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1、外文资料翻译PLAIN CARBON STEELAny steel-making process is capable of producing a product that has 0.05% or less carbon. With this small amount of carbon, the properties approach of pure iron with maximum ductility and minimum strength. Maximum ductility is desirable from the standpoint of ease in deformat
2、ion processing and service use. Minimum strength is desirable for deformation processing. However, higher strengths than that obtainable with this low carbon are desirable from the standpoint of product design. The most practical means of increasing the strength is by the addition or retention of so
3、me carbon. However, it should be fully understood that any increase of strength over that pure iron can be obtained only at the expense of some loss of ductility, and the final choice is always a compromise of some degree. Because of the difficulty of composition control or the additional operation
4、of increasing carbon content, the cost of higher carbon, higher strength steel is greater than of low carbon.Plain Carbon Steels Most Used. Because of their low cost, the majority of steels used are plain carbon steels. These consist of iron combined with carbon concentrated in there ranges classed
5、as low carbon,medium carbon, and high carbon. With the exception of manganese used to control sulphur, other elements are present only in small enough quantities to be considered as impurities, though in some cases they may have minor effect on properties of the material.Low Carbon. Steel with appro
6、ximately 6 to 25 points of carbon (0.06%0.25%)are rated as low carbon steels and are rarely hardened by heat treatment because the low carbon content permits so little formation of hard magnesite that the process is relatively ineffective. Enormous tonnages of these low carbon steels are processed i
7、n such structural shapes as sheet, strip,rod,plate,pipe,and wire. A large portion of the material is cold worked in its final processing to improve its hardness, strength, and surface-finish qualities.the grades containing 20 points or less of carbon are susceptible to considerable plastic flow and
8、are frequently used as deep-drawn products or may be used as a ductile core for casehardened material. The low lain carbon steels are reality brazed, welded, and forged.Medium Carbon. The medium carbon steels (0.25%0.5%)contain sufficient carbon that they may be heat treated for desirable strength,
9、hardness, machinability, or other properties. The hardness of plain carbon steels in this range cannot be increased sufficiently for the material to serve satisfactorily as cutting tools,but the load-carrying capacity of the steels can be raised considerably, while still retaining sufficient ductili
10、ty for good toughness. The majority of the steel is furnished in the hot-rolled condition and is often machined for final finishing. It can be welded,but is more difficult to join by this method than the low carbon steel because of structural changes caused by welding heat in localized areas. High C
11、arbon. High carbon steel contains from 50 to 160 points of carbon (0.8%1.6%). This group of steels is classed as tool and die steel, in which hardness is the principal property desired. Because of the fast reaction time and resulting low hardenability, and its associated danger of distortion or crac
12、king, it is seldom possible to develop fully of heat-treat-hardened plain carbon steel is low compared to that of alloy steels with the same strength, but, even so, carbon steel is frequently used because of its lower cost.ALLOY STEELSAlthough plain carbon steels work well for many uses and are the
13、cheapest steels and therefore the most used, they cannot completely fulfill the requirements for some work. Individual or groups of properties can be improved by addition of various elements in the form of alloys. Even plain carbon steels are alloys of at least iron, carbon, and manganese, but the t
14、erm alloy steel refers to steels containing elements other than these in controlled quantities greater than impurity concentration or, in the case of manganese, greater than 1.5%.Alloys Affect Hardenability. Interest in hardenability is indirect. Hardenability is usually thought of most in connectio
15、n with depth-hardening ability in a full hardening operation. However, with the isothermal transformation curves shifted to the right, the properties forging operations, the materially usually air cools. Any alloy generally shifts the transformation curves to the right, which with air cooling result
16、s in finer pearlite than would be formed in a plain carbon steel. This finer pearlite has higher hardness and strength, which has an effect on machinability and may lower ductility.Weldability. The generally bad influence of alloys on weldability is a further reflection of the influence on hardenabi
17、lity. With alloys present is a further reflection of the influence on hardenability. With alloys present during the rapid cooling taking place in the welding area, hard, nonductile structures are formed in the steel and frequently lead to cracking and distortion.Grain Size and Toughness. Nickel in p
