Induction hardening 4140/4340 with corrosion protection

[coolbreeze]

Greetings,

I am working on a project that will require a case hardened hollow shaft (100mmX77mm) The case depth will be about 5mm. Can I corrosion coat the shaft afterwards with a zinc phospate or Xylan coating successfully? I've just not tried this before and I am wondering if it will still work on on the surface hardened 4140/4340 steel alloy.

 

[tbuelna]

coolbreeze-

Xylan is just a sprayed-on and baked dry film, so it should pose no problems. However, I believe the zinc phosphate process does generate some hydrogen, so a hydrogen embrittlement relief would seem to be in order immediately after coating.

Take a look at MIL-DTL-16232 for more details on zinc phosphate coating.

Hope that helps.
Terry

 

[TVP]

Case hardened parts are phosphated all the time. Just follow appropriate guidelines such as those mentioned by Terry. Make sure that the curing temperature for the Xylan is not higher than the tempering temperature used on the shaft.

 

[redpicker]

I agree with TVP, zinc phosphate isn't going to hurt anything.

About 30 years ago, I spent 2 to 3 months trying to find any evidence of embrittlement or any loss in ductility on carburized 4815/8620 and induction hardened 4140/4145 steel as a result of zinc phosphate coatings. Tensile tests, notched tensiles, charpy impact tests; none indicated any significant change.

I would be somewhat concerned about a 5mm case on 11.5 mm wall material, however. If that 5mm is "effective case depth", then the total case depth is 50% of the wall, or more. That could cause countless problems.

rp

 

[israelkk]

redpicker

Did you put your parts to the 200 hours tension load torture?

Here is what MIL-DTL-16232G PHOSPHATE COATING, HEAVY, MANGANESE OR ZINC BASE requires:

4.7.2 Hydrogen embrittlement testing. Unless otherwise specified, testing to determine the
adequacy of the hydrogen embrittlement relief treatment shall be performed in accordance with the
following:
a. For parts that are surface or through hardened at Rockwell C 39 and above, testing shall be
performed in accordance with ASTM F519 using Type 1a cylindrical specimens to represent the
parts. Phosphated specimens shall be subjected to a sustained tensile load equal to 75 percent of
the ultimate notched tensile strength of the material. Loading of the specimen shall be
accomplished within one hour after completing the hydrogen embrittlement relief treatment stated
in the approved procedure. The steel, 4340 at Rockwell C51-54, is acceptable for worse case
situations unless otherwise specified on the drawing or in the contract.
b. Unless otherwise specified (see 6.2) the specimens shall be held under the load for a
minimum of 200 hours and then examined visually under lox magnification and an illumination of
1100 lux (lx) for cracks. The production parts covered by the test period shall be rejected if any
coated specimen develops any crack or breaks as a result of the test.

 

[coolbreeze]

Thanks for the posts guys! I have been reading about induction hardening lately, lots of great posts from "Redpicker" on the subject...I dont think it will be a problem to gun drill afterwards, I have read about the lack of cold sink effect & cooling severity with hollow shafts, if those are the countless problems being refering too. I am also considering a QPQ process...any thoughts? The machined features can be completed prior to surface treatment, rather than grinding afterwards, and I think it will give me the wear & fatique resistance + corrosion protection I'm looking for.