機(jī)械外文翻譯材料的機(jī)械加工性-文庫(kù)吧資料
2025-05-20 01:08本頁(yè)面
【正文】 toxic, though, it requires machining in a controlled environment.Cast gray irons are generally machinable but are abrasive. Free carbides in castings reduce their machinability and cause tool chipping or fracture, necessitating tools with high toughness. Nodular and malleable irons are machinable with hard tool materials.Cobaltbased alloys are abrasive and highly workhardening. They require sharp, abrasionresistant tool materials and low feeds and speeds.Wrought copper can be difficult to machine because of builtup edge formation, although cast copper alloys are easy to machine. Brasses are easy to machine, especially with the addition pf lead (leaded freemachining brass). Bronzes are more difficult to machine than brass.Magnesium is very easy to machine, with good surface finish and prolonged tool life. However care should be exercised because of its high rate of oxidation and the danger of fire (the element is pyrophoric).Molybdenum is ductile and workhardening, so it can produce poor surface finish. Sharp tools are necessary.Nickelbased alloys are workhardening, abrasive, and strong at high temperatures. Their machinability is similar to that of stainless steels.Tantalum is very workhardening, ductile, and soft. It produces a poor surface finish。 this improves machinability. The size, shape, distribution, and concentration of these inclusions significantly influence machinability. Elements such as tellurium and selenium, which are both chemically similar to sulfur, act as inclusion modifiers in resulfurized steels.Phosphorus in steels has two major effects. It strengthens the ferrite, causing increased hardness. Harder steels result in better chip formation and surface finish. Note that soft steels can be difficult to machine, with builtup edge formation and poor surface finish. The second effect is that increased hardness causes the formation of short chips instead of continuous stringy ones, thereby improving machinability.Leaded Steels. A high percentage of lead in steels solidifies at the tip of manganese sulfide inclusions. In nonresulfurized grades of steel, lead takes the form of dispersed fine particles. Lead is insoluble in iron, copper, and aluminum and their alloys. Because of its low shear strength, therefore, lead acts as a solid lubricant and is smeared over the toolchip interface during cutting. This behavior has been verified by the pr
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