指出下列零件的锻造毛坯进行正火的主要目的及正火后的显微组织：
（1）20钢齿轮（2）45钢小轴（3）T12钢锉刀
参考答案：
（1）目的：细化晶粒，均匀组织，消除内应力，提高硬度，改善切削加工性。组织：晶粒均匀细小的大量铁素体和少量索氏体。
（2）目的：细化晶粒，均匀组织，消除内应力。组织：晶粒均匀细小的铁
素体和索氏体。
（3）目的：细化晶粒，均匀组织，消除网状Fe3CⅡ，为球化退火做组织准备，消除内应力。组织：索氏体和球状渗碳体。
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| Dick was a sailor (海员) on a big ship. He went to Japan and Australia, 1 Dick was often on the ship for several months at a time. When he woke up in the morning and 2 out,he only saw the sea, or sometimes a port (海港). When he was 23, Dick got married and bought a small house 3 a garden 4 his wife's town. It was far away from the sea. Then he had to go back to his 5 , and he was away from his home for 2 months. Then h  e went from the port to the 6 by bus,and was very happyto see his wife 7 . The next morning he 8 until nine o'clock. Then he woke up suddenly and looked out of the window. There were trees a few metres 9 . He was very surprised and jumped out of bed, shouting, "We've 10 land." | ||||
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