RESIDUAL STRESSES IN HOT-ROLLED ALLOY STEEL SOLID ROUND BARS

摘要

Residual stresses in seven hot-rolled alloy steel solid round specimens were determined using "boring-out" method. The diameters of specimens ranged from 4.0 to 6.0 inches. The bars were rolled and straightened according to current rolling practices. The average value of yield strength was 66.1 ksi (with a range of 5.3 ksi) and average tensile strength was 92.9 ksi (with a range of 9.5 ksi). The elongation was 24% (with a range of 5%) and reduction in area was 62% (with a range of 17%). Residual strains were measured by means of four strain gages (90 degrees apart) located at mid-height of the specimens. Extreme care was taken to ensure that no additional stresses were introduced during the "boring-out" process. The strain readings were corrected for temperature variation during the test period (approximately three to four days). In order to facilitate holding of the specimen during drilling and boring, the bottom part of the specimen was not bored. This ensured that the boundary conditions were not changed during the test. An accurate relationship between the residual force released and the strain measured at mid-height of the specimen was obtained by the commercial finite element program ABAQUS. It was observed that the compressive residual stresses were only about 3 to 4 ksi (approximately 5% to 6% of the yield strength), which are considerably less than the residual stress levels in other rolled shapes. Since the current SSRC column curves are based on much higher residual stress levels, there is a need to develop a new column curve applicable to solid round bars rolled and straightened according to the current mill practice.