ニッケル,鉄-ニッケル及びステンレス鋼心線溶接棒による水中溶接

In multi-pass welding of high manganese austenitic steel, weld metal is solidified in austenite single phase and hot cracking may occur depending on residual stress. In order to identify the cracking morphology, a fracture surface of the cracking of weld metal in multi-pass welding test was observed. The fracture surface indicated a dendritic morphology and a bunching pattern; therefore, it is considered that the crack in the multi-pass weld metal is caused by residual liquid film or remelting liquid film. Varestraint test was carried out in order to clarify the characterization of the crack, and then the fracture surface of cracks obtained by the test was observed. Transverse-type and longitudinal Varestraint test were used for getting typical fracture surfaces of solidification cracking in weld metal, and liquation cracking in reheat weld metal and heat affected zone of base metal, respectively. Comparing the fracture surfaces of cracks of Varestraint test and crack in practice, the fracture surface of the solidification cracking was most similar to the crack in multi-pass weld metal in this study. Thus, it is considered from comparing the fracture surfaces that solidification cracking might mainly occur in the multi-pass welding of the high manganese steel.

The welding of ultra-high hard armour (UHA) steel is highly challenging due to their higher hardness (600 HV) and higher carbon equivalent (0.80). In this investigation, 15-mm-thick UHA steel plates are welded by shielded metal arc welding (SMAW) process using three different consumables such as austenitic stainless steel (ASS), low-hydrogen ferritic steel (LHF), and duplex stainless steel (DSS). The joints were tested against a 7.62 × 54 mm Armor-piercing (AP) projectile. All three joints successfully stopped the projectile at weld metal and interface (weld/HAZ) without perforation. The ballistic performance and mechanical properties are improved than the currently used ASS electrodes, and a new method to study the mode of failure at weld metal and interface was introduced. Striations and microcracks are preferred modes of failure than wear debris in the weld metal, and soft/hard mode is preferred over soft/soft and hard/hard modes of failure at the interface.

Cracking susceptibility control of 7075 aluminum alloy in pulsed laser welding with filler strip

There are many practical applications in which austenitic stainless steel electrodes are utilized in welding of various plain carbon and alloy steels (low and high). Since the above joining is also considered as a so-called disimilar-metal welding from the standpoint of chemical composition, it is naturally expected that penetration ratio of base metal to the austenitic stainless steel weld metal, in other words, the degree of dilution of austenitic stainless steel weld metal by base metal may depend upon several welding conditions, and the mechanical and chemical properties may accordingly he different, too. The present researches were conducted in order to disclose, systematically and fundamentally, the relation between the above properties of austenitic stainless steel weld metal and several welding conditions.In this report, relations between polarity and welding current, amount of penetration and penetration ratio of base metal to the austenitic stainless steel weld metal, hardness of austenitic weld metal and microstructure, etc., in each single bead which was deposited on four kinds of carbon steel plates with plain 18-8 austenitic stainless steel electrode consisting of commercial 18-8 austenitic stainless steel core wire of 4mm. in diameter and suitable coating, were studied. D. C. (straight and reverse polarity) and a. c. were used. Welding speed and thickness of base metal were constant, 203mm/min and 10 mm respectively. The results obtained are as follows :(1) In either d. c. (straight and reverse polarity) or a. c., the amount of penetration and penetration ratio, . etc., have a tendency to increase linearly as welding current increases. And also in this case, the above penetration ratio increases from about 20 to 60 percent as welding current increases from 95 to 175 amperes.(2) Penetration ratio has a little, tendency to increase, as carbon content of base metal increases.(3) Penetration ratio with a. c. is smaller than with d. c., in the same welding current value. (4) There is only a little difference between penetration ratio in d. c. straight polarity and that' in d. c. reverse polarity. In this experiment, however, penetration ratio in d. c. straight polarity is larger than that in d. c. reverse polarity for the range of lower welding current value. On the contrary, penetration ratio in d. c. reverse polarity is larger than in d. c. straight polarity for the range ot higher welding current value.(5) Vickers hardness of austenitic stainless steel weld metal is comparatively high. And Vickers hardness of austenitic weld metal containing high carbon base metal is lower for the range of smaller penetration ratio, but higher for the iange of larger penetration ratio, than that of the metal containing low carbon base metal.(6) Micro-hardness at the side of austenitic stainless steel weld metal of the vicinity of weld fusion line increases linearly as welding current increases, and is higher in the weld metal containing high carbon base metal than in the one containing, low carbon base metal. Consequently, the tendency of the above micro-hardness change is clearly different from that of Vickers hardness change.(7) Both maximum Vickers hardness of heat-affected zone and micro-harness of the vicinity of weld fusion line of that same zone in base metal, tend to decrease as welding current increases.

