A number of rotating blades in a diffuser at a sugar beet processing plant fabricated from rectangular bars cut from rolled carbon-manganese steel plate fractured brittlely. However, apparently identical blades underwent significant plastic deformation without fracture. Inspection of both fractured and bent blades revealed similar preexisting cracks at the toes of bar attachment welds. Metallographic examination of the bent and the fractured bars revealed they had been cut parallel and transverse, respectively, to the rolling direction of the steel plate. Due to the combined effects of the low fracture toughness of the plate on planes parallel in the rolling direction, the presence of the preexisting cracks, and the relatively large section thickness of the bars, the bars whose lengths were transverse to the rolling direction fractured brittlely when subjected to impact loads. Had the poor transverse properties of thick-section plate been recognized, and all the bars properly cut with respect to the rolling direction, the premature fractures would not have occurred.

A special eyebolt was used to lift prefabricated concrete panels weighing approximately 16 cwt. Two eyebolts were used with a spreader bar to give a vertical lift on each eyebolt. Following failure of one eyebolt, which resulted in dropping of the load and subsequent failure of the other one, a complete eyebolt was submitted for assessment. Microscopic examination indicated a medium carbon-manganese steel had been used for the lower screwed portion of the eyebolt. Failure may have been due to brittle fracture or to fatigue, both of which could have been initiated at cracks in the hardened material in the region of the weld securing the screwed portion to the intermediate collar and which may have formed at the time of manufacture. Out-of-squareness of the thread with the collar, as was seen in the example submitted, gave rise to bending stresses when the bolt was tightened down, and this could have been a further factor which promoted failure. It was suggested that the design and construction could be improved by either making the component in one piece or, if it was desired, to adapt a standard eyebolt.

The source of cracking in the circumferential weld seam in a JIS-SM50B carbon-manganese steel pipe used in a CO2 absorber was investigated, the absorber had been in service for 18 years. The seam had been weld-repaired twice, and the repair welds had been locally stress relieved. Longitudinal seams in the same vessel, which had been stress relieved in a furnace, showed no tendency toward cracking. The solution passing through the vessel contained CO2-CO-H20, KHCO, and Cl− ions. Nondestructive testing revealed that the cracks originated in the heat-affected zone and propagated into the base metal and weld. Severe branching of the cracks characteristic of stress-corrosion cracking was observed. Microexamination revealed that crack propagation was transgranular further supporting the possibility of stress-corrosion cracking. Simulation tests carried out in the vessel confirmed this mode of cracking. It was recommended that weld seams be furnace heat treated at a temperature of 600 to 640 deg C (1110 to 1180 deg F) for a minimum of 1 h per inch of section thickness.

Failure of carbon-manganese steel wheel studs caused by improper tightening of the inner wheel nuts resulted in separation of a dual wheel assembly on a heavy truck. The benchmark pattern observed on the fracture surfaces of the studs evidenced fatigue cracks emanating from multiple origins around the circumference. There was no indication that any microstructural characteristics of the material contributed to the failure. Inclusions that were present were small and relatively few in number. Failure to check the torque of the inner wheel nuts as per the manufacturer's recommendation caused the inner wheel nuts to loosen during break-in and lose the required clamping force. The development and promotion of educational programs on proper wheel tightening procedures was recommended.

Several case-hardened and zinc-plated carbon-manganese steel wheel studs fractured in a brittle manner after very limited service life. The fracture surfaces of both front and rear studs showed no sign of fatigue beach marks or deformation in the form of shear lips that would indicate either a fatigue mechanism or ductile overload failure. SEM analysis revealed that the mode of fracture was intergranular decohesion, which indicates an environmental influence in the fracture mechanism. The primary fracture initiated at a thread root and propagated by environmentally-assisted slow crack growth until final fracture. The natural stress concentration at the thread root, when tightened to the required clamp load concomitant with the presence of cracks in the carburized case, was sufficient to exceed the critical stress intensity for hydrogen-assisted stress cracking (HASC). The zinc plating exacerbated the situation by providing a strong local corrosion cell in the form of a sacrificial anode region adjacent to the cracked thread. The enhanced generation of hydrogen in a corrosive environment subsequently lead to HASC of the wheel studs.

