Investigation on the nickel content design and the corrosion resistance of low alloy steel welded joint in tropical marine atmosphere environment

In this study, three kinds of welding materials (WMs) with different Ni contents were designed for low alloy steel welded joints made by CO₂ gas-shielded welding technique. The corrosion resistance of welded joint was studied through the atmosphere exposure test in Trat, Thailand. Results show that there was a hardening in the heat-affected zone after welding, and the average hardness slightly increased with the increase of Ni in WM. The electrochemical activity at the fusion line zone enhanced with the addition of Ni in WM, indicating a more obvious local galvanic corrosion effect there. Ni promoted the generation of NiFe₂O₄ and the transformation from γ-FeOOH to α-FeOOH, which increased the impedance modulus of the rust film on WM. More important, the corrosion performance assessment illustrated that the addition of Ni in WM hardly had an effect on the corrosion step values after half a year test, which confirmed that there is no need to add excessive content of Ni.     

Weatherability of 09CuPCrNi steel in a tropical marine environment

The stability of weathering steel (09CuPCrNi) exposed at tropical marine environments for varied periods was investigated. The synergistic effect of exposure environment and alloy elements on weatherability was also studied. The classical weight loss method was used to evaluate weatherability, while the iron rust layers formed on weathering steel under different conditions were analyzed by using Infrared spectroscopy (IR), electron probe of mass analysis (EPMA) and electrochemical techniques. The results show that under low chloride deposition, the enrichment of Cr plays an important role on improving weatherability; conversely chloride ion is primary factor to whittle weatherability in high chloride deposition.     

E690平台用钢耐海洋大气腐蚀模拟

用周浸加速腐蚀试验、力学性能试验并结合扫描电镜、能谱分析以及透射电镜等方法对比研究了2种满足E690要求的低碳贝氏体钢(3种热处理方式)在模拟海洋大气环境中(0.5 wt%NaCl水溶液)的耐腐蚀性能和拉伸性能的变化。结果表明,在腐蚀初期晶粒越小越容易被腐蚀,成膜更快,有利于锈层的形成;Cu的析出会加速钢的初期腐蚀,在腐蚀后期形成致密锈层后这种影响变小。3种实验钢的腐蚀产物相组成差别不大,但锈层致密程度存在差异,并且锈层越致密,对应的钢的腐蚀速率越低。在试验环境中腐蚀对2种试验钢和3种处理方式的力学性能影响较小,说明没有产生严重的局部腐蚀。     

GMAW焊接熔池形状和表面变形的数值模拟

采用双椭球体热源分布模式,把过热熔滴带入熔池的热焓量处理为特定区域的均匀热源,建立了运动电弧下GMAW焊接热过程的数值分析模型.利用Visual For-tran编写数值计算程序,预测了从电弧引燃到准稳态过程中焊接熔池形状和熔池自由表面变形的动态演变,并进行了对比试验.基于数值模拟和工艺试验结果,可以看出达到宏观准稳态时计算所得的焊缝形状尺寸与试验结果基本吻合,因此验证了所建模型和采用的计算方法是正确、可靠的.     

Zinc runoff from galvanised steel materials exposed in industrial/marine environment

Abstract

An investigation has been carried out to assess the zinc runoff from a variety of galvanised materials over 16 months at the industrial/marine Port Talbot weathering site. Over 16 months of exposure, bare zinc, and Electrozinc have the highest levels of zinc runoff (4·38 and 4·20 g m^-2) followed by general galvanised steel substrates, i.e. hot dip galvanised (HDG) steel (0·15 wt-%Al) (2·87 g m^-2) and iron zinc intermetallic galvanised steel (galvanneal, 2·36 g m^-2). Galvanneal (IZ) has a higher initial runoff rate than HDG due to the presence of iron/zinc intermetallic in the coating that promotes anodic zinc dissolution. The HDG has a more constant runoff rate that exceeds IZ after 7-8 months due to build up of corrosion products on the IZ surface. Aluminium/zinc alloy coated steels have a much lower runoff rate than general galvanised materials as the aluminium present in the structure provides a strongly protective oxide barrier coating improving corrosion resistance (Galfan 5 wt-%Al, 2·04 g m^-2, and Z alutite 55 wt-%Al, 0·67 g m^-2). Organically coated steels show relatively little zinc runoff (< 0·25 g m^-2) indicating their effectiveness in preventing surface corrosion. Runoff levels measured do not exceed permissible levels of zinc for drinking water and the measured zinc runoff levels pose little threat to organisms if leached into soil. Using an accelerated laboratory test in which distilled water is sprayed onto specimen panels in a recirculatory system for 100 h a good correlation can be obtained with external exposure for up to 6 months exposure. For 12 months exposure iron zinc intermetallic galvanising (galvanneal) begins to become covered in a protective oxide layer, which cannot form under the conditions of the accelerated test. Despite this, the fit for most specimen types is excellent. Where the predictive test fails is when the galvanising layer is breached revealing an efficient iron cathode site. This occurs first for electrocoated zinc after 16 months exposure. Similar predictive results can be obtained using a scanning vibrating electrode technique (SVET) in a semiquantitative manner and an immersion electrolyte of 0·1 wt-%NaCl. Again the predictions are initially very accurate but following 12 months exposure the fit for specimens of electrozinc is poor due to the breaching of the galvanising layer.     

