1、附录一 外文翻译 原文： Heat Treatment The understanding of heat treatment is embraced by the broader study of metallurgy. Metallurgy is the physics, chemistry, and engineering related to metals from ore extraction to the final product. Heat treatment is the operation of heating and cooling a metal in its soli
2、d state to change its physical properties. According to the procedure used, steel can be hardened to resist cutting action and abrasion, or it can be softened to permit machining. With the proper heat treatment internal stresses may be removed, grain size reduced, toughness increased, or a hard surf
3、ace produced on a ductile interior. The analysis of the steel must be known because small percentages of certain elements, notably carbon, greatly affect the physical properties. Alloy steel owe their properties to the presence of one or more elements other than carbon, namely nickel, chromium, mang
4、anese, molybdenum, tungsten, silicon, vanadium, and copper. Because of their improved physical properties they are used commercially in many ways not possible with carbon steels. The following discussion applies principally to the heat treatment of ordinary commercial steels known as plain carbon st
5、eels. With this process the rate of cooling is the controlling factor, rapid cooling from above the critical range results in hard structure, whereas very slow cooling produces the opposite effect. If we focus only on the materials normally known as steels, a simplified diagram is often used. Those
6、portions of the iron-carbon diagram near the delta region and those above 2% carbon content are of little importance to the engineer and are deleted. A simplified diagram, such as the one in Fig.2.1, focuses on the eutectoid region and is quite useful in understanding the properties and processing o
7、f steel. The key transition described in this diagram is the decomposition of single-phase austenite() to the two-phase ferrite plus carbide structure as temperature drops. Control of this reaction, which arises due to the drastically different carbon solubility of austenite and ferrite, enables a w
8、ide range of properties to be achieved through heat treatment. To begin to understand these processes, consider a steel of the eutectoid composition, 0.77% carbon, being slow cooled along line x-x in Fig.2.1. At the upper temperatures, only austenite is present, the 0.77% carbon being dissolved in s
9、olid solution with the iron. When the steel cools to 727 (1341 ), several changes occur simultaneously. The iron wants to change from the FCC austenite structure to the BCC ferrite structure, but the ferrite can only contain 0.02% carbon in solid solution. The rejected carbon forms the carbon-rich c
10、ementite intermetallic with composition Fe3C. In essence, the net reaction at the eutectoid is austenite 0.77%Cferrite 0.02%C+cementite 6.67%C. Since this chemical separation of the carbon component occurs entirely in the solid state, the resulting structure is a fine mechanical mixture of ferrite a
11、nd cementite. Specimens prepared by polishing and etching in a weak solution of nitric acid and alcohol reveal the lamellar structure of alternating plates that forms on slow cooling. This structure is composed of two distinct phases, but has its own set of characteristic properties and goes by the
12、name pearlite, because of its resemblance to mother- of- pearl at low magnification. Steels having less than the eutectoid amount of carbon (less than 0.77%) are known as hypo-eutectoid steels. Consider now the transformation of such a material represented by cooling along line y-y in Fig.2.1. At hi
13、gh temperatures, the material is entirely austenite, but upon cooling enters a region where the stable phases are ferrite and austenite. Tie-line and level-law calculations show that low-carbon ferrite nucleates and grows, leaving the remaining austenite richer in carbon. At 727 (1341 ), the austenite is of eutectoid composition (0.77% carbon) and further
