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1、附录5Ferrous Metals Metals are divided into two general groups: ferrous metals and nonferrous metals. Ferrous metals are those metals whose major element is iron. The major types of ferrous metals arc irons, carbon steels, alloy steels and tool steels. Iron The iron ore which we find in the earth is n
2、ot pure. It contains some impurities which we must remove by smelting. The process of smelting consists of heating the ore in a blast furnace with coke and limestone, and reducing it to metal. Blasts of hot air enter the furnace from the bottom and provide the oxygen which is necessary for the reduc
3、tion of the ore, The ore becomes mohen, and its oxide combines with carbon kom the coke. The non-metallic constituents of there combine with the limestone to form a liquid slag. This floats on top of the molten iron, and passes out of the furnace through a tap. The metal which remains is pig-iron, a
4、nd consists of approximately 93 percent iron, 5 percent carbon, and 2 percent impurities. Remehing pig iron and scrap iron in a furnace to remove some of the impurities produces cast iron. The type, or grade, of cast iron is determined by the extent of refining, the amounts of pig iron and scrap iro
5、n, and the methods used to cast and cool the metal.The three primary types of cast iron are gray cast iron, white cast iron, and malleable iron.Gray cast iron is primarily used for cast frames, automobile engine blocks, handwheel, and east housings. White cast iron is hard and wear resistant and is
6、used for parts such as train wheels. Malleable cast iron is a tough material used for tools such as pipes and wrenches. Generally, cast irons have very good compressive strength, corrosion resistance, and good machinability. The main disadvantage of cast iron is its natural brittleness. Carbon Steel
7、 Carbon steel is made from pig iron that has been refined and cleaned of most impurities. Most of the original carbon in the metal is burned out during the refining process. Measured amounts of carbon are then added to the molten metal to produce the exact grade of carbon steel desired. After the st
8、eel is poured into ingots and allowed to cool, it is usually sent to a rolling mill to be rolled and formed into specific shapes. The three principal types of carbon steel used in industry are low, medium, and high carbon steel. The percentage of carbon :is the most important factor in determining t
9、he mechanical properties of each type of carbon steel. : Low carbon contains between 0. 05% and O. 30% carbon and is primarily used for parts that do not require great strength. Typical uses of low carbon steel include chains, bolts, screws, washers, nuts, pins, wire, shafting, and pipes. This metal
10、 is also known as machine steel, mild steel, and cold-rolled steel. Low carbon steel is tough, ductile material that is easily machined and welded. It is useful for parts that must be stamped or formed. Containing between 0. 30 and 0.50% carbon, medium carbon steel is used for parts that required gr
11、eat strength than is possible with low carbon steel, such as gears, crankshafts, machine parts and axles. Because this steel has higher carbon content, it can be heat-treated to increase both hardness and wear resistance. Medium carbon steel is a tough, hardenable metal that has good machinability a
12、nd is easily welded. Containing between 0.50 and 1.70% carbon, high carbon steel is used for parts that require hardness and strength, such as files, knives, drills, razors, and woodworking tools. Due to their increased carbon content, high carbon steels can be heat-treated to make them harder and m
13、ore wear resistant than low or medium carbon steels. Due to their great hardness, high carbon steels are often brittle. Alloy Steels Alloy steels are basically carbon steels with elements added to modify of change the mechanical properties of the steel. All steels are alloy steels because each is a
14、combination of elements, including carbon steel, a mixture of iron and carbon. To identify the two groups, one is called carbon or plain steel and the other is referred to as alloy steel. Alloying elements are added to the molten steel in measured amounts. The desired end product determines the elem
