The short answer is it depends on the product form (hot-rolled wire rod vs. cold drawn wire) and the thermomechanical history at the hot rolling mill. Intercritical annealing is really only needed for breaking up the poor microstructure (large pearlite size, presence of bainite, etc.) that occurs in some higher carbon steels after hot-rolling. Most of the modern steel mills with Stelmor cooling beds are capable of producing relatively fine ferrite + pearlite structures that respond well to subcritical annealing. Exceptions are larger diameter rods that cannot be properly Stelmor cooled, garbage grades like SAE 1541, and steel producers that don't like their wire drawing mill customers. Newer techniques like thermomechanical rolling (hot rolling at low temperatures in the austenite region) produce even more refined structures, especially in highly alloyed grades that are prone to formation of bainite & martensite, which also favor subcritical annealing over intercritical.
If you are talking about annealing cold-drawn wire, then there is essentially no contest: the strain induced during the cold-drawing process accelerates the breakdown of pearlite during subcritical annealing. The research by O'Brien & Hosford (also published in
Industrial Heating and
Met Trans) was very good. Some other good references on this subject are as follows:
Robert L. Draker and Krish Naidu, “Control of Surface Carbon During Intercritical And Subcritical Annealing”,
Wire Journal International, January 2000, p 96-103.
Krish Naidu, et al, "Quality annealing economically",
Wire Journal International, May 1983, p 63-73.
D. Hernández-Silva, et al, "The Spheroidization of Cementite in a Medium Carbon Steel by Means of Subcritical and Intercritical Annealing",
ISIJ International vol 32, no. 12 (1992)
K. Aihara & S. Kanbara, "Influence of Prior Structure upon Spheroidization Rate and Cold Forgeability of Annealed Wire",
The Sumitomo Search, No. 42, April 1990, p 1-8.
R. Kienreich, et al, "Improved Cold Formability by Thermo-Mechanical Rod Rolling",
Steel Research International, Vol 74 (No. 5), 2003, p 304–310.
H. Hata, et al, "Development of High Quality Wire Rod through Thermomechanical Control Processes",
Kobelco Technology Review, No. 25, April 2002, p 25–29.
T. Ochi, et al, "Special Steel Bars and Wire Rods Contribute to Eliminate Manufacturing Processes for Mechanical Parts",
Nippon Steel Technical Report, No. 80, July 1999, p 9–15.
Ebner Industrieofenbau GmbH
LOI Thermprocess
