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Unraveling the effects of surface preparation on the pitting corrosion resistance of austenitic stainless steel

Sohrabi M. J., Mirzadeh H., Dehghanian C.

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 1

99--108

EN

The effects of surface preparation on the corrosion resistance of AISI 316L austenitic stainless steel were studied using the cyclic potentiodynamic polarization method. Grinding, mechanical polishing, and electropolishing were considered as the surface modifier methods. Regarding the surface roughness parameters, besides the conventional height parameter (Ra), the kurtosis (Rku) as the shape parameter was also considered to rationalize the pitting resistance for the first time. Based on the results of the Tafel extrapolation method, it was revealed that the uniform corrosion can be adequately correlated to Ra. However, the pitting resistance was found to mainly relate to the kurtosis, where by decreasing Rku (increased bluntness of topographic features), the pitting resistance enhanced. It was also found that a surface with Rku less than three (platykurtic) is resistant to pitting attack, where this surface can be obtained via electropolishing performed for an optimum time. The effect of electropolishing on the chromium content at the surface and its relation to the corrosion properties were also discussed.

2

Toward understanding the origins of poor ductility in a metal-matrix composite processed by accumulative roll bonding (ARB)

Gharechomaghlu M., Mirzadeh H.

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 4

958--966

EN

The importance of second phase particles has received less attention for metal-matrix composites (MMCs) processed by one of the most common severe plastic deformation (SPD) techniques known as accumulative roll bonding (ARB). Accordingly, the present work has been dedicated to the processing and evaluating the effects of ARB on the tensile properties, work-hardening behavior, distribution of particles, and fracture surface appearance of a typical Al-B4C particulate composite. It was found that bonding between the reinforcement and the matrix is not good enough to grant the effective strengthening effect. As a result, both tensile strength and ductility of ARB processed aluminum were higher than those of ARB processed Al-B4C composite. Moreover, by increasing ARB pass number, the tensile strength and total elongation of composites increased, where the latter was related to the enhancement of particle distribution, improvement of the particle/matrix interface, and enhancement of the work-hardening behavior. It was revealed that particle distribution affects the ductility but its effect on the tensile strength is less pronounced.

3

Aging kinetics and mechanical properties of copper-bearing low-carbon HSLA-100 microalloyed steel

Sohrabi M. J., Mirzadeh H., Mehranpour M. S., Heydarinia A., Razi R.

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 4

1409--1418

EN

The precipitation kinetics of HSLA-100 steel and the correlation between tensile and impact properties were studied. According to the modified Johnson–Mehl–Avrami–Kolmogorov (JMAK) analysis and based on the analysis of the time corresponding to the transformed fraction of 0.5 (t0.5), the activation energy for the precipitation of copper during aging of martensite was determined as ~111 and 105 kJ/mol, respectively. These values are much smaller than the activation energy for the diffusion of Cu in a-iron, which was related to the effect of high dislocation density of the quenched martensitic microstructure on the aging process. These results were verified based on the diffusional calculations. Based on the analysis of mechanical behavior, no reasonable correlation was found between strength of the material and the impact energy. However, the impact energy was found to be propor-tional to the UTS-YS, where the latter is an indicator of the work-hardening capability of the material. This revealed that the work-hardening capacity of the material is a much more important factor for determining the impact toughness compared to its strength.

4

Contribution of Different Hardening Mechanisms during Cold Working of AISI 304L Austenitic Stainless Steel

Mirzaie T., Mirzadeh H., Naghizadeh M.

Archives of Metallurgy and Materials

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2018

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Vol. 63, iss. 3

1317--1320

EN

The contributions of work-hardening of austenite and the presence of martensite on the hardening of an AISI 304L stainless steel were evaluated based on plastic deformation under different reductions in thickness at two rolling temperatures. The cold deformation temperatures of 300 K and 373 K were chosen to induce strain-hardening plus strain-induced martensitic transformation in the former and strain-hardening in the latter. This made it possible to elucidate the real effects of strengthening mechanisms of metastable austenitic stainless steels during mechanical working.