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Multi-analytical investigation of stainless steel grade AISI 420 in simulated food contact
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0002-2123-2201
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science (closed 20081231).
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science (closed 20081231).ORCID iD: 0000-0003-2206-0082
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science (closed 20081231).ORCID iD: 0000-0002-9453-1333
2009 (English)In: Journal of Food Engineering, ISSN 0260-8774, Vol. 93, no 1, 23-31 p.Article in journal (Refereed) Published
Abstract [en]

Martensitic stainless steel grade AN 420 intended for cutlery knives and scissor blades has been investigated in all attempt to correlate microstructure and surface finish (polishing procedure) to metal release rates of the main alloy constituents, iron and chromium. Metallographic investigations proved the knife steel and, in particular the scissor steel to have very inhomogeneous microstructures. The knife steel contained bands of ferrite in the martensitic structure while the scissor steel revealed large amounts of tempered martensite and inclusions of manganese sulphides and silicon oxides. Samples of different surface finish were immersed in 3 vol% acetic acid at 40 degrees C from 1 to 10 days for metal release testing. simulating food contact. The largely inhomogeneous microstructure of the scissor steel results in high and greatly varying metal release rates. despite a fairly high chromium content Of the Surface oxide. Areas of inclusions seem to act as initiation points for accelerated metal release and the forming of a surface oxide depleted in chromium, but rich in copper. The generation Of high Surface temperatures during polishing was found beneficial from a metal release perspective as a result Of the formation of a surface oxide of improved passivating properties.

Place, publisher, year, edition, pages
2009. Vol. 93, no 1, 23-31 p.
Keyword [en]
Metal release; Martensitic stainless steel; Acetic acid; Surface finish
National Category
Other Chemistry Topics
Identifiers
URN: urn:nbn:se:kth:diva-8530DOI: 10.1016/j.jfoodeng.2008.12.019ISI: 000265133700004Scopus ID: 2-s2.0-61849172424OAI: oai:DiVA.org:kth-8530DiVA: diva2:13878
Note

QC 20100810. Uppdaterad från submitted till published (20100810). Tidigare titel: Multianalytical investigation of stainless steel grade AISI 420 in simulated food contact

QC 20150731

Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2015-07-31Bibliographically approved
In thesis
1. Bioaccessibility of Stainless Steels: Importance of Bulk and Surface Features
Open this publication in new window or tab >>Bioaccessibility of Stainless Steels: Importance of Bulk and Surface Features
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

With increasing environmental awareness, the desire to protect human beings and the environment from adverse effects induced by dispersed metals has become an issue of great concern and interest. New policies, such as REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) within the European Community, have been implemented to reduce hazards posed by the use of chemicals on producers and downstream users. The generation of exposure assessment data and relevant test procedures able to simulate realistic scenarios are essential in such legislative actions.

This doctoral study was initiated to fill knowledge gaps related to the metal release process of stainless steels. A wide range of stainless steel grades, fourteen in total, were investigated. They cover a very broad range of applications, and the focus in the thesis was to simulate a few selected exposure scenarios: precipitation, the human body and food intake. Comparisons were made between metal release from stainless steel alloys and the pure metals that constitute each stainless steel in order to explore the differences between alloys and pure metals, and to provide quantitative data on metal release rates of different alloy constituents. Because of similar surface properties between stainless steel and pure chromium, this metal exhibits similar release rates, whereas iron and nickel exhibit significantly lower release rates as alloy components than as pure metals. Detailed studies were also performed to elucidate possible relations between metal release and steel surface properties. Key parameters turned out to be chromium enrichment of the self-passivating surface film, surface roughness, the electrochemically active surface area and the microstructure of the steel substrate. The degree of metal release increased with decreasing chromium content in the surface oxide, increasing surface roughness, and increasing presence of inhomogeneities in the bulk matrix.

More detailed studies were initiated to possibly correlate the nucleation of metastable pits and the extent of metal release. Evidence was given that metastable pits exist even when the stainless steel is passive, and may cause extremely short-lived bursts of released metal before the surface film repassivates again.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 73 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:39
Keyword
Stainless steel, iron, chromium, nickel, corrosion, metal release, artificial rain, synthetic body fluids, acetic acid, surface oxide, surface finish
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-4773 (URN)978-91-7178-977-8 (ISBN)
Public defence
2008-06-03, F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00
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Note
QC 20100810Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2010-08-10Bibliographically approved

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Herting, GunillaOdnevall Wallinder, IngerLeygraf, Christofer

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