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Any danger to iron/steel from low temperatures

Bill D

Diamond
Joined
Apr 1, 2004
Location
Modesto, CA USA
I know for removing stuck things like pulleys and stuck bolts many recommend heating and cooling cycles to break the rust bonds. Being careful not to overheat the metal and affect the temper, if any.
Is there any reason not to cold soak it instead?
I have access to a freezer that runs around -120F that I can leave small parts in overnight. Is there any danger to the metal of stress cracking or changing tempers? I have read that pure zinc will crack at about -40. Russian pipe organ pieces used to be zinc until they realized there was a problem in extreme cold weather. I have aslo heard the rail will crack in extreme cold. Is this true or just old wives tails?
How about dry ice temperatures?
Bil lD
 
Bill,

No first hand info but I do remember that when they built the Alaska pipeline there were structural failures in some of the vehicles mechanical components.. they attributed it to the freezing temps..steel parts just snapped.

Stuart
 
When the difficulty is iron oxide, rust, corrosion, etc. call it what you want. HEAT is the magic element.

Why? Because "rust" is hundreds of times more volume than the parent iron/steel.
The lions share of that added volume is chemically combined water.

Heat , and I mean a lot of heat, drives the water off those bonds and so reduces the volume.
gentle "expansion to break the grip" is a waste of time and O/A.

Cast iron has no "temper", nor does most common steel assemblies that one might find "jambed up".

I use the smoke wrench ALOT!
 
I use welding to remove the most severely stuck bolts. This involves drilling a hole in the broken off bolt, and then filling the hole back up with weld metal. The upsetting force produced by the shrinking of the weld metal far exceeds any other method of removal. And, the effect on the bolt is permanent, so once it all cools down, the bolt will usually be shrunk enough that THEN, penetrating oil can actually get down the threads and you can weld something onto the bolt for leverage and get it to loosen off, working back and forth while the penetrant works its way down the threads.

There are special high strength SMAW rods designed for this type of work. Handy to have in sizes as small as 1/16". The only hiccup in this process, as that a modern electronic welding helmet can trigger off while the arc is down the hole and give you a surprise flash. Of course, there's still enough protection that you don't get an actual flash, just the bright dazzle.
 
And don't forget about "tin pest" - I heard it affects only pure tin so old solder with lead should be safe, no idea what about modern lead-free solders

Wysłane z mojego SM-N950F przy użyciu Tapatalka
 
When the difficulty is iron oxide, rust, corrosion, etc. call it what you want. HEAT is the magic element.

Why? Because "rust" is hundreds of times more volume than the parent iron/steel.
The lions share of that added volume is chemically combined water.

Heat , and I mean a lot of heat, drives the water off those bonds and so reduces the volume.
gentle "expansion to break the grip" is a waste of time and O/A.
From the chemical point, I'm pretty sure no amount of "heat" is going to "reduce" iron oxide to metalic iron. :-)
..lewie...
 
It is not the heat or cold, per se, that loosens the stuck member. It is the differential heating which shrinks the heated part because it is restrained by the cooler (unexpanded) part surrounding the heated part. The heating can't be a gradual process. The more violently the interior part can be heated, the more effective the heating cycle.
 
I understood that the two parts have slightly different diameters. They expand a equal percentage but that is two different lengths so they move relative to each other. I think they only have to move one molecule of distance to break the chemical bond. Ounce the chemical bond is broken then it is only a much weaker mechanical bond which can be forced apart.
 
I am not an expert, but I think -120F has a good chance of changing the properties of the steel even after it warms to room temperature. Dry ice is routinely used for that purpose, and you can search on that topic.

The topic of brittle steel fracture in ships due to low temperature operation is very interesting. Ships that operate in arctic waters (and the extremely cold air temps) use specialized steel.

www.safeship.ca - Brittle Fracture in Ships
 
Use the search engine of your choice to look for 'brittle to ductile transition temperature'. If you've got access to a Charpy or Izod impact tester and a bucket of liquid nitrogen, you can work out what the transition temperature is of any alloys that you use.

You may find the answers on the interweb for the alloys you are coming across, but you'll get a lot of false hits before you come up with any good numbers.
 
If you try what Mark suggests, don't "dump" the part directly in the LN2, suspend it over a pail of the liquid to allow it to get cold more slowly, then you can place it directly in the LN2 for final temp. Using a thermistor or thermocouple will allow you to hit a target temperature.

A Styrofoam cover will help prevent excess frost buildup and LN2 loss.
 
From the chemical point, I'm pretty sure no amount of "heat" is going to "reduce" iron oxide to metalic iron. :-)
..lewie...

If it was just pure iron oxide and oxygen, the temperature needs to be pretty high - around 1500°C - to directly reduce rust to elemental (liquid!) Fe. But if you set up your O/A to have a reducing flame, there is some carbon monoxide. CO will react with iron oxide at about 700°C to produce CO2 and elemental ferrite (that is, Fe, or pure iron).
 
I'm with the heat-it crowd. Several reasons:

1) You only get from room temp to -120F with your cold scenario - maybe 200F differential. With heat typically easy and safe to get maybe 300F differential and still be below typical tempering zone. Considerably more if you're just trying to get something apart.

2) As Gbent noted, it's differential expansion you really want. Often easy to keep one part pretty cool with either a heat sink or wet rag and the other hot as the material will stand. Temperature crayons can gage that if it's critical.

3) As the part opens, easier to add something like Kroil at the interface and have it drawn in.

4) Cheaper, usually easier.

Something like a bearing fit, different story with a bit of cold, bit of heat. Could be cool, literally and figuratively, to have a cold source then.
 
If it was just pure iron oxide and oxygen, the temperature needs to be pretty high - around 1500°C - to directly reduce rust to elemental (liquid!) Fe. But if you set up your O/A to have a reducing flame, there is some carbon monoxide. CO will react with iron oxide at about 700°C to produce CO2 and elemental ferrite (that is, Fe, or pure iron).

Red rust turns black after the smoke wrench has done it's thing. There must be something changing ;-)
 








 
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