Effect of Ferrite content and weld heat input on the room temperature stress corrosion cracking resistance of austenitic clad metals

Austenitic stainless steel claddings with different ferrite contents (2, 4, 10, 12 FN) were obtained by the submerged are welding (SAW) strip cladding process. In order to study the effect of heat input the claddings were removed from the base plate and TIG remelted. Stress corrosion cracking (SCC) tests were carried out with notched tensile specimens in 5 N H₂SO₄ + 0.5 N NaCl at room temperature. A net-section stress required to break the specimen in 100 hours was taken as a criterion of relative SCC susceptibility. The effect of cathodic protection was studied by coupling the specimens with zinc. The results showed that increasing ferrite content decreases SCC resistance. TIG remelted material exhibited better SCC resistance than the SAW specimens. Cathodic protection improves the SCC resistance of all the specimens. Cracking was found to be due to strain-assisted ferrite dissolution and SCC in austenite. SCC in austenite was due to tunnelling mechanism.     

Intergranular corrosion resistance of microstructure- modified type 316 austenitic stainless steel

Cold working and a double aging treatment was used to produce a microstructure with fine nuclei of carbides distributed throughout the grains to improve the intergranular corrosion (IGC) resistance of austenitic stainless steel. The treatment was carried out on type 316 stainless steel as follows: cold working (20,30, and 40% reductions in thickness), sensitization (923 KJ5 h), and aging each for 1173,1223,1273, and 1323 K/l h, respectively. Specimens in the solution annealed condition (0% cold work) were also given the above treatment. All of the specimens were resensitized at 923 KJ5 h and tested for IGC resistance as per ASTM A262, Practice A(oxalic acid etch test) and Practice E (24 h immersion in boiling Cu-CuSO.₄-H₂SO₄ and the U- bend test). Microhardness measurements were also carried out on all specimens. The results indicated that at an optimum treatment (30% cold work + sensitization + aging) all the specimens showed improved IGC resistance. The 0 and 20% cold worked specimens showed improvement at higher aging temperatures only. Specimens undergoing 40% cold work exhibited a decrease in IGC resistance. Compared to as-cold-worked specimens, an improvement in IGC resistance was obtained with 30% cold working.     

温度对X65/316L机械复合管焊接接头CO2腐蚀的影响

在模拟CO2腐蚀环境中,采用高温高压釜对复合管内层不锈钢焊接接头的CO2腐蚀行为进行了试验研究.结果表明,焊接接头随着腐蚀温度的升高,腐蚀产物膜上微孔越来越多,腐蚀速率随温度升高不断增加.通过EDS分析结果可知,复合管内层发生CO2腐蚀的产物可能为FeCO3和Cr2O3的混合物.经去膜后,焊接接头经不同温度腐蚀后为均匀...     

F65/316L与X65/Inconel625复合管焊接接头耐腐蚀性能研究

为了研究采用ERNiCrMo-3焊丝焊接F65/316L与X65/Inconel625复合管焊接接头在特殊油气田气体中的耐腐蚀性能,参照ASTM G39、ASTM 71和DNV-OS-F101标准对复合管焊接接头进行了CO2应力腐蚀试验、高温高压CO2腐蚀、电偶腐蚀性能测试,考察了腐蚀试样表面形貌和成分。结果表明,复合管焊接接头经四点弯曲抗CO2应力腐蚀在母材和焊缝处均未出现裂纹,腐蚀速率满足标准要求;高温高压CO2腐蚀速率为0.002 mm/a,腐蚀类型为均匀腐蚀,腐蚀程度为轻度腐蚀;在3.5%NaCl溶液环境中,电偶腐蚀试验结果表明,焊缝的失重率大于316L和Inconel625母材,其耐蚀性与母材相当。     

Ru含量对镍基高温合金抗热腐蚀性能的影响

采用沉浸法研究了不同Ru含量镍基高温合金的热腐蚀过程。采用扫描电镜观察了合金腐蚀层表面形貌,并利用电子探针观察腐蚀层横截面元素分布。结果表明,随着Ru含量增加,Al的氧化物层逐渐变得连续、致密。经相同时间腐蚀后,随着Ru含量的增加,表层腐蚀产物脱落程度逐渐变轻,合金的腐蚀增重速率逐渐降低。在本试验条件下,合金中加入3%的Ru就可以显著提高其热腐蚀抗力。     

