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Thread: Annealing vs Normalizing vs Spheroidizing vs Stress relieve - need some info please

  1. #1
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    Question Annealing vs Normalizing vs Spheroidizing vs Stress relieve - need some info please

    Hi Everyone,

    I have been searching the Web (including this Forum) for some time now looking for specific information/data regarding the "softening" processes of steel (i.e. Annealing, Normalizing, Spheroidizing and Stress relieving...), but I could not find much definitive information specifically relating to treating of knife steels - not even from the steel manufacturers' websites!

    The best description/explanation that I could find was from efunda.com:



    • Full annealing is the process of slowly raising the temperature about 50 C (90 F) above the Austenitic temperature line A or line A in the case of Hypoeutectoid steels (steels with < 3CM 0.77% Carbon) and 50 C (90 F) into the Austenite-Cementite region in the case of Hypereutectoid steels (steels with > 0.77% Carbon). It is held at this temperature for sufficient time for all the material to transform into Austenite or Austenite-Cementite as the case may be. It is then slowly cooled at the rate of about 20 C/hr (36 F/hr) in a furnace to about 50 C (90 F) into the Ferrite-Cementite range. At this point, it can be cooled in room temperature air with natural convection.


    • Normalizing is the process of raising the temperature to over 60 C (108 F), above line A or 3 line A fully into the Austenite range. It is held at this temperature to fully convert the structure CM into Austenite, and then removed form the furnace and cooled at room temperature under natural convection. This results in a grain structure of fine Pearlite with excess of Ferrite or Cementite. The resulting material is soft; the degree of softness depends on the actual ambient conditions of cooling. This process is considerably cheaper than full annealing since there is not the added cost of controlled furnace cooling.

    The main difference between full annealing and normalizing is that fully annealed parts are uniform in softness (and machinablilty) throughout the entire part; since the entire part is exposed to the controlled furnace cooling. In the case of the normalized part, depending on the part geometry, the cooling is non-uniform resulting in non-uniform material properties across the part. This may not be desirable if further machining is desired, since it makes the machining job somewhat unpredictable. In such a case it is better to do full annealing.

    • Stress Relief Anneal is used to reduce residual stresses in large castings, welded parts and cold-formed parts. Such parts tend to have stresses due to thermal cycling or work hardening. Parts are heated to temperatures of up to 600 - 650 C (1112 - 1202 F), and held for an extended time (about 1 hour or more) and then slowly cooled in still air.


    • Spheroidization is an annealing process used for high carbon steels (Carbon > 0.6%) that will be machined or cold formed subsequently. This is done by one of the following ways:

    - Heat the part to a temperature just below the Ferrite-Austenite line, line A or below the 1 Austenite-Cementite line, essentially below the 727 C (1340 F) line. Hold the temperature for a prolonged time and follow by fairly slow cooling.
    - Cycle multiple times between temperatures slightly above and slightly below the 727 C (1340 F) line and slow cool.
    - For tool and alloy steels heat to 750 to 800 C (1382-1472 F) and hold for several hours followed by slow cooling.


    This structure allows for improved machining in continuous cutting operations such as lathes and screw machines. Spheroidization also improves resistance to abrasion.

    Here on SA Blade, I've found the following:

    Graham Knight
    Regarding stress relieving:
    the rule of thumb states that should you work (drill, machine, grid, forge, form) an material to the extent where 10% or more of the components structure (shape) is affected or removed then a stress releiving cycle is required. these opperations introduce residual stress into the steel which makes it more prone to distortion and cracking during the quenching stages of heat treatment. Stress releiving is a heat treatment process that will not hurt your product if carried out, it will only have a positive influence on it. This cycle is carried out just before you hardening cycle. place the item in the furnace, heat to the specified temperature and cool inside the furnace. in this instance the item must be allowed to cool down as slowly as possbile as to avoid picking up stresses during the cooling cycle.


    mete:
    steels above the eutectoid ,especially the 1.00 % carbon grades present a problem that you must understand . The slow cooling from the austenitizing range gives lots of time for the carbon to diffuse to the grain boundaries .You can get continuous grain boundary carbide and that is extremely brittle !!! So no cooling in the furnace or sand . Air cool to give a pearlitic structure or quench and temper at 1200-1300 F to give a fine spheroidized structure .

    On hypefreeblades.com I found the following:
    So the standard three step process (for spheroidizing) is:
    1) Austenitize at about 200 above Ac1 ( 1550F), and quench. This clearsall previous structures in the steel, and forms a martensite structure.
    2) Austenitize at just above Ac1 ( 1350F), and quench to form martensite with a very fine grain.
    3) Spheroidize at 1250F for 10-15 minutes and cool to below 900F slowly.

    This should give you a steel that will drill, mill, and grind the easiest.

    It appears to me that some of these processes are more applicable to large industrial steel manufacturing processes, and might not be necessary for knife making. Some of these processes might also be more applicable to knife forgers, and not necessarily to knife grinders?

