AISI 4145 at temp

[EngineerPhil]

I have two 4145 steel cans with an ID of 60mm and thickness 3mm in contact with each other on a shaft. There is a load and pressure from other components attached to either can but they (combined) fall short of the tensile or yield strength of the steel.

These cans fail at temp of 200degs C. basically one bells over and snuggly fits inside the other. I have double checked the load cases and I still can't find any missed out loads.

Does 4145 change at this temp? I didn't think most steels change physical properties at temp. Yes, there is expansion but surely not max strength and yield too? I think it may also be a design problem- two cans touching each other on such a small contact area would be susceptible to tolernace stack and also mating face out-of-plane-ness.

What does everyone think about the steel at temp? Any effects?

All answers greatly appreciated as I have until Friday to solve this one.

thanks

EngineerPhil.

 

[metengr]

At 200 deg C there should be no appreciable drop in yield or tensile strength for AISI 4145. Several questions;

1. What is the specified heat treatment for this alloy in this application?

2. Could you be more specific regarding design?

3. Is the load and pressure you are referring to centrifugal and internal pressure, respectively?

 

[EngineerPhil]

I didn't think there would be any drop in physicals at this temp.

To answer your questions metengr,
1) There is no specified heat treatment for this steel. It is machined from solid bar and used. The properties according to the material specs are yield 110k psi and strength 130k psi.

2) It is actually to can onto which rubber is bonded and creates a seal on the solid core running through each can and to the annulus of the test rig.

3) The load cases are a combined effect of internal pressure of the test rig acting on the 3mm area of the can (also radiall) and on the rubber. The seal is set with a compressive force as well which acts through both cans. These cans can be thought of as being back to back such that two seals are created.

There must be either a location fit or a missed out load. Time to re-do the Free Body Diagram and check tolernaces. If the steel doesn't get weaker with temp then there must be aforce I have not considered.

Arrrgh.

 

[Carburize]

If there is no heat treatment specified for the 4145 material the base material properties could be less than you think they are from the specification. I would recommend that you have the material quenched and tempered to a hardness of 363 - 415 BHN. 4145 should through-harden easily at the diameter you are working with and at the 363 hardness will give you around 135,000 psi yield strength and 170,000 psi UTS.