低合金船体钢点蚀敏感性的研究

通过极化试验比较了4种含有不同合金元素的低合金钢的点蚀诱发敏感性，并用电子探针对钢中的主要夹杂物及点蚀诱发后的腐蚀形态作了鉴定。结果表明：镍—铬系钢比锰系钢具有更好的耐点蚀性能；点蚀总是从夹杂物与周围钢基体毗邻的界面处开始诱发；含有硫化物的复相夹杂对点蚀的敏感性更强。     

脱氧对碳钢耐点蚀性能的影响

选择四种不同脱氧程度的碳钢,在pH=10的3%(质量分数)NaCl溶液中进行极化试验,比较钢的点蚀诱发敏感性;在人造海水中进行模拟闭塞腐蚀电池试验和室内挂片试验,评价钢的点蚀扩展速度.结果表明:沸腾钢A,B钢中的主要夹杂物为橄榄状硫化物和土豆状氧化锰夹杂,镇静钢C,D钢的主要夹杂物为条片状硫化物夹杂和硅酸盐夹杂.在相同条件下,沸腾钢比镇静钢表现出更弱的点蚀诱发敏感性和更小的点蚀扩展速度.同是镇静钢,过低的磷含量可显著促进蚀孔的扩展.     

碳钢中夹杂物诱发点蚀的规律和特性研究

选用5种低碳钢，通过浸泡试验、显微腐蚀试验和极化试验，考察了碳钢在3％NaCl(质量分数，下同)溶液中夹杂物诱发点蚀的规律和特点．结果表明：样品刚浸入溶液时其最初电位高于点蚀电位，钢中一些夹杂物活化，先诱发点蚀；局部活化使钢样的电位迅速下降，当降至点蚀电位之下，未发生点蚀或未充分诱发点蚀的夹杂物受到保护，不再活化；在阳极极化试验中，当钢样的电位极化到点蚀电位或点蚀电位以上，钢中的夹杂物几乎都会活化而诱发点蚀．     

钙处理对AH36船体钢耐点蚀性能的影响

为提高AH36钢的耐海水腐蚀性能,炼钢时引入了钢水钙处理工艺.本文通过室内间浸挂片试验、交流阻抗试验、动电位极化试验及极化试验后的SEM分析,研究了钙处理对AH36钢中的夹杂物及耐点蚀性能的影响.结果表明:变性夹杂物中的CaS对钙处理钢的耐点蚀性能有明显的影响.通过钙处理把钢中氧化铝夹杂、硅铝酸盐夹杂等球化变性成无CaS或低CaS的球状CaO-Al2O3复合夹杂,可有效提高钢的耐点蚀性能;变性球状复合夹杂中含较多的CaS会促进诱发夹杂物周围基体腐蚀,提高点蚀诱发敏感性;含硫量较高的AH36钢在钙处理不充分时,形成CaS夹杂或以CaS为主的复合夹杂,会使AH36钢的耐点蚀性能恶化.     

热加工对硫化物及氧化物夹杂的影响

随着制造业的发展,人们对钢材的质量提出了更高的要求,而夹杂物是影响钢材质量十分重要的因素之一.特别是对高强钢而言,夹杂物对其韧性的影响更加敏感.因此,研究冶炼过程中对夹杂物的控制及后续热轧和热处理工艺对钢中夹杂物的影响,是钢铁材料制造和加工过程中的一个重要课题.夹杂物对钢材的强度、塑性、韧性、抗疲劳性能、耐腐蚀性能都会产生重要影响.要减少夹杂物对钢材性能的影响,需从优化冶炼工艺开始.随着气泡去除夹杂物技术、真空碳脱氧技术及中间包电磁搅拌技术在冶炼过程中的应用,钢材中的夹杂物含量明显降低.然而,在目前工业化的生产环境中,仍然无法实现将钢中的非金属夹杂物完全消除.目前的研究已经表明,热轧和热处理过程对夹杂物也有重要影响,这对进一步控制夹杂物的尺寸、分布、形态,达到减轻夹杂物对钢材性能影响的目的具有重要的意义.因此,目前除了发展新的冶炼工艺以进一步降低钢中的夹杂物含量外,研究和阐明热加工工艺对夹杂物的影响也是研究重点.文中归纳了冶炼过程中先进的夹杂物控制技术及其原理,评述了热变形和热处理过程对夹杂物的数量、尺寸、分布、形态特征及类型产生的影响,对研究钢材在制造、加工过程中夹杂物的变化规律及控制具有参考价值.     

