Effect of Mechanical Surface Treatments on the Surface State and Passive Behavior of 304L Stainless Steel

At a Glance

Metadata	Details
Publication Date	2021-01-12
Journal	Metals
Authors	Kathleen Jaffré, Benoît Ter-Ovanessian, Hiroshi Abe, Nicolas Mary, Bernard Normand
Institutions	Tohoku University, Centre National de la Recherche Scientifique
Citations	24
Analysis	Full AI Review Included

Executive Summary

This study investigates the critical influence of mechanical surface finishing (dry grinding vs. fine polishing) on the subsurface microstructure, residual stress, and passive film stability of 304L Stainless Steel (SS).

Surface Disorder Correlation: The degree of surface disorder (roughness, plastic deformation, residual stress) is directly correlated with the quality and stability of the native passive film.
Grinding Detriment: Dry grinding creates the most detrimental surface state, characterized by high roughness (1300 nm RMS), maximum compressive stress (-432 MPa), and a deep work-hardened zone beneath the ultrafine grain layer.
Passive Film Quality: The passive film formed on the ground surface was the thinnest (1.4-1.6 nm) and contained the highest concentration of point defects (N_A and N_D), indicating high reactivity and instability.
Optimal Finish: Polishing down to 1 µm diamond paste resulted in the lowest residual stress (-110 MPa), minimal subsurface damage, and the thickest (3-3.5 nm) and most stable passive film with the lowest defect density.
Corrosion Resistance: Electrochemical testing confirmed that the ground surface exhibited enhanced reactivity and poor corrosion resistance, losing its passive behavior quickly in chloride solution, while the finely polished surfaces maintained superior stability.
Engineering Implication: Surface finishing must be precisely controlled to minimize subsurface defects and residual stresses, as these factors are essential determinants of the long-term corrosion and Stress Corrosion Cracking (SCC) resistance of 304L SS components.

Technical Specifications

Parameter	Value	Unit	Context
Material	304L Austenitic	Stainless Steel	Commercial plate
Buffer Solution pH	9.2	(Unitless)	H₃BO₃ (0.05 M) / Na₂B₄O₇ 10H₂O (0.075 M)
Reference Electrode Potential	0.65	V vs. SHE	Mercury/Mercurous Sulfate (MSE)
Grinding Roughness (RMS)	1300 ± 200	nm	Top surface texture
1 µm Polish Roughness (RMS)	16 ± 4	nm	Top surface texture
Grinding Residual Stress	-432 ± 17	MPa	Compressive stress (XRD)
1 µm Polish Residual Stress	-110 ± 84	MPa	Compressive stress (XRD)
Grinding Ultrafine Layer Thickness	150-280	nm	Subsurface microstructure (TEM)
1 µm Polish Ultrafine Layer Thickness	150	nm	Subsurface microstructure (TEM)
Grinding Passive Film Thickness (δ)	1.4-1.6	nm	Determined by EIS/Capacitance
1 µm Polish Passive Film Thickness (δ)	3-3.5	nm	Determined by EIS/Capacitance
Grinding Acceptor Density (N_A)	8.0 x 10²⁰	cm^-3	Mott-Schottky analysis (p-type region)
1 µm Polish Acceptor Density (N_A)	2.2 x 10²⁰	cm^-3	Mott-Schottky analysis (p-type region)
Grinding Donor Density (N_D)	6.0 x 10²⁰	cm^-3	Mott-Schottky analysis (n-type region)
1 µm Polish Donor Density (N_D)	3.8 x 10²⁰	cm^-3	Mott-Schottky analysis (n-type region)
Polarization Scan Rate	0.5	mV·s^-1	Potentiodynamic measurement

Key Methodologies

The study employed a multi-scale approach combining surface characterization, microstructural analysis, and advanced electrochemical techniques.

