连铸球墨铸铁扭转缺口强度的研究

研究了一种用水平连铸技术生产的球墨铸铁型材的扭转强度和缺口扭转强度。实验发现光滑扭转试样是沿４５°方向开裂，开裂面是最大拉应力面，表现为典型的脆性断裂。缺口试样的断裂模式分两种情况：当为钝缺口时（即（ρ≥０．７５ｍｍ，Ｋｔ≤１．６），其断裂特征与光滑试件相同；而当为尖锐缺口时（即ρ＜０．３７５ｍｍ，Ｋｔ＞２．１）的开裂出现在缺口根部，并且开裂面垂直于轴线方向，是剪应力作用。实验结果还表现出扭转缺口强度与应力集中系数的关系，即应力集中系数越大，扭转缺口强度反而越高。该球墨铸铁的缺口敏感性（ＮＳＲ）大于１，故缺口完全不敏感。

Notch Strength of Spheroidal Graphite Cast Iron under Torsion Loading

The torsional strength of the notch of spheroidal graphite (SG) cast iron by continuous casting was tested. The fracture of the smooth specimens of SG iron is a typical brittle fractured characteristics, the angle between the fractured section and the axis of specimen is about 45°. The fracture sections of the notched specimens have two types :when the radii of specimens;when the radii of notched root are less than 0.375mm(K t>2.1),the fracture is restrained in the notched minimum section, and the fractured section is nearly perpendicular to the axis of specimen. The mean value of the torsional strength of the notch of SG cast iron increases with increasing value of the shear concentration factor(Kt). Notch sensitivity rate(NSR)is morn than 1,so SG cast iron is not complete notch sensitivity.