18-8不銹鋼熔接棒によるα系鋼材熔接の基礎研究(第1報)

Improved design fatigue curves were developed in the Subcommittee on Design Fatigue Curve in the Atomic Energy Research Committee in the Japan Welding Engineering Society (JWES). Working Group on Design Fatigue Curves (WG DFC) in the JSME has studied the validity and the applicability of the improved design fatigue curves developed in the JWES to incorporate into the JSME Environmental Fatigue Evaluation Method. The authors propose a fatigue analysis method using the design fatigue curves developed in the JWES that are applied revised factors to optimize the environmental fatigue analysis. Also, the Japanese pressurized water reactor (PWR) utility group developed equations of environmental fatigue factors (Fen) for austenitic stainless steel base metal, weld metal and cast stainless steel in PWR environment. The WG DFC has investigated the Fen equations and concluded that the Fen equation of austenitic stainless steel base metal is the most conservative among the three equations and close to NUREG/CR-6909 Rev.1 [24]. The authors propose to use the Fen equation for base metal for austenitic stainless steels for all of the base metal, weld metal and cast stainless steel. In addition, the authors have confirmed that the employment of the proposed Fen equation to the proposed design fatigue curves of austenitic stainless steels accurately predicts the existing environmental fatigue test data of austenitic stainless steels, which were used in the development of the current Fen equation of austenitic stainless steels in PWR environments in the JSME Environmental Fatigue Evaluation Method. Therefore, the proposed Fen equation can be applied to environmental fatigue evaluation for austenitic stainless steels.

The corrosion resistance of a newly developed iron-base, Fe-Mn-Al austenitic, and duplex weld metal has been examined in the NACE solution consisting of 5 wt.% NaCl, 0.5 wt.% acetic acid, and the balance distilled water. The electrochemical techniques such as potentiodynamic polarization, Tafel plots, linear polarization, cyclic polarization, and open-circuit potential versus time were employed. The Fe-Mn-Al weld metals did not passivate and exhibited high corrosion rates. Fe-Cr-Ni (310 and 316) weld and base metals were also examined in the NACE solution at room temperature. The 310 and 316 base metals were more resistant to corrosion than the as-welded 310 and 316 weld metals. Postweld heat treatment (PWHT) improved the corrosion performance of the Fe-Mn-Al weld metals. The corrosion resistance of Fe-Mn-Al weld metals after PWHT was still inferior to that of the 310 and 316 weld and base metals.

Impact behavior of different stainless steel weldments at low temperatures

Mechanism of δ-ferrite decomposition in high Si-bearing austenitic stainless steel weld metal during aging at 550°C

In this research, variations of tensile properties and fracture behavior of 316L austenitic stainless steel weld metal as a function of aging temperature and time have been investigated. Stainless steel plates were butt-welded using GTAW process. Weld metal tensile specimens were subjected to various aging heat treatments at temperatures of 750 and 850°C for periods of 1 to 100 hours prior to tensile tests at 25 and 500°C. Dissolution of delta-ferrite and formation of sigma phase network during aging resulted in a mild increase in tensile strength and significant reduction in ductility, particularly at 25°C. Although fracture surfaces exhibited ductile features, the dimple morphology and the macroscopic fracture mode were found to be affected by aging. The unaged weld metal exhibited a classic mode of cup and cone fracture, whereas slant and flat types of fracture modes were observed in the aged weld metals, with the slant mode being dominant at 500°C. The slant mode was associated with deformation localization along arrays of primary voids, nucleated at cracked sigma phase particles, oriented at about 45° to loading direction. The transition in the fracture mode is further discussed based on variations in the dimple morphologies and strain hardening exponent.

In this study, an attempt on pulsed-fiber laser welding on an austenitic-duplex stainless steel butt joint configuration was investigated. The influence of various welding parameters, such as beam diameter, peak power, pulse repetition rate, and pulse width on the weld beads geometry was studied by checking the width and depth of the welds after each round of welding parameters combination. The weld bead dimensions and microstructural progression of the weld joints were observed microscopically. Finally, the full penetration specimens were subjected to tensile tests, which were coupled with the analysis of the fracture surfaces. From the results, combination of the selected weld parameters resulted in robust weldments with similar features to those of duplex and austenitic weld metals. The weld depth and width were found to increase proportionally to the laser power. Furthermore, the weld bead geometry was found to be positively affected by the pulse width. Microstructural studies revealed the presence of dendritic and fine grain structures within the weld zone at low peak power, while ferritic microstructures were found on the sides of the weld metal near the SS 304 and austenitic-ferritic microstructure beside the duplex 2205 boundary. Regarding the micro-hardness tests, there was an improvement when compared to the hardness of duplex and austenitic stainless steels base metals. Additionally, the tensile strength of the fiber laser welded joints was found to be higher when compared to the tensile strength of the base metals (duplex and austenitic) in all of the joints.

