Papers by Author: C. Herrera

Abstract: The phenomena of strain hardening, strain induced martensite formation, recovery, martensite reversion and recrystallization have been studied in austenitic stainless steels of the AISI 304L and 316L types, after solution annealing, followed by rolling at different temperatures (-196, 25, 100 and 200°C) and subsequent annealing of the worked samples. Strain hardening and the percentage of α’ martensite formed showed strong dependency with the deformation temperature and with the austenite chemical composition. As expected, both strain hardening as well as the amount of the martensite formed was higher in the 304L steel and for lower temperatures. Reversion temperature of the α’ martensite was close to 550°C for both steels, independent of the amount of martensite. The 316L steel presented a higher resistance to recrystallization when compared to the 304L steel. The recrystallization temperature of both steels was about 150°C higher than the α’ phase reversion temperature. Rolling temperature did not influence significantly the recrystallization temperature. Proper thermal and mechanical treatments lead to interesting combinations of mechanical properties in both steels with values such as yield strength YS of about 1000 MPa, with an elongation around 10%.

Abstract: The evolution of the crystallographic texture of ferritic stainless steels, starting from the as received (hot rolled) condition from the steel mill, going through cold rolling, annealing and final stamping is analyzed in this paper. Two ferritic stainless steels (Nb stabilized) having a thickness of 3.0 and 0.7mm, have been employed. The thicker one has been cold rolled to 40 and 73% thickness reduction, annealed at 750 and 850°C for 1 hour. The thinner one, with a similar composition, has been 77% cold rolled and annealed at 870°C at the steel plant and subsequently submitted to deep drawing in order to evaluate texture and drawability. Texture has been evaluated using DRX in the as received, cold rolled, annealed and after drawing conditions. Drawability has been evaluated using tensile testing in order to obtain the FLC curves. AISI 430 stainless steel, in the as received condition presented a strong {100} texture in the <110> and <120> directions and the gamma fiber. After cold rolling, the material presented stronger gamma and weaker alpha fibers. Annealing of the cold rolled samples conduced to the vanishing of the alpha and strengthening of the gamma fiber, adequate for deep drawing operations. In spite of the AISI 430 of 0.7mm having presented a strong gamma fiber, other deep drawing properties were not adequate and the material cracked during stamping.