Improving intergranular corrosion resistance of sensitized type 316 austenitic stainless steel by laser surface melting

An attempt was made to modify the surface microstructure of a sensitized austenitic stainless steel, without affecting the bulk properties, using laser surface melting techniques. AISI type 316 stainless steel specimens sensitized at 923 K for 20 hr were laser surface melted using a pulsed ruby laser at 6 J energy. Two successive pulses were given to ensure uniform melting and homogenization. The melted layers were characterized by small angle X- ray diffraction and scanning electron microscopy. Intergranular corrosion tests were carried out on the melted region as per ASTM A262 practice A (etch test) and electrochemical potentiokinetic reactivation test. The results indicated an improvement in the intergranular corrosion resistance after laser surface melting. The results are explained on the basis of homogeneous and nonsensitized microstructure obtained at the surface after laser surface melting. It is concluded that laser surface melting can be used as an in situ method to increase the life of a sensitized component by modifying the surface microstructure.     

稀土La对铁基耐蚀合金抗氧化性能的影响

通过X射线衍射(XRD)、扫描电镜(SEM)及能谱分析(EDS)等手段对不同La含量的铁基耐蚀合金850 ℃下的抗氧化性能进行了研究。结果表明,在850 ℃条件下,随着稀土La含量的增加,在一定程度上降低了合金的抗氧化性能,但氧化膜与基体的粘附性却得到了大大提高。La含量增加后,促进了氧的内扩散,使内氧化层呈树枝状深入合金基体,对氧化膜起到钉固作用。氧化膜主要由3个区域组成:外层是Fe₂O₃与CuO混合层,并含有少量CuFe₂O₄;中间层是以NiFe₂O₄为主的保护层,并含有少量的Fe₂O₃、NiO;内层则是以Fe₂O₃为主并含有少量NiO氧化物的内氧化区。     

Si含量对Fe-Cr-Si系合金组织与耐蚀性能的影响

利用电弧熔炼工艺制备了不同Si含量(6wt%、8wt%、10wt%、12wt%)的Fe-Cr-Si系合金,系统研究了Si含量对Fe-Cr-Si系合金组织和耐腐蚀性能的影响。结果表明,4种不同Si含量的Fe-Cr-Si合金均由初生树枝晶和枝晶间基体组成,Si含量的增加促进了合金中金属硅化物Fe₃Si的形成。Fe-Cr-Si系合金在10%HCl中均表现出良好的耐蚀性能,浸泡72 h后合金表面形成的SiO₂具有钝化作用,且Si含量的增加可以显著提高合金的耐蚀性能,当Si含量达到12%时,耐蚀能力为2Cr13不锈钢的26倍。     

激光熔覆Ni-Si金属硅化物复合材料涂层显微组织与耐蚀性

以Ni,Si,Cr元素粉末为原料 ,利用激光熔覆技术在A3钢表面制得了Ni Si金属硅化物复合材料涂层。分析了该涂层的显微组织 ,采用测定阳极极化曲线的方法评价了该涂层在 0 .5mol/LH2 SO4 及 3 .5 %NaCl水溶液中的耐蚀性能。结果表明 :激光熔覆Ni Si金属硅化物复合材料涂层组织由Ni2 Si初生胞状树枝晶及枝晶间少量FeNi/Ni31Si12 共晶组成 ,涂层表面平整、组织细小、与基体间为完全冶金结合 ;涂层组织显微硬度在HV80 0～ 95 0之间且沿层深分布均匀 ;由于涂层组织组成相Ni2 Si和Ni31Si12 等本身均具有很好的耐蚀性并具有快速凝固细小均匀的显微组织 ,激光熔覆Ni Si金属硅化物复合材料涂层在 0 .5mol/LH2 SO4 及 3.5 %NaCl水溶液中均表现出优良的耐蚀性能。激光熔覆Ni Si金属硅化物复合材料涂层可望成为一种很有发展前景的耐蚀涂层新材料。     

