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专业英语第二课


Lesson 2 Carbon and Alloy Steel Steel is probably the most widely used 钢由于其高强度,高刚度,良好的稳定性 material for machine elements because of 和构件间相对缓和的作用成为机械元素应 its properties of high strength ,high 用最广

泛的材料。 stiffness ,durability and relative ease of 钢是指有铁、碳、锰和一个或更多的其他 fabrication .the term steel refers to an alloy 重要元素组成的合金。 of iron ,carbon ,manganese and one or 碳对合金钢的强度、硬度、稳定性有非常 more other significant elements .carbon has 大地影响。 a very strong effect on the strength , 其他元素影响淬透性、韧性、耐腐蚀性、 hardness and ductility of any steel alloy . the 可加工性和高温下的强度保持能力。 other elements affect hardenability , toughness , corrosion resistance , machinability and strength retention at high 各种合金钢中基本的合金元素有: 硫、 磷、 temperature .the primary alloying elements 硅、镍、铬、钼、钒等。 present in the various alloy steels are sulfur ,phosphorus , silicon , nickel ,chromium , molybdenum and vanadium . 1. 碳的重要性 1. Importance of carbon 虽然大多数合金钢碳的含量不到 1%, 但它 although most steel alloys contain less than 出现在合金钢的标号中,主要是因为碳对 1.0% carbon ,it is included in the 于钢的性能有重要的影响。 如图 1.2 所示, designation because of its effect on the 最后两位数字代表碳含量的百分之一百个 properties of steel . as figure 1.2 点。 illustrates ,the last two digits indicate 随着碳含量的增加,合金钢的强度和硬度 carbon content in hundredths of a 在相同的加工、热处理条件下也会相应的 percent .as carbon content increases , 增加。但是,稳定性会下降随着碳含量增 strength and hardness also increase under 加, the same condition of processing and heat 所以,钢的合适选择应对强度和稳定性的 treatment .since ductility decrease with 惊醒综合考虑。 increasing carbon content , selecting a suitable steel involves some compromise between strength and ductility .

as a rough classification scheme ,a low-carbon steel is one having fewer than 30 points of carbon (0.30%) . these steels have relatively low strength but good formability . in machine element applications where high strength is not required , low-carbon steels are frequently specified . if wear is a potential problem , low-carbon steels can carburized to increase the carbon content in the very outer surface of the part and to improve the combination of properties . medium-carbon steels contain 30 to 50 points of carbon (0.30%-0.50%) . most machine elements having moderate of high strength requirement with fairly good ductility and moderate hardness requirement come from this group . high-carbon steels have 50 – 95 points of carbon (0.50%-0.95%) .the high carbon content provides better wear properties suitable for applications requiring durable cutting edges and for applications where surfaces are subjected to constant abrasion . tools ,knives , chisels and many agriculture implement components are among these uses . 2. Stainless steels The term stainless steel characterizes the high level of corrosion resistance to be classified as a stainless steel , the alloy must have a chromium content of at least 10% . most have 12% to 18% chromium . The three main groups of steels are austenitic , ferritic , and martensitic . austenitic stainless steels fall into the AISI 200 and 300 series . they are general-purpose grades with moderate strength .most are not heat-treatable , and their final properties are determined by the amount of working . these alloys are nonmagnetic and are typical used in food processing equipment

按照一个大致的分类,低碳钢的碳含量不 足 30 个点(0.3%) 。 这些钢的强度相对较差,但具有较好的成 形性。 低碳钢往往用于机械元件的强度要求不高 的情况下。

如果磨损是一个潜在的问题,可以通过渗 碳处理来提高部分外表面的碳含量来提高 其综合性能。

中碳钢的碳含量一般在 30 点到 50 点 (0.3%—0.5%) 。大多数需要具有较好的稳定性 的适度高强度和适度硬度的机械元件常常 采用这种低碳钢。

高碳钢的碳含量一般在 50—95 点(0.35% —0.95%) 。高的碳含量,能够提供更好的 磨损性能,适合需要持久的切削和不断受 磨损的表面。其中,工具、刀具、凿子和 农用机械零件等都是采用了这种高碳钢。 2. 不锈钢 不锈钢由于比较好的抗腐蚀能力被划分为 不锈钢, 这种合金一般至少含有 10%的铬。 大多数铬的含量在 12%—18%。 这中钢主要有三个群体: 奥氏体, 铁素体, 马氏体。奥氏体的不锈钢属于 AISI200 和 300 系列。它们是中等强度的通用牌号。 大多数都不进行热处理,则最终的性能取 决于工作量。这类合金没有磁性,一般用 于食品加工的机械。

