No abstract

A comprehensive fatigue program was undertaken at room temperature and −45°C (−50°F) for five representative carbon or low alloy cast steels. Constant amplitude low and high cycle axial fatigue behavior, cyclic stress-strain behavior, constant-amplitude fatigue-crack-growth behavior and variable-amplitude fatigue-crack-initiation and -growth behavior were determined. The fatigue resistance at low temperature was usually equal to or better than at room temperature except for one material under variable amplitude fatigue crack growth conditions. SEM analysis revealed similar fatigue crack growth mechanisms at both room and low temperature, even though some tests were well below the NDT temperature. Most fatigue resistance for the five cast steels was consistent with that for wrought steels. Fatigue test procedures generally developed with wrought steels were completely satisfactory for these cast steels.

Five common carbon or low-alloy cast steels—SAE 0030, SAE 0050A, C-Mn, Mn-Mo and AISI 8630—were subjected to constant-amplitude fatigue tests at room temperature and at the common low climatic temperature of −45°C (−50°F). Tests included smooth specimen axial low and high cycle fatigue and compact type (CT) specimen crack growth behavior from 10−5 n/cycle (4 × 10−4 in./cycle) to threshold values at 10−10 m/cycle (4 × 10−9 in./cycle). Three of the five steels had nil ductility transition temperatures above the low test temperature. Despite this, all five cast steels showed equivalent or better fatigue resistance at the low temperature, except for some very short life low-cycle fatigue tests and for some very high fatigue crack growth rates where fracture was imminent. Scanning electron fractographic analysis indicated that ductile type fatigue crack growth mechanisms with or without striations occurred for all steels at both test temperatures except for a few interdispersed cleavage facets in 0050A steel at very high crack growth rates. At the low temperature, monotonic and cyclic stress-strain properties Su, Sy, and Sy' increased by an average of about 10%, fatigue limits increased from 2 to 25%, and ΔKth increased from 0 to 90%. No consistent correlations existed between fatigue and monotonic properties at either temperature. Mean stress effects at near ΔKth levels appeared to be influenced by crack closure.

The effects of hot rolling temperature nd alloying elements on the textures and " values of cold rolled and annealed extra low carbon steel sheets hve been investigated. The steels examined were one extra low carbon Al-killed steel and two Ti-IP (Interstitial Free) steels with or without phosphorus. (200) pole figures and relative intensities of various reflections from the rolling plane ere determined for hot bands and annealed sheets. The hot rolled textures are found, when finish-rolled at

JIc tests using the multiple specimen procedure described in ASTM standard E813 were conducted at room temperature and −45°C (−50°F) with five common carbon or low alloy cast steels, viz., 0030, 0050A, C-Mn, Mn-Mo, and 8630. Specimen thickness was 25.4 mm (1 in.). Valid JIc values were obtained with four of the cast steels at room temperature and only two of the cast steels at −45°C (−50°F). Only Jcl (Jcleavage) values were obtained with the four other tests due to unstable brittle or cleavage fracture. Valid JIc values were obtained if the test temperature was above the mid-point temperature of the Charpy V notch energy transition region as measured along the temperature axis. Conservative estimates of KIc were calculated from JIc test results and a preliminary empirical equation involving KIc and Sy at room temperature and upper shelf CVN energy was suggested for cast steels. Room temperature JIc values were higher for the three tempered martensitic cast steels than for the two ferritic-pearlitic cast steels.