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Up Topic Welding Industry / Metallurgy / REGARDING COOLING RATE CALCULATION FOR DELTA T 8/5 CELCIUS
- - By vino2488 Date 04-11-2015 13:11
dear prof.,,, tell me how to calculate this cooling rate Delta t8/5 i.e change in temperature from 800 to 500 celcius

my guide said me to refer welding metallurgy by g e linnert but i dont have any resource for this book
Parent - By kcd616 (***) Date 04-11-2015 15:46
vino.
for what info that book has it well worth the price
hope this helps
sincerely.
Kent
Parent - - By electrode (***) Date 04-14-2015 12:05
vino2488,

Linnert's book (my volume at least) does advise the reader to make use of nomographs. This is known as one among different approaches to what you wish to figure out. The nomographs nowadays available; i.e. not only those found in Linnert's handbook, are based upon a high amount of practical welding, accomplished on different parent metal grades to evaluate their cooling behaviour and how this affects the final microstructure.

As you were asking though on how to "calculate" this, find embedded the fundamental equations to compute 'delta t_8/5' both for 3- and 2-dimensional heat conduction conditions. You may find expression (1) to refer to the former, as equation (2) relating to the latter.

You will see specific heat, parent metal density as well as the part's wall thickness comes into play for 2-dimensional heat conduction; i.e. lower wall thicknesses. These parameters play no role when welding "thicker" parts; i.e. the heat is conducted along 3 workpiece dimensions.

When uncertain of which of both heat conduction conditions is given, pay note to expression (3), which provides you with the transition wall thickness between the 2- and 3- dimensional case.

Note. It needs particular attention that these expressions reflect for bead on plate welding (BOP) only. The whole subject of predicting microstructural changes is of course somewhat more intricate when assessing for multipass welding conditions.

I am almost sure however, that - amongst others - especially Henry aka "ssbn727" is capable of literally overwhelming you through sharing further - maybe more valuable - material; surely exceeding the amount of what a human being is able to read in a single lifetime.

Finally, a friendly recommendation from myself.
If you have access to codes and standards you may wish to have a very close look at British Standard 'BS EN 1011-2:2001; Welding — Recommendations for welding of metallic materials — Part 2: Arc welding of ferritic steels'. This does most detailed provide you with all you need as when it comes to how calculating "Delta t8/5".

As "kcd616" did so eloquently put in another thread; I also hope "this helps".
Parent - - By ssbn727 (*****) Date 04-16-2015 08:13 Edited 04-16-2015 09:28
"Weldcome" vino2488 to the AWS forum!

Based on the OP's request, I believe that Electrode has provided exactly what vino2488 was asking for... So I'm not going to muddy the waters anymore to potentially confuse this individual with overwhelming amounts of references to these, and other equations other than to add that there are currently some recent advances in software applications from a few different companies that can perform these and many other equations and formula's related to Welding Engneering/Metallurgy... Although, here's a link or more that may be of interest to vino2488 and anyone else for that matter::grin::wink::cool:

http://www.ceweld.com/en/content/cooling-times-delta-t85-s355-till-s960

And this one:

http://www.academia.edu/6664056/Chapter_4_-_Classification_of_Steels_Welding_of_Mild_Steels

Equation(s) of welding thermal history - The calculation is based on the following equation in which the effects of
finite plate thickness and heat transfer on the plate surfaces are considered on the original Rosenthal equation:

http://homepage3.nifty.com/yurioka/exp.html

From my German friends @ Dillinger:

http://www.dillinger.de/dh/e-service/hilfsprogramme/schweisstechnik/hilfe/index.shtml.en

And finally, here's a somewhat interesting article on the Effect of the Thermal Cycle on the Microstructure and Mechancal Properties of CLAM Steel (China Low Activation Martensitic) Weld CGHAZ:

http://www.researchgate.net/publication/256773913_Measurement_and_analysis_of_SHCCT_diagram_for_CLAM_steel

So if the OP or anyone else is interested please respond and I'll post up some links... I believe Tyrone also knows of a few as well as Metrinka and some other folks in here too... Good to see you posting again Electrode.:grin::lol::smile::cool:

Respectfully,
Henry
Parent - - By electrode (***) Date 04-16-2015 09:14
Thank you very much, Sire!
To be honest. As much as I personally feel pleased to read your and Brent's response; I think it's a true pity that the OP shows even no reaction on literally all replies/comments he was allowed to receive in general on his posts from yourself as well as from other distinguished forum fellow members.

