Fig. 24 Network of microcracks(arrows) on the outside diameter surface of the sleeve (lower portion of the micrograph) Fig. 25 Microstructure of cross section through outside diameter surface of sleeve adjacent to fracture. Fracture surface is along top of micrograph. Outside diameter surface is along right side of the micrograph Note slip banding(arrows) emanating from microcrack, 116x analysis revealed that during the hydroforming process, heavy biaxial strains were imparted to the sleeve wall, in the s between the bulb and cylindrical portions of the sleeve. When combined with the heavy strains inherently present in the full-hard 300 series stainless steel, the hydroforming strains in the radius caused the microcracking. The ductile sulting in fatigue cracks initiating and propagating from these flaws through the wall, causing the leak Service stresses, shear areas observed at the origins(see Fig. 23 )are microcracks that served to intensify the cyclic service stresses The physical root cause for this failure is a manufacturing process that omitted an intermediate stress relief or annealing treatment prior to hydroforming to the final shape Some time later, a similar complaint was received at the factory for a nonstart condition in cold weather. The sleeve was again identified to be leaking due to a through-wall crack. Analysis of the broken-open crack(Fig. 26) revealed fatigue cracks initiated on the inside diameter (ID)of the sleeve. This time, the flaw that led to the failure was shallow (approximately 0.005 mm, or 0.0002 in ) intergranular attack on the Id surfaces due to overly aggressive acid cleaning insufficient rinsing after the acid-cleaning operation. Examination of the OD surfaces revealed no microcracking or evidence of localized strain. Thus a second manufacturing defect affecting the same component was identified through failure analysis to have caused the identical complaint from the field Thefileisdownloadedfromwww.bzfxw.comFig. 24 Network of microcracks (arrows) on the outside diameter surface of the sleeve (lower portion of the micrograph). Fig. 25 Microstructure of cross section through outside diameter surface of sleeve adjacent to fracture. Fracture surface is along top of micrograph. Outside diameter surface is along right side of the micrograph. Note slip banding (arrows) emanating from microcrack. 116× The analysis revealed that during the hydroforming process, heavy biaxial strains were imparted to the sleeve wall, in the radius between the bulb and cylindrical portions of the sleeve. When combined with the heavy strains inherently present in the full-hard 300 series stainless steel, the hydroforming strains in the radius caused the microcracking. The ductile shear areas observed at the origins (see Fig. 23) are microcracks that served to intensify the cyclic service stresses, resulting in fatigue cracks initiating and propagating from these flaws through the wall, causing the leak. The physical root cause for this failure is a manufacturing process that omitted an intermediate stress relief or annealing treatment prior to hydroforming to the final shape. Some time later, a similar complaint was received at the factory for a nonstart condition in cold weather. The sleeve was again identified to be leaking due to a through-wall crack. Analysis of the broken-open crack (Fig. 26) revealed fatigue cracks initiated on the inside diameter (ID) of the sleeve. This time, the flaw that led to the failure was shallow (approximately 0.005 mm, or 0.0002 in.) intergranular attack on the ID surfaces due to overly aggressive acid cleaning or insufficient rinsing after the acid-cleaning operation. Examination of the OD surfaces revealed no microcracking or evidence of localized strain. Thus a second manufacturing defect affecting the same component was identified through failure analysis to have caused the identical complaint from the field. The file is downloaded from www.bzfxw.com