高温时效对T23钢粗晶热影响区显微组织及再热裂纹敏感性的影响

利用热模拟机制备T23钢粗晶热影响区(CGHAZ)试样,对其进行650℃、0～48 h时效实验,对时效前后的试样进行高温短时蠕变破断实验,评价其再热裂纹敏感性,采用OM、SEM、TEM+EDS等手段分析CGHAZ在时效过程中的显微组织演变,对断口形貌及断口附近显微组织进行观察,分析合金元素在晶界附近的分布,揭示T23钢CGHAZ形成再热裂纹的机理,探究时效改善再热裂纹敏感性的原因.结果表明,T23钢CGHAZ在焊态下为马氏体/贝氏体混合组织,硬度较高;经650℃时效后组织发生回复及再结晶,位错密度下降,亚晶粒(板条)尺寸增大,M23C6、M7C3和MX碳(氮)化物等在晶内、晶界逐渐析出,硬度逐渐下降.焊态CGHAZ对再热裂纹敏感,时效后CGHAZ的再热裂纹敏感性下降;当时效时间超过24 h时,对再热裂纹不敏感.焊态CGHAZ产生再热裂纹主要是由于M23C6在晶界析出长大,导致晶界形成软化区,并促进孔洞的形成,减弱了晶间结合力.时效使不稳定的CGHAZ组织发生预先转变,碳化物大量析出,基体发生回复与再结晶,降低了晶内强度,同时晶界附近合金元素贫化消除,晶内和晶界强度的差异减小,塑性变形能力明显提升,故再热裂纹敏感性降低.CGHAZ时效后的硬度与再热裂纹敏感性有一定的对应关系,当硬度高于250 HB时对再热裂纹敏感,硬度低于250 HB时对再热裂纹不敏感.     

T23低合金耐热钢再热裂纹敏感性研究

试制了4种改进型即改变了碳、钨、钼、铬和铌含量的T23低合金耐热钢。试验用钢经锻造和轧制后,进行了1 060℃正火和770℃回火。检测了改进的T23钢和原T23钢的再热裂纹敏感性、拉伸性能和显微组织。结果表明:改进型T23钢的再热裂纹敏感性均小于原T23钢,并且其屈服强度、抗拉强度和断后伸长率均满足ASME要求。改进型T23钢中,含0. 045%C、2. 640%Cr、0. 630%Mo、0. 440%W和0. 020%Nb(质量分数)的D钢的再热裂纹敏感性最小,屈服强度和抗拉强度最高,分别为637和720 MPa。碳、铬、钨、钼和铌改善T23钢的再热裂纹敏感性的机制为:这些元素影响晶内MX析出相的数量、晶内的固溶强化以及晶界M_(23)C_6析出相的数量,从而改变晶内、晶界的强度差进而影响再热裂纹敏感性。     

T23钢再热裂纹敏感性的改善及其组织

通过高温时效方法分析了焊后未热处理T23水冷壁管焊接接头粗晶热影响区(coarse grained heat affected zone,CGHAZ)在服役过程中形成再热裂纹的微观机理,揭示了工程中未热处理T23水冷壁接头在机组启机后,短期运行容易发生开裂泄漏的内在原因. 采用材料表征手段对未时效和高温时效处理后的水冷壁焊接接头CGHAZ硬度、微观组织、析出物物相等进行系统分析. 结果表明,在530 ℃时效100 h后,CGHAZ硬度出现由晶内弥散强化导致的二次硬化现象,随着时效(运行)时间增加,CGHAZ硬度逐渐降低,但时效1000 h后,CGHAZ硬度仍有319 HV高于标准要求;在600 ℃温度下,随着时效时间的增加,CGHAZ硬度随之降低,组织回复、再结晶、马氏体板条宽化、位错密度降低、C元素及合金元素从基体析出等因素导致的CGHAZ硬度降低作用高于MX碳化物在晶内弥散析出导致的硬度升高,M₂₃C₆型碳(氮)化物在晶界、亚晶界逐渐析出和长大.

     

T23钢再热裂纹影响因素和预防措施的研究

通过试验研究了冶金因素和焊接工艺因素对T23钢再热裂纹的影响,化学成分w(Ti)和CSR对T23钢再热裂纹的影响比较明显,且有一定的规律性,根据这一规律性提出T23钢的优化措施,并总结了T23钢再热裂纹敏感性评判关系式;另外,焊接热输入对再热裂纹的产生也有一定的影响,热输入越大,T23钢产生再热裂纹的倾向越大。     

