热处理对9Cr低活化马氏体钢组织和力学性能的影响

研究了热处理对9Cr低活化马氏体钢显微组织和力学性能的影响.用光学显微镜和扫描电子显微镜观察了材料的显微组织、拉伸断口和冲击断口;用X射线衍射仪检测了材料的晶体结构.结果表明:9Cr低活化马氏体钢的晶粒尺寸从950℃的6.28μm增加到1200℃的66.5μm.两种热处理工艺(950℃×30min水冷+780℃×90min空冷和1050℃×30min水冷+780℃×90min空冷)处理后的9Cr低活化马氏体钢显微组织为全马氏体.二种工艺处理后拉伸力学性能相近,但冲击性能差别明显.二者的韧脆转变温度分别为-72℃和-62℃.选择950℃×30min水冷+780℃×90min空冷的热处理工艺能够提高9Cr低活化马氏体钢的冲击韧度.     

冷变形和再结晶退火对TP304钢晶粒度的影响

对TP304钢实施19%和25%的冷塑性变形后,分别在650℃、700℃、800℃及900℃下进行30 min再结晶退火,研究变形率和再结晶退火温度对TP304钢晶粒度的影响。结果表明,TP304钢在650℃、700℃及800℃下再结晶退火30 min,不能实现完全再结晶;900℃下再结晶退火30 min,可获得完全再结晶组织;19%冷变形+900℃再结晶退火30 min,TP304钢晶粒平均直径从40μm细化到22μm;25%冷变形+900℃再结晶退火30 min,TP304钢晶粒平均直径从40μm细化到17μm,二者晶粒度级别均由6级细化到8级,25%冷变形+900℃再结晶退火30 min的细化晶粒效果最优。     

1Cr18Ni9Ti奥氏体不锈钢冷变形与再结晶组织及性能

研究了1Cr18Ni9Ti奥氏体不锈钢加工硬化时组织的演变过程及其对性能的影响。结果表明，冷变形可提高钢的各种强度性能指标，尤其大大改善疲劳性能。经60％变形后，钢的疲劳强度提高了65％左右。随着加热保温时再结晶过程的进行，钢的强度下降而塑性逐步恢复。     

低活化铁素体/马氏体钢的静态再结晶行为

在Gleeble-3500热模拟试验机上采用双道次压缩试验对低活化铁素体/马氏体（RAFM）钢在高温热变形道次间隔时间内的静态再结晶行为进行了研究,分析了不同间隔时间、变形温度、应变速率和变形量等因素对静态再结晶行为的影响。采用2%应力补偿法计算了不同变形条件下,钢的静态再结晶软化百分数。结果表明,在其它变形条件不变的情况下,道次间隔时间的延长、变形温度的升高、应变速率的增大及变形量的加大均加速静态再结晶软化行为的进行;RAFM钢静态再结晶激活能为293 335 J/mol,通过对试验结果进行回归建立了静态再结晶动力学模型,且模型计算值与实测值吻合良好。     

1Cr18Ni9Ti冷拉钢丝的再结晶退火

探索了再结晶退火加热温度和保温时间对?0.4 mm的1Cr18Ni9Ti冷拉钢丝力学性能的影响。将再结晶退火保温时间设置为6 min不变,再结晶退火加热温度在800～940℃范围内变化时,钢丝的抗拉强度随着加热温度升高逐渐下降,伸长率随着加热温度升高呈现先升高后下降趋势;将再结晶退火加热温度设置为860℃不变,再结晶退火保温时间在1～14 min范围内变化时,钢丝的抗拉强度随着保温时间延长逐渐下降,伸长率随着保温时间延长呈现下降趋势。1Cr18Ni9Ti冷拉钢丝采用不完全再结晶退火工艺时,通过"进炉计时"替代常规的"到温计时"方式,能够获得相对稳定的力学性能。     

再结晶退火对冷变形00Cr22Ni5Mo3N双相不锈钢显微组织的影响

对一定冷变形00Cr22Ni5Mo3N双相不锈钢再结晶退火后的显微组织进行了研究.结果表明:退火温度从1000℃开始依次增加50℃至1200℃,通过XRD的检测,确定了试样组织由β、γ两相组成,在再结晶退火温度下没有新相产生;经退火处理后得到大小均匀的等轴晶;在较高退火温度下的铁素体的体积分数明显比在较低退火温度下的铁素体的体积分数要高;较低退火温度比较高退火温度的品粒细化的效果要好.在较高退火温度下导致晶粒的长大;不同的再结晶退火温度与试样的显微硬度表现出复杂关系.     

