Heat Treating Ferrous Metals

There are certain limitation concerning the effectiveness of it. The heat treatment consist of a broad spectrum and the end result (or the type of treatment) defines what you get.

You may aim for a particular type of microstructure (SGI, Flaked Graphitic, White, Mottled...) in Cast iron, Fine Grained, Coarse Grained, tempered, hardened, Austempered... in steel can not keep on adding all of them.

The carbon (and quite a few other elements) as well as the rate of cooling do define what you get as the end result.

So now what you expect after the treatment ?

Is it homework?

I have not seen any onn chosing between CS and SS based on its heat-treatability or do they?

Dear Sb.

After going through your profile, now it is understood, why such types of silly question may irritate professional with load of experience like you.

Let me share with you, being highly enthisiastic & passionate in learning new technical thing and always try to learn & absorb things which are related to technical matter compell me to post this (seems to be) silly qusestion on this forum.

-while in casual conversation with a highly experienced people in the field of stem turbine design field , he was reffering/ evaluating a GET in terms of his technical basic knowledge as - " He (that GET) is a mild steel even a strong heat treatment can't convert him into material like INCONEL suitable for steam turbine component".

Here of course I am aware that Inconel materials ( ~at some extent SS series) can't be compared with MS, but notable point is heat treatment of MS is not done and that is the point i wanted do differ but couldn't make my point.

My point is - whether Anealing, quenching etc are heat treatment or not ? And whether these treatment is done on mild steel or not ? So, why that experienced man is saying,mild steel is not ment for heat treatment ? Ok, understand even after quenching mild steel properties are not comparable with Inconel or SS, but certainly heat treatment may carried out in mild steel and so some physical properties like hardness will improve upto next level.

Point by point

1. Annealing, Quenching etc all are heat treatment.

2. Mild steel is heat treated but not normally what your person meant (ie likely hardening and tempering).

3. Normalising (another heat treartment) that is what we usually carry out with the plain CS items.

4. However the MS forgings (if you can call it MS ) that we buy are in Hardened and tempered condition.

check this site

http://www.azom.com/details.asp?ArticleID=543

The end point is any of the steel (and that includes mild steel) can be heat treated to improve some properties at the expense of some other.

However how much you can gain is limited for each composition and that is obvious, since else why should anyone go for alloy steel if the MS or any other CS can attain the same properties?

Mild steel is not heat treatable to any great properties nor depth (getting structure change and thus hardness at greater depth).

Not all stainless steels areheat treatable, by the meaning in common use of hardening.

Martensitic stainlesses, and precipitation hardening stainless grades are candidates for 'heat treatment' - austenitics won't respond to heat treatment.

If you mean by heat treatment Annealing to soften or stress releif using thermal means, than the question is nonsense.

The secret of steel is carbon, carbon, carbon. To understand stainless, its structure, structure, structure.

Without qualifying the type of stainless by family/structure, the question is defective because of many possible stainlesses.

Without sharing your application or 'reason to heat treat" (improve ductility, increase tensile or whatever), we cannot give a good answer.

I would urge you to look up the term "hardenability."

milo

Dear Milo,

"Mild steel is not heat treatable" This line in your post is really my concern and that's why this discussion was initiated to understand in depth knowledge of heat treatment.

Yes, i am a mechanical engineer ( at early age of my profession )& not a metallurgist but may differ because of following reason :

Quenching/Anealling may makes mild steel harder or softer and quenching/Anealing is a heat treatment process, so why generally expert/experienced professional use "Mild steel is not heat treatable".

Please correct me if my little knowledge is dengerous in the new field. There is no specific application this is simply inhancing/improving understanding in some other specific field.

I said "

Mild steel is not heat treatable to any great properties nor depth (getting structure change and thus hardness at greater depth)."

What you omitted is indeed the kernel of the answer to your original question. If you will look up the concept of "hardenability," aand "jominy test," I believe that you will have a frame work to see how it is that mild steel lacks the ingredients to allow it to achieve the great things through heat treatment that other materials can achieve.

In very simple terms , carbon content gives hardness, alloy content gives depth of hardness.

Mild steel has very little of both.

Data 15B21 H max hardness at J1 = 48HRC; hardness at j8 (1/2 inch)=20

1038H max hardness at j1 =58; hardness at j8 (1/2 inch)=26

5150H max hardness at j1 =65; hardness at j8 (1/2 inch)=59

Do look up Hardenability and jominy testing.

Data from AISI Carbon and alloy steel products manual quoted in my bethlehem Steel analysis and other useful data hand book.

milo