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螺栓是使用极其广泛的零件,一般按其自身所具备的力学性能分级,GB及ISO标准均将螺栓分为十个级别。其中的3.6、4.6、4.8级螺栓,常用A2、A3、B1～B3及10、15、20号钢制作。普碳钢螺栓质量之优劣表现为:1)必须保证相应级别螺栓的强度极限,如4.8级螺栓的σ_(bmin)>420N/mm~2;2)不允许螺栓头部与杆部或支撑面的交接处断裂。断裂后的特征见图1,习惯称之为脱头。螺栓头部系冷镦成型,典型宏观流线如图2所示,图中虚线即为断裂的惯发部位。用金相观察,该处显微组织呈纤维状,晶粒间界模糊。
Bolt is the use of a very wide range of parts, generally classified according to their own mechanical properties, GB and ISO standards will be divided into ten levels of bolts. One of the 3.6,4.6,4.8 bolts, commonly used A2, A3, B1 ~ B3 and 10,15,20 made of steel. The quality of general carbon steel bolt performance as follows: 1) The corresponding level of bolt strength limit must be guaranteed, such as the 4.8 bolt σ bmin> 420N / mm ~ 2; 2) does not allow the bolt head and the shaft or support The junction of the face is broken. The characteristics of the fracture shown in Figure 1, used to call it off. Bolt head cold heading, the typical macro-streamline shown in Figure 2, the dotted line is broken habitus. Metallographic observation, where the microstructure was fibrous, fuzzy grain boundaries.