Effects of MnS Inclusions on the Banded Microstructure in Non-quenched and Tempered Steel
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NON-QUENCHED and tempered steel has been widely used and studied in various applications due to its advantages related to energy consumption during processing.[1,2] Conventional non-quenched and tempered steel is based on carbon manganese steel containing alloying elements, such as Ni, Cr, V, and Ti. The mechanical properties of these non-quenched and tempered steels can be improved through solid solution strengthening of these alloying elements. The amount, size, and distribution of ferrite and pearlite within the microstructure play an important role in the enhancement of toughness and tensile strength. A microstructure formed by ferrite nucleation at both the austenite grain boundaries and intra-granular sites increases
KAI WANG and TAO YU are with the College of Materials Science and Engineering of Chongqing University, 174 Shapingba Main Street, Chongqing 400030, China and also with the Chongqing Key Laboratory of Metal Additive Manufacturing (3D Printing), 174 Shapingba Main Street, Chongqing 400030, China. Contact e-mail: [email protected] YANG SONG, HONG-XU LI, and MENG-DI LIU are with the College of Materials Science and Engineering of Chongqing University. RONG LUO, JING-YU ZHANG, and FEI-SONG FANG are with the Chongqing Jianshe Industry (Group) Co., LTD., Chongqing 400054, China. XUE-DONG LIN is with the College of Mechanical engineering, Chongqing Vocational institution of Engineering, Chongqing 402260, China. Manuscript submitted February 8, 2018.
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resistance to crack propagation. Second phase particles such as manganese sulfide (MnS), titanium oxide (Ti2O3), and vanadium nitride (VN) usually act as potential sites for intra-granular ferrite (IGF) nucleation in non-quenched and tempered steels.[3,4] Banded microstructure is usually observed in nonquenched and tempered steels containing MnS inclusions.[5] Elongated inclusions and banded microstructures have an adverse effect on the entire down-stream processing and eventually the mechanical properties of products. The origin of banding is usually due to the limited solid solubility of alloying elements during the solidification process, which subsequently leads to the banded segregation of these alloying elements. The studies of Thompson and Howell[6] and Zhang et al.,[7] showed that banded microstructure is caused by micro-chemical banding of Mn. Their EMPA studies showed that alternative bands of ferrite and pearlite are located in solute-poor and solute-rich regions, respectively. Khalid et al.[8] found that banded pearlite structure accumulates several kinds of elements, such as Mn, Si, S, and P. Additionally, banded microstructure can also be influenced by process parameters. For example, Offerman et al.[9] pointed out that both cooling rate and prior austenite grain size (PAGS) can affect the banded ferrite and pearlite microstructure. Krebs et al.[10] proposed that ferrite transformation mode can influence the banded microstructure formation, and cooling rate would affect the morphology of ferrite in a banded
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