氮含量对高氮钢PMIG焊接头组织和性能的影响

文中采用H307Mo焊丝,开展了高氮钢PMIG焊接工艺试验,重点分析了焊缝中氮含量对接头组织和性能的影响,并通过调整工艺参数,控制焊缝中氮的含量.结果表明,当焊缝中氮含量低于0.24%时,焊缝以FA模式凝固,焊缝组织为骨架状铁素体枝晶和奥氏体基体组成,并且随着氮含量的提高,铁素体含量降低,显微硬度逐渐下降;当焊缝中氮含量高于0.30%时,焊缝以A模式凝固,组织为单相奥氏体枝晶组织,随着焊缝氮含量的提高,奥氏体枝晶不断增大,显微硬度逐渐提高.随着氮含量的提高,焊缝中气孔逐渐增多,冲击韧性呈现先增大后减小的趋势.     

冷却速度对奥氏体不锈钢Cr15Mn9Cu2Ni1N组织与凝固模式的影响

利用控制冷却速度的凝固实验,研究连铸坯奥氏体不锈钢Cr15Mn9Cu2Ni1N不同冷却速度下的组织和凝固模式.结果表明,缓慢冷却时,显微组织为奥氏体基体上分布着蠕虫状残留铁素体;其凝固模式为全部液相先析出δ铁素体,随后通过固相转变形成奥氏体基体.较高冷却速度时,奥氏体组织有两种形态,一是分布着侧板条残留铁素体的奥氏体,二是圈状的分布在第一种奥氏体晶界的单相奥氏体.分析发现,冷却速度的增加使凝固模式发生如下变化:大部分液相先析出δ铁素体,随后固相转变为奥氏体;剩余液相直接转变为奥氏体.同时发现,氮含量的增加可以减小奥氏体晶粒尺寸.     

Cr15Mn9Ni1N不锈钢焊接接头的组织及凝固模式

分析了Cr15Mn9Ni1N奥氏体不锈钢钨极氩弧焊接头的组织.结果表明:在靠近熔合线的热影响区,经过高温焊接热循环后析出较多的δ铁素体.大线能量时其范围增大;靠近熔合线焊缝金属的组织为奥氏体胞晶中分布着残留蠕虫状δ铁索体:焊缝中心区域为奥氏体树枝晶中分布着残留骨架状δ铁素体;大线能量接头的熔合线处的组织为奥氏体晶粒上分布侧板条形8铁素体,而小线能量时为奥氏体品粒.分析认为:焊缝金属的凝固模式为δ铁素体先从液相中析出,随后通过固态相变转变为奥氏体,未转变的残留δ铁素体以蠕虫状、骨架形或侧板条的形态分布于奥氏体中.Hammar-Svensson Cr、Ni当量公式适于预测这种钢焊缝金属的凝固模式.     

大厚度电子束焊接接头厚度方向的组织差异性

利用K110型电子束焊机焊接50 mm厚的304不锈钢板,并对焊接接头深度方向的微观组织及硬度进行分析. 结果表明,利用电子束焊接方法能够一次性焊透50 mm厚不锈钢板,得到成形良好的焊接接头. 焊缝深宽比较大,约为18:1. 焊缝组织由奥氏体和铁素体组成. 从焊缝上表面到深约39 mm处,铁素体形态依次为网状,板条状/骨架状和树枝状分布于奥氏体枝晶间或晶界处. 在焊缝的下层,亚稳的胞状奥氏体将取代稳定铁素体相作为初生相直接从熔体中析出. 沿焊缝中心深度方向,接头的凝固模式由primary ferrite with second-phase austenite,FA转变成primary austenite with second-phase ferrite,AF模式,晶粒尺寸减小,硬度呈波动性增加趋势.     