Effect of surface oxide properties on corrosion resistance of 316L stainless steel for biomedical applications

Surface passivation is a promising technique for improving the corrosion resistance both in vitro and in vivo as well as the biocompatibility of 316L stainless steel. In this work, we studied the effect of different passivative processes on the in vitro corrosion resistance of 316L stainless steel wire. Characterization techniques such as anodic polarization test, scanning electron microscopy, auger electron spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy were employed to co-relate the corrosion behavior to various surface characteristics and surface treatments. Results showed that all of these surface treatments did not improve the corrosion resistance of the alloy satisfactorily except amorphous oxidation. This improvement is attributed to the removal of plastically deformed native air-formed oxide layer and the replacement of a newly grown, more uniform and compact one which is composed of nano-scale oxide particles with higher oxygen and chromium concentrations. The properties of surface oxide layer, rather than its thickness, seem to be the predominant factor to explain the improvement of in vitro corrosion resistance.     

N含量对13Cr超级马氏体不锈钢耐蚀性的影响

对13Cr超级马氏体不锈钢进行氮合金化,采用淬火-配分热处理工艺,研究了不同N含量对13Cr钢的微观组织及电化学腐蚀行为的影响。结果表明:随N含量增加,板条马氏体组织表现出明显的细化行为,奥氏体含量增加,且有VN生成,从而防止N与Cr结合生成Cr₂N,促使Cr在材料表面形成以Cr₂O₃为主的致密腐蚀产物膜,提高材料耐蚀性;试验钢表面以局部腐蚀为主,试样表面有点蚀发生。随着N含量的增加,形成腐蚀产物膜的孔隙度减小;表面钝化膜为双电层结构,增加了钝化膜的稳定性,点蚀坑数量明显减少且变小;提高N含量有利于试样耐点蚀性能的改善,0.35%N试验钢表面腐蚀产物附着牢固,平整且致密,晶粒大小均匀,可起到良好的保护作用。     

Effect of metallurgical variables on the stress corrosion crack growth behaviour of AISI type 316LN stainless steel

Mill-annealed AISI type 316LN stainless steels, received from two different sources (one indigenous (SS-2) and the other foreign (SS-1)), were tested for stress corrosion cracking (SCC) resistance in a boiling acidified environment of NaCl. SCC results indicated a remarkably lower value of plateau crack growth rate (PCGR) and higher values of K_ISCC and J_ISCC for SS-2, which was attributed to the lower effective grain boundary energy resulting from a higher amount of copper in it. Cold working reduced K_ISCC and PCGR; while thermal aging and welding decreased K_ISCC and increased PCGR vis-à-vis the annealed material.     

Enhancing the corrosion resistance of metals by laser processing

The influence of a laser surface treatment via short ultraviolet pulses on the electrochemical and corrosion characteristics of stainless steel and aluminum alloys was investigated. By choosing the laser parameters appropriately, a significant improvement in the corrosion behavior of the components can be achieved; the laser treatment was successfully applied to protect susceptible surface areas locally (e.g., at welder joints).     

Co对CrNiMo双相不锈钢组织及耐蚀性能的影响

采用TIG粉末堆焊的方式,在304奥氏体不锈钢基板上制备Co含量分别为0％、1％、2％和3％的CrNiMo双相不锈钢堆焊层.经1100?℃固溶处理后,通过金相组织观察、显微硬度测试、动电位极化曲线和交流阻抗谱(EIS)测试研究了Co对CrNiMo双相不锈钢的显微组织、硬度及耐蚀性能的影响.结果表明:随Co含量的增加,C...     

