ig. 6 Fracture surface of a carburized and hardened steel roller. As a result of banded alloy segregation circumferential fatigue fracture initiated at a subsurface origin near the case -core interface (arrow) Excessive segregation also can have an adverse effect on subsequent fabrication and heat treatment. In heat treatable alloys, variations in composition can produce unexpected responses to heat treatments, which result hard or soft spots, quench cracks, or other flaws. Excessive segregation that leads to significant variations hardness can lead to premature failure and extreme difficulties during cold working or forming. In this case one of the simplest and most effective tests for incoming material is a simple standard upset test. The details of such a test can be worked out between the supplier and the cold forger The methods to reveal the presence of segregation may depend on the alloy and expected impurities Macroetching is commonly used, and the American Society for Testing and Materials(AsTM) has established a graded series(ASTM E 381) of macroetching for center segregation in steel product. Segregations are revealed by differences in the severity of the etchant attack; segregations at the center may appear as a pipe or may be grouped in some fairly regular form about the center, depending on the shape of the ingot and the mechanical work done on it. Segregation as revealed by macroetching does not al ways indicate defective metal A polished specimen should also be examined under the microscope to determine whether the revealed segregation is metallic or a concentration of nonmetallic impurities Sulfur Print Test. The microscopic identification of segregation may be supplemented by chemical or other means of testing. For regions with expected regions of sulfide sulfur-rich segregation, the sulfur print test(Ref 3)can be used. An example of a failure of a steel I-beam with high levels of carbon, sulfur, and phosphorus segregation in the middle of the section is given in Ref 4. The beam was lying flat on the ground near the seacoast under normal weather conditions. It was flame cut into two sections, as required for construction, and approximately -h after cutting, a violent sound was heard. The shorter section of the cut beam had split catastrophically into two portions along the entire length and approximately through the middle of the web Various samples were taken from both the broken and unbroken sections of the beam for analysis(chemistry metallography, macroetching, impact testing, tensile testing) and sulfur printing. Sulfur prints taken at various locations indicated segregation of sulfides within a central zone approximately 2 mm(0.08 in ) wide in the thickness direction of the web that extended throughout the length of the beam. The breadth of the segregation zone varied from 60 mm(2.4 in. ) at the end face of the unfractured section of the I-beam to almost the total idth of the web in most of the fractured section. Sulfide segregation was not found in the flanges of the beam Failures similar to the one investigated have occasionally occurred in structural beams in the shop under no load, and a contributing factor was the presence of residual stresses in the material. Flame cutting caused a quality of the beam, resulted in failure. The failure of the I-beam was probably caused by segregation of carban change in the distribution of the residual stresses, which, aided by low fracture toughness due to the po sulfur, and phosphorus within its web section, which resulted in decreased notch sensitivity and low fracture toughness with respect to crack propagation through the web. The detailed investigation(Ref 4) revealed segregation of high levels of carbon, sulfur, and phosphorus in the middle of the web and high residual stresses attributed to rolling during fabrication Thefileisdownloadedfromwww.bzfxw.comFig. 6 Fracture surface of a carburized and hardened steel roller. As a result of banded alloy segregation, circumferential fatigue fracture initiated at a subsurface origin near the case-core interface (arrow). Excessive segregation also can have an adverse effect on subsequent fabrication and heat treatment. In heat treatable alloys, variations in composition can produce unexpected responses to heat treatments, which result in hard or soft spots, quench cracks, or other flaws. Excessive segregation that leads to significant variations in hardness can lead to premature failure and extreme difficulties during cold working or forming. In this case, one of the simplest and most effective tests for incoming material is a simple standard upset test. The details of such a test can be worked out between the supplier and the cold forger. The methods to reveal the presence of segregation may depend on the alloy and expected impurities. Macroetching is commonly used, and the American Society for Testing and Materials (ASTM) has established a graded series (ASTM E 381) of macroetchings for center segregation in steel product. Segregations are revealed by differences in the severity of the etchant attack; segregations at the center may appear as a pipe or may be grouped in some fairly regular form about the center, depending on the shape of the ingot and the mechanical work done on it. Segregation as revealed by macroetching does not always indicate defective metal. A polished specimen should also be examined under the microscope to determine whether the revealed segregation is metallic or a concentration of nonmetallic impurities. Sulfur Print Test. The microscopic identification of segregation may be supplemented by chemical or other means of testing. For regions with expected regions of sulfide sulfur-rich segregation, the sulfur print test (Ref 3) can be used. An example of a failure of a steel I-beam with high levels of carbon, sulfur, and phosphorus segregation in the middle of the section is given in Ref 4. The beam was lying flat on the ground near the seacoast under normal weather conditions. It was flame cut into two sections, as required for construction, and approximately 1 2 h after cutting, a violent sound was heard. The shorter section of the cut beam had split catastrophically into two portions along the entire length and approximately through the middle of the web. Various samples were taken from both the broken and unbroken sections of the beam for analysis (chemistry, metallography, macroetching, impact testing, tensile testing) and sulfur printing. Sulfur prints taken at various locations indicated segregation of sulfides within a central zone approximately 2 mm (0.08 in.) wide in the thickness direction of the web that extended throughout the length of the beam. The breadth of the segregation zone varied from 60 mm (2.4 in.) at the end face of the unfractured section of the I-beam to almost the total width of the web in most of the fractured section. Sulfide segregation was not found in the flanges of the beam. Failures similar to the one investigated have occasionally occurred in structural beams in the shop under no load, and a contributing factor was the presence of residual stresses in the material. Flame cutting caused a change in the distribution of the residual stresses, which, aided by low fracture toughness due to the poor quality of the beam, resulted in failure. The failure of the I-beam was probably caused by segregation of carbon, sulfur, and phosphorus within its web section, which resulted in decreased notch sensitivity and low fracture toughness with respect to crack propagation through the web. The detailed investigation (Ref 4) revealed segregation of high levels of carbon, sulfur, and phosphorus in the middle of the web and high residual stresses attributed to rolling during fabrication. The file is downloaded from www.bzfxw.com