Darn it Cliff, I am trying to keep my self-imposed limits on participation so that I can effectively moderate, but your questions are some of the best I have seen in a long, long time. Your hunger for knowledge is what makes guys like you the real purpose and driving force of a proper educational forum and I cannot bring myself to let the opportunities your threads present for learning to pass me by.
Most of what you get from folks who may balk at us who take a metallurgical approach to our craft is natural human reaction of feeling threatened by what we do not understand, but if we get too bogged down in every detail of some of those specs sheets we can actually risk becoming the caricatures that we are portrayed as. As you have already surmised, the trick is educating one’s self enough to be able to sort the relevant from the irrelevant to our purposes. The spec sheet you have is primarily for engineers more than knifemakers or heat treaters.
I am trying to learn how to look at the specs on steel and tell what the proper quench time is!
What am I missing here on this for example on this spec sheet on AISI 1080. Does it say somewhere in there what is the proper quench time, IE 8-10 seconds at proper heat.
I know that 790*C converts to 14548F So I know that is optimum working temp but how do you find out by the data what is the optimum quench time for full hardness.
Unless I am missing something I don't see that information. Or I may just not understand how to read what I am looking at. Can anyone help me out here. I figure if I can understand the info in the charts better I can understand how to produce a better knife from a given steel be it 1080 or 1095! Help anyone!
I know some of you are going to say this is not the right forum for this and maybe so. I figure though if you can't read the steel specs you don't know what to use for quench and how to heat treat. So I guess I am looking at this as a hand in hand thing. If I understand the specs then I can quench with proper medium by getting the quench in that time frame that allows for the optimum hardness of that given steel.
AISI 1080
Category Steel
Class Carbon steel
Type Standard
Designations United States: AMS 5110 , AMS 5110B , ASTM A29 , ASTM A510 , ASTM A576 , ASTM A682 , FED QQ-S-700 (1080) , MIL SPEC MIL-S-16974 , SAE J403 , SAE J412 , SAE J414 , UNS G10800
The above section only matters if we are looking to buy the steel from odd sources or foreign suppliers that may use other designations that you would want to cross reference.
Composition
Element Weight %
C 0.75-0.88
Mn 0.60-0.90
P 0.04 (max)
S 0.05 (max)
While this stuff needs a lot of interpretation, it can tell you a lot about the properties of the steel and how it will respond to your heat treatments. Without even knowing the name of the steel the .75-.88% carbon tells you that it should hold a pretty good edge, it will not be too much of a challenge to anneal, normalize, or heat to harden (a nice range from 1475F- 1500F will do). You will not have to deal with extra carbon that will give problems on cooling rates, but on the other hand it will not have carbide to give extra boosts in abrasion resistance, but it sure will be good enough. The .60-.90 Mn tells you that you will get a boost in hardenability allowing you to forgo water in knife blade thickness, if it got above 1% you would even be flirting with full oil hardening steel. The P and S contents being below .09% makes them inconsequential trace elements.
Properties Conditions
T (°C) Treatment
Density (×1000 kg/m3) 7.7-8.03
The density is what it is, and you aren’t really going to change it with what you do, although some bladesmiths used to believe you could.
Poisson's Ratio 0.27-0.30
This is interesting, I have rarely seen this included on a spec sheet but it is cool to see. I am not an engineer or good enough with the numbers to get into the specifics of it, but Poisson’s Ratio deals with the compressibility of the material, i.e. the ratio of expansion in the transverse direction from which you compress it. Once again, bladesmiths can benefit from understanding that steel moves under the hammer because when you squeeze it in one direction it expands in another and does not just get smaller and denser. A cork would have the lowest since it just compresses while rubber is very high, incompressible, since it expands proportionally to its compression. You won’t find a dimes worth of difference between most steels unless you get radically different like stainless or cast iron, so for the most part it is not relevant to what we do.
Elastic Modulus (GPa) 190-210
This is yet another technical tidbit that would be great for all bladesmiths to know about in order to understand how blades flex and bend, but for your purposes it is not very useful. With almost every steel we work with, the Modulus will be around 29-30 PSI x 10 to the 6th, and we can’t change it with heat treatment at all.
Tensile Strength (Mpa) 615.4 annealed at 790°C
This is interesting in that is specifies an annealed condition. I am particularly interested since I just got my portable tensile tester up and running and am stretching and breaking everything I get my hands on with the new toy. This can be of value if you want to bend blades and would like to know what steel would resist the bend the most. You can adjust the point at which the needle quits climbing with heat treatment but to be honest there are much more important things for knifemakers to focus on, especially if they don’t want to play with tensile testers. In either case just one value is nowhere near as useful as a stress /strain curve to put it all in perspective.
Yield Strength (Mpa) 375.8
Elongation (%) 24.7
Reduction in Area (%) 45.0
All of the above falls into the same category of usefulness as tensile strength and would be included on things like the stress strain/curve I mentioned.
