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Microstructure and corrosion behaviour of gas tungsten arc welds of maraging steel

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Defence Technology（防务技术） 2015年第1期11卷 48-55页

作者： g.madhusudhan reddy K.SRINIVASA RAO Defence Metallurgical Research Laboratory Department of Metallurgical Engineering Andhra University

Superior properties of maraging steels make them suitable for the fabrication of components used for military applications like missile covering, rocket motor casing and ship hulls. Welding is the main process for fabrication of these components, while the maraging steels can be fusion welded using gas tungsten arc welding(gTAW) process. All these fabricated components require longer storage life and a major problem in welds is susceptible to stress corrosion cracking(SCC). The present study is aimed at studying the SCC behaviour of MDN 250(18% Ni) steel and its welds with respect to microstructural changes. In the present study, 5.2 mm thick sheets made of MDN 250 steel in the solution annealed condition was welded using gTAW process. Post-weld heat treatments of direct ageing(480 C for 3 h), solutionizing(815 C for 1 h) followed by ageing and homogenizing(1150 C for 1 h) followed by ageing were carried out. A mixture of martensite and austenite was observed in the microstructure of the fusion zone of solutionized and direct aged welds and only martensite in as-welded condition. Homogenization and ageing treatment have eliminated reverted austenite and elemental segregation. Homogenized welds also exhibited a marginal improvement in the corrosion resistance compared to those in the as-welded, solutionized and aged condition. Constant load SCC test data clearly revealed that the failure time of homogenized weld is much longer compared to other post weld treatments, and the homogenization treatment is recommended to improve the SCC life of gTA welds of MDN 250 Maraging steel.

关键词： 18% Ni maraging steel gas tungsten arc welding Post weld heat treatment Solutionising Ageing treatment Pitting corrosion Stress corrosioncracking (SCC)

Microstructure and pitting corrosion of shielded metal arc welded high nitrogen stainless steel

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Defence Technology（防务技术） 2015年第3期11卷 237-243页

作者： RAFFI MOHAMMED g.madhusudhan reddy K.SRINIVASA RAO Department of Metallurgical Engineering Andhra University Defence Metallurgical Research Laboratory

The present work is aimed at studying the microstructure and pitting corrosion behaviour of shielded metal arc welded high nitrogen steel made of Cromang-N electrode. Basis for selecting this electrode is to increase the solubility of nitrogen in weld metal due to high chromium and manganese content. Microscopic studies were carried out using optical microscopy(OM) and field emission scanning electron microscopy(FESEM). Energy back scattered diffraction(EBSD) method was used to determine the phase analysis, grain size and orientation image mapping. Potentio-dynamic polarization testing was carried out to study the pitting corrosion resistance in aerated 3.5% NaCl environment using a gillAC electrochemical system. The investigation results showed that the selected Cr-Mn-N type electrode resulted in a maximum reduction in delta-ferrite and improvement in pitting corrosion resistance of the weld zone was attributed to the coarse austenite grains owing to the reduction in active sites of the austenite/delta ferrite interface and the decrease in galvanic interaction between austenite and delta-ferrite.

关键词：耐点蚀性能高氮不锈钢焊缝金属电弧焊接研究组织屏蔽场发射扫描电子显微镜奥氏体晶粒

Microstructure and pitting corrosion resistance of AA2219 Ale Cu alloy friction stir welds e Effect of tool profile

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Defence Technology（防务技术） 2015年第2期11卷 123-131页

作者： Ch VENKATA RAO g.madhusudhan reddy K.SRINIVASA RAO Department of Metallurgical Engineering Andhra University Defence Metallurgical Research Laboratory

