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Microstructure and cleavage in lath martensitic steels.

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Title: Microstructure and cleavage in lath martensitic steels.
Authors: Morris, John W1 (AUTHOR) jwmorris@berkeley.edu, Kinney, Chris1 (AUTHOR), Pytlewski, Ken1 (AUTHOR), Adachi, Y2 (AUTHOR)
Source: Science & Technology of Advanced Materials. 2013, Vol. 14 Issue 1, p1-N.PAG. 9p.
Subjects: Martensitic stainless steel, Grain size, Fracture mechanics, Brittle fractures
Abstract: In this paper we discuss the microstructure of lath martensitic steels and the mechanisms by which it controls cleavage fracture. The specific experimental example is a 9Ni (9 wt% Ni) steel annealed to have a large prior austenite grain size, then examined and tested in the as-quenched condition to produce a relatively coarse lath martensite. The microstructure is shown to approximate the recently identified 'classic' lath martensite structure: prior austenite grains are divided into packets, packets are subdivided into blocks, and blocks contain interleaved laths whose variants are the two Kurjumov-Sachs relations that share the same Bain axis of the transformation. When the steel is fractured in brittle cleavage, the laths in the block share {100} cleavage planes and cleave as a unit. However, cleavage cracks deflect or blunt at the boundaries between blocks with different Bain axes. It follows that, as predicted, the block size governs the effective grain size for cleavage. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:In this paper we discuss the microstructure of lath martensitic steels and the mechanisms by which it controls cleavage fracture. The specific experimental example is a 9Ni (9 wt% Ni) steel annealed to have a large prior austenite grain size, then examined and tested in the as-quenched condition to produce a relatively coarse lath martensite. The microstructure is shown to approximate the recently identified 'classic' lath martensite structure: prior austenite grains are divided into packets, packets are subdivided into blocks, and blocks contain interleaved laths whose variants are the two Kurjumov-Sachs relations that share the same Bain axis of the transformation. When the steel is fractured in brittle cleavage, the laths in the block share {100} cleavage planes and cleave as a unit. However, cleavage cracks deflect or blunt at the boundaries between blocks with different Bain axes. It follows that, as predicted, the block size governs the effective grain size for cleavage. [ABSTRACT FROM AUTHOR]
ISSN:14686996
DOI:10.1088/1468-6996/14/1/014208