高强度航空结构钢电镀Zn-Ni合金的氢脆性能

目前,对航空300M超高强度结构钢电镀Zn-Ni合金的氢脆性能研究鲜见报道。采用正交试验法研究了工艺参数对300M钢Zn-Ni合金镀层含Ni量和氢脆性能的影响规律;采用EDA能谱分析、SEM形貌观察、缺口拉伸试验和断口分析等方法,对Zn-Ni合金镀层的氢脆性能和断口特征进行了分析研究,探讨了其代替松孔镀镉层的可行性。结果表明:从工程应用安全性出发的氯化物-硫酸盐体系Zn-Ni合金电镀优化工艺条件为镀液Ni2+/Zn2+质量浓度比0.53、温度30℃、电流密度4 A/dm2,所得镀层的氢脆敏感性低,符合航空工业高强度钢氢脆性能要求,可以代替剧毒镀镉工艺用于航空结构钢的表面防护处理。     

高强度钢低氢脆光亮镀镉

为防止氢脆、高强度钢的电镀一般不使用光亮剂，但镀层耐蚀性较差。本文研究了一种高强度钢低氢脆氢脆光亮镀镉工艺。首先筛选出合适的光亮剂，然后对镀层性能进行了分析测试。结果表明，在一定浓度下使用自制光亮剂所获镀层，不仅耐蚀性和结合强度良好，而且其氢脆性能也能满足一定要求，达到或接近了国外商品光亮剂的水平。     

高强度钢电镀Zn—Ni合金研究

一、前言 近年来,人们对镀锌基合金代替镀锌、镀镉层在严酷腐蚀环境中的应用产生了极大的兴趣。这是因为镀锌基合金具有优良的耐蚀性,而且对于高强度钢还具有低氢脆性。锌基合金电镀在日本、美国、中国等国都有一定的应用,以Zn—Ni,Zn—Co,Zn—Fe合金为主要代表。本文研究并应用了以碱性锌酸盐体系的镀锌镍合金和氯化物等其它Zn—Ni合金电镀工艺相比,具如下工艺特点:1)镀液具有非常优良的分散能力和覆盖能力;2)镀液不会对电镀设备造成腐蚀;3)由于不使用有机光亮添加剂,而镀层脆性小,内应力也小;4)镀液易于进行污水处理;5)可在很宽的工艺条件范围内稳定获取含Ni量为10～15wt％的Zn—Ni合金镀层;6)镀层硬度是普通镀锌层的3倍;7)镀层的耐蚀性是镀锌层的3～6倍;8)电镀工艺不会对高强度材料带来氢脆的危险。 经生产实践证明,这种碱性体系的镀液是非常稳定的,而且工艺操作简便,是应用于航空等工业的一种高耐蚀、低氢脆防护性电镀工艺。     

高强度钢氢脆检测方法及其镉钛镀层性能研究

本文介绍了高强度钢氢脆产生的机理、条件、检测方法、测氢仪检测氢脆的原理及其在控制低氢脆镀镉钛工艺中的应用,并对镉钛镀层的性能进行了研究。     

镉-钛电镀工艺对高强度钢焊接件氢脆性能的影响

一、前 言 镉-钛电镀工艺是目前国内外用于高强度钢防护的一种较好工艺。镉-钛镀层不但具有显著的低氢脆性,而且还有良好的抗腐蚀性。国外氰化镉-钛电镀工艺已获得广泛的应用,如美国波音公司已用于波音707、727、737、747等飞机的起落架上,而起落架都是焊接件。过去我国研制的无氰镀镉-钛工艺,仅对高强度钢(非焊接)氢脆性能的影响做过大量工作,而对高强度钢焊接件的影响尚未做过研究,因     

30CrMnSiNi_2 A钢的电化学渗氢研究

一、前言 1.试验目的镉-钛镀层是目前防护高强度钢的一种较好镀层,有优良的低氢脆性及耐腐蚀性。但是,被复镉-钛镀层的高强度钢,在腐蚀性介质中有由于腐蚀而产生氢脆断裂(即后脆)的明显倾向。为了研究这种后脆现     

锌酸盐体系Zn-Fe合金电镀阴极电流效率的研究

对碱性锌酸盐体系电镀Zn-Fe合金阴极电流效率的影响因素进行了系统的研究,并分析了镀层中铁原子的引入对Zn-Fe合金电镀阴极电流效率的影响原因及合金镀层中铁含量与阴极电流效率的关系,以期通过控制镀液组成及工艺条件在一定程度上提高阴极电流效率.增加电镀液中锌铁离子总摩尔浓度,提高镀液中锌铁离子摩尔比,降低铁离子浓度,适当控制阴极电流密度,升高镀液温度均可提高锌铁合金电沉积的阴极电流效率.添加剂ZFA的加入使Zn-Fe合金电镀的阴极电流效率降低.合金镀层中引入Fe明显降低了电沉积的阴极电流效率,镀层中的Fe含量从0升高至0.73%,合金电沉积的阴极电流效率却从79.48%降低至68.23%.这是由于碱性溶液中,氢气在金属Fe上析出的过电势明显小于在金属Zn上的过电势,使析氢容易进行引起的.     

