Stress relieve - 1200F, will oxide scale form?
Stress relieve - 1200F, will oxide scale form?
(OP)
I found that 750F is not a great enough temperature to relieve all the residual stresses in 4130 steel sheet. I'd like to go up in temperatiure to 1200F (that is what ASME recommends).. but 1200F is so hot I'm worried about decarburization, oxide scales (hematite, etc.).
What is the highest temp i can stress relieve at w/o worries of decarburization and scale build up?
Thanks, twistedneck.
What is the highest temp i can stress relieve at w/o worries of decarburization and scale build up?
Thanks, twistedneck.





RE: Stress relieve - 1200F, will oxide scale form?
Decarburization is not a concern below 1600 deg F for this steel. At 1200 deg F, slight surface oxidation will occur in air. Can you deal with this? If not you can mask the steel surface with a high temperature masking compound, but it will require mechanical cleaning after stress relieving.
RE: Stress relieve - 1200F, will oxide scale form?
Is there a point where minimal scale will form kind of like the thinner oxide layers at lower tempering temps?
Thanks for the reply.
RE: Stress relieve - 1200F, will oxide scale form?
What exactly is your application? You mentioned ASME required PWHT. Are you sure about this for only a 1mm sheet thickness?
Oxide formation is primarily driven by metal temperature in air. So, lowering the metal temperature, results in less oxidation. This analogy is similar to the formation of temper colors on steel where the steel is heated thru various temperature ranges, and different colors appear on the surface.
RE: Stress relieve - 1200F, will oxide scale form?
RE: Stress relieve - 1200F, will oxide scale form?
Ok. I don't believe adding a stress relief heat treatment step prior to your normal heat treatment after fabrication, as you stated, is going to help.
The distortion occurs because of the geometry and thickness of the sheet during subsequent heating and quenching for normal heat treatment. You need to provide some support or fixturing during the heating process for normal heat treatment. By the way for normal heat treatment you will need to use a protective atmosphere furnace to avoid decarburization.
RE: Stress relieve - 1200F, will oxide scale form?
Experiments with fixturing only caused peralite to form in areas contacting these.. due to slow quench times related to large heat mass of fixtures.
What i'm gathering from you is going to a 1200F pre-soak wont do much if anything better than the 750F pre-soak.
RE: Stress relieve - 1200F, will oxide scale form?
Working with only 1mm sheet thickness for a quench and temper heat treatment is very difficult, at best. I am going to ask the obvious - why do you need to heat treat this sheet at this thickness range? I would think that the material could be used "as-is" after forming. What are you expecting to gain from heat treatment after forming?
RE: Stress relieve - 1200F, will oxide scale form?
I hear you on the why bother part, to answer, these parts routenely yield in service when left in the as formed state.
RE: Stress relieve - 1200F, will oxide scale form?
http://www.appliedprocess.com/index.html
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Stress relieve - 1200F, will oxide scale form?
RE: Stress relieve - 1200F, will oxide scale form?
Salt quench and Austemper reduced warp significantly, but did not eliminate it. I can't afford to fix the burners right away so i've tried many types of quench and brine works the best apart from molten salt.
I think you guys answered my question though, stress relieve can only go so far. I'll up the temp on stress relieve to 800F for 2hrs.. I doubt it will help. I'll also agitate my quench bath (seems i'm getting most warping where two sheets are spot welded together).
RE: Stress relieve - 1200F, will oxide scale form?
As a famous actor was once quoted as saying in a movie, " A man has got to know his limitations" and apparently you reached your limit. Get the burner's fixed or outsource the austempering operation.
RE: Stress relieve - 1200F, will oxide scale form?
However, that doesn't change facts, Austempering did not solve the problem, fixturing did not solve it, quench medium, etc.. I'm focusing on the last two factors - agitation and pre-stress relieving.
RE: Stress relieve - 1200F, will oxide scale form?
RE: Stress relieve - 1200F, will oxide scale form?
I got the answers i ask for, i can go higher with diminished returns, and there will be scale build up.. but decarb wont be an issue.. (more stuff like pitting).
Thanks, Jeff
RE: Stress relieve - 1200F, will oxide scale form?
RE: Stress relieve - 1200F, will oxide scale form?
RE: Stress relieve - 1200F, will oxide scale form?
BK
RE: Stress relieve - 1200F, will oxide scale form?
SMF1964, vibratory? holy crap.. way over my head on that one. Can you elaborate?
bklauba, its a sheet metal box 10" log 1.5" square. Its got some weldments on each side, slightly thicker 1.5mm spot welded on - the problem area!