HEAT TREATMENT CARBURIZATION

[OOOARRR]

I AM TRYING TO FIND A METHOD TO AVOID CARBURIZATION OF 25CR MO4 WHILST HARDENING AT 960'C. THEY PIECES ARE SMALL TUBES AND HAVE PROBLEM CONTROLLING ATMOSPHERE WITHIN TUBES. CANT FIND A 6M VACUUM FURNACE IN EUROPE. CAN ANYONE HELP?

 

[redpicker]

You can look into various stop-off paints, but they can be messy and difficult to remove after treatment.

How is your heat treater producing the atmosphere? I've heard it's easier to hold a neutral atmosphere with nitrogen/methanol than with endo gas.

You can try to reduce the furnace time and lower the temperature. Carburization is time and temperature controlled, so reducing time and temperature will reduce the amount of carburization.

Depending on the parts, you might be able to find a salt bath that can do the job.

rp

 

[TVP]

960 C is very high for normal hardening and excessive for this alloy. 25CrMo4 (1.7218) should be hardened at 840-900 C. If you need a reference see Table 11 (page 32) of EN 10083-3 Steels for quenching and tempering – Part 3: Technical delivery conditions for alloy steels. Use the lowest temperature possible and find a heat treater with good atmosphere control. Even with an endo atmosphere there should not be excessive carburization if the carbon potential is monitored and controlled properly. I would agree that neutral hardening using nitrogen/methanol can more consistently maintain carbon potential than endogas.