07MnNiCrMoVDR钢焊接热影响区性能预测和工艺参数的优化

采用热模拟技术对07MnNiCrMoVDR钢焊接热影响区的组织转变和低温韧性进行了研究.结果表明,粗晶区的低温韧性最差,临界区和临界粗晶区的低温韧性相对较好.在小热输入和较高的预热温度工艺下,能够得到最佳的低温冲击韧性.文中给出了热影响区如上三个局部脆化区的性能预测模型,在相当的工艺参数下对组织性能有一定的预测价值.最后以低温韧性最优解作为目标函数优化了焊接工艺,小热输入和高预热温度是焊接的最佳工艺参数.     

Ni9钢焊接热影响区低温韧性的研究

采用焊接热模拟技术、-196℃示波冲击试验、金相显微分析、透射电镜分析技术考察了Ni9钢焊接热影响区粗晶区(CGHAZ)的低温韧性及其与焊接热循环的关系。结果表明,焊接热循环次数以及二次焊接热循环的峰值温度是影响其CGHAZ低温韧性的主要工艺因素;二次热循环在适当的峰值温度作用下促使钢原焊接粗晶区组织分解,并在晶界位置获得部分富Ni回转奥氏体,是原焊接粗晶区低温韧性得以改善和提高的组织成因。     

Ni9钢焊接热影响区低温韧性的研究

采用焊接热模拟技术、-196℃示波冲击试验、金相显微分析、透射电镜分析技术考察了Ni9钢焊接热影响区粗晶区（CGHAZ）的低温韧性及其与焊接热循环的关系。结果表明，焊接热循环次数以及二次焊接热循环的峰值温度是影响其CGHAZ低温韧性的主要工艺因素；二次热循环在适当的峰值温度作用下促使钢原焊接粗晶区组织分解，并在晶界位置获得部分富Ni回转奥氏体，是原焊接粗晶区低温韧性得以改善和提高的组织成因。     

焊接热循环对09MnNiDR钢热影响区低温韧性的影响

利用Gleeble-3800研究了焊接热循环对09MnNiDR钢焊接热影响区粗晶区（CGHAZ）和中间临界再热粗晶区(IRCGHAZ)低温韧性的影响. 结果表明,热输入为15 kJ/cm、层间温度为150 ℃时,CGHAZ组织形态为板条状马氏体+下贝氏体,下贝氏体的存在限制了马氏体的生长,提高了低温韧性,而IRCGHAZ继续保持了CGHAZ的组织. ?70 ℃冲击试验中,IRCGHAZ相比于CGHAZ具有较好的低温冲击韧性,热输入为15 kJ/cm、层间温度为150 ℃时,冲击吸收能量最高为65 J. 根据热模拟结果,采用焊接热输入15 ~ 22 J/cm、层间温度为150 ℃的工艺参数对09MnNiDR钢进行焊接,?70 ℃冲击试验中热影响区冲击吸收能量值为101 J,冲击断口存在大量的等轴韧窝,具有较好的低温韧性;?70 ℃拉伸试验屈服强度为477 MPa、抗拉强度607 MPa、断后伸长率为28.5%,表现出较好的强度和塑性;硬度试验结果表明母材、焊缝和热影响区硬度依次增大,且没有软化现象.     

多次热循环对9Ni钢热影响粗晶区低温韧性的影响

采用焊接热模拟、电子显微分析、力学性能测试等技术手段,研究了国产9Ni钢在多种焊接热输入条件下焊接热影响粗晶区的低温韧性,讨论了多次焊接热循环对9Ni钢焊接热影响区组织性能的影响规律,以及不同焊接热过程中的组织特征和脆化倾向.研究结果表明,9Ni钢并不适合采用单道焊,在多道焊接过程中,后续焊道的热作用可以良好地改善其低温韧性,粗大晶粒组织的重结晶是提高低温韧性的主要因素.     

超低碳9Ni钢焊接接头低温韧性

针对新研制的通过淬火、中间淬火和回火处理工艺获得的超低碳9Ni钢,对其进行了实际焊接接头和模拟焊接热影响区低温韧性的研究.经-196℃低温夏比V形缺口冲击试验、金相显微观察、透射和扫描电镜分析.结果表明,单道焊粗晶区组织为粗大的板条状马氏体,低温冲击韧性较低.多道焊热影响区组织中,在马氏体板条间析出了逆转奥氏体,这种呈弥散分布的逆转奥氏体能细化晶粒、提高焊接热影响区的低温韧性.认为采用小热输入、多层焊、低的层间温度,可使焊接接头获得高的低温冲击韧性.     

