问题
问答题 简答题
什么叫回火？为什么要回火？
答案
参考答案：
将淬火后的钢件加热到Ac1以下的任意温度，保温一段时间后冷却的操作称回火。
淬火组织很不稳定，具有较大的内应力和高硬度、高脆性，不能满足所要求综合机械性能。为了消除内应力或得到所需要的组织和性能，必须进行回火处理。
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什么叫回火？为什么要回火？
参考答案：
将淬火后的钢件加热到Ac1以下的任意温度，保温一段时间后冷却的操作称回火。
淬火组织很不稳定，具有较大的内应力和高硬度、高脆性，不能满足所要求综合机械性能。为了消除内应力或得到所需要的组织和性能，必须进行回火处理。
| Martin Luther King, Jr., is well known for his work in civil rights and for his many famous speeches, among them his moving "I Have A Dream" speech. But fewer people know much about King’s childhood. M. L., as he was called, was born in 1929 in Atlanta, Georgia, at the home of his maternal grandfather. M.L.’s grandfather, the Reverend A. D. Williams, purchased their home on Auburn Avenue in 1909, 20 years before M. L. was born. The Reverend Williams, an eloquent speaker, played an important role in the community since so many people’s lives centered around the church. He allowed his church and his home to be used as a meeting place for a number of organizations dedicated to the education and social advancement of blacks. M.L. grew up in this atmosphere, with his home being used as a community gathering place, and was no doubt influenced by it. M. L.’s childhood was not especially eventful. His father was a minister and his mother was a musician. He was the second of three children, and he attended all-black schools in a black neighborhood. The neighborhood was not poor, however. Auburn Avenue was the main artery through a prosperous neighborhood that had come to symbolize achievement for Atlanta’s black people. It was an area of banks, insurance companies, builders, jewelers, tailors, doctors, lawyers and other black-owned or black-operated businesses and services. Even in the face of Atlanta’s segregation, the district thrived. Dr. King never forgot the community spirit he had known as a child, nor did he forget the racial prejudice that was a seemingly insurmountable barrier that kept black Atlantans from mingling with whites. |
According to the author, King was influenced by ______.
A．community spirit
B．black lawyers
C．his mother
D．his speeches