# 热处理[编辑]

**热处理**是將金属材料加熱到一定的溫度，保溫一定的時間後，以一定的速率降溫到常温或更低，從而達到改善材料組織結構獲得性能優異的材料，一般是指對金屬材料特別是鋼材的處理。常用的分類方法有正火、退火、淬火、回火和表面硬化等几种。

## 概念

工業生產中，熱處理可以視為一系列的用來改變材料的物理性質，偶爾也用來改變材料的化學性質冶金工程步骤。熱處理在冶金學方面有非常普及的應用，但是陶瓷、玻璃材料的生產過程中也常有熱處理程序的出現。熱處理用升高或冷卻的方式進行，通常涉及極端的溫度，以其改變材料的硬度、韌性等一系列性質。

随着热处理技术的进步，热处理的定义可以改写成透过温度的控制与冷却速率的调整，来改变材料的特性。比如说目前的深冷技术（或称深冷处理），便是將钢材在淬火后冷却到零下七八十度到一百多度的热处理技术。

正處於980℃的熱處理爐
被推進淬火（Quenching）車床的焦炭（Coke）。攝於1942年11月，位於美國密歇根州底特律的大湖區鋼鐵公司（Great Lakes Steel Corporation）。

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| 金属热处理
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| 退火
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完全退火：将钢加热到Ac3以上20~30℃，保温一段时间后缓慢冷却（随炉）以获得接近平衡组织的热处理工艺（完全奥氏体化）。

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扩散退火（均匀化退火）

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不完全退火

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球化退火

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再结晶退火（中间退火）

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去应力退火：将钢件加热至低于Ac1的某一温度（一般为500~650℃），保温，然后随炉冷却。

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石墨化退火

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磁场退火

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正火：将钢构件加热到Ac3温度以上30〜50℃后，保温一段时间出炉空冷。冷却速度快于退火而低于淬火。

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| 淬火
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| 普通淬火
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一般淬火

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双液淬火

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等温淬火

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固溶处理

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| 其他淬火
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形变淬火

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磁场淬火

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| 回火及时效
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低温回火

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中温回火

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高温回火

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时效处理

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磁场回火

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形变时效回火

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循环热处理

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| 表面热处理
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| 表面淬火
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火焰加热表面淬火

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| 感应加热表面淬火
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高频加热表面淬火（20-10000kHz）

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中频加热表面淬火（<10kHz）

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激光加热表面淬火

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电子束加热表面淬火

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电解液加热表面淬火

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激光上光

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激光共晶化

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化学气相沉积

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物理气相沉积

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等离子体化学气相沉积

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| 化学热处理
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| 气体化学热处理
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渗碳

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碳氮共渗

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渗氮（氮化）

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渗金属

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渗非金属

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多元共渗

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离子化学热处理

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电解化学热处理

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真空化学热处理

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* 退火（英語: Annealing）是为了软化钢材、调整结晶组织、去除内部应力、改善冷轧加工及切削性。根据使用目的，退火细分为完全退火，球化退火、去应力退火、中间退火等。

* 正火（英語: Normalising；在臺灣稱為「正常化」）是为了细化钢材晶粒，均匀内部组织，消除内应力。在如德國的西方國家，正火（德文：Normalglühen）只是退火（德文：Glühen）的一個子類。

* 淬火（英語: Quenching）是将钢材经过高温加热后快速冷却处理，提高硬度和强度。根据冷却条件分为水淬、油淬、真空淬火等。淬火后的材料必须经过回火处理。

* 回火（英語: Tempering）是钢件淬硬后再度加热到某一温度，然后以适当的速度冷却。目的是调整材料硬度、提高韧性及消除内部应力。回火可分为低温回火和高温回火。回火温度越高，材料的硬度降低越多，韧性越强。调質处理加工采用高温回火。高频淬火、渗碳淬火等表面硬化处理后的回火处理为低温回火。
* 形变热处理是将塑性变形和热处理结合。如高温形变热处理是将钢加热到奥氏体状态，进行塑性变形，然后立即淬火和回火。

### 化学热处理

钢的化学热处理是将工件置于一定温度的活性介质中保温，使一种或几种元素渗入其表层，以改变表层化学成分、组织和性能的热处理工艺。根据渗入元素的不同有渗碳、渗氮、碳氮共渗、渗硼、渗硫、渗铬、渗铝及多元共渗等。

