《火力发电厂金属焊接手册》
第四篇 金属材料焊接
第十七章 铁素体耐热钢的焊接
第五节 铁素体系不锈耐热钢的焊接
目 录
《火力发电厂金属焊接手册》 ···························································································································· 2 第四篇 金属材料焊接 ········································································································································· 2 第十七章 铁素体耐热钢的焊接························································································································ 2 第五节 铁素体系不锈耐热钢的焊接··············································································································· 2 一、 铁素体系不锈耐热钢介绍·························································································································· 2 1、铁素体系不锈耐热钢概述····························································································································· 2 2、铁素体不锈钢牌号及其化学成分 ··············································································································· 4 3、铁素体不锈钢的相图与基本相···················································································································· 7 4、铁素体不锈钢性能与用途··························································································································· 11 二、铁素体不锈钢的焊接性 ······························································································································ 14 1、 铁素体型不锈钢的焊接特点 ················································································································ 15 2、铁素体型不锈钢焊接接头易出现的问题与其焊接性 ········································································· 15 2.1焊接接头的晶间腐蚀 ·································································································································· 15 2.2 焊接接头的脆化 ········································································································································ 17 三、铁素体不锈钢的焊接及焊后热处理工艺 ······························································································· 19 1、铁素体不锈钢的焊接工艺原则·················································································································· 19 2、铁素体不锈钢的焊接工艺··························································································································· 20 2.1 普通纯度高铬铁素体不锈钢焊接 ··········································································································· 20 2.2 超高纯度高铬铁素体不锈钢焊接 ··········································································································· 21 3、铁素体不锈钢的焊接方法··························································································································· 21 3.1 普通纯度铁素体型不锈钢焊接方法 ······································································································ 21 3. 2 超高纯度高铬铁素体型不锈钢焊接方法 ··························································································· 24 四、铁素体不锈钢与异种钢焊接以及焊接的典型构件 ············································································· 25 1、铁素体不锈钢与珠光体钢的焊接 ············································································································· 26 2、铁素体不锈钢与马氏体型不锈钢的焊接································································································ 27 3、典型构件焊接：铁素体型不锈钢（1Crl7）与碳钢（Q235）的电弧焊 ······································· 29
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《火力发电厂金属焊接手册》
第四篇 金属材料焊接
第十七章 铁素体耐热钢的焊接
第五节 铁素体系不锈耐热钢的焊接 一、 铁素体系不锈耐热钢介绍
1、铁素体系不锈耐热钢概述
不锈钢(stainless steel)和耐热钢（heat-resistins steel）均属特殊性能钢，它们在电力、化工、石油行业有着广泛的用途。不锈钢是以不锈、耐蚀性为主要特性，且铬含量至少为10.5％，碳含量最大不超过1.2％的钢；耐热钢是指在高温下具有良好的化学稳定性或较高强度的钢[1]。铁素体型不锈钢是含有足够的铬或铬加一些铁素体形成元素（如铝、钼、钛）的Fe-Cr-C三元合金，其中奥氏体形成元素，如碳和镍的含量比较低。该类钢与奥氏体型不锈钢一样，加热过程中不会发生相变，也不能热处理强化，其力学性能、耐腐蚀性能和焊接性均不如奥氏体型不锈钢。但其制造成本较低，抗氧化性较好，且具有较好的耐应力腐蚀性能。主要用于电力、化工、石油等行业制造耐氧化、耐腐蚀的设备，以及汽车工业和家用电器工业等。
金属的腐蚀形式有化学腐蚀和电化学腐蚀两种，前者是金属直接与周围介质发生化学反应，后者是金属在电解质溶液介质中由于本身各部分微区成分和电极电位的差异而产生不同区域的电位差，形成腐蚀原电池而引起的腐蚀。钢中的阳极区是组织中化学性较活泼的区域，例如晶界、塑性变形区、温度较高的区域等，相对应的晶内、未塑性变形区、温度较低的区域则为阴极区。显然钢的组织和化学成分不均匀会形成原电池，钢的电化学腐蚀也就是由于电化学不均匀性引起的。例如钢中碳化物、硫化物、夹杂物等第二相和基体，晶内和晶界都会产生电极电位差；变形和应力的不均匀分布也会造成各部分之间产生电极电位差。微阴极和微阳极电极电位差越大，阳极电流密度越大，钢的腐蚀速度越大。
提高钢的耐腐蚀性的方法很多，如常见的表面处理（镀金属、涂油漆等非金属层、电化学保护），改变腐蚀环境和介质等。但在高温高压和强腐蚀性介质中工作的钢，最根本的办法是利用合金化原理，即在钢中加入Cr、Ni、Si等能提高金属电极电位的元素，减少微电池数目。当Cr在加入铁中形成固溶体时，其电极电位的突变式提高符合
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“n/8规律”，即Cr与Fe的摩尔比rCr达12.5%（1/8）、25%（2/8），……时，铁的电极电位突然显著升高，腐蚀则跳跃式地显著减低。考虑到钢中的C和Cr形成的一系列碳化物会夺走基体中的一部分Cr，一般不锈钢中的含Cr量均在13%以上。
