Production of thick plate on the hot strip mill at the Rourkela steel plant (RSP)

Abstract

Thick plate producers worldwide have shifted from the ingot casting route to the concast route owing to certain inherent advantages, namely, low cost, high yield, low energy consumption and high quality of the cast product. The major challenge towards adoption of concast technology has been achieving the desired mechanical properties and internal soundness in the final product using a low reduction ratio (approximately 3–5) during hot rolling. Steelmakers across the world have resorted to microalloying, adequate soaking and heavy reductions during hot rolling using modern high powered plate mills to overcome this impasse. This is not possible at Rourkela steel plant (RSP), which is equipped with an underpowered plate mill with low load bearing capacity (∼ 3000 t). Thus, the novel ideal of utilising the roughing section of the hot strip mill of RSP was conceived, whereby the R₀ and R₁ stands could serve as the roughing and finishing stands of a 'plate mill'. As the maximum permissible reduction per pass is significantly higher in the R₀ and R₁ stands (15–25%), compared with the plate mill (10–15%), the rolling of thick plates became a reality. With the objective of producing ultrasonically sound thick plate (>40 mm) via the hot strip mill route at RSP, experimental rolling of 50 mm thickness plate of plain C–Mn steel (IS 2062 Gr. B) was undertaken. Slabs processed through the basic oxygen furnace–vacuum arc degassing– continuous casting (LD–VAD–CC) route were rolled into thick plate using a specially designed draft schedule in order to weld the internal defects in slabs and achieve high strength with good toughness properties in the final product. The rolled plates were subjected to an ultrasonic test according to ASTM standard A578 level 3, and were found to be satisfactory. The present paper describes the rolling practice for the production of 50 mm thickness plate of plain carbon steel having minimum yield and tensile strengths of 230 and 410 MPa, respectively, with guaranteed ultrasonic soundness.