Effect of Preliminary Deformation of Continuously Cast Billets by Radial-Shear Rolling on the Structure and Properties of Hot-Rolled Chromium-Containing Steel Pipes

Abstract

The paper analyzes the effect of preliminary deformation of continuously cast billets (CCB) made of chromium-containing grades of steel by radial-shear rolling (RDR) on the structure and properties of seamless pipes. A bar stock measuring 105 mm in diameter was obtained using an RDR mill at large feed angles (β = 21°). A comparative analysis of the microstructure of the initial CCB and hotrolled bars has shown that radial-shear rolling enables intensive refinement of the structure of continuously cast billets, and ensures a high-quality (70 to 90%) work-up of the cast structure at reduction ratios of 2.0 to 2.2. A pipe-rolling mill (PRM) installed at the Pervoural’sk New Pipe Plant JSC (PNPP JSC) was used to obtain seamless pipes from the deformed bars, and the mechanical properties of such pipes were studied. It was found that the pipes obtained from the experimental billets are fully compliant with the ISO 11960:2004 requirements for strength group J55 (σt > 517 MPa; σ0.2 > 379 MPa; δ > 16%). In addition, the level of plastic properties of the experimental pipes (based on present elongation δ5, %) exceeds the ISO 11960:2004 requirements by 1.6–1.8 times. To achieve a comparable level of properties using the existing technology, an additional heat treatment (HT) is required, which points to the potential advantages of using RDR pre-deformed billets to obtain seamless pipes with the required properties.