Heat Treatment Processes

Start here:

Heat treatment - Wikipedia, the free encyclopedia

Then, check other web sites as required. Then maybe you will have specific questions.

Please check out the following link:

http://www.esabna.com/us/en/education/knowledge/weldinginspection/What-The-Welding-Inspector-Should-Know-About-Preheating-And-Postweld-Heat-Treatment.cfm

Good reading on the subject of PWHT

these links kind of miss your query. Heat treatment is a code word that means diffeerent things to different folks, even the folks at wiki. At first the added energy allows theintracrystalline stresses to relieve; added energy allows the material to change phase, and finally additional energy allows these new crystals to grow. The amount of energy/ temperature varies per material and amount of cold work. milo

Milo,

You have such a way with words.

Cheers, Lyn

Don't encourage Him!

<Thanks Lyn>

milo

How does the heat "break the dislocation" and allow the retained energy to be released? Is it by breaking the bonds between the molecules?

And why are there new small crystals that starts appearing during recrystallization? I mean, if recovery stage breaks the bonds, it doesn't make sense that new crystals will appear by adding even more heat into it? Sorry for the noob questions :)

Ask Asked: "How does the heat break the dislocation?"

We had posted :"This thermally driven rearrangement permits the bulk material to regain or RECOVER its prior to cold work properties. So this part of the curve is called Recovery."

By adding thermal energy to the material the crystal lattice can "heal" by permitting movement. (increased diffusion) This allows out of place atoms to find their way into the place that they 'want to be' by their size and properties. Conversationally, the added heat permits the material to relax by allowing the atoms under stresses to move the imperfections.

In crystal structure, its atoms, not molecules.

Next question was "And why are there new small crystals that starts appearing during recrystallization?"

I lack divine omniscience to answer "Why?" but I think that what we observe is that the material reorders itself into its prefferred crytalline arrangement, driven by the added energy. The dislocations act as speed bumps or wedges to keep atoms from moving; the added energy kicks those wedges out of the system. And the material at those dislocations is the place to start because it is that with the most degrees of freedom to do so. as the energy increases more and more atoms are able to diffuse into the new crystal structure/order.

Conversationally (metaphorically) I think of the heat as a neighborhood watch committee at the crystal lattice level. The more neighborhood watch volunteers you put in the neighbor hood, the more graffitti and litter gets cleaned up. (recovery) Keep adding volunteers, and soon small businesses appear.(recrystallization). And if the small businesses cater to the neighborhood watch people with valuable services these new business (grains or crystals) will grow (grain growth.)

No need to apologize for a question that seeks genuine insight.

Nice to meet you.

milo

See if you can borrow a copy of MAKING, SHAPING, and TREATING of STEEL, published by U S Steel

Good reference book, My copy is a Fourth Edition, 1925

With the two color pullouts?

I cherish my older copies too!

milo

Did you try to talk to your professor?

It would appear that your main concern is about gray cast iron.

Try this site:http://steel.keytometals.com/Articles/Art112.htm\

It has a fairly good explanation.

You have to say what type of metal you are planning to heat treat first. Is it low carbon steel, stainless, duplex, chrome moly, ands o on? After you figure this out you would have to know and say what end result you want accomplish, stress relieving, normalizing , annealing , hardening and so on.

Once you know the material then you can go to ASME sec. II part A for ferrous metals and B as for non ferrous metals well as part D for metal properties, and look it up for the alloy the ASME code has figures, tables and written criteria to follow for heat treating and find the proper hold time for each 1" of thickness of most metals. Another good source of heat treating parameters for different metals is the
Machinests Handbook.

Generally low carbon steel does not need post weld treatment under 3/4" thickness but Chrome moly steels nearly always requires PWHT at any thickness. Also many stainless type alloys react differently than carbon steel in that stainless would many times get a water quench at a high temperature if normalizing and no PWHT where the higher carbon content steels and chrome moly would require slow cool down from critical temperature for normalizing and PWHT.

The thing is different alloys will require different high temperature parameters and cooling mediums and/or rates that must be met to accomplish a certain type heat treatment. I am not sure if this is the type of heat treatment you are looking at doing. If you have this information and can let me in on it I might could help more.

How does the heat "break the dislocation" and allow the retained energy to be released? Is it by breaking the bonds between the molecules?

And why are there new small crystals that starts appearing during recrystallization? I mean, if recovery stage breaks the bonds, it doesn't make sense that new crystals will appear by adding even more heat into it? Sorry for the noob questions :)

The book you want is "Introduction To Ceramics" by Kingery from MIT. When I was a student at Alfred University, we students referred to this book as the Ceramic Engineer's "Bible"

You have austenite and martensite in ceramics?

Sorry Guest,

I did not mean to mislead. I focused in on recrystallization, graingrowth, dislocations and ferrites. The first three are common to Ceramics and Metallurgy. Ferrites to me are Iron Oxides commonly used as inductors or magnets. Without looking closely the austenite and martensite sounded like they could be typical ceramic mineral names with which, I am not so familiar (my bad). I worked in Ferroelectrics, Piezoelectrics and low band pass filters.

The Kingery book does however, cover extensively the crystalization of Glass Ceramics, dislocations, grain boundary and grain growth phenomena.

Now if only I could find my Kingery book after 37 years.

Ferrites to you are iron oxides???? No offense, but I would be careful posting information like that...forums are supposed to help people not completely confuse them.

On steel I know of 3 kinds of Iron oxides (from my days in the pickling house):

Hematite Fe2O3 ,Red, Insoluble in acid 1030 DPH microhardness.

Magenetite, Fe3O4 Black, insoluble in acid, 420-500 Dph microhardness.

Wustite, FeO greyish, soluble in acid 270-350 Dph microhardness.

The first two are the outermost scales on rolled steel products, the third is the innermost scale. Wustite is also found in some meteoric irons. It's actually an umlaut "U" in wustite. Source: my 1985 Jr. Metallurgist Pickle house notes.

Guest is correct, no Ferrite oxides of iron.

Ferrite magnets contain Iron oxide, but that iron oxide is not Ferrite:

A ferrite oxide magnetic material containing, as basic composition, 11 to 19 mol % of iron oxide calculated in terms of Fe2 O3, 11 to 25 mol % of zinc oxide calculated in terms of ZnO, 0 to 10 mol % of copper oxide calculated in terms of CuO, and a residual part of nickel oxide, and further containing, as components subsidiary to the basic composition, 0.01 to 15 wt % of lead oxide calculated in terms of PbO, and 0.01 to 15 wt % of silicon oxide and/or talc calculated in terms of SiO2, wherein the ferrite oxide magnetic material has an initial magnetic permeability of not higher than 8, a sintered density of not lower than 4.8 g/cm3 and a stress-resisting and magnetic-field-resisting characteristic in a range of &#b1;5% calculated in terms of the rate ƊL/L of the change of inductance due to the condition of a magnetic field of 1000 G under a compressive stress P=5 (kg/mm2) parallel with a direction of magnetization.

Source:http://www.patentstorm.us/patents/6183659.html

milo

Dear Guest,

Just Google Ferrites. Hope that will clear up some confusion.