver in my pocket!
Reply:Thats some good info. Joe, Thanks  JohnSMAW,GMAW,FCAW,GTAW,SAW,PAC/PAW/OFCand Shielding Gases.  There all here. :
Reply:Hi Andy,The question as you've posed it would take an entire 16 week college semester to answer...But let's see if I can address a few details here...Most of the processes you mention are completed using gas fired industrial furnaces.  Speaking in the broadest terms, these furnaces enable a heat treat shop to control the temperature, temperature gradient(s), and atmosphere around the items being treated.  Most are gas fired, although I have seen electric radiant furnaces, a blacksmith's coal-fired forge, and other, more exotic heat sources used.  There's a whole seperate class of hardening processes, known as induction hardening, that use electricity and magnetism to harden steel.  We need to break down the topics you mentioned into at least 2 groups; Heat treatments designed to modify the physical properties of a steel part, and processes designed to alter the surface of a steel part, but leave the core of the component essentially unchanged.It sounds like you're already familiar with the ideas that all these processes are primarily driven by time and temperature; with temperature being the more important process parameter.  All the changes that can be induced in steel occur as a function of these two parameters(and several others that I won't even try to talk about here).  Temperature is like the accelerator on your car; it drives the speed at which changes take place in steel.  Too low a temperature, and nothing happens in your life time.  A gross generalization would be that most of these processes need to be run at about half the melting temperature of steel; or 1000-1400°F.  (Yes, a bunch of case hardening and tempering is done at lower temps, but it would take forever to outline every possible example).The other big factor in all heat treatment and like processes is the atmosphere, the gas environment, that the process occurs in.  It should be obvious that if you heat steel to these kinds of temps in air, all sorts of scaling occurs; which is generally undesireable for a whole host of reasons.  So, most processes are run in some kind of non-oxygen atmosphere.  Sometimes the furnace environment is inert(He, Ar, N2) or even evacuated.  In 'case hardening' processes the furnace is filled with a gas that is enriched in some element, usually Carbon(CO2, CO, or some other hydrocarbon) or Nitrogen(present most often as NH3, ammonia), or some combination of both.  These chemicals can dissolve into the surface of the steel, much like salt in boiling water or CO2 in your favorite carbonated beverage.Suffice to say that if you add carbon or nitrogen to steel, it can become harder, more abrasion resistant, and/or more rigid.  The extent of the change depends on how much carbon or nitrogen are added and how deep they penetrate into the steel.  Both concentration and penetration are controled by atmosphere chemistry, temperature, and time.Most of these case hardening processes do not lend themselves to backyard, do-it-yourself operations; excepting on very small parts, in very small numbers.  Oxy-acetylene carburizing, and quenching-and-tempering of mid- and high carbon steels are the most frequently done by individuals.  The processes do not require control of the atmosphere around the parts, beyond that which is already available(setting your torch to a fuel rich mix, which creates a surplus of carbon that can diffuse into the steel).  Annealing and normalizing are usually done on finished assemblies, which are frequently too large for a home shop to heat in a protected atmosphere.  It's usually impossible to heat them evenly for enough time(several hours to several days) without a furnace that's big enough to hold the entire object.  Localized heating, often done to "anneal" a weld by the uninformed, frequently does more harm than good.  Be aware that pre-and post heating are not true annealing, by the strict definition of the term.  They can be beneficial with a number of steel and other metal alloys; but throwing a rosebud torch on a weld isn't really annealing the whole component.  It's spreading out the temperature gradient of the weld HAZ so that thermal stresses are spread out, which reduces the chances of cracking as the weld cools.  True annealing removes all the residual stresses in an entire component or assembly.    Normalizing isn't usually done as a part of welding.  It's heating the steel to at least half the melting temp in order to produce steel grain structure that is very uniform throughout the bulk of the raw material.  Normallizing steel is normally done to improve stamping, drawing and forging, which often require material with very homogeneous properties.  If the steel is slightly harder in one area, because of work-hardening, the raw material may fail during the shaping/forming operations.When people speak of case hardening, most often they are refering to gas carburizing, gas-nitriding, or some hybrid of these two processes.Gas - surface hardening processes , commonly called 'case hardening', aren't often done outside of the industrial environment.  The atmospheres used are often extremely flammable, volatile, corrosive, and or toxic.  