Impact toughness of reinforcing steels produced by (ⅰ) the Tempcore process and (ⅱ) microalloying with vanadium

摘要

A "direct measurement" of the impact toughness of both Tempcore and microalloyed with vanadium reinforcing steel bars, of the same strength class (500 MPa nominal yield stress), is undertaken. The term "direct measurement" means that V-notched specimens with the original round section of the bars (and not with the standard rectangular one) are used, mentioned here as direct V-notched (DVN) specimens. The major complications encountered with them are the use of non-standard geometry (Charpy V-notched, CVN), the variable size of the bars and the composite microstructure of the Tempcore reinforcing steel. It has been shown that the toughness characteristics of reinforcing steels may be estimated by the CVN impact test using direct (DVN) specimens. It is found that if the notch exceeds a critical depth, meaningful measurements may be obtained, regardless of the diameter of the reinforcing steel bar and that the transition temperature may be estimated from the residual fracture angle of direct (DVN) specimens. The microalloyed with vanadium reinforcing steel has a lower temperature-transition range from ductile-to-brittle fracture (—10℃), compared to the AISI 1020 steel, attributed to the vanadium micro-additions, but it is higher compared to the Tempcore steel (—30℃).