试题与答案

塑性和韧性较好,强度和硬度低,伸长率约50%的钢材,基本晶体组织为()。A、铁素体

题型:单项选择题

题目:

塑性和韧性较好,强度和硬度低,伸长率约50%的钢材,基本晶体组织为()。

A、铁素体

B、渗碳体

C、珠光体

D、固溶体

答案:

参考答案:A

解析:

[点评] 钢是以铁为主的铁碳合金,固溶体是以铁为溶剂,碳为溶质,它们二者共溶后所形成的固态溶液;常温下铁和碳所形成的固溶体称为铁素体,铁素体的塑性和韧性较好,但强度和硬度较低,伸长率约为50%;渗碳体表现为明显的硬脆特点,塑性和韧性非常低,伸长率几乎为零;珠光体介于铁素体和渗碳体之间,既有一定的强度和硬度,也有一定的塑性和韧性,伸长率约为20%。

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题型:单项选择题

Questions 61-70 are based on the following passage.


While some international couriers are showing signs of exhaustion, EMS (Express Mail Service), the generic name for the courier services of post offices, seems to be finding its stride. Known as Datapost in Britain, as Chronopost in France, and as A1-Barid al-Mumtaz in Saudi Arabia, EMS is now second in the international courier business (jointly with TNT Skypack). Last year it delivered 5.6 million items, weighing less than 20 kilograms each, across borders. That and its annual growth rate of around 5 percent have worried DHL, the market leader, enough for it to counter-attack in the Courts.
On October 26, a Dutch judge ruled against DHL on all three counts filed against the Dutch post office: that the three-initial name was too close to DHL’s; that the orange lines in the EMS logo were too similar to DHL’s dark red ones; and that the claim to the widest route system in the world was unfounded. DHL has threatened the Swiss post office with similar action, but it may reconsider after the Dutch ruling.
EMS has some advantages over the private couriers. One is a dense ready-made network of offices, especially in Europe, the avowed target area of the private couriers. Another advantage is a long tradition of working with customs authorities. In a business where minutes count, it pays to have good friends at customs. That advantage particularly irritates the private couriers because there is no legal way to combat such unquantifiable coziness.
The private courier services are also annoyed because in countries like Switzerland and Italy, where the post office is officially a monopoly, they pay it a fee. In Switzerland DHL says it pays more than SFr lm ($ 708,000) "to the competition" each year. In France the couriers have won a battle for exoneration.
Although governments are under little pressure to keep prices artificially low, EMS is often cheaper than the private couriers, but not always. A recent test in Britain (on a domestic route) showed Datapost about halfway between the least and the most expensive, but gave it full marks for speed and service.
Each national EMS is free to set its rates and follow its own rules on things like bulk discounts. The Universal Postal Union, based in Berne, determines how costs and revenues are split between sending and receiving countries, and standardizes procedures. More than 100 postal administrations have linked into the system—and more are coming, including Russia’s. That makes the feisty EMS particularly happy since its rivals have not been allowed to serve anywhere in Russia.

Which of the following is true of DHL according to the passage

A. It cooperates with TNT Skypack.
B. It is showing signs of exhaustion.
C. It might have a leading position in the international courier business.
D. It has an annual growth rate of 5%.

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