Percent of retained austenite in CPM10V

[is2634]

I'm reviewing some heat treat specifications for our company. I would prefer to specify results (i.e. hardness)rather than process (i.e. heat to 2100°F ...). However, we curently require cold treatment of CPM10V to -105 F.

Should I write the specifcation to state "62-64 Rockwell C hardness with less than X% retained austenite"? If so what number should I use for X percent? Or is it better to specify "Cool to -105°F and hold for six hours"?

What is the percent of retained austenite at various time/temperatures of cold treatments for CPM10V?

 

[EdStainless]

Do you have an old Crucible steel CPM handbook? They spelled this out. The target value was (I think) <1%.

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Plymouth Tube

 

[metengr]

http://www.crucibleservice.com/eselector/prodbyapp/tooldie/cpm10vt.html

 

[Maui]

What is your company manufacturing from CPM 10V? Would it be detrimental to have any significant amount of retained austenite in the microstructure when the part is placed in service? If so, then an upper limit for the amount of retained austenite should be stated in the specification that you are writing. Keep in mind that if you don't specify the heat treatment procedure but only specify the end result in terms of hardness, then you may not get the best combination of properties for your application. There are several routes that can be taken to achieve the same level of hardness in this grade, but they don't all end up with the same level of toughness. The cold/cryogenic treatment that you specify will certainly minimize the amount of retained austenite in the microstructure, and it is extremely unlikely that you would have even 5% retained austenite before performing this treatment. Current methods that are commonly used to detect retained austenite in this type of alloy system are accurate to levels of about 1 or 2%. Testing certificates from independent labs will usually state that "less than 2%" or "less than 1% retained austenite was detected".

 

[is2634]

Thanks for the input! The applications are tooling for forming and stamping equipment. The additional wear resistance from cold treatment is desired, but I'm not sure the gain was ever quantified when this practice was put in place years ago. Literature appears to suggest that better wear resistance is gained.

I have suppliers with different equipment (e.g. vacuum vs nitrogen blanket furnace) so that is why I am trying to avoid specifying required equipment and processing. How do others specify heat treat processes? Any other suggestions are appreciated.

This is what I have drafted...
CPM10V
REQUIREMENTS
3.1 The resulting Rockwell C hardness shall be 60-62 HRC when tested in accordance with ASTM E18.
3.2 The process shall protect the material from exposure to oxygen to avoid scaling and decarburization.
3.3 The process shall include three tempers at 975 - 1025 F to relieve stresses.

3.4 The process shall include a cold treatment after the first temper to reduce the level of retained austenite to less than 3% by volume.
or
3.4 The process shall include a cold treatment after the first temper at -105 F or below for 6 hours.

3.5 The supplier shall be responsible for retaining documentation that shows the material has been heat treated in accordance with this specification for a period of six months after shipment.

OPTIONAL INFORMATION
4.1 Typical processing to achieve the required results consists of:
4.xxx Use of a furnace capable of a controlled temperature of at least 2200 F, with a controlled atmosphere of vacuum.
4.1.1 Preheat to 1500 - 1550 F and equalize.
4.1.2 Second preheat to 1850 - 1900 F and equalize.
4.1.3 High heat: Heat to 2100 F and hold for 15 - 20 minutes.
4.1.4 Pressure quench in nitrogen, helium or argon to 700 - 800 F and equalize.
4.1.5 Cool in air or gas to below 125 F.
4.1.5 Temper at 975 - 1025 F and hold for 2 hours.
4.1.6 Cold treatment at -105 F or below for 6 hours.
4.1.7 Temper at 975 - 1025 F and hold for 2 hours.
4.1.8 Air cool to ambient temperature
4.1.5 Temper at 975 - 1025 F and hold for 2 hours.

4.2 Provided the requirements are satisfied, alternate processing such as the following is acceptable:
4.2.1 Use of multiple furnaces.
4.2.2 Use of a furnace with an atmosphere of nitrogen.
4.2.2 Wrapping of the material in foil to limit exposure to oxygen.
4.2.3 Quench in circulated air.

4.3 Estimated longitudinal size change during heat treating: +.0004 in/in.