Sa 516 Gr70 annealing?

Date 06-13-2012 03:12

Hello

I am curious about some damage that has occurred on a dome shaped part. The part in question is 3/16" sa 516 gr 70 sheet. During the forming process the part was annealed without regard to temperature control. I am fairly confident the part temperature exceeded 2000 deg F a minimum of 20 times in various random areas. The heat ("annealing") was applied with hand torches in approximately 6" to 8" circles. Once the part was completely shaped there were bands of stress crazing from heating and forming again in various random places. The damamge is approximately 1/2" w X 8"L. My question, what factors would determine if the part is good or bad? Can it be repaired in any way? Any help in this problem would be appreciated.

Rod

By Eutectic (**)

Date 06-19-2012 14:21

rangerod,

Typical damage for over heating 517 Gr 70 would be possible grain growth that would result in a loss in toughness and strength properties. ANothe issue with this method of non uniform heating and cooling cylce is that you may now sit with residual stress that already exceeded or are vey close to your yield strengh. Not ideal for any stress corrosion service. In fact i will scrap this part. i have never heard of an anneal being performd by hand torches. You may use it for a giant frying pan or wok or something.

regards
Hanre

By RonG

Date 06-21-2012 13:44

I did not see any thing to help understand the application of this material. How can you say it's good or bad if you have no idea what it's function will be?

516 GR70 is not a hardenable material as compared to some like 4140 and not likely but possiblely been set to a condition (Quinched & Tempered) I am not sure even that would make it hard. If so, you must know that condition to determine what repairs would be required. If the material was purchased in a Normalized condition then you may only need to bring it to a uniforn temperature and allow it to slow cool.

By js55

Date 06-21-2012 14:22

It can certainly be repaired. But that isn't really your problem.
What you have is not annealing but more of a normalizing, I assume, since hand torches would imply that it was air cooled.
To repair you need to re-anneal the part properly to homogenize the microstructure, but now your problem is you don't really know the resulting properties.
Re-annealing will not return you to a pristine state. You will lose tensile/yield/ductility slightly.
And, you cannot now call it SA-516-70. So you would have to do some destructive testing and jump though special hoops depending upon where you wish to use it which is an engineering decision.

By rangerod (**)

Date 06-22-2012 21:56

Thanks to all for the help.

The part is due to be a vessel head 70" in diameter. Do not have oven big enough to normilize properly. The forming process would stop with the cold working being performed becuse the metal would not move anymore. It would then be normilized, forming would continue and cycle would be repeated until the final shape was achieved. Final inspection detected stress crazing in the dimensions I stated previously. I am worried about the random areas of residual stresses and the loss in strength. Detecting ALL of the damage in such a large area is also a major concern. I appreciate the background information on this problem. It is now managements decision on how to proceed.

Rod