Tham khảo tài liệu 'friction and lubrication in mechanical design episode 2 part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 530 Chapter 13 Table Hardness Data for the Test Specimens Material Hardness BHN 1020 untreated 1020 treated 170-180 4340 low hardness untreated 4340 low hardness treated 285-311 4340 high hardness untreated 4340 high hardness treated 363-375 4350 low hardness untreated 4350 low hardness treated 321-331 4350 high hardness untreated 4350 high hardness treated 375-388 Similar tests were also performed on 1020 steep specimens for comparison. The chemical composition of the 4340 and 4350 steel used in the test is given in Table . Sample results of the unidirectional bending fatigue test data for the different materials with and without the 40 thermal cycles are given in Figs . It can be seen in Fig. that the high-hardness 4350 steel had an endurance limit of approximately 108 ksi as would be expected from the published data on the material. The 40 thermal cycles in this case caused a reduction of approximately 45 in the value of the endurance limit. Figure shows similar results for the low-hardness 4350 steel specimens where the same thermal cycles caused a 42 reduction in the endurance limit. Similar results for the 4340 steel are given in Figs and where the reduction in the endurance limit is found to be approximately 20 . It is interesting to note from the fatigue data for the 1020 steel specimens that the endurance limit was reduced by only 12 to a value of 55 ksi. This value is the mean value of the endurance limits under the same condi- Table Chemical Properties of 4340 and 4350 Steel Steel c Mn p s Si Cr Ni Mo 4340 4350 Figure Fatigue data for 4350 steel high hardness o without thermal cycles with thermal cycles. Figure Fatigue data for 4350 steel low hardness o without thermal cycles with thermal cycles. 531 Figure Fatigue data for 4340 steel high hardness o without thermal cycles with thermal cycles. Figure