Strictly speaking 'Case Hardening' was originally done by packing the part to be hardened in charcoal, or some other combustible material(hay, or horse hair for example) and sealing the whole mess inside a metal or ceramic container.  The container is heated in a fire or furnace, and the packing material burns, consuming the oxygen in the container and producing a carbon rich atmosphere.  You might also here the term pack-carburizing applied to this process.There are other means of solid-state hardening, which involve immersing the parts to be hardened in a molten, liquid salt bath.  Arsining(using arsenic salts), nitriding(using various nitrate compounds), and cyaniding(using various cyanide compounds) can all produce a hardened surface layer on steel.  All are potentially very dangerous and not to be attempted by a novice.  Possible explosions, fires, and deadly toxic gas are possible if these processes are not properly controlled.Contrary to your statement below, a variety of case-hardening and partial penetration hardening processes are used in industrial knives and cutting tools.  Higher strength steels are also used with great frequency.  But there's nothing intrinsicly wrong with using surfacing hardening techniques to produce a tough sharp cutting edge.  In fact, in many circumstances, a hard outer layer on top of a softer, more ductile core produces a superior cutting tool.  It all depends on what you're doing, how long it has to last, what it's cutting, how much money you want to spend, and a dozen other variables.I'm not sure that I've answered your whole question.  But at least we have a place to start talking.  If you ask some more probing questions, I'll be glad to share what I know.Being that I've written a good book chapter here, I suggest that you seperate questions into seperate replies to this post.  One question per reply.; that way the conversation is a little easier to follow.Regards,Dave Originally Posted by aczelleras a continuation/slight change in course from my previous topic relating to center punches, i have decided to take the advice given and buy one. as far as my original intent goes, i guess i can't really do too much with a panzy-assed propane torch, so i plan on getting an O/A rig within the next year, probably this summer.Now to the question. what kinds of ways are best suited for case hardening, heat treating, normailzing, and annealing metals and weld joints? i understand the chemistry of what is occuring with the carbon atoms and the crystaline structure that is formed when the metal is hardened. i also understand that there are differences in how each process will affect the metal, i.e. case hardending will not completely harden the core of the metal, thus making it not well suited for knives or other items that are wear-and-tear that require a constant hardness thu-out the piece. please try and get some good details about WHY things are working like they do during these processes. i find that it is very beneficial to understand the chemistry and molecular physics of the metal and it's composition(s).Thanks in advance!Later,Andy
Reply:thanks guys. i really appreciate all the info. Dave, you really seem to know your stuff. thanks for taking the time to share all that with us. since my whole center-punch issue is dead and gone, i think my next project that i could learn to heat-treat/harden steel is going to be a knife. i have heard a few things and seen a number of home-made steel forges for hobby blacksmithing. i don;t really want to build one since i don;t plan on using it very often, but is there anyway that i can build a small charcoal fire without one? i'll leave that question for now.Thanks.Later,Andy
Reply:I've seen small forges built using a cast iron brake drum from a truck and the aforementioned hair dryer.Anvilfire also has links to small temporary propane-fired furnaces that you can assemble with your barbeque tank, a burner, and some firebrick.  I lost several hours a few years ago reading all the stuff that is stored on Anvilfire's website.  Really is a good reference.Both can probably handle heat treating your knife, without breaking the bank.  Both can be packed up when you're not using them too. Originally Posted by aczellerthanks guys. i really appreciate all the info. Dave, you really seem to know your stuff. thanks for taking the time to share all that with us. since my whole center-punch issue is dead and gone, i think my next project that i could learn to heat-treat/harden steel is going to be a knife. i have heard a few things and seen a number of home-made steel forges for hobby blacksmithing. i don;t really want to build one since i don;t plan on using it very often, but is there anyway that i can build a small charcoal fire without one? i'll leave that question for now.Thanks.Later,Andy
Reply:Just build a little forge. There's really nothing to a simple charcoal forge. All you need is something to build a fire in, and something to blow air through it.A charcoal grill with a pipe shoved in it. Connect the pipe to a hairdyer.Use hardwood charcoal, not briquettes. You can buy it at the grocery store.Miller EconotigCutmaster 38Yes ma'am, that IS a screwdriver in my pocket!