The atmospheric corrosion kinetics of low carbon steel in a tropical marine environment

The atmospheric corrosion kinetics of low carbon steel exposed for up to 36 months in marine and industrial sites was studied by weight loss measurements. The results show that the mechanism and kinetics of the atmospheric corrosion process presents transition behaviour in marine environments with high chloride ion content and high relative humidity, whereas no transition appears in industrial environment. The average corrosion velocity in marine site reaches a maximum during the period of transition and then fluctuates in a certain range; however, the instantaneous corrosion velocity follows different exponential functions before and after the period of transition.     

结构钢在模拟海洋大气环境中的腐蚀行为研究

利用模拟海洋大气环境的加速腐蚀实验,对比研究了两种结构钢(低碳铁素体钢和耐候钢09CuPCrNi)朝天面与朝地面的腐蚀行为及相应锈层,结果表明两种结构钢的朝地面均比朝天面腐蚀严重.电化学阻抗谱(EIS)结果表明朝天面锈层对氯离子的阻碍能力高于朝地面锈层,X射线衍射(XRD)结果表明朝天面锈层中X射线无定形锈含量高于朝地面锈层,N2吸附结果表明朝天面锈层比朝地面锈层致密.两面腐蚀条件的差异造成了两面锈层相组成和致密度的不同,从而导致相应锈层保护性能的区别.提出锈层孔隙模型,解释了锈层保护性能差异的原因是锈层干/湿交替频率的不同.     

Identification and formation of green rust 2 as an atmospheric corrosion product of carbon steel in marine atmospheres

Green rust 2 (GR2(SO^2?₄ )) was detected amongst the products formed on a carbon steel rod exposed to atmospheric corrosion using X‐ray diffraction (XRD). The presence of green rust 2 has been related to sulphate reducing bacteria (SRB) in the sea spray. These were detected using test catch rods made out of inert material and posterior lab identification using Starkey culture. Likewise, after the exposure of said rods to sea environmental conditions, SRBs have been isolated from among the carbon steel corrosion products. The evolution of GR2(SO^2?₄ ) from GR1(SO^2?₄ ) was ruled out due to the tendency of this compund to produce GR2(SO^2?₄ ) in the presence of sulphate ions, as is the case here. Likewise, the evolution from GR1(Cl^?) has also been ruled out since in such case as this compound should be formed (it has not been detected in any of the 39 stations studied), the enormous affinity of the GRs with divalent anions (such as is the case with SO^2?₄ ) as opposed to the monovalent ions (such as is the case of the Cl^?) makes GR1(Cl^?) transform into GR2 (SO^2?₄ ).     

模拟海洋大气环境对XCS-lode钢与30CrNi3Mo钢腐蚀行为的影响

采用盐雾腐蚀试验方法,研究了模拟海洋大气环境下XCS-lode钢与30CrNi3Mo钢的腐蚀性能,通过极化曲线及电化学阻抗谱(EIS)试验研究了两种钢在腐蚀行为上的差异.结果表明:XCS-lode钢相比30CrNi3Mo钢具有更高的自腐蚀电位,XCS-lode钢腐蚀产物膜的阻抗明显大于30CrNi3Mo钢,XCS-lo...     