冷变形低碳马氏体钢的回火塑性

研究回火温度对15钢冷变形低碳马氏体塑性的影响.获得板条马氏体的试样经大量冷拔变形后在200～600℃进行了回火处理并测试了抗拉强度和伸长率.结果表明,随回火温度的提高拉伸强度连续降低,且伸长率在200～500℃范围内始终保持不变,当回火温度超过500℃后伸长率才开始急剧上升.而未冷变形的低碳马氏体钢在同温度范围回火时其伸长率随回火温度的提高连续增长.透射电镜分析结果表明,这种冷变形低碳马氏体的回火特性是,由于马氏体再结晶晶界上大量析出渗碳体所致.     

正火温度对低活化马氏体钢组织及力学性能的影响

对低活化马氏体钢丝材进行1000~1100 ℃保温60 min的正火处理,随后在790 ℃保温90 min进行回火处理,研究正火温度对低活化马氏体钢丝的显微组织及力学性能的影响。结果表明,正火后,丝材的显微组织由粒状珠光体转变为板条状马氏体,碳化物粒子大部分回溶于基体中,正火温度的升高加速碳化物粒子的回溶,在1100 ℃实现完全回溶;原奥氏体晶粒尺寸随正火温度升高显著增大(由1000 ℃的7.4 μm增至1100 ℃的34.9 μm)。回火处理后,马氏体板条尺寸变宽,板条间的位错密度显著降低,析出相沿晶界、晶粒内部析出、球化及长大,其中M₂₃C₆(M以Cr为主)相为短棒状,分布在晶界,而MX(M以Ta为主)相为椭球状,分布在马氏体板条内部。经1000 ℃×60 min正火+790 ℃×90 min回火后能够获得最佳的综合力学性能,其抗拉强度为745.7 MPa,断后伸长率为18.9%。     

冷变形钢件的球化退火

针对目前常规球化退火工艺周期长、能耗大、效率低的弊病,经过一系列工艺试验,推荐了一种适于冷拉钢丝、冷轧薄带的低于临界温度的球化退火新工艺。它不仅工艺简单、质量稳定,且省时节能,很值得推广应用。     

Metallurgical characterization of Ti-bearing 9Cr low activation martensitic steel

Two heats of low activation martensitic (LAM) steels with Ti and Ta (denominated as 9Cr-Ti and 9Cr-Ta),respectively,developed as candidate structure materials for nuclear reactor were characterized.This paper was focused on the effect of titanium on the microstructures and mechanical properties of 9Cr LAM steel in as-received condition (normalized at 950 ℃ for 30 min with water quenching plus tempered at 780 ℃ for 90 min with air cooling).Chemical analysis and microstructure observation were conducted on 9Cr-Ti and 9Cr-Ta with optical microscopy,X-ray diffraction analysis,scanning electron microscopy and transmission electron microscopy.Impact properties and tensile strengths were measured with Charpy impact experiments and tensile tests.The results indicated that 9Cr-Ti and 9Cr-Ta were fully martensitic steels in as-received condition.MX type and M23C6 type precipitates were observed distributing along boundaries of prior austenite grains and martensite laths in 9Cr-Ti.The addition of titanium accelerated the precipitation of TiC and TiN,and produced much finer grains in 9Cr-Ti than 9Cr-Ta at the same normalization temperature.Mechanical properties tests showed the ductile brittle transition temperatures of 9CrTi and 9Cr-Ta were about-90 ℃ and-85 ℃,respectively.The ultimate tensile strengths at room temperature and 600 ℃ were 680 MPa and 365 MPa for 9Cr-Ti,and 660 MPa and 335 MPa for 9Cr-Ta,respectively.The favorite impact toughness and tensile properties of 9Cr-Ti could be attributed to the fine grains in as-received condition.     