AA2219 Ale Cu alloy is widely used in defence and aerospace applications due to required combination of high strength-to-weight ratio and *** of components used for defence always involves *** though the mechanical properties of the base metal are better,but the alloy suffers from poor mechanical and corrosion properties during fusion *** overcome the problems of fusion welding,friction stir welding(FSW) is recognized as an alternative solid state joining method aimed to improve the mechanical and corrosion *** profile is one of the important variables which affect the performance of the friction stir *** the present work the effect of tool profile on the microstructure and pitting corrosion of AA2219 aluminiumecopper alloy was *** backscattered diffraction results established that the grain size and orientation of weld nugget of triangle profile is finer than that of conical *** scanning calorimetric results show the evidence of precipitate dissolution during *** was found that the microstructure changes,such as grain size and its orientation precipitate dissolution during FSW influence the hardness and corrosion *** corrosion resistance of friction stir welds of AA2219 was found to be better for triangle profile tool compared to conical profile which is attributed to material flow and strengthening precipitate morphology in various *** amount of heat generation during FSW made using triangle profile tool may be the reason for greater dissolution of strengthening precipitates in nugget zone and coarsening in thermo mechanically affected zone(TMAZ) and heat affected zone(HAZ).

关键词： Al-Cu合金搅拌摩擦焊接微观结构轮廓点蚀摩擦搅拌焊接电子背散射衍射机械性能

Pitting corrosion resistance and bond strength of stainless steel overlay by friction surfacing on high strength low alloy steel

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Defence Technology（防务技术） 2015年第3期11卷 299-307页

作者： Amit Kumar SINgH g.madhusudhan reddy K.Srinivas RAO Defence Metallurgical Research Laboratory Andhra University

Surface modification is essential for improving the service properties of components. Cladding is one of the most widely employed methods of surface modification. Friction surfacing is a candidate process for depositing the corrosion resistant coatings. Being a solid state process, it offers several advantages over conventional fusion based surfacing process. The aim of this work is to identify the relationship between the input variables and the process response and develop the predictive models that can be used in the design of new friction surfacing applications. In the current work, austenitic stainless steel AISI 304 was friction surfaced on high strength low alloy steel substrate. Friction surfacing parameters,such as mechtrode rotational speed, feed rate of substrate and axial force on mechtrode, play a major role in determining the pitting corrosion resistance and bond strength of friction surfaced coatings. Friction surfaced coating and base metal were tested for pitting corrosion by potentiodynamic polarization technique. Coating microstructure was characterized using optical microscopy, scanning electron microscopy and X-ray diffraction. Coatings in the as deposited condition exhibited strain-induced martensite in austenitic matrix. Pitting resistance of surfaced coatings was found to be much lower than that of mechtrode material and superior to that of substrate. A central composite design with three factors(mechtrode rotational speed, substrate traverse speed, axial load on mechtrode) and five levels was chosen to minimize the number of experimental conditions. Response surface methodology was used to develop the model. In the present work, an attempt has been made to develop a mathematical model to predict the pitting corrosion resistance and bond strength by incorporating the friction surfacing process parameters.

关键词：奥氏体不锈钢摩擦堆焊粘结强度低合金高强度抗蚀性钢表面耐点蚀性能

Influence of process parameters on physical dimensions of AA6063 aluminium alloy coating on mild steel in friction surfacing

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Defence Technology（防务技术） 2015年第3期11卷 275-281页

作者： B.VIJAYA KUMAR g.madhusudhan reddy T.MOHANDAS Department of Mechanical Engineering Guru Nanak Institute of Technology Defence Metallurgical Research Laboratory Department of Mechanical Engineering Nalla Malla Reddy Engineering College

An attempt is made in the present study to obtain the relationships among process parameters and physical dimensions of AA6063 aluminium alloy coating on IS2062 mild steel obtained through friction surfacing and their impact on strength and ductility of the coating. Factorial experimental design technique was used to investigate and select the parameter combination to achieve a coating with adequate strength and ductility. Spindle speed, axial force and table traverse speed were observed to be the most significant factors on physical dimensions. It was observed that the thickness of the coating decreased as the coating width increased. In addition, the width and thickness of the coatings are higher at low and high torques. At intermediate torque values, when the force is high, the width of the coating is high, and its thickness is thin; and when the force is low, the width and thickness are low. The interaction effect between axial force(F)-table traverse speed(Vx) and spindle speed(N)-table traverse speed(Vx) produced an increasing effect on coating width and thickness, but other interactions exhibited decreasing influence. It has also been observed that sound coatings could be obtained in a narrow set of parameter range as the substrate-coating materials are metallurgically incompatible and have a propensity to form brittle intermetallics.