Hardness (HB) 174 25 annealed at 790°C more
This would only be good for the steel as it arrives from you in the designated annealed condition, knifemakers could use it to determine how easy it will be to cut or machine, but it will all be meaningless as soon as you start heating the steel. The hardness listed is in Brinell, which converted to Rockwell C would be around 7, but the “C” scale is all but useless in that range so you would need to consider it more an 88 Rockwell B which at least uses a ball instead of pointed penetrator.
Impact Strength (J)
(Izod) 6.1 25 annealed at 790°C
Impact strength can be useful to us more nerdy knifemakers, but this is Izod (I mostly use Charpy) and it is in Joules (my tester likes Ft. Lbs.), it is also in the annealed state so a chart with the values for other hardness ranges would be of much more use. You can look for steel with higher numbers to make your big choppers and camp knives out of, which is much more relevant than simple tensile strength and slowly bending a blade. But steel in the range of 60HRC is like splitting hairs in getting dramatic Charpy results.
Thermal Properties
Properties Conditions
T (°C) Treatment
Thermal Expansion (10-6/ºC) 14.7 20-700 annealed
Thermal Conductivity (W/m-K) 48.1 100
Specific Heat (J/kg-K) 490 50-100
Electric Properties
Electric Resistivity (10-9W-m) 180 20
Of the above the only one of any possible relevance would be thermal expansion often also referred to on spec sheets as “Mean Coefficient of Thermal Expansion”, once again I'm not the one to go into the numbers but if you were making very complex parts with thicker cross sections you may want to consider it in heating if things have to stay in very tight tolerances. For knives, it rarely means anything.
Since the vast majority of what you have in this spec sheet is fairly very handy for engineers but not of much use to knifemakers. A better place to start is with a page on your steel from something like the ASM “Heat Treater’s Guide” which will give you all the specs on the processing procedures for your steel. Many have found even that information not to apply to their methods but we need to remember that we can’t pick and choose which specs we will follow and which ones we won’t and still expect the numbers to match up.
I have much of the information on 1080 from the “Heat Treater’s Guide” here at my webpage:
[url]http://www.cashenblades.com/steel/1080.html[/URL]
Of the information there that you could use the most would be the I-T curve:
A CCT cooling curve for 1080 would be really useful but I don’t have one so we will have to work with this. The answer to your primary question in this thread is right there on the curve between 1200F and 800F. to the right of this zone you will see a “nose” sticking out from the curve on the right that makes a narrow channel on the left hand side of the chart. This is the critical zone that you need to cool through to avoid making the soft stuff you do not want if you want to fully harden your steel. That nose is known as the “pearlite nose” and if you draw an imaginary straight line from your estimated hardening temperature (1475F to 1500F) diagonally down to the bottom, it will tell you then maximum number of seconds you have to cool the steel and not make the soft stuff. But since the curve moves drastically to the right once you are below 800F you only need to really sweat it until that point. In this case you will need to cool 1080 from 1500F to below 900F in less than .75 seconds to avoid any pearlite and fully harden your blade below the Ms mark at around 430F. It is only necessary to cool that fast in that initial phase; in fact it is detrimental to cool too fast below 400F.
It is also worth noting that these phases occur on cooling or with extreme time, so the clock starts when you hit the oil, not when you pull from the oven, so please don’t hurt yourself rushing to the oil. Air is an insulator and it takes quite a while to start forming pearlite in it, but oil that cools the steel through the pearlite zone too slowly will not give maximum hardness. To test this heat a bar of your 1080 to 1500F and cool it in total darkness while timing things. At the pearlite zone you will see the dull red steel suddenly grow brighter as the exothermic pearlite reaction occurs (this is called recalescence). You will notice that it took minutes, not seconds for this to occur in the air, but in a liquid it will be less than a second and that is why using the right quenchant is so critical. Now with something like 1095 that has extra carbon to give you troubles on cooling before you reach the quench you may want to get a little more uptight but with 1080 you can relax.
Basically I get what you are saying about going directly from critical temp to the quench medium. What I am trying to understand is how to look at the specs on any given piece of steel and know what I need to know about quench. Because quench is the first step in getting it right…
I know exactly where you are coming from here, and I can’t tell you how much I respect your concern for getting it right, but I would also stress the importance of the heating, as well as the quenching. In fact I might say that the quench is actually the final thing a line of processes that are critical to get the most out of the steel. Most of the problems I see people struggle with can be traced to before the quench during the heat, but the quench is so dramatic that we tend to focus more on it. You can quench two knives identically in every way and still have one dramatically outperform the other based solely upon soak time and temperature. Once again, you are working with 1080 so you don’t need to lose too much sleep over it but tight temperature controls that allow a thorough solution will be the key to unlocking the best in any steel.
Edited to add: I don't like borrowing material and then using it on my site or elsewhere on the internet, so that I-T chart is was done by me, please be repectful of that as well.