Effect of alloying on the properties of 9Cr low activation martensitic steels

Two types of 9Cr low activation martensitic steels (named 9Cr-1 and 9Cr-2) were developed in University of Science and Technology Beijing. 9Cr-1 and 9Cr-2 were produced by vacuum induction melting method, and examinations of the microstructures were carried out with X-ray diffraction analysis, optical microscopy, scanning electron microscopy and transmission electron microscopy. The ultimate tensile strength and yield tensile strength were evaluated with tensile tests. The impact properties were characterized with Charpy impact experiments. The results indicated that 9Cr-1 and 9Cr-2 on as-received condition (95℃/30~min/water quenching plus 780℃/90~min/air cooling) were fully martensitic steels free ofβ-ferrite. The ultimate tensile strength of 9Cr-1 and 9Cr-2 were 695~MPa and 680~MPa, respectively. However, 9Cr-2 showed a fine grain size of 4.8 μm, and its value of ductile-brittle transition temperature (DBTT) was -90℃ under as-received condition. The additions of vanadium, titanium and boron accelerated the formation of MX precipitates and resulted in fine grains and precipitates. The fine grains effectively reduced the value of DBTT from -60℃ to -90℃ with identical upper shelf energy (USE). The decrease in silicon concentration of 9Cr-2 induced a slight reduction in ultimate tensile strength from 695 MPa to 680 MPa.     

低碳Ti-Mo微合金马氏体钢的热变形行为

利用Gleeble-3800热模拟试验机对试验钢在950~1100 ℃,应变速率为0.1~5.0 s^-1,最大应变量为60%的条件下进行了热压缩模拟试验。结果表明：高变形温度、低应变速率和大变形量有利于动态再结晶,试验在1050 ℃、变形量60%、变形速率1 s^-1条件下得到圆整均匀再结晶晶粒,平均晶粒尺寸为14.84 μm;推演出低碳Ti-Mo微合金马氏体钢的形变激活能为462.8 kJ/mol及Z参数与动态再结晶变形条件的关系;建立起试验钢动态再结晶临界应变公式ε_c=0.3729Z^0.3496。     

13Cr超级马氏体不锈钢热压缩变形行为与组织演变

通过Gleeble-3500热模拟试验机对13Cr超级马氏体不锈钢进行单道次压缩变形试验,系统研究变形温度在950~1150 ℃、应变速率为0.001~10 s^-1条件下的热变形行为。利用双曲正弦模型建立了13Cr超级马氏体不锈钢的流变应力本构方程,求得试验钢的热变形激活能为412 kJ/mol,并基于动态材料模型(DMM)理论绘制了材料的热加工图,得出材料的最佳热变形工艺参数窗口为:变形温度1032~1072 ℃,应变速率0.039~0.087 s^-1。组织演变结果表明,试验钢在高变形温度和低应变速率的条件下,容易发生动态再结晶。当应变速率一定时(0.01 s^-1),变形温度从950 ℃升到1050 ℃,动态再结晶的体积分数从18.7%升高到60.1%,组织的再结晶程度提高,晶粒均匀细小;当变形温度一定时(1050 ℃),随着应变速率的降低,动态再结晶的晶粒长大粗化。     

9Cr马氏体耐热钢膨胀-温度曲线上的斜率变化研究

9Cr马氏体耐热钢在发生α→γ相变前的升温过程中其膨胀-温度曲线的斜率发生了偏折,偏折点处的温度为660 ℃左右.采用相同的升温速率将该钢样品升温至600、660和750℃三个温度,保温15 min后水淬,利用金相显微镜和扫描电镜分析各样品中组织的差异.研究结果表明,9Cr钢加热至660 ℃和750℃的样品中析出相的数量较600℃明显增加,因此钢中碳氮化物在偏折点温度处的大量析出是膨胀曲线斜率发生明显改变的原因.     

