问题 问答题 简答题

指出下列组织的主要区别:⑴索氏体与回火索氏体;⑵屈氏体与回火屈氏体;⑶马氏体与回火马氏体。

答案

参考答案:

由奥氏体冷却转变而成的屈氏体(淬火屈氏体)和索氏体(淬火索氏体)组织,与由马氏体分解所得到的回火屈氏体和回火索氏体组织有很大的区别,主要是碳化物的形态不同。由奥氏体直接分解的屈氏体及索氏体中的碳化物是片状的,而由马氏体分解的回火屈氏体与回火索氏体中碳化物是颗粒状的。回火索氏体和回火屈氏体相对于索氏体与屈氏体其塑性和韧性较好。马氏体(M)是由A直接转变成碳在α—Fe中过饱和固溶体。回火马氏体是过饱和的α固溶体(铁素体)和与其晶格相联系的ε碳化物所组成,其淬火内应力和脆性得到降低。

填空题

在短文的空格内填入适当的词,使其内容通顺,每空格限填一词,首字母已给。

     Reading books is a good hobby for all kinds of reasons.

     First, reading books is f   1   . You can always keep yourself amused if you like reading. This is especially

useful when the weather is bad. It is a relaxing hobby too. You can really become lost in a book.

     Next, you can read a book a  2   : in a car, in a waiting-room, on a plane, in bed - even in the bath. All you

need is a book! Reading is a convenient hobby as it is easy to stop and then start again.

      A  3    good reason for reading books is that it is useful. If you read as a hobby you will get better and

better at it. This m   4    that you will read faster and will become better at understanding what you read. As

your reading improves, you will probably find your schoolwork becomes much e   5   . Many school subjects

depend on good reading and, as you read, you learn more and more.

     Some people say that reading is out of date. This is not true. You have to be able to read to use a computer

and, the better you read, the better your computer skills will be. Reading is n   6    out of date!

      Good readers are most likely to be good writers, too. They are usually good at spelling as well, and have

more things to write about. Reading books is a wonderful hobby, one of the best.W   7    other hobby could

be more useful, or more enjoyable?

1._____ 2._____ 3._____ 4._____ 5._____ 6._____ 7._____

填空题