Through-thickness microstructural evolution during grain boundary engineering type thermomechanical processing and its implication on sensitization behavior in austenitic stainless steel

Large amount of nitrogen addition into an austenitic stainless steel can improve the mechanical properties and corrosion resistance remarkably as far as the nitrogen is in solid solution. However, once the nitrogen precipitates as nitride, it results in deteriorations in the properties of the high nitrogen austenitic stain steel. During welding, a high nitrogen austenitic stainless steel is ready to precipitate rapidly immense amounts of chromium nitride in the heat affected zone (HAZ), as intergranular or cellular morphologies at or from grain boundaries into grain interiors. The nitride precipitation reduces seriously the local mechanical properties and corrosion resistance. The present authors have demonstrated that a thermomechanical-processing as grain boundary engineering (GBE) inhibited intergranular chromium carbide precipitation in the HAZ of a type 304 austenitic stainless steel during welding and improved the intergranular corrosion resistance drastically. In the present study, the thermomechanical-processing was applied to a high nitrogen austenitic stainless steel containing 1 mass% nitrogen to suppress the nitride precipitation at or from grain boundaries in the HAZ during welding by GBE. GBE increases the frequency of coincidence site lattice (CSL) boundaries in the material so as to improve the intergranular properties, because of strong resistance of CSL boundaries to intergranular deteriorations. The optimum parameters in the thermomechanical-processing brought a very high frequency of CSL boundaries in the high nitrogen austenitic stainless steel. The GBE suppressed the intergranular and cellular nitride precipitation in the HAZ of the high nitrogen austenitic stainless steel during welding.

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Arrest of weld-decay in 304 austenitic stainless steel by twin-induced grain boundary engineering

Acta Materialia ◽

10.1016/j.actamat.2007.06.005 ◽

2007 ◽

Vol 55 (16) ◽

pp. 5401-5407 ◽

Cited By ~ 84

Author(s):

H. Kokawa ◽

M. Shimada ◽

M. Michiuchi ◽

Z.J. Wang ◽

Y.S. Sato

Keyword(s):

Stainless Steel ◽

Austenitic Stainless Steel ◽

Grain Boundary ◽

Grain Boundary Engineering ◽

304 Austenitic Stainless Steel

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Prevention of Corrosion in Austenitic Stainless Steel through a Predictive Numerical Model Simulating Grain Boundary Chromium Depletion

Modeling and Simulation Techniques in Structural Engineering - Advances in Civil and Industrial Engineering ◽

10.4018/978-1-5225-0588-4.ch013 ◽

2017 ◽

pp. 374-389

Author(s):

M.K. Samal

Keyword(s):

Mathematical Model ◽

Stainless Steel ◽

Austenitic Stainless Steel ◽

Numerical Model ◽

Low Temperature ◽

Grain Boundary ◽

Stainless Steels ◽

Predictive Models ◽

Chromium Depletion ◽

Sensitization Behavior

In this chapter, a mathematical model for rate of formation of chromium carbides near the grain boundary, which is a pre-cursor to chromium depletion and corresponding sensitization behavior in stainless steels, is presented. This model along with the diffusion equation for chromium in the grain has been used to obtain chromium depletion profiles at various time and temperature conditions. Finite difference method has been used to solve the above equations in the spherical co-ordinate system and the results of time-temperature-sensitization diagrams of four different types of alloys have been compared with those of experiment from literature. For the problem of low temperature sensitization and corresponding inter-granular corrosion in austenitic stainless steel, it is very difficult to carry out experiment at higher temperatures and justify its validity at lower operating temperatures by extrapolation. The development of predictive models is highly useful in order to design the structures for prevention of corrosion of the material in aggressive environments.

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Arrest of Intergranular Corrosion in Austenitic Stainless Steel by Twin-induced Grain Boundary Engineering(Student Poster Session)

Proceedings of the Asian Pacific Conference on Fracture and Strength and International Conference on Advanced Technology in Experimental Mechanics ◽

10.1299/jsmeatemapcfs.2.01.03.0_1036 ◽

2001 ◽

Vol 2.01.03 (0) ◽

pp. 1036-1040

Author(s):

Masayuki Shimada ◽

Hiroyuki Kokawa ◽

Zhan Jie Wang ◽

Yutaka S. Sato

Keyword(s):

Stainless Steel ◽

Austenitic Stainless Steel ◽

Grain Boundary ◽

Intergranular Corrosion ◽

Poster Session ◽

Grain Boundary Engineering ◽

Engineering Student

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Grain Boundary Engineering for Intergranular Corrosion Resistant Austenitic Stainless Steel

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.261-263.1005 ◽

2004 ◽

Vol 261-263 ◽

pp. 1005-1010 ◽

Cited By ~ 8

Author(s):

Hiroyuki Kokawa ◽

Masahiko Shimada ◽

Zhan Jie Wang ◽

Yutaka S. Sato ◽

M. Michiuchi

Keyword(s):

Stainless Steel ◽

Corrosion Resistance ◽

Sulfuric Acid ◽

Austenitic Stainless Steel ◽

Grain Boundary ◽

Thermomechanical Treatment ◽

Intergranular Corrosion ◽

Ferric Sulfate ◽

Grain Boundary Engineering ◽

Intergranular Corrosion Resistance

Optimum parameters in the thermomechanical treatment during grain boundary engineering (GBE) were investigated for improvement of intergranular corrosion resistance of type 304 austenitic stainless steel. The grain boundary character distribution (GBCD) was examined by orientation imaging microscopy (OIM). The intergranular corrosion resistance was evaluated by electrochemical potentiokinetic reactivation (EPR) and ferric sulfate-sulfuric acid tests. The sensitivity to intergranular corrosion was reduced by the thermomechanical treatment and indicated a minimum at a small roll-reduction. The frequency of coincidence-site-lattice (CSL) boundaries indicated a maximum at the small pre-strain. The ferric sulfate-sulfuric acid test showed much smaller corrosion rate in the thermomechanical-treated specimen than in the base material for long time sensitization. The optimum thermomechanical treatment introduced a high frequency of CSL boundaries and the clear discontinuity of corrosive random boundary network in the material, and resulted in the high intergranular corrosion resistance arresting the propagation of intergranular corrosion from the surface.

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