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Influence of grinding operations on surface integrity and chloride induced stress corrosion cracking of stainless steels
Dalarna University, School of Technology and Business Studies, Materials Technology. KTH.
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Stainless steels were developed in the early 20th century and are used where both the mechanical properties of steels and corrosion resistance are required. There is continuous research to allow stainless steel components to be produced in a more economical way and be used in more harsh environments. A necessary component in this effort is to correlate the service performance with the production processes.

The central theme of this thesis is the mechanical grinding process.  This is commonly used for producing stainless steel components, and results in varied surface properties that will strongly affect their service life. The influence of grinding parameters including abrasive grit size, machine power and grinding lubricant were studied for 304L austenitic stainless steel (Paper II) and 2304 duplex stainless steel (Paper I). Surface integrity was proved to vary significantly with different grinding parameters. Abrasive grit size was found to have the largest influence. Surface defects (deep grooves, smearing, adhesive/cold welding chips and indentations), a highly deformed surface layer up to a few microns in thickness and the generation of high level tensile residual stresses in the surface layer along the grinding direction were observed as the main types of damage when grinding stainless steels. A large degree of residual stress anisotropy is interpreted as being due to mechanical effects dominating over thermal effects.

The effect of grinding on stress corrosion cracking behaviour of 304L austenitic stainless steel in a chloride environment was also investigated (Paper III). Depending on the surface conditions, the actual loading by four-point bend was found to deviate from the calculated value using the formula according to ASTM G39 by different amounts. Grinding-induced surface tensile residual stress was suggested as the main factor to cause micro-cracks initiation on the ground surfaces. Grinding along the loading direction was proved to increase the susceptibility to chloride-induced SCC, while grinding perpendicular to the loading direction improved SCC resistance.

The knowledge obtained from this work can provide a reference for choosing appropriate grinding parameters when fabricating stainless steel components; and can also be used to help understanding the failure mechanism of ground stainless steel components during service.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2016. , 72 p.
National Category
Corrosion Engineering
Research subject
Steel Forming and Surface Engineering
Identifiers
URN: urn:nbn:se:du-23198ISBN: 978-91-7595-838-5 (print)OAI: oai:DiVA.org:du-23198DiVA: diva2:974906
Presentation
2016-02-25, Sal Q34, Osqualdas väg 6, KTH, 13:00 (English)
Opponent
Supervisors
Available from: 2016-09-28 Created: 2016-09-28 Last updated: 2016-09-28Bibliographically approved
List of papers
1. Surface integrity of 2304 duplex stainless steel after different grinding operations
Open this publication in new window or tab >>Surface integrity of 2304 duplex stainless steel after different grinding operations
2016 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 229, 294-304 p.Article in journal (Refereed) Published
Abstract [en]

Surface integrity has significant effect on service performance of a component. In this study, the evolution of the surface and sub-surface changes induced by grinding duplex stainless steel (DSS) 2304 was studied with regard to the residual stress, the microstructure, surface roughness and surface defects. The results provide insights into the effect of abrasive grit size, grinding force and lubrication on the surface integrity. The abrasive grit size was found to have the largest influence. Surface defects, a highly deformed surface layer and the generation of tensile residual stresses along the grinding direction have been found to be the main types of damage induced by the grinding operation. Residual stresses induced by mechanical effects dominate over thermal effects in this study. The results obtained can be used to understand the contribution of surface condition and residual stress on failure of duplex stainless steels in service by fatigue or stress corrosion cracking.

Keyword
duplex stainless steel 2304, grinding, residual stress, surface integrity
National Category
Materials Engineering
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-20324 (URN)10.1016/j.jmatprotec.2015.09.031 (DOI)000367106000029 ()2-s2.0-84942475434 (Scopus ID)
Available from: 2015-12-01 Created: 2015-12-01 Last updated: 2016-09-28Bibliographically approved
2. Effect of surface grinding on chloride induced SCC of 304L
Open this publication in new window or tab >>Effect of surface grinding on chloride induced SCC of 304L
2016 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 658, 50-59 p.Article in journal (Refereed) Published
Abstract [en]

The effect of surface grinding on the stress corrosion cracking (SCC) behavior of 304L austenitic stainless steel in boiling magnesium chloride has been investigated. SCC tests were conducted both without external loading and with varied levels of four-point bend loading for as-delivered material and for specimens which had been ground parallel or perpendicular to the loading direction. Residual stresses due to the grinding operation were measured using the X-ray diffraction technique. In addition, surface stress measurements under applied load were performed before exposure to evaluate the deviation between actual applied loading and calculated values according to ASTM G39. Micro-cracks initiated by a high level of tensile residual stress in the surface layer were observed for all the ground specimens but not those in the as-delivered condition. Grinding along the loading direction increased the susceptibility to chloride induced SCC; while grinding perpendicular to the loading direction improved SCC resistance. Surface tensile residual stresses were largely relieved after the initiation of cracks. (C) 2016 Elsevier B.V. All rights reserved.

Keyword
Stress corrosion cracking, Residual stress, Austenitic stainless steel 304L, Grinding
National Category
Materials Engineering
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-21370 (URN)10.1016/j.msea.2016.01.078 (DOI)000372560800007 ()
Available from: 2016-04-18 Created: 2016-04-18 Last updated: 2016-09-28Bibliographically approved

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