18、articular has a very beneficial effect by retarding grain growth in the austenite range. As with hardenability, it is the secondary effects of grain refinement that are noted in properties. A finer grain structure may actually have less hardenability, but it has its most pronounced effect on toughne
19、ss; for two steels with equivalent in the chart as improved toughness. This improved toughness, however, may be detrimental to machinability. Corrosion Resistance. Most pure metals have relatively good corrosion resistance, which is generally lowered by impurities or small amounts of intentional all
20、oys. In steel, carbon in particular lowers the corrosion resistance very seriously. In small percentages, copper and phosphorus are beneficial in reducing corrosion. Nickel becomes effective in percentages of about %, and chromium is extremely effective in percentages greater than %,which leads to a
21、 separate class of alloy steels called stainless steels. Many tool steels,while not designed for the purpose, are in effect stainless steels because of the high percentage of chromium present.LOW ALLOY STRUCTURAL STEELS Certain low alloy steels sold under various trade names have been developed to p
22、rovide a low cost structural material with higher yield strengh than plain carbon steel. The addition of small amount of some alloying elements can raise the yield strength of hot-rolled sections without heat treatment to 30%40% greater than that of plain carbon steels. Designing to higher working s
23、tresses may reduce the required section size by 25%30% at an increased cost of 15%50%,depending upon the amount and the kind of alloy.The low alloy structural steels are sold almost entirely in the form of hot -rolled structural shapes. These materials have good weldability, ductility, better impact
24、 strength than that of plain carbon steel, and good corrosion resistance, particularly to atmospheric exposure. Many building codes are based on the more conservative use of plain carbon steels, and the use of alloy structural steel often has no economic advantage in these cases.LOW ALLOY AISI STEEL
25、SImproved Properties at Higher Cost. The low alloy American iron and steel institute (AISI) steels are alloyed primarily for improved hardenability. They are more costly than plain carbon steels, and their use can generally be justified only when needed in the heat-treat-hardened and tempered condit
26、ion. Compared to plain carbon steels, they can have 30%40% higher yield strength and 10%20% higher tensile strength. At equivalent tensile strengths and hardnesses, they can have 30%40% higher reduction of area and approximately twice the impact strength.Usually Heat Treated. The low alloy AISI stee
27、ls are those containing less than approximately 8% total alloying elements, although most commercially important steels contain less than 5%. The carbon content may very form very low to very high, but for most steels it is in the medium range that effective heat treatment may be employed for proper
28、ty improvement at minimum costs. The steels are used widely in automobile, machine tool, and aircraft construction, especially for the manufacture of moving parts that are subject to high stress and wear.STAINLESS STEELS Tonnage-wise, the most important of the higher alloy steels are a group of thes
29、e steels have much better mechanical properties at high temperatures. This group was first called stainless steel. With the emphasis on high temperature use, they are frequently referred to as heat and corrosion-resistant steels.Martensitic Stainless Steel. With lower amounts of chromium or with sil
30、icon or aluminium added to some higher chromium steels, the material responds to heat treatment much as any low alloy steal. The gamma-to-alpha transformation in iron occurs normally, and the steel may be hardened by heat treatment similar to that used on plain carbon or low alloy steels. Steels of
31、this class are called martensitic, and the most used ones have 4%to 6% chromium.Ferritic stainless steel. With large amounts of chromium, as great as 30% or more,the austenite region of the iron-carbon equilibrium diagram is suppressed, and the steel loses its ability to be hardened by normal steel
32、heat-treating procedures. Steels of this type are called ferritic and are particularly useful when high corrosion resistance is necessary in cold-worked products.Austenitic Stainless Steel. With high chromium and the addition of 8% or more of nickel or combinations of nickel and manganese, the ferri
33、te region of the diagram is suppressed. These steels, the most typical of which contains 18%chromium and 8% nickel, are referred to as austenitic stainless steels. They are not hardenable by normal steel heat-treating procedures, but the addition of small amounts of other elements makes some of them
34、 hardenable by a solution-precipitation reaction.TOOL AND DIE STEELS The greatest tonnage of tools (other than cutting tools) and dies are made from plain carbon or low alloy steels. This is true only because of the low cost these materials as their use has a number of disadvantages. They have low h
35、arden-ability, low ductility associated with high hardness, and do not hold their hardness well at elevated temperature.Manganese Steels. Manganese tool and die steels are oil hardening and have a reduced tendency to deform or crack during heat treatment. They contain from 85100 points of carbon, 1.
