Curious about powder steels?

[Ankerson]

Very juicy, I'm expecting my own in orange G10:thumbup:. Though it seems like that level of edge holding is so far beyond conventional steels that one can't fully appreciate it without doing what you're doing. I for one just use my knives for mundane tasks like food processing. Probably won't notice a thing until I go a year without sharpening.

Once you get into this range and at High Hardness to maximise edge retention and cutting efficiency things really get different in a real hurry.

Then add on Phil Wilson's knives are designed to give maximum performance with highly optimized designs and he is a Master at Heat Treating.

Steels like M390 and ELMAX really take off once we get into the high hardness range of 61-62+.

 

[Bill1170]

I liked the part of the video where they show the spherical particles being smooshed together during the hot isostatic pressing so that the interstices are eliminated. As someone else noted, I now know how to pronounce the company name, too. Thanks for posting this video.

 

[Premiumsteel]

For knifemakers the point of the Third Generation powder steel discussed in the video is that Uddeholm ELMAX, Bohler M390 and the other BU powder metals can be hardened to a higher Rockwell number and still be very tough. These steels can be hardened between one and two Rockwell points higher.

An example; we tested ELMAX at 61 and the toughness (impact resistance) was greater than any competitors premium stainless we tested regardless of the Rockwell hardness. When bumped to 62 Rc ELMAX was at least as tough as any other stainless we tested.
M390, VANAX and others Bohler-Uddeholm steels were comparable.

The edge retention improvement is significant. Typical conventional stainless knife steels, score in the 500 cuts in a CATRA test. Powder stainless at 60 Rc score in the 700 range. But M390 and ELMAX at 62 Rc both score above 900 and retain good tougness. See the rope cutting tests for Phil Wilson's knives in ELMAX and M390.

We are working to translate this performance to production knives.

 

[marthinus]

bohler n690

O yes. I forgot about N690. Good steel I agree.

 

[Premiumsteel]

HEAT TREATMENT of Bohler-Uddeholm powder stainless. In an earlier post a comment was made that the Uddeholm ELMAX and Bohler M390 are difficult to heat treat commercially. Difficult, but done reqularly by a number of heat treat companies.

Both grades do require 2100F for best performance, but the key is a fast quench. Custom makers who cool one or two blades with forced air or a "plate" quench can cool the steel in less than a minute. Commercial heat treaters doing a full furnace load of knives can get the same results if they either salt bath quench or use a minimum 4 bar vacuum quench. To acheive 62 Rc with either ELMAX or M390 do the following:

1200F stress relieve, ramp up to 2100F, soak for 15-20 minutes. 4 bar or higher quench followed as soon as the steel is at room temperature with a deep freeze, either -120 or -300, both work. Finally two tempers for two hours each at 390F.

If 62 Rc is too hard for the specific knife application increase the tempering temperature. The exact same receipe with 480 tempers drops the Rc from 1 to 2 points again depending on the furnace load and the number of bars in the quench.

M390 does need the 2100F heat, but ELMAX can be hardened at 1985, soaked for 30 minutes, 4 bar quench and 390F tempers for 60+.

 

[Ankerson]

HEAT TREATMENT of Bohler-Uddeholm powder stainless. In an earlier post a comment was made that the Uddeholm ELMAX and Bohler M390 are difficult to heat treat commercially. Difficult, but done reqularly by a number of heat treat companies.

Both grades do require 2100F for best performance, but the key is a fast quench. Custom makers who cool one or two blades with forced air or a "plate" quench can cool the steel in less than a minute. Commercial heat treaters doing a full furnace load of knives can get the same results if they either salt bath quench or use a minimum 4 bar vacuum quench. To acheive 62 Rc with either ELMAX or M390 do the following:

1200F stress relieve, ramp up to 2100F, soak for 15-20 minutes. 4 bar or higher quench followed as soon as the steel is at room temperature with a deep freeze, either -120 or -300, both work. Finally two tempers for two hours each at 390F.

If 62 Rc is too hard for the specific knife application increase the tempering temperature. The exact same receipe with 480 tempers drops the Rc from 1 to 2 points again depending on the furnace load and the number of bars in the quench.

M390 does need the 2100F heat, but ELMAX can be hardened at 1985, soaked for 30 minutes, 4 bar quench and 390F tempers for 60+.

Awesome information. :thumbup:

I didn't say it couldn't be done or wasn't being done, I just said it was difficult and pointing out why we see M390 in the 59-60 HRC range in production blades.

Knowing that both steels can be taken to higher hardness and the edge retention increases are incredible at 61 HRC and harder.

 

[twistedneck]

Both grades do require 2100F for best performance, but the key is a fast quench. Custom makers who cool one or two blades with forced air or a "plate" quench can cool the steel in less than a minute. Commercial heat treaters doing a full furnace load of knives can get the same results if they either salt bath quench or use a minimum 4 bar vacuum quench. To acheive 62 Rc with either ELMAX or M390 do the following:

1200F stress relieve, ramp up to 2100F, soak for 15-20 minutes. 4 bar or higher quench followed as soon as the steel is at room temperature with a deep freeze, either -120 or -300, both work. Finally two tempers for two hours each at 390F.

If 62 Rc is too hard for the specific knife application increase the tempering temperature. The exact same receipe with 480 tempers drops the Rc from 1 to 2 points again depending on the furnace load and the number of bars in the quench.

M390 does need the 2100F heat, but ELMAX can be hardened at 1985, soaked for 30 minutes, 4 bar quench and 390F tempers for 60+.

Premiumsteel, can you explain the commerical salt quenching that is done? What should the temp of the salt quench medium be? I think the quenching salts turn liquid at 275F, is that cool enough to transform everything to martensite on these alloys? if i then pull the blade out of the salt and let it air cool to room temp, and then into a poor man's deep freeze (dry ice and acetone).

I know a 4 bar is probably superior, but i'm just trying to figure out both ways of doing this and to get more use from my salt pot. Thanks for the excellent post.