Cast iron does not cut with a torch.
I wondered....
I broke a carbon steel 9/16 or 1/2" tap off in my 460. I had it chucked up in a drill and was "speed cleaning" the threads.
it worked great until it hit a metal chip or something to make it catch then with the momentum of the drill it snapped off like chalk way down the hole.
I was already being unorthodox so I just got the trusty torch out (Torch wasn't a nickname I picked for myself guys at work were poking fun...)
I heated the tap till it was glowing and gave it a blast of oxygen.
The Tap disappeared with a *pop* and the cast iron threads were not even damaged
The difference between iron and steel isn't the ingredients so to speak...it's the crystaline structure of the elemental iron in the cast iron or the iron in the steel which is determined by the other elements added to alloy the iron into steel.
Both different ingredients and different handling form different metals from elemental iron.
something interesting here.."Phosphorus and sulphur are undesirable elements to have in iron and steel and need to be burnt out. Unfortunately the desirable carbon burns away first so the carbon then has to be replaced. Allegedly the cheapest steel as used by budget quality car manufacturers has the sulphur and phosphorus left in. This latter allegation will be very much a trade secret, however the evidence of excessive corrosion can be found in scrapyards all over the world. Some steels known as "weathering steels" hardly rust at all. (see the Angel Of The North in north east England)
read these wikis in this order:
http://en.wikipedia.org/wiki/Pig_iron
http://en.wikipedia.org/wiki/Cast_iron
http://en.wikipedia.org/wiki/Austenite
http://en.wikipedia.org/wiki/Martensite
http://en.wikipedia.org/wiki/Steel
If you make it through the wikis you'll find the dominant difference between Iron and steel is the percentage of carbon.
The alloying elements and method of formation and heat treating being something that makes a difference but doesn't make THE difference between Iron and steel.
Most often when we think of iron and steel we think of the differences in the things that are made from them.
When we look at bendable bars, pipe, and sheet that are much softer than a cast iron block, we think hey that's steel... But it might not be.
If the carbon level is too high to meet the definition of steel it is wrought iron not steel.
Wrought iron is worked iron. it's the work process that changes the granular structure and rearranges the grains. A samurai sword starts out as brittle cast lumps of iron and is wrought into a strong flexible tool.
Same thing with steel plate which becomes rod, beams, sheet, and tube.
It is worked from low carbon cast alloy and is wrought into what we think of as steel.
Cheap cast iron has more impurities than good steel. steel has more austenite and martesite iron crystals where cast has more iron carbonite crystals which are a ceramic and could be why cast doesn't burn like steel.
Cast can burn though. If you run excessive exhaust gas temperatures, the heat will burn out the cast leaving it looking like a partially dissolved sugar cube or looking like acid ate it.
The high heat also makes it more brittle.
Putting TURBOS on older non turbo diesels who's parts are not cast from alloys anticipating higher exhaust gas temperature has caused head problems for some people
Tempering is a heating process that removes some of the brittleness from work hardening steel so it can have flexibility.
quenching locks the high temperature grain structure in before slow cooling can form the low temperature grains.
It takes several heat-cool cycles to rearrange most of the grains in the metal. the more you do it, the more even the grain structure throughout the thing your making.
Cryogenics has been added to the tempering in an interesting way.
cooling the metal to near absolute zero repeatedly has an effect on the metal that is similar to a forging process.
By cryonizing castings you rearrange the grain structure more uniformly. when returned to room temperature the item returns to standard dimensions but has been "forged"
A cast steel crankshaft when struck with a hammer emits a dull thud because of the globular arrangement of iron, carbon, and other elements in the cast.
A forged steel crank will ring when struck. It has a tighter grain structure.
If you cryonize a cast crank it will then ring more like a forged crank because you have in effect forged it not with a hammer and anvil but by compacting the atoms with extreme cold.
A friend who teaches industrial engineering at Bellvue University and who was a maintenance engineer at Loziers here in Omaha told me that cryonizing the copper tips for the mig welders made them last 3x longer. he coached me on welding cast.
The industry method for repairing cast is a section repair. They grind out the crack and form up the area so the damaged section can be recast. Then they heat the whole casting hotter than red hot then they pour molten cast into the section repair and let it cool as if they had cast the whole thing from scratch.
His method is an even preheat as much as you can. you use 100% nickel rod if it is not a surface that needs a hard face.
You weld about an inch then pick at it with a welding hammer until the temperature of the bead is about the same as the casting.
Make sure you burn through the "carbony" areas and get a good penetration into the metallic areas. The carbony areas are where the cast iron disintegrates while your welding on it
The pinging and hammering equalizes stress risers as the bead cools.
As you work around on the piece welding and stress releaving, microscopic fracturing in the cast near the weld that will most definitely occur from the heat and the contraction as it cools, will not travel. They will meet microscopic dead ends.
"cast steel" having lower carbon and a more flexible alloy than cast iron welds up about just like cold rolled or forged. Pre heating, pinging, and slow cooling the weld on cast steel can still prevent a brittle weld and stress risers.
side note:
Cast cranks are used in some engines in preference to forged where vibration dampening is desired.
steel is better for high speed high powered engines but if a cast crank has the strength for how it's going to be used in an engine it will have less vibration = engine lasts longer.
A forged crank will whip and vibrate more than a cast one... think one made from a spring
and the other made from frozen mashed potatoes.
