GH34钢的热—机械疲劳性能和等温低周疲劳性能

本文研究了珠光体耐热钢GH34的热—机械疲劳性能。热—机械疲劳试验在最大应变与最高温度同相位和逆相位两种情况下进行。控制波形为三角波,频率为0.008Hz,温度范围为200(?)550℃。GH34在淬火+高温回火状态下,经受热—机械循环,表现出循环软化的特性。热—机械疲劳时的循环应变硬化指数,大于上限温度的等温循环应变硬化指数。同相位和逆相位热—机械疲劳抗力相差不大,但都稍高于550℃等温循环时的疲劳抗力。用550℃等温低周疲劳寿命代替200(?)550℃的热—机械疲劳寿命是可行的,且结果偏于安全。     

3Cr2W8V钢热疲劳特性的研究

本文研究了3Cr2W8V 钢的热疲劳特性。试验结果表明,热疲劳裂纹优先萌生于热应力最大和弱化最严重的局部地区。在一定尺寸范围内,裂纹的亚稳扩展速率近似是常数。裂纹扩展方式除条带模型外,还有不连续突进。长期冷热循环引起钢软化,软化机理是累积回火,热应力对循环软化有加速作用。热疲劳抗力随热处理温度改变呈非单调变化,分别有一个最佳淬火温度和最佳回火温度。随着循环上限温度的升高,热疲劳抗力显著下降,最佳回火温度向高温方向移动,最佳淬火温度基本不变。热疲劳抗力主要取决于材料的高温屈服强度,在强度、塑性及循环热稳定性取得适当配合时最大。     

A100钢镀Cr防护技术在海洋环境下的腐蚀行为研究

通过海南户外暴露实验研究了A100钢表面镀铬层的腐蚀行为.使用扫描电镜观察了腐蚀后镀层的表面和截面形貌,利用交流阻镜技术表征了镀层在不同腐蚀阶段的特征;并讨论了腐蚀对力学性能的影响.结果表明:镀层表面存在的显微裂纹是腐蚀发生、发展过程中的主要影响因素,腐蚀对镀层力学试样的力学性能影响很大,导致抗拉强度降低,断口呈脆性断...     

Fatigue Failure of 321 Stainless Steel Superheater Tubes from a Thermal Incinerator

Several boiler superheater tubes showed circumferential cracking at weld seams after 2 years in noncontinuous service (several shutdowns). On-site inspection revealed that several tubes were cracked and leaked; while many others were cracked, however, the severity was less pronounced. Two types of superheater tubes samples were collected: one with butt-welded tubes and the other with fillet-welded sleeve. The latter was found to be out of the boiler fireplace, and the sleeve was used as tubing support to the boiler shell. Detailed investigation showed that the butt-welded tubes contained circumferential fatigue cracks that initiated from the internal surface. The cracks initiated in the heat-affected zone and propagated as a result of tube vibration. The variations in the tube internal diameter and tube wall thickness are expected to play a role in tube fatigue failure. On the other hand, tubes with fillet-weld sleeve showed circumferential cracking as a result of fatigue crack initiation from weld defects on the tube external surface. The high vibration during several unscheduled shutdowns in addition to several other factors such as variations in tube inside diameter, wall thickness, and weld defects resulted in the initiation and propagation of fatigue cracks and premature failure. White deposits, similar to those observed when boiler tubes failed by caustic exposure, were seen in the vicinity of the tube cracks. Therefore, it was difficult to confirm whether the boiler tubes failed because of the fatigue cracks or because of the caustic salts (pH control chemical).     

Fatigue strength improvement of a hard chromium plated AISI 4140 steel using a plasma nitriding pre-treatment

The effect of a plasma nitriding (PN) pre‐treatment on the fatigue performance of hard chromium (HC) plated AISI 4140 steel has been investigated by conducting a series of rotary bending fatigue tests at a frequency of 95 Hz. hourglass shaped test specimens of 4‐mm diameter had been plasma nitrided at 510°C for 4, 8 and 12 h. It was found that HC‐plated specimens with a coating layer of 23 ± 2 μm thickness showed approximately 33% reduction in fatigue strength when compared to quenched and tempered (Q&T) specimens. An application of the PN pre‐treatment before the plating process was effective in improving the fatigue performance of HC‐coated steel. An improvement of 71% in the fatigue strength of pre‐treated specimens was recorded as compared with the specimens, which were HC plated only. The results also indicated that prolonged nitriding time did not cause better improvement in the fatigue performance.     

