钢

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钢(steel)

铁的合金，约含2%以下的碳。纯铁质地柔软，添加碳大幅增加其硬度。数种不同成份或晶体结构的铁－碳组合：沃斯田铁、肥粒铁、波来铁、雪明碳铁、麻田散铁，以复杂的混合物和组合共存，取决於温度与碳的含量。每种微构造有不同的硬度、强度、韧度、耐蚀力以及电阻率，因此调整碳含量就能改变这些性质。热处理法、在冷热温度下的机械加工、或加入合金元素也可以赋予更佳的特性。钢主要分为三类：碳钢、低合金钢与高合金钢。低合金钢（合金元素含量小於8%）异常强韧，用作机械零件、飞机起落架、机轴、手工具和齿轮，还有建筑物与桥梁。高合金钢的合金元素超过8%（如不锈钢）提供特殊材质。炼钢包括融化、纯化（精炼）及合金，在1,600℃左右进行。钢的取得可由精炼铁（从鼓风炉）或是废钢，藉由硷性氧化钢法、平炉法，或是在电炉内，然後去除多余的碳和杂质，并加入合金元素。融化的钢可以倒入铸模，凝固成铸锭；经过再加热及辊轧变成半成品形状，在经过加工做出成品。经由连续铸造可以省去铸锭浇铸的一些步骤。将半成品的钢塑造成成品形状主要有两种方法：热加工主要是在高热之下用鎚击和热压（合在一起称为锻造）、挤压、辊轧钢；冷加工包括辊轧、挤压及抽伸，通常用来制作钢条、钢线、钢管、钢片和钢带。融化的钢也可以直接铸造成制品。某些产品，特别是钢片藉由电镀、镀锌、镀锡来防蚀。

English version：

steel

Alloy of iron and about 2% or less carbon. Pure iron is soft, but carbon greatly hardens it. Several iron-carbon constituents with different compositions and/or crystal structures exist: austenite, ferrite, pearlite, cementite, and martensite can coexist in complex mixtures and combinations, depending on temperature and carbon content. Each microstructure differs in hardness, strength, toughness, corrosion resistance, and electrical resistivity, so adjusting the carbon content changes the properties. Heat treating, mechanical working at cold or hot temperatures, or addition of alloying elements may also give superior properties. The three major classes are carbon steels, low-alloy steels, and high-alloy steels. Low-alloy steels (with up to 8% alloying elements) are exceptionally strong and are used for machine parts, aircraft landing gear, shafts, hand tools, and gears, and in buildings and bridges. High-alloy steels, with more than 8% alloying elements (e.g., stainless steels) offer unusual properties. Making steel involves melting, purifying (refining), and alloying, carried out at about 2,900°F (1,600°C). Steel is obtained by refining iron (from a blast furnace) or scrap steel by the basic oxygen process, the open-hearth process, or in an electric furnace, then by removing excess carbon and impurities and adding alloying elements. Molten steel can be poured into molds and solidified into ingots; these are reheated and rolled into semifinished shapes which are worked into finished products. Some steps in ingot pouring can be saved by continuous casting. Forming semifinished steel into finished shapes may be done by two major methods: hot-working consists primarily of hammering and pressing (together called forging), extrusion, and rolling the steel under high heat; cold-working, which includes rolling, extrusion, and drawing (see wire drawing), is generally used to make bars, wire, tubes, sheets, and strips. Molten steel can also be cast directly into products. Certain products, particularly of sheet steel, are protected from corrosion by electroplating, galvanizing, or tinplating.

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