"Annealing" vs. "stress relieving" ?'s
I do a lot of plate work out of 1045 hot roll steel and typically have the plate "stress relieved" after being burned out and prior to grinding. I received a quote today from a vendor who recommended "annealing" versus "stress relieving." I asked them what the difference was in this application since I normally think of annealing as softening something that has been hardened. They state that "annealing" involves a longer soak time at the same temperature you'd use to stress relieve; basically, if something was annealed it was also stress relieved but if something was stress relieved it was not relieved. Any ideas as to whether this is a matter of semantics or have I just been in the dark? The material in question is 1045 HRS but I suppose it could apply to any low or medium carbon steel.
Annealing means raising to austenizing temperature and cooling at a rate (usually slow) determined by the steel composition and usually puts the steel in it's softest state. Stress relieving might mean raising it to the same temperature but is often done to a lower temperature and is even air cooled, much the same as nomalizing. Done to relieve stresses from flame-cutting, welding or forming.
Stress relieving can also include specific ramp ups time/temp related and ramp downs. As per ASME post weld heat treat.
You can "stress relieve" a steel that has been heat treated and tempered without annealing it.
One shop I worked at did a lot of cold header dies and die cases, they were often stress relieved every time we had them in house if the customer so specified.
If the draw temp for the hardness they were was say 450 degrees and the stress relieve temp was 400 then the hardness would remain what it was supposed to be.
Flame cutting 1045 can leave hard spots along the cut in more or less random or unpredictable places determined by localized cooling rates after the torch passes. Annealing will assure that there are no hard spots, so it seems like a good idea.
you know your stuff =) couldn't of put it more simple!
Originally Posted by nakedanvil
you cannot anneal a peice of metal without first cold working it, recrystalisation comes from the points within the crystal structure where disslocations have piled up due primarily to cold work ie work hardening, when heated a new grain will form at this point, you can make a good lump of steel course grained and brittle by annealing when not required, i dont really get the austinizing temp comments, austempering and martempering arent the same
Ok. Annealing a bit of steel involves heating it to above its lower critical range (723 deg C for mild steel (the critical range lowers as the carbon content increases)) but usually 850 deg C, holding it to soak (approx 1 hour per inch of thickness) and allowing it to cool as slowly as possible (usually within the furnace it was heated in). Annealing will as already suggested produce a steel in its softest state. This may or may not be to your advantage as the stated tensile strenght of your fabrication could be below what is required of the steel in as rolled.
Stress relieving usually does not involve heating above the lower critical range, for mild steel we would heat to 650 deg C and hold to soak, then allow to cool in still air. Annealing does not require cold working first. Annealing can be performed on as rolled, as forged, cold worked etc, we often have to deliver forgings in steels such as XK5160, Xk1345, En26, K1070 in their annealed state to allow machining. After machining these steels are normally hardened and tempered, then are surface ground to finished dimensions and then often are stress relived before use. Stress reliving in this case would involve not heating above the tempering temp.
Stress reliving will not really remove the hardened edge of 1045 caused by flame cutting as the edge was raised above its critical range and cooled rapidly (by losing its heat into the parent or remaining plate)
In my opinion you would be better not going for annealing, stick to stress reliving, or better still go for a normalising proceedure. (normalising is heating to 850 deg C soak and allow to cool in still air). But I'm only a dumb metalbasher.
Too much info
The question is- should 1045 steel be annealed or stress relieved so that the steel is easier to machine.
The steel as purchased was cut using some process which makes the edges harder to cut. There are hard/soft areas, the cutting tool jumps from soft to hard areas, reducing cutter life, etc.
You are not going to anneal 1045 steel so that it is as gummy as annealed copper. Same with stress relieving.
The choice then becomes which is more economical? To anneal 1045, heat to 1700 degree F, soak according to size of material to ensure the whole piece reaches 1700F, air cool results in lower Rockwell C hardness than water quenching. Stress relieving is completed at ~1200 F for 1045 steel. Lower temp equals less money to have the operation completed.
Other option is to select different cutting tools, flood the machining operation. This is all assuming you are manufacturing enough parts to make the anneal/stress relief operation economical. If you're making only a few parts, choose proper cutting tools.
