###### Abstract  
Economic welding of thick steel plates is an emerging challenge for various engineering applications. However, tungsten inert gas (TIG) arc welding, as an economic and widely used method, is not regarded as a suitable tool to weld thick steel plates due to the shallow penetration in a single-pass operation. In this technical progress, the joining of austenitic high manganese steel of 8 mm thickness was successfully performed using nanowire flux activated TIG welding with a full penetration and a narrow bead geometry. Fe\({}_{2}\)O\({}_{3}\) nanowire was used as flux and compared with microscale Fe\({}_{2}\)O\({}_{3}\) flux. Experimental results showed that with nanowire fluxes, the welding yielded the maximum of more than 8 mm thick penetration (full penetration and melt over the plate) with proper operating parameters in a single pass. In sharp contrast, the penetration is only less than 4 mm for a single pass welding without Fe\({}_{2}\)O\({}_{3}\) flux with the similar parameters. Arc voltage--time variation during welding process was analyzed and the angular distortion was measured after welding to understand the activating effect of optimized flux mixture. Compared to welding joint without flux and with microscale Fe\({}_{2}\)O\({}_{3}\) flux, nanoscale Fe\({}_{2}\)O\({}_{3}\) flux has a larger arc voltage and higher energy efficiency, higher joint strength and less angular distortion. The developed joint with nanowire flux qualified the tensile test with tensile strength of 700.7 MPa (82.38% of base material strength) and 34.1% elongation. This work may pave a way for nanotechnology-enabling welding innovation for engineering application. annoscale Fe\({}_{2}\)O\({}_{3}\); microscale Fe\({}_{2}\)O\({}_{3}\); A-TIG welding; activating flux; penetration Article]Fe\({}_{2}\)O\({}_{3}\) Nanowire Flux Enabling Tungsten of High-Manganese Steel Thick Plates with Improved Mechanical Properties. 17 April 2021  
tough once the manganese content exceeded 10%. Manganese steels are further defined by the range of Mn content as regular manganese steel (11-15%) and high manganese steel (over 15%) [6]. The high manganese steel (HMS) is an austenitic alloy with high yield strength, high hardness and high ductility at room temperature. Manganese increases the hardness of the metal as it reduces the critical cooling rate during hardening, meaning that it increases the hardenability of steel and allows for the required combination of higher strength and higher uniform elongation [7; 8; 9]. Meanwhile, due to an intense twinning of the alloy, the steel also has impressive properties at low temperatures [10; 11]. It is also a kind of non-magnetic steel, in which the so-called non-magnetism originates essentially from the low permeability of paramagnetic austenite matrix [12; 13; 14]. All these desirable combinations of properties have resulted in numerous applications of this alloy, especially in liquid gas storage, pipelines for petroleum transporting, railway rail steel, producing automobile parts and marine risers. Other applications range from noiseproof floor panel used in construction, wear-resistant slurry transportation ore pipes, and cryogenic steel for LNG storage tanks [15]. HMS steel welding has been achieved using conventional tungsten inert gas welding (TIG welding). However, the low productivity (less than 1.5 mm/s) and shallow depth of penetration (1-3 mm) in single pass limited its application [16; 17]. There are therefore other advanced ways for welding HMS steels, such as laser beam welding with both high penetration and speed, and friction-stir welding with better joint performance and finer grains. Nevertheless, according to the previous studies, laser beam welding on HMS can cause alloy element loss due to its thermal vaporization at extremely high welding temperatures [18; 19; 20; 21], which is a fetal defect because of the loss of manganese from the weld pool leading to the microstructure and properties modification.