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Microstructure and cleavage in lath martensitic steels.
John W Morris1, Chris Kinney1, Ken Pytlewski1
1Department of Materials Science and Engineering, University of California, Berkeley, CA 94620, USA.
Science and Technology of Advanced Materials
|November 24, 2016
Summary
The block size in lath martensitic steels controls brittle cleavage fracture by influencing crack propagation. Understanding this microstructure is key to improving steel toughness.
Area of Science:
- Materials Science
- Metallurgy
- Fracture Mechanics
Background:
- Lath martensitic steels are crucial engineering materials.
- Cleavage fracture is a critical failure mechanism in these steels.
- The role of microstructure in controlling fracture is not fully understood.
Purpose of the Study:
- To investigate the microstructure of lath martensitic steels.
- To elucidate the mechanisms by which microstructure controls cleavage fracture.
- To determine the effective grain size for cleavage in 9Ni steel.
Main Methods:
- Microstructural characterization of as-quenched 9Ni steel.
- Mechanical testing to induce brittle cleavage fracture.
- Analysis of crack propagation paths in relation to microstructural features.
Main Results:
- The microstructure consists of packets, blocks, and laths.
- Laths within a block cleave as a unit.
- Cleavage cracks deflect at block boundaries with different Bain axes.
- Block size governs the effective grain size for cleavage.
Conclusions:
- The block size is the critical microstructural feature controlling cleavage fracture in lath martensitic steels.
- This finding provides a pathway for designing tougher steels.
- The study validates predictions regarding block size and effective grain size.
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