• Journal of the Korean Society for Heat Treatment
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• v.23 no.2
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• pp.90-95
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• 2010

The effects of grain size on the corrosion resistance of 429EM ferritic stainless steels for automobile exhaust system were investigated. Using specimens held at maximum service temperature of $950^{\circ}C$ for 10~70 hours, electrochemical polarization tests were conducted. While corrosion current density, $I_{corr}$, was influenced little by grain size, pitting potential, $E_p$, was increased with an increase of grain size. Sensitizaton at grain boundary occurred when the specimen were held at $950^{\circ}C$ for above 50 hours because of the dissolution of precipitates and grain coarsening.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.4
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• pp.427-434
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• 2004

Ferritic stainless steel is recently used in high temperature structures because of its good properties of thermal fatigue resistance, corrosion resistance, and low price. Tensile and low-cycle fatigue (LCF) tests on 429EM stainless steel used in exhaust manifold were performed at several temperatures from room temperature to 80$0^{\circ}C$. Elastic Modulus, yield strength, and ultimate tensile strength monotonically decreased when temperature increased. Cyclic hardening occurred considerably during the most part of the fatigue life. Dynamic strain aging was observed in 200~50$0^{\circ}C$, which affects the cyclic hardening behavior. Among the fatigue parameters such as plastic strain amplitude, stress amplitude, and plastic strain energy density (PSED), PSED was a proper fatigue parameter since it maintained at a constant value during LCF deformation even though cyclic hardening occurs considerably. A phenomenological life prediction model using PSED was proposed considering the influence of temperature on fatigue life.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.7 s.250
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• pp.757-764
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• 2006

Isothermal cyclic stress-strain deformation and thermomechanical deformation (TMD) of 429EM stainless steel were analyzed using a rheological model employing a bi-linear model. The proposed model was composed of three parameters: elastic modulus, yield stress and tangent modulus. Monotonic stress-strain curves at various temperatures were used to construct the model. The yield stress in the model was nearly same as 0.2% offset yield stress. Hardening relation factor, m, was proposed to relate cyclic hardening to kinematic hardening. Isothermal cyclic stress-strain deformation could be described well by the proposed model. The model was extended to describe TMD. The results revealed that the hi-linear thermomechanical model overestimates the experimental data under both in-phase and out-of-phase conditions in the temperature range of $350-500^{\circ}C$ and it was due to the enhanced dynamic recovery effect.

• Journal of Welding and Joining
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• v.29 no.4
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• pp.85-92
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• 2011

Microstructures and tensile properties in arc brazed joints of ferritic stainless steel, 429EM using Cu-8.6%Al insert metal was investigated as function of brazing current. The brazing speed was fixed at 800mm/min and brazing current varied in the range of 80A to 120A. The initial phase of filler metal was Cu single phase. However, the insert metal structures of brazed joints was composed of Cu matrix and intermetallic compound such as ${\gamma}_1(Al_4Cu_9)$, and flower-shape Fe-Cr. The fraction of ${\gamma}_1(Al_4Cu_9)$ phase was similar with 80A and 100A brazing currents while that of brazed with 120A was decreased. On the other hand, the fraction of Fe-Cr phase increased with increasing of the brazing current. A reaction layer at the base metal/insert metal interface was observed and this reaction layer was thickened with increasing of the brazing current. In the brazed joints with the current lower than 100A, crack was grew up along the interface which was perpendicular to the tensile stress, and then, passed through the insert metal in the final stage of fracture. As the brazing current increased to 120A, fracture occurred at the base metal.

• Korean Journal of Metals and Materials
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• v.48 no.4
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• pp.289-296
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• 2010

The effects of heat input and different microstructureswere investigated on the tensile-shear properties of an arc-brazed joint of theferritic stainless steel 429EM using a Cu-Si insert alloy. The brazing speed was fixed at 800 mm/min whilethe brazing current varied from 80 to 120A. For abrazing current lower than 100A, fracturing occurred at the joint root in the direction perpendicular to the tensile load. As the brazing current increased to 120A, fracturing occurred at the base metal or the joint root. The joint and the base metal had very similar yield and tensile load values. However, the amount of elongation was decreased considerably compared to when the base metal was used. The fracturing began at the triple point of the root part and was classified into three types. The difference in the tensile-shear properties was closely related to the three fracture types.