问题 问答题 简答题

根据什么原则选择回火热处理规范?

答案

参考答案:

回火热处理规范包括,加热速度、加热最高温度、保温时间和冷却速度四个方面,它们的选择原则如下:

(1)加热速度:上限要避免工件整个截面加热不均匀,下限要求尽量缩短热处理时间;

(2)加热最高温度:上限低于Ac1,一般低于钢材原始回火温度,下限选钢材的最高使用温度加100--150℃。

(3)保温时间:上限要防止性能劣化,缩短热处理时间,下限降低残余应力,改善全相组织和机械性能;

(4)冷却速度:上限避免重新产生残余应力,下降要求能防止再热裂纹的产生和性能的劣化。

阅读理解

阅读下列对话,回答后面的问题。

Sam: Excuse me. Could you tell me the way to the People's Park?

Jack: I'm sorry, I am new in the city. 

Sam: Thank you all the same. Are you American?

Jack: No, I come from Canada. What about you?

Sam: I'm from America. I come here with my parents. But now I can't find them. 

Jack: Do you know where they're going?

Sam: Yes. We're going to the People's Park. 

Jack: Oh, it's about thirty minutes' walk from here. Do you have a travel map?

Sam: Yes. But I am not good at reading a map. 

Jack: Don't worry. I'll help you. I think it's easy to read a map. Look. We're standing here, in front of the

         shopping center. You'd better go along this street, take the first turning on the right, then take the

         fourth turning on your left, walk on until you see a lot of tall trees, the park is behind the trees. 

Sam: Oh, dear! I can't remember so much. 

Jack: Why not take a taxi? It can take you right there. 

Sam: A good idea! Thank you very much. 

Jack: You're welcome. 

1. Where's Jack from?

                                                                                                         

2. Who's Sam looking for?

                                                                                                         

3. Where's Sam going?

                                                                                                         

4. Who is better at reading a map, Sam or Jack? 

                                                                                                         

5. How do you think Sam is going to the park?

                                                                                                         

阅读理解

.

This is a web version of October15,2009 which Live Earth emails to members. Click here to join and receive weekly updates from Live Earth 

Live Earth is pleased to announce the largest worldwide water initiative(倡议) in history to help fight the global water crisis. The Dow Earth Run for Water-----to take place on April 18,2010----will consist of a series of 6 km run/walks ( the average distance many women and children walk every day to get water ) talking place over the course of 24 hours in countries around the world featuring concers and water education activities, raising awareness and funds to help solve the water crisis. Jessica Biel, Alexandra Cousteau, Pete Wentz, Angelique Kidijo and Jenny Fletcher will lend their time in support of this global event.

Water shortage is a major issure affecting countries, communities and families all over the wold .One in eight people don’t have access to safe,clen drinking water, Communities in Farica,

Latin America and Asia suffer 1.8 million deaths every year from diarrhea diseases and the death of 5,000 children each day due to inadequate(不足) water infrastructure (基础设施) . In these areas, women and children are forced to walk 6 km (3.7 miles ) each day to get water that is likely unsuitable for drinking .However, the water crisis not only limited to developing nations. Adding to these existing issures, the effects of climate change are increasing affecting both supply and quality of available fresh water throughout the world.

In 60﹪of European cities with population greater than 100.000, groundwater is being used faster than it can be replenished{补充}。 By 2025,two-thirds of the world’s population could be living under water__stressed conditions.

You can help solve the water crisis by participating in the April 18th even.Run/walk registration is now officially open! Sign up now at

Thanks and be sure to visit liveearth. Org for the latest water conservation tips and more on The Dow Live Earth Run!

LIVE EARTH

72.Which of the following activities will the Dow Live Earth organize on April 18,2010 ?

A.Receing the latest news from Live Earth.

B.Putting on musical performances.

C.Calling on pop stars to walk 6 km to get water.

D.Lending names and time to support the event.

73. According to the passage , which of the following statements is tue?

A. You can turn to http://live earth.org for water statements is true?

B. Jessica Biel can’t take part in event if she signs up.

C. The information on Live Earth is updated every month.

D. Every year 1.8 million people in the world die from the disease related to water.

74. Which of the following would be the best title for the passage?

A.An Introduction tohe April 18 Event

B. An Email to Live Earth

C.Global Water Crisis Is Becoming Serious

D.Live Earth Announces an Initiative to Water Crisis