Frank Turley Posted March 20, 2011 Share Posted March 20, 2011 Is hot forging a heat treatment? Quote Link to comment Share on other sites More sharing options...
jimbob Posted March 21, 2011 Share Posted March 21, 2011 It is for me! Quote Link to comment Share on other sites More sharing options...
Rhrocker Posted March 21, 2011 Share Posted March 21, 2011 I'd vote yes Frank, because hot forging will re-arrange the structure of the steel. So I'd think that it's a treatment of the steel just based on that. Also, almost everyone advocates that while forging, a blade for example, that the temp of the forge be reduced with each forging cycle because in part of the grain growth that heat can cause. Robert Quote Link to comment Share on other sites More sharing options...
Ric Furrer Posted March 21, 2011 Share Posted March 21, 2011 Is hot forging a heat treatment? No and neither is throwing it on the floor to cool after forging. But Oddly enough...heating it up to very low forging temperature and doing nothing but watching the color drain away...IS.... a form of heat treatment used to refine grain...riddle that one out. One definition I found was this: "A process where solid steel or components manufactured from steel are subject to treatment by heating to obtain required properties, e.g. softening, normalising, stress relieving, hardening. Heating for the purpose of hot-working as in the case of rolling or forging is excluded from this definition. " Obviously a term used for all metals and some ceramics and glasses as well as baked goods such as bread, but....its a start. Why do you ask Frank? Another book? Ric Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted March 21, 2011 Share Posted March 21, 2011 I would say "yes" and often have. Might not be a deliberate heat treatment, but it's effects need to be taken into account. I buy 4140 bar stock that is designated "as rolled" to differentiate it from "annealed" or "heat treated". In industry forging are often designated "as forged" "normalized" or "quenched & tempered". Quote Link to comment Share on other sites More sharing options...
patrick Posted March 21, 2011 Share Posted March 21, 2011 Hot forging is NOT a heat treatment because the microstructure and properties developed during hot forging are typically not controlled. This is especially true of open die or hand (hammer and anvil) forgings. While some forgings are used in the 'as-forged" condition (especially in the ornamental field) most idustrial type forgings undergo a seperate heat treating step. The forging process is done over range of temperatures so that when the forging is completed, there typically will be a variety of microstructures AND stresses present. Re-heating to a temeperature above the transformation temperature and controling the cooling rate from this point will result in controlled and predictable transformations of the microstructure which is how we get the properties we want out of a finished piece. Grant is correct that many forgings are shipped with a designation of "as-forged" but this is to distiguish them from those forgings which have been subjected to controlled thermal processing and in my experiece these pieces will undergo heat treatment at a later stage of processing. A simple way to think about this is that forging allows us to control the shape while heat treatment allows us to control the performace characteristics such as hardness, strength, ductility etc. Forging can have an influence on these properties, but in MOST cases, as long as you have the shape you want after forging is complete, the exact technique you use to get there is not critical since properties are developed during heat treatment. Patrick Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted March 21, 2011 Share Posted March 21, 2011 I know what you're saying Patrick, but if the metallurgical properties have been altered by heat, wouldn't that qualify as "heat treating"? However unintended.Broadly speaking. Many blacksmiths use tools "as forged" because that is enough heat treatment for their purpose compared to the annealed material they start with. Why? Because it has become heat treated from forging. Quote Link to comment Share on other sites More sharing options...
thingmaker3 Posted March 21, 2011 Share Posted March 21, 2011 Heat treatment is the intentional change in temperature to bring about an intentional change in microstructure. Forging is an intentional change of shape performed at an unspecified temperature. Forging of steel can be done at room temperature with enough force. "Hot forming" is forging above a critical temp for the metal - ie forging lead at room temperature. Microstructural changes accompanying forging are seldom the primary intent of forging. See also: ausforming. So my answer is a firm and unshakable "maybe." Quote Link to comment Share on other sites More sharing options...
Larry H Posted March 21, 2011 Share Posted March 21, 2011 yup, YOU know when, how and why, me too Quote Link to comment Share on other sites More sharing options...
Ramsberg Posted March 21, 2011 Share Posted March 21, 2011 My vote is YES! I had this one guys ask me why blacksmiths heated the metal to forge it. At first I thought that it was the stupidest question that I had ever heard. . . but the more I thought about it the more I realized that most people wouldn't realize that heating the metal up that hot makes it that soft. One thing I like to do to show people what heat will do is to have them try to bend a long 1/2" square bit of steel, then heat up the middle of it, put it in a vice and have them try again. They are usually astonished by how easy it is to bend. A quote from the description that Ric found, "A process where solid steel or components manufactured from steel are subject to treatment by heating to obtain required properties, e.g. softening, normalising, stress relieving, hardening. Heating for the purpose of hot-working as in the case of rolling or forging is excluded from this definition. " In that quote it states one form of treatment as softening, so thusly one would have to treat the steel with heat prior to forging it! OK, this is the definition from my 1942 Chambers's Technical Dictionary: "Heat Treatment. Generally any heating operation performed on a solid metal; e.g. heating for hot-working, or annealing after coldworking. Particularly, the thermal treatment of steel by normalising, hardening, tempering, etc.; used also in connexion with aluminium and other precipitation-hardening alloys." So I supose that one could say that the heating of the steel prior to forging it, for forging it is a heat treatment operation, but maybe not the actual forging of it. Inless one imparted enough energy into the forging that it was re-heated. . . then that could be considered heat treatment! HA! Caleb Ramsby Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted March 22, 2011 Share Posted March 22, 2011 Interesting Caleb! Got me to thinking; So, if you heat a piece and let it cool, it's heat treated. If you heat a piece, hit it with a hammer and let it cool, it's NOT heat treated? Why? I concur with Chambers's Technical Dictionary definition. Quote Link to comment Share on other sites More sharing options...
