Normalising

[aansssa]

I want to disscuse very simple issues but it is happend 2-3 parts in our heat treatment process.
part name Socket 304 wt per pc 0.520kg,material used EN8D C%-0.42, Mn%-0.85 and Raw material hardness is 179-187 BHN
loading per tray is 180 pcs
normalising temperature is set 860 degree and time 1hr 20min soaking ,7 tray furnace
part hardness required 162-210 BHN and hardness observed 156-170 BHN only proper fan cooling
than increase temperature 10 degree than little bit hardness achived 163 BHN
so plz suggest to me what can i do to improved hardness.

 

[aansssa]

will u tell be if Skt 220 we will increase tempreature 880°C against 860°C and time 25min against 20 mins /tray soaking than pc will burn.
and pc wt is 0.320kg loading 300 pc per tray.becoz specification is 175-220 BHN .material used EN8D C% 0.42,Mn%-0.86,Si%-0.25