Effect of normalizing before QT on the mechanical properties 2

[stanislasdz]

My question is :

Did the normalizing heat treatment before quenching and tempering increase the mechanical properties in steel casting ?

What differences are in the mechanical properties in steel casting between N+Q+T and Q+T ?

Thanks !

 

[arunmrao]

It depends on the carbon content and alloying elements. also it depends on what stage you do the fettling operation. Lastly if the casting is subsequently machined or welded or used directly unmachined.


It is always best to Normalise and then harden and temper as the possibility of cracking is reduced . Also the response to heat treatment is better ,in the sense you get uniform hardness and microstructure as the segregation effect is reduced by normalising.



Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)

 

[stanislasdz]

thanks Arunmrao

i agree with you but :

is there any data ?
is there any study about this ?

What the normalizing heat treatment before QT improve : Rm, Re, A%, Kv .... ?

Any data are welcome !


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"In God We Trust, all others bring data." -Edward Deming
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[salmon2]

No guarantee that I am correct, just discussion.

N right before Q+T is not necessary to me since Q+T properly can get whatever you want as long as the chemistry permits.

But N + cold work + Q&T is quite often because N will give the ductility needed for cold work.

But I would not totally shut the door. N+Q&T may possibly give you some minor improvement than pure Q+T but I think it require very thoughtful design on the temperatures and probably not worth of it. The possibly items you can target are probably grain size and secondary hardening for rich alloyed steel.

 

[dbooker630]

I agree with salmon2. If you give your part a sufficient time at austenitizing temperature, you should not have to add the added expense of a second reheat.

As far as normalizing a forged product for machinability, that is a different story, as some higher alloyed steels can harden in air after cooling from forging temps.

 

[stanislasdz]

arunmrao, salomn2 and dbooker630
thanks guys !!!

 

[stanislasdz]

AS i said many studies show the effect of heat treatment on the méchnical properties, but i don't see a study wich can show clearly the effect of normalization or homgenization on mechanical properties

Exemple :
here above a study wich can show the mechanical properties after each heat treatment : H+Q+T

The question is : if we don't do homogeneization these results keep the same ? is H+Q+T = Q+T

===========================================================
"In God We Trust, all others bring data." - Edward Deming
===========================================================

 

[Metalmeister]

Stan,

There is essentially no difference in result, only in purpose and timing during manufacturing.

Homogenization occurs at austenitizing temperatures to redistribute segregants in the steel via diffusion. Typically done on ingots & large casting, prior to subsequent hot working or further processing. If subsequently hotworked, homgenization temperature is at high end of gamma range.

Normalizing by definition is air cooled from a narrow and lower austinitizing temperature to limit growth of austenite grains, which if large, could reduce subsequent impact toughness.

Q&T is performed after bringing the steel into a fully austenitic condition. It is usually just called Q&T as the austenitizing treatment (not N or H) is assumed.

The curves you presented appear to be of a precipitation hardening steel; that's why UTS/YS is higher after tempering

 

[strider6]

i don't think it's a usual practice to perform a N+Q+T, usually the heat treatment are Q + T or N + T.

Q + T gives higher tensile strenghts vs N + T.

this articles can give you some good informations on this issue.

Hardenability and Heat Treatment
A booklet showing step-by-step the process for determining the hardenability of a steel casting.

http://www.sfsa.org/sfsa/pubs/hbk/s11.pdf

hope this help
S

Corrosion Protection & Corrosion Control

 

[metengr]

For some low alloy steels, prior to a quench and temper heat treatment that is the final heat treatment that is specified, material like 4130 or other low alloy steels can be normalized, prior to final heat treatment to enhance a more uniform structure for quench and tempering, especially if prior fabrication was performed. I have seen it done before.