焊接专业英语1

The welders must be familiar with how to heat treat metals．Heat treatment is a method by which the physical properties of a metal can be changed．There are three main operations in the heat treatment of steel：hardening，tempering，and annealing．

The hardening operation consists of heating the steel above its critical range and then quenching it，that is，rapidly cooling it in a suitable medium such as water，brine，oil，or some other liquid. Having been hardened，the metal must be given a tempering treatment which consists of reheating the hardened steel to a temperature below the critical range，thus producing the required physical properties．Tempering is also called drawing the temper，because this operation gives a steel object the temper being required．

The critical points or critical temperatures are the temperatures at which a certain change takes place in the physical condition of the steel．These points are very important because，in order to properly harden a piece of steel，it must be heated to a temperature above the upper critical point．Having known the critical points for certain steel，we can easily control the heat in the furnace．Gas，oil，and electric furnaces are the most commonly used for heat treating metal．Annealing is the uniform heating of a metal above usual hardening temperatures followed by very slow cooling．Annealing may be carried out either to soften a piece that is too hard to machine or to remachine a piece having been hardened．Annealing also relieves internal stresses produced by machining．

翻译：焊工一定要熟悉金属进行热处理。热处理是一种改变金属物理性能的方法。钢的热处理主要有三种方法：淬火、回火和退火。淬火是将钢加热到临界点温度以上，然后使之淬冷，即在一种合适的介质如水、盐水、油或某些其他液体中使钢快速冷却。钢经过淬火以后，必须进行回火处理，即将淬硬的钢重新加热到临界点温度以下，从而获得所要求的物理性能。回火也叫做韧性处理，因为回火能够使钢具有所需的韧性。

临界点或临界温度就是钢的物理状态发生某种改变时的温度。这些点是很重要的，因为要把钢淬硬，就必须把钢加热到上临界点温度以上。知道了某种钢的临界点，就很容易对炉子加热温度进行控制。金属热处理最常用的炉子有气炉、油炉和电炉。

退火通常是将金属均匀加热到淬火温度以上，随后缓慢冷却。退火既可以使太硬而不能进行机加工的工件变软，又可以对已经被淬硬的工件进行重新加工。退火也可以消除由于机加工所产生的内应力。

1.用英文简要叙述MIG焊较重要的优点。

1．Since there is no flux or slag and very little spatter to remove，there is a considerable saving in total welding cost．Generally speaking，weld cleanup is often more costly than actual welding time．

2．Less time is required to train an operator

3．The welding process is faster especially when compared with metallic arc stick welding．4．Because of the high speed of the MIG process，better metallurgical benefits are imparted to the weld area．

5．Although originally TIG welding was considered more practical for welding thin sheet，because of its lower current，the development of the short circuiting transfer technique now makes it possible to weld thin stock equally as effectively with the MIG process．

6.Since MIG welding has deep penetrating characteristics，narrower beveled joint design can be used．Furthermore，the size of fillet welds is reduced by comparison to other welding methods．