Your carburize cycle doesn't sound right to me. Years ago, when I was carburizing 8620 regularly, a 0.030" case would take 6-8 hours at 1700 with a carbon potential of 0.90/0.95%. Even with such a high carbon potential, I doubt you are getting high enough carbon on the surface to form 100% martensite.
Check your carbon content in the case. Running a round coupon and collecting turnings at 0.005" depth works well. With 8620, I'm guessing you'd need over 0.60%C to eliminate the pearlite. I'd be suprised if your getting over 0.40% at 0.005" deep. I'm guessing you'll need longer time at a lower carbon potential to acheive your goals.
rp