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In another question, I had a little comment-discussion with TFD on the effect of shock cooling on pans. In a nutshell, I said that it is bad for the pan, and he said that especially if the pan is made of steel, it should have been at 500°C for the shocks to have consequences, not at candy cooking temperature. I think that if it happens often, even at low temperatures, the internal structure of the pan would be less even (because of microcracks, or maybe some difference in the crystalline structure of the metal), leading to hot spots.

I'd like to broaden the question a bit. I think we will all agree that big temperature shocks have bad consequences on metals (think forging). I think that smaller shocks will have some (but smaller consequences), but after TFD's comments I am not sure. Could please somebody with better knowledge about metals explain what happens in different combinations of following combinations:

  1. Cooling method
    1. Immersion of the whole pan in cold water (as in, I have hot sugar syrup in it, and want to stop the heating immediately).
    2. Pouring a small amount of cold liquid into the empty hot pan (as in deglazing).
  2. Pan material
    1. Stainless steel
    2. Aluminum
    3. Sandwiched bottom
    4. Coated (e. g. enamel, PTFE, ceramic)
    5. Copper
    6. Iron
  3. Temperature difference (our cold water is in all cases in the range 5°C (fridge) - 15°C (tap))
    1. Steak/candy temperature (let's pick a range of 160°C - 200°C because of caramelisation and Leidenfrost)
    2. Hottest stove temperature (because I want to know about the extreme case. 400°C or 500° should do, the first because that's what I am sure have had on my stove, the second because TFD mentioned it).

Let's assume not a single shock, but regular shocks (maybe two shocks a week over the lifetime of the pan). What will be the effects? And also, is there a combination which can (but will not always result in) crack a cast iron pan immediately?

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+1. Very interesting question. –  yossarian Apr 14 '11 at 17:19
    
I like the question. Is therea metallurgist in the house? –  Carmi Apr 14 '11 at 18:19
    
You should add copper to the list of materials. I'd say cast iron too, but I think we all know what'll happen to that... –  Aaronut Apr 14 '11 at 18:39
    
@Aaronut, I added both. I won't make the assumption that "we all know", because the reason this question exists is that I thought we all know that it is bad for all pans (but in different degrees of bad), and now I doubt it. Maybe iron can handle the 170°C difference after all, I never tried myself. –  rumtscho Apr 14 '11 at 18:45
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2 Answers 2

I have never conducted scientific tests on pans, but from many years of experience I have observed this using domestic electric stove, oven, and gas hobs

Cast Iron: A good quality pan seems indestructible, low quality with flaws will crack randomly, but more often when suddenly heated or cooled. When you buy a new cast iron pan give it a few extreme thermal shocks on your domestic stove before you bother seasoning it. If it cracks send it back under warranty. I have a pan that is older than me that has been thermally shocked repeatedly including tossed into super hot fires, and shows no sign or damage. In fact it's seasoned surface is better than some PTFE pans

Coated Aluminium: (PTFE) The aluminium quickly becomes weaker and warps with thermal shock. Just using too high a heat will cause warping and the coating rapidly deteriorates as well. After a while you can use hand pressure to 'reshape' the bottom :-)

Stainless Steel: Good quality seems indestructible, this pas may warp very slightly but tend to settle back with regular use. Pans that are used for de-glazing seem to get slicker (less sticky) over time (this is good). I have a 55cm stainless steel wok that has had regular use over the last ten years, and is washed every time by dumping in cold water and scrubbing immediately after serving

Sandwiched bottom: I have never thermally shocked this type of pan intentionally, not normally used for this type of cooking. Used for low even heat

I would be surprised if a domestic stove could get to 400°C let alone 500°C. Most ovens can't go past 260°C (500°F) and that's in a closed box

Steels are generally hardened above 500°C (930°F), typically above 700°C (1300°F). This also make them brittle. The hardening processes ends with the hot metal being rapidly cooled with air, oil, or water. For high stability steel the parts may be cooled to below -75°C (-100°F)

They are them tempered from 230°C (445°F), typically 270°C (520°F). Tempering makes metal tough but not brittle. The tempering process ends with gradual cooling to room temperature

The 400°C (750°F) - 510°C (950°F) range is avoided for any length of time as this can cause embrittlement

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Coated (e. g. enamel, PTFE, ceramic)

I can't answer in general, but that one's easy. Sudden thermal shock causes strain in a material by unequal expansion, either in the same material by high thermal gradients, or in interfaces between materials with different coefficients of thermal expansion. The strain in this case (two different materials) can be very high. If the material in question is not elastic (e.g. enamel + ceramic; I would think PTFE is different, but I'm not sure), then the bonds between the coating and the metal would be severely strained and it would likely crack and chip.

I can tell you from personal experience that I have actually used this to my advantage:

In the spring, I produce a small quantity of maple syrup by boiling sap in an uncoated stainless steel pan. On rare occasions, accompanied by the release of many expletives, I have let the syrup boil down too far, at which point it burns and seems to coat the bottom of the pan with a thin but hard and very resilient layer of carbon black. The trick to removing this stuff is to get some kind of stress crack started, e.g. by scrubbing w/ steel wool or a copper pad, and then what I do is I put the pan on the stove for a while to let it heat up hot (but not red hot), and then bring it over to the sink and spray cold water on the inside pan bottom where the carbon black has stuck to. After a few times, the carbon black will start to flake off and then it becomes easier to remove by a combination of abrasion and thermal shock. (The two pans I've done this on have been fine; both are stainless steel with a thick (>8mm) bottom, and I've put them through at least 30 or 40 thermal cycles of this type.)


edit re: general topic:

Wikipedia says this:

The robustness of a material to thermal shock is characterized with the thermal shock parameter:

R_T = k * sigma_T * (1-nu) / (alpha * E)

where

  • k is thermal conductivity,
  • σT is maximal tension the material can resist,
  • α is the thermal expansion coefficient
  • E is the Young's modulus, and
  • ν is the Poisson ratio.

Higher thermal conductivity means it's more difficult to get a large thermal gradient across the material (less prone to shock); higher thermal expansion means more strain (more prone to shock), and higher Young's modulus means more stress for a given strain (more prone to shock).

So theoretically you could compare the different materials. (exercise for the reader ;) Most likely copper would be more resilient than the other metals, because of its higher thermal conductivity and higher ductility.

Thermal conductivity k: Copper = 401, Aluminum alloys = 120-180, stainless steel = 12-45 (units = W/m*K)

σT: no idea:

Coefficient of thermal expansion α: Copper = 17, Aluminum = 23, iron = 11.1, stainless steel = 17.3 (units = 10−6/°C)

Young's modulus E: Copper = 117, Aluminum = 69, iron/steel = around 200 (units = GPa)

Poisson's ratio ν: Copper/stainless steel/aluminum are all around 0.3-0.33, cast iron = 0.21-0.26

So stainless steel is worse than aluminum or copper (much lower thermal conductivity, higher Young's modulus).

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