镉-钛电镀中钛析出机理的探讨

一、前言 镉-钛电镀是目前国内外用于防护高强度钢的一种较好的低氢脆性电镀工艺。这种工艺所得镀层的钛含量一般在0.1～0.7％,然而这种镀层却具有优良的耐腐蚀性和低氢脆性。 钛是一种很活泼的元素,一般从水溶液中难以沉积出金属钛及其合金。那么镉-钛镀层中的钛是如何沉积出来的呢?     

高强度钢无氰镀镉-钛的研究

一、高强度钢的防护与 镉—钛电镀 随着航空工业的发展,高强度钢的使用日趋广泛。但是,高强度钢的防护,一个众所周知的难题就是氢脆,即材料受氢的影响,在低于其屈服强度的应力条件下,容易发生早期脆性断裂。而且,材料强度越高,受氢程度越严重,所受应力越大,氢脆危险性也越大。电镀及表面处理作业中的酸洗、腐蚀、阴极除油、电镀等     

低氢脆（LHE）刷镀镉工艺

飞机起落架镀镉－钛时，由于零件形状复杂而镀不进去的部位，必须用ＬＨＥ刷镀镉工艺来弥补。对国外ＬＨＥ刷镀镉溶液、北京装甲兵工程学院的ＬＨＥ刷镀镉溶液以及自行研制的ＬＨＥ刷镀镉溶液的电化学性能、镀层的氢脆性能及耐蚀性能进行了研究，表明这几种溶液都能用于飞机高强度钢的ＬＨＥ刷镀，镀后不用除氢。     

Hydrogen embrittlement in power plant steels

In power plants, several major components such as steam generator tubes, boilers, steam/water pipe lines, water box of condensers and the other auxiliary components like bolts, nuts, screws fasteners and supporting assemblies are commonly fabricated from plain carbon steels, as well as low and high alloy steels. These components often fail catastrophically due to hydrogen embrittlement. A brief overview of our current understanding of the phenomenon of such hydrogen damage in steels is presented in this paper. Case histories of failures of steel components due to hydrogen embrittlement, which are reported in literature, are briefly discussed. A phenomenological assessment of overall process of hydrogen embrittlement and classification of the various damage modes are summarized. Influence of several physical and metallurgical variables on the susceptibility of steels to hydrogen embrittlement, mechanisms of hydrogen embrittlement and current approaches to combat this problem are also presented.     

Micromechanical aspects of hydrogen degradation in high-strength structural steels

We analyze micromechanical aspects of hydrogen degradation in high-strength structural eutectoid steels under the conditions of various triaxial stress states and hydrogen embrittlement generated by cathodic charging. Hydrogen causes microdamage in the form of different microscopic modes of fracture associated with different stages of the process of hydrogen degradation so that the evolution of hydrogen-assisted microdamage strongly depends on macroscopic variables such as the triaxiality of stresses in the critical region. We show that the zone microscopically affected by hydrogen can be modeled as a macroscopic crack growing in the subcritical model until final fracture, which is an unstable process.     

Effect of grain size on the hydrogen-assisted cracking in duplex stainless steels

The embrittlement behavior of 2205 duplex stainless steels with two different grain sizes in 26 wt% NaCl (pH 2) under cathodic potential were investigated by slow strain rate testing. The electrochemical permeation technique was used to characterize the permeation rate and effective diffusivity of hydrogen. The results indicated that both the effective diffusivity and the susceptibility of hydrogen embrittlement were lower for the finer grain size specimen. Ultimate tensile strength (UTS) and uniform elongation (UEL) decrease linearly with decreasing logarithm of strain rate. The dependence of UTS and UEL on the logarithm of strain rate was higher for the finer grain specimen. The microstructural examination revealed that internal cracks resulted from hydrogen embrittlement of the ferrite phase under cathodic charging conditions were arrested by austenite in duplex stainless steels.     

Rißfortschritt an Baustählen in Meerwasser

Crack Growth Behaviour of Structural Steels in Seawater The influence of a synthetic seawater environment upon the crack growth behaviour of two structural steels was investigated. The results were presented in terms of the stress intensity fracture toughness parameter. Data were generated in air and in seawater with or without a cathodic protection. Results show that seawater environment and a cathodic protection influence the crack propagation at the applied frequencies of 0,04 and 0,25 Hz. The use of cathodic protection raises questions concerning the resistance to hydrogen embrittlement of the two steels. Some fractographic examinations of selected specimens show the microstructure of the two steels at various test conditions.     

Passivation treatment for inhibition of hydrogen absorption in chromium-plated steel

Hydrogen permeation transients for passivated chromium-plated steels were measured at room temperature as a function of cathodic charging current density. The passivated film on chromium plating is shown to be an effective barrier to hydrogen at low cathodic charging current density (40 and 100 A cm^–2). The passivated film can be reduced to chromium at higher cathodic charging current density (1 and 10 mA cm^–2), promoting hydrogen absorption significantly.     