During a refit of a twenty-year-old Naval destroyer, two cracks were found on the inside of the killed carbon-manganese steel hull plate at the forward end of the boiler room. The cracks coincided with the location of the top and bottom plates of the bilge keel. Metallurgical examination of sections cut from the cracked area identified lamellar tearing as the principle cause of the cracking. This was surprising in 6 mm thick hull plates. Corrosion fatigue and general corrosion also contributed to hull plate perforation. Although it is probable that more lamellar tears exist near the bilge keel in other ships and may be a nuisance in the future, the hull integrity of the ships is not threatened and major repairs are not needed.

A metallurgical failure analysis was performed on pieces of the cracked vent header pipe from the Edwin I. Hatch Unit 2 Nuclear power plant. The analysis consisted of optical microscopy, chemical analysis, mechanical Charpy impact testing, and fractography. It was found that the material of the vent header met the mechanical and chemical properties of ASTM A516 Grade 70 carbon-manganese steel material and microstructures were consistent with this material. Fracture faces of the cracked pipe were predominantly brittle in appearance with no evidence of fatigue contribution. The NDTT (Nil ductility Transition Temperature) for this material was approximately -51 deg C (-60 deg F). The fact that the material's NDTT was significantly out of the normal operating range of the pipe suggested an impingement of low temperature nitrogen (caused by a faulty torus inerting system) induced a thermal shock in the pipe which, when cooled below its NDTT, cracked in a brittle manner.

Erosion of solid surfaces can be brought about solely by liquids in two ways: from damage induced by formation and subsequent collapse of voids or cavities within the liquid, and from high-velocity impacts between a solid surface and liquid droplets. The former process is called cavitation erosion and the latter is liquid-droplet erosion. This article emphasizes on manifestations of damage and ways to minimize or repair these types of liquid impact damage, with illustrations.

Results of failure analyses of two aircraft crankshafts are described. These crankshafts were forged from AMS 6414 (similar composition to AISI 4340) vacuum arc remelted steels with sulfur contents of 0.003% (low sulfur) and 0.0005% (ultra-low sulfur). A grain boundary sulfide precipitate was caused by overheat of the low sulfur steel, and an incipient melting of grain boundary junctions was caused by overheat of the ultra-low sulfur steel. The precipitates and incipient melting in these two failed crankshafts were observed during the examination. As expected, impact fractures from the low sulfur steel crankshaft contained planar dimpled facets along separated grain boundaries with a small spherical manganese sulfide precipitates within each dimple. In contrast, planar dimpled facets along separated grain boundaries of impact fractures from the ultra-low sulfur crankshaft steel contained a majority of small spherical particles consisting of nitrogen, boron, iron, carbon, and a small amount of oxygen. Some other dimples contained manganese sulfide precipitates. Fatigue samples machined from the ultra-low sulfur steel crankshaft failed internally at planar grain boundary facets. Some of the facets were covered with nitrogen, boron, iron, and carbon film, while other facets were relatively free of such coverage. Results of experimental forging studies defined the times and temperatures required to produce incipient melting overheat and facets at grain boundary junctions of ultra-low sulfur AMS 6414 steels.

A number of failures involving carbon and alloy steels were analyzed to assess the effects of inclusions and their influence on mechanical properties. Inclusions, including brittle oxides and more ductile manganese sulfides (MnS), affect fatigue endurance limit, fatigue crack propagation rates, fracture toughness, notch toughness, and transverse tensile properties, and do so in an anisotropic manner with respect to rolling direction. Significant property anisotropy has been documented in the failures investigated, providing evidence that designers failed to account for it. Typical fracture morphologies observed in such cases and metallographic appearances of MnS-containing materials are illustrated.

