Difference betwen Homogenizing and normalizing iun steel casting

[stanislasdz]

hi,

Please what this the difference betwen this two heat treatments for steel casting :

1- Homogeneizing + Quenching + Tempering
2- Normalizing

In wich case we choose each treatment

 

[metengr]

stanislasdz;
Homogenizing is a separate heat treatment method where the casting is brought to a significantly elevated temperature (at or above 2000 deg F) to allow for the reduction or elimination of chemical segregation and dendritic structures within a casting. It is a separate heat treatment step that requires many hours at elevated temperature and furance cooling to allow for diffusion of alloying elements, and formation of grains from the as-cast dendritic structure.

Austenitizing heat treatment is where the casting (after a homogenization heat treatment) is heated to about 1600-1750 deg F to allow for the complete formation of austenite before quenching or rapid cooling.


Normalizing heat treatment is where the casting is heated to about 100 deg F above the upper critical transformation temperature of the casting, and is held until austenite formation is completed. The casting is then removed from the furnace at temperature and is cooled in moving or still air conditions.

 

[metengr]

stanislasdz;
Tempering is a separate process or treatment that is done to a casting after it has been air cooled or quenched from austenitizing (mentioned above). The casting is reheated to a temperature that is below the lower critical transformation temperature to achieve certain mechanical properties (strength, ductility and toughness).

There are significant differences between "quench and temper", and normalization heat treatments. Selection of either heat treatment method is based on desired properties of the casting for use in service.

There is plenty of information on the internet regarding these heat treatment methods.

 

[stanislasdz]

Hi metengr ....tnaks a lot ...

But on wich criteria you decide that this steel part will be homogensed? quenched and tempered and other parts wil be normalizef only.

Other thing when you homogeneize a part you will reduc the microségrégation but you wil lalso increse the the coarsing austenitic grain...

 

[metengr]

But on which criteria you decide that this steel part will be homogenized? quenched and tempered and other parts will be normalized only.

Homogenization is normally done shortly after the ingot has solidified. Once this step is completed, you would either austenitize-quench-temper or you would normalize-temper

Other thing when you homogenize a part you will reduce the microségrégation but you will also increase the the coarsing austenitic grain...

Yes, this is correct, the grains will probably coarsen because of the exposure to elevated temperature.

 

[kenvlach]

stanislasdz,
Re: "on which criteria you decide?"

It's good to understand more about heat treating, but the learning curve is too expensive for guesswork. Depending on the alloy and application, there is most likely an applicable ASTM standard for your product. See the listing for Annual Book of ASTM Standards, Volume 01.02, January 2007, Ferrous Castings; Ferroalloys at

http://www.astm.org/cgi-bin/SoftCar...2007/01.02.html?L+mystore+jsgv4065+1169421158

An abstract of each standard is available, e.g., ASTM A389/A389M-03 Standard Specification for Steel Castings, Alloy, Specially Heat-Treated, for Pressure-Containing Parts, Suitable for High-Temperature Service
This one gives normalizing & tempering times & temperatures for the 2 grades: C23 (UNS 12080) & C24 (UNS J12092). Also, the chemical composition & mechanical properties required, plus minimum preheat temperatures if need to make welding repairs.

http://www.astm.org/cgi-bin/SoftCar...EDLINE_PAGES/A389A389M.htm?L+mystore+zwny0778

Compliance to ASTM standards may be mandatory for your product, so don't guess -- get the facts. Each standard costs about $30. If you need several, buy the entire volume 1.02 for $185.

To continue metengr's heat treating/metallurgy lession, see the on-line Key to Steel. Some info is free; some is for paid subscribers. Check it out:

http://www.key-to-steel.com/default.aspx?ID=Articles

Also, check ASM Int'l. books on heat treating:

http://www.asminternational.org/Tem...Topic&template=Ecommerce/Topic.cfm&TopicID=11

Also consider Steel Castings Handbook, 6th Edition

http://www.asminternational.org/Tem...=Ecommerce/ProductDisplay.cfm&ProductID=11274