Reply:hmmm... interesting... i never thought about using a brake drum. is there any specific types i shoudl stay away from? my hyundai drum is a bit smaller than my uncle's F-350 drum. lol... will my extra one work, or should i try to get a thicker one? i think i'll use a bit of extra exhaust tube that i have laying around to hook up the hair dryer. what about supports? should i be worried about keeping it off the ground?Later,Andy
Reply:http://www.anvilfire.com/21centbs/forges/brkdrum1.htmThis should about do the trick.All the other info on this site is also interesting reading-whether you do the activities or just read about how.
Reply:All the heat and process knowledge in the world will not do you much good if you do not use steel that you know the properties of. I have been making custom knives for about 15 years and have made hundreds of them. You will be able to do a decent job with some unknown steels just by luck but knowing the exact properties of the steel and the intended use of the knife will allow you to customize the heat treatment for the best blade possible.For example; A lot of people make knives by forging leaf spring steel into knives. However, the most common steels for leaf springs are 5160 and 1084 both of which need completely different hardening and tempering processes.A lot of people will tell you to heat steel to "Cherry red" and dunk it in oil then toss it in an oven for an hour. Good luck.You need to heat just past critical and quench in heated oil to avoid a vapor barrier. 125 degree oil will harden your blade faster than 70 degree oil.There is science involved and many overlook that. Do you want to have a hard edge that will hold that edge for a long time or do you want something that can chop down a tree? Both require different heat treatment.Decide what you want to do and go to the people that are doing it for advise. I come here for welding information because the people here are welders. If you want to make knives or tools, go to those that do that.I doubt that anyone here would give bad advise on purpose but not everyone with an opinion has the correct information.Now before I get stomped, to the guys that already posted replies, I am not saying your replies are inaccurate but just recommend that people go to the experts in the field they are wanting to work in instead of asking people that "MAY" know. There is a lot of work wasted if the advise is incorrect and I know I don't have enough of my life left to spin my wheels and not move forward on what I am trying to do.
Reply:Originally Posted by Bob WarnerThere is science involved and many overlook that. Do you want to have a hard edge that will hold that edge for a long time or do you want something that can chop down a tree? Both require different heat treatment.
Reply:Bob,If Andy wanted to heat treat transmission gears or splined driveshafts, or springs, or bearings, I might be able to give him some specific advice.I agree completely with your advice to seek out experts when you know exactly what you want, but not how to get it.  I also agree with your comments about using steel with known properties.  I might debate with you however that in some cases, the fabricator and even the end user won't know exactly what they need in a hardened part.  It's not until they try a couple different processes and/or materials that they settle in on a specific set of properties that works in each application.  Sometimes trial-and-error is the only way to find the best solution.  So whether you talk to a specialist, or a generalist for advice, may make little difference.I suspect that Andy's plans aren't completely formed yet, and even he hasn't decided exactly what to make, what purpose it will serve, and how to go about fabricating a suitable tool....Regards,Dave Originally Posted by Bob WarnerAll the heat and process knowledge in the world will not do you much good if you do not use steel that you know the properties of. I have been making custom knives for about 15 years and have made hundreds of them. You will be able to do a decent job with some unknown steels just by luck but knowing the exact properties of the steel and the intended use of the knife will allow you to customize the heat treatment for the best blade possible.For example; A lot of people make knives by forging leaf spring steel into knives. However, the most common steels for leaf springs are 5160 and 1084 both of which need completely different hardening and tempering processes.A lot of people will tell you to heat steel to "Cherry red" and dunk it in oil then toss it in an oven for an hour. Good luck.You need to heat just past critical and quench in heated oil to avoid a vapor barrier. 125 degree oil will harden your blade faster than 70 degree oil.There is science involved and many overlook that. Do you want to have a hard edge that will hold that edge for a long time or do you want something that can chop down a tree? Both require different heat treatment.Decide what you want to do and go to the people that are doing it for advise. I come here for welding information because the people here are welders. If you want to make knives or tools, go to those that do that.I doubt that anyone here would give bad advise on purpose but not everyone with an opinion has the correct information.Now before I get stomped, to the guys that already posted replies, I am not saying your replies are inaccurate but just recommend that people go to the experts in the field they are wanting to work in instead of asking people that "MAY" know. There is a lot of work wasted if the advise is incorrect and I know I don't have enough of my life left to spin my wheels and not move forward on what I am trying to do.
