Fracture toughness tests were conducted at room temperature and at – 196°C on a martensitic stainless steel that had been quenched and tempered to a hardness of Rockwell C 61-63. The fracture toughness specimens were chevron-notch, short-bar specimens for which B was 12.7 mm and W was 25.4 mm. Tests were conducted in accordance with ASTM Test Method for Plane-Strain (Chevron Notch) Fracture Toughness of Metallic Materials (E 1304-89).
Five tests were conducted at each temperature, and each test produced a valid KIv result. Test results were unusually reproducible for plane-strain fracture toughness tests; the standard deviation for room temperature tests was approximately ±5% and for -196°C tests was approximately ±2% of the mean value of KIv.
For comparison with the chevron-notch test results, three standard KIc tests were conducted on fatigue-precracked compact (tension) specimens at room temperature. The tests were conducted in accordance with ASTM Test Method for Plane-Strain Fracture Toughness of Metallic Materials (E 399). As was the case for the KIv tests, the KIc tests produced very reproducible results: the standard deviation for three tests was approximately ±2% of the mean value. However, it was found that the mean KIv values for this high-hardness steel were approximately 18% greater than the mean KIc values. That result confirms the warning included in ASTM E 1304 that KIc values may be larger than KIc values in some materials.