炼钢脱氧制度对碳锰钢坑孔腐蚀扩展的影响

选用脱氧制度不同的碳锰钢,通过冶金分析考察了试验用钢的冶金特点、夹杂物及组织特征,分析了冶金工艺对组织及夹杂物类型的影响。通过挂片试验比较了不同脱氧制度钢的坑孔腐蚀速度,并结合闭塞腐蚀电池及特殊的金相分析方法,研究了脱氧制度对蚀坑扩展的影响及影响机理。结果表明,炼钢脱氧制度对锰铌钢的组织与夹杂物有重要影响,沸腾钢脱氧差,硫化物夹杂为土豆状Ⅰ类硫化物;镇静钢脱氧程度高,其硫化物夹杂为共晶态Ⅱ类硫化物,轧制后为条片状;半镇静钢的脱氧情况介于前二者之间,硫化物夹杂轧制后为短条状或长雪茄状。随着钢的脱氧程度下降,在同样外阴极极化条件下,其闭塞腐蚀电流减小。挂片结果表明,脱氧程度较差的半镇静锰铌钢的耐蚀性明显优于镇静锰铌钢,它们之间的局部腐蚀程度差异基本与室内闭塞腐蚀电池测试结果相同。     

单轴拉伸下AerMet100钢中稀土夹杂物开裂过程的原位观察

扫描电镜观察了AerMet100钢中稀土夹杂物的形貌、尺寸;原位观察了单轴拉伸条件下稀土夹杂物的微观力学行为。结果表明:稀土夹杂物呈球状或椭球状,拉伸过程中稀土夹杂物内部最先萌生裂纹。建立了裂纹萌生的应力判据。裂纹在夹杂物内部扩展,不易向基体延伸。数值模拟单轴拉伸试验和理论计算结果与原位观察基本一致。     

用金相法检验精炼前后Q235B钢液中的夹杂物

对某一炉Q235B钢液精炼前后的夹杂物从尺寸、分布密度、形状及数量的角度进行了金相检验及分析。结果表明：精炼后,小颗粒状夹杂物尺寸及分布密度均有所增加;而尺寸大于20μm的球状或近球状夹杂物和非球状夹杂物的数量减少了43％,其中非球状夹杂物尺寸及数量均大幅度降低,而球状或近球状夹杂物的比例提高了40％;同时尺寸大于50μm的夹杂物尺寸及数量也均有不同程度的降低;因此使用的精炼合成渣对改变夹杂物的形状和净化钢液起到了一定作用。     

Q345E钢低温冲击性能不合格原因

某批次Q345E钢在进行低温冲击试验时，发现其低温冲击性能不满足标准要求。采用扫描电镜分析、夹杂物评定、金相检验、晶粒度评定等方法，分析了其冲击性能不合格的原因。结果表明：钢材中的硫化物在心部偏聚，夹杂物的存在导致基体连续性被破坏，当受到冲击作用力时，钢材的有效受力面积和冲击吸收面积变小，裂纹在该处萌生并快速扩展；钢材的晶粒尺寸较大，使金属间的结合力变小，最终导致该钢材的低温冲击性能不合格。     