Reply:Points taken Dave.OK, first off I don't know squat about factory knives, not my thing. I am strictly custom.However I do know that Buck knives are general purpose knives and therefore pretty tough. I will explain it this way:We will assume the steel for these blades are 1084.A skinning knife must be sharp and stay sharp and therefore should be hard to withstand the abrasion it is subjected to while skinning. Unfortunately, being hard also means a bit on the brittle side. This would skin deer, several deer without needing sharpening but would break if used to pry or to chop due to the brittleness.A camp knife would be expected to withstand chopping, prying and other abuse so obviously it must be less brittle and a lot tougher. To get less brittle and more toughness you must sacrifice edge retention. It can withstand a hard shock like chopping through a bone and not crack.A fillet knife would not be used to chop or skin and would be expected to be flexible so it would have to be even less brittle to withstand flexing without breaking.So we have three different requirements for the three knives above. Each could be made of the exact same steel and possess the three different properties needed.The skinning knife would be heated to critical temp (up to the point of non-magnetic) and quenched in 125 degree oil. This would make the knife very hard and brittle. To brittle to use and easily breakable. So we would reheat this blade (Temper) to about 375 degrees for an hour and repeat twice. Now we would have a hard blade that would retain its edge.The camp knife made of the same material would also be heated to critical temp but instead of quenching in 125 degree oil, I would "marquench" by quenching in 425 degree oil and just leave the blade in the oil for several hours. This makes the knife tough as he!! and it can take a lot of abuse without breaking. Chop away at those trees, you won't hurt it but you will need to sharpen it more often.Then the fillet knife with its thin blade. Heat to critical and quench in 125 degree oil. Then temper at a higher temp than the skinner to make the blade less brittle. So we would go up to (just guessing) 450 degrees for three cycles. This softens up the blade to handle the flexibility but the edge would be soft and require frequent sharpening.Now, we could make the same three knives out of 5160 steel but the hardening and tempering would involve an entirely different processes.We could also use O1 or W2 steels and different processes to get the same results.If you want to learn more about knife making I suggest you go to http://www.knifenetwork.com/forum/index.php join the forum and read, read, read. There is more info here than you could ever learn by trial and error.
Reply:Points taken Dave.OK, first off I don't know squat about factory knives, not my thing. I am strictly custom.However I do know that Buck knives are general purpose knives and therefore pretty tough. I will explain it this way:We will assume the steel for these blades are 1084.A skinning knife must be sharp and stay sharp and therefore should be hard to withstand the abrasion it is subjected to while skinning. Unfortunately, being hard also means a bit on the brittle side. This would skin deer, several deer without needing sharpening but would break if used to pry or to chop due to the brittleness.A camp knife would be expected to withstand chopping, prying and other abuse so obviously it must be less brittle and a lot tougher. To get less brittle and more toughness you must sacrifice edge retention. It can withstand a hard shock like chopping through a bone and not crack.A fillet knife would not be used to chop or skin and would be expected to be flexible so it would have to be even less brittle to withstand flexing without breaking.So we have three different requirements for the three knives above. Each could be made of the exact same steel and possess the three different properties needed.The skinning knife would be heated to critical temp (up to the point of non-magnetic) and quenched in 125 degree oil. This would make the knife very hard and brittle. To brittle to use and easily breakable. So we would reheat this blade (Temper) to about 375 degrees for an hour and repeat twice. Now we would have a hard blade that would retain its edge.The camp knife made of the same material would also be heated to critical temp but instead of quenching in 125 degree oil, I would "marquench" by quenching in 425 degree oil and just leave the blade in the oil for several hours. This makes the knife tough as he!! and it can take a lot of abuse without breaking. Chop away at those trees, you won't hurt it but you will need to sharpen it more often.Then the fillet knife with its thin blade. Heat to critical and quench in 125 degree oil. Then temper at a higher temp than the skinner to make the blade less brittle. So we would go up to (just guessing) 450 degrees for three cycles. This softens up the blade to handle the flexibility but the edge would be soft and require frequent sharpening.Now, we could make the same three knives out of 5160 steel but the hardening and tempering would involve an entirely different processes.We could also use O1 or W2 steels and different processes to get the same results.If you want to learn more about knife making I suggest you go to http://www.knifenetwork.com/forum/index.php join the forum and read, read, read. There is more info here than you could ever learn by trial and error.