铁素体不锈钢/奥氏体不锈钢焊接接头的组织和性能

对443铁素体不锈钢与304奥氏体不锈钢焊接接头的显微组织以及其对显微硬度和冲击韧性的影响进行了研究。结果表明:焊缝显微组织由δ铁素体+奥氏体两相组成,焊缝不同区域δ铁素体形貌和含量存在明显差异;焊缝显微硬度随δ铁素体形貌和含量变化而变化,针状δ铁素体使焊缝显微硬度提高;443铁素体不锈钢母材及热影响区的冲击韧性较差,且随温度的降低,其冲击吸收功显著降低,室温时为韧性断裂,-20℃时发生脆性断裂。     

冷金属过渡丝弧成形奥氏体不锈钢工艺特征研究

采用冷金属过渡(CMT)焊接技术对奥氏体不锈钢进行了立体成形试验,重点研究了热输入对焊缝成形特征的影响规律。结果表明,随着热输入增大,单道焊缝熔宽明显增大,熔深略微增加,润湿角整体呈下降趋势。单壁墙堆焊层显微组织主要为枝状晶奥氏体和较多的骨架状δ铁素体。随堆焊层数增加,铁素体含量增加,而热输入较低时柱状枝晶细化,铁素体含量减少。随单壁墙层数的增加,低热输入下堆焊层硬度逐渐升高,大热输入下堆焊层硬度变化不明显。     

冷却速度对CAP1400核主泵泵壳用奥氏体不锈钢铸造组织的影响

采用OM、SEM和EPMA手段分析了CAP1400泵壳用奥氏体不锈钢在1480℃重熔后以不同速度冷却至1340℃后水冷的凝固组织,研究了不同冷却速度对铁素体相分数及成分的影响规律。结果表明,CAP1400泵壳用奥氏体不锈钢重熔后的凝固组织主要由奥氏体相和残余δ铁素体相组成。凝固速度越快,残余δ铁素体相含量越多,奥氏体含量越少,且粗大的奥氏体相变得更为细小。在同一凝固速度下,δ铁素相中Cr、Si、Mo、Mn元素含量均高于奥氏体相。随着凝固速度的加快,δ铁素体相和奥氏体相中的Cr含量升高,而Ni、Si、Mo、Mn含量的波动幅度较小。     

C-1.5Mn-2.5Ni-0.5Cr-0.5Mo合金焊缝组织的演化机制

利用光学显微镜、扫描电镜和透射电镜研究了C-1.5Mn-2.5Ni-0.5Cr-0.5Mo合金系焊缝金属的微观组织,并通过Thermal-calc软件计算焊缝金属Fe-Ni相图,进而研究了焊缝金属从液相凝固到室温组织整个相变过程。此外还测试了焊缝金属的基本力学性能。研究表明:液态金属初生相为δ-铁素体,并以柱状方式生长,形成δ-铁素体柱状晶。温度下降,δ-铁素体开始向奥氏体转变,奥氏体晶粒也以柱状方式生长,形成柱状奥氏体晶粒。温度继续下降,在奥氏体晶界处最先发生相变形成贝氏体,而奥氏体内部最后发生相变转变成马氏体。原奥氏体晶界形核以及贝氏体侧向形核导致贝氏体呈交织状分布。焊缝金属具有良好的低温韧性,这是因为组织中含有大量交织状贝氏体。     

应变强化对304不锈钢焊接接头应力腐蚀的影响

采用室温应变强化技术对304不锈钢焊接接头进行了5%, 10%, 15%, 20%, 30%的应变强化。通过磁性测试、金相检验、硬度测试和w(NaCl) 5%溶液应力腐蚀试验,研究了应变强化量大小对304不锈钢焊接接头应力腐蚀敏感性的影响。结果表明:304不锈钢焊接接头在应变强化过程中显微组织变化不明显,金相组织均为柱状奥氏体和δ铁素体双相组织,焊缝结晶模式为铁素体—奥氏体结晶模式;焊缝显微硬度都有明显增加,应力腐蚀敏感性总体呈增加趋势,但敏感性指数处于低应力腐蚀敏感性区域。这是由于焊接接头试样内部组织变化较小,但焊缝内部位错和缺陷的增加使得应力腐蚀敏感性指数有所上升,连续分布的网状δ铁素体阻断了应力腐蚀裂纹快速扩展的通道。     