Fe-Wood Posted March 22, 2011 Share Posted March 22, 2011 Interesting! so in reading everyones thoughts on this- is it the various ways of manipulation and cooling that result in a form of heat treatment? Heating the metal for forging (or not) does nothing but make the metal more pliable for forging? I was going down the road of the after affects of heating and forging but to forge the material, it has been heat treated from the beginning... to make it forgeable. So my simple answer is YES! hot forging is a form a heat treating- regardless of how it is cooled after forging. Quote Link to comment Share on other sites More sharing options...
patrick Posted March 22, 2011 Share Posted March 22, 2011 I cannont, in good conscience as a metallurgist, agree with the idea that hot forging is a form of heat treatment. Forging and heat treating are two distinctly different operations with different microstructural and mechanical property outcomes. While a object may be usable in the "as-forged" condition it has not been heat treated with the intention of controling properties. The properties attained during forging may or may not be suitable for the intended service. The term "heat treated" is broad and applies to a variety of operations but those operations are recognized in industry as being distinctly seperate from the forming operation. Heat treatments are performed for the following reasons: Make a part harder or softer, to reduce residual stress, to dissolve undesirable precipitates, to refine or control grain size. Parts can be made harder through normalizing, quenching, nitriding, and carburizing followed by quenching. Forging is done for the following reasons: to get rid of shrinkage cavities inherant to the casting process, to develop anisotropic propties (that is align material grain flow in a way most favorable to the intended application), and to create a part that is near net shape requiring minimal machining. Let's do a thought experiement. If I have 4320 steel which I purchase annealed to a hardness of less than 20 HRc and I then put that bar in a cold heading tool and form a gear blank which gets hot during the forming process purely from the metal deformation and I then take that gear with no further heating operations and machine and use it, has it been heat treated? NO. Did it get hot? Yes. Is it fit for my application? Yes. But it it was not heat treated, only formed. If I take the same gear blank and after machining I carburize the surface then quench and temper it to a hardness of 58 HRc has it been heat treated? Yes. The part did get hot in both the forming and the subsequent manufacturing operatioins. After both forming and subsequent case hardening the part was fit for some (but different) applications. But the steps associated with case hardening are the heat treatment. The same is true with hot forging. The heat is added soley for the purpose of aiding the forming process and not with any expectations regarding the microstructure or properties. To suggest otherwise is not in keeping with good metallurgical terminology and in my opinion is likely to confuse people who are interested in better understanding the concepts of controlled heat treatment. If hot forging is considered a form of heat treatment then so is casting. If the casting is usable as it comes out of the mold, then by the logic applied earlier in this discussion that casting has also been heat treated. Patrick Quote Link to comment Share on other sites More sharing options...
Ric Furrer Posted March 22, 2011 Share Posted March 22, 2011 I would have to agree with Patrick. As an aside: Years ago in knife making the term "edge packing" in which a smith would take a low heat and work the blade with many light blows to "pack the edge" and beat the "molecules closer together" for a stronger edge. Besides the fact that metal has no molecules the reality is one can not make a solid more solid unless there is space to get rid of (as in Patricks example of reducing porosity in a casting). What IS being done is that it may be the first time that smith has bothered paying attention to the temperature and by working near the low side of forging he is bringing the blade just into austenite phase and allowing it to cool ... in doing this several times the smith has normalized the blades and this thermal-cycling just above austenitic and then to black heat has allowed the steel to refine its grain and equal out stresses from forging...the hammer blows are insignificant at that point metallurgically speaking...though he may be removing his hammer marks...or putting new ones in...who knows. So...in the case of edge packing you have grain refinement and normalization being done under the guise of forging....heat treatment being done without knowing about it. Ric Quote Link to comment Share on other sites More sharing options...
patrick Posted March 22, 2011 Share Posted March 22, 2011 I neglected to answer Grant's question directly in my post above. The differnce between heatign and cooling with and without deformation is as follows: When you deform a piece of metal, the crystal structure breaks up and may or may not recrysalize depending on the grade, temperature and time. Without deformation, you do not have that same change in crystal structure (and stress) hence heating and and cooling down without deformation in distinctly different that heating and deforming before cool down is complete. In addition, the temperatures generally used for forging are much higher than those used for intentional heat treat applications. If I load more pieces in the fire than I can forge in a day, those pieces which were heated and not deformed would not, in my opinion, be heat treated. The reason is two fold. First, the temperature is so much higher for forging than for heat treating that I would have to re-heat and control cool to get the properties of interest. The second is that the intention behind that heating cycle was NOT to develop final properties, or even intermediate properties, but only to aid the forming process. Patrick Quote Link to comment Share on other sites More sharing options...