关键词：合金涂层摩擦表面尺寸物理工艺参数碳钢涂层厚度试验设计技术

Effect of welding processes and consumables on fatigue crack growth behaviour of armour grade quenched and tempered steel joints

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Defence Technology（防务技术） 2014年第1期10卷 47-59页

作者： g.MAgUDEESWARAN V.BALASUBRAMANIAN g.madhusudhan reddy Department of Mechanical Engineering PSNA College of Engineering & Technology Kothandaraman Nagar Muthanampatti Centre for Materials Joining & Research Department of Manufacturing Engineering Annamalai University Metal Joining group Solidification Technology Division Defence Metallurgical Research LaboratoryKanchanbagh

Quenched and Tempered(Q&T) steels are widely used in the construction of military vehicles due to its high strength to weight ratio and high hardness. These steels are prone to hydrogen induced cracking(HIC) in the heat affected zone(HAZ) after welding. The use of austenitic stainless steel(ASS) consumables to weld the above steel was the only available remedy because of higher solubility for hydrogen in austenitic phase. The use of stainless steel consumables for a non-stainless steel base metal is not economical. Hence, alternate consumables for welding Q&T steels and their vulnerability to HIC need to be explored. Recent studies proved that low hydrogen ferritic steel(LHF) consumables can be used to weld Q&T steels, which can give very low hydrogen levels in the weld deposits. The use of ASS and LHF consumables will lead to distinct microstructures in their respective welds. This microstructural heterogeneity will have a drastic influence in the fatigue crack growth resistance of armour grade Q&T steel welds. Hence, in this investigation an attempt has been made to study the influence of welding consumables and welding processes on fatigue crack growth behaviour of armour grade Q&T Steel joints. Shielded metal arc welding(SMAW) and Flux cored arc welding(FCAW) were used for fabrication of joints using ASS and LHF consumables. The joints fabricated by SMAW process using LHF consumable exhibited superior fatigue crack growth resistance than all other joints.

关键词：焊接工艺疲劳裂纹扩展行为消耗品钢接头装甲回火淬火

Influence of tool pin profile on microstructure and corrosion behaviour of AA2219 Al-Cu alloy friction stir weld nuggets

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Defence Technology（防务技术） 2015年第3期11卷 197-208页

作者： Ch.VENKATA RAO g.madhusudhan reddy K.SRINIVASA RAO Department of Metallurgical Engineering Andhra University Defence Metallurgical Research Laboratory

To overcome the problems of fusion welding of aluminium alloys, the friction stir welding(FSW) is recognized as an alternative joining method to improve the mechanical and corrosion properties. Tool profile is one of the important variables which affect the performance of the FS weld. In the present work, the effect of tool profile on the weld nugget microstructure and pitting corrosion of AA2219 aluminium-copper alloy was studied. FSW of AA2219 alloy was carried out using five profiles, namely conical, square, triangle, pentagon and hexagon. The temperature measurements were made in the region adjacent to the rotating pin. It was observed that the peak temperature is more in hexagonal tool pin compared to the welds produced with other tool pin profiles. It is observed that the extensive deformation experienced at the nugget zone and the evolved microstructure strongly influences the hardness and corrosion properties of the joint during FSW. It was found that the microstructure changes like grain size, misorientation and precipitate dissolution during FSW influence the hardness and corrosion behaviour. Pitting corrosion resistance of friction stir welds of AA2219 was found to be better for hexagon profile tool compared to other profiles, which was attributed to material flow and strengthening precipitate morphology in nugget zone. Higher amount of heat generation in FS welds made with hexagonal profile tool may be the reason for greater dissolution of strengthening precipitates in nugget zone.

