Heat Treatment Process

[class022]

Hey all,

I have been on the site for a little while now and have read a few of the metallurgy books recommended on this site. I have tried to piece the heat treatment process together but I'm still having some trouble understanding.
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As far as I am aware, normalizing and annealing reduce stresses caused by forging, additional heat treatments, etc. The differences between them seem to be annealing is done through heating to either at or slightly above critical temperature and then placing the metal in a temp-controlled substance, such as vermiculite, to slow the cooling process. Normalizing is essentially the same thing except the metal is brought to a temperature higher than annealing and the metal is then allowed to air-cool to room temperature.

After hardening, tempering is used to reduce some of the brittleness caused by the quench by bringing the metal below critical temperature (for most medium carbon steels I seem to get answers in the brown-blue oxidizing region for this) and then quenching again to prevent additional heat build-up and start the hardening process over again.

My first question is do I have my terminology correct?

My second question is when is annealing more preferable to normalizing or does one try to use them both when forging, for instance, medium carbon steel?

My last question is how many times should one try to use annealing or normalizing during forging? Some will recommend performing these during forging to prevent warping and to prevent cracking when quenching. However, as far as I understand, too many heatings weaken the metal by either decarbonizing it or allowing too much grain growth.

I have a propane forge very similar to Larry Zoeller's metal bucket forge only I used an old propane tank instead.

I apologize if there is any information I didn't think to put into my question and will add that information when needed.

[jimmy seale]

well..here goes.. in my limited experience,you would anneal already hardened pieces like files to soften then up for drilling,shaping and such.normalizing will help releave stress and grain growth, and should be done when your finished or when the forging session is over but the piece isn't done yet.as far as multuple hardenings (on steels that i use) when you reheat to critical to harden you lose any hardness you gained the first time. tempering is done way below the forging temp. i usually start low and cycle till i get the color i want.i am sure more knowledeable folks will give you a better/more indepth definition,as i have little knowledge of alot of tool steels. yes too many heat cycles will hurt but with experence comes knowledge and speed also watch your heat...carbon/alloy steels don't like heat that mild will use, use a magnet to find critical and in time you will know what color is right for forging. have fun and i hope this helps some,jimmy

[John B]

Hi, Basically your terminology seems OK, just to recap

Steel is heat treated to give it certain desired properties, These properties are determined by the heat treatment to which the metal is subjected to, the governing factor of which is the rate of cooling.

When steel is required in the softest condition it is ANNEALED

After forging or after cold working, the metal is NORMALISED

To enable steel to cut another metal and/or to prevent wear, the material is HARDENED

To relieve brittleness, and to obtain toughness, the steel is TEMPERED


Normalising and annealing are carried out from a similar temperature 30 to 50 degrees celsius above the metals upper critical point.

Normalising and annealling are more essential when making blades or tools, much more information can be found on the Blademaking forum

If you are forging steel then during the forging processes you will not need to anneal/normalise, If you quench your steel after forging, then you may need to normalise/anneal depending on its intended use.

You will have difficulty in tempering in a gas forge unless you are using an idndirect heating method to obtain the temper.

How many times can you use the process, as few as necessary would be my response, others may have more pedantic advice based on their experiences.

[ThomasPowers]

If you are going to drill or file a piece annealing is called for, otherwise I normalize and only do that formally when I am working with medium to high carbon steels. Mild steel items just get tossed on the dirt floor to cool.

[MattBower]

I've admitted this before, but I throw it out there again just for the record. WIth the relatively simple steels I work with, I don't bother annealing before doing stock removal. I just normalize a few times at the end of forging. Yes, I know I could get them softer if I annealed, But I also know that in some steels, my simple annealing methods could cause more problems than they solve.

[thingmaker3]

First off, Welcome to IFI!

Annealing is for making the steel as soft as we can get it. Normalizing is for relieving stress, thereby minimizing distortion and/or cracking when we go to harden the thing. Note well: normalizing does not work for those steels with the most hardenability. Their stresses may only be relieved with a full anneal. (Normalizing is sometimes called "process annealing.")

For machining or other stock reduction, it is often better to spheroidize. Depends on the steel.

Grain growth is caused by too much time at temperature or too high a temperature. We re-nucleate new grain each time we heat the steel into austenite. This is why many smiths prefer to thermally cycle some parts. (They call it "normalizing three times.")

"Too many" heats for one steel will be a different range than for another steel. Decarburisation is something of a boogeyman. To hear some smiths talk, you can turn 5160 into 1018 by heating it once too often. For a better understanding of what decarburisation is all about, look up "Fick's Second Law of Diffusion." Yes, it is a problem (even a big problem) with some steels. But normalizing heats with oil-hardening or water-hardening steels will not see significant decarburisation.

I hope this is of some help.

[class022]

thank you for all the help. I, like most young men it seems from reading the articles, intended to make blades initially. The more I read the more I become convinced that is a gradual process and can be dangerous without experience. I think for the moment I will stick with tools, like iron pokers and tongs. As such, I don't believe I will be annealing them much since I don't need to drill a hammer (punch it yes, drill it no). I have a class soon my an ABANA organization here that will show me how to forge some tongs, I will let you all know how I do.

[Frank Turley]

It depends on the steel and how it's alloyed. For example, 01 and S1 are never normalized, as it affects the steel adversely. S7 can't be normalized, because it is air hardening. Plain carbon steel and some low alloy steels are normalized in order to refine the grain structure in preparation for hardening. On these steels, it is better to normalize than to anneal prior to hardening, as these grades retain large carbides (undesirable) after annealing. Annealing can be done, if you want to do cold work, such as sanding, filing or drilling. Builder's lime or fine wood ashes are good insulators and can be used for annealing.

In a small shop situation, hardening is done in brine, water, oil, or air. Brine is the fastest quench. The metallurgist's spec sheet or pamphlet will give the quenchant and the proper temperatures for the steel's heat treatment.

There is a wide range of tempering temps depending on the steel. Some hot work steels get tempered to a dull red incandescent color. On plain carbon, high carbon steels, surface oxide colors are often used to show temperature, from approximately 430ºF. a straw color to 630ºF. a pale blue color. Each tool, depending on its end use, has it's own ideal temperature for tempering.

My favorite chart for showing tools and tempering temperatures is in the British book, "Metals for Engineering Craftsmen."

[Old N Rusty]

I want to say this is the finest thread i have ever read on IFI !!!!! properly posed questions and clear, precise answers. This is what blacksmithing needed for a very long time.

[hans138]

I want to say this is the finest thread i have ever read on IFI !!!!! properly posed questions and clear, precise answers. This is what blacksmithing needed for a very long time.

i would agree, this is why im here. although im familiar with the subject matters in this thread, im glad there are noligable people willing to share there knowlegde