Extended TOF-SIMS analysis on low-nickel austenitic stainless steels: The influence of oxide layers on hydrogen embrittlement

by Chika Izawa
Doctoral thesis
Date of Examination:2015-07-21
Date of issue:2016-01-18
Advisor:Prof. Dr. Astrid Pundt
Referee:Prof. Dr. Astrid Pundt
Referee:Prof. Dr. Reiner Kirchheim
Persistent Address: http://dx.doi.org/10.53846/goediss-5460

 

 

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Abstract

English

Hydrogen embrittlement (HE) of low-nickel austenitic stainless steels were studied with special attention to the impact of the microstructural properties such as strain induced α’-martensite, grain size, dislocation density and dislocation structure, and oxide layer. The susceptibility of the steels to HE was judged in accordance with the relative reduction of area (RRA). With careful evaluation, Md30 temperature (Nohara), which assesses martensitic transformability of steels, is adopted as a new indicator to predict HE of austenitic stainless steels. The RRA-values obtained in this study and reported data vs Md30 temperature (Nohara) reveals three distinct regions; (1) above -80 °C of Md30, RRA-values decrease with increasing Md30 temperature, (2) around -80 °C, a large variation in RRA-values (threshold band), (3) below -80 °C, constant RRA-values of nearly 100 %. Some data points deviated from the trend line in the RRA-values vs Md30 is attributed to the microstructural properties. With the careful evaluation of the impact of the oxide layer, the RRA values higher than the trend line are linked with the oxide layer type of “high constant oxide level” characterized by TOF-SIMS. 
Keywords: Oxide layer; Hydrogen Embrittlement; Austenitic Stainless Steel; TOF-SIMS; SIMS; Md30; Surface Analysis; Martensite Transformation
 
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