heat treat SAE 1095 1

[Dobe]

I am having cracking issues after heat treat and draw. Heat treating at 1550°, quench oil is at 165°, 15 second dwell, draw on flattening fixtures at 720°to obtain a C47-52 hardness. Most all of our 1095 material is not heat treated so this is new to me.

 

[TVP]

Can you provide some additional information on the part geometry? Unless the parts are very thin, 15 seconds is not sufficient dwell time in the quenchant. Probably this should be more like 60 seconds minimum.

 

[Dobe]

the part is small, Ø2.12, ID 1.131, .058 thick

 

[redpicker]

Cracking is due either to material problem (check residuals and/or stringers) or having the material get too cold during/after quenching.

You need to keep the temperature of the material above 300F (preferably 400F) before quenching. This is easy to check these days with a infrared non-contact thermometer (in the old days, you had to use tempil-sticks). Your actual maximum quench exit temperature will have to be determined by trial and error, but I'd guess around 450F. You may find that quench exit at 500F is fine as long as it cools below 350 before temper.

Which makes me think, your flattening fixtures are just heavy pattens, right? Maybe you need to preheat them to 350F to keep them from quenching your blanks to below 300 before the tempering furnace can get the temp high enough to prevent cracking.

rp

 

[redpicker]

Upon review, the first sentence of the second paragraph:

You need to keep the temperature of the material above 300F (preferably 400F) before quenching.

Should read
You need to keep the temperature of the material above 300F (preferably 400F) before tempering.

The point is not to let the material cool to too low a temperature before you temper it. Most quench cracking occurs below 300 F, so if you can keep the material above 300 F, you can prevent the cracking

rp

 

[Dobe]

I understand what you are saying "rd". I was thinking when the part comes out at like 1500° and we put it on the waffle plate to go into the quench oil it cools down considerably. Our quench oil is set at 165°. I will have to check the part temperature just before it goes into the quench. I do know that it turns black as soon as it hits the plate. Its geometry doesn't allow for much surface area. I do not know how we are going to heat up the plate to keep the part temperature high enough going into the quench oil.

The part gets degreased after quench, which means at this point it is room temperature. I am going to put them in a pre-draw furnace at 350° before tempering on a fixture to maintain flatness in draw.

 

[redpicker]

Check the temperature as they are coming out of the oil. I mistakenly said "before quenching" instead of "before tempering". Another way of looking at "before tempering" is "after quenching". A major cause of cracking is allowing the material to cool off too much. You can prevent cracking by not allowing the material to cool all the way to room temperature.

If the oil temperature is 165F, they cannot be below 165. With only a 15 second quench, I wouldn't be surprised if they were a bit higher. Check the temperature with a non-contact thermometer and see what it is.

By waffle plate, I am guessing you have a quench fixture. The fixture should be at oil temperature (165F). If the fixture is at room temperature, that could cause cracking.

rp