    All I want when making a knife is for the steel to be workable (and new steel is usually sold in an annealed state...), and to not distort or crack during hardening. Obviously, I would also want the steel to be as "good" as possible in it's final heat treated state (i.e. tough, hard, retain edge, etc.), without having to take extraordinary steps for only very small improvements.

    Now, with regards to applying these various processes to knife making, specifically utilising the STOCK REMOVAL (GRINDING) method of knife making, can someone please clarify the following:


    1. What process/es do I use before starting to work on a knife (if any...)?
    2. What process/es do I use after completion of shaping & drilling the knife (I grind after hardening...) before heat treatment(hardening), and why?
    3. Are these recommended processes applicable to all types of steel (i.e. tool steels such as O1, D2, 5260, etc. AND stainless steels such as N690, 12C27, 44C, etc. What about powder steels?
    4. When annealing/spheroidizing, etc. should the knife also be wrapped in foil to prevent oxidation/decarburation?
    5. When "quenching" as described for spheroidizing (above quote from hypefree blades), how is this done?

    Regarding the specifics of the above-mentioned processes, can someone also please post the actual recommended treatment "recipes" (i.e. stress relieve temp, annealing temp, spheroidising temps, normalizing temp, hardening temp, and soak times for each process), and either the TTT diagrams or the A3/Acm temperatures (I assume the A1 temperature for all steels is the same, being 727C, but if this is not so, then also the A1 temperature...) for the following steels (and any others that you have information of...):

    • 1060
    • 1095
    • 5160
    • D2
    • O1
    • N690
    • 12C27
    • 14C28N

    Thanks
    Last edited by HennieL; 11-30-2012 at 05:27 PM. Reason: corrected error - 5160 and not 5260

  2. #2
    Hennie

    There are a few things to remember.

    - The steels used for knife making in general were not always made for knives specifically, only a few were specifically designed.
    - Many alloys have been in the market for some time. M390 for example and then someone tried it for knives.

    Most steel can be bought annealed from a supplier. Therefore you only have to do the heat treatment.

    Here is some good information:

    http://www.smt.sandvik.com/en/produc...-knife-steels/

    The heat treat process that you usually do yourself is:

    Austenitizing
    Quench (if applicable)
    Deep freezing (if applicable)
    Tempering

    Here is the process in visual form by Sandvik for 12C27M


    As you wondered what Quenching is:

    In the heat treating of metals, the step of cooling metals rapidly in order to obtain desired properties; most commonly accomplished by immersing the metal in oil or water. In the case of most copper base alloys, quenching has no effect other than to hasten cooling.

    http://www.mtpinc-exporter.com/metal...y/dictlist.htm

    I would recommend you contact a local knife maker and have a sit down. You will have many questions and though the internet is a great resource, nothing beats hands on or face to face communication.
    Last edited by marthinus; 11-30-2012 at 03:35 PM.
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  3. #3
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    Quote Originally Posted by marthinus View Post
    Hennie

    There are a few things to remember.

    - The steels used for knife making in general were not always made for knives specifically, only a few were specifically designed.
    - Many alloys have been in the market for some time. M390 for example and then someone tried it for knives...

    ...I would recommend you contact a local knife maker and have a sit down. You will have many questions and though the internet is a great resource, nothing beats hands on or face to face communication.
    Hi Marthinus,

    Thanks for your response. I am not totally unfamiliar with the heat treating process, having HT'd about 10 knives during the past year. I am also a member of the Bloemfontein knife club, and have received some very good info from the other members

    The heat treat process that you usually do yourself is:

    Austenitizing
    Quench (if applicable)
    Deep freezing (if applicable)
    Tempering
    My questions specifically relate to the "softening" processes applied to the steel before austenizing - there are some real benefits in "pre-treating" the steel before the hardening process (such as reducing warpage and ensuring smaller grain size), but the reason for my question/post is the scarcity of actual data specific to the various types of steels, and the contradictions in advice from some of the gurus (such as the quotes from mete and Graham Knight in the OP, one saying: "heat to the specified temperature and cool inside the furnace. in this instance the item must be allowed to cool down as slowly as possbile as to avoid picking up stresses during the cooling cycle." and the other: "The slow cooling from the austenitizing range gives lots of time for the carbon to diffuse to the grain boundaries .You can get continuous grain boundary carbide and that is extremely brittle !!! So no cooling in the furnace or sand")

    THIS is a very good example of my frustration - the Sandvik website you referred me to does not even mention stress relieve or normalization temperatures or procedures, and there is NO information on spheroidizing! hence my request for the relevant information for the various steels mentioned in my original post

    As you wondered what Quenching is:
    Oh, I think that you mis-understood my question/point. I do know what quenching is as applied to "normal" heat treating. I asked this question in the context of "quenching" between the three spheroidizing cycles as described in the quote from the hypefreeblades.com thread, where the poster mentions: "austenitize at about 200 above Ac1 ( 1550F), and quench; Austenitize at just above Ac1 ( 1350F), and quench to form martensite". If you read the full text of the quoted post, the OP talks about cooling to "black heat" (about 900F) and THEN quenching, whilst on the efunda website they describe one of the spheroidizing methods to be: "Cycle multiple times between temperatures slightly above and slightly below the 727 C (1340 F) line and slow cool.". My question thus relates to the quenching technique one should employ to drop the temperature to "slightly below the 727C" line.