Effect of La2O3 on corrosion resistance of laser clad ferrite-based alloy coatings

The ferrite-based alloy powders with different contents of La₂O₃ were laser clad on a steel substrate. The microstructural features and phase structure of these coatings were studied by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The results showed that the microstructure of the coatings with La₂O₃ was refined and purified. The main phase of the coatings was γ (Fe, Ni). Moreover, the electrochemical properties of the coatings were investigated by anodic polarization curves and electrochemical impedance spectroscopy (EIS). Anodic polarization results indicated that both polarizing voltage and polarization current density were reduced with the addition of La₂O₃. EIS results showed that, with the increment of La₂O₃, the inductive arcs shrunk and capacitive arcs expanded. The inductive arc at low frequency was disappeared and changed to capacitive arc thoroughly when the content of La₂O₃ reached 1.2 wt.%. The corrosion weight loss experiment results showed that the corrosion rate was lower and the corrosion attack was lighter in the coatings with La₂O₃ than that without La₂O₃, resulting in a substantial improvement of the corrosion resistance.     

316L表面制备Ni-Al系金属间化合物层的耐铅铋腐蚀性能

利用激光熔覆技术在316L不锈钢表面熔覆一层Ni60合金粉末,采用热喷涂技术在Ni60合金涂层表面制备纯Al涂层,再通过620 ℃×5 h高温扩散试验,使Ni60合金涂层和纯Al涂层中间生成Ni-Al金属间化合物。最后把制备有Ni60合金和Ni-Al金属间化合物涂层试样置于液态铅铋合金中进行400 ℃×500 h腐蚀试验。采用SEM,XRD对金属间化合物涂层腐蚀前后的表面、截面的形貌、物相组成及元素分布进行测试,分析Ni60合金涂层和金属间化合物涂层在400 ℃液态铅铋合金中的腐蚀情况。试验结果表明,经过高温扩散试验,试样表面生成了一层由Ni3Al,NiAl等组成的Ni-Al系金属间化合物;经过400 ℃液态铅铋合金腐蚀试验,Ni60合金涂层表面腐蚀较为严重,表面大量金属元素被氧化、溶解,在试样表面形成了不连续金属氧化物和腐蚀坑;Ni-Al金属间化合物涂层被氧化成为稳定的金属氧化物涂层,可以有效阻止Pb,Bi,O等元素渗透进入基体,提高316L的耐液态铅铋腐蚀性能。创新点： 利用激光熔覆、热喷涂、高温扩散相结合的方法制备了金属间化合物,并研究了金属间化合物涂层在液态铅铋合金中的腐蚀情况。     

SUS316ss钢包埋粉末渗铝的高温腐蚀研究

,SUS316ss发生了严重孔蚀,渗铝后表面发生轻微孔蚀;渗铝SUS316在1000℃下加热,表面和断面形貌完好,耐高温氧化性提高了5～8倍;在500℃下表面沉积多相混合物,渗铝的SUS316ss耐腐蚀性提高7～8倍.     

On the influence of the water content on corrosion of metals in mono-carboxylic acids

Corrosion rates of Fe, Zn, Al and stainless steel AISI 304 in oxygen-free formic, acetic, propionic, and butyric acids with water contents between 0.06M and 4.0M have been obtained by polarisation resistance and mass loss measurements. In addition, the influence of temperature and chloride content on the corrosion of stainless steel has been investigated. The less water-like the organic solvent, the more significant is the influence of water in the sense of stimulating the corrosion reaction. The temperature dependence of corrosion is analogous to that in aqueous solutions.     

Effect of GTAW remelting on the corrosion performance of AISI 316L cladding

Gas tungsten arc welding (GTAW) process was used for remelting of the top clad layers of austenitic stainless steel 316L deposited on low-carbon steel using gas metal arc welding (GMAW) process. Different electrochemical techniques were used for assessing and comparing sensitization and pitting corrosion performance of these clads (both in the as-welded as well as aged condition), besides comparing their passive film characteristics. Top clad layer remelting was influential upto a penetration depth of around 2.34 mm. Aging of clads at 750°C/24 hr accelerated the precipitation of carbides, which suppressed partially due to their remelting as indicated by electron probe microanalysis studies. Due to this GTAW remelted clads exhibited a relatively lesser degree of sensitization and higher pitting corrosion resistance as compared to the conventional GMAW clads. X-ray photoelectron spectroscopy studies revealed a relatively higher concentration of O, Cr, Ni, and Mo in the passive film of remelted clad surfaces than the conventional ones, which accounted for enhanced protectiveness of passive film on remelted surfaces as indicated by electrochemical impedance spectroscopy studies.