Crystalline Phase Changes due to High-Speed Projectiles Impact on 304L Steel

Abstract

High yield 304L steel is well known for its employment in manufacturing. The quenched and tempered low-carbon alloy has a minimum yield strength of 40-50 ksi. Also, 304L offers good corrosion resistance and weldability. Traces of Chromium and Nickel in 304L give it the desired corrosion resistance properties. So, it is an ideal candidate for pressure vessels and the petrochemical industry applications. The physical characteristics and molecular structure of 304L steel are also well known; however, little is known about the high-velocity impact on this metal alloy’s crystalline structure and material phase changes. The effects of high-speed velocity impact on the crystalline structure and material phase changes due to impacts are studied herein experimentally. The high-speed impact on the crystalline structure’s inevitable phase change is examined, let alone the atomic reorganization resulting from the impact on the 304L steel. The effects of an impact on the crystalline structure are assessed by impacting 304L steel plates (15.4 x 15.4 x1.27 cm) with Lexan projectiles. A two-stage light gas gun accelerates these projectiles to a velocity of 6.70 km/s at the point of the impact. The impacted plates’ surfaces are prepared for the Electron Back Scatter Diffraction (EBSD) microscope inspection. Nine regions on each impacted plate area are examined and analyzed. Each part (90x90) square microns were cut off the test samples, keeping with the required surface finish standards. These regions are selected from the area immediately under the impact crater to locations not physically affected by the impact. Observations of collected EBSD images show that the predominant phase is Body-Centered Cubic (BCC); Face-Centered Cubic (FCC) and Hexagonal-Close-Packed (HCP) phases are also indexed. Since these crystalline structures are the most expected lattice formations, the samples are post-impact examined for molecular structure allocation changes. The results were then tabulated according to the region’s relative impact crater. Previous research, A36 steel results show that post-impact inspection of HCP phase chage, in iron specifically, is completely and rapidly reversible during impact. However, in this study, traces of HCP were found at some locations in all post-impact stages. This study also indicates that the BCC crystalline structure remained the dominant phase structure after impact, and it is valid with all test samples and all levels of shock loading. High pressure and the temperature quickly affect the target material at 6.70 km/sec velocity. The damage zone develops within 5 microseconds at this velocity due to impacting momentum