Enhanced intergranular corrosion resistance and tensile strength in 304 stainless steel with dispersed nanocrystallines
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Tibor Donic Faculty of Mechanical Engineering, University of Zilina, Zilina, 101026, Slovikia
Hongding Wang School of Mechatronic Engineering, Lanzhou Jiaotong University, Lanzhou, 730070, China (Received 18 December 2015; accepted 4 April 2016)
Microstructure evolution and tensile properties of large dimensional bulk 304 stainless steel after being rolled with different thickness reductions were characterized in detail. The results showed that the steel consisted of nano-submicro-microcrystalline austenite and nanocrystalline ferrite. Submicrocrystalline austenite was broken down with the thickness reduction, when thickness reduction was 70%, all submicrocrystalline were broken down to nanocrocrystalline, and dispersed more uniformly in the microcrystalline austenite phase in the steel, but the grain size of the nanocrystalline austenite increased to 70 nm. Tensile strength increased from 850 MPa to 965 MPa, yield strength increased from 652 MPa to 837 MPa, elongation decreased from 33% to 19%, intergranular corrosion rate decreased from 1.36 g/(m2 h) to 0.46 g/(m2 h). Strength and intergranular corrosion properties increased much. When the thickness reduction was 70%, the tensile strength, yield strength, elongation, and intergranular corrosion properties were the best in the reported value of the steel.
I. INTRODUCTION
304 stainless steel is widely used in industry and daily life owing to its excellent corrosion resistance. But its low yield strength forced the increase of parts thickness, which caused materials waste, the burdens of environmental pollution, and high cost. In general, the yield strength of alloys could be greatly enhanced by precipitation, phase transformation, and grain refinement.1–6 However, there is considerable loss of ductility and corrosion resistance at the same time,1–6 which limited their industrial applications. It is found that the existence of some amount of nanograins embedded in the microcrystalline grains matrix to form a micro-nanocrystalline structure could obtain high tensile strength and good ductility in steel.7,8 The micro-nanocrystalline structure is successfully developed by powder metallurgy method,9,10 but the method is complicated and difficult to scale up for Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] Foundation Project: National Natural Science Foundation of China (No. 50674051) and Program for New Century Excellent Talents in University of China Education Ministry. DOI: 10.1557/jmr.2016.167 J. Mater. Res., 2016
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industrialization. Furthermore, it has porous inevitably, which decrease the uniform elongation of the steel. Rolling is a simple method to produce micronanocrystalline structure, which is nonporous and has high tensile strength and ductility.11 In this paper, we found a new nanostructure design route in which the nanocrocrystalline austenite was well dispersed in a microcrystalline austenite matrix. After being processed, the tensile strength
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