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用球墨铸铁制造一些在交变载荷条件下工作的零件(曲轴、发动机活塞、气缸套等),尽管球铁铸态疲劳强度比灰铁高,但仍显不足。原因是铸态球铁的化学成份和基体组织不均匀,而且有较高的内应力。球铁的基体组织主要为铁素体和珠光体。含铁素体越多,疲劳强度越低,因为它的性能不仅决定于多余的铁素体数量,而且与铁素体的分布情况有关,铁素体越粗大,性能越低。提高球铁的疲劳强度,单靠增加它的静强度来获得良好结果是有限的。当σ_b>80公斤力/毫米~2时,球铁的疲劳强度实际上已不再增加。
With ductile iron to make some work under alternating load conditions (crankshaft, engine piston, cylinder liner, etc.), although the ductile iron as-cast fatigue strength is higher than gray iron, but still not enough. The reason is cast ductile iron chemical composition and the matrix structure is not uniform, but also has high internal stress. The matrix of ductile iron is mainly ferrite and pearlite. Ferrite containing more, the lower the fatigue strength, because its performance depends not only on the amount of excess ferrite, but also with the distribution of ferrite, the more coarse ferrite, the lower the performance. Improving ductile iron ductility is limited by increasing its static strength to obtain good results. When σ_b> 80 kgf / mm ~ 2, ductile iron fatigue strength has virtually no longer increased.