High strength steels have provided a unique opportunity for the automotive industry to achieve weight reduction via reduced material thickness whilst maintaining performance requirements such as crash worthiness. However, the initial success of HSLA steels was constrained by inconsistencies in the final mechanical properties. Although significant improvements in both mechanical and dimensional properties have since been made, increasingly stringent customer specifications for high strength steels mean that the challenge to reduce variability in automotive HSLA steel products and enure their continued competitiveness has never been greater. This investigation addresses the issues concerning the controlled hot rolling of Nb-HSLA strip steels through a series of laboratory and commercial trials, both to optimise the mechanical properties and uniformity of properties. Both sets of data established that: (i) the strength was decreased by reducing the soak temperature from 1250°C to 1150°C; (ii) the presence of furnace skid chills during soaking locally reduced the strength; (iii) lowering of the finishing temperature towards the Ars reduced the overall strength, but improved the coil-width property consistency, and; (iv) the existence of an optimum coiling temperature developed higher strengths and improved property consistency. The programme of work conducted also observed that by finishing near the Ars temperature, very fine ferrite subsurface grains are created which limit the fall in strength. Additionally, the commercial trials highlighted the need to compensate for the exposure-related cooling effects of the inner and outer most laps of the hot-rolled coil, thereby reducing any potential for developing further inconsistencies. Furthermore, the work undertaken has established that prudent additions of niobium, coupled with the use of a low finishing temperature and an optimum coiling temperature, will lead not only to higher strengths steels but also to significant improvements to the through-coil uniformity of properties
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:547855 |
| Date | January 2000 |
| Creators | Patel, Jitendra Kumar |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0013 seconds