800MPa级钢悬臂弯曲加载低周腐蚀疲劳表面裂纹扩展特性研究

在悬臂弯曲加载方式下,研究了800MPa级10CrNiMo结构钢在3.5%NaCl水溶液中的低周腐蚀疲劳表面裂纹扩展特性,采用金相显微镜、扫描电子显微镜及X射线能谱仪观察并分析了腐蚀疲劳试样断口,与空气中相同加载方式下该材料的低周疲劳表面裂纹扩展速率进行了比较,结果表明,在表面裂纹扩展初期,在3.5%NaCl水溶液中的表面裂纹扩展速率较空气中的快,但随着总应变范围的增加,这种快的趋势在逐渐减小,当总应变范围达到约1%时,在两种环境中的表面裂纹扩展速率基本相当;在表面裂纹扩展的后期,裂纹内部聚集了大量的腐蚀产物,该腐蚀产物主要为铁的氧化物,氧化物的存在增加了裂纹扩展的闭合效应,减缓了表面裂纹的扩展。     

EFFECT OF ENVIRONMENT ON THE BEHAVIOR OF FATIGUE CRACK GROWTH IN AN AS-ROLLED DUAL-PHASE STEEL

本文研究了一种热轧双相钢在空气和3.5%NaCl 溶液中的疲劳裂纹扩展行为,这种双相钢在空气中具有较好的疲劳裂纹扩展阻力。在3.5%NaCl 溶液中的门槛值比空气中高,这是裂纹内腐蚀产物的楔子作用所致。随着应力比的增加,门槛值降低,并符合应力比对门槛值影响的竞争模型。在较高△K 下,扩展速率符合Paris 公式。在3.5%NaCl 溶液中的腐蚀为活性腐蚀。     

环境对热轧双相钢疲劳裂纹扩展行为的影响

本文研究了一种热轧双相钢在空气和3.5%NaCl 溶液中的疲劳裂纹扩展行为,这种双相钢在空气中具有较好的疲劳裂纹扩展阻力。在3.5%NaCl 溶液中的门槛值比空气中高,这是裂纹内腐蚀产物的楔子作用所致。随着应力比的增加,门槛值降低,并符合应力比对门槛值影响的竞争模型。在较高△K 下,扩展速率符合 Paris 公式。在3.5%NaCl 溶液中的腐蚀为活性腐蚀。     

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。     

用示波冲击法测定42CrMo钢的冲击韧性

用示波冲击法测定了在冲击载荷下,淬回火态42CrMo钢的载荷-挠度曲线,并将冲击总功分成裂纹萌生功和裂纹扩展功;研究了回火温度对42CrMo钢回火组织与冲击韧性的影响。结果表明42CrMo钢在回火过程中,随回火温度升高,弹性功基本不变,裂纹萌生功略有升高,而裂纹扩展功迅速增加,42CrMo钢对缺口敏感,随回火温度升高,缺口敏感性降低,淬火态42CrMo钢经500—590℃回火,其组织由板条马氏体和条状及粒状θ-Fe_3C组成;冲击断口为准解理与韧窝混合断裂,随回火温度升高,韧窝增多,准解理减少。     

回火温度对42CrMo4高强钢力学性能及应力腐蚀敏感性的影响

以42CrMo4高强钢为研究对象,采用光学显微镜(OM)、慢应变拉伸(SSRT)和透射电镜( TEM)等研究了42CrMo4显微组织中碳化物形貌和分布随温度变化的情况及其对力学性能和应力腐蚀敏感性的影响.结果表明,42CrMo4高强钢在500～650℃回火后,组织均为回火索氏体,随着回火温度的提高,碳化物由片状不均匀分布逐渐转变为短棒状,最终呈颗粒状弥散分布于基体上;回火过程中碳化物由不均匀片状分布转变为颗粒状弥散分布是42CrMo4高强钢综合力学性能和抗应力腐蚀敏感性持续改善的主要原因.随着回火温度上升,42CrMo4 高强钢0 ℃冲击韧性逐渐提高,拉伸强度逐渐降低;回火温度为500～600 ℃时,试样具有较高的应力腐蚀敏感性,且在相同热处理条件下EH(42CrMo4 充氢后的脆化指数)＞ENaCl(42CrMo4在3. 5% (质量分数)NaCl介质中的脆化指数),回火温度为620～650 ℃时,EH 和ENaCl均低于25% ,具有较低的应力腐蚀敏感性.     

