Effect of Mo content on the thermal stability of Ti-Mo-bearing ferritic steel

Abstract

The effects of tempering holding time at 700°C on the morphology, mechanical properties, and behavior of nanoparticles in Ti-Mo ferritic steel with different Mo contents were analyzed using scanning electron microscopy and transmission electron microscopy. The equilibrium solid solution amounts of Mo, Ti, and C in ferritic steel at various temperatures were calculated, and changes in the sizes of nanoparticles over time at different Mo contents were analyzed. The experimental results and theoretical calculations were in good agreement with each other and showed that the size of nanoparticles in middle Mo content nano-ferrite (MNF) steel changed the least during aging. High Mo contents inhibited the maturation and growth of nanoparticles, but no obvious inhibitory effect was observed when the Mo content exceeded 0.37wt%. The tensile strength and yield strength continuously decreased with the tempering time. Analysis of the strengthening and toughening mechanisms showed that the different mechanical properties among the three different Mo content experiment steels were mainly determined by grain refinement strengthening (the difference range was 30–40 MPa) and precipitation strengthening (the difference range was 78–127 MPa). MNF steel displayed an ideal chemical ratio and the highest thermodynamic stability, whereas low Mo content nano-ferrite (LNF) steel and high Mo content nano-ferrite (HNF) steel displayed relatively similar thermodynamic stabilities.

Keywords

ferritic steel / nanoparticles / interphase precipitation / thermal stability / ostwald ripening rate

References

[1] J.B. Seol, S. H., Na, B. Gault, J.E. Kim, J.C. Han, C.G. Park, and D. Raabe, Core-shell nanoparticle arrays double the strength of steel, Sci. Rep., 7(2017), art. No. 42547.

[2] Rahnama A, Clark S, Janik V, Sridhar S. A phase-field model for interphase precipitation in V-micro-alloyed structural steels. Comput. Mater. Sci., 2017, 137, 257.

[3] Mukherjee S, Timokhina I, Zhu C C, Ringer SP, Hodgson PD. Clustering and precipitation processes in a ferritic titanium-molybdenum microalloyed steel. J. Alloys Compd., 2017, 690, 621.

[4] Chen CY, Yang JR, Chen CC, Chen SF. Microstructural characterization and strengthening behavior of nanometer sized carbides in Ti-Mo microalloyed steels during continuous cooling process. Mater. Charact., 2016, 114, 18.

[5] Mukherjee S, Timokhina IB, Zhu C, Ringer SP, Hodgson PD. Three-dimensional atom probe microscopy study of interphase precipitation and nanoclusters in thermomechanically treated titanium-molybdenum steels. Acta Mater., 2013, 61(7): 2521.

[6] Huang Y, Zhao AM, Wang XP, Wang XM, Yang JB, Han JK, Yang FL. A high-strength high-ductility Ti- and Mobearing ferritic steel. Metal. Mater. Trans. A, 2016, 47(1): 450.

[7] Huang Y, Zhao AM, Cheng YF, Wang XP, Yang JB, Liu HQ. Interphase precipitation behavior of nano-sized carbides in low carbon steel. Chin. J. Eng., 2015, 37(7): 896.

[8] Wang XP, Zhao AM, Zhao ZZ, Huang Y, Geng ZD, Yu Y. Mechanical properties and characteristics of nanometer-sized precipitates in hot-rolled low-carbon ferritic steel. Int. J. Miner. Metal. Mater., 2014, 21(3): 266.

[9] Wang XP, Zhao AM, Zhao ZZ, Huang Y, Geng ZD, Yu Y. Precipitation strengthening by nanometer-sized carbides in hot-rolled ferritic steels. J. Iron Steel Res. Int., 2014, 21(12): 1140.

[10] Funakawa Y. Mechanical properties of ultra fine particle dispersion strengthened ferritic steel. Mater. Sci. Forum, 2012, 706–709, 2096.

[11] Funakawa Y, Seto K, Nakamichi H. Strengthening of ferritic steel by interface precipitated carbides in rows. Mater. Sci. Forum, 2010, 638–642, 3218.

