Drop-Weight NDT Temperature Test Results for Five Heats of ASTM A517 Steel

Abstract

This paper describes the results of drop-weight (DW) nil-ductility transition (NDT) temperature testing (according to the ASTM Method for Conducting Drop-Weight Test to Determine Nil-Ductility Transition Temperature of Ferritic Steels [E 208-69(1975)]) of “as fabricated” surfaces as well as quarter-point (subsurface) material from five plates of ASTM A517 steel, each plate from a different heat of steel. The steel was from two California bridges, one of which developed brittle fracture of a main-load-carrying flange during erection of the bridge. The five plates were characterized by Charpy V-notch impact, precracked Charpy impact, dynamic tear, and plane-strain fracture toughness testing; these results were compared with the results obtained from the drop-weight test. One plate showed 66.7°C (120°F) difference between the NDT temperatures for surface and subsurface material. Heat tinting “unbroken” drop-weight specimens revealed further complications in using ASTM Method E 208, including cracked tension surfaces not revealed in evaluation by the ASTM test and specimens with uncracked corners (and therefore rated “unbroken” by the ASTM test) but with virtually completely fractured cross sections. Both the dynamic tear and precracked Charpy impact tests were evaluated for usefulness in estimating the drop-weight NDT temperature; the correlation of test results was made uncertain, if not precluded, by through-thickness inhomogeneity and complications in the ASTM DW test method. Recommendations are made to improve ASTM Method E 208 by heat tinting. The five heats of ASTM A517 steel were shown to have widely variable fracture characteristics.