30CrMnSiA钢在盐雾腐蚀条件下疲劳裂纹扩展的初步研究

本文用断裂力学的方法对30CrMnSiA结构钢在盐雾介质和室温空气下的疲劳裂纹扩展特性进行了初步研究。 用紧凑拉伸试样,在应力强度因子△K=70～200kg/mm~3/~2范围内,其试验结果表明:试验初期,盐雾介质中的裂纹扩展速率比室温空气中的要高,并随着试验频率的降低而急剧增加,这种情况通常是氢脆机制造成的。当盐雾介质中的试验进行到20～40小时以后,由于裂纹表面腐蚀产物的堆积,裂纹扩展速率逐渐减缓,甚至低于室温空气下的da/dN曲线。在试验的最后阶段,由于应力强度因子幅值的增大,上述两种介质中的裂纹扩展速率趋于接近。     

激光合成Ni_3Al金属间化合物的腐蚀行为

通过激光技术合成单Ni3Al相金属间化合物,利用电化学方法及盐雾试验研究了Ni3Al金属间化合物在Na Cl溶液中的腐蚀行为特征、耐腐蚀性能及腐蚀机理。结果表明:激光合成Ni3Al金属间化合物在不同浓度的Na Cl腐蚀介质中均能形成保护性钝化膜,当Na Cl溶液浓度低于2%时,钝化膜具有良好的稳定性和耐腐蚀性能。当Na Cl溶液浓度高于3.5%时,钝化膜产生活化溶解,稳定性下降,Ni3Al金属间化合物表面形成点蚀坑,并且随腐蚀介质浓度增大,腐蚀加剧。Ni3Al金属间化合物表面点蚀坑边缘规整、腐蚀界限清晰,腐蚀机制为典型的晶内腐蚀,腐蚀过程中未形成应力腐蚀微裂纹等破坏性缺陷,具备在沿海湿热盐雾环境下使用的潜在价值。     

不同腐蚀环境对7475-T7351铝合金疲劳性能及裂纹扩展速率的影响

采用轴向加载疲劳和疲劳裂纹扩展速率性能测试方法,研究了不同腐蚀环境对7475-T7351铝合金厚板疲劳及裂纹扩展性能的影响.结果表明:腐蚀环境对7475铝合金的疲劳性能有较大影响,油箱积水和3.5%(质量分数,下同)NaCl溶液中光滑试样的疲劳强度较室温下降约68%,油箱积水和3.5%NaCl溶液环境对材料疲劳强度的影响程度基本相同;不同环境腐蚀(空气和3.5%NaCl)和不同温度(室温和125℃)对材料的低周疲劳性能影响不大;腐蚀环境对裂纹扩展有较明显的加速作用,油箱积水和3.5%NaCl溶液环境对裂纹扩展的加速规律基本一致.     

静电喷涂聚酰亚胺涂层的防腐蚀性能

聚酰亚胺(PI)在防腐蚀方面前景良好,但目前国内报道不多。采用静电喷涂的方法在N80钢表面制备了一种聚酰亚胺防腐蚀涂层。通过盐雾试验、浸泡试验评价了涂层在不同腐蚀环境中的耐蚀性能;通过硬度测试和抗冲击试验评价了涂层的力学性能;采用红外光谱、电化学方法交流阻抗、扫描电镜(SEM)、能谱(EDS)等方法研究了涂层的失效过程。结果表明:涂层耐盐雾性能良好,3 080 h盐雾试验后仅表面发生微观物理破坏,在人工划痕处产生少量腐蚀产物;涂层在3.5%NaCl溶液和25%HCl溶液中耐蚀性能优异,电化学性能不随时间发生显著变化,但在涂层表面产生少量微观缺陷;涂层力学性能良好,但提高腐蚀介质温度会使得力学性能下降。     

Effect of Hydrogen on Plastic Deformation near Crack-tipof A537 Steel in 3.5%NaCl Solution

A computerized digital speckle-intederometry system was set up to study in-situ the influence of cathodic hydrogen charging on the crack opening displacement and on the plastic strain distribution at corrosion fatigue crack tip for the singIe-edge notched plate specimens of structural steel in 3.5%NaCl solution with an applied potential of -1400 mV (SCE). Meanwhile, the mono-directional tension tests with smooth specimens were pedermed in both air and 3.5%NaCl solution under the hydrogen charging conditions. The fracture sudece morphology from corrosion fatigue and tension was examined by SEM. The experimental results show that the existence of hydrogen in crack tip material caused an increase of both yield strength and hardening exponent and a decrease of plastic zone size at the corrosion fatigue crack tip.     

