问题 问答题 简答题

何谓调质钢?为什么调质钢的含碳量均为中碳?合金调质钢中常含哪些合金元素?它们在调质钢中起什么作用?

答案

参考答案:

通常把经调质处理后才使用的钢称为调质钢。从碳含量上看,低碳钢在淬火及低温回火状态虽具有良好的综合机械性能,但它的疲劳极限低于中碳钢,淬透性也不如中碳钢。高碳钢虽然强度高,但它的韧性及塑性很低。因此,调质钢的含碳量均为中碳。

合金调质钢中常含合金元素有铬、锰、镍、硅、钼、钨、钒、铝、钛等。合金调质钢的主加元素有铬、锰、镍、硅等,以增加淬透性。它们在钢中除增加淬透性外,还能强化铁素体,起固溶强化作用。辅加元素有钼、钨、钒、铝、钛等。钼、钨的主要作用是防止或减轻第二类回火脆性,并增加回火稳定性;钒、钛的作用是细化晶粒;加铝能加速渗氮过程。

单项选择题
阅读理解

     Parents have to do much less for their children today than they used to do, and home has become

much less of a workshop. Clothes can be bought ready made, washing can go to the laundry, food can

be bought cooked, canned or preserved, bread is baked and delivered by the baker, milk arrives on

the doorstep, meats can be had at the restaurant, the work's canteen, and the school dining-room.

     It is unusual now for father to pursue his trade or other employment at home, and his children rarely,

if ever, see him at his place of work. Boys are therefore seldom trained to follow their father's

occupation, and in many towns they have a fairly wide choice of employment and so do girls. The young

wage-earner often earns good money, and soon acquires a feeling of economic independence. In textile

areas it has long been customary for mothers to go out to work, but this practice has become so

widespread that the working mother is now a not unusual factor in a child's home life, the number of

married women in employment having more than doubled in the last twenty-five years. With mother earning and his older children drawing substantial wages father is seldom the dominant figure that he still was at the beginning of the century. When mother works,economic advantages accrue, but children lose something of great value if mother's employment prevents her from being home to greet them when they return from

schoo1. 

1. The writer mentions home as workshop because            .

A. fathers often pursue employment at home

B. parents had to make food and necessity themselves for their daily-life

C. many families produce goods at home for sale

D. both fathers and mothers in most families are workers

2. The word "accrue" in the sentence "When mother accrue," is  closest in meaning to           .

A. change    

B. dwindle    

C. double

D. increase

3. The chief reason that boys are seldom trained to follow their father's occupation is _______.

A. that children nowadays rarely see their fathers at their place of work

B. that fathers do not like to pursue employment at home any more

C. that there is a wide choice of employment for children

D. that children also like to have jobs outside