焊接热输入对天然气储罐用钢接头冲击韧性的影响

以9Ni钢为研究对象,采用Gleeble-3500热模拟试验机制备了经不同热输入焊接热循环的粗晶热影响区(CGHAZ)样品,研究了t_(8/5)对高Ni天然气储罐用钢粗晶热影响区低温韧性的影响。利用SEM观察了不同t_(8/5)样品的冲击断口形貌,采用光学显微镜观察了热影响区的显微组织和Packet结构的形貌。结构表明,随着t_(8/5)的增加,试验钢焊接热影响区粗晶的韧脆转变温度降低,组织中出现粒状贝氏体,使马氏体形成的空间减小,细化了晶粒,提高了高Ni钢的低温韧性。     

10Ni8CrMoV钢热影响区粗晶区在二次焊接热循环中的组织转变与韧性

采用焊接热模拟试验及金相、透射电镜分析技术研究了10Ni8CrMoV钢一次热循环的粗晶区在二次热循环过程中的组织转变与韧性特征,结果表明:由于马氏体板条间奥氏体薄膜的存在,10Ni8CrMoV钢在二次热循环作用下仍具有良好的低温冲击韧度,再热粗晶区、临界再热粗晶区均未出现局部脆化现象。但试验钢临界再热粗晶区因发生组织遗传,其低温冲击韧度相对于一次热循环粗晶区稍有降低。     

热输入对9Ni钢焊接接头组织及低温冲击性的影响

采用不同焊接工艺对9Ni低温钢进行埋弧焊接,通过金相显微镜和扫描电镜对其焊缝和热影响区微观组织及断口形貌进行了观察,研究了热输入对焊缝组织及低温韧性的影响.结果表明,随着热输入的增大,9Ni钢的焊缝中枝晶偏析减弱,析出相含量减少,断口韧窝尺寸变大变深,使焊接接头低温冲击性升高.不同热输入下焊接接头各个部位-196℃的冲击吸收功也高于标准值,硬度均小于标准规定的400HV,均满足使用要求.研究结果对9Ni钢的实际焊接提供了理论依据,对正确制订焊接工艺具有一定的指导意义.     

10Ni8CrMoV钢热影响区粗晶区在二次焊接热循环中的组织转变与韧性

采用焊接热模拟试验及金相、透射电镜分析技术研究了10Ni8CrMoV钢一次热循环的粗晶区在二次热循环过程中的组织转变与韧性特征，结果表明：由于马氏体板条间奥氏体薄膜的存在．10Ni8CrMoV钢在二次热循环作用下仍具有良好的低温冲击韧度，再热粗晶区、临界再热粗晶区均未出现局部脆化现象。但试验钢临界再热粗晶区因发生组织遗传，其低温冲击韧度相对于一次热循环粗晶区稍有降低。     

ASTM4130钢再热粗晶热影响区组织及韧性分析

采用金相、扫描电镜、透射电镜和焊接热模拟方法,研究了二次热循环对ASTM4130钢焊接粗晶热影响区(CGHAZ)显微组织、冲击韧性和断口形貌的影响.结果表明,再热粗晶热影响区低温冲击韧性均低于母材,发生热影响区整体脆化.临界粗晶区(IRCGHAZ)冲击吸收功损失分别为母材和CGHAZ的96.6%和37.9%,脆化现象最...     

超低碳QT钢焊接二次热循环的组织转变与局部脆化

采用焊接热模拟实验及透射电镜分析技术研究了一种超低碳QT钢在多道焊接二次热循环过程中的组织转变与韧性间的关系,结果表明,由于在一次焊接热循环过程中的晶粒粗化和未回火马氏体的形成,使得粗晶我的韧性明显降低,在多道焊的二次热物质 时,实验钢不存在临界粗晶区局部脆化现象,但表现为亚临界粗晶区局部脆化,引起亚临界粗晶区局部脆化的原因是碳化物的析出粗化和残余奥氏体的热失稳分解。     

欧标低合金结构钢粗晶热影响区组织和韧性的热模拟研究

利用Gleeble-3500热模拟试验机模拟粗晶热影响区的焊接热循环,研究了热输入对欧标低合金结构钢粗晶热影响区晶粒长大、硬度及韧性和组织的影响。结果表明,随着峰值加热温度的提高和高温停留时间的延长,奥氏体晶粒将发生不同程度的长大,粗晶热影响区的最高硬度也逐渐提高;同时随着t_(8/5)的延长,粗晶热影响区的组织将由少量低碳马氏体、针状铁素体以及粒状贝氏体和大量块状铁素体组织,逐渐转化为大量侧板条贝氏体、粒状贝氏体以及粗大长条状M-A组元,甚至出现一定数量的上贝氏体,使得粗晶热影响区的低温冲击韧度急剧下降,由低温韧性断裂转化为低温脆性断裂。     

热输入对WEL—TEN780A高强钢焊接热影响区断裂性能和组织的影响

研究了焊接热输入对ＷＥＬ－ＴＥＮ７８０Ａ高强度钢热影响区断裂性能的影响。结果表明,通过控制焊接热输入可以获得理想的焊接热影响区断裂性能。     

Effect of martensite–austenite constituent on toughness of simulated inter-critically reheated coarse-grained heat-affected zone in X70 pipeline steel

