Isoforming and wárm rolling of low-carbon structural steels

1. By means of mathematically planned experiments it was found that the isoforming temperature has the largest effect on the mechanical properties of steels in comparison with other isoforming parameters. 2. The optimal combination of mechanical properties of steels of the 10GN, 09G2, and 15G types is obtained after isoforming at 650–680°C (total reduction 50%, holding time ∼12 min); for steels with vanadium and niobium the isoforming temperature is ∼700°C (total reduction 50%, holding time 10–12 min). Use of combined hardening (isoforming and microalloying) increases the strength (σ0.2 by 45–50%, σb by 25%) in comparison with that obtained after normalization withan=7.0 kgf-m/cm2 and TX=−60 to −80°C. 3. The optimal combination of mechanical properties of low-alloy structural steels after isoforming is due to the formation of a perfect subgranular structure in excess ferrite and pearlite with fragmented and clustered particles of cementite. In steels with vanadium and niobium the carbides are precipitated in the boundaries and within subgrains, which leads to additional hardening. 4. Warm rolling and isoforming under similar conditions produce similar mechanical properties and identical structures in low-alloy structural steels.