Does fire damage metal?

[jeryst]

A guy I know has a 69 Super Bee that caught fire last year. The whole interior was pretty much destroyed.
The heat was pretty intense, and paint on the roof, doors, etc burned off.

I talked to him the other day and he is planning on restoring the car. I remember reading somewhere that metal exposed to a fire loses some of its properties, or something like that, and that it is very prone to rusting from that point on, even if sealed, painted. etc.

I was just wondering if anyone knows about that, and if the car could be restored, or if all of the metal exposed to the fire would have to be replaced?

 

[SilverTBM]

I don't know about how the rust or how more prone to oxidization the metal would be. I would worry more about how hot it got and did it warp the sheet metal. If it has buckles in it, it has been hardened by the heat and will never be flat again. The molecular structure changes from heat treat and is not easily reverse w sheet metal.

 

[Mooky]

if it was an interior fire I don;t think I would hesitate to try and fix it up....at worst you source out a couple doors and glass as well as an interior....the rest could be sandblasted and cut in with an inhibitor/preventive the stuff inside is the worry...getting it cleaned up enough to replace the interior is going to be a challenge believe me..I bought a 68 sport fury that had a dash fire and for the life of me I couldn't get the dam dash frame cleaned up enough and it was warped...just found another and was good...coated the fire wall and replaced the dash/glass/wiring/ect. and drove it ...good luck

 

[WileE]

The simple answer to your thread question is: maybe. Here's a simple, silly example: a matchstick is on fire... if you hold it up against your engine block, will it affect the block ? Not really. But in the context of your post, regarding a vehicle fire affecting the sheet metal, most likely. It depends on the temperature. Heat applied to metal causes the atoms to vibrate. More heat changes their crystalline structure. More heat changes the metal from a solid to a liquid (heat of fusion). More heat changes the liquid to a gas (heat of vaporization). The bottom line is, enough heat can change the molecular structure, but how much ? Can you paint metal burned by fire ? You paint welded metal, and that went through the heat of fusion as it turned into a liquid & again as it turned back into a solid. But that wasn't oxidized (inert gas shields the weld from oxygen). In your case, if the fire was hot enough it exposed all the metal of the part to oxygen, not just the surface, so it would have to be replaced. Less so, the metals molecular structure was changed, so thin metal is now warped, even if it still has paint on it. It also depends on how quickly, or not, the metal was cooled, whether it got hardened or softened. This is a very basic simplification, each area or part must be evaluated for the extent of heat damage.

 

[joshb1983]

iv always herd paint wont stick too good to a car thats been on fire..not sure if its true but at the worst he could replace the roof skin

- - - Updated - - -

i looked it up and couldn't find much about it..wilerobby seems to hit it on the head with his post..

 

[Cranky]

Years back I bought a Dodge Shadow with 30k miles on it for cheap because some idiot tried to go to the other side by lighting it off with him in it. The whole back of the car was burned and well, I fixed it. The quarters were not warped and just had to replace the hatch, bumper cover, lights etc and clean up a blackened interior. Had no problems with the paint sticking to it. I sand blasted the burned areas, primer/sealed and painted it. Drove it for 10 years and the paint stayed. If the metal isn't warped, it's probably fine. It doesn't take much heat to burn off the paint....

 

[HT413]

Yeah, i'd agree - paint not sticking i'm sure has more to do with poor prep. I could see a collision shop not realizing (or caring) that even though some of the paint is still intact, it's chemically changed and will peel eventually.

 

[Photon440]

While fire CAN damage the steel in your car, it probably won't. Most car fires are relatively low temperature, being composed mostly of burning plastics. Even if the gas tank lets go, the gasoline won't get much over 1000f. Since we're mostly dealing with mild steel in our cars, that temperature is at the threshold of where steel begins to weaken structurally, beginning to soften to about 60% of the initial strength. However, when cooled, it will get almost all of it back.

The important thing with car fires is that most of the time the upper surfaces - hood, roof and interior - get the heat because of flames traveling upwards, but the bottom frame area, where much of the structural strength is built, stays far cooler and isn't affected. A car upside down and burning would be a different story. Besides putting more heat into the frame or unibody/frame area, the suspension items such as control arms and springs, anything with high carbon content, would be affected and likely unsafe.

Modern cars using higher strength steels to save weight (stronger but thinner) may be affected more, but should still retain around 90% strength after cooling. But we're not talking about modern cars here anyway.

As long as the undercarriage didn't get badly burned, the SuperBee in question will likely be just fine. It's just a matter of whether it's worth the cost of renewing what's needed.

 

[WileE]

Exactly... depending on what temperature each area was subject to, you may not even have to replace anything... or maybe just a roof skin... evaluate each part/area... just because a part/area was subject to fire, if the temperature was not hot enough, it will not damage it beyond repairability or the ability of paint to adhere with proper preparation.

 

[tallhair]

The experts have spoken. Is the metal warped or not?