The front of this blade was under a lot of tension and accumulating with age, eventually cracked. I highlighted - your ht process - with possible causes for tension and perhaps changes which might help
1725- 20 minutes, plate quench. Ramped oven to 1975. *2*Inserted blades *1* once oven stabilized. Once oven got back to 1975- *3*12 minutes. *4*Plate quench to too temp, *5* straight into DI bath for 20 minutes. Tempered at 325- for two 1 hour cycles. RC was 61-62 at completion
*1* - Although TC seem to stabilized at 1975, it takes at least 30 minutes heat up fire-bricks to 1975F at 5-10F delta. So temperature gradient between front & back of chamber is easily exceed 50F.
Try: ramp9999 to 2050 hold 30 minutes; ramp9999 1975F then *2*
*2* - Back of chamber always hotter than TC 1975. Guessing your blades were inserted tip-in.
Try: Insert blades tang-in first = ok to compromise tang (full thickness) to over heating
*3* - 12minutes is fine for tip-in but.
Try: soak 15-20 minutes to assure blades tip are close to 1975F/10-12m soak
*4* - Fine but nitrov has N & some small% alloy elems so M% is lower than aebl at room temp.
Try: after remove from plates, hang in air for 5 minutes - giving a bit more time for martensite conversion *gripe about it if any stabilized aust bug you.
*5* - Try: slowly (~1 minute) dip blade into DI with spine down, tang first at 45 degrees angle and slowly lower angle to zero (submerge). Basically lower the thermal and transformation shock.
*6* - speculation: aging (sat around for a week in block) lead to cracked may indicate that some aust to mart conversion occured = brittle mart initiated fracture/crack at edge.
Try: 350F temper, of course will lower hrc by ~1
Nitro-V is just a little bit less ht forgiving than aebl. In my limited experience: bcmw ht 63 & 65rc nitro-v blades performed similar to aebl at same hrc. btw - my ht doesn't do pre-harden 17xxF quench.
