Effect of Mn Addition on Microstructural Modification and Cracking Behavior of Ferritic Light-Weight Steels

Abstract

In the present study, effects of Mn addition on cracking phenomenon occurring during cold rolling of ferritic light-weight steels were clarified in relation to microstructural modification involving j-carbide, austenite, and martensite. Four steels were fabricated by varying Mn contents of 3 to 12 wt pct, and edge areas of steel sheets containing 6 to 9 wt pct Mn were cracked during the cold rolling. The steels were basically composed of ferrite and austenite in a band shape, but a considerable amount of j-carbide or martensite existed in the steels containing 3 to 6 wt pct Mn. Microstructural observation of the deformed region of fractured tensile specimens revealed that cracks which were initiated at ferrite/martensite interfacial jcarbides readily propagated along ferrite/martensite interfaces or into martensite areas in the steel containing 6 wt pct Mn, thereby leading to the center or edge cracking during the cold rolling. In the steel containing 9 wt pct Mn, edge cracks were found in the final stage of cold rolling because of the formation of martensite by the strain-induced austenite to martensite transformation, whereas they were hardly formed in the steel containing 12 wt pct Mn. To prevent or minimize the cracking, it was recommended that the formation of martensite during the cooling from the hot rolling temperature or during the cold rolling should be suppressed, which could be achieved by the enhancement of thermal or mechanical stability of austenite with decreasing austenite grain size or increasing contents of austenite stabilizers.

Austenite-Based Fe-Mn-Al-C Lightweight Steels: Research and Prospective

“…The cellular transformation is a form of continuous reaction which occurs during the transformation of high-temperature austenite into lamellae of austenite, α-ferrite, and κ-carbide [62]. The formation of coarse second-phase particles which have a lamellar morphology was also observed after aging for a longer period of time in a solution treated Fe- (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)Mn-(7.8-10)Al-(0.8-2.0)C alloys [45,58,90,91,99,119].…”

“…Ferrite-based duplex and triplex Fe-Mn-Al-C steels with moderate Mn (Mn: 2-12%) and C contents (C: 0.05-0.5%) possess the microstructures consisting of austenite + δ/αferrite and austenite + δ/α-ferrite + martensite, respectively, in which the fraction of ferrite is higher than 50% [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. In this kind of steels, the transformation-induced plasticity (TRIP) effect is a very important mechanism in enhancing the strength and ductility of the materials.…”