New metallurgy for microalloyed TRIP steels
This project investigated the application of precipitation hardening to TRIP metallurgy. The objective was to obtain a TRIP grade in hot and cold rolled formats with a tensile strength of 1000MPa based on: (1) existing 800MPa high-Si TRIP (0.2C- 1.5 Mn- 1.5 Si) compositions microalloyed with titanium or vanadium with a high nitrogen content; (2) a new low-Si microalloyed TRIP grade suitable for continuous galvanising. Concerning high-Si TRIP hot strips, good results were obtained with additions of 0.2 % wt. V and 0.1 % wt. Ti using two steps cooling in the intercritical region to promote interphase precipitation. Strength levels of 936 MPa with a total elongation of 25 % were achieved for 0.2V steels coiled at 400 °C. For high-Si cold strips excellent mechanical properties were obtained with additions of 0.15 % wt. V. After intercritical annealing at 775 °C and overageing at 400 °C strength levels up to 999MPa with total elongations > 25 % were achieved. A new low-Si high-P microalloyed TRIP composition (0.2C-0.4Si-1.8Mn-0.08P-0.2V-0.01N) was determined on the basis of laboratory simulations. A first industrial trial produced galvanised cold strips with a dual phase microstructure that was attributed to the lack of overageing section on the galvanising line. A second industrial trial (same composition) using a lower coiling temperature (550 °C) and a galvanizing line with an overageing section produced a final microstructure with 15 % retained austenite in a ferrite/bainite matrix with some martensite. The mechanical properties were improved (YP = 425MPa, UTS = 922MPa, A80 = 17.5 %) however a true TRIP effect could not be observed.
Bibliographic Reference: EUR 22391 EN (2007), 130 pp. Euro: 25
Availability: Katalogue Number: KI-NA-22391-EN-S The paper version can be ordered online and the PDF version downloaded at: http://bookshop.europa.eu
ISBN: ISBN: 92-79-03031-0
Record Number: 200719233 / Last updated on: 2007-07-05
Original language: en
Available languages: en