P/M materials-Xref to cast materials
P/M materials-Xref to cast materials
(OP)
I am wondering if anyone out there knows of a specific powder metal that has nearly exact, or better qualities than an Investment Cast 8620/4140.
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P/M materials-Xref to cast materials
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RE: P/M materials-Xref to cast materials
Forces (magnitude, direction, frequency)
Environment (temperature, corrosive media, wear, etc.)
Geometry (general dimensions, wall thickness, etc.)
RE: P/M materials-Xref to cast materials
Forces are tensile and produce a bending moment on a shape similar to one below (arrows indicate force direction)
MMM<--- --->MMM
MMMMMMMMMMM
May your -dv/dt always be small.
RE: P/M materials-Xref to cast materials
1. Density of the PM part?
2. Process used for PM? Was it press, pre-sinter, re-press, and final sinter?
3. Are the castings heat treated?
What I can tell you right now is that the PM part will be extremely notch sensitive, due to its very low toughness. The lack of toughness is due to the porosity, and the poor microstructure that develops in these materials. In order to achieve the desired macrohardness/tensile strength, the microstructure is essentially as-quenched martensite with a microhardness that converts to ~ 60 HRC. The combination of hard martensite and porosity produces a macrohardness level more like 29 HRC.
So, what to do? There are a number of things to investigate, depending on your answers to the above questions. Increasing the density will improve toughness somewhat. However, this still produces an extremely brittle part. The low-alloy steel powders that contain Ni, Mo, and Cu will provide higher fracture toughness for a given strength level (FLNC-4405). A change in geometry may be necessary, such as including a generous radius.
RE: P/M materials-Xref to cast materials
I feel that a change in material may be called for here. Also, I have experience with an air hardening P/M on another part we produce...would this be an avenue to consider?
May your -dv/dt always be small.
RE: P/M materials-Xref to cast materials
Next, there is a big difference between 90% density and 94% density, in terms of strength, fracture toughness, etc. In order to maximize the properties of the PM part, you should investigate making the minimum density = 94%. This should be achieved by pressing, pre-sintering, re-pressing, and final sintering. The part should feature as large of a radius as possible in the critical area.
If I understand correctly, a Rockwell hardness test using the Brale indenter and 150 kgf (Rockwell C scale parameters) on this part gives a hardnes number of 55 HRC. Are you sure the 55 HRC is not converted from microhardness (Vickers or Knoop)? If it is a true HRC reading, then the hardness is WAY too high. PM parts have terrible fracture toughness as it is, and 55 HRC macrohardness is essentially untempered martensite. Have you had any metallographic analysis performed to confirm that the martensite is tempered? I would recommend doing so if you have not.
As I mentioned previously, look into the Ni-Mo-Cu alloys for improved toughness. Personally, I really dislike working with PM parts, for this very reason. You may want to consider a parallel investigation for converting the part back to a casting or some other form (fineblanking, etc.). Good luck.
RE: P/M materials-Xref to cast materials
RE: P/M materials-Xref to cast materials
Also, the hardness of about 55 was a microharndess as they come out at about 30 on the RHC scale (per testing at our facility).
May your -dv/dt always be small.