Cr微合金化低碳钢热变形行为

采用Gleeble-3500热模拟机对一种含微量合金元素Cr、Mn、Ti的低碳钢在变形温度700～1050℃.应变速率0.01～0.1s~(-1)条件下的热变形行为进行研究.结果表明:单相奥氏体区和铁索体区,峰值应力随变形温度的降低而升高,在两相区,峰值应力随着变形温度的降低而降低;在775～850℃与950～1050℃的温度区间,峰值应力的大小基本相当.建立了热加工图,并通过组织观察对其热加工图进行了解释.根据流变应力曲线,确定了试验低碳钢铁素体区的热变形激活能和热变形方程.     

中国低活马氏体钢熔化焊接头硬度与微观组织

针对4 mm厚的中国低活马氏体钢,采用TIG焊接方法分别对预热和未预热两组试样进行了焊接和焊后回火处理,对焊接接头的硬度和微观组织结构进行了测试和观察.结果表明,焊缝区硬度值偏高,靠近母材的热影响区出现较窄的软化带;焊接接头金相组织为板条特征明显的回火马氏体组织,未预热试样的马氏体含量与预热试样相比较,两者之间没有明显的差异.在晶内和晶界处分布大量的碳化物,焊缝区为尺寸较小的棒状,母材和热影响区为尺寸较大的颗粒状,接头的组织和碳化物的析出对焊接接头的硬度有很大的影响.

Abstract：

The preheated and non-preheated 4 man China low activation martensitic steel (CLAM) plate were welded by TIG welding and post-weld heat treating, and the hardness and micrcstructure in welded joint were tested and observed. The results show that the hardness in the weld metal is higher and the softening band in the heat-affected zone (HAZ) closing to the base metal. The tempered lath martensite is observed in welded joints. There is no significant difference in martensite content between the preheated and non preheated weldments. A large amount of carbide particles are observed in the grains and at the grain boundary. The carbides are small rods in weld metal and large granular in the HAZ and base metal respectively. The mierostrueture and carbides in welded joints have great effect on the hardness.     

低活化马氏体钢真空扩散焊接工艺

在不同工艺参数下对低活化马氏体钢进行真空扩散焊接试验,通过比较试样显微组织形态、界面结合率及抗拉强度,探究焊接温度、焊接压力对接头组织演化及力学性能的影响. 结果表明,马氏体组织在扩散焊接过程中发生了奥氏体化现象,且焊接温度越高时,奥氏体化程度越高;在一定范围内,提高焊接温度及焊接压力均可增强原子的自扩散效果,从而提升焊缝接头的力学性能,其中焊接温度1 000 ℃,焊接压力20 MPa,保温时间120 min参数下焊接试样的抗拉强度达到1 013 MPa,焊接面结合状况良好.     

中国低活化钢激光焊接接头微观组织与硬度分析

采用功率为4 kW的Nd:YAG激光器,对6 mm厚CLAM钢板采用不同的焊接参数进行了激光焊接试验,焊后对部分试样进行回火处理.分别对焊后和回火试样的硬度和微观组织结构进行了测试和观察.结果表明,回火处理前焊接接头金相组织主要为粗大的板条马氏体,随着焊接速度的提高,焊缝硬度有所提高;回火处理后焊接接头金相组织为板条特征明显的回火马氏体,使用扫描电镜对回火后焊接接头进行观察发现在原奥氏体晶界和马氏体板条上有碳化物析出,导致焊缝区的硬度相对母材略有提高,焊接热影响区未出现软化现象.     

低活化马氏体钢真空扩散焊接头力学性能

在不同焊接工艺参数下对低活化马氏体钢进行真空扩散焊接试验,分别对焊缝区进行光学显微观察(OM)与扫描电镜观察(SEM)分析,并对焊件进行力学性能测试. 结果表明,低活化马氏体钢的焊后组织主要为板条马氏体及少量的残余奥氏体,焊缝结合状况良好;在一定范围内提高焊接温度、延长保温时间可以提升接头抗拉强度,但过高的温度及保温时间会导致奥氏体晶粒粗化,损害接头的抗拉强度及冲击韧性. 经过焊后热处理(正火+回火)的接头抗拉强度相对于热处理前有所降低,但组织稳定性及冲击韧性有一定改善.