* 渗碳淬火是将低碳钢表面渗入碳素后淬火再低温回火。淬火硬度50~63HRC，硬化层深度0.3~1.2mm。
* 渗氮是将氮素扩散深入钢材表面的热处理方法。含有铝、铬、钼的钢材容易通过渗氮提高硬度。
	+ 气体氮化是将工件放入密闭的炉内加热到500-600℃，通入氨气，氮化层一般为0.1-0.6mm。氮化后随炉降温到200℃以下停止供氨，工件出炉。缺点是渗氮时间长，成本高；渗氮层很薄，脆性大。
	+ 离子氮化是利用稀薄的含氮气体，在高压直流电场作用下产生辉光放电现象而进行的，又称辉光离子氮化。
* 碳氮共渗是向零件表面同时渗入碳原子和氮原子。
	+ 中温气体碳氮共渗常采用煤油和氨气等作为共渗剂，温度在700-880℃范围，高温以渗碳为主，低温以渗氮为主。
	+ 低温气体碳氮共渗（又称气体软氮化）温度为520-570℃，氮化层为0.1-0.4mm，不宜用于重载零件。
* 真空热处理是在0.1-0.001Pa的环境中加热的热处理工艺，包括真空淬火、真空退火、真空回火等。真空热处理的工件氧化和脱碳少，升温慢，热处理变形小，表面氧化物、油污在真空加热时分解，被真空泵排出，使表面光洁美观。
* 可控气氛热处理是为达到无氧化、无脱碳或按要求增碳，在成分可控的炉气中进行的渗碳、碳氮共渗等化学热处理。

### 高能束表面淬火

高能束表面淬火是利用激光、电子束、等离子弧、感应涡流或火焰等高功率密度能源快速加热使钢件表层迅速奥氏体化，而心部仍处于临界点一下，随之淬火，使表面硬化，而心部组织并不发生变化。

* 火焰淬火是用明火进行的表面热处理，主要在钢铁的任意表面或某一部分需要淬火时使用。
* 感应加热表面淬火是将含碳量在0.30%以上的钢材通过感应加热，使材料表面变硬的工艺。淬火硬度50~60HRC，硬化层深度1~2mm。频率越高，电流透入深度越浅，淬透层越薄。

感应加热表面淬火的电流频率选择
| 类别 | 频率范围 | 淬硬层深度 | 应用举例
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| --- | --- | --- | --- |
| 高频感应加热 | 200-300 kHz | 0.5-2 mm | 小齿轮、小轴
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| 中频感应加热 | 1-10 kHz | 2-8 mm | 承受扭曲、压力载荷的零件，如曲轴、大齿轮、主轴
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| 工频感应加热 | 50 Hz | 10-15 mm | 承受扭曲、压力载荷的大型零件，如冷轧辊、火车车轮
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* 激光加热表面淬火是依靠工件本身的传热来冷却淬火。表面硬度高于高频淬火。

## 物理過程

金屬材料在微觀結構下有很多細小的晶體稱為晶粒。晶粒的大小、組成可謂影響金屬機械性質因素之一。熱處理提供一種有效的方式來控制金屬微觀結構下的擴散速率與冷卻速率，來達到需要的金屬性質。通常熱處理要改變的機械性質不外乎五種：1.硬度
2.應力-應變性質
3.韌性
4.延性
5.彈性

熱處理有兩種重要的機轉可以改變合金的性質：1.麻田散鐵轉變，用來產生形變
2.金屬擴散機轉，用來改變同質性（使材料呈現單一特徵的傾向）

## 組成的影響

合金系統的確切組成對於熱處理的結果有巨大的影響。若合金中各組成物的比例正確無誤，則冷卻後該合金將呈現單一且連續的微觀結構，此混合物稱之為共晶系統。然而，若是合金中組成物溶質的比例異於共晶系統，則兩種或兩種以上的微觀結構將同時形成。溶質的含量以過共析溶液高於共晶混合物，共晶混合物又高於亞共析溶液。

## 缺陷

过热与过烧
* 过热指加热温度过高或保温时间过长，使奥氏体晶粒显著粗大的现象，通过正火可消除。
* 火烧指加热温度接近开始熔化的温度，使晶界处产生熔化或氧化的现象，无法挽救。

氧化与脱碳
* 氧化指工件表面形成氧化皮的现象。
* 脱碳指工件表层的碳被烧损，使表层含碳量下降的现象。

变形与开裂
零件的变形与开裂都是由淬火时的内应力引起的。