Crystalline Phase Change due to High Speed Impact on A36 Steel

Abstract

The well-known industrial standard called A36 alloy steel is an iron-based alloy that has many applications due to its ability to be easily machined and welded. The alloy has less than 0.3% carbon by weight and is therefore considered a low carbon alloy. Because of this low carbon content, the alloy is useful as a general-purpose steel. It is altogether strong, tough, ductile, weldable, and formable. It is used in the construction of bridges, buildings, automobiles, and heavy equipment as well as in the construction industry. A36 steel also contains small amounts of other elements including manganese, sulfur, phosphorus, and silicon. These elements are added to give the steel alloy desired mechanical and chemical properties. The A36 steel alloy gets the number 36 in its name because of its yield strength. The steel, in most to all configurations, will have a yield strength of a minimum of 36,000 pounds per square inch. This shows high ductility in the material. The physical characteristics and molecular structure of A36 steel are also well known. However, there is little known about the effect of high-velocity impact on the crystalline structure and material phase of this metal alloy. Sections of approximately 90 × 90 square microns were cut off the test samples, keeping with the required standards for surface finish. These surfaces were examined and analyzed after impact. The surface sections were selected from a range of areas including those immediately under the impact crater to locations not physically affected by the impact. Three different impact speeds were applied, and the prepared samples were examined. An EBSD (Electron Backscatter Diffraction) imaging microscope is used to examine the crystalline structure of the test sample post-impact. Most metals crystallize in one of three prevalent structures: body-centered cubic (BCC), hexagonal close-packed (HCP), or face-centered cubic (FCC). Since these crystalline structures are the most expected lattice formations, the samples are examined post impact for changes in the allocation of molecular structure. The results were then tabulated according to the regions relative to the impact crater. In previous research, results show that post-impact inspection of HCP phase change, in iron specifically, is completely and rapidly reversible during impact. However, in this study, traces of HCP were found at some locations in all stages of post-impact. This study also found that the BCC crystalline structure remained the dominant phase structure after impact. This is true with all test samples and all levels of shock loading.