In this report, the effect of microstructural change during aging at around 1000 K on the susceptibility of reheat cracking in the FCAW weld metal of Type 308 stainless steel was investigated. Precipitates in the weld metal sampled from actual equipment, which was damaged during operation, were identified and the change in the microstructures were observed with aged weld metals which were made from the flux cored wires with various Bi contents.Ferrite contents were depressed compared with the as-welded condition and it was observed that most of the ferrite phases were transformed to σ phases and carbides in the weld metal sampled from the actual equipment. As for the aged specimen, σ phases and carbides precipitation were observed under specific aging conditions, however, Bi had no effect on incubation time for precipitation of the σ phase. Therefore, Bi does not promote the precipitation of the brittle phase. On the other hand, oxygen contents of the weld metal and hardness of the austenite phases increased with increasing Bi contents in the weld metal. This phenomenon is considered to be the dispersion hardening by oxide particles including Bi oxide and can be the secondary factor that increases the susceptibility of the reheat cracking in the FCAW weld metal.

Prediction of hydrogen cracking in the wet welding of structural steels with ferritic stick electrodes down to 20 m

A low transformation temperature (LTT) welding consumable has been developed to prevent cold cracking in high strength steel welded joints without preheating. In the LTT welded joint, the residual tensile stress is reduced by martensitic expansion of weld metal formed by the LTT consumable. In the weld cracking tests, cold cracking in the LTT weld metal is successfully prevented under high restraint conditions, but cold cracking occurs at very low joint restraint strength in case the weld metal is fully martensitic. Chemical compositions of the consumable are designed to retain austenite in martensite in the newly developed weld metal to absorb the diffusible hydrogen into the austenite to prevent cold cracking. In the newly developed LTT weld metal, cold cracking is almost fully suppressed without preheating under every joint restraint condition.

Toughness and weld solidification cracking in the weld metal of martensitic stainless steel containing Ni were investigated. The weld metal of martensitic stainless steel with low C and proper Ni can be applied without PWHT (Post weld heat treatment) due to the microstructure mainly consisting of soft martensite including retained austenite resulting in enough toughness though PWHT is necessary in conventional one because of high hardness as weld condition. However by the addition of Ni the susceptibility to weld solidification cracking can be higher. As the experimental evaluation was conducted in terms of solidification cracking test and Charpy impact test using the weld metal of 12/16%Cr-3/14%Ni steels. As the results the slight amount of ferrite phase caused the lowering of notch toughness within the weld metal including the same level of retained austenite. The excess Ni addition to decrease ferrite phase in solidification process increased the susceptibility to solidification cracking in during solidification process by austenite phase. In conclusion optimum Cr and Ni content to achieve the both of low susceptibility to solidification cracking and high toughness was clarified.

Austenitic stainless steel is more or less difficult with conventional gas nitriding treatment, but it can be nitrided after appropriate pre-heat treatment. The pretreatment was more effective upon nitriding for austenitic stainless steel than martensitic stainless steel. Both thickness and microhardness measurements indicated that effect of the nitriding treatment was more sensitive in austenitic stainless steel than martensitic stainless steel with nitriding time. Fatigue strength was most increased with SACM 645 steel among three steels.

Energy crisis and global warming demand development of high-performance structural materials to improve energy efficiency.For efficient energy conversion,the operating temperature and pressure of a heat engine used in boiler/steam turbine power plants should be as high as possible and materials used for the engine components must be able to withstand the high operating temperature.As such,next-generation structural materials simultaneously possessing higher creep strength and larger oxidation-resistance at elevated temperatures than those currently used are required.The conventional austenitic stainless steels,which rely on the formation of a tenacious Cr2O3 scale,would lose its protection capability at temperatures above 923 K,in particular in the presence of sulfur and water vapor.The alumina-forming austenitic(AFA) stainless steels are a relatively new class of dispersionstrengthened austenitic steels which showed superior oxidation-resistance to conventional stainless steels due to formation of the Al2O3-based protective scale at high temperatures.Recently,research focuses in this field have been mainly placed on high temperature oxidation-resistance,while little attention was paid to the mechanical property of these steels,particularly at elevated temperatures.In order to fully understand the deformation mechanisms at high temperatures,the recrystallization behavior in a typical AFA stainless steel under different conditions,including different annealing temperatures and durations,were investigated.The high-temperature mechanical properties of the AFA stainless steel samples heat-treated under different conditions were also studied.The sample was fully recrystallized upon heat treatment at 1473 K for at least 2 h and showed tensile strength about 130 MPa when tested at 1023 K with a strain rate 6.4×10-7s-1.The specimen was partially recrystallized upon heat treatment at1373 K for 0.5 h and exhibited a higher tensile strength of 150 MPa with decreased plasticity when tested under the same condition.Further investigation shows that the grain growth was influenced by the precipitation of NbC.The grain growth exponent,n,was determined to be 3 and the apparent activation energy for grain growth is 234.7 kJ/mol,which is consistent with that of the Nb diffusion along the grain boundary in the austenite.