超超临界锅炉T23钢水冷壁管开裂分析

以超超临界锅炉SA213?T23钢水冷壁失效管为试验对象,通过宏观检查、化学成分分析、金相检验和硬度试验,分析失效原因。结果表明:该水冷壁管化学成分正常,材质性能未发生明显劣化;水冷壁失效原因为鳍片焊缝开裂,该裂纹为沿晶界扩展的再热裂纹,起源于焊缝熔合线附近的热影响区粗晶区域,先沿热影响区横向扩展,然后扩展至母材区域,最终导致管壁泄漏失效;热影响区粗晶区域显微组织为粗大的马氏体和贝氏体组织,硬度明显偏高于焊缝熔合线另一侧的焊缝区域,脆性增大。两者在显微组织和硬度上的明显差别,使焊缝熔合线附近的热影响区粗晶区域容易产生应力集中,在高温运行中发生晶间开裂。     

热处理温度对长期服役T23钢CGHAZ微观组织的影响

以服役时间超过6×10⁴ h的T23水冷壁管对接接头作为研究对象,对焊接接头进行不热处理(焊态)、520℃×1 h,580℃×1 h,650℃×1 h,720℃×1 h及760℃×1 h等6种不同参数的热处理试验。为研究不同热处理后粗晶热影响区(CGHAZ)微观组织变化,分析合金碳化物在晶界的分布规律,同时探索CGHAZ再热裂纹形成原因与析出物之间的内在联系,重点对粗晶区进行了显微硬度分析、金相组织分析、扫描电镜形貌分析及能谱分析。结果表明,焊态T23钢CGHAZ为粗大板条马氏体与贝氏体的混合组织,经测算最大晶粒尺寸约100μm,大部分晶粒尺寸30～50μm;在580℃热处理时,由于晶粒细化及析出物在晶内弥散强化作用,CGHAZ出现了二次硬化现象,根据再热裂纹形成理论,此时晶内强度与晶界强度差较大,应力松弛主要集中于晶界,CGHAZ产生再热裂纹的倾向较大;在720℃热处理时,在CGHAZ晶界位置出现了密集孔洞及合金碳化物,并且空洞与合金碳化物之间存在伴生关系,但短时间内孔洞在后续正常服役条件(560～600℃)下能否发展成为再热裂纹有待商榷。     

焊后热处理对T23钢热影响粗晶区微观组织的影响

采用Gleeble-3500热模拟试验机和热处理炉对T23钢进行了焊接热模拟和焊后热处理试验,并运用金相、硬度、扫描电镜试验,研究了不同的焊后热处理温度对T23钢热影响粗晶区(CGHAZ)微观组织的影响.结果表明,焊态热模拟CGHAZ组织类型主要是板条马氏体和贝氏体的混合组织,具有很高的硬度.随着热处理温度的提高,CGHAZ晶粒趋于细化,硬度逐渐降低.但在700℃下,晶界出现了微孔洞和含W碳化物,硬度剧烈升高,应避免在此温度进行热处理.最后确定T23钢合理的焊后热处理为750℃×2h,可以获得良好的强韧性匹配.     

07MnNiCrMoVDR钢再热裂纹敏感性试验

采用断面收缩率为判据,在热模拟试验机上用高温缓慢拉伸方法,研究了07MnNiCrMoVDR钢的再热裂纹敏感性.分别采用蠕变试验机和小铁研试验,并对研究结果进行了验证.结果表明,采用小热输入焊接时,该钢种对再热裂纹不敏感;大热输入情况下,该钢的再热裂纹敏感温度在600℃左右;实际焊接接头中一般不会出现再热裂纹.     

热模拟法研究07MnNiCrMoVDR钢再热裂纹敏感性

利用热模拟试验机模拟出了07MnNiCrMoVDR钢不同的热影响区组织,并对模拟组织进行高温缓慢拉伸试验,采用断面收缩率为判据,研究了该钢种的再热裂纹敏感性,验证了敏感温度下再热裂纹的实际存在.结果表明,采用小热输入焊接时,该钢种对再热裂纹不敏感;大热输入情况下,其再热裂纹敏感温度在600℃左右;实际焊接结构热处理应避开敏感温度区间以防止产生再热裂纹.     

600MW超临界机组T23钢末级再热器管焊缝裂纹分析

某电厂600 MW超临界机组锅炉末级再热器焊缝在运行过程中发生开裂,研究了焊缝起裂位置、宏观形貌、金相组织、力学性能等特征,确定该焊缝开裂属于再热裂纹性质,并提出了相应的防范措施.     

07MnNiVDR再热裂纹敏感性及试验

采用热模拟后缓慢拉伸试验、夏比摆锤冲击试验、插销试验以及小铁研试验等方法,研究了调质高强钢07MnNiVDR的再热裂纹敏感性.热模拟研究表明,采用小热输入焊接时,该钢对再热裂纹不敏感;大热输入情况下,敏感温度在600℃左右.插销试验表明,该钢具有一定的再热裂纹敏感性,敏感温度在600℃左右.热模拟试验和插销试验的结果一致,小铁研试验不适合试验材料的再热裂纹敏感性研究.热模拟后缓慢拉伸是判断材料再热裂纹敏感性的有效方法,插销临界断裂初应力对生产有指导意义.尽管未在小铁研试验中发现明显再热裂纹,对该钢实施焊后热处理还应慎重.     