Effect of bainitic microstructure on the susceptibility of pipeline steels to hydrogen induced cracking

Hydrogen induced cracking (HIC) of API X80 and API X100 pipeline steels have been investigated in high pH carbonate-bicarbonate environment using slow strain rate testing (SSRT) method. It has been found that while both steels are highly susceptible to HIC, and diffusible hydrogen content is higher in API X80 than in API X100, the later steel is more vulnerable than the former at high (more negative) cathodic potential. This higher susceptibility can be primarily attributed to the combined effect of (1) separation of bainitic lath boundaries due to hydrogen trapping in these locations, (2) mobile hydrogen, and (3) stress. The charging-discharging experiments followed by SSRT experiments in air suggest that, the cracks that appeared due to lath boundary separation did not cause the reduction of ductility by themselves, rather it was the diffusible hydrogen that forced these cracks to propagate and, ruptured the steel with very low percent reduction of area (%RA). Despite the fact that the mobile hydrogen content plays a key role in causing the embrittlement, the large number of cracks in API X100 steel, resulting from the bainitic lath boundary separation at high cathodic potential, superseded the effect of higher diffusible hydrogen content in API X80 steel. The general conclusion is that bainitic lath type microstructure is more vulnerable to HIC at high cathodic potential than the ferritic/granular bainitic ones. It has been also found that applying cathodic protection can lead to excessive hydrogen embrittlement in both of the abovementioned steels in high pH carbonate-bicarbonate environment and, therefore, efforts need to be invested in developing nobler (more positive corrosion potential) and better HIC resistant steels.     

Effects of nitrogen on hydrogen embrittlement in AlSl type 316, 321 and 347 austenitic stainless steels

Hydrogen embrittlement of AlSl type 316, 321 and 347 stainless steels with nitrogen alloying has been studied by a tensile test through cathodic charging. The results show that addition of nitrogen improved resistance to hydrogen cracking regardless of the failure mode. Fracture surfaces of cathodically charged steels showed intergranular brittle zones on each side of the fracture surfaces. AlSl type 316 with nitrogen alloying stainless steel is more resistant to hydrogen embrittlement than AlSl type 321 with nitrogen alloying steel, whereas AlSl type 347 with nitrogen alloying steel is susceptible to hydrogen embrittlement. Nitrogen alloying of stainless steel increased the mechanical properties in hydrogen environments by increasing the stability of austenite.     

Influence of the structural embrittlement of metal alloys on their short-term crack resistance

We perform the comparative analysis of the sensitivity of short-term crack resistance and conventional mechanical characteristics of brittleness to typical symptoms of metallurgic and structural embrittlement of metal alloys. For this purpose, we studied various structural steels in the state of reversible or irreversible temper embrittlement, quenched steels with coarse original austenitic grain structure after overheating, steels susceptible to hydrogen embrittlement, high-chromium steels in the state of “475° brittleness,” and steam-pipe steels subjected to in-service thermal aging. Despite fairly high sensitivity of the parameterK _lc to these types of embrittlement, this parameter exhibits quite low sensitivity to the embrittlement of high-strength steels, in particular, in the case where it is caused by the processes running on grain boundaries. This phenomenon is explained by the difference between the sizes of the “fracture zone” and the original structure of embrittled cells. We formulate structural and mechanical conditions guaranteeing the required sensitivity of the characteristics of short-term crack resistance to possible metallurgic embrittlement. In the indicated anomalous cases, the desired correspondence can be attained by testing smaller specimens and, hence, by using milder loading modes, i.e., by passing to the determination of the parameterK _c and the characteristic of critical crack opening displacement δ_c introduced by V. V. Panasyuk. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv. Vol. 32, No. 1, pp. 9–21, January–February, 1996.     

Characterization of Hydrogen Embrittlement in 2.25cr-1mo-0.25v Steel by Eddy Current Method

Eddy current method has been recently developed to characterize mechanical properties of materials and assess internal hydrogen content of high strength low alloy steels. The application of eddy current testing in evaluating hydrogen embrittlement state of 2.25Cr-1Mo-0.25V ferritic steel has been investigated using tensile test and electrochemical hydrogen charging test. The relationship between the embrittlement index and eddy current signal is well established. It found that there is a good linear relation between the hydrogen-induced plasticity loss and the eddy current signal. This shows eddy current testing is an effective method for evaluating hydrogen embrittlement state of 2.25Cr-1Mo-0.25V steel.     

Characteristics of hydrogen embrittlement,stress corrosion cracking and tempered martensite embrittlement in high-strength steels

Characteristics of tempered martensite embrittlement (TME), hydrogen embrittlement (HE), and stress corrosion cracking (SCC) in high-strength steels are reviewed. Often, it is important to determine unambiguously by which of these mechanisms failure occurred, in order to suggest the right actions to prevent failure recurrence. To this aim, samples made of high-strength AISI 4340 alloy steel were embrittled by controlled processes that might take place, for example, during the fabrication and service of aircraft landing gears. The samples were then fractured and characterized using light and scanning electron microscopy, microhardness tests, and X-ray diffraction. Fractography was found to be the most useful tool in determining which of these mechanisms is responsible for a failure, under similar conditions, of structures made of AISI 4340 alloy steel.