关键词： Al-Cu合金搅拌摩擦焊微观结构焊缝区刀具腐蚀行为焊接接头性能耐腐蚀性能

Microstructure,mechanical and corrosion behavior of high strength AA7075aluminium alloy friction stir welds-Effect of post weld heat treatment

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Defence Technology（防务技术） 2015年第4期11卷 362-369页

作者： P.Vijaya Kumar g.madhusudhan reddy K.Srinivasa Rao Department of Mechanical Engineering R.I.T. Defence Metallurgical Research Laboratory Department of Metallurgical Engineering Andhra University

High strength aluminium alloy AA7075(Al-Zn-Mg-Cu) is a precipitate hardenable alloy widely used in the aerospace,defense,marine and automobile *** of the heat treatable aluminium alloys in all these sectors is ever-increasing owing to their excellent strength-toweight ratio and reasonably good corrosion *** shortage in corrosion resistance,however,usually poses negative concern about their reliability and lifetime when they service in the variable marine *** alloys also exhibit low weldability due to poor solidification microstructure,porosity in fusion zone and lose their mechanical properties when they are welded by fusion welding *** stir welding(FSW) is a reliable technique to retain the properties of the alloy as the joining takes place in the solid *** welds are susceptible to corrosion due to the microstructural changes in the weld nugget during *** this work,the effect of post weld treatments,viz.,peak aging(T6) and retrogression & reaging(RRA),on the microstructure,mechanical properties and pitting corrosion has been *** stir welding of 8 mm-thick AA7075 alloy was carried *** microstructural changes of base metal and nugget zone of friction stir welds were studied using optical microscopy,scanning electron microscopy and transmission electron *** and hardness test of base metal and welds has been carried *** corrosion resistance was determined through dynamic polarization *** was observed that the hardness and strength of weld were observed to be comparatively high in peak aged(T6) condition but the welds showed poor corrosion *** resistance to pitting corrosion was improved and the mechanical properties were maintained by RRA *** resistance to pitting corrosion was improved in RRA condition with the minimum loss of weld strength.

关键词： 7075铝合金高强度铝合金搅拌摩擦焊耐腐蚀性热处理效果微观结构焊缝机械性能

Microstructure and pitting corrosion of armor grade AA7075 aluminum alloy friction stir weld nugget zone-Effect of post weld heat treatment and addition of boron carbide

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Defence Technology（防务技术） 2015年第2期11卷 166-173页

作者： P.VIJAYA KUMAR g.madhusudhan reddy K.SRINIVASA RAO Department of Mechanical Engineering R.I.T. Defence Metallurgical Research Laboratory Department of Metallurgical Engineering Andhra University

Friction stir welding(FSW) of high strength aluminum alloys has been emerged as an alternative joining technique to avoid the problems during fusion *** recent times FSW is being used for armor grade AA7075 aluminum alloy in defense,aerospace and marine applications where it has to serve in non uniform loading and corrosive *** though friction stir welds of AA7075 alloy possess better mechanical properties but suffer from poor corrosion *** present work involves use of retrogression and reaging(RRA) post weld heat treatment to improve the corrosion resistance of welded joints of aluminum *** attempt also has been made to change the chemical composition of the weld nugget by adding B4C nano particles with the aid of the FSW on a specially prepared base metal plate in butt *** effects of peak aged condition(T6),RRA and addition of B4C nano particles on microstructure,hardness and pitting corrosion of nugget zone of the friction stir welds of AA7075 alloy have been *** though RRA improved the pitting corrosion resistance,its hardness was slightly *** improvement in pitting corrosion resistance was achieved with addition of boron carbide powder and post weld heat treatment of RRA.

关键词： 7075铝合金搅拌摩擦焊焊后热处理碳化硼颗粒抗点蚀微观结构装甲 7075合金