SR19 The 19th Research Committee Further Investigation on the Testing Method for the Notch Sensitivity of Steels 1957

§1. Introduction In order to establish the testing method for the notch sensitivity of steels, further investigations on the following testing methods, namely (1) Schnadt test, (2) Lehigh bend test, (3) Charpy impact test, (4) Kahn tear test, (5) Tipper test, and (6) Van der Veen test. were carried out. Two charges of ingot, a killed mild steel and Mn-Si type high tensile steel, were used for the tests. The radius and the depth of the notch were changed in series to know the effects of notch shape on the transition temperature. Also double blow impact test were performed in addition to the above test to make clear the characteristics of Charpy-impact test. As a reference the flow curve test was made to investigate the stress-strain relations in plastic deformation. In addition to the above notch sensitivity tests, the following experiments were carried out to investigate some special problems, (1) Crack-starter impact bend test, and (2) Strain-aging test. §2. Schnadt and Charpy-impact Tests Schnadt test on a killed mild steel and high tensile steel were performed with specimens having notch radius of 0.1mm, 0.25mm, 0.5mm and 1.0mm respectively. The test results show that the transition temperatures determined using various criteria always rise with the decrease of notch radius, and the absorbed energy at a definite low temperature (for example 0℃ or -20℃) falls with the decrease of notch radius. The transition temperature and the absorbed energy are calculated by the same stress theory for Charpy test and show good coincidence with the experimental results. Also to get the verification of the proposed stress theory for notch brittleness of mild steel, Charpy impact test was performed with specimens of various notch radii and depths taken from a killed mild steel and high-tensile steel. The experimental results well coincided with the theoretical values both in the transition temperatures and the absorbed energy, and the validity of th e theory was confirmed. It was proved that the constants obtained by the experiments which were the characteristics to the material for the transition temperature in Charpy test were applicable to Schnadt test with a small amendment considering the difference in stress distribution. §3. Lehigh Bend Test (Impact) The effects of notch radius and specimen width on the transition temperatures of Lehigh type specimens were investigated by impact loading using 1500kg-m large impact testing machine. Transition temperatures by energy, fracture and lateral contraction criteria were measured for comparison. Fracture transition temperatures were not changed by impact loading compared with the static loading, while energy transition temperatures were raised remarkably by impact loading. Also specimen width and notch radius affected considerably the energy and lateral contraction transition temperatures. §4. Kahn Tear Test To know the effects of notch radius on the transition temperatures of Kahn tear test, experiments were done using the specimens with various notch radii, 0. 1mm, 0.5 mm, lmm, 2mm and 8mm. respectively. The test results showed that the obserbed fracture transition temperatures were practically not influenced by the notch radius. However the critical crack length, i. e. the distance from the notch root to the critical point where the ductile crack changed abruptly to the brittle one, increased with the notch radius. §5. Tipper Test Series of notched bar tensile test (Tipper test) with specimens of varying notch radius, 0.05mm, 0.10mm, 0.25mm, 0.50mm and 1.00mm were performed. It was found that the transition temperatures determined by 50% of the maximum total energy absorbed, the elongation in 100mm gauge length, the 4% reduction in thickness and the difference of tensile and yielding strengths fell as the notch root radius increased, but the one defined by the 50% shear fracture was practically not affected by notch radius. §6. Van der Veen Test The test result s on mild and high tensile steels, 20mm thick, proved that the transition temperatures TE at which the depth of shear fracture decrease to 32mm, and T_I when the deflection at maximum load becomes 6mm were correlated well to T_<rs> and T_<r15> respectively determined by the standard V-Charpy test. §7. Double Blow Impact Test Series of double blow impact test were performed on V-notch Charpy specimens to divide the total energy absorbed (W_c) into two parts, the one for crack initiation (W_i) and the other for crack propagation (W_p), after examining the W_i and W_p～temperature curves, it was found that the notch contour strongly altered the shape of W_i curve, but, practically not the shape of W_p curve. Also the charateristics of transition temperatures determined by various criteria were made clear. T_<r15> is the typical ductility transition temperature, and is closely associated to the ^-^temperature curve. T_<rE> is of the intermediate nature of ductility and fracture transition temperature, and correlates wel ...