17-4 Forging Metallurgy 3

[USMechE6]

Hi All,

I'm tasked with specifying a hollow cylinder to be made out of 17-4 PH (H900 heat treatment) and to be used in a high pressure and wear application. The O.D. will be 12" and it will be in excess of 100" long. I can't go into too much more detail but I'm hoping for some insight into the metallurgy I should call out. I do not have much experience with metallurgy other than what I've tried to learn on my own so any general info would be great.

If I call out a forging, will the recystallization during the solution anneal at 1900 F 'cancel out' the effect on grain structure of the forging, or is there some HWRR that would maintain a finer grain structure post treatment? I imagine this depends on the duration of the soak at 1900 and I.D. of the cylinder.

I've read some literature to indicate that finer grain structure will lead to better wear characteristics (I know it depends on what's wearing on what). This is something I would like to achieve. Would a minimum of HWRR of 4:1 enable finer grains than if it were say, spun-cast? Also I'm thinking that calling out 'open-die forging' will be specific enough?

Thank you for any help.

 

[tbuelna]

USMechE6-

I'm sure there are several US forging houses with automated equipment that can mandrel forge your flanged thick-wall cylinder shape. Since you mentioned fatigue life is a concern with your cylinder, mandrel hammer forging is definitely the way to go. This process is used to forge cannon barrels. Here is a good video of the process. Note the spiral pattern on the material surface produced by the hammer strikes.

The extra cost (maybe $3/lb) for vacuum melt quality raw material might also be worthwhile for a couple reasons. The cleaner material should help with fatigue performance. If your company offers a warranty for this product, the better reliability provided by vacuum melt quality material can be helpful. Depending on how stringent your NDI acceptance criteria is for the finish machined cylinder, using vacuum melt quality material can minimize part rejections. For example, there are 5 grades of acceptance criteria for mag particle inspection listed in AMS 2442 table 1, grades A,1,2,3 & 4, with grade A being the most stringent and grade 4 being the least stringent. The subsurface indication limits for grade 3 are based on what would be typical for an air melt quality steel produced to AMS 2301 cleanliness requirements, and grade 1 limits are based on what would be typical for a vacuum melt quality steel produced to AMS 2300 cleanliness requirements. So if you were to specify grade 2 (or better) acceptance limits for mag particle inspection of a cylinder made from air melt quality material, there is a good chance it may not pass. It can be very expensive to scrap a part that you have significant amounts of money and time invested in.

Good luck with your project.

 

[USMechE6]

Thank you all very much for the help and wealth of information and advice.