The structural features and phase composition are examined in near-surface layers of specimens of Al-Mg, Al-Cu-Mg alloys and commercially pure titanium obtained by plasma cutting using direct current straight polarity (DCSP) and direct current reverse polarity (DCRP). It is found that the flows of molten metal ejected by the gas stream from the cut cavity during cutting form the fusion and heat-affected zones, whose structural morphology, phase composition, and thickness depend on both the selected material and the cutting mode. The fusion zone is thicker in specimens cut using DCRP than in those cut with DCSP. The thickness of the adjacent heat-affected zone is also the largest in the mode that provides a thicker fused layer. Aluminum alloy specimens cut in ambient air are characterized by the presence of oxygen in the near-surface layers. The lowest degree of oxidation is observed in Al-Mg alloy. Oxygen penetrates into the fused layer to a depth of 350–500 μm in Al-Cu-Mg and up to 200–250 μm in Al-Mg alloy. In titanium alloy, the thickness of oxide layers does not exceed 100–150 μm during straight polarity cutting and 200–250 μm during reverse polarity cutting. A thin brittle layer of TiO and TiO2 oxides is formed on the titanium alloy surface. It is shown that the generation of “water mist” around the plasma jet when cutting materials of all types with DCRP leads to a more intensive oxidation of metal, less thermal effect on the material, and reduced roughness of the cut face.

The effect of water environment on microstructural characteristics, compositional heterogeneity and microhardness distribution of 16Mn/304L dissimilar welded joints

Work rele vance. The using of mechanical harmonic oscillations of welding pool or tool are inexpensive and quite simple procedure formation desirable degree of dispersion structure it means weld metal strength. Possibility of oscillations differently applied relative of the surfacing (welding) process axis lets welding seam or surfacing bead formation with certain anizotropy of mechanical properties in given direction.Many works have dedicated of researches of microstructure formation by conditions of periodic action on weld melt. However, the most part of it are devoted mostly researching to influence oscillations with frequency much superior value of 5 Hz and amplitude value range from some microns to 2–3 mm.Purpose of work is getting quantity dependencies which defining hardness value of weld metal and metal of HAZ as a function of technological and oscillations modes parameters.Research methods. For researchers the samples have had prepared and polished to #8 Mirror Finish by ISO (ГОСТ 25593 – 83). The surfacing process in CO2 protection environment had has carried out by alloy wire named G3Si1 by EN 13479 ISO 143341 (ТУ У 322-4-392-96) which diameter1.2 mm. Base metal was common quality carbon steel type Е 235-С by ISO 630:1995, ISO 1052:1982 (ДСТУ 2651:2005). Measurement of hardness (by Vickers) had carried out on hardness tester named LECO M-400 under indenter load1 kgby ISO 6507-1:2007 (ДСТУ ISO 6507-1:2007). Research resultants had treatment by regression analysis methods with application of analytics software package STATISTICA 12 and engineering math software PTC Mathcad Prime 3.1.Results. Regressive models of hardness value as function magnitudes arc current, the surfacing process velocity, amplitude and frequency oscillations have received. Contour plots of depend of hardness value from amplitude and frequency magnitudes were created. Variant of predict of the receiving maximum value hardness weld metal and metal of HAZ at arc current125 Aand the surfacing process speed 14 m/h are presented.Scientific novelty. The experiments were carried out with different amplitude and frequency values which were given through programming step motor.Empirical depends of influence of technological and oscillation modes parameters of certain range on weld metal hardness and metal HAZ hardness values are created.Practical value. An increase possibility of hardness values of weld metal and metal of HAZ due to use weld pool oscillations with frequency value range 2.5–4.5 Hz and amplitude value range 3–7 mm was proven. The magnitudes of amplitude and frequency permitting receives maximum hardness values at optimal values of arc current and the surfacing velocity were obtained.