16Mn钢在空气和3.5% NaCl溶液中的疲劳行为

采用哑铃状平板试样,分别研究了16Mn钢在空气中和3.5%NaCl溶液中的疲劳行为,获得了S-N曲线,并对疲劳试样的表面和断口形貌进行了观察。结果表明:3.5%NaCl溶液(与空气相比)使16Mn钢的疲劳强度有较大程度的降低,在空气中16Mn钢的疲劳极限为200 MPa,而在3.5%NaCl溶液中该钢则不存在疲劳极限;空气中的疲劳试样只有一个萌生于试样表面基体的裂纹源,而3.5%NaCl溶液中该钢的疲劳试样一般有多个裂纹源,除了极少数萌生于试样表面基体处,其余均萌生于表面的点蚀坑;空气中疲劳试样裂纹扩展区的断口形貌以疲劳辉纹为主,而3.5%NaCl溶液中的则以沿晶开裂等脆性特征为主。此外还对空气中16Mn钢的疲劳极限进行了预测,预测值与试验值基本吻合。     

Ni-P化学镀层对20CrMo钢腐蚀疲劳强度的影响

对比研究了不经热处理和经热处理的Ｎｉ－Ｐ化学镀层对抽油杆用２０ＣｒＭｏ钢的腐蚀疲劳强度的影响。结果表明，不经热处理的Ｎｉ－Ｐ化学镀层明显提高了钢基体的腐蚀疲劳强度，但却降低了基体的疲劳强度。经热处理后，腐蚀疲劳强度有所下降。Ｎｉ－Ｐ化学镀层中的磷含量的电子探针测量和镀层的Ｘ射线衍射分析结果表明，Ｎｉ－Ｐ化学镀层为非晶态结构。此外，还用扫描电镜观察分析了疲劳断口。     

低合金高强度钢的微观组织和疲劳裂纹扩展行为

用透射电镜观察了３０ＣｒＭｎＳｉＮｉ２Ａ钢等温的微观组织，疲劳裂纹扩展行为、裂纹尖端塑性区和位错结构，结果表明，等温状态组织由马氏体和贝氏体组成。在一个奥氏体晶粒内一般存在四个板条领域、裂纹尖端的塑性区内存在主位错带，疲劳断裂的基本组织单元为板条晶或板条束。裂纹遇到板条束界时方向发生较大偏斜。     

贝氏体钢疲劳性能的研究进展

本文介绍了贝氏体钢的滚动接触疲劳裂纹,比较了贝氏体钢、珠光体钢和高锰钢的抗疲劳性能．     

Finite Element Simulation on Thermal Fatigue of a Turbine Blade with Thermal Barrier Coatings

In this paper, a finite element model was developed for a turbine blade with thermal barrier coatings to investigate its failure behavior under cyclic thermal loading. Based on temperature and stress fields obtained from finite element simulations, dangerous regions in ceramic coating were determined in terms of the maximum principal stress criterion. The results show that damage preferentially occurs in the chamfer and rabbet of a turbine blade with thermal barrier coatings and its thermal fatigue life decreases with the increase of thermal stress induced by high service temperature.     

硫酸盐三价铬镀液中次磷酸钠浓度对不锈钢阳极电化学溶出的抑制作用

为了进一步完善以316不锈钢为阳极的硫酸盐三价铬镀铬新工艺,考察了镀液中次磷酸钠等对316不锈钢阳极电化学溶出的抑制作用.利用Hull槽试验、能量射散谱(EDS)和扫描电子显微镜(SEM)研究了次磷酸钠浓度对镀层外观、组分和表面形貌的影响.结果表明,次磷酸钠可以有效地抑制316不锈钢阳极的电化学溶出:当其浓度为0.02...     

钢领镀铬故障处理一例

由于钢领形状复杂,曾长期使用象形阳极,在镀铬过程中出现了毛刺、发花、局部无镀层,镀层不均等质量问题.通过去掉象形阳极并改善挂具设计等手段,使产品成品率由40%提高到95%.     

不锈钢镀铬预处理新型活化液的电化学特性

不锈钢电镀铬的预处理--活化处理可有效去除不锈钢表面的钝化膜,解决镀层与基体的结合力问题.通过测定18-8不锈钢在各活化液中的稳态电位、腐蚀速度和阳极极化曲线,结合镀层综合性能的检验,获得最佳活化液配方:98～102 g/L (NH4)2SO4,85～90 g/L H2SO4(分析纯),5～6 g/L H3PO4(分析纯),5～6 g/L H2SiF6.该活化液的稳态电位为-0.55 V,腐蚀速率在12 h内为2 g/(m2·h),随后缓慢下降.它能有效去除不锈钢表面的钝化膜,且对不锈钢基体的腐蚀很小;用该配方活化的不锈钢电镀后,可获得光亮平滑、均匀致密、硬度较高、结合力好的镀铬层.     

