Abstract
ABSTRACTA Fe-0.20C-1.49Mn-1.52Si-0.58Cr-0.05Nb (wt%) steel was treated by a novel quenching-partitioning-tempering (Q-P-T) process and traditional quenching and tempering (Q&T) for comparison, respectively. The researches of the mechanical properties and forming limit diagrams reveal that Q-P-T martensitic steel has more retained austenite (10.8%) than the Q&T martensitic steel (less than 3%), which makes Q-P-T martensitc steel possess higher strain hardening exponent and true uniform elongation than the Q&T martensitic steel. The high value of hardening exponent (n) and true uniform elongation (Īµu) stem from the low initial dislocation density in martensitic matrix in Q-P-T martensitic steel before deformation and the high strain hardening rate and dislocation absorption by retained austenite (DARA) effect of retained austenite during deformation. Moreover, the n, or the Īµu, is a most important parameter in all the apparent parameters affecting the formability of metal sheets, and this conclusion is of practical importance in the comparison of several steelsā formability.
Highlights
Advanced high strength steels (AHSSs) have rapidly developed in recent ten years due to the requirement of lightweight, environmental protection and safety in modern automotive industries [1]
These results indicate that the yield strength (YS) and ultimate tensile strength (UTS) of Q-P-T steel is lower in all three directions than in the quenching and tempering (Q&T) steel
The forming limit diagrams (FLDs) of Fe-0.20C-1.49Mn-1.52Si-0.58Cr-0.05Nb steel treated by a novel Q-P-T process and Q&T one for comparison were measured through both uniaxial tensile tests and Nakazima punching tests, respectively. the microstructures were characterized by X-ray diffraction (XRD), and transmission electron microscope (TEM), and main conclusions are described as follows
Summary
Advanced high strength steels (AHSSs) have rapidly developed in recent ten years due to the requirement of lightweight, environmental protection and safety in modern automotive industries [1]. As an aid to evaluating the success of sheet forming operations, forming limit diagrams (FLDs) have proven to be a very useful and popular technique for the manufacturers and users of sheet metal [14] Research in this field was pioneered by Keeler [15] based on the observations of Gensamer [16] that instead of using global indices, local deformations should be considered. Of the various AHSSs available, Q&P and Q-P-T steels possess the highest strength due to their martensitic matrix As they are a relatively new development, much less is known about their formability than DP, TWIP and TRIP steels [23,24]. This study [25] on the formability of high strength low-carbon Q-P-T martensitic steel is to reveal the effects of microstructure on apparent parameters and formability by compared to traditional quenching and tempering (Q&T) martensitic steel with the same composition
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