No offence at all, but giving and taking, sharing experiences, opinions and "personal treasures".
I think that is the secret of this "world's greatest welding forum of the AWS".

Regards.
Parent - - By ssbn727 (*****) Date 04-16-2015 09:39
I just wanted to add this article from "the Practical Welding Letter" regarding Delta t 8/5:

Article: t8/5

You may have met the expression t8/5 and, unless you know what it is, you may have wondered on its meaning. It is simply a shorthand way of saying how long it takes, for a given weld bead including nearby material, to cool down from 800 0C to 500 0C after welding.

The reason why it is so important to know how much it is and if and which means should be taken to either increase or decrease it, depends on the great influence that this parameter has on certain mechanical properties of the finished weld, especially with high strength steels.

It is also a practical way of concentrating the influence of different factors in a single parameter for appreciating the relationship between welding conditions and mechanical properties.

In particular the Hardness of the Heat Affected Zone (HAZ) bordering on the weld will be higher the shorter is this specific cooling time. This condition might promote the formation of cold cracks.

If the cooling time is extended, possibly by increasing the Preheating temperature, the HAZ hardness will decrease, but also the impact properties of the weld may be impaired. If those are specification requirements, one has to make sure that they will not fall below the minimum acceptable value for the case in question.

The factors that influence the selection of suitable welding parameters for given situations are:

    The chemical composition of the base metal
    The maximum thickness
    The hydrogen content of the welding consumables
    The heat input of the process used
    The Preheating/Interpass temperature

The chemical composition is evaluated by calculating the Carbon Equivalent, a composite number that takes into account weighted proportions of the alloying elements present.

A few common formulas are known, usually selected according to their ability to provide more accurate simulations in typical cases.

The welding processes suitable to weld large thicknesses in a limited number of passes are also those who provide the highest heat input. Therefore they should be scrutinized to determine if their influence on the weld outcome is not going to impair the mechanical properties required.

Empirical relations and formulas were proposed by various sources and their predictions were confirmed by actual testing. In general the applicability is limited to a range of validity based on the cases where basic data are quite similar to those that were used to develop the expressions in the first place.

The calculation of acceptable welding parameters can be based on the methods presented in the European Standard EN 1011-2.

See the following additional information:

1.) Software support for plate welders: ProWeld Version 5.0:

http://www.thyssenkrupp.com/en/presse/art_detail.html&eid=tk_pnid1240
ProWeld can be obtained on a CD-ROM without charge from the
Heavy Plate profit center of ThyssenKrupp Stahl AG.

2.) See also, downloadable from the University of Cambridge:

Program MAP_Neural_NNWork

http://www.msm.cam.ac.uk/map/neural/programs/nnwork-e.html

and:

3.)Program MAP_Steel Weldsoft:

http://www.msm.cam.ac.uk/map/steel/programs/weldsoft-e.html

4.) To readers wishing to exercise their patience and solve specific problems by applying these principles to practical cases we would suggest to look for Weldability Calculations - Nippon Steel:

http://homepage3.nifty.com/yurioka/exp.htm 

Well, that's enough from me for now since I'm tired and need to get some rest... I hope that this is helpful.:grin::smile::wink::cool:

Respectfully,
Henry
Parent - By electrode (***) Date 04-16-2015 17:17
As I was presuming: "ssbn727" = source of knowledge.
That should serve the OP more than well in understanding the concept.
Parent - By welderbrent (*****) Date 04-14-2015 13:26
I believe that Electrode has given you more of what you are after than will Linnert's book.  As I am currently reading through 'Welding Metallurgy' I took a moment to quickly scan for what you asked.

While his discussions on heat, conductivity, convection, radiation, etc discusses this topic I do not see any formula's that will satisfy your question for the application you appear to be searching.

And now, we can patiently await the suggestions of others much more capable and knowledgeable about these things than myself.

He Is In Control, Have a Great Day,  Brent
Up Topic Welding Industry / Metallurgy / REGARDING COOLING RATE CALCULATION FOR DELTA T 8/5 CELCIUS

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