Sheet Stock Replacement for 1215 Steel 5

[evtuck93]

I am attempting to simulate the wear characteristics of a PTFE coating on a 1215 bearing surface. 1215 is only available in bars and my wear tester is designed for thin coupons. Ideally I would punch 1215 coupons from sheet stock but since it is not available, is there any kind of equivalent steel that is available in sheet for me to use and coat? The possibility exists of having bar stock machined into coupons but that adds expense and time to a project which is limited in both. Any information would be appreciated.

 

[swall]

Is this a Tabor abrasion test apparatus?

 

[TVP]

There is no point in simulating this environment using punched/stamped sheet. If you want it to be at all representative, then machine specimens that are of similar steel, surface roughness, etc.

 

[tbuelna]

I agree with TVP. If you expect to achieve valid results from your testing, then you should use test specimens that resemble your production component as closely as possible. This would include the metallurgy and processing of the test specimens.

What you say about the availability of 1215 steel in sheet form is true. In fact, I can't recall seeing 1215 steel in anything other than bar form. But if you can't find even a limited quantity of 1215 sheet for your testing, where do you expect to get the material you will need for production?

Good luck to you.
Terry

 

[swall]

There are some free machining plate alloys, such as Kleen-Kut 20 FM from Peerless Steel that might serve as a proxy for 1215. I understand where TVP and tbuelna are coming from, but at this point, we are in the dark, as evtuck93 has not defined the test nor the geometry of the actual components.

 

[evtuck93]

So a little more information then:
The parts will be cylindrical and oscillate axially along a ceramic surface so the production will use 1215 bar. The goal of these tests are to determine wear trending as the coating application process conditions change which leads to a need for a high number of samples that can be produced readily meaning sheet steel with a repeatable surface finish and adhesion properties is preferred.

If an equivalent material is not available then would an experimental redesign be the correct course of action? The coating will be on the order of 50 microns in thickness and the test can be designed not to wear through the entire thickness. By designing the experiment so as to never approach the interface, the surface characteristics shouldn't come into play (as long as there isn't de-lamination of the coating and substrate) correct? Which would free me up to use a more readily available sheet material for the purpose of testing the coating alone I believe.

Thanks for the advice,
E.

 

[metengr]

Yes, under your stated condition above coating wear characteristics are being evaluated and not the substrate material.

 

[tbuelna]

If your testing effort is simply intended to characterize the effect of process variations on the life and wear of a PTFE coating, then any substrate material with similar physical properties should work OK.

However, based on the description of your testing approach and the related application, I would question whether your test results will be valid or how you will correlate them. For example, your test specimens are coated flat discs, and your production parts are internal bushing surfaces sliding on a cylindrical shaft. The 50 micron PTFE coating will readily displace under even modest contact pressures, so the conformal geometry and stiffness of the mating components would seem to have a significant effect on the test results.

Good luck to you.
Terry

 

[mrfailure]

I may be overthinking this, but I wonder if the substrate has to at least be resulfurized steel. I wonder specifically whether the high sulfide content could affect the adhesion of PTFE during the wear test, resulting in spallation. Any thoughts?

 

[evtuck93]

That was my initial consideration in searching for a sufficient replacement material. I don't know if there is any significant chemical bonding interaction between these type of coatings and the substrate. If the adhesion mechanism is primarily mechanical then any equivalently textured low carbon steel should suffice.

 

[CoryPad]

mrfailure has made a good point, best to stick with the exact material (composition, microstructure, processing methods, etc. ).

Adhesion depends on the specific coating. Many PTFE coatings use polymeric binders (e.g. epoxy, phenolic, PAI) that provide adhesion via chemical bonding.

 

[evtuck93]

I agree that the same material would be preferred. Would the coating thickness help to negate some of the differences caused by using alternate materials? In essence, does the chemical make up of the substrate impact the mechanical properties of the coating?

 

[CoryPad]

Yes I think the thickness may negate some of the effects. If the test replicates the correct failure mode (e.g. gradual wear), then the substrate's exact composition may be unimportant.

 

[mrfailure]

While a couple of other substrate alloys can be considered equivalent to 1215 resulfurized rephosphorized steel (e.g. 1213 and 1214), they and other resulfurized steels also do not come in sheet form, which makes sense because of the detrimental effects of the inclusions during forming.

You want your test to most accurately simulate what the part you plan to use and what it sees in service. One variable of this experiment is the effect of using resulfurized steel on wear properties, while another is the effect of coating thickness. For this reason, I would suggest cutting and machining your test specimens out of 1215 bar. You can try various thicknesses of coating then to see determine when you would get spallation (higher thickness will reduce interface stress during contact). I would also suggest machining test specimens from a 1000-series carbon steel bar heat treated to about the same hardness. This show you whether the high inclusion content is really a factor in wear spallation.