Fundamental Research On Ultra-high Strength Steel By Arc-Rolling Hybrid Forming Process

Ultra-high strength steel has become more and more widely used in the field of aerospace, especially A100 steel with high strength and toughness has a good performance on improving the properties of the aircraft. Traditional processing methods have limitations on the aerospace parts with complex shape, however, Arc-Rolling Additive Manufacturing Process System developed by our laboratory has the characteristics of high degree of freedom, high efficiency and excellent comprehensive performance. It can be used for rapid prototyping of complex parts, which greatly reduces the cost. Forming process of ultra-high strength steel A100 by using Arc-Rolling Additive Manufacturing Process System is studied in this paper. The main results are as follows.For the aspect of the forming process, ultra-high strength steel A100 is suitable for TIG forming method. High purity argon is used as the protection gas of TIG welding, and the gas flow rate is 15L/min. The tungsten electrode diameter is 4mm and the tip is conical. The extended length of the tungsten electrode is 6mm, and the nozzle height is 14 mm. Quadratic general rotary unitized design was used to establish the relationship between the welding parameters and the weld geometry size.For the aspect of the mechanical property, Arc-Rolling process is better than arc welding process in three respects of tensile properties, impact toughness and hardness. In the respect of tensile properties, the average tensile strength of Arc-Rolling process, comparing to arc welding process, has respectively increased by 13%, 17%, 1% in the three directions of X, Y and Z. The average yield strength has respectively increased by 16%, 23%, 5% and the average elongation has respectively increased by 49%, 47% and 26%. In the respect of impact toughness, it has respectively increased by 4%?16%?20%. In the respect of hardness, the average rockwell hardness has respectively increased by 11%?7%?18% on three cross sections.For the aspect of the microcosmic grain, the grains of arc welding process are mainly coarse columnar crystal and have a certain direction which is along with the larger supercooling. However, the grains of Arc-Rolling process are mainly composed of large quantity fine equiaxial grains and a small amount of columnar crystal. After rolling, columnar crystal is broken by large rolling force and turn into fine equiaxial grain by dynamic recrystallization. Comparing to arc welding process, the grain of Arc-Rolling process is finer and the average grain size is between 8~8.5 grade, and the improvement of the mechanical properties was explained by the fine grain strengthening.