Tham khảo tài liệu 'asm metals handbook - desk edition (asm_ 1998) episode 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | b Hardness of matrix measured with superficial hardness tester and converted to Rockwell C. c Although this value was obtained in the specific test cited it is not typical of gray iron of C. Ordinarily the hardness of such iron is 48 to 50 HRC. If any hardness correlation is to be attempted the type and amount of graphite must be constant in the irons being compared. Rockwell hardness tests are considered appropriate only for hardened castings camshafts for example and even hardened castings Brinell tests are preferred. Brinell tests must be used when attempting any strength correlations for unhardened castings. Fatigue Limit in Reversed Bending Because fatigue limits are expensive to determine the designer usually has incomplete information on this property. Figure 8 shows fatigue-life curves at room temperature for a gray iron under completely reversed cycles of bending stress. Each point represents the data from one specimen. Table 5 list additional data. Fig. 8 Reversed bending fatigue life at room temperature for gray iron containing C Si Mn P S Cr Ni and Cu. Open circles represent notched specimens closed circles represent unnotched specimens. Axial loading or torsional loading cycles are frequently encountered in designing parts of cast iron and in many instances these are not completely reversed loads. Types of regularly repeated stress variation can usually be expressed as a function of a mean stress and a stress range. Whenever possible the designer should use actual data from the limited information available. If precisely applicable test data are not available the reversed bending fatigue limit of machined parts may be estimated as about 35 of the minimum specified tensile strength of the particular grade of gray iron being considered. This value is probably more conservative than an average of the limited data available on the fatigue limit for gray iron. Ductile Iron Introduction DUCTILE CAST IRON also .
