• Journal of Korea Foundry Society
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• v.35 no.5
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• pp.109-113
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• 2015

In this study, the measurement of FN (ferrite volume fraction) and the solution annealing ratio at a temperature of $1130^{\circ}C$ were determined with 15A elbow fittings of shell cast SSC13, and the corrosion resistance with and without austenitizing solution annealing were investigated in comparison with AISI304. The delta ferrite phase was observed in the material due to the slow cooling effect of the shell mold casting. However, the delta ferrite phase decreased gradually with the solution annealing at a temperature of $1130^{\circ}C$. The hardness generally decreased with a heat treatment; however, its corrosion resistance was improved with the heat treatment. In addition, when a passivation treatment was applied, its corrosion ratio showed the lowest value. The pattern of general corrosion decreased due to the decrease in the delta ferrite phase with the solution annealing treatment. Consequently, it is suggested that the corrosion resistance of SSC13 elbow fittings can be improved by increasing the ratio of any solution annealing treatment used and by decreasing the ferrite phase. The relationship between the ratio of solution annealing and delta ferrite is expressed as follows: SA (solution annealing ratio,%) = 98 - FN (ferrite volume fraction, %).

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1343-1349
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• 1988

In this study, it is investigated for the effects of stress ratio and grain size on fatigue crack growth behavior and crack closure, in ferrite-martensite dual phase steels. The results obtained are as follows ; .DELTA. $K_{th}$ is independent of the ferrite grain size, but decreases with increasing stress ratio. The relation between .DELTA. $K_{th}$ and stress ratio R is as follows : .DELTA. $K_{th}$ =15.1(1-0.95R). But (.DELTA. $K_{eff}$)$_{th}$ in terms of crack closure is approximately 2.5 MPa.root.m. Also, variation of the degree of crack deflection to crack tip opening displacement at the minimum load is considered as a parameter of crack closure.e.e.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.1
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• pp.34-40
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• 1984

In this study, martensite-ferrite dual phase steel composed of martensite in hard phase and ferrite in soft phase is made as model material, and the difference of fatigue crack propagation behavior resulted from the structural size is investigated by fracture mechanics and microstructural method. The main results obtained are as follows; 1)Fatigue crack propagation rate is influenced by ferrite grain size. In other words, in the low .DELTA. K region fatigue crack propagation rate is decreased with decreasing of grain size but the difference of propagation rate resulted from the structural size is decreased as .DELTA.K is increased. 2)The above result is explained by the degree of crack arrest effect of second phase for fatigue crack propagation depending on the ratio of reversed plastic zone size to ferrite grain size.

• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1090-1096
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• 2010

This pitting corrosion study of welded joints of austenitic stainless steels (AISI 304L and 316L) has addressed the differentiating solidification mode using three newly introduced filler wires with a flux-cored arc welding process (FCAW). The delta ferrite (${\delta}$-ferrite) content in the welded metals increased with an increasing equivalent weight ratio of chromium/nickel ($Cr_{eq}/Ni_{eq}$). Ductility dip cracking (DDC) was observed in the welded metal containing ferrite with none of AISI 304L and 0.1% of AISI 316L. The potentiodynamic anodic polarization results revealed that the $Cr_{eq}/Ni_{eq}$ ratio in a 3.5% NaCl solution didn't much affect the pitting potential ($E_{pit}$). The AISI 316L welded metals with ${\ddot{a}}$-ferrite content of over 10% had a superior $E_{pit}$ value. Though the AISI 316L welded metal with 0.1% ferrite had larger molybdenum contents than AISI 304L specimens, it showed a similar $E_{pit}$ value because the concentration of chloride ions and the corrosion product induced severe damage near the DDC.

• Korean Journal of Materials Research
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• v.13 no.4
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• pp.228-232
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• 2003

The effects of$ Nd_2$$O_3$addition on the properties of Mn-Zn ferrite were investigated in the doping concentration range from 0.05 to 0.25 wt%. All samples were prepared by standard fabrication of ferrite ceramics. With increasing the Neodymium oxides, specific density and initial permeability increased on the whole. But, the tendencies such as upper result had the measured value on limitation and characteristics saturated or decreased properties after that. With increasing the content of Neodymium oxides. both the real and imaginary component of complex permeability and the magnetic loss(tan$\delta$) increased. Because reason that magnetic loss increases is high ratio that a real department increases than imaginary department. Magnetic loss increased none the less for increasing the real department related with magnetic permeability. But, the magnetic loss of ferrite doped with the Neodymium oxides were lower than that of none doped Mn-Zn ferrite. The small amount of percent Neodymium oxides in Mn-Zn ferrite composition led to enhancement of resistivity in bulk, and more so in the grain boundary.