15、ents and amounts added. The primary alloying elements and their effect on the steel are as follows: Boron The hardenability of an alloy is increased by boron. Only very small amounts of boron are needed to increase the hardenability characteristics of the other elements in the alloy. Chromium When u
16、sed in small amount, chromium increases the depth hardness of the metal. The more chromium used, the better the alloy resists corrosion. Chromium is a principal element in stainless steels. Cobalt Cobalt is added to an alloy to increase wear resistance and increase red hardness, which is the ability
17、 of a metal to maintain a cutting edge at elevated temperature. Cobalt is a valuable addition to some high-speed tool steels. Lead By reducing the cutting friction, lead improves machinability. Leaded steels also have good weldability and formability. Manganese Impurities in alloy steels are control
18、led by using manganese as a purifier and scavenger. When added in larger amount ( 1 to 15 percent) , manganese produces good hardness and wear resistance. Molybdenum A tough alloy suitable for a wide range of high-strength applications, molybdenum steel permits good depth hardness and strength at el
19、evated temperatures. Nickel High-strength alloys resistant to both elevated temperatures and corrosion are produced by nickel. When alloyed with molybdenum, nickel steel becomes a very tough alloy, which is often used for many aircraft parts. Larger amounts of nickel greatly add to the corrosion res
20、istance of stainless steels. Phosphorus and Sulfur Free-machining carbon steels are produced with phosphorus and sulfur. When alloyed with carbon steels, phosphorus and suffer produce alloys with excellent machining characteristics. Tungsten When alloyed with steel, tungsten produces a variety of hi
21、gh-speed tool steels and adds hardenability and strength at elevated temperatures as well as high resistance to wear. Vanadium A tough, fine-grained steel that acts as a cleanser and purifier to eliminate many of the impurities of steel is produced by vanadium. Tool SteelsTool steels are a special g
22、rade of alloy steels used for making a wide variety of tools. Depending on their composition, tool steels are highly resistant to wear, shocks, and heat. These alloys gener ally contain more carbon, tungsten, and cobalt than do the standard alloy steels, i41 Another principal difference between most
23、 alloy steels and tool steels is the control with which elements are added.Tool steels are made with much closer quality controls than are other alloy steels.铁类金属金属材料分为两种类型：铁类金属和非铁金属。主要合金元素是贴的金属材料是铁类金属。铁类金属主要有铁、碳钢、合金刚和工具钢。铁我们在地下找到的铁矿石并不是纯净的，其中含有一些杂质，必须通过冶炼去除。冶炼过程是把铁矿石同焦炭合石灰石装入高炉加温，使他还原成金属。热风从高炉底部吹入高
24、炉内，供给铁矿石进行氧化还原反应所需的氧气。铁矿石变成熔融状态后，其氧化物便与焦炭中的碳化合。矿石里的非金属成分与石灰石结合形成液态炉渣。炉渣浮在铁液上面，经过出渣口排出炉外。剩下的金属就是生铁，生铁中含有约93%的铁，5%的碳和2%的杂质。将生铁与废铁在炉子中重新融化，除去杂质后得到铸铁。铸铁的类型和质量等级决定于精炼程度、生铁和废铁的比例，以及浇注方法和冷却方式。铸铁主要分三种：灰铸铁、白口铸铁和可锻铸铁。灰铸铁主要用于制造支架、汽车发动机气缸、手轮和机架。白口铸铁硬度高、耐磨性好，可用于制造如火车车轮之类的零件。可锻铸铁是韧性较好，可用来制造如管道和扳手之类的零什。一般来说，铸铁有较好的
25、抗压强度，较好的耐腐蚀性能和良好的机械加工性能，其主要缺，：壬是脆性较大。 碳钢 碳钢是生铁经过精炼后除去大部分杂质后得到的。由刁：生铁中含有的碳在精炼过程中大部分被烧损，因此需要在金属液中加入一定量的碳，以获得所需等级的碳钢。金属液浇铸到铸型中并冷却后，将其送人辊轧轧制成不同的形状。 工业亡使用的碳钢主要有三种：低碳钢、中碳钢和高碳钢。碳含量是影响碳钢力学性能的最重要因素。 低碳钢碳含量为005030，主要用于制造强度要求刁；高的零件。低碳钢主要用于制造链条、螺钉、螺杆、垫圈、螺母、销钉、电线、籼和管道。低碳钢又称为结构钢、软钢和冷轧钢。其韧性、延展性较好，易于切削加工和焊接，也有利于零伺：
26、的卅，压成形。 中碳钢含碳量为030050，用于制造强度要求高于低碳钢的零件，如齿轮、曲轴、机器零件和：乍轴。由于碳含量较高，可以对中碳钢进行热处理来提高其硬度和耐磨性。中碳钢韧性较好，强度较高，机械加工性能和焊接性能好。 高碳钢含碳量为050170，用于制造要求强度和硬度高的零件，如锉刀、钻头、剃刀和木工刀具。由于碳含量高，高碳钢可以通过热处理获得比低碳钢和中碳钢更高的硬度和更好的耐磨性。由于其高硬度，高碳钢通常也很脆。 合金钢 合金钢是在碳钢中加入一定的合金元素以改变或提高其力学性能的钢铁材料。任意一种钢铁材料都含有一种以上的元素，因此，所有钢铁材料都是合金，其中包括普通碳钢铁和碳的合金。
27、为了区分这两类材料，一类称为碳钢或普通钢，另类称为合金钢。 加入熔融钢铁中的合金元素是定量的。添加合金元素种类和数量决定于最终产品的性能要求。钢铁中主要合金元素以及它们的作用如下： 硼硼的加入可提高合金的淬透性。只需添加少量的硼元素就能提高合金中其他元素的淬透性。 铬添加少量铬元素能提高合金淬硬层深度。添加的铬元素越多，合金的耐腐蚀性能越好。铬是不锈钢的主要合金元素。 钻钻用来提高合金的耐磨性和热硬性。热硬性指金属在高温下保持高硬度的能力。钴是一些高速工具钢中重要添加元素。 铅铅的加入可减少切削摩擦，提高切削加工性能。添加铅的合金钢可提高焊接性能和锻造性能。 锰锰元素用来作净化剂，控制合金中的
28、杂质含量。当合金中锰元素的含量在115之间时，合金具有较高的硬度和较好的耐磨性。 钼含钼钢铁合金具有良好的韧性、淬透性和热强性，广泛应用于强度要求高的场合。 镍耐高温和腐蚀的高强度合金是通过添加镍元素生产出来的。添加了钼元素的镍合金钢韧性很高，常用来制造航空器零件。不锈钢中含有大量的镍，极大地提高了合金的耐腐蚀性。磷和硫一易切削钢中添加了磷和硫。碳钢中的合金元素磷和硫能提高合金的切削加工性能。钨在钢中加入合金元素钨，可获得多种高速工具钢。钨能提高淬透性、热硬性和耐磨性。钒钒可作为净化剂去除钢中的杂质元素，获得高韧性、晶粒尺寸细小的合金钢。工具钢合金工具钢是用来制作各种工具的钢。由于其成分特点，工具钢具有高耐磨性、耐冲击性和耐热性。这种合金一般比普通合金含更多的碳。钨和钴。工具钢与其他合金钢的另一区别是对添加合金元素的控制。与其他合金相比，工具钢生产的质量控制要求更高。