一种低磁钢耐海水腐蚀性能的研究

45Mn17Al3低磁钢质优价廉,但在海水中使用腐蚀严重.通过对45Mn17Al3奥氏体低磁钢试样进行室内腐蚀挂片试验、电化学性能测试、显微腐蚀试验及冶金因素分析,初步探讨了该型钢在海水介质中发生腐蚀的微观机制.室内腐蚀挂片试验和电化学性能测试结果表明,低磁钢的耐蚀性比3C钢要差;显微腐蚀试验结果证明,钢中的夹杂会诱发点蚀;冶金因素分析结果显示,钢中存在大量的AlN夹杂物,而且其微观组织比3C钢的粗大.45Mn17Al3中高的Al含量和大量的AlN夹杂的存在对该型钢耐海水腐蚀性能有重要的影响.     

Effects of electropulsing on inclusion size and corrosion-resistance of 304 stainless steel

Electropulsing has been imposed on molten AISI 304 stainless steel and its effects on the inclusion size and corrosion properties have been investigated. The average size of inclusions in electropulsing-treated samples was finer than that in untreated ones. A theoretical analysis shows that the mobility of solute atoms increases with electropulsing treatment. This promotes the nucleation of inclusions. Owing to a smaller inclusion size, the electrochemical experiments reveal that the pitting corrosion resistance of the electropulsing-treated stainless steel is significantly improved. The beneficial effects of electropulsing on the refinement of inclusions and the resistance to pitting corrosion increase with an increase in current density. Electropulsing treatment, therefore, provides a promising means to improve pitting corrosion resistance.     

微观组织对0Cr17Ni4Cu4Nb马氏体不锈钢的耐点腐蚀性能的影响

采用化学浸泡法和模拟闭塞电池方法研究了固溶+时效和固溶+调整+时效处理的0Cr17Ni4Cu4Nb马氏体不锈钢的耐点腐蚀性能,并与18-8型奥氏体不锈钢(316L)耐点蚀性能进行了对比。结果表明,0Cr17Ni4Cu4Nb马氏体不锈钢组织内富Cu析出相促进了点蚀坑萌生,而点蚀坑发展则与组织形貌有关。固溶+调整+时效处理的0Cr17Ni4Cu4Nb马氏体不锈钢因组织内析出富Cu相多而大,其萌生的点蚀坑密度较高,但由于马氏体板条较细,其点蚀坑尺寸和深度较小;固溶+时效处理的0Cr17Ni4Cu4Nb马氏体不锈钢因组织内析出富Cu相少而小,萌生的点蚀坑密度较低,但粗大的板条马氏体组织导致点蚀坑尺寸和深度较大。与18-8型奥氏体不锈钢耐点蚀性能对比表明,通过对0Cr17Ni4Cu4Nb马氏体不锈钢进行合理的热处理,其耐点蚀性能可与18-8型奥氏体不锈钢相当。     

特种设备用双相不锈钢抗点蚀性能研究

点蚀是不锈钢最有害的腐蚀形态之一,点蚀往往是应力腐蚀裂纹和腐蚀疲劳裂纹的起始部位。点蚀是一种腐蚀集中于表面的很小范围内,并深入到金属内部的腐蚀形态,一般形状为小孔状,其危害性比均匀腐蚀严重得多,会引起爆炸、火灾等事故。双相不锈钢兼有铁素体和奥氏体的特性,它将铁素体良好的强度、硬度和奥氏体优良的塑性和韧性结合起来,并具有优良的耐点蚀性能,无论是在力学性能上还是在耐腐蚀性上,双相不锈钢都明显优于铁素体不锈钢和奥氏体不锈钢,可以在点蚀环境中的特种设备上广泛使用。     

Initiation and early growth mechanisms of corrosion fatigue cracks in stainless steels

The mechanism of corrosion fatigue crack initiation in stainless steels was examined in both air and chloride solutions. For a tempered martensitic, a duplex and a soft martensitic steel it is shown that the decrease of the fatigue strength from the value measured in air to that measured in corrosive environments depends primarily upon the stability of the protective film. If the passivity is stable, cracks are found to originate almost exclusively at oxide inclusions. Cracking or debonding were found to occur. For the duplex steel in the vicinity of the inclusion there were pronounced emerging persistent slip bands. They cause localized corrosion attack, thus allowing cracks to be formed more easily. If pitting is superposed, crack nucleation always occurs at the base of the pit. Pit formation and growth rate are accelerated by cyclic loading.     