The inter-critically reheated coarse-grained heat-affected zone (ICCGHAZ) of X70 pipeline steel with different second peak temperature and heat input was simulated in this study by means of Gleeble3500 simulator. The volume fraction, size, shape and distribution of martensite–austenite (M–A) constituent were analysed. The toughness of ICCGHAZ and corresponding fractographs were examined. The results showed that the distribution of M–A was strongly influenced by second peak temperature, and M–A constituent with necklace structure at lower second peak temperature led to worse toughness. The volume fraction and size of M–A were strongly affected by heat input, the volume fraction of M–A constituent increased with the increase of heat input; the volume fraction and size of M–A were key factors of toughness deterioration; the interfacial energies and the initiation of crack were related to the shape of M–A constituent.     

Evaluation of cryogenic fracture toughness in SMA-welded 9% Ni steels through modified CTOD test

As the first step of the study for the safety performance of LNG storage tank based on the concept of fitness-for-purpose, the change of cryogenic toughness within the X-grooved weld HAZ (heat-affected zone) of SMA (shielded metal arc)-welded QLT (quenching, lamellarizing, and tempering)-processed 9% Ni steels, was investigated qualitatively and quantitatively. In general, CTOD (crack tip opening displacement) test is widely used to determine the fracture toughness of steel weldments. But there is no standard or draft for evaluating the toughness of thick weldment with X-groove such as in this case. Therefore, in this study, modified CTOD testing method for fatigue precracking. calculation of CTOD, examination of fractured specimen was proposed and used. And the results of modified test were compared with those of conventional CTOD test and Charpy V-notch impact test. In addition, the relationship between the fracture toughness and microstructure was analyzed by OM, SEM and XRD. The cryogenic toughness in HAZ decreased as the evaluated region approached the fusion line from base metal. The decrease in toughness was apparently caused by the reduction of the retained austenite content and the absence of grain refinement effect in the coarse-grained zone in HAZ. The austenite reduction resulted from the decrease in nucleation sites for α’γ reverse transformation due to the increase in fraction of coarse-grained zone within HAZ. More complex thermal cycles in the mixed zone of weld metal and base metal caused the poor stability of retained austenite in the zone by the redistribution of alloying element in retained austenite. Due to this reason, the toughness drop with decreasing test temperature in F.L. (fusion line)-F.L.+3 mm was larger than that in F.L.+5 mm and F.L.+7 mm.     

大线能量焊接DH36钢焊接热影响区组织与性能研究

利用双丝埋弧焊接试验,对比分析了传统DH36钢和大线能量焊接DH36船板钢焊接热影响区的组织与性能。结果表明,利用新型的Ti处理技术生产的大线能量DH36钢母材具有良好的强韧性和大线能量焊接性。经大线能量(100 kJ/cm)焊接后,传统DH36钢焊接热影响区低温韧性显著降低,不能满足指标要求(34 J)。大线能量DH36船板钢在50 kJ/cm和100 kJ/cm热输入焊接时均表现出良好的低温韧性,-20℃冲击功大于100 J。同传统的DH36钢相比,大线能量DH36钢焊接接头出现了软化区,但接头强度并未显著下降。总体上大线能量焊接DH36钢优越性在于:大线能量焊接时,焊接热影响区主要得到大量交错排列的晶内针状铁素体组织,热影响区硬度降低,低温韧性显著提高。     

Carbide and hardness development in the heat-affected zone of tempered and postweld heat-treated 2.25Cr-1Mo steel weldments

The temper-bead and the conventional weaving, multipass welding procedures have been developed to eliminate postweld heat treatment (PWHT) of creep resistant 2.25Cr-1Mo steel. Both procedures aim to refine and temper the heat-affected zone (HAZ). The temper-bead procedure resulted in a martensitic HAZ and a homogeneous fine-grain size. Hardness was not decreased by high heat input weaving fillout passes. Upper bainite developed in the conventional weaving HAZ, although grain refinement was inhomogeneous and some martensite was present. However, the conventional weaving procedure appears to produce a lower as-welded hardness than the temper-bead procedure. The carbides within the temper-bead HAZ aged more rapidly than those in the conventional weaving HAZ as a result of the initial martensitic temper-bead HAZ microstructure. Previous work indicated that the temper-bead HAZ toughness decreased after 1000 h of tempering at 538°C. This correlated with the coarsening and the agglomeration of the carbides. The maximum hardness occurred within the as-welded coarse-grained HAZ. The PWHT resulted in the greatest decrease in hardness and also reduced hardness variability throughout the HAZ. The hardness decreased to postweld heat-treated values after approximately 1000 h at 538°C and softening was associated with the precipitation and coarsening of acicular carbides and the development of coarse grain-boundary carbides.