鋼の冷間成形の際の中間焼なましについて

抄録

Although annealing at around 700°C (below A₁) is commonly recommended as the intermediate annealing during cold forming processes of steels, sometimes it does not necessarily gain satisfactory results, because the cold forming is generally heterogeneous deformation of steel. In this investigation, cold hubbed S15CK, S30C, S50C, SK5 and SNC21 steels were annealed at 700°C and 950°C, and their structure ferrite grain size and hardness were examined. As for the 700°C-annealing of mild steel (S15CK) and low carbon alloy steel (SNC21), it was found that cementite was spheroidized, but the annealed steels showed much heterogeneities among severely deformed region and slightly deformed region in the structure, the ferrite grain size and the hardness. By the 950°C-annealing, disadvantage from a small amount of lamellar pearlite colonies was negligible, homogeneities of structure and hardness were excellent and. the grain size was refined and homogenized. The 950°C-annealing was, therefore, more desirable than the 700°C-annealing for mild steel and low carbon alloy steels. With carbon content of steel exceeding 0.3%, the heterogeneities grew a little even by the 700°C-annealing, because the cementite particles could obstruct the grain coarsening. Also, the cementite was spheroidized and the hardness lowered. In such cases, the 700°C-annealing was desirable.