船用薄板焊接接头残余变形有限元模拟

运用热弹塑性有限元法,对不同焊接工艺条件下板厚6 mm的AH36钢薄板焊接接头残余变形进行了有限元模拟研究.结果表明,使用不同的焊接方法,纵向挠曲变形和角变形量发生显著变化,采用单一CO2气体保护焊,焊接残余变形量较小;采用CO2气体保护焊+埋弧焊的混合焊方法,焊接残余变形量有所增大;在焊缝背面施加雾化水冷,可以有效控制焊接残余变形,尤其对于控制采用单一CO2气体保护焊的角变形成效显著.为了验证有限元模拟结果的准确性,采用与有限元模拟完全相同的工艺条件对AH36钢薄板进行了焊接残余变形试验,试验结果与数值模拟结论存在一定误差,但基本变化趋势一致,表明采用有限元模拟技术可以预测AH36钢薄板焊接残余变形.     

E550钢埋弧焊接接头在模拟海洋大气环境中的腐蚀行为

采用增重测量、锈层截面观察、物相定量分析和电化学实验等方法研究了低合金耐候钢E550埋弧焊焊接接头在室内干湿循环加速腐蚀中的行为。结果表明:E550钢焊接接头的腐蚀速率低于母材。E550母材与焊缝的成分差异导致焊接接头不同部位的电位不同,并引起电偶腐蚀。电偶腐蚀对常规的大气腐蚀产生了抑制作用,造成焊接接头腐蚀前沿平整,锈层缺陷减少。随着表面锈层的生长,焊接接头表面不同部位的电位发生不同程度变化,并造成反复发生极性逆转,使腐蚀变得均匀,减弱了电偶腐蚀的局部腐蚀特征。     

Interaction of impact-compressed gas in the welding gap with the welded surfaces in explosive welding

It is shown that in explosive welding in conditions preventing the formation of a cumulative jet, the cleaning and activation of the welded surfaces take place ahead of the contact point by the plasma flows. Impact plasma forms in the welding gap during the hypersonic discharge of the high-temperature impact-compressed gas at its boundary with the welded surfaces.     

Influence of the meshing clearance on the performance of conjugate helical surfaces

Meshing clearance is significant in both the manufacturing and operating practice of products applying conjugate helical surfaces. Based on the clearance-caused rotation angle of the return stroke for different meshing clearance, the influence of the meshing clearance on the performance of conjugate helical surfaces, such as conjugation interaction, contact area, continuity of the contact line, noise level and smooth running, etc., is explored in depth in this paper. It is concluded that the meshing clearance should be so designed that the resulting clearance-caused rotation angle of the return stroke is as uniform as possible.     

Corrosion behaviors of carbon steel induced by life activities of Phaeodactylum tricornutum in a marine environment

Microbiologically influenced corrosion induced by bacteria has been studied for many years. Corrosion is known to be sensitive to the presence of microalgae, such as Phaeodactylum tricornutum. However, the life activity of P. tricornutum that influences the general and localized corrosion of carbon steel is not fully understood. The current study uses a combination of immersion tests and electrochemical experiments with a detailed surface characterization to reveal the naturally formed corrosion products with/without the presence of P. tricornutum. The results show that samples suffer from pitting corrosion and the averaged pit depths are approximately 15 μm under a light–dark cycle condition or a 24-h constant light condition. Meanwhile, the corrosion products are mainly comprised of γ-FeOOH and Fe₃O₄ in a constant light condition. However, γ-FeOOH, Fe₃O₄, and FeCO₃ are found in a light–dark cycle. This study proposes the fundamental mechanisms of the effect of P. tricornutum life activities on the corrosion performance of Q235 carbon steel, to fulfill the knowledge gaps of the presence of microalgae inducing the general and pitting corrosion of carbon steel.     

浅谈Q235普通碳素钢与16MnR低合金钢的焊接

根据Q235普通碳素钢与16MnR低合金钢焊接的实例分析和试验结果，阐述了Q235普通碳素钢与16MnR低合金钢焊接结构，在选择焊缝金属填材料时的方法。     

离心铸造WC颗粒增强钢基复合材料辊环的研制

介绍了WCp/钢基复合材料轧辊的材料选择和制备工艺 ,并对其显微组织及力学性能进行了分析。工业实验结果表明 :复合材料轧辊的寿命比普通Cr12轧辊高 3倍以上     

基于弹性模型的三角网格曲面优化展开

根据材料力学中杆件的变形及弹性变形能分析,提出了曲面展开的弹性变形模型。根据边的变形情况,将曲面展开分为约束展开和无约束展开,并对每种展开方法进行分析。特别是约束展开时产生的变形能,根据曲面展开时的判断准则,对弹性变形能进行释放,得到优化的曲面展开。最后给出了曲面展开的算法步骤及实例。该方法中曲面展开的局部精度较易控制,因此较之以前的方法,更能有效地解决CAD/CAGD中曲面展开问题。