Heat Treat 1045 Flame Cut Ring 1

[Dobe]

I am having problems holding Rc 25-32, heat treating 1045 flame cut rings. We currently heat treat 1045 forgings with no problems. Our process is 7.875 OD x 4.5 ID x .75 thick rough:

rough machine, leaving .015 for finish machine
heat treat 1575F
draw 900-980F depending on results from HT

Do we need to normalize or stress relieve. I have tried stress relieve with no better results.

 

[redpicker]

What do you mean when you say "heat treat 1575F"?

There is an implied hold time at the temperature and a cooling method/rate from the temperature, but you don't mention what those are. That could be where your problem lies.

rp

 

[Dobe]

I place the parts stacked 6 high in the furnace at 1575 degrees F., carbon set point at 50, minimum of 1 hour, usually around 3 hours. We then remove 1 at a time and quench in oil, from the inside out at 165 degrees and air cool. We then draw temper for a minimum of 3 hours at 900-980. This temperature can vary depending on a 5 pc outcome. Parts from heat treat and quench have ranged from 48-51 and my parts out of draw are 21-28; but very inconsistant on the same part. One side can be 21 and 180 degrees can be 28.

 

[redpicker]

1045 is a very shallow hardening steel, which means it will harden only with fast cooling rates. Since your rings are only 0.75" thick, you should be able to harden them in oil, but the oil quench will have to be well agitated.

It sounds as if your problem is a spotty hardenss. Some areas harden fine, while others do not. As I mentioned, a well agitated quench is necessary. If some areas see poor circulation, those areas may be soft.

Another factor is surface scale. You mention a controlled atmosphere. Does the steel plate you are using have a mill scale on the surface? Reactions between the scale and the furnace atmosphere and change the mill scale so it becomes loose and insulates the underlying steel during quenching, resulting in a low hardness. Are your forgings free of scale? Often a forge shop will shot blast their forgings to remove all scale, so you may be seeing the difference between a scale free forging and a flame-cut plate that has a mill scale on the surface. If so, you could have a few of the rings from plate shot blast to clean metal, and see if they respond to the heat treatment better.

rp

 

[Dobe]

thanks, I will check this info out and come back to you next week.

 

[Dobe]

Our parts are rough machined before heat treat so there is no scale. When the rings come in we stress relieve, and there is some scale and rust on the parts before SR and then rough machine. We leave about .015 machine stock on the parts.
The parts are staked 6 high in the furnace, maybe this has something to do with the high/low RC. We check Rc on this surface. From the furnace they are placed on a waffle plate for quench. The quench press ocillates up and down in the oil for 40 seconds. Our oil is also ocillated and goes thru a cooler to maintain the 165 degree temp.

 

[unclesyd]

{b]redpicker[/b] is dead on about the shallow hardening properties of 1045. A slight change in cross section can make an appreciable difference in as quenched hardness and subsequent temper hardness if you look at the mass effect data.
I would break up your stack with some type of rack to separate the parts in the austenitizing step. Your quenching setup looks fine.

One question is the furnace door being left open during the quenching step?

 

[metman]

Ditto with unclesyd but with following comments:
6pcs X .75" = 4.5" equivilent section size (if not broken up as uncle suggests) means 4.5 hours at temp if using the 1hr per inch thickness rule of thumb.

From the furnace they are placed on a waffle plate for quench

I would expect to find a different hardness on the side against the waffle plate vs the side freely exposed to the quench oil. Also I would expect to find a difference in hardness where the part is in intimate contact with the waffle plate vs where the part on that same side is not in contact with the waffle plate. You might try quenching by hanging the ring from a J-hook which would give more uniform quenchant contact and less distortion.

 

[Dobe]

Thank you for the tips. One thing I am thinking is there may not of been enough time in the furnace, as metman says for the stack. I will try some of these suggestions and get back to you.