一、球铁曲轴的机械性能在国外,评定球铁曲轴多以抗拉强度和抗弯疲劳强度为指标。抗拉强度的提高是通过铁素体向珠光体的转变来实现的;淬火加回火或等温淬火能使强度显著提高(达100～110公斤/毫米~2)。球铁的疲劳强度并非完全随抗拉强度的增加而增加。当抗拉强度小于70～75公斤/毫米~2时,疲劳强度是随抗拉强度的增加而增加;当抗拉强度大于70～75公斤/毫米~2时,抗拉强度的增加对疲劳强度几乎不发生影响。曲轴的实物试验也进一步证实了这一点。因为提高抗拉强度,增加了铸铁应力集中的敏感性。因此球铁曲轴的抗拉强度σ_b由45提高到79公斤/毫米~2, First, the mechanical properties of ductile iron crankshaft In foreign countries, the assessment of ductile iron crankshaft to the tensile strength and bending fatigue strength as an indicator. Tensile strength is improved by the transformation of ferrite to pearlite to achieve; quenching and tempering or isothermal quenching can significantly improve the strength (up to 100 ~ 110 kg / mm ~ 2). Ductile iron fatigue strength does not completely increase with the increase of tensile strength. When the tensile strength is less than 70 ~ 75 kg / mm ~ 2, the fatigue strength increases with the increase of tensile strength; when the tensile strength is more than 70 ~ 75 kg / mm ~ 2, the tensile strength increases with the fatigue strength Almost no effect. Crankshaft in-kind test also further confirmed this point. Because of increased tensile strength, increased sensitivity to stress concentration of cast iron. So the ductile iron crankshaft tensile strength σ_b increased from 45 to 79 kg / mm ~ 2,