Nanolaninate Steels: Pealite and Martensite-Austenite Reversion Steels

Many different types of steels consist of micro- or nanoscale laminate microstructures. 
A typical example are pearlitic steels which consist of a lamellar structure of alternating iron and iron carbide (cementite) layers. 
Cementite is an iron carbide with Fe3C stoichiometry and orthorhombic crystal structure. The eutectoid concentration of the alloy lies at the eutectoid temperature-composition intersection where the austenite phase transforms directly into a layered ferrite-cementite solid. This is referred to as a pearlitic reaction. 

Upon heavy deformation this laminate microstructure undergoes substantial refinement down to the nanometre scale. 
Upon further large straining the carbide phase dissolves via mechanical alloying, rendering the initially two-phase pearlite structure into a carbon-supersaturated iron phase. 

Another case where laminate steels have been designed are martensite reversion steels. In these materials the alloy is first rendered austenitic and then quenched into the martensitic state. After that the so quenched material is subjected to a martensite-to-austenite reversion heat treatment. 
This works by annealing the martensite into a temperature regime where local austenite formation can occur, either at segregation decorated defects for instance at grain (lath) boundaries. 
Since many types of martensite steels can contain very fine lath grain boundary structures such a reversion heat treatment can be used to create very fine damask-type nanlaminate microstructures leading to steels with superior mechanical properties for instance when subjected to fatigue loading scenarios. 
Below are some more specific examples for such nano-laminate steels.

 

Nanolaminate Steels based on Pearlite

Pearlitic steel can exhibit tensile strengths above 7 GPa after severe plastic deformation, where the deformation promotes a refinement of the lamellar structure and cementite decomposition.

With is they are the strongest formable bulk metallic alloys.

A clear correlation between deformation and cementite decomposition in pearlite is still absent. In our recent works, a local electrode atom probe was used to characterize the microstructural evolution of pearlitic steel, cold-drawn with progressive strains up to 5.4. Transmission electron microscopy was also employed to perform complementary analyses of the microstructure. Both methods yielded consistent results. The overall carbon content in the detected
volumes as well as the carbon concentrations in ferrite and cementite were measured by atom probe. In addition, the thickness of the cementite filaments was determined. In ferrite, we found a correlation of carbon concentration with the strain, and in cementite, we found a correlation of carbon concentration with the lamella thickness. Direct evidence for the formation of cell/subgrain boundaries in ferrite and segregation of carbon atoms at these defects was found. Based on these findings, the mechanisms of cementite decomposition
are discussed in terms of carbon–dislocation interaction.

3D atom probe tomography maps of cold-drawn pearlite wires, Y.J. Li et al. / Acta Materialia 59 (2011) 3965–3977 3D atom probe tomography maps of cold-drawn pearlite wires, Y.J. Li et al. / Acta Materialia 59 (2011) 3965–3977
Pearlitic nanolaminate steel: Ultra-strong and damage tolerant metallic bulk materials: A lesson from nanostructured pearlitic steel wires
Scientific Reports | 6:33228 | DOI: 10.1038/srep33228
Ultrastrong damage tolerant Scientific R[...]
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Mechanical alloying of nanolaminate steels: Deformation-induced cementite decomposition in pearlite
Acta Materialia 59 (2011) 3965
Acta Materialia 59 (2011) 3965 pearlite [...]
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3D atom probe tomography maps of cold-drawn pearlite wires, Y.J. Li et al. PRL (2014) 3D atom probe tomography maps of cold-drawn pearlite wires, Y.J. Li et al. PRL (2014)
Nanolaminate steels: strength and microstructure of heavily cold-drawn 6.3 GPa pearlite
Acta Materialia 60 (2012) 4005
Acta Materialia 60 (2012) 4005–4016 heat[...]
PDF-Dokument [2.7 MB]
Mechanical properties of carbon-supersaturated nanocrystalline hypereutectoid pearlite
Acta Materialia 84 (2015) 110
Acta Materialia 84 (2015) 110-123 atom p[...]
PDF-Dokument [2.4 MB]
Deformation-Induced Martensite: A New Paradigm for Exceptional Steels
Djaziri et al. Advanced Materials, Vol 28, IS 35, pages 1521-4095
Djaziri_et_al-2016-Advanced_Materials.pd[...]
PDF-Dokument [1.2 MB]
Pearlite Nanolaminate: Nanocrystalline Bulk Steel with Near Theoretical Strength
PRL 113, 106104 (2014)
Li and Raabe Phys Rev Lett vol 113 page [...]
PDF-Dokument [1.6 MB]
Atomic-Scale Quantification of Grain Boundary Segregation in Nanocrystalline Material
PRL 112, 126103 (2014)
Phys Rev Lett. 2014 grain boundary segre[...]
PDF-Dokument [842.8 KB]

 

 

Martensite-to-Austenite Reversion Steels

Steels containing reverted nanoscale austenite laminate regions or reverted austenite islands or films dispersed in a martensitic matrix show excellent strength, ductility and toughness. They can be synthesized by a simple reversion heat treatment of as-quenched martensite to bring the material locally into the two-phase austenite-martensite region.

Martensite-to-Austenite Reversion Steels Martensite-to-Austenite Reversion Steels
Nanolaminate Steels: Bone-like crack resistance in hierarchical metastable nanolaminate steels
Koyama et al., Science 355, 1055–1057 (2017)
Koyama Bone-like Steels Science 355 (201[...]
PDF-Dokument [745.8 KB]
Nanolaminate Steel: Transformation-induced plasticity–twinning-induced plasticity steel with dynamic strain partitioning and enhanced damage resistance
Acta Materialia 85 (2015) 216
Acta Materialia 85 (2015) 216 Nanolamina[...]
PDF-Dokument [1.3 MB]
M. Koyama, Z. Zhang, M. Wang, D. Ponge, D. Raabe, K. Tsuzaki, H. Noguchi, C.C. Tasan, Bone-like crack resistance in hierarchical metastable nanolaminate steels. Science 355(6329) (2017)1055-1057 M. Koyama, Z. Zhang, M. Wang, D. Ponge, D. Raabe, K. Tsuzaki, H. Noguchi, C.C. Tasan, Bone-like crack resistance in hierarchical metastable nanolaminate steels. Science 355(6329) (2017)1055-1057
Nanolaminate Steel: Segregation engineering enables nanoscale martensite to austenite phase transformation at grain boundaries: A pathway to ductile martensite
Acta Materialia 61 (2013) 6132
Acta Materialia 61 (2013) 6132–6152 Nano[...]
PDF-Dokument [2.3 MB]
Nanolaminate Steels: Linear complexions: Confined chemical and structural states at dislocations
Science 349, 1080 (2015); M. Kuzmina et al.
Linear Complexions Science vol 349 (2015[...]
PDF-Dokument [1.5 MB]
Nanolaminate Steels: Nanoprecipitate-hardened 1.5 GPa steels with unexpected high ductility
Scripta Materialia 60 (2009) 1141
Raabe Scripta Materialia 60 (2009) 1141 [...]
PDF-Dokument [342.1 KB]

 

Acta Mat. 2011, 59, p. 364