BOSLAB: Wow! Have you never used a bar of HR ANNL (HOT rolled & ANNEALED)? While cold drawn (or cold worked in any way) can be annealed, ANY bar of steel can (and often is) annealed to make it soft, stress-free or to refine the grain. You WILL NOT make a bar "course grained and brittle" by annealing. Although "normalizing" probably gives the best grain refinement.
You also show your ignorance with your comment about austenzing temperature. Austenizing temperature (also known as Ac1 on a transformation diagram) is the point where the steel changes from ferrite to austenite. This is the temperature (or slightly above) for "full annealing" or for quenching. No one was talking about austempering or martempering, and I certainly didn't infer they were the same thing or even had anything to do with the subject at hand.(??????????)
Be sure of your facts before you start giving advise. There are lots of questions here that ask OPINIONS. When people ask for facts, don't spout stuff you have little or no knowlege of. Often a LITTLE knowlege is worse than no knowlege.
Forgemaster gave the most complete answer, thanks.
Nic Danger: thanx! Wait, are you saying I'm simple?
Duke 58: You are right on in what you say on cost vs result. There is also the problem with many thermal cutting processes that the edge is not just hard in spots, it's also shrunk. This usually causes the plate to "cup" and can cause problems with holding shape as machining is done on different sides or edges.
Some people might think I'm being too hard on "Boslab", but it's different if someone says "I always thought..........", rather than stating an obvious obsurdity as Gods own truth.
This thread seems to be as good a place as any to ask my question.
I have a customer supplying me with laser cut blanks that we will be surface grinding and then machining.
They sent me a few that were annealed and some that were not. The idea was to try both so that we can see if annealing is really necessary to soften the edge prior to machining.
My grinder wants to stress relieve them so that they don't end up cracking (they are ~19" long and narrow pieces made from 420 SS and we're shooting for .250" thick).
Now I'm curious.... If the grinder wants to stress relieve them so that they don't snap when he goes to grind them, is the annealing really necessary to soften up that lasered edge?
If you want the steel in best machinable condition, I would harden, oil quench and temper at 400F. According to the handbook I have, this should result in a uniform hardness of high 40's Rc. Temper at a higher temp if a softer condition is desired.
I've never machined 420 so I can't dispute this, but I would have thought that spheroidized annealed would be the most machinable condition and the material is usually delivered from the mill that way.
Originally Posted by TDegenhart
You probably don't want a normal anneal with a slow cool down because that will result in a coarse pearlite structure which, in a steel of this chemistry, would likely result in large bands chromium carbides which will behave as hard spots.
For these parts I think you'd want a sub critical anneal (below austenitizing temperature, probably around 1,400 deg) and a cool down in still air. That will have no effect on the spheroidized material that was away from the HAZ and will leave the affected material in condition that is reasonably machinable and stress free.
The op says 1045, not 420. Two different animals. Problem with 1045 is that there is enough carbon to harden out at 60+ Rc where the flame cut occurred. To stress relief anneal will leave the edges hard, in the range of 30-40 Rc where the rest would be in the 20's. Not terrible. A full anneal would would make it somewhat "gummy". Perhaps normalizing is a good compromise.
Originally Posted by NTM
Why do you use 1045 instead of A36 or something with less carbon?
Can you educate me on the effect of normalizing? Does it refine the grain structure or do something else?
Originally Posted by forgemaster
Naw, man, the original OP was talking about 1045. That was four years ago! I was referencing the new OP posted directly above your post.
Originally Posted by TDegenhart
...this is why folks should just start new threads...
Normalizing heats it up hot enough for long enough to evenly disperse the carbon and when done properly wipes the slate clean. It can then be annealed or spheroidized for subsequent operations such as machining.
Originally Posted by Sea Farmer
Grain refinement is done with descending heat thermal cycles on simple steels. More complex steels are a little different.
It is quite simple to refine the grain with heat. In fact it can be done to the point it is too fine, moving the pearlite nose to the left of the quench speed. It is also easier to blow up into very coarse grain if overheated in spots.
Have you considered having them cut it running nitrogen as the assist gas? Makes for a much nicer edge than O2 or air on stainless. All be it at only a little higher cost. That cost is tiny compared to getting bits annealed! The edge still won't cut as soft as a annealed edge would, but its a night and day diffrence - may well be all you need.
Or just waterjet it... The grinder will still want to stress relieve though if it's CRS.