AF1410与300M钢的腐蚀冲击疲劳行为

根据舰载飞机起落的服务条件提出了腐蚀冲击概念和试验方法，考察了两种起落架材料在盐水中的腐蚀冲击疲劳行为，包括冲击疲劳寿命，裂纹萌生与扩展速率。尽管两种材料在空气中的冲击疲劳寿命几乎相等。但300M钢在盐水中的冲击疲劳寿命下降幅度较大。在盐水介质中，氢脆加速300M钢冲击疲劳裂纹的萌生和扩展。局部塑性变形区优先腐蚀促使AF1410钢的裂纹萌生，盐水对AF1410钢的裂纹扩展速率没有影响。     

FATIGUE LIFE DISTRIBUTION AND GROWTH OF CORROSION PITS IN A MEDIUM CARBON STEEL IN 3%NaCl SOLUTION

Abstract— Statistical fatigue tests have been conducted on a structural medium carbon steel, S45C, in room air and in 3%NaCl solution, using five cantilever-type rotary bending fatigue testing machines which were specially manufactured for the purpose of the present study. Fatigue life distribution was examined at three and five stress levels in air and in 3%NaCl solution, respectively, and twenty specimens were allocated to each stress level. In room air, it was found that fatigue life distributions followed the three-parameter Weibull distribution, which were closely related to fracture morphology. In 3%NaCl solution, they also followed the Weibull distribution, but the scatter in fatigue life was smaller in comparison to that in air. It is suggested that the decrease in the scatter of fatigue life may be attributed to a smaller fraction of crack initiation life in 3%NaCl solution. The growth of corrosion pits was investigated using a laser microscope. The distribution of corrosion pit depths followed the log-normal distribution, and the corrosion pit depths increased with increasing time or the number of cycles. It was found that the growth of corrosion pits was accelerated by stress cycling and the depths increased with increasing stress level. Based on these results, a growth law of corrosion pits, including the effect of stress cycling, is proposed.     

Influence of Inhibitor Concentration on Corrosion Fatigue Crack Initiation and Propagation

The paper reports the effect of0.01,0.1 and 1%NaNO2, a passive inhibitor, on corrosion fatigue (CF) crack initiation and propagation for a low strength structural steel A537 in 3.5%NaCl aqueous solution. The experimental results show that inhibitor increases the required cycles of CF crack initiation effectively, and this effect increases with increasing inhibitor concentration.However, there is nearly no effect of NaNO2 on CF crack propagation. The same CF crack propagation rate was found in all kinds of solutions. The results also indicate that the passive time in 1%NaNO2 solution during plastic deformation is much longer than cyclic time. NaNO2 passivates the specimen sudece and repairs passive film damaged by cyclic loading during the crack initiation. while the passsive film is not formed fully due to continuous plastic deformation at the crack tip during the CF crack propagation, which is much different from that in the stress corrosion cracking and general corrosion     

Fatigue Crack Growth of Al-Li Alloy 2091 in 3.5% NaCl Solution and at 130℃

A study has been made of the fatigue crackgrowth in an Al-Li alloy 2091 in 3.5%NaCl solu-tion and at an elevated temperature of 130℃.Theaging and environmental effects on the crackgrowth behaviour were examined.It is shown thatthe fatigue crack growth resistance decreases withaging.The specimen with underaged structuresshows the highest resistance to fatigue crack growthdue to more deflected crack paths and the resultinghigh crack closure levels.As compared to laborato-ry air,both 3.5% NaCl solution and elevated tem-perature of 130℃ cause an increase of near-thresh-old crack growth rates and a decrease of thresholdlevels.The elevated temperature is more effective.The effect of elevated temperature is mainly due tothe precipitate coarsening which results in anenhancement of slip irreversibility.Hydrogenembritttlement is supposed to be responsible for thedegradation of fatigue crack growth resistance in3.5%NaCl solution     