Reply:Not sure why that posted twice. If a moderator sees this please delete the redundant post.Thanks,BobLast edited by Bob Warner; 12-29-2007 at 01:08 AM.
Reply:thanks bob... i'll take a look at that other forum this weekend. interesting how the temperature of the oil can make such a difference. i was thinking that i could make a knife somewhat in between the skinner and the chopper for in the field for more of a "practice piece", and after i get that down pat make a super-sharp, super-hard skinner for in the shop when we butcher the game. the main one i want is the skinner... the buck knives don't hold up well to the deer hair. is there one type of steel that would work better for this than others? i know it's about 4 times as expensive, but what about A2 (air cooled) steel? from what i hear, it is the most brittle and strongest steel out there, but i have only really talked about it for 10 minutes a few years ago. other than that, it's just been sitting at the top of the price list on www.JLIndustrial.com . so what would you recommend for a good skinner knife with the most durable edge? most butcher's knives i have used are still somewhat soft it seems like, probably to keep the vast majority of the consumer base happy by not making their knives shatter when they hit it on the counter. however, i do not really want a knife like that. i want to make a knife that will cut thru damn near anything and still hold its edge for a few hundred more cuts.Thanks again.Later,Andy
Reply:you better be really carefull heating an oil to temps near or above 400f. that exceeds the flash point of most and it can flare up like a rocket. kind of like turkey deep-frying for dummies.if you want to avoid scale on something he size of a knife blade ,stainless steel foil can be used to wrap the blade while it heats.
Reply:hows your chemistry? if you want to learn more on the theory side try googling some of the terms used to describe the various crystal lattice structures- martensite, pearlite, cementite, austenite etc. there's probably plenty of articles that aren't written for those studying a degree in metallurgyeutectic, hypereutectic and hypoeutectic will yield some results tooto get you started here's one result of 'eutectic composition of steel',...http://www.key-to-steel.com/Articles/Art3.htmclick on the 'articles' tab and you'll find loads more, although it's not the lightest reading. for a lighter read get a copy of 'engineer to win' by Carroll Smith. covers the basics of ferrous and non-ferrous metallurgy begining with basic chemistry (atomic bonds, crystalline structure, allotropes etc) and goes on to cover smelting and heat treatment including a light look at the history of metallurgy- old world quenching (endowing a Damascus blade with it's legendry strength by thrusting it -red hot-  through the belly of a slave) and nitriding (piss on it!). about half the book is basic metallurgy (including fatigue), the rest is real world applications  with respect to motor racing
Reply:Bob Warner,AFAIK most Buck knives (the stainless ones) are (or were) a modified 425 stainless steel.And Andy, like Bob and the others have mentioned, you can ask here and -usually- get some reasonable answers.  But for hard-core knife and metals and forging/heat-treating/etc questions, search the knife forums or blacksmith-bladesmith forums.For a knife, like in many many things, there are balances and trade-offs to be made.  Hard (and brittle) or tough (and softer)?  What quenching medium?  How expensive on the raw materials?  How tricky or picky on the heat treat requirements?  etc, etc, etc.  And then you also have the trade-offs on the shape and edge geoemetry, thick axe edge versus thin razor edge, etc, etc, etc.Andy, search the web for something along the lines of Joe Talmadge's blade steel FAQ.
Reply:thanks guys for the info. i really appreciate when people are able to admit that they do not know everythig and turn me towards some reliable, credible, and helpful information. i'm hoping that i can get the knife made for his birthday at the end of April. with my new house and shop, i should have enough time and what-not to play around for a while.Thanks again!Later,Andy
Reply:Andy,You may have difficulty getting the perfect knife by April. You have a lot to learn and to TEST.  In knifemaking and home heat treatment there are a lot of "what works for me may not work for you" situations.EVERYTHING influences the final product. If your piece of steel came from a different run than mine, they will have minor differences. These affect the outcome of the heat treatment. Your quenching medium may not transfer heat as fast as mine. Your temp may be off a bit. Your tempering oven may not hold heat as well as mine, blah, blah, blah.Every time I buy steel I ask for the composition or amounts of everything in it.  I make a knife and destroy it to be sure I am getting what I want. You should do the same.Read, read, read.Last edited by Bob Warner; 01-02-2008 at 05:27 PM.