Tantalum, niobium, stainless steels, and nickel are corrosion-resistant metals that have become critical in many industrial sectors. Due to the demanding environments and temperatures in which they operate, few materials can serve as substitutes. The advantages of these materials are offset by the difficulties in their machining. Belonging to a group of metals and alloys often referred to as ‘gummy’, their poor machinability or gumminess is manifest as thick chip formation, large cutting forces, and poor finish on cut surface. Hence, machining costs can be prohibitive, and applications limited. The gumminess has been attributed broadly to their high strain-hardening capacity. To examine why these metals are difficult to machine, we used direct in situ observations of the cutting process with a high-speed imaging system, complemented by force measurements. The observations showed that chip formation occurred by repeated large-amplitude folding of the material – sinuous flow – with vortex-like components and extensive redundant deformation. The folding was particularly severe in Ta and Nb. Although Ta and Nb displayed a higher rate of fold nucleation than the Ni and stainless steel, the flow dynamics underlying chip formation across the metals was the same – sinuous flow nucleated by a plastic (buckling-type) flow instability on the workpiece surface just ahead of the advancing tool. The large strains and energy dissipation associated with sinuous flow is the reason for the poor machinability of these metals. Prior work with Cu and Al has shown that sinuous flow can be disrupted and replaced by an energetically more favorable (segmented) flow mode, characterized by quasi-periodic fracture, when suitable chemical media are applied to the initial workpiece surface – a mechanochemical effect. The segmented flow is beneficial for machining processes since it involves much smaller forces and plastic strains. It has been hypothesized that the chemical media influence the flow through their adsorption onto the workpiece surface, thereby altering the surface energy and/or surface stress, and effecting a local embrittlement (ductile-to-brittle transition). We demonstrate similar media (mechanochemical) effects and segmented flow development in cutting of the corrosion-resistant metals, with significant benefits for their machining. These benefits include > 35 percent reduction in the cutting force/energy, and an order of magnitude improvement in cut surface quality (finish, tears and residual strain). Importantly, the experiments with the corrosion-resistant metals provide strong evidence that it is indeed adsorption – not corrosion, as in case of hydrogen embrittlement – that underpins the mechanochemical effect. The experiments used chemical agents well-known for their strong adsorption to metal surfaces, namely green corrosion inhibitors (e.g., plant extracts, propolis) and other natural organic molecules (e.g., dyes, antibacterial drugs, cow’s milk). Lastly, the suitability and application of the mechanochemical effect at industrial cutting speeds is explored in turning experiments with these corrosion-resistant metals. Collectively, our observations, measurements, and analysis show that the gumminess of metals in cutting is due to sinuous flow; the gumminess can be eliminated by use of chemical media; and adsorption is the key to engendering the mechanochemical effect. Implications of the results for industrial processes ranging from machining to particle comminution, and for sustainable manufacturing are discussed.

Basic-coated electrodes are preferred for welding medium and thick section austenitic stainless steels because these consumables provide weld metal with high toughness, quality and resistance to cracking. Strength and toughness of weld metals depend on their microstructure, which is determined by the concentration of various alloying elements, impurities as well as the welding thermal cycle. However, in basic-coated electrodes, optimisation of flux formulation is complex because slag detachability is a problem with basic fluxes that confer high weld metal toughness. This study investigates the effects of systematically varying the cerium oxide content in the flux coating used in a basic-coated austenitic stainless steel electrode for shielded metal arc welding (SMAW). SMAW process with 16-mm-thick stainless steel plates and in-house-developed electrodes of 3.15 mm in size added with different levels of cerium oxides in the flux coating was used to prepare the weld pads. The weld pads were qualified with radiography examination as per ASME section III class I components. Tensile specimens were prepared as per American Society for Testing and Materials (ASTM) E8 and tensile properties were evaluated at both ambient and service temperatures. Charpy ‘U’ notch impact specimens were prepared in the as-welded and fully sensitized conditions (1,023 K/100 h) and the impact tests were carried out as per ASTM E23. Variation in the weld metal chemistry, mechanical properties, oxygen content, inclusion morphology and microstructure with cerium oxide content in the flux was examined. The results indicated that at an optimal level of cerium oxide addition in the flux coating played a major role in reducing sulphur and oxygen content; subsequently, it improved the mechanical properties of the weld metal. In this paper, the results of detailed studies and analysis were discussed on microstructures using optical and scanning electron microscope carried out on the weld metals produced with different levels of cerium oxide in the flux.

