Investigation of abnormal tensile behavior of DIN 16MnCr5 low carbon low alloy steel under ferrite-martensite dual-phase microstructures in comparison with full martensitic condition

Subject Areas : journal of New Materials

Hamid Reza Pakzaman ¹ , sadegh ghasemi banadkouki ²

1 - department of mining and metallurgical engineering, Yazd university, Yazd, Iran
2 - department of mining and metallurgical engineering, yazd university, yazd, iran

Received: 2020-02-23 Accepted : 2021-01-11 Published : 2020-11-21

Keywords: Inter-critical annealing, Ferrite-martensite dual-phase microstructure, Full martensitic microstructure, Tensile properties, Combination of strength and ductility,

Abstract :

In this research, the microstructures and mechanical properties of DIN 16MnCr5 low alloy steel under ferrite-martensite dual-phase (with various martensite volume fraction) were compared to full martensitic condition. Dual-phase microstructures were developed by inter-critical annealing. For this purpose, the samples were heated at various inter-critical temperatures (from 740 to 840 °C) for 60 minutes and then water quenching to room temperature. Also, to develop full martensitic microstructure, steel samples were immediately quenched in water after austenitization at 900 ˚C for 60 minutes. The microstructure and mechanical properties of the specimens were analyzed by scanning electron microscope equipped with EDS analyzer, X-ray diffraction and tensile and microhardness tests, respectively. Metallographic observations showed that by increasing the inter-critical annealing temperature from 740 to 840 °C, the martensite volume fraction (Vm) increased from 23 to 87%. Comparison of mechanical properties of dual-phase samples showed that by increasing Vm from 23% to 87%, there was an abnormal tensile behavior at Vm=73%, so that the energy absorption capability (product of tensile strength and uniform elongation) for ferrite-martensite dual-phase samples is much higher than to full martensitic samples. This remarkable modification in the mechanical properties of the dual-phase samples is due to the different hardening responses of the ferrite and martensite microconstituents because of the interaction between them. By increasing the Vm from 23 to 87%, the martensite microhardness decreased continuously from 717 to 471 HV10g, while the ferrite microhardness showed a peak value at Vm=73%.

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