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Inter-relationship between microstructure evolution and mechanical properties in inertia friction welded 8630 low-alloy steel

Banerjee Amborish, Ntovas Michail, Da Silva Laurie, Rahimi Salaheddin, Wynne Bradley

Archives of Civil and Mechanical Engineering

2021

Vol. 21, no. 4

244--262

The evolution of microstructure and mechanical properties in AISI 8630 low-alloy steel subjected to inertia friction welding (IFW) have been investigated. The effects of three critical process parameters, viz. rotational speed, friction and forge forces, during welding of tubular specimens were explored. The mechanical properties of these weld joints, including tensile and Charpy V-notch impact were studied for determining the optimum welding parameters. The weld joints exhibited higher yield strength, lower hardening capacity and ultimate tensile strength compared to base metal (BM). The maximum strength and ductility combination was achieved for the welds produced under a nominal weld speed of ~ 2900–3100 rpm, the highest friction force of ~ 680–720 kN, and the lowest axial forging load of ~ 560–600 kN. The measured hardness distribution depicted higher values for the weld zone (WZ) compared to the thermo-mechanically affected zone (TMAZ), heat-affected zone (HAZ) and BM, irrespective of the applied welding parameters. The substantial increase in the hardness of the WZ is due to the formation of microstructures that were dominated by martensite. The observed microstructural features, i.e. the fractions of martensite, bainite and ferrite, show that the temperature in the WZ and TMAZ was above Ac3, whereas that of the HAZ was below Ac1 during the IFW. The fracture surface of the tensile and impact-tested specimens exhibited the presence of dimples nucleating from the voids, thus indicating a ductile failure. EBSD maps of the WZ revealed the formation of subgrains inside the prior austenite grains, indicating the occurrence of continuous dynamic recrystallisation during the weld. Analysis of crystallographic texture indicated that the austenite microstructure (i.e. FCC) in both the WZ and TMAZ undergoes simple shear deformation during IFW.

Experimental and numerical investigation on the impact resistance of high-carbon low-alloy steel

Banerjee Amborish, Prusty B. Gangadhara, Zhu Qiang

Archives of Civil and Mechanical Engineering

2020

Vol. 20, no. 3

1--17

Duplex high-carbon steel is widely used in ball mills in the form of grinding balls and thus subjected to impact loads during the normal operation of the mill. The influence of impact loading at different impact energies is investigated in this paper. Impact tests using a drop tower were performed in the regime of 100–150 J, and the mechanical response of the material was recorded. The deformation behaviour of the material was classified into two groups: (a) low-impact-energy regime (100–120 J) where the material bulged without fracture and (b) high-impact-energy regime (130–150 J) where the material faced catastrophic failure. An overall increase in the load-bearing capacity of the material was found with an increase in the impact energy. The energy–time curves exhibited both linear and nonlinear regions which were attributed to the nucleation and propagation of cracks. Shear bands were observed in the specimens which underwent catastrophic fracture (i.e. 130 J and above); however, significant changes in the features of shear bands were noticed with increase in the impact energy. Fracture surfaces displayed the presence of microvoids, dimples, knobby fracture and river pattern, thus indicating ductile as well as a brittle mode of failure. Transmission electron microscopy results revealed the presence of much finer nano-grains inside the shear bands as compared to the surrounding regions. Finite element simulations exhibited an increase in the shear stress with the propagation of shear bands during the ongoing deformation process.