    As per my original post, I would really appreciate any further enlightenment, and the specific data for the steels mentioned, if anyone can help

    Hennie

  4. #4
    Hennie

    In all honesty I for one cannot help you with your questions.

    Only advice I can give is try sending your questions to a steel manufacturer or try to contact someone at University that is a metallurgist.

    Hope you find your answers.
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  5. #5
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    In all honesty I for one cannot help you with your questions.
    Hi Marthinus,

    No problem, and thanks for trying

    Only advice I can give is try sending your questions to a steel manufacturer or try to contact someone at University that is a metallurgist.
    Yes, I had hoped that mete or Graham (and other experienced Forum members) would responded (is Graham still around, he has not been active for quite some time now...)

    I have managed to find a few titbits of data off discussions on other forums, but unfortunately nothing "official" or confirmed by more than one person (although I do tend to believe data given by people like mete, Landes, Koval and Cashen) - hence my request for data from knife makers on this Forum. I don't think universities will be of much help, as knife making heat treatment is a rather specialized field (and I tend to rather trust experience than academics in any case

    Hennie

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    Marthinus, from those sources you'll only get some cranky old metallurgist to give info !!
    Actually there are some metallurgist/makers out there which would be the best source like Roman Landes and Haakonsen.
    The hypefreeblades "Spheroidize 1200F for 10-15 minutes" . I don't think that is enough time .More like 1 hour will work.
    You've asked too many questions to answer at once. You must understand that each steel is different and must be handled to get the best properties from that steel.
    All forged blades must be normallized after forging to make the structure uniform throughout.
    Some steps must consider the next process .For example for best machining large spheroidized is best . For quicker and more uniform austenitizing small spheroidized is better.
    1200 F isn't high enough to cause much scale so no need to wrap in foil.
    Stress relieve is a good practice before austenitizing.
    It's 5:00am here so I'll be back when I'm more awake !

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    Thanks, mete - I'll have an afternoon nap while I wait

    You've asked too many questions to answer at once.
    That's OK - please take your time, and answer as you see fit.

    I do think it would be a great source, especially for new/beginner heat-treaters like myself, if we (i.e. you and the other experienced members of SA Blade ) could compile a compendium of data for whatever steels we have data for, not only regarding the freely available austenizing temperatures, but also (specifically) the "other" temperatures such as stress relief, normalize, anneal and spheroidize, as asked for in my original post.

    Hennie

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    Wake up Hennie !
    Graham and I are both right about slow cooling ! But we speak of different conditions. My comments pertain to 1 % C or higher such as 1095. I think I have some photos somewhere but it would take me forever to find them .The photos show a continuous carbide grain boundary which is very brittle !! You don't want to sell a knife in such condition as even dropping it on a hard surface can fracture it and of course the safety factor is important.
    Graham's very slow cooling is for complex shaped parts which are obviously not knives. Those of us metallurgists with industrial experience have to shift gears and that may be difficult. Part of choosing a steel depends on many things and complex shapes should be avoided if possible .I couldn't count all the failures I've seen due to poor basic design like sharp interior corners .They all seem to have early failures in manufacture , HT or use . BTW one of the reasons for development of air hardening tool steels is to deal with complex shapes. As are marquenching and other slow quenches.
    Three cycle spheroidizing - are you taking this out of context ? When you have screwed up HT and gotten lots of carbides in the grain boundary it can be fixed .First you have to completely dissolve all carbides .That means high temperatures which cause other problems .The homogenious structure has large grains etc' . the other two steps then get a nice distribution of carbides and proper grain size.BTW always deal with carbides first then deal with grain size.
    'Powder steel' is a manufacturing method not a difference in chemistry .For example 154CM has the same chemistry as CPM154. Someone recently asked about 690 but was confused by various types but they are modifications of the basic chemistry . Here 690Co is used but that seems to me an advertizing thing, ESR [electroslag refining] and VAR [vacuum arc remelting] are methods to remove more nonmetallic inclusions. That's very important for bearing but no so much for knives .

  9. #9
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    Yawn... OK, I'm awake

    Graham and I are both right about slow cooling
    Now THAT's where you evil metallurgists create much of the confusion, being both right about different things that appears to be the same to us plebs

    Anyway, back to the topic... let's take one question at a time...

    Given that I'm a grinder and not a forger, what "pre treatments" do you recommend for "pre-grinding" and "post-grinding, before HT", assuming that I have not over-heated the steel, and that I have not buggered up any previous hardening (given that no hardening have been done yet ) for the steels mentioned in my first post:

    • 1060
    • 1095
    • 5160
    • D2
    • O1
    • N690
    • 12C27
    • 14C28N

    Hennie

  10. #10
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    Pre grinding- if the steel is properly treated then nothing should be needed. If improperly done then stress relieve temper is he answer, but that would be rare.

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