yield point of auto sheet metal at low heat graph. 1

[mendadent]

can anyone point me to a graph (source unknown) of yield point vs. temperature for automotive sheet metal?

i'm curious to see the effects below 400 degrees fahrenheit.

 

[NickE]

very small.

(How's it goin, ready for some more lessons in metal and materials?)

This mil-hdbk has bunches of that type of information, but I've never looked for DDQIF steels.

400F is not very hot for steel in general though.

 

[mendadent]

yea, nicke, i missed our question and answer series.
thanks nick.

 

[NickE]

ooopssss.... forgot to post the links....

Here is the MIL-HDBK

http://assist.daps.dla.mil/quicksearch/basic_profile.cfm?ident_number=53876

here is the old thread where we chatted about dent repair and Materials Science...

thread330-111423

 

[mendadent]

i can't seem to pull up the link.

 

[mendadent]

you still sweeping floors, lol

 

[mendadent]

DDQIF steels?

 

[mendadent]

by the way. the reason i'm back and looking for the graph, is i'm in a position where i need to prove to myself that heat below 240 degrees is useless.

 

[NickE]

Deep Drawing Quality Interstial Free - Steels commonly used in stamped automotive panels. Also used are the bake hardenable steels. And I'm certain that the lower drawing quality steels get used too, it all depends on how much stretch is needed to form the shape out of a flat blank.

Generally bake hard steels (as they are commonly called) have more carbon, manganese, and phosphorous. They, as stated in the previous thread have a certain amount of strength after forming, then are painted. Then heating to 170-177C for 20-30min. This increases the strength anywhere from 80-140Mpa (in the Sae paper I have in front of me).

I cut and pasted the link to a new window nad it worked, I'll try clicking after I finish this post.
Although I checked and that information is not in that book...

otherwise I dont know.. I'll look around though for you.



Example of [e]DDQIF

Chemistry (DDQIF)
C: .0034   Mn:.147  P:.005  S:.006    Si:<.001
Ti:.0694   Cr: .013 Mo:.002 Cu:.015   Al:.0444
Cb:.005    B:<.0000 Ni:.007
Fe:99.680 <-Calc as remainder.

Mechanicals
HRb: 24 Yield:18.7ksi Tensile:41.6ksi
Elong: 44.9% N-value: .274 R-value:2.728
Thickness:.0285"

Nick
I love materials science!

 

[mendadent]

thanks nick.

here's the delimma; is their enough heat at 240 degrees or lower, say 160 degrees, to effect a change in the molecular structure of a stamped and painted automobile exterior painted to make the metal more malleable even slighly if being manipulated with a very sharp tool?now i mean heated all the way through, placing a thermo thermometer for accuracy.

thanks again nick

 

[NickE]

no there will be no effect of heating automotive body steels to 160-240F. Heck thats barely above water boiling.. What do you think the skin temp is for a black car w/ neglected paint in the summer sun in arizona?

 

[mendadent]

laughed on that one nick. so.... it has to be what, 400 degrees to make a difference?

 

[CoryPad]

The ASM Handbook Vol. 1 has a graph for carbon steels (similar to automotive sheet steels) that have ~ 35 ksi yield stress at 70 [°]F and ~ 30 ksi yield stress at 400 [°]F. The change is essentially linear over this range. So, you can reduce the yield stress ~ 14% at 400 [°]F, which isn't a large change. At 240 [°]F, you would have less than 10% change in yield stress, which isn't much help during deformation.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mendadent]

thank you cory. now don't laugh on this, but if you already have deformation, and are attempting to move body panel back to flat will this small % help at moving back to flat.ie door ding.

 

[CoryPad]

The small strength reduction could help a small amount. I don't know if a 7% strength reduction is worth the effort to heat the panel.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mendadent]

hmmm 7% huh? not a lot is it? well, from experience on thinner panels at 180 degrees measuring from the back side it always seems to become spongy feeling.(entire panel) now granted i'm usually pushing with a very sharp tool at this point as well.and i can never tell any difference on a body roll which is much stiffer, say.. as in the top part of a fender.

 

[mendadent]

is the coefficient of thermal expansion a fancy name for what we're discussing above?

 

[CoryPad]

No, that is an elastic property that characterizes the dimensional changes due to temperature changes. We are discussing the elastic and plastic mechanical properties due to temperature changes.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mendadent]

last question for a while.
could it be that when i am not using heat, and since i'm at times pressing a dent up to 400 times with tool tip, that possibly this is cold working the metal thus increasing strength,stiffnes,and hardness. whereas if i were using the small 7 % of heat at 160 degrees to 240 degrees we discussed above, may be alleviating the possibility of cold mechanical deformation, hence benefiting from the small amount of heat and preventing the cold working. and that all along this alone is what gives me the spongy malleability i've been experiencing with the heat?

in other words it's never been the heat, but rather the lack of cold working?

 

[NickE]

nope, cold working of steels occurs whenever you're deforming it and the temp is below the re-crytallization temp or aproximately 800F.