Corrosion fatigue crack propagation testing with the KRAK-GAGE® in salt water

The application of a relatively new, thin-film bondable transducer, commercially available under the name KRAK-GAGE®2, was evaluated for corrosion fatigue crack propagation tests in a sea water (3.5%NaCl) environment at ambient temperature on an HY 80 steel. Fatigue crack growth data generated by this method are shown to be consistent with those obtained by the compliance method and the commonly used optical/visual measurements. Thus, this new instrumentation system appears to be a valuable addition for corrosion fatigue crack growth testing. Furthermore, test data acquisition and analysis of the KRAK-GAGE and the compliance method were computer automated, which results in considerable cost savings for such customarily labor intensive fatigue crack propagation experiments. Additionally, the FRAC-TOMAT/KRAK-GAGE instrumentation system can be utilized for direct test machine control, permitting completely automated fatigue crack growth testing.     

SO42-浓度对304不锈钢在NaCl溶液中点蚀行为影响的研究

利用动电位极化、电化学阻抗谱(EIS)和激光电子散斑干涉(ESPI)研究了3.5%NaCl溶液中,SO24-浓度对304不锈钢点蚀行为的影响。使用0.3V(vs SCE)极化条件下的计时电流法结合ESPI确定了点蚀诱导时间。结果表明:当SO24-浓度为0.5%时,不锈钢的耐蚀性最差;当SO24-浓度低于1%时,不锈钢的耐蚀性较不存在SO24-时的耐蚀性差;当SO24-浓度高于1%时,不锈钢的耐蚀性较不存在SO24-时的耐蚀性好。在3.5%NaCl+0.5%Na2SO4溶液中,点蚀诱导时间是4s,在3.5%NaCl溶液中和3.5%NaCl+4%Na2SO4溶液中点蚀诱导时间分别是9s和94s。     

低温高锰钢的局部腐蚀行为研究

采用间浸腐蚀试验、极化曲线测试、扫描观察(SEM)和透射电镜观察(TEM)等方法研究了在3.5%NaCl溶液中添加氧化剂以及敏化处理对低温高锰钢局部腐蚀性能的影响。结果表明:经间浸腐蚀试验后,各试样均主要发生全面非均匀腐蚀,局部可见点腐蚀特征。试样在3.5%NaCl溶液中腐蚀产生的锈层疏松,在3.5%NaCl+0.25%Na₂S₂O₈溶液中腐蚀,试验初期自腐蚀电流密度提高两个数量级,在较短时间内产生致密的锈层,阻止了试验后期腐蚀向内层的快速扩展,试样平均腐蚀速率降低,点腐蚀深度减小。800 ℃×5 h敏化处理后,高锰钢的组织结构没有发生改变,晶界析出了断续分布的碳化物,其抗腐蚀性能与原始态相当,极化曲线印证了这一结果。      

Corrosion fatigue behaviour and fracture mechanisms in nitrided low alloy steel

Rotary bending fatigue tests have been performed in 3%NaCl aqueous solution using specimens of a low alloy steel (Cr–Mo steel) with different nitride case depths. The effect of case depth on corrosion fatigue strength, the fracture process and mechanisms were studied. The corrosion fatigue strengths of the nitrided materials increased compared with the untreated material and increased with increasing thickness of the compound layer, but tended to saturate above a certain thickness. All the materials showed lower fatigue strength in 3%NaCl aqueous solution than in laboratory air and the reduction of fatigue strength decreased with increasing thickness of the compound layer, but remained nearly constant above a certain thickness. Corrosion pits were seen underneath the compound layer, from which cracks initiated. The corrosion fatigue strengths of the specimens whose compound layer was completely removed by electropolishing were almost the same as that of the untreated material, indicating a very significant role of the compound layer in improving corrosion fatigue strength. Because of the porous nature of the compound layer, particularly in the surface‐adjacent part, the solution penetrated the compound layer and reached the base steel, thus the corrosion fatigue strength of the nitrided materials was controlled by the penetration of corrosive media.