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

Abstract

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.

Near-Net Shape Manufacture of Ultra-High Strength Maraging Steel Using Flow Forming and Inertia Friction Welding: Experimental and Microstructural Characterization

“…The difference in the grain morphology and size at the weld interface compared to the PM along with the occurrence of severe plastic deformation is an indication of straininduced dynamic recrystallisation. From our previous findings [8,10], similar evidence of formation of recrystallised grains has been witnessed during the rotary friction welding of different metals in the WZ and TMAZ because of the peak temperature (≈ Ac3) attained in these regimes. The recrystallised grains are then subjected to intense plastic deformation before further growth and finally turns to fine grains in the weld interface.…”

“…The Ac1 and Ac3 temperatures of MLX ® 19 were calculated to be ≈ 687 ± 5 °C and 778 ± 13 °C, respectively based on the empirical equation provided by Mesplont [33]. From our previous studies on different steels [8,9], it has been inferred, that the temperature in the WZ and TMAZ during the IFW is expected near Ac3, leading to the complete transformation of the child phases into parent phase i.e. austenite.…”

“…The flywheel is disconnected from the motor once the targeted speed is reached and the workpieces are then welded using friction and forge forces. The detailed description about this process is provided elsewhere [7] In recent times, the use of IFW has steadily increased because of significant reduction in solidification defects and improved joint quality [8]. Other advantages of IFW over fusion welding are (a) no use of shielding gas or filler material, (b) low residual stresses, (c) reduced weld time etc.…”

The Microstructure Evolution and Mechanical Properties of Rotary Friction Welded Duplex Stainless Steel Pipe

“…As cooling continues, the nucleation sites of the ferrite grain boundaries decrease, and Widmanstätten austenite forms at the ferrite/austenite grain boundaries, with intragranular austenite forming within the ferrite grains. Due to the relatively rapid cooling rate of solid-phase welding [21,28], which is approximately 10 2 -10 4 K/s, only grain boundary austenite is found in the weld zone. The absence of σ and chi phases guarantees a good joint quality.…”

Fatigue strength of 30ХГСА–40ХМФА welded joints produced by rotary friction welding

“…Поиск и анализ работ, направленных на подробное изучение микроструктуры и свойств фрикционных сварных соединений из среднеуглеродистых легированных сталей, показал ограниченность информации в данной области. Имеются отдельные публикации, в которых приведены результаты исследований микроструктуры и свойств сварных соединений бурильных труб из сталей N80 (аналог 35Г2) в нормализованном состоянии со сталью 42CrMo4 (аналог 40ХМ) после закалки и отпуска [1], стали AISI 8630 (аналог 30ХМН) [2], сварных соединений сталей ASTM A 106 Grade B (аналог 20Г) в горячекатанном состоянии и 4140 (аналог 40ХГМ) после нормализации и после улучшения [3; 4]. Эти работы, а также другие исследования [5; 6] свидетельствуют, что механические свойства сварных соединений при испытании на растяжение при правильно подобранных режимах сварки не уступают, а в ряде случаев и превосходят механические свойства наименее прочного привариваемого материала.…”