[12] Chen CY, Yen HW, Kao FH. Precipitation hardening of high-strength low-alloy steels by nanometer-sized carbides. Mater. Sci. Eng. A, 2009, 499(1–2): 162.

[13] Lee WB, Hong SG, Park CG, Park SH. Carbide precipitation and high-temperature strength of hot-rolled high-strength, low-alloy steels containing Nb and Mo. Metall. Mater. Trans. A, 2002, 33(6): 1689.

[14] Lee WB, Hong SG, Park CG, Kim KH, Park SH. Influence of Mo on precipitation hardening in hot rolled HSLA steels containing Nb. Scripta Mater., 2000, 43(4): 319.

[15] Funakawa Y, Seto K. Coarsening behavior of nanometer-sized carbides in hot-rolled high strength sheet steel. Mater. Sci. Forum, 2007, 539–543, 4813.

[16] Jang JH, Lee CH, Heo YU, Suh DW. Stability of (Ti, M)C (M = Nb, V, Mo and W) carbide in steels using first-principles calculations. Acta Mater., 2012, 60(1): 208.

[17] Wang ZQ, Zhang H, Guo CH, Liu WB, Yang ZG, Sun XJ, Zhang ZY, Jiang FC. Effect of molybdenum addition on the precipitation of carbides in the austenite matrix of titanium micro-alloyed steels. J. Mater. Sci., 2016, 51(10): 4996.

[18] Wang ZQ, Sun XJ, Yang ZG, Yong QL, Zhang C, Li ZD, Weng YQ. Effect of Mn concentration on the kinetics of strain induced precipitation in Ti microalloyed steels. Mater. Sci. Eng. A, 2013, 561, 212.

[19] Uemori R, Chijiiwa R, Tamehiro H, Morikawa H. AP-FIM study on the effect of Mo addition on microstructure in Ti-Nb steel. Appl. Surf. Sci., 1994, 76–77, 255.

[20] Akben MG, Bacroix B, Jonas JJ. Effect of vanadium and molybdenum addition on high temperature recovery, recrystallization and precipitation behavior of niobium-based microalloyed steels. Acta Metall., 1983, 31(1): 161.

[21] Joon Chun E, Do H, Kim S, Nam DG, Park YH, Kang N. Effect of nanocarbides and interphase hardness deviation on stretch-flangeability in 998 MPa hot-rolled steels. Mater. Chem. Phys., 2013, 140(1): 307.

[22] Saini N, Pandey C, Mahapatra MM, Mulik RS. On study of effect of varying tempering temperature and notch geometry on fracture surface morphology of P911 (9Cr-1Mo-1W-V-Nb) steel. Eng. Fail. Anal., 2018, 85, 104.

[23] Cao JC, Yong QL, Liu QY, Sun XJ. Precipitation of MC phase and precipitation strengthening in hot rolled Nb-Mo and Nb-Ti steels. J. Mater. Sci., 2007, 42(24): 10080.

[24] Q.L. Yong, Second Phase in Iron and Steel Materials, Metallurgical Industry Press, 2006.

[25] Lifshitz IM, Slyozov VV. The kinetics of precipitation from supersturated sold solutions. J. Phys. Chem. Solids, 1961, 19(1–2): 35.

[26] Wagner C. Theorie der alterung von niederschlägen durch umlösen (ostwald — reifung). Zeitschrift Für Elektrochemie Berichte Der Bunsengesellschaft Für Physikalische Chemie, 1961, 65(7–8): 581.

[27] Speight MV. Growth kinetics of grain-boundary precipitates. Acta Metall., 1968, 16(1): 133.

[28] Huang Y. Study on the Precipitation Mechanism of Carbides in Ti-Mo Bearing High Strength steel, 2014, Beijing, University of Science and Technology Beijing [Dissertation]

[29] Pickering FB. Physical Metallurgy and the Design of Steels (Materials Science Series), 1978, London, Applied Science Publishers