Forgings need to be heat treatment before and after machining,The heat treatment before machining we say forging heat treatment.different material,different mechnical property requirements product after forging need to be heat treatment,even microstructure,refine grain,reduce forging stress,adjust hardness for next process,machining and final heat treatment

       Large forgings first heat treatment process technology is complicated,long period,The main purpose as follows:

1.To Prevent white dot

2.To enhance chemical elements’ homogeneity,refine and adjust large and uneven microstructure,in order to creat interal microstructure condition of final heat treatment and UT inspection.important forgings,such as large forigns of thermal power equipment after first heat treatment need to be inspected by UT,if forging grain is big and uneven,it will enlarge supersonic absorb and scatting,so that can not receive reflect signal.reduce segregation,refine and adjust microstructure after forged,reduce quenching cracked risk and improve forgings microstructrure and mechanical property after final heat treatment

3.Regarding to the forgings that don’t need to be final heat treatment,such as most of carbon steel and some of low alloy steel forgings.first treatment has to reach technical specifications and mechanical property.

         Forgings are made of atmosphere teeming ingot,The key factor of first heat treatment of large forgings is to prevent white dot.liquid steel after vacuum treatment,Original hydrogen content of ingot can reduce to below 3×10^-6,technology process period greatly shorten.although white dot can not be ignored entirely,but it goes back to the second position,refine and adjust grain to enhance supersonic penetrability,improve microstructure and machanical property after final heat treatment become the key factor of first heat treatment.refers to some Ni-Mo-V and NI-Cr-Mo-v steel large forging needs to be special treatment to reach this demand.

        Intermediate annealing of foring process can scatter sulfide to improve forging crosswise property.