高氮奥氏体不锈钢的δ相转变研究

分别用金相法和铁素体测量仪测量0Cr20Mn19N0.58高氮奥氏体不锈钢铸态、锻态和固溶态组织中的δ相含量。结果表明:不同测量方法下铸态和锻态组织的测量结果存在显著差异,而固溶态组织的测量结果基本相符。形成这一现象的原因是:0Cr20Mn19N0.58高氮奥氏体不锈钢的凝固模式为FA模式,该模式下凝固过程中生成的δ相在1000℃以下发生δ→σ+γⅡ的相转变,由磁性相转变为非磁性相;在1000℃以上会发生σ+γⅡ→δ的相转变,由非磁性相转变为磁性相。     

Solidification behaviour of laser welded type 21Cr–6Ni–9Mn stainless steel

The solidification mode and microstructures were characterised for various processing parameters for laser welding 21Cr–6Ni–9Mn stainless steel. Two heats with varying nitrogen content showed both primary ferrite and primary austenite solidification. Weld ferrite content varied from 1 to 11 vol.-%, and decreased as travel speed increased. Base metal nitrogen content affected both solidification mode and weld ferrite content. Nitrogen loss from the weld pool was found to range from 10 to 45%, and decreased with increasing travel speed. Solidification mode was dependent on both chemical composition and processing parameters. The solidification mode shifted from primary ferrite to primary austenite as travel speed increased due to increased undercooling. Solidification mode varied within welds with constant nitrogen content, and the change in solidification mode was attributed to changes in undercooling along the weld cross-section. It is proposed that the variation of solidification mode with undercooling is affected by both the solidification rate and thermal gradient.     

Comparison of two types of low-transformation-temperature weld metals based on solidification mode

Two types of low-transformation-temperature weld metals were devised, one associated with primary austenite solidification, the other primary ferrite solidification. The martensite start temperature of both low-transformation-temperature weld metals was about 125°C. Experimental results showed that low-transformation-temperature weld microstructure associated with primary austenite solidification was martensite with 8.0% retained austenite, whereas that one related to primary ferrite solidification primarily consisted of martensite and δ-ferrite. Accordingly, both welded joints had little distinction between distortion and residual stress, indicating that weld metal associated with primary ferrite solidification played the same function as primary austenite solidification on residual stress reduction. Moreover, the low-transformation-temperature weld metal associated with primary ferrite solidification had higher tensile strength and hardness than that based on primary austenite solidification.     

The effect of solidification behaviour of austenitic stainless steel on the solidification cracking susceptibility

0Introduction Oneofthemainproblemsinweldingausteniticstain lesssteelsishotcracking[1,2].Inweldingofsingle phase austeniticstainlesssteels,thetendencyofhotcrackingis moreserious[3].Inordertopreventhotcrackingofthis kindofmaterial,itwasattemptedtogaintwo p…     

低镍不锈钢激光-电弧复合焊接头组织性能研究

低镍含氮奥氏体不锈钢强度高,韧性佳,在化工装备及建筑装饰等领域广泛应用。为揭示保护气体对低镍含氮奥氏体不锈钢焊接接头微观组织和力学性能的影响机制,分别采用92%Ar+8%N2与95%Ar+5%CO2两种混合比例的保护气体对08Cr19Mn6Ni3Cu2N低镍含氮奥氏体不锈钢进行了激光-MAG电弧复合焊。研究表明：氮气的加入使焊接接头平均显微硬度有所下降;电弧收缩明显,焊接飞溅增加且体积增大,电弧稳定性变差;焊缝中奥氏体含量增加约20%,而铁素体枝晶变细,二次枝晶臂变短。焊缝组织中未发现σ相及氮化物析出;从四个晶面观察奥氏体晶粒尺寸也是由于氮气的加入而减小;焊接接头拉伸性能略微下降,但耐腐蚀性能提高。     