In this paper, shielded metal arc welding on the dissimilar joint between 2205 duplex stainless steel and composite bimetallic plates (304 L stainless steel/10CrNi3MoV steel) with a filler metal E2209 was performed. Furthermore, the microstructure, phase, mechanical properties and intergranular corrosion resistance of the joints were investigated and element distributions of the interfaces were characterized. The results show that austenite transformed to ferrite under the influence of welding thermal cycle, and then a large amount of ferrite appeared in heat affected zone (HAZ) of 2205 duplex stainless steel. Coarse bainite grains were formed in HAZ of the 10CrNi3MoV steel near the fusion line with high temperature welding thermal cycle. Fine granular bainite was also generated in HAZ of 10CrNi3MoV steel due to the relatively short exposure time to the active temperature of grain growth. Local peak temperature near the base 10CrNi3MoV steel was still high enough to recrystallize the 10CrNi3MoV steel to form partial-recrystallization HAZ due to phase change. The filler metal was compatible with the three kinds of base materials. The thickness of the elemental diffusion interfaces layers was about 100 µm. The maximum microhardness value was obtained in the HAZ of 2205 duplex stainless steel (287 ± 14 HV), and the minimum one appeared in HAZ of SS304L (213 ± 5 HV). The maximum tensile strength of the welded joint was about 670 ± 6 MPa, and the tensile specimens fractured in ductile at matrix of the composite bimetallic plates. The impact energy of the weld metal and HAZ of the 10CrNi3MoV steel tested at –20 °C were 274 ± 6 J and 308 ± 5 J, respectively. Moreover, the intergranular corrosion resistance of the weldment including 304 L stainless steel, weld metal, HAZs and 2205 duplex stainless steel was in good agreement with the functional design requirements of materials corrosion resistance.

The purpose of this work was to study the hot-corrosion behavior of dissimilar weldments of AISI 304 stainless steel and AISI 1015 low carbon steel assembled with consumable-309L stainless steel wires at 750 °C in static air with 2 mg/cm^2 mixture of various ratios of NaCl-Na_2SO_4 deposits. It was found that the HAZ of weldments revealed the coarse grain structure and the around 304 HAZ. Moreover, the carbon migrated from the substrate of low carbon steel of the higher chromium weld metal side and formed chromium carbide adjacent to the interface between the low carbon steel HAZ and weld metal. The results of hot corrosion showed that both 304 and 309L appeared the subscale attack while low carbon steel revealed the uniform corrosion. The depth of attack increased with increasing exposure duration of time. The 309L weld metal had the smallest metal loss because of its high chromium content. Due to sensitized reaction the 304 HAZ had the highest metal loss and the total depth of attack. The galvanic effect to the low carbon steel resulted in a serious corrosion with sufficient molten salts at low carbon steel HAZ/WM interface.

s: Effect of post solutionand stress relieftreatment on the stress corrosion cracking (SCC) resistance via U-bend specimens test in 42% boiling MgCl2 solution, as well as the microstructure, residual strain and mechanical properties of the forged 316LN stainless steel was studied. Results showed that the yield stress was reduced and the residual strain was eliminated through post solution-treatment for the forged steel. After immersion in boiling MgCl2 solution for 24, 48 and 72 h, respectively, all the U-bend specimens of either the solution-treated or the stress relieftreated steels suffered from clearly transgranular stress corrosion cracking (TGSCC). Furthermore, of which all the stress relief-treated specimens were entirly cracked, while the solution-treated specimens were only locally cracked after immersion for 72 h, suggesting higher SCC resistance for the forged steel after a proper post solution-treatment. Finally, the mechanism of the effect of post-heat 定稿日期:2014-11-05 基金项目:国家科技重大专项项目 (2011ZX06004-009)资助 作者简介:郭跃岭,男,1990年生,硕士生 通讯作者:韩恩厚,E-mail:ehhan@imr.ac.cn,研究方向为苛刻环境中材料的腐蚀与防护 (核电高温高压水、石油化工环境等等) DOI:10.11902/1005.4537.2014.223 6期 郭跃岭等:锻后热处理对核级316LN不锈钢在沸腾MgCl2溶液中应力腐蚀行为的影响 treatments on the SCC resistance was discussed in terms of the residual strain and yield stress of the forged steel.