hardening heat treatment 1

[bubble13]

I have 100Cr6 bearing steel.I want to harden it to get a hardness level of around 63HRC.the initial structure is spherodised carbide in the ferrite matrix.the procedure i aim is that to austenitise it to 850C and hold for 20 min at this temperature, quench it in oil and then finally tempering it at 160C for 2 hours. My problem is during austenitising ! should I wait the furnace to reach 850C first and then put the samples in the furnace for 20 min or should i put the samples inside the furnace while heating up the oven to 850C and then hold them for 20 min at 850C??
1.will there be a hardness difference between the two?
2.will there be more carbon dissolution on the the second approach?
3.I have read that the carbon dissolution is mainly dependent on the holding time not on the heating time,can this be true for this kind of steel?

Thank you and I like to discuss them well

 

[CoryPad]

Your questions are irrelevant. The only option should be wait for the furnace to reach temperature then put the part in for 20 minutes.

 

[redpicker]

Take a closer look at what you are doing.

If you are heating in a controlled atmosphere furnace, you will need to build the furnace atmosphere at temperature prior to charging the parts. If you are going to heat in an open furnace, you won't achieve 63 HRC due to decarburization.

Are your parts intricate and need to hold tight tolerances? If so, charging them in a high temperature furnace might cause problems. Some parts will require charging into a warm furnace and raising the temperature to lower the thermal shock.

A shperodized structure can be difficult to austenitize. You will want adequate time at temperature to allow the parts to reach furnace temperature plus time for austenitization to be complete. Temperature has a bigger effect on this than time, so if you can go to 860 or 875 you will get better results.

The heat treater only knows the time his furnace instruments report. Generally, this means he will start his clock once the furnace reaches set-point; heat-up time is not usually taken into account. A major part of successful heat treating is repeatability. Therefore, the soak time needs to be adequate for both slow and rapid heating rates. If not, you won't get consistent results.

I know this doesn't directly answer your questions, but maybe it points you in a direction that will allow you to make a better decision.

rp

 

[1toolsteelguy]

The 20 minutes is the time the part should be at temp for proper solutioning. As the above poster stated for complicated parts it may make sense to heat the part with the furnace to minimize thermal gradients. In any case, the part should be protected against decarburization due to the high Carbon content of Bearing steels. A foil wrap is sometimes used when the furnace does not have protected atmosphere.