general heat treating

[saintjohnbarleycorn]

I see a lot of people refer to soaking. Is this better in all cases, such a high carbon steel with no other elements in it, or more for the more complex steels? I am thinking of making an oven for soaking and wondering if I would use it for all types of tempering. I can see the advantage of controlled temp.
In the more traditional way where you heat to color how effective is that vs. soaking, 90% as good on just carbon steel? thanks for any insight on this.

[Steve Sells]

in most cases, soaking is needed to get alloys into suspension. Its not normally needed for plain steels. A tempering oven is not the in the same temp ranges as the hardening furnace temps.

[thingmaker3]

You want your carbon dispersed evenly so that your martensite may be equiaxed (all the same size and shape). The more complex a steel, the more stuff in the way of carbon. Soaking allows carbon time to diffuse. Simpler steels may only need a minute per inch of thickness. Fancy steels may need five or more.

[Nakedanvil - Grant Sarver]

I see a lot of people refer to soaking. Is this better in all cases, such a high carbon steel with no other elements in it, or more for the more complex steels? I am thinking of making an oven for soaking and wondering if I would use it for all types of tempering. I can see the advantage of controlled temp.
In the more traditional way where you heat to color how effective is that vs. soaking, 90% as good on just carbon steel? thanks for any insight on this.

Not sure if you're talking about heating for quenching or drawing. I assume the question is more about working by eye or with temperature control. Really depends on who's eye it is and how much experience is behind it. Some people might be 90% as good while others might be 50%. Temperature control should give more consistent results, but no guarantee. Even pyrometers are not perfect. We used to have ours calibrated on a regular basis. As they age and oxidize their resistance changes and they will give false readings.

Also depends on the application. How close does it need to be? Also doesn't help to have temperature control if you don't know what the perfect temperature is.

[saintjohnbarleycorn]

thanks for the info.

[Frank Turley]

I've not done large, industrial forging but from my reading, I think that soaking has to do with large cross sections of steel where you have a heater who can heat and soak at a specific temperature before handing it to the smith or heat treater. The directions are specific. For example, D2 is heated slowly and uniformly to 1250ºF and held to thoroughly soak the piece. This means a through and through heat. It is then heated to between 1950 and 2050ºF for forging.

Annealing is done by heating slowly to 1600 to 1650ºF and held a 1½ hours for each inch of greatest cross section. Specific slow cooling follows.

Hardening is done in a salt bath or controlled atmosphere furnace to protect the surface of the D2. The steel is heated slowly and there are two soaking periods, the first at 1200ºF. When thoroughly heated, the steel goes to 1850ºF and is held for one hour for each inch of greatest cross section. Air cooled.

This doesn't sound like something I would have fun with in my little shop. I seldom forge anything above 1½" thick and I don't have the temperature controls for prolonged heats.

In the small, coal forge vernacular, soaking has the meaning of getting the fire hot and then quitting the blower entirely. The tool, usually small, is placed in the fire and will come up to hardening temperature without the blower. We do our scribers (scratch awls) that way, so that they will get a uniform red heat from thick to thin. If the blower is used, the thinner end area will get too hot, causing an unequal hardening heat.

http://www.turleyforge.com Granddaddy of Blacksmith Schools

[bigfootnampa]

D2 though has a very high carbon content and will exhibit some air hardening characteristics. This is especially true in thin cross sections (like maybe a knife blade?). So these industrial specs should not scare you away from a steel that can make nice blades. Even unhardened, D2 would probably make a decent working blade. Maybe not but I'd expect it to. You could get a fair amount of decarb while working a D2 knife and STILL have enough to make a nice cutting edge. I'll bet that there are smiths here who have made good blades from D2 without benefit of professional heat treating kilns. I have a few pieces and I intend to make some blades from it when I get the time.

[ThomasPowers]

Problem is you *don't* get unhardened D2 without the fancy anneal!

To get the best from it you really need the high tech heat treat to process all those different carbides it has out the wazoo!

Yes you can take your jaguar and use it as a manure wagon; but it'd be better on the road and something more appropriate for in the fields...

I spent a year working for a swordmaker who loved D2 and had the ramping furnace in a vertical configuration, electric and with inert atmosphere. (His father was a research metallurgist...)

[Frank Turley]

Pardon me for breathing. I picked D2 out of the hat, so to speak. I could have picked another alloy steel. Let's say you're doing an industrial forging out of 4"x4" cross section, and the end use is specific. Then you follow all heat treatment directions specifically, including proper soaking.

I don't know that much about knives, but on thin sections in my shop, I have forged high-alloy steels by taking slooow-rising heats without soaking, say on S7. I fudge on the S7 anneal; I use lime for cooling. If I could be higher tech, I would rapidly heat to 1500 to 1550ºF and soak for one hour per inch of thickness. I would then cool slowly to 1000ºF and then air cool. I'm just not set up for all of that, so I leave it in the lime to ambient temperature. So slap my wrist with a wet noodle.

[Steve Sells]

While I do not do a lot of larger cross section items in my shop, I have been involved in enough automotive heat treat applications to know about larger items, and to know that blades, being thin cross sections are very different than "normal" larger cross section items most make as smiths. This is the main reason there is a separate section about HT in the knife section. D2 is a great steel for many applications. But even outside of knife making, it being a high alloy, it is best to have a ramp controlled oven for getting it up to proper temperature for hardening it.

We still have not been answered If the OP was talking about hardening or tempering. Tempering most always does better with long soak times, as some steel alloys will not be effected by short times at even 500 F or 600 F heats. Annealing also needs time.

Not all things happen just because we think the outside is at a specified temperature. As stated already, time to penetrate the piece, and time to allow the metal to react to the reached temp is mainly what HT is about. Time AND temperature, and this is all dependent on the alloy used for getting the best performance from it. In some cases a bad HT to a great steel is worse for the end result than a plain carbon steel part with a good HT for the same job !

[saintjohnbarleycorn]

I was talking about tempering. I had just been hardening to non-magnetic then quench in water or oil. I have mostly been working with just high carbon, maybe .9 or 1 steel. I now have some spring steel that I have been working with and just doing it by eye. I just did get an oven so now maybe I can get a little more complicated with soaking. If i get it working I should be able to have time and temp, and possibly ramping also. ., thanks sorry it took so long to get back to you.

[thingmaker3]

"Soaking" is a term normally applied to the higher heats. But, yes, tempering is both time and temperature dependent. Tempering for an hour at a lower temperature can provide similar results to tempering for seconds at a higher temperature - but with much more controllable variables. (For most shops, that is. There are those fancy computer controlled induction tempering machines...)

Palmer & Leurssen's Tool Steel Simplified has a good explanation of what happens during tempering. So too for Krauss' Principles of Heat Treatment of Steel.

But the short answer to the first question is time and temperature do matter for simple steels as well as the fancy ones.

[saintjohnbarleycorn]

thanks I hope to get some time in the shop to do some experimenting on this, thanks for all the help.