A steel socket pipe conduit NW 150 cracked open during pressure testing next to the weld seam almost along the entire circumference. The crack occurred in part in the penetration notch and in part immediately adjacent to it. While the uncracked pipe showed the light etch shading of a low-carbon steel in which the zone heated during welding was delineated only slightly next to the seam, the other pipe was etched much darker, i.e., higher in carbon, and the heated zone appeared to stand out darkly against the basic material. The overlapping weld was defect-free and dense. The uncracked pipe consisted of soft steel that obviously was made for this purpose, while the cracked pipe consisted of a strongly-hardenable steel which contained not only more carbon and manganese than customary but also a considerable amount of chromium. Therefore, the damage was caused by a mix-up of materials that allowed an unsuitable steel to be used for the weldment.

A 230 mm (9 in.) thick casing, fabricated from ASTM 235-55 low-carbon steel, of a 450 Mg (500 ton) extrusion press failed after 27 years of service. Initial visual examination revealed an area that exhibited multiple origins and classic beach marks radiating out approximately 75 mm (3 in.) from the origin along the wall of a hydraulic-oil bleed hole. Investigation with a SEM showed corrosion pits along the bleed hole wall, but oxidation and corrosion prevented review of microfractographic details. Vacuum epoxy encapsulation, sectioning of the bleed hole, and metallographic examination revealed a basic microstructure of pearlite and ferrite with bands of slightly finer pearlite, with a large concentration of inclusion stringers in the area of the fracture origin. Further investigation using an energy-dispersive x-ray analyzer showed high concentrations of sulfur and manganese. Thus, the failure appeared to have resulted from corrosion-assisted fatigue, and the inclusion concentration in the fracture-initiated area indicated that the chemical-composition limits for sulfur and manganese would have greatly exceeded material specifications. A higher quality steel was recommended for the replacement unit to lessen the possibility of such gross inclusion segregation and to improve the fracture toughness of the cylinder.

On 15 March 2000, a National Railroad Passenger Corporation (Amtrak) train traveling from Chicago to Los Angeles derailed in Carbondale, KS. After the initial on-scene investigation, 12 pieces of rail were sent to the materials laboratory for examination. Ten of them were from the point of derailment (POD). A vertical crack was observed in the head of the rail (vertical split head). The crack was at least 233 in. (591 cm) long, continuing through the entire lengths of most pieces recovered from the POD. The vertical fracture surface had features consistent with overstress fracture with short-term exposure to an oxygen-rich environment. Fracture features emanated from longitudinally-aligned inclusions rich in aluminum.

In 1979, during a routine bridge inspection, a fatigue crack was discovered in the top flange plate of one tie girder in a tied arch bridge crossing the Mississippi River. Metallographic analysis indicated a banding or segregation problem in the middle of the plate, where the carbon content was twice what it should have been. Based on this and results of ultrasonic testing, which revealed that the banding occurred in 24-ft lengths, it was decided to close the bridge and replace the defective steel. The steel used in the construction of this bridge was specified as ASTM A441, commonly used in structural applications. Testing showed an increase in hardness and weight percent carbon and manganese in the banded region. Further testing revealed that the area containing the segregation and coarse grain structure had a lower than expected toughness and a transition temperature 90 deg F higher than specified by the ASTM standards. The fatigue crack growth rate through this area was much faster than expected. All of these property changes resulted from increased carbon levels, higher yield strength, and larger than normal grain size.

A riveted 0.25% carbon steel oil-storage tank in Oklahoma was dismantled and reassembled in Minnesota by welding to form a storage tank for soybean oil. An opening was cut in the side of the tank to admit a front-end loader. A frame of heavy angle iron was welded to the tank and drilled for bolting on a heavy steel plate. The tank was filled to a record height. In mid-Jan the temperature dropped to -31 deg C (-23 deg F), with high winds. The tank split open and collapsed. The welding used the shielded metal arc process with E6010 electrodes, which could lead to weld porosity, hydrogen embrittlement, or both. At subzero temperatures, the steel was below its ductile-to-brittle transition temperature. These circumstances suggest a brittle condition. Steps to avoid this type of failure: For cold conditions, the steel plate should have a low carbon content and a high manganese-to-sulfur ratio and be in a normalized condition, low-hydrogen electrodes and welding practices should be used, all corners should be generously radiused, the welds should be inspected and ground or dressed to minimize stress concentrations, postweld heating is advisable, and radiographic and penetrant inspection tests should be performed.