Ferritic stainless steels belong to the AISI 400 series , designated as 405 ,409 , 430 , 446 , and so on . they are magnetic and perform well at elevated temperature , from 1300 Fto 1900 F°(700 C° — 1040 C°) . they are not heat-treatable , but they can be cold-worked to improve properties . typical applications include heat exchanger tubing , petroleum refining equipment , automotive trim ,furnace parts , and chemical equipment . Martensitic stainless steels are also member of the 400 series , including 403 , 410 ,414 ,416 ,420 ,431 , and 440 typeset ,they are magnetic ,can be heat-treated , and have higher strength than the AISI 200 and 300 series , while retaining good toughness . typical uses include turbine engine parts , cutlery ,scissor , pump parts ,valve parts ,surgical instruments ,aircraft fittings , and marine hardware . 3. Structure steels Most structure steels are designated by ASTM numbers established by American society for testing and materials . the most common grade is ASTM A36 , which has a minimum yield point of 36000 psi (245 MPa ) and is very ductile . it is basically a low-carbon , hot-rolled steel available in sheet , plate , bar , and structural shapes , such as wide-flange beams , American standard beams , channels and angles . Most wide-flange beams are currently made using ASTM A992 structural steel , which has a yield point of 50 ksi to 65 ksi and a minimum tensile strength of 65 ksi . an additional requirement is that the maximum ratio of the yield point to the tensile strength is 0.85 . this is a highly ductile steel , having a minimum of 21% elongation in a 2.00-inch gage length .using this steel instead of the lower strength ASTM A36

铁素体的不锈钢属于 AISI400 系列,其中 405,409,430,446 等被编排到其中。它们具 有磁性,在 1300F°—1900F°(700C°— 1040C°) 的高温下性能也很好。 它们不热 处理,但可以通过冷加工来提高其性能。 典型的应用包括热交换器管、石油精炼设 备、汽车装饰、炉零件以及化工设备等。 马 氏 体 不 锈 钢 也 属 于 400 系 列 , 由 403,,410,414,420,431,440 组成。它们有 磁性,和 AISI 相比强度更强,同时还能保 持很好的韧性。典型的应用主要有涡轮发 动机零件,餐具,剪刀,泵部件,阀门零 件,手术器械,飞机配件,船用五金。 3. 结构钢 大多数结构钢由美国社会建立的美国材料 实验协会规定。最常见的是最小屈服点 30000 psi(245MPa)的 ASTM A36,具有 良好的延展性。它一般适用于低碳钢热轧 钢板片材,板材,棒材和型材,像宽翼缘 梁,美国标准梁,渠道和角度。目前大多 数宽缘翼梁使用 ASTM A992 结构钢,这种 钢具有 50 psi 到 65 psi 的屈服点,最小 65 ksi 的屈服极限。 但是,额外的要求是抗拉强度与屈服点的 最大比率不能大于 0.85。 这种钢具有很好的延展性,2 英寸标准长 度的钢件至少有 21%的伸长率。使用这种 钢材,代替典型的低强度的 ASTM A36 钢,

steel typical allows smaller , lighter structural members at little or no additional cost . Hollow structural sections (HSS) are typical made from ASTM A500 steel that is cold-formed and either welded or made seamless . included are round tubes and square rectangular shapes . there are different strength grades can be specified . some of these HSS products are made from ASTM A5001 hot-formed steel having properties similar these the ASTM A36 hot-rolled steel . Many higher-strength grades of structural steel are available for use in construction , vehicular , and machine applications . they provide yield points in the range from 42000 psi to 100000 psi (290 MPa — 700 MPa ) . 4. Tool steel Tool steels refers to a group of steels typical

允许使用更小,更轻和少的结构成员或不 增加额外的费用。 中空结构型钢 (HSS) 一般有冷弯和焊接或 做出无缝的 ASTM A500 钢制成。 包括圆管, 方矩形形状,被划分为多个不同的等级。 这 些 HSS 产 品 , 有 些 是 由 热 成 型 的 ASTM5001 组成,这种的性能和 ASTM A36 的钢类似。 许多高等级的高强度钢适用于建筑,车辆 和机器。 它 们 的 屈 服 点 (290-700MPa) 。 4. 工具钢 工具钢,是指用于切削工具,冲床,模具, 42000-100000psi

used for cutting tools ,punches , dies , 剪切刀片, 凿子以及类似用途的一类的钢。 shearing blades , chisels and similar uses . the numerous varieties of tool steel materials have been classified into seven 的类型。 general types . whereas most uses of tool 而大多数使用的工具钢与工程制造领域密 steels are related to the field of 切相关,也是对于一些需要在特定的刃磨 manufacturing engineering , they are also 条件下能够保持良好的性能的机械设计满 pertinent to machine design where are 足要求。 ability to maintain a keen edge under abrasive conditions is required . also , some 此外,一些工具钢具有相当高的抗冲击性 tool steels have rather high shock 能。 这就适用于机械部件, 如部分离合器, resistance . which may be desirable in 棘爪,刀片,移动零件和夹具的导轨。 machine components such as parts for mechanical clutches ,pawls , blades , guides for moving materials and clamps . 工具钢材料的品种繁多,被分为 7 个一般


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