36、5%1.75% of manganese to improve hardenability, and small amounts of chromium, vanadium, and molybdenum to improve hardness and toughness qualities.Chromium Steels. High chromium tool and die steels are usually quenched in oil for hardening, but some have sufficient hardenability to develop hardness
37、with an air quench. One group of the high chromium steels, called high speed steel, has substantial additions of tungsten, vanadium,and sometimes cobalt to improve the hardness in the red heat range.钢 1、 普通碳素钢任何炼钢方法都能炼出只含有0.05%（甚至更少）碳的钢。由于只有少量的碳，钢的性能接近于纯铁，具有很高塑形和很低的强度。从便于成形和使用的角度看，高塑性和低强度是变形所需要的，然而，
38、从产品设计角度来说，需要比这种低碳钢更高的强度。增加强度最适用的方法是在钢中增加或保留一些碳。然而，必须明白，强度的增加只有在损失塑性的情况下才能实现，因此，最终总是在塑性和强度之间形成某种折衷。因为成分控制和增碳过程有一定的难度，高碳高强度钢的成本比低碳钢高。最常用的普通碳素钢 因为成本低，实际使用的大多数是普通碳素钢，它们由铁和碳组成，普通碳素钢的碳含量可分为低碳、中碳、高碳三类。除了用来控制硫和锰元素以外，其他元素只有很少而被认为是杂质，有时它们对材料的性能可能有较小的影响。低碳钢 含碳大约0.06%0.25%的钢称为低碳钢，他们很难通过热处理淬硬，因为碳的含量太低，很难形成硬的马氏体结
39、构，从而使热处理相对不起作用。大量的低碳钢被做成薄板材、带材、棒材、板材、管材和线材等结构。很多这类材料最后通过冷加工来提高硬度、强度和表面质量。含碳小于等于20%的钢可以经受较大的塑性流动，经常用作深拉成形零件或可用表面硬化材料的塑性心部。低碳钢容易铜焊、熔焊和锻造。中碳钢 中碳钢(0.25%0.5%)含有足够的碳，可以通过热处理得到所需强度、硬度、切削加工性和其他特性。此类普通钢的硬度不能显著提高到满意的作为切削刀具，但承载能力可提高很多，同时保留足够的塑性和良好的韧性。大多数钢在热轧状态提供，经常需进行切削加工。它能焊接，但比低碳钢难得多，因为焊接热量在局部区域引起了组织结构的变化。高碳
40、钢 高碳钢含有0.5%1.6%的碳，这类钢称为工具和模具钢，硬度是这类钢所需的主要性能。因为组织转变快，淬透性低这种钢几乎都是用水淬火。即使用这种激烈的处理方式，并有变形和开裂的危险，这种钢很少能完成淬透，淬硬层厚度不超过1英寸。实际上，在同样强度下，热处理淬硬的普通碳素钢的塑性比合金钢的低，但即使如此，因其成本低，仍常使用碳素钢。2、 合金钢普通碳素钢可用于许多场合，也是最便宜的钢种，因此使用最多，但它们对某些工作要求不能完全满足。这是可通过加入一些元素形成合金的方式来提高钢的某一项或几项性能。即使是普通碳素钢，也是铁、碳和锰的合金，但合金钢中除了这些元素外，其他元素含量大于普通碳素结构钢的