Effect of the direction of the inclusions on the tested surface on susceptibility to pitting corrosion in stainless steels

A study was made of the induction time of pitting (t _i) at constant potential in a stainless steel 316 L specimen in deareated NaCl solutions. The influence of the inclusion content in the steel on t _i was examined, in particular the effect of the inclusions' orientation on the surface of the specimen tested. It was found that the induction time at constant potential and under similar experimental conditions depends on the inclusions' orientation on the test specimen surface; when the direction of the inclusions is transverse to the rolling direction, t _i is shortened in comparison with the tested surface planes containing the rolling direction. The pitting initiation sites were the matrix-sulphide inclusions interphase. The microcavities associated with them could be preferential sites for pit nucleation.     

Nd:YAG laser surface melting of aluminium alloy 6013 for improving pitting corrosion fatigue resistance

Laser surface treatment of aluminium alloy 6013 was conducted with the aim of improving the alloy’s resistance to pitting corrosion fatigue. The study showed that laser melting using a high power Nd:YAG laser increased the resistance of the alloy to pitting corrosion and pitting corrosion fatigue. As corrosion pits are favourable sites for the initiation of fatigue cracks, and the process of crack initiation often takes up most of the fatigue life, especially at low stress levels, a high pitting corrosion resistance resulted from the laser treatment improved fatigue crack initiation resistance. With regard to fatigue crack propagation, although interdendritic boundaries are vulnerable to corrosion attacks due to the presence of second phase particles, nonetheless, due to the nature of the rough and undulating fracture surface, fatigue growth would be retarded. Under the present experimental conditions, the improvement in corrosion resistance brought about by laser surface melting was found to prevail over the adverse effect caused by the residual stresses induced by laser melting.     

A New Approach to Characterization of Gas Turbine Components Affected by Pitting Corrosion

Among gas turbine components such as compressor blades made of precipitation-hardened martensitic stainless steel, a phenomenon known as pitting corrosion can occur on the surfaces of components during exposure to a marine environment. This can lead to surface degradation followed by crack initiation and further propagation with high-cycle fatigue as the main mode of damage. In order to obtain detailed statistical characterization of pitting severity, which may enable obtaining preventive models of the phenomena, a new study on pit size analysis and pitting inspection technique is proposed. In this investigation, pit depth values are considered as the main factor behind this type of failures. This article presents the results of pit depth assessment and other pitting characteristics with the use of confocal microscopy as a non-destructive technique. The results obtained show that confocal microscopy can be successfully used as a non-destructive tool for the evaluation of pitting severity.     

The effect of TiN inclusions and deformation-induced martensite on the corrosion properties of AISI 321 stainless steel

Stainless steel of type 321 is commonly used for the production of exhaust systems because of its temperature resistance and welding properties, which are better than those of AISI 304 or similar steels. AISI 321 is a titanium stabilized austenitic stainless steel, where this element is added to form carbides in order to avoid chromium impoverishment due to chromium carbide formation. Cold shaping can, in the case of austenitic stainless steel, cause the formation of deformation induced martensite, which can improve its mechanical properties, but unfortunately can also spoil its good resistance to corrosion. Titanium nitride inclusions are cathodic with respect to steels, and therefore cause their anodic dissolution. Martensite is, however, more susceptible to the corrosion than austenite in steels. The main aim of this study was to analyze the pitting corrosion and stress corrosion cracking which is initiated on prototype cold-formed outer exhaust sleeves during the testing of different cleaning procedures before chromium plating. Various microscopic methods were used to identify the initiation of corrosion and its propagation.