Sherodized annealed steel 3

[srivarma]

When you heat treat ( hardening & tempering)a steel which was spherodized annealed before cold working,
do you follow the same heat treatment cycle as you would do in case of non-spherodized annealed steel of
the same grade of steel , or is it different?

 

[Prasham]

As far as I know there is no difference in the HT process whether the steels is annealed by spherodized or any other process.

 

[metengr]

Yes, you can conduct a quench and temper heat treatment cycle similar to that for a non-spheroidized, same grade steel to achieve similar results.

 

[redpicker]

Not quite so fast (pun intended).

The spheroidized steel will be difficult to austenitize. A lot depends on the chemistry, but if you have Cr and Mo (as in 41XX, 43XX etc...), and you end up with a structure of ferrite and speheroidized carbides, the ferrite isn't going to want to change to austenite until it gets above 1725F, or it absorbs enough carbon from the carbides. But, the carbides are M23C6 with all of the Chrome and Moly being tied up in the carbides, so they aren't going to dissolve very quickly.

The short version is, yes you can harden a spehrodized structure just by austentitizing as, say 1500F, but you will need a much longer holding time than you would with either a normalized or as-rolled structure. Much longer. If you don't hold it long enough, you will not get all of the carbon and alloy into solution with the austenite and, while you will harden, you be effectively be hardening an alloy with a lower carbon content and lower Cr and Mo (since these will still exist in the undissolved carbides). You can avoid this by either an normalizing treatment prior to hardening, or by austenitizing at 1700F and cooling to 1500F prior to quenching (assuming 0.35-0.45C).

 

[srivarma]

Thank you very much. Material in consideration is SAE 52100. I am facing brittleness after heat treatment.
Could you please suggest an appropriate cycle.

 

[redpicker]

It would be a lot easier if you were to tell us what cycle you are using, what results you are getting, and what you expect to achieve.

However, for a staring point, you can try heating to 1550F for one hour plus an extra hour per inch of thickness, oil quenching, and tempering for 1.5 times your hardening time at a suitable temperature for your desired hardness, followed by air cooling from tempering.

 

[Maui]

If you can provide us with the heat treatment cycle that was used, some images of the microstructure, and the hardness values that were obtained we will be in a much better position to give you advise.

Maui

 

[srivarma]

Thank you for your suggestions.
Cycle followed now is 1600 F -20 min- Mar quenching @ 240 -40 minutes.
Tried 1550 F -5 min-Mar quenching @ 240 -40 minutes, But did not find any improvement.
I will try cycles suggested by you & let you know.

 

[Maui]

The recommended austenitizing temperature range for AISI 52100 is 1500 F to 1550 F. An austenitizing temperature of 1600 F is not recommended because it will result in a relatively large amount of retained austenite upon quenching. If you only temper one time, then most of this retained austenite will transform to martensite. And if you don't temper again to soften the newly transformed martensite, then you may end up with a brittle condition as you describe.

Are you tempering once or twice? At what temperature, and for what length of time?

Why are you marquenching?

Maui

 

[dbooker630]

In my ball bearing days we would heat treat 52100 from the spheroidized condition. Marquenching was used only for the large rings, which were immediately ring-rolled in the warm condition prior to tempering. Standard temper was 350F and if very low retained austenite was required, a -100F deep freeze and then a second furnace temper was performed.

For smaller rings with less distortion potential, we quenched in conventional 150F oil

You did not mention the atmosphere conditions, i.e. dewpoint, carbon potential. Have you looked at a microstructure? Have you seen any evidence of decarburization, or the opposite, saturated carbon at the surface? Either condition can contribute to brittleness.