Analysis on SH-CCT curves of HD15Ni1MnMoNbCu steel for nuclear power station

The microstructural evolution and Vickers hardness measurement in the welding heat-affected zone (HAZ) of HD15Ni1MnMoNbCu steel for nuclear power station were investigated by Gleeble-3180 thermal mechanical simulator, and the simulated HAZ continuous cooling transformation curves (SH-CCT) were measured simultaneously. With t_8/5 increasing from 3.75 s to 15 000 s, the product was obtained martensite, bainite, ferrite and pearlite, successively. The result of microstructure and Vickers hardness in the heat-affected zone was in good agreement with those measured by SH-CCT diagram with the heat input 16.2 kJ/cm as an example to weld the HD15Ni1MnMoNbCu steel pipe using TIG/SMAW/SAW welding methods.     

高温再热器用T23/TP347H异种钢管接头失效分析

针对某600 MW超临界机组锅炉运行约40000 h后,高温再热器T23/TP347H异种钢管接头出现的开裂泄漏失效情况进行了理化分析。结果表明,异种钢管焊接接头的失效原因主要是由T23钢管焊接热影响区再热裂纹引起的,裂纹沿钢管周向分布,起裂于T23侧热影响区的粗晶区,沿晶界扩展,呈典型的脆性断裂特征。     

Reheat cracking studies on simulated heat-affected zones of CrMoV turbine rotor steels

The reheat cracking susceptibility of the heat-affected zone (HAZ) of a CrMoV turbine rotor steel was investigated. Two base materials, one with a coarse-grain (155 μxm) and the other with a fine-grain (55 μim@#@) microstructure, were submitted to Gleeble HAZ weld simulations. Three peak temperatures were utilized: 1350,1150, and 950 °. Some samples were single cycled, and others were exposed to a double cycle. The samples that were double cycled experienced a second peak temperature 150 to 250 ° lower than the first peak temperature. The samples were then stressed in bending for different amounts and stress relieved under load to determine their reheat cracking susceptibility. All samples were metallurgically evaluated before and after the reheat cracking test. It was found that the prior-austenite grain size of the original base metal did not influence the reheat cracking susceptibility, but increases in peak temperature did. It was observed that the grain size and grain matrix microhardness that developed after the Gleeble cycles affected reheat cracking. It was found that reheat cracking did not occur when the microhardness was below 350 DPH and the prior-austenite grain size was less than about 80 μm.     

高强度桥梁钢焊接冷裂纹敏感性研究

通过冷裂纹敏感指数计算、热影响区最高硬度实验和斜Y型坡口实验分析了高强度桥梁钢Q460q的焊接冷裂纹敏感性。结果表明:Q460q冷裂纹敏感指数Pcm=0.17%,不产生冷裂纹的预热温度为60℃;常温和预热60℃条件下的热影响区最高硬度分别为282 HV和271 HV,均小于最大允许硬度410 HV;斜Y型坡口实验在室温条件下焊接时,焊缝表面裂纹率为0,平均断面裂纹率为7.8%,在60℃预热条件下焊接时,焊缝表面和断面裂纹率均为0。以上三种实验结果均表明高强度桥梁钢Q460q焊接冷裂纹敏感性较低。     

Oblique Y-groove cracking test of the welding cold cracking susceptibility of domestic X-70 pipeline steel

“Gas Transmitting From West to East Project“ is significant.it should ensure the welding quality and safety of pipeline.The task is very arduous to guarantee the quality of the projcet in the condition of long line.complex weather and geolgy features.in this paper,the welding cold cracking susceptibility of domestic X-70 pipeline steel adopted by the project, which is one of the most interesting questions of welding quality about petrol pipeline,was studied by means of oblique Ygroove cracking test.The crack ration of surface and section was tested under the conditions of different welding materials and preheat temperature.The thickness of plate stell was 14.7mm and 10.3mm.The results reveal that X-70 pipeline steel has good crack resistance.The research has important value for the construction of large-scale pipeline engineering and the application of domestic X-70 pipeline steel.     

二次热循环对X100管线钢粗晶热影响区组织与性能的影响

通过热模拟技术与显微分析方法研究了二次热循环对X100管线钢粗晶热影响区组织的影响规律,再热粗晶区的性能通过夏比V型缺口冲击试验表征。试验结果表明,当二次热循环的峰值温度处于(α+γ)两相温区,试验钢的临界粗晶热影响区出现局部脆化。局部脆化的原因主要有两个:一是临界粗晶热影响区组织粗化;另一是该区MA组元数量多,尺寸大,硬度高。