If I understand it correctly, oil quenching of a hot forged iron / steel piece provides for a slower quench as compared to water quenching, affecting the temper of the object. I think that the oil quench also leaves a rust resistant film / finish on the steel. I'll presume that more knowledgeable smiths will offer better (more accurate?) explanations. This is what I recall from my years of demonstration blacksmithing, long ago. If I remember the details of Moby Dick correctly, Captain Ahab tempered his harpoons in blood, to kill the White Whale.
@snwcmpr The process of quenching hot steel in mineral oil is sometimes called “oil bluing”. It provides a coating to the steel that is somewhat rustproof. Use mineral oil, not synthetic oil (mineral oil has higher carbon content). I do this with bolts and nuts that are prone to rust. Cheers Tony
It also case hardens the steel by adding carbon to the surface. Very good for knives but I wouldnt use it just as a rust coating as it will affect the structure of the bolt possibly weakening them
@geeves I'm talking (above) about small bolts/screws such as the ones that hold the Optimus 111 in place, not structural steel fittings. Tony
@geeves When this is done to high carbon steel knives the whole heated material is hardened. Tempering is required after. I understand case hardening is different. This process is interesting @Tony Press . Does it require the high temp as in heat treatment of tools/knives?
That is true in general but some carbon does enter the surface of the knife. This is compared to water quenching which cools faster but adds no carbon. The faster the cooling the more hardening effect but oil cooling can create a very hard surface without causing the brittleness associated with overhardening. Its one of the processes used on samari swords. The other was wrapping the back of the blade in clay so only the cutting edge gets fully hardened giving a very hard cutting edge with the toughness of unhardened steel
Ken, are you asking about quenching an item that has been forged to effect the hardness of the item or oil blackening to impart a color and rust resistance? Up through about 1939 Lee-Enfield rifles were oil blackened during manufacture to impart a black color and some rust resistance, but instructions were always that the rifle should be lightly oiled. This treatment did not affect the hardness or temper of the steel. Oil quenching a red hot part causes a slower cooling with less distortion. Water quench is quicker but may cause distortion or cracking.
I thought it was obvious that we were in the stove forum, so the reference was towards stove parts treatment. Now, I see it was not clear enough to disway tangential thinking.
@snwcmpr Here is a live example of “oil quenching” or “oil bluing”. This is a steel packing nut from an old regulated burner. It was rusty, so it was de-rusted in citric acid, then cleaned with a Dremel brush. Oil bluing process: 1. Cleaned steel packing nut. 2. Mineral oil. 3. Heating to dull red hot with propane. 4. Drop into oil; clean; repeat three times. End result: Cheers Tony
Very cool Tony. I appreciate that. I have heat treated knives and strikers. Never knew about oil bluing.