41、杂质含量，如锰含量要大于1.5%。合金元素影响淬透性 人们对淬透性的兴趣是间接的。淬透性通常与完全淬火时硬化深度的能力有关系。然而，随着等温曲线右移，即使在完全硬化时，材料性能也能显著改变。在热轧或锻打后，材料通常采用空冷。所有合金通常使等温曲线右移，空冷时得到比普通钢细的珠光体。这种细珠光体有较高的硬度和强度，可能会降低塑性，对切削加工性也有影响。可悍性 总的来说，合金元素对可悍性产生坏影响，这也是影响淬透性的一种反应，焊接区快冷时，合金会使焊接区形成硬的、韧性差的结构，经常导致开裂和变形。晶粒尺寸和韧性 在奥氏体阶段，镍对防止晶粒长大有特别优异的作用。对淬透性而言，对性能影响大的晶粒细化过
42、程就只是次要影响。细晶粒结构会使淬透性变差，但对韧性影响很大。对硬度和强度相等的两种钢，细晶粒的钢塑性较好，反映在图表中就是韧性高，但这种高韧性，对切削加工形式有害的。耐腐蚀能力 总的来说，大多数纯金属耐腐蚀能力相对较好，含有杂质或少量合金元素时会降低其耐腐蚀能力。对钢而言，碳会显著降低其耐腐蚀能力。铜和磷含量少时对减轻腐蚀有利，镍在含量大约5%时对减轻腐蚀也是有利的，铬在含量大于10%时特别有益，会产生一种称为不锈钢的合金钢。许多工具钢，因其镉含量高而实际上也是不锈钢，虽然设计中没做这种要求。3、 低合金结构钢市场上已有多种多样的低合金结构钢，他们是屈服强度比普通碳钢高的低成本结构材料。外加
43、少量的一些合金元素不需经过热处理就可以提高热轧钢的屈服强度，比普通碳钢高30%40%。在高应力条件下，可减少横截面尺寸25%30%，同时增加成本15%50%，这取决于合金元素的量和种类。4、 低合金AISI钢高性能高成本 低合金AISI（美国钢铁协会）钢中的合金元素主要用于提高淬透性，他们比普碳钢贵得多，通常只在必须是使用，用于热处理硬化和回火条件下。与普碳钢相比，屈服强度高30%40%，抗拉强度高10%20%。同样的拉伸强度和硬度时面积可减少30%40%,冲击强度大约提高两倍。通常需热处理 低合金AISI钢的总合金元素含量小于8%，虽然工业上大多数重要钢的合金元素的含量少于5%。碳含量可从很
44、低变到很高，但大多数为中碳钢，可用最小成本进行热处理来有效改善性能，这种钢广泛用于汽车、机床、飞机，特别随时用于制造承受高应力且磨损大的运动零件。5、 不锈钢大量使用且最重要的高合金钢是一组抗化学腐蚀能力极高的高铬钢。这类港的大多数在高温下好的的力学性能，这类钢最早称为不锈钢，随着在高温下使用的增加，它们经常也称为耐热耐腐蚀钢。马氏体不锈钢 在钢中加入少量铬，或在一些高铬钢中加入硅或铝，这种钢称为马氏体钢，其中含铬4%到6%的钢最常用。铁素体不锈钢 含铬量达30%或更多时，铁碳平衡相图的奥氏体区缩小，钢失去了用通常热处理方法硬化的能力。这种钢称为铁素体钢，特别适用于由高耐腐蚀性要求的冷加工产品
45、。奥氏体不锈钢 高铬钢再加上8%以上的镍或镍与锰，相图的铁素体区就会缩小。最典型的钢含18%和8%镍，称为奥氏体不锈钢。他们不能用通常钢的热处理方法硬化，但可附加少量的其他元素通过固溶强化使它们硬化。6、 工具模具钢大量的工具（与切削刀具不同)和模具用普通钢或低合金钢制造，这只是因为他们价格便宜，但这些材料有很多缺点。它们的淬透性差，硬度高而塑性低，温度升高时不能很好的保持硬度。锰钢 钢工具模具钢是油淬硬化钢，在热处理是很少变形或开裂。为提高淬透性，钢中含有0.85%到1.00%的碳和1.5%1.75%的猛，并有少量铬、钒、钼来提高硬度和韧性。铬钢 高铬工具模具钢通常在油中淬硬，但有一些铬钢淬透性好，在空冷时就能淬硬。有一组高铬钢加油许多钨、钒（有时还有钴）其提高起高温硬度，它们成为高速钢。