铁素体不锈钢（ferriticgrade stainless steel）是指含铬大于14％的低碳铬不锈钢、含铬大于27％的任何含碳量的铬不锈钢，以及在上述成分基础上再添加有钼、钛、铌、硅、铝、钨、钒等元素的不锈钢，化学成分中形成铁素体的元素占绝对优势，基体组织为铁素体。铁素体型不锈钢在加热和冷却过程中基本没有α?γ转变，基体以体心立方晶体结构的铁素体组织（α相）为主，有磁性，一般不能通过热处理硬化，但冷加工可使其轻微强化，退火及时效状态的组织中则可见到少量碳化物及金属间化合物。铁素体不锈钢除具有不锈性和耐一般腐蚀性能外，其耐氯化物应力腐蚀、耐点蚀，耐缝隙腐蚀等局部腐蚀性能优良是此类钢耐蚀性方面的主要特点。与Cr-Ni奥氏体不锈钢相比，铁素体不锈钢不含镍或仅含少量镍，因而是一种节镍不锈钢；铁素体不锈钢的强度高，而冷加工硬化倾向较低，导热系数为奥氏体不锈钢的1.3～1.5倍，线膨胀系数仅为Cr-Ni奥氏体不锈钢的60％～70％。铁素体不锈钢可根据钢中铬含量的不同大致分为Cr11％～15％，Cr16％～20％和Cr21％～30％三类。也可按照碳和氮的（C+N）总含量，将高铬铁素体不锈钢分为普通纯度高铬铁素体型不锈钢（其碳的质量分数为0.1％左右并含少量氮）和超高纯度高铬铁素体型不锈钢（C+N总的质量分数≤0.025％～0.035％）两个系列。
铁素体不锈钢主要有：0Cr13、1Cr14Si、1Cr17、0Cr17Ti、1Cr17Ti、1Cr17Mo2Ti、1Cr25Ti、1Cr28等。其实在不锈钢的分类中（图××-1），除了奥氏体类不锈钢和奥氏体-铁素体（双相）类不锈钢外，还有一类马氏体不锈钢（如1Cr13、2Cr13、3Cr13、4Cr13、9Cr18等，其基体组织为马氏体，有磁性，可通过热处理调整其力学性能），从严格意义上讲，它们也应属于铁素体类不锈钢。因为实质上马氏体是碳在α-Fe（铁素体）中的过饱和固溶体，属铁素体的一种变形体，其体心立方晶格被固溶在其间的碳“挤”（晶格畸变）成了体心正方，二者的主要区别是能否通过热处理改变其力学性能（马氏体不锈钢能够通过热处理调整其力学性能）。在本章节中，我们还是尊重传统的分类，仅对铁素体不锈钢阐述，而把马氏体类不锈钢的焊接另作它述。
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图××-1 不锈钢类别的演化
2、铁素体不锈钢牌号及其化学成分
铁素体不锈钢的成分特点是含铬高，含碳量低，在加热和冷却过程中没有或很少有α?γ转变。铁素体型不锈钢的具体牌号可查阅有关国家标准。如GB3280-92（不锈钢冷轧钢板），GB4237-92（不锈钢热轧钢板），GB4239-91（不锈钢和耐热钢冷轧钢带）以及GB4238-92（耐热钢板（钢板及钢带标准规范））。最新的国标GB/TXXXX-XXXX《不锈钢和耐热钢牌号—化学成分》已在2006年4月由冶金工业信息标准研究院完成送审稿，并已在网上公布，其中的表3列出了铁素体类不锈钢和耐热钢牌号及其化学成分（见表××-1）；这里仅对其新旧钢号及化学成分特点作些简要说明。
新牌号08Cr13Al钢，即原牌号0Cr13（Al），是典型的铁素体不锈钢，在新牌号中，钢中的含碳量标明的更为准确具体。Al是在炼钢脱氧时加入的，做为脱氧剂，铝量适宜可使钢的脆性转变温度下移；当铝量高时（＞0.05％），则随铝量增加，钢的脆性转变温度提高。Al和Cr都是缩小和封闭γ相区的元素，即铁素体形成元素，可细化晶粒，对钢的晶界强化有贡献，能强烈抑制和推迟钢在回火过程中ε碳化物的生成和转变[3]。Al又是非碳化物形成元素，可固溶于α-Fe（铁素体）中或形成非金属夹杂物和金属间化合物（Al2O3、AlN、Ni3Al等），能形成与钢件表面牢固结合的Al2O3、Cr2O3等致密氧化膜，因而也是提高钢的抗氧化性能的重要元素。
新牌号08Cr11Ti（即原牌号0Cr11Ti）、新牌号08Cr11Ti、03Cr11Ti、03Cr11NbTi、03Cr12Ni等新钢种，由于加入了Ti和Nb强碳化物形成元素，它们会以离位析出的方式形成特殊碳化物。Ti会在钢中生成一种极稳定、结合力极强、细小且不易分解的碳化
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物TiC；Nb与碳形成NbC或Nb4C3，在高温下也极为稳定，仅次于碳化钛，它们不但使钢中的有效碳含量和实际碳含量降低，从而在铬含量稍高于10.5％时即能形成铁素体不锈钢，而且这些细小弥散的特殊碳化物颗粒能使钢的强度和硬度显著提高；Ti还能提高钢的抗晶间腐蚀能力和改善焊接性。
新牌号03Cr12（即原牌号00Cr12），新牌号12Cr15（即原牌号1Cr15），基本化学成分与0Cr13相近，仅是和其性能有所不同。新牌号12Cr17（即原牌号1Cr17），新牌号Y12Cr17（即原牌号1Cr17），其中“Y”表示易切削钢，其中Mn含量较高，为1.25％，S含量≥0.15％。
新牌号03Cr18Ti（即原牌号00Cr17），是比0Cr13铬含量较高的超低碳铁素体不锈钢。
新牌号12Cr17Mo（即原1Cr17Mo）、新牌号12Cr17MoNb和03Cr18MoTi都加入了0.75~1.25％左右的钼，Mo在钢中存在于固溶体中，也可以形成碳化物。当钼含量较低时，与碳、铁形成复合渗碳体，当含量较高时，则形成其特殊碳化物，有利于热强性。
新牌号03Cr18Mo2NbTi（即原00Cr18Mo2），新牌号20Cr25N（即原2 Cr25N），新牌号01Cr27Mo（即原00Cr27Mo），新牌号01Cr30Mo2（即原0030Mo2），铌在周期表中和钒同族，因此性能与钒有较多相似之处。铌和钼在矿石中总是共生，在冶炼提取时难于分离，所以作为炼钢用的铁合金中，两者是并存的，铌与碳形成NbC或Nb4C3，在高温下极为稳定，仅次于碳化钛。低合金钢中加入少量的铌，对蠕变极限和持久强度有良好的影响，特别是钒与铌复合加入时，其效果更为明显。
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