Sensitization of an austenitic stainless steel due to the occurrence of δ-ferrite

2019 ◽  
Vol 37 (2) ◽  
pp. 179-186 ◽  
Author(s):  
Carlos R. Arganis-Juárez ◽  
Audi Vázquez ◽  
Nelson F. Garza-Montes-de-Oca ◽  
Rafael Colás
Keyword(s):  
Stainless Steel ◽  
Annealing Treatment ◽  
304 Stainless Steel ◽  
Solution Temperature ◽  
Force Microscopy ◽  
Ferrite Number ◽  
Δ Ferrite ◽  
Phase Images ◽  
Degree Of Sensitization ◽  
High Degree

AbstractA series of analyses were conducted on samples of an austenitic type 304 stainless steel that exhibited a high degree of sensitization (DOS) after being subjected to a solution annealing treatment at 1050°C. The DOS was detected by electrochemical potentiokinetic tests. Examination by scanning electron microscopy of etched samples revealed the presence of δ-ferrite within the austenitic matrix, and of the segregation of chromium and nickel in either phase; images obtained by atomic force microscopy revealed localized attack at the austenite/δ-ferrite interface. It was found that the DOS and the ferrite number of the steel were reduced as the material was held at the solution temperature for longer times. Aging at 650°C showed precipitation of chromium carbides at grain boundaries and at the austenite/δ-ferrite interface; this treatment increased the DOS.

The effects of morphology of ferrite and non-metallic inclusions on corrosion behaviour of as-cast 304 stainless steel

CORROSION ◽  
10.5006/3763 ◽  
2021 ◽  
Author(s):  
Danbin Jia ◽  
Liangcai Zhong ◽  
Jingkun Yu ◽  
Zhaoyang Liu ◽  
Yuting Zhou ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Corrosion Resistance ◽  
Corrosion Behaviour ◽  
Solidification Process ◽  
Inclusion Size ◽  
304 Stainless Steel ◽  
Experimental Conditions ◽  
Quenching Temperature ◽  
Δ Ferrite ◽  
Metallic Inclusions

The effects of morphology of ferrite and non-metallic inclusions on corrosion resistance of as-cast 304 stainless steel (304 SS) were investigated. With the decrease in quenching temperature from 1723 K to 1648 K, the different microstructures of the as-cast 304 SS were obtained as the following series: austenitic-lathy δ ferrite, austenitic-colony δ ferrite and austenitic-blocky δ ferrite, and the average inclusion size increased. The electrochemical results show that the sample with the microstructure of austenitic- lathy δ ferrite and smaller size inclusions had a higher corrosion tendency and the lower pitting resistance. Furthermore, the effect of morphology and content of ferrite on corrosion resistance was greater than that of inclusion size under the current experimental conditions. Therefore, a promising method was developed to improve the corrosion resistance of as-cast 304 SS by changing the solidification process.

Eddy current technique as a nondestructive method for evaluating the degree of sensitization of 304 stainless steel

2020 ◽  
Vol 173 ◽  
pp. 108742
Author(s):  
Yeganeh Kelidari ◽  
Mehrdad Kashefi ◽  
Mostafa Mirjalili ◽  
Mahla Seyedi ◽  
Thomas W. Krause
Keyword(s):  
Stainless Steel ◽  
Eddy Current ◽  
Nondestructive Method ◽  
304 Stainless Steel ◽  
Current Technique ◽  
Degree Of Sensitization

Effect of Cold Rolling on Sensitization of 304 Stainless Steel Weldments

2013 ◽  
Vol 856 ◽  
pp. 60-63
Author(s):  
M. Milad ◽  
N. Zreiba
Keyword(s):  
Stainless Steel ◽  
Heat Input ◽  
Cold Work ◽  
304 Stainless Steel ◽  
Optimum Level ◽  
Microstructural Investigation ◽  
Welding Heat Input ◽  
Degree Of Sensitization ◽  
Electrochemical Potentiokinetic Reactivation ◽  
Cold Rolled

The sensitization of stainless steel type AISI304 (304SS) is evaluated as a function of pre-welding cold work and welding heat input. 304SS is cold rolled to various percentages of thickness reduction of up to 50% at ambient temperature before being TIG welded. The susceptibility of 304SS to sensitization (weld decay) is evaluated using ASTM A262, practice A and electrochemical potentiokinetic reactivation tests. The results indicate that the influence of pre-welding cold work on the degree of sensitization (DOS) is distinct and appreciable within the range of 10% to 35% CR. In addition, within this range the optimum level of cold work after which the DOS starts to decrease is found to be inversely related to the amount of welding heat input. At higher levels of cold work of ≥ 35% CR, it is found that neither the cold work nor the heat input significantly influences the amount of DOS. Microstructural investigation showed that the predominant intergranular corrosion (IGC) occurs at austenite grain boundaries and less likely at ferrite / austenite interfaces of the weld metal. Meanwhile, transgranular attack at austenite bulk matrix along the defects is rarely observed.

Electrochemical Atomic Force Microscopy Study of the Dissolution Kinetics of 304 Stainless Steel

1996 ◽  
Vol 451 ◽  
Author(s):  
T. J. Mckrell ◽  
J. M. Galligan
Keyword(s):  
Stainless Steel ◽  
Electrical Potential ◽  
Dissolution Kinetics ◽  
Microscopy Study ◽  
304 Stainless Steel ◽  
Electrochemical Characteristics ◽  
Surface Kinetics ◽  
Chemical Surface ◽  
Force Microscopy ◽  
Atomic Force

ABSTRACTAn electrochemical atomic force microscope (ECAFM) has been employed to observe, in situ, the topographical and electrical changes that occur on 304 stainless steel as a function of an electrical potential. The concurrent acquisition of a polarization curve and topographical data allows direct correlation of variations in the surface roughness with the electrochemical characteristics of the passivation process. Also, the large AFM scan size, employed in this study, allows for the delineation and determination of the interdependence of the surface kinetics at various regions of the surface. Simultaneous measurements of topographical and electrical changes at these regions have established a correspondence of the competing kinetics between the reactions of dissolution and passivation. This provides a way to relate chemical surface reactions to surface topography.

Investigations on the Microstructure and the Fracture Surface of Pulsed Nd: YAG Laser Welding of AISI 304 Stainless Steel

2012 ◽  
Vol 445 ◽  
pp. 418-423
Author(s):  
Seyed Ali Asghar Akbari Mousavi ◽  
A. Garehdaghi
Keyword(s):  
Stainless Steel ◽  
Laser Welding ◽  
Cooling Rate ◽  
304 Stainless Steel ◽  
Chemical Compositions ◽  
Operational Parameters ◽  
Δ Ferrite ◽  
Higher Power ◽  
304 Austenitic Stainless Steel ◽  
Pulsed Nd:Yag Laser Welding

The paper presents pulsed Nd:YAG laser welding of the 304 stainless steels. The welding tests were carried out with various operational parameters. The effects of laser welding variables on the geometry, microstructure and solidification of the weld are considered. The austenitic or ferritic solidification is produced in the 304 austenitic stainless steel depended upon the cooling rate and its chemical compositions. The possiblity of austenitic solidification compared with the ferritic solidification decreases with the chromium to nickel equivalent ratio and that increases with cooling rates. Moreover, more δ ferrite is obtained if the cooling rate is increased or the higher power laser is used. The surface of fracture samples was considered and the reason for failure was investigated. The study shows that the fracture is in ductile type.

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