Summary This paper describes an investigation of the grain boundary migration occurring at the weld metal surface, comparing the actually observed grain boundary migration and the results predicted by the thermal grooving theory of grain boundary migration based on the flow of surface atoms. The relationship between the solidification grain boundary plane angle in relation to the direction normal to the surface and the amount of grain boundary migration are discussed. The results obtained may be summarised as follows. 1. The grain boundary migration occurring at the weld metal surface differs in a number of important respects from that which occurs inside. Grain boundary migration is here basically observed to occur from the columnar crystals towards the axial crystals. In this case, the solidification grain boundary plane is inclined at less than around 40° in relation to the direction normal to the surface. The cross sectional shape of the grain boundary groove qualitatively resembles the analytical solution predicted by the thermal grooving theory of grain boundary migration based on the flow of surface atoms. The direction of grain boundary migration also agrees with the analytical solution. In the weld metal, grain boundary migration therefore occurs through being susceptible to the effect of the flow of surface atoms depending on the angle at which the solidification grain boundary plane is inclined in relation to the direction normal to the surface. 2. As the solidification grain boundary plane becomes increasingly inclined in relation to the direction normal to the surface, the amount of grain boundary migration at the weld metal surface increases. At a solidification grain boundary plane angle of less than around 40°, however, the amount of grain boundary migration at the surface sharply decreases. The grain boundary migration induced by the flow of surface atoms also only ever occurs near the surface. This is due to the fact that the grain boundary plane inside migrates in the wake of the grain boundary groove migration at the surface. That is to say, the grain boundary plane inside acts as a friction coefficient in relation to the velocity of migration itself. This friction coefficient is proportional to the third power of the grain boundary length (corresponding to the number of atoms migrating across the grain boundary plane). Incidentally, fewer atoms migrate across the inside grain boundary plane as the solidification grain boundary plane becomes increasingly inclined in relation to the direction normal to the surface, the velocity of grain boundary migration consequently increases and the amount of grain boundary migration increases.

Clarifying the effect of irradiation and thermal treatment on the austenitic microstructure and austenitic hardening in austenitic stainless steel weld metal

Effects of pretest aging on creep crack growth properties of type 308 austenitic stainless steel weld metals

Extruded plates of pure magnesium and AZ31 magnesium alloy were welded by TIG without using the filler metal and sound joints free from weld defects were obtained. Tensile strength of the welded joints were compared with that of the base metals at room and elevated temperatures and the results were discussed in relation to the crystallographic textures of the base and weld metals. It has been confirmed by XRD and EBSD analyses that the base metals show strong basal plane textures, whereas the weld metals have more random orientation distribution. At room temperature, the TIG welded joints of wrought magnesium materials show appreciably lower tensile strength than that of the base metals. However, tensile strength of the welded joints becomes nearly the same as that of the base metals at elevated temperatures. The low joint efficiency at room temperature observed in the weld joints can be attributed to the difference in the Taylor factor between the weld and base metals. The base metals with a strong basal plane texture have higher values of Taylor factor, and hence have higher yield and tensile strength than the weld metals. At elevated temperature, plastic anisotropy of magnesium decreases to such an extent that the effect of texture on the tensile strength disappears, and thus the joint efficiency increases to about 100%.

High hardness and wear resistance of bucket tooth are required in the face of abrasion and impact. High manganese steel is hard and ductile, making it more suitable for bucket tooth materials. Bucket tooth can wear out and need to be returned to their original size, so that bucket tooth that have been eroded must be coated with a hard material, using a hard facing process. In this study, the hard facing process was carried out in bucket tooth containing 10.4%, 11.60%, 12.70%, 13.60%, and 14.60% men (manganese) elements, using hard facing electrodes of the AWS A5.13 (JIS Z 3251). Hard facing process was using SMAW welding with an average heat input of 1087.43 J/mm. The hard facing process shown that the hardness of weld metal was always lower than of HAZ (Heat Affected Zone) and base metal. The hardness of the weld metal was almost the same for all types of the bucket tooth, which was about 233.478 HVN.

Microstructure and properties of titanium alloy electron beam weldments based on the different heat input conditions of the same line energy