LABORATORY SIMULATION OF SEAMLESS-TUBE ROLLING

In the manufacture of high-strength seamless tubing at the Algoma Steel Corporation, a post-hot deformation quench and temper treatment is employed to produce the higher yield-strength grades. In this laboratory study, the aim was to determine the microstructures and associated strength levels that can be achieved in the as-hot-rolled condition using Ti-V-N microalloyed steel chemistries. The benefits are significant savings in handling and energy costs and a substantial increase in productivity. The # seamless-tube mill, which consists of a piercer, a multi-pipe mill (MPM) and a stretch-reducing mill (SRM), was characterized in terms of the key hot-working variables: strain, strain rate, temperature and interpass delays. Torsional simulations of this process were carried out. The dependent variables of interest were the flow resistance during the simulated passes, the final microstructure and the room temperature yield strength. The results indicate that the candidate steels can be readily rolled in the mill without exceeding the force limitations. The as-hot-rolled microstructures were composed of fine grained polygonal ferrite-pearlite. The yield strengths associated with these microstructures varied from 553 to 629 MPa (77 to 91 ski): these cover much of the strength range of current quench and temper seamless products.