Maximum hardness of material D2 2

[040622386]

Hello!
We produce knives from D2 material. We reach 60 - 61 HRc by heat treatment in vacuum furnace (hardening 1040 C, 5 bars, tempering 510 C).
Can we reach 62 - 63 HRC and how?

 

[adyonel]

Temper the parts at 100 C for 63 HRC and at 200 for 62 HRC

 

[Maui]

The relationship between heat treatment parameters and the resulting hardness that can be expected from salt bath heat treatment are contained in the following link:

http://www.crucibleservice.com/eselector/prodbyapp/tooldie/airdi150t.html

Salt bath heat treatment will give you the maximum hardening response from the material. By using a vacuum furnace you will normally end up with a slightly lower maximum hardness (depending upon quench rate). As you can see from the table in this link, by air quenching from an austenitizing temperature of 1850 F (1010 C) the as-quenched hardness is 63 HRC. Since you are using a higher austenitizing temperature, you can expect to obtain a higher as-quenched hardness: under ideal conditions I would expect the as-quenched hardness to be in the range of 64 - 65 HRC. I am very surprised that you are able to obtain a hardness of 60 - 61 HRC after tempering at 950 F (510 C). I would expect your hardness to be lower, in the neighborhood of 58 HRC.

D2 typically has a rather large amount of retained austenite in a properly heat treated microstructure. By using a lower tempering temperature, as suggested by adyonel, you will end up with a higher hardness but at the expense of more retained austenite than you would have obtained using the tempering temperature of 510 C. I suggest that you perform a cryogenic treatment after the first temper has been completed, and then follow this cryo treatment with another standard temper cycle. The cryo treatment can be performed in a dry ice solution at -110 F. This will transform as much of the retained austenite as possible, and will likely result in a slightly higher hardness than you would otherwise obtain. And it would improve the quality of the product by resulting in a more fully transformed microstructure. I strongly recommend that you have a commercial heat treat facility perform this type of service for you if your company is not familiar with this type of operation.


Maui

 

[feraidoon]

in my experiance as you are hardening a thin part you shoud cool it alitelbeat slower or austenitize it in lower temperatur so you will have less retained austenite and more hardness.