Surface Preparation Protocols:
- Grinding: Manual dry grinding using Green Ace Gold (#46) followed by Mac flat disc (#60), designed to induce significant thermomechanical damage.
- Polishing (2400 SiC): Manual polishing using sequential SiC emery papers up to 2400 grit.
- Polishing (1 µm): SiC polishing followed by sequential diamond paste polishing down to 1 µm.
Microstructural and Stress Characterization:
- Roughness: Measured using a MICROMAP 3D optical profilometer, focusing on the Root Mean Square (RMS) parameter.
- Subsurface Microstructure: Transmission Electron Microscopy (TEM) performed on Focused Ion Beam (FIB) cross-sections to identify the ultrafine grain layer and plastic deformation zones.
- Residual Stress: Measured by X-ray Diffraction (XRD) using the cosα method on the austenite (311) plane, providing an average stress value within the top 10 µm.
Passive Film Formation and Stability:
- Immersion: Samples were immersed for 24 h in the borate buffer solution (pH 9.2) to stabilize the passive film.
- Potentiodynamic Polarization: Used to determine the Open Circuit Potential (OCP) and characterize the passive plateau current density and transpassivation behavior (oxidation of Cr³⁺ to Cr⁶⁺).
- Mott-Schottky (MS) Analysis: Performed via Multi-Frequency Electrochemical Impedance Spectroscopy (EIS) to determine the semiconductive type (p-type at low potential, n-type at high potential) and quantify the doping densities (N_A and N_D).
- Passive Film Thickness (δ): Calculated from the complex capacitance representation derived from EIS data, assuming a relative dielectric constant (ε) of 12.
Corrosion Susceptibility Testing:
- Pitting Test: Cyclic Potentiodynamic Polarization (CPP) was conducted in a highly aggressive 2.5 M NaCl solution (pH 6.5) to evaluate resistance to localized corrosion based on the pitting potential (E_p).

Commercial Applications

The findings directly impact industries where the long-term reliability and corrosion resistance of stainless steel components are critical, particularly in environments prone to localized corrosion or SCC.

Nuclear Energy Sector: Essential for qualifying surface finishing procedures (e.g., grinding vs. electropolishing) for components exposed to primary circuit water, where residual stresses and surface defects significantly increase susceptibility to SCC.
Oil and Gas / Chemical Processing: Used in the design and maintenance of pressure vessels, piping, and reactors where 304L SS is exposed to high-temperature or chloride-rich process streams. Controlling surface finish minimizes pitting initiation sites.
Infrastructure and Construction: Applications involving stainless steel reinforcement or structural elements exposed to marine or high-chloride environments, where surface preparation dictates the lifespan of the passive layer.
High-Purity Systems: Equipment used in semiconductor or pharmaceutical manufacturing, where surface quality must be maximized to prevent contamination and ensure optimal corrosion performance.
Manufacturing Quality Control: Provides quantitative metrics (residual stress, RMS roughness, N_A/N_D defect density) for establishing strict quality standards for post-machining surface treatments.

View Original Abstract

The effect of dry grinding on 304L stainless steel’s passive behavior is compared to two other surface finishing (mechanical polishing down to 2400 with SiC emery paper and 1 µm with diamond paste, respectively). The characterization of the surface state was performed using scanning electron microscopy, transmission electron microscopy, 3D optical profilometer, and X-ray diffraction. Results indicate that each surface treatment leads to different surface states. The ground specimens present an ultrafine grain layer and a strong plastic deformation underneath the surface, while an ultrafine grain layer characterizes the subsurface of the polished specimens. Grinding induces high residual compressive stresses and high roughness compared to polishing. The characterization of the passive films was performed by electrochemical impedance spectroscopy and Mott-Schottky analysis. The study shows that the semiconductor properties and the thickness of the passive films are dependent on the surface state of the 304L stainless steel.

Tech Support

Original Source

DOI: https://doi.org/10.3390/met11010135

References

2002 - Semiconducting properties of oxide and passive films formed on AISI 304 stainless steel and Alloy 600 [Crossref]
2000 - Chemical composition and electronic structure of the oxide films formed on 316L stainless steel and nickel based alloys in high temperature aqueous environments [Crossref]
1995 - Electrochemical and surface studies of the passive layers grown on sputter-deposited nitrogen-stainless steel alloys in 1M H2SO4 solution [Crossref]
1998 - EIS and XPS study of surface modification of 316LVM stainless steel after passivation [Crossref]
2006 - Electrochemical & optical characterisation of passive films on stainless steels [Crossref]
1998 - Examination of the Role of Molybdenum in Passivation of Stainless Steels Using AC Impedance Spectroscopy [Crossref]
2014 - Passivity of Sanicro28 (UNS N-08028) stainless steel in polluted phosphoric acid at different temperatures studied by electrochemical impedance spectroscopy and Mott-Schottky analysis [Crossref]
2003 - Passive films on stainless steels—Chemistry, structure and growth [Crossref]
1978 - Composition of passive films on ferritic 30Cr stainless steels in H2SO4 [Crossref]
2019 - Behavior of hardened steel grinding using MQL under cold air and MQL CBN wheel cleaning [Crossref]