• Journal of Welding and Joining
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• v.18 no.1
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• pp.59-69
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• 2000

The purpose of the present study was to investigate weld metallurgical phenomena such as primary solidification mode, microstructural evolution and hot cracking susceptibility in nitrogen-bearing austenitic stainless steel GTA welds. Eight experimental heats varying nitrogen content from 0.007 to 0.23 wt.% were used in this study. Autogenous GTA welding was performed on weld coupons and the primary solidification mode and their microstructural characteristics were investigated from the fusion welds. Varestraint test was employed to evaluate the solidification cracking susceptibility of the heats and TCL(Total Crack Length) was used as cracking susceptibility index. The solidification mode shifted from primary ferrite to primary austenite with an increase in nitrogen content. Retained delta ferrite exhibited a variety of morphology as nitrogen content varied. The weld fusion zone exhibited duplex structure(austenite+ferrite) at nitrogen contents less than 0.10 wt.% but fully austenitic structure at nitrogen contents more than 0.20 wt.%. The weld fusion zone in alloys with about 0.15 wt.% nitrogen experienced primary austenite + primary ferrite solidification (mode AF) and contained delta ferrite less than 1% at room temperature. Regarding to solidification cracking susceptibility, the welds with fully austenitic structure exhibited high cracking susceptibility while those with duplex structure low susceptibility. The cracking susceptibility increased slowly with an increase in nitrogen content up to 0.20 wt.% but sharply as nitrogen content exceeded 0.20 wt.%, which was attributed to solidification mode shift fro primary ferrite to primary austenite single phase solidification.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.28 no.2
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• pp.208-215
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• 1992

Concept of primary solidification mode control was adopted to obtain optimal solidification crack resistance, hot ductility, corrosion resistance and toughness for austenitic stainless steel. By controlling primary solidification phase as primary $\delta$ and containing no ferrite at room temperature, optimal solidification crack resistance, hot ductility, corrosion resistance and cryogenic toughness could be obtained. The optimum chemical composition of austenitic stainless steel ranges 1.46~1.55(Creq/Nieq ratio) calculated by Schaeffler's equation.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.4
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• pp.372-379
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• 1990

The effect of primary solidification phase on the solidification cracking sensitivity, corrosion resistance and toughness at cryogenic temperature was investigated for the austenitic stainless steel welds. The conclusions were summarized as follows; 1. Soldification crack sensitivity of austenitic stainless steel welds depends on the primary solidification mode. 2. Austenitic stainless steels were very susceptible to solidification cracking in case of solidification as primary ${\gamma}$ and immune when solidified as primary $\delta$. 3. When the ratio of Creq/Nieq is in the range of 1.46 to 1.55, the most resistance against solidification cracking was obtained. These results agreed well with the relationship between primary solidification mode, corrosion resistance and toughness at cryogenic temperature. 4. Optimum toughness, corrosion and solidification cracking resistance can be obtained when alloys having chemical compositions described above and solidifies as primary $\delta$ containing no ferrite at room temperature.

• Journal of Welding and Joining
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• v.26 no.1
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• pp.69-75
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• 2008

Spot welding which use the main process for side block production of stainless steel railway vehicle is legged behind in laser welding about a quality and productivity. Although the laser welding has many potential advantages such as low heat input and aspect ratio of weld bead, its application to a new structural component still is required many engineering data including mechanical properties such as tensile, fatigue strength, etc on. Therefore, experimental analysis was carried out to understand the fatigue phenomena of different thickness stainless steel overlap joining panels by Nd:YAG laser welding. The fatigue life curves were obtained through fatigue tests with the various levels of applied load. The fatigue life is related with the parameters such as gap size and penetration depth through experiment. As the results, tensile strength and fatigue life were proportional in heat input level and gap was identified the major factor for fatigue life. Also we could know that deferent a-ferrite content at HAZ depend on welding heat input was important factor to determine a formation of initial crack and total fatigue life cycle.

• Corrosion Science and Technology
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• v.19 no.3
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• pp.146-155
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• 2020

To elucidate the effect of heat inputs on phase transformation and resistance to intergranular corrosion of F316 austenitic stainless steel (ASS), thermodynamic calculations of each phase and time-temperature-transformation diagram were conducted using JMaPro simulation software, oxalic acid etch test, double-loop electrochemical potentiokinetic reactivation test (DL-EPR), field emission scanning electron microscopy with energy dispersive spectroscopy, and transmission electron microscopy analyses of Cr carbide (Cr₂₃C₆), austenite phase and ferrite phase. F316 ASS containing a relatively low C content of 0.043 wt% showed a slightly sensitized microstructure (acceptably dual structure) due to a small amount of Cr carbide precipitated at heat affected zone irrespective of heat inputs. Based on results of DL-EPR test, although heat input was increased, the ratio of I_r to I_a was only increased very slightly due to a slight sensitization. Therefore, heat inputs have little influences on resistance to intergranular corrosion of F316 austenitic stainless steel containing 0.043 wt% C.