Fe-Wood Posted March 22, 2011 Share Posted March 22, 2011 Patrick- I don't mean to argue with you. You clearly have a better understanding of metallurgy than I. Frank's question was "Is hot forging a heat treatment? " This is a very broad and open question. I think it speaks more to the broad discipline of Blacksmithing than the specific science of metallurgy. Your answer although very well thought out put very specific peramitters on the outcome. I'm not saying your wrong- I just don't agree. If the question had been something more specific like "Is hot forging a reliable heat treatment for intended use?" Your answers would be spot on. So I guess hot forging is a heat treatment that is not reliable, a verifiable process or reproducible with a consistent outcome. Quote Link to comment Share on other sites More sharing options...
Maillemaker Posted March 22, 2011 Share Posted March 22, 2011 I would think that it is based upon intent. Hot forging is not intended to refine or change the crystalline/grain structure, but to change the shape of the workpiece. Heat treatment (annealing/tempering/hardening) is not intended to change the shape of the workpiece, but to modify the mechanical properties of the metal, e.g relieving stresses, refining grain structure, etc. The problem with these definitions is that there is an amount of overlap. What makes us able to form metal the way we do is because we change the crystal structure while hot forging. I hope this makes at least an iota of sense. Quote Link to comment Share on other sites More sharing options...
thingmaker3 Posted March 22, 2011 Share Posted March 22, 2011 One can indeed change the shape of a piece of steel with heat alone. Anyone who has run a welder knows this. Some weldors can intentionally correct a shape with heat alone. Does that count as forging or as heat treating? Or niether? Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted March 22, 2011 Share Posted March 22, 2011 Looks like "intent and control" are needed. Intent is often used to separate things that may be quite close---when is a knife a tool and when is it a weapon? Intent. Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted March 22, 2011 Share Posted March 22, 2011 Dang you Frank! I know you're just sitting back laughing and thinking of the next thing you can ask to make us think! Quote Link to comment Share on other sites More sharing options...
Ramsberg Posted March 22, 2011 Share Posted March 22, 2011 Now how about heating the steel to burn on oil or brush on brass for a finish. If "heat treatment" is defined by heating the metal to give it a require property. . . well the required property there would be for it to be hot! HAha! I think that there is a big riff here between the very techinical focused aspects of metallurgy and general broad metal work definitions. That definition I posted was from the 40's and made a distinction between a general(metal working) definition and a more specific(metallurgy) one. Do any of you metallgury guys have a modern technical dictionary and if so, would you post the definition(s) of heat treatment here? Caleb Ramsby Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted March 22, 2011 Share Posted March 22, 2011 I would think that it is based upon intent. Well, I don't think the steel gives a rat rip what our "intent" is. If I forge a piece of air-hardening steel, it's going to be hard after it cools down regardless of my intent. So why is it hard, if it hasn't been heat treated? If I sent it out for analysis, the report would say "heat treated". Hot forging is not intended to refine or change the crystalline/grain structure, but to change the shape of the workpiece. I've made forged bar for Jorgenson Steel. Start with 6" bar, forge it down to 3". Only reason is to "refine or change the crystalline/grain structure". All steel starts as a casting and then it is hot worked (rolled) to "refine or change the crystalline/grain structure". Otherwise they would just cast it into bars. Quote Link to comment Share on other sites More sharing options...
Rhrocker Posted March 22, 2011 Share Posted March 22, 2011 Well, I don't think the steel gives a rat rip what our "intent" is. If I forge a piece of air-hardening steel, it's going to be hard after it cools down regardless of my intent. So why is it hard, if it hasn't been heat treated? If I sent it out for analysis, the report would say "heat treated". Good example Grant. Up until I read Grants post here, I was standing by my "yes" answer. So now I'm for sure staying with it. It just makes sense, but I'm not conversant in Metalurgy at all, so I'm really not 100% sure of what Frank is hatching up here for us. He's probably horselaughing at the monitor right now. For the record, I can't dispute Patrick's information however, but being a blacksmithing bladesmith (bladesmithing blacksmith?), and looking at it from that perspective, I'll stay with "yes" to the question. Quote Link to comment Share on other sites More sharing options...
Maillemaker Posted March 23, 2011 Share Posted March 23, 2011 Oops. As it is written, "better to be thought a fool than to speak and confirm it". I guess I'm the fool. :blink: Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted March 23, 2011 Share Posted March 23, 2011 Sorry Maillemaker, wasn't trying to beat up on you. Quote Link to comment Share on other sites More sharing options...
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