外文翻译--钢

STEElPLAIN 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 those of pure iron with maximum ductility and minimum strength.Maximum ductility is desirable from the standpoint of ease in deformation 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 some carbon.However ,it should be fully understood that any increase of strength over that of 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 of increasing carbon content,the cost of higher carbon,higher strength steel is greater than that 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 therr ranges classed 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 impurityes ,though in some cases they may have minor effect on properties of the material.Low Carbon. Steel with approximately 6 to 25 point of carbon(0.06%-0.25%) are rated as low carbon steels and are rarely hardened by heat treatment because the low carbon content pernmits so little formation of hard martensite that the process is relatively ineffective.Enormous tonnages of these low carbon steels are processed in such structural shapes as sheet ,strip ,rod,plate ,pipe ,and wire.A large portion of the material is cold worked grades containing 20 points or less of carbon are susceptilbe to considerable plastic flow and are frequently used as deep-drawn products or may be used as a ductile core for casehardened material.The low lpain carbon steels are readily 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,hardness,machinability,or other properties.The hardness of plain carbon steels in this range connot 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 ductility 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 Carbon. High carbon steel contains from 50 to 160 points of carbon (0.05%-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,plan carbon steels nearly always must be waterquenched.Even with this drastic treatment and its accociated danger of distortion or cracking,it is seldom possible to develop fully hardened structure in material more than about 1 inch in thickness.In practice the ductility of heat-treat-hardened plain carbon steel is low compared to that of alloy steels with the same strength,but ,even so ,conbon steel is frequently used because of its lower cost.ALLOY STEELSAlthough plain carbon steels work well for many uses and are the cheapest steels and therefore the most used,they connot 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 manganses,but the term blloy 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 connection with depth-hardening ability in a full hardening operation. However,with the isothermal transformation curves shifted to the right,the properties forging ooperations ,the material usually air cools .Any alloy generally shifts the transformation curves to the right ,which with air cooling results 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 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 hardenability.With alloys present during the rapid cooling taking place in the ewlding area, hard ,nonductile structures are formed in the steel and frequently lead to cracking and distortion.LOW ALLOY STRUCTURAL STEELS Certain low alloy steels sold under various trade names have been developed to provide a low cost structural material with higher yield strength than plain carbon steel. The addition without heat treatment to 30%-40% greater than that of plain carbon steels.Designing to higher working stresses may reduce the required section size by 25%-30% at an increased cost of 15%-50%,depending upon the amount and the king of alloy.The low alloy structural steels are sold almost entirely in the form of hot-rolled structural shapes.These materials have 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 STEELS Improved Properties at Higher Cost. The low alloy American Iron and Steel Institute (AISI) steels are alloyed primarily for improved hardenability.They are more coslty than plain carbon steels ,and their use can generally be justified only when needed in the heat-treat-hardened and tempered condition.Compared to plain carbon steels,they can have 30%-40% higher yield strengh 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 steels are those containing less than approximately 8% total alloying elements,although most commercially inportant steels contain less than 5%.The carbon content may vary form very low to very high,but for most steels it is in the medium range that effective heat treatment may be employed for property 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 STEELSTonnage-wise,the most important of the higher alloy steels are a group of high chromium steels with extremely high corrosion and chemical resistance. Most of these steels have much better mechanical properties at high temperatures. This group was first called stainless .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 silicon or aluminum added to some higher chromium steels ,the material responds to heat treatment much as any low alloy steal. The gamma-to-alphatransformation in iron occurs normally,and the steel may be hardened by heat treatment similar to theat used on plain carbon or low alloy steels.Steels of this class are called martensitic,and the most used ones have 4% to 6% chromium.Austenitic Stainless steel. With larger amounts of chromium,as great sa 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 heat-treating procedures.Steels of this type are called ferritic and are particularly useful whenhigh corrosion resistance is necessary in cold-wored products.Austenitic Stainless Steel. With high chromium and the addition of 8% or more of nickel or combinations of nickel and manganese,the ferrite 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 heattreating procedures,but the addition of small amounts of other elements makes some of them hardenable by a solution-precipittion reaction.TOOL AND DIE STEELSThe greates tonnage of tools (other than cutting tools ) and dies are made from plain carbon or low alloy steels.This is true onlly because of the low cost of these materials as their use has a number of disadvantages.THey have low harden-ability,low ductility associated with high hardness,and do not hold their hardness well at elevatesd temperature.Mangnaese Steels. Manganese tool and die steels are oil hardening and have a reduced tendency to deform or crack during heat treatment .They contain from 85-100 points of carbon,1.5%-1.75% of manganese to improve hardenability,and small amounts of chromium. vanadium,and molybdenum to improve hardnwss 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 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 .钢一、普通碳素钢任何炼钢方法都能炼出只有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，具有很高的塑性和很低的强度。从便于成形和使用角度看，高塑性和低强度是变形所需要的，然而，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 碳。然而， ，强度的增加只在有 塑性的 能 ， ，最 是在塑性和强度 形成 种 。 成 和增碳 有 度，高碳高强度钢的成比低碳钢高。最常用的普通碳素钢 成低， 使用的是currency1碳“钢，由铁和碳成，currency1碳“钢的碳fi量fl 低碳 中碳 高碳。用来 的“，”“只有很少量而 是 ，有 的性能fl能有的。低碳钢 fi碳0.06%-0.25%的钢 低碳钢，很 ， 碳的fi量低，很形成的 ，从而使 用。量的低碳钢 成 和 。很这最 加来 高度 强度和 量。fi碳于 于20%的钢fl的塑性， 用 成形 fl用 的塑性。低碳钢 钢 和 。中碳钢 中碳钢（0.25%-0.5%）fi有的碳，fl 所需强度 度 加性 ” 性。比currency1碳钢的度 能显著 高 满意的 刀具，但承载能力fl 高很，同 的塑性和良好的韧性。钢在轧状态 供， 需进行 加。能接，但比低碳钢， 接量在局 区域引 织 的变 。高碳钢 高碳钢fi有 0.5%-1.6%的碳，这钢 具和模具钢，度是这钢所需的主要性能。 织转变快，透性低，这种钢几乎都是用水火即使用这种激烈的 方式，并有变形和开裂的危险，这种钢很少能完全透，层厚度 超 1英寸。 上，在同样强度 ， 的currency1碳“钢的塑性比合金钢的低，但即使如 ， ”成低，仍堂使用碳“钢。二、合金钢currency1碳“钢fl用于许场合，也是最便宜的钢种， 使用最，但 要求 能完全满。这 fl 加入 “形成合金钢的方式来 高钢的 项 几项性能