高钨不锈钢合金电镀硬铬工艺

为了在高钨不锈钢基体上获得符合技术要求的电镀硬铬层,研制了一种特殊的镀铬新工艺.由于高钨不锈钢合金零件表面具有比一般不锈钢更不易活化的特性,采用前处理以及特殊的电镀方法能有效地解决这个问题.经试验得出的在高钨不锈钢合金上电镀铬层的各项性能数据均符合QQ-C-320的技术要求.实践证明,该工艺能较好地指导实际生产.     

Thermomechanical Fatigue Behaviour of a Nickel Base Superalloy

The isothermal low cycle fatigue (LCF)and thermomechanical fatigue (TMF) behaviourof a Ni-base superalloy was investigated. Theresults show that temperature plays an importantrole in both LCF and TMF. The alloy shows thelowest LCF fatigue resistance in the intermediatetemperature range (～760℃). For strain-controlledTMF, in-phase (IP) cycling is more damagingthan out-phase (OP) cycling. The high tempera-ture exposure in the TMF cycling influencesthe deformation behaviour at the low temperature.LCF lives at different temperatures, and IPand OP TMF lives are successfully correlatedby using the hysteresis parameter Δσ·Δε_p.     

金属结构中螺栓联接的疲劳设计

本文论述了金属结构中螺栓联接抗疲劳设计的必要性，介绍了受轴向变载荷作用的螺栓联接载荷计算及疲劳设计的方法，并用实例进行了分析论证。     

叠片结构对铜抗热疲劳性能的影响研究

研究了一种多层铜箔构成的叠片式表面结构, 与铜块体同时在10^-5Pa真空下进行电子束热疲劳, 电子束的功率密度28 MW/m², 循环3000次。采用扫描电子显微镜 (SEM) 对热疲劳后的铜箔与铜块体的表面损伤进行了分析, 结果表明, 由于铜箔处于单轴应力状态, 表面产生的热应力较小, 导致表面裂纹较细较少, 且多产生垂直于箔片方向的裂纹, 难以扩展。结合SEM照片, 利用计算机图片处理软件, 对叠片结构的铜箔与铜块体表面裂纹损伤进行了定量分析。结果表明, 叠片结构的铜箔表面的裂纹密度和宽度均远小于铜块体, 表现出更好的抗热疲劳开裂性能。而且, 铜箔的厚度越小其抗热疲劳开裂性能越优异。该思路将为解决面向等离子体、非晶甩带冷却辊等材料的热疲劳问题提供有益参考。     

13Ni马氏体时效钢的疲劳性能

本文研究了13Ni(2750MPa 级)马氏体时效钢的疲劳性能及其影响因素。研究结果表明,本合金的单向拉伸疲劳报限为σ(?)的1/4左右。时效条件、变形情况和钢中非金属夹杂物等均影响合金的疲劳性能。     

温度对GH34钢低周疲劳性能的影响

本文用应变控制的低周疲劳试验方法,研究了室温、350、450和550℃下,燃气轮机叶轮用钢GH34的低周疲劳性能。试验表明,各温度下的循环应力——应变特性均为循环软化。试验温度提高,低周疲劳性能下降。由于蓝脆性的发展,450℃的低周疲劳性能迅速下降,接近550℃的低周疲劳性能。COFFIN—MANSON方程中的指数α随试验温度提高而增大。高温低周疲劳裂纹的扩展,主要为Ⅱ阶段扩展,在所采用的试验条件下,没有发现蠕变引起的治晶疲劳断裂。     

热作模具钢DM的高温稳定性和热疲劳性能

研究了热作模具钢DM的高温稳定性和热疲劳性能。结果表明,DM钢在620℃热稳保温过程中马氏体板条内的薄片状M₃C型碳化物逐渐向条块状M₇C₃型碳化物转变,在板条的边界生成M₇C₃、M₂₃C₆型碳化物。DM钢的短循环周次热疲劳性能受控于位错重排和湮灭,长循环周次热疲劳性能受控于碳化物的粗化程度。DM钢中M₃C、M₇C₃、M₆C型碳化物的生成自由能分别为27765.5 J/mol、3841.5 J/mol、-7138.1 J/mol,表明在热稳保温与热疲劳试验过程中碳化物的演变机理一致,发生了M3C→M7C3→M6C类型演变。