Brazing of UNS S32101 and UNS S32304 lean duplex stainless steels and UNS S32750 super duplex with AWS A5.3 BNi-7 (Ni–Cr–P) filler metal

Summary

Weld metals solidified in the ferritic-austenitic solidification mode (FA mode) have dual phases of ferrite and austenite in their as-solidified condition, where ferrite exhibits different morphologies depending on the chemical composition and welding conditions. This paper describes an investigation of the effect of the solidification and transformation sequence on the formation of final ferrite morphologies. Austenite is formed through either a eutectic reaction or peritectic reaction at the dendrite boundaries after the primary formation of ferrite. During the eutectic formation of austenite, the <100>_δ direction of the primary ferrite and the <100>_γ direction of the eutectic austenite are parallel to each other and lie along the growth direction of the primary dendrites. However, any specific lattice plane relationship between the two phases is not identified. During cooling after solidification, the austenite extends into the primary ferrite via solid-state transformation, and the final morphology of the ferrite is vermicular without any coherent orientation relationship between the primary ferrite and eutectic austenite. During peritectic formation of austenite, the Kurdjumov-Sachs orientation relationship is established between the primary ferrite and peritectic austenite, and the <100>_γ direction of the peritectic austenite is not parallel to the growth direction of the primary dendrites. During cooling after solidification, the primary ferrite transforms into austenite, and the final morphology of the ferrite is lathy, since the primary ferrite and peritectic austenite have a favourable coherent orientation.     

低镍含氮奥氏体不锈钢激光-电弧焊电弧特性及组织性能

采用100％Ar2,98％Ar+2％N2,92％Ar+8％N2,85％Ar+15％N2四种混合比例的保护气体对08Cr19MnNi3Cu2N低镍含氮奥氏体不锈钢进行激光-脉冲MAG电弧复合焊接,研究保护气体中氮气比例对焊缝中气孔数量、焊缝熔深和熔宽、电弧形态、微观组织及铁素体含量等影响机制.结果表明,随着保护气体中氮气...     

The Microstructure and Pitting Resistance of Weld Joints of 2205 Duplex Stainless Steel

2205 duplex stainless steel (DSS) was welded by submerged arc welding. The effects of both heat input and groove type on the ferrite/austenite ratio and elemental diffusion of weld joints were investigated. The relationships among welding joint preparation, ferrite/austenite ratio, elemental diffusion, and pitting corrosion resistance of weld joints were analyzed. When the Ni content of the weld wire deposit was at minimum 2–4% higher than that of 2205 DSS base metal, the desired ratio of ferrite/austenite and elemental partitioning between the austenite and ferrite phases were obtained. While the pitting sensitivity of weld metal was higher than that of base metal, the self-healing capability of the passive film of weld metal was better than that of the base metal when a single V-type groove was used. Furthermore, the heat input should be carefully controlled since pitting corrosion occurred readily in the coarse-grained heat-affected zone near the fusion line of welded joints.     

外层氧气引入对GPCA-TIG焊焊缝性能的影响

针对SUS304不锈钢,采用传统TIG焊和GPCA-TIG焊进行工件表面熔焊,对外层气体引入氧气的GPCA-TIG焊和传统TIG焊焊缝的氧含量、显微组织、拉伸性能和低温冲击韧性进行了测定. 结果表明,GPCA-TIG焊焊缝组织主要为奥氏体和铁素体,铁素体形态以骨架状和板条状为主. 外层引入氧气时,焊缝中的氧含量增加,耦合度为+2时焊缝中的氧含量高于耦合度为0时的,焊缝的抗拉强度均略低于母材的. 耦合度为0的GPCA-TIG焊焊缝冲击性能与传统TIG焊的相同,耦合度为+2的焊缝低温冲击韧性有所降低,达到传统TIG焊的85%.