Annealing 52100 steel to tight hardness range

[Lyrl]

I work at a commercial heat treater, and have a customer with about a hundred cone rings (small ones - about 1/2 pound and 2-3 inches across) made of 52100 material. The end user is going to press fit these parts and wants them a particular hardness for best conformance to the press fit: they've requested 90-94 HRB.

I believe our customer bought the material annealed, machined them and then sent to the end user. The end user rejected the parts and returned them "too hard".

We 100% tested the parts and found them in the hardness range 85-98 HRB. We are going to re-anneal the parts that are above 94 HRB.

I've been asked to recommend a heat treatment for the parts that are less than 90 HRB, to bring them into the 90-94 HRB range. Would the anneal process (1500 controlled/step cool to 1000°F - 12 hour cycle) have any chance of increasing hardness (by dissolving some of the carbides?) Or would the parts have to be hardened and then annealed to have a chance at the 90-94 HRB range?

What are the chances of maintaining this tight of a hardness range on this material? Any information or thoughts would be much appreciated.

 

[CoryPad]

You should not need to harden the parts reach 90 HRBW. Grade 52100 has plenty of carbon to produce pearlite that would meet the hardness range. However, grade 52100 is an unusual choice for this hardness range, unless the plan is to harden later. I would expect difficulty in meeting this hardness range unless a lot of effort is put into controlling composition, microstructure and process parameters like temperatures and times.

 

[arunmrao]

I agree with Corypad, 52100 is a bearing steel used in hardened and tempered condition. How is the customer benefitted by using in fully annealed condition.


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[tbuelna]

Seems odd that the customer was asking for a narrow range of hardness from an annealed material. A max hardness limit would seem reasonable for annealed material, but why impose a lower limit? 52100 bearing steel is often supplied as spheroidize annealed tube stock that is cut into rings. Spheroidize annealed 52100 should be around 95 HRB max.

 

[metman]

Quote: "Would the anneal process (1500 controlled/step cool to 1000°F - 12 hour cycle) have any chance of increasing hardness (by dissolving some of the carbides?) Or would the parts have to be hardened and then annealed to have a chance at the 90-94 HRB range?"

yes and yes. By accelerating the cooling rate in the annealing process you will develop a little Bainite or intermediate microstructure which will be harder than the spherodite matrix. You might even get lucky enough to hit the desired hardness range or you could then temper to the desired range. But why play all this guess work since hardness or strength do not affect the application because heat treatment does not affect the modulus of elasticity?

This is a strain related problem so the only tolerance they need to closely hold is diameter differential between the two parts to be pressed.

E = stress/strain
Stress = Load/Area = P/A
Therefore E = (P/A)/Strain
and:
Strain x E = P/A
hence:
P = Strain x E x A
Strain or diametral tolerance is the variable since E and A are given.


Design for RELIABILITY, manufacturability, and maintainability

 

[metman]

The equation above does not exactly apply directly but the principle applies. Friction must be taken into account also as shown in the link below:

http://www.tribology-abc.com/calculators/e3_8.htm

Design for RELIABILITY, manufacturability, and maintainability

 

[metman]

Here is a link provided by desertfox (a contributor here on eng-tips):

http://www.eng-tips.com/faqs.cfm?fid=1230

please note that strength is not a factor in these eqautions rather poissons ratio which involves Modulus of Elasticity.

Design for RELIABILITY, manufacturability, and maintainability

 

[Maui]

Lyrl, I suggest using the following cycle for annealing 52100:

Heat slowly to 1440F (780C) and soak for at least 2 hours (longer if the part thickness requires it), slow cool at a rate of 25F(15C)/hour Max. to a temperature of 1200F(650C), then either air or furnace cool.

The resulting hardness should be in the range of 183 - 212 BHN, which closely corresponds to the range of 90 - 94 Rockwell B that your customer provided.

Maui

 

[Lyrl]

We ran the anneal cycle over the weekend, both on already annealed parts (but too hard for the end user's preference) and on parts that had been below spec and were hardened before the anneal.

All the annealed parts are 85-89 HRB. I've told the customer that is the closest we can get to the end user's target hardness.

The cycle we used had a faster cooling rate than that suggested by Maui, although we cooled to 1000°F before bringing the parts to room temperature.

That the press fit application is unaffected by part hardness is very interesting. I don't think our direct customer would understand or care, but if I end up in contact with the end user I'll try to find a delicate way to bring that up.

Thank you for all the responses!

 

[metman]

Qoute:
"That the press fit application is unaffected by part hardness is very interesting. I don't think our direct customer would understand or care, but if I end up in contact with the end user I'll try to find a delicate way to bring that up."

Yes I meant to say it might be difficult to broach the subject with your customer. If they are interested, a stress/strain curve might be helpful.

Design for RELIABILITY, manufacturability, and maintainability

 

[MagBen]

Both accelerating the cooling rate, and hardening then re-annealing could increase hardness, however, I did not see the benefit of doing that in terms of applications. This alloy is normally supplied with annealed condition (soft) for a suitable machinability/workability, and eventually it is to be hardened and tempered for a final application.

A min of hardness after annealing seems unusual.

 

[Maui]

Lyrl, it also appears that you used a higher annealing soak temperature (1500F) than I recommended (1440F).

Maui