Abstract
The paper presents the microstructural investigation of a friction-welded joint made of 316L stainless steel with an ultrafine-grained structure obtained by hydrostatic extrusion (HE). Such a plastically deformed material is characterized by a metastable state of energy equilibrium, increasing, among others, its sensitivity to high temperatures. This feature makes it difficult to weld ultra-fine-grained metals without losing their high mechanical properties. The use of high-speed friction welding and a friction time of <1 s reduced the scale of the weakening of the friction joint in relation to result obtained in conventional rotary friction welding. The study of changes in the microstructure of individual zones of the friction joint was carried out on an optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and electron backscattered diffraction (EBSD) analysis system. The correlation between the microstructure and hardness of the friction joint is also presented. The heat released during the high-speed friction welding initiated the process of dynamic recrystallization (DRX) of single grains in the heat-affected zone (HAZ). The additional occurrence of strong plastic deformations (in HAZ) during flash formation and internal friction (in the friction weld and high-temperature HAZ) contributed to the formation of a highly deformed microstructure with numerous sub-grains. The zones with a microstructure other than the base material were characterized by lower hardness. Due to the complexity of the microstructure and its multifactorial impact on the properties of the friction-welded joint, strength should be the criterion for assessing the properties of the joint.
Highlights
Introduction published maps and institutional affilThe basic criteria determining the suitability of a material for a particular construction are, among others, its rigidity and strength
This paper presents an analysis of changes in the microstructure of individual zones of joints caused by the high-speed friction welding process
Joint0.6 was characterized by weld a narrow heat-affected heat-affected zone The withfriction-welded a width of approx
Summary
The basic criteria determining the suitability of a material for a particular construction are, among others, its rigidity (represented by an appropriate modulus of elasticity) and strength (interpreted in different ways depending on the type of material). It has been well known that strength and toughness of polycrystalline metals are improved with decreasing the grain size. Concerning the strength, Hall-Petch relationship was empirically described in the formula (1). Where: σy is the yield strength of the polycrystalline material, σ0 the friction stress, k the. Hall-Petch constant, and d the average grain size [1]. Significant refinement of the microstructure can be achieved through, among others adding more alloying elements and/or applying complex thermomechanical treatments [2]
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