TY - JOUR
T1 - Analysis of a New High-Toughness Ultra-high-Strength Martensitic Steel by Transmission Electron Microscopy and Atom Probe Tomography
AU - Hartshorne, Matthew I.
AU - McCormick, Caroline
AU - Schmidt, Michael
AU - Novotny, Paul
AU - Isheim, Dieter
AU - Seidman, David N.
AU - Taheri, Mitra L.
N1 - Funding Information:
Mitra L. Taheri and Matthew I. Hartshorne acknowledge funding support from the Carpenter Technology Corporation and the National Science Foundation’s Faculty Early Career Development Program (Grant 1150807). The local-electrode atom-probe tomograph at the Northwestern University Center for Atom-Probe Tomography (NUCAPT) was acquired and upgraded with equipment grants from the MRI Program of the National Science Foundation (Grant Number DMR-0420532) and the DURIP program of the Office of Naval Research (Grant Numbers N00014-0400798, N00014-0610539, N00014-0910781). NUCAPT is a Research Facility at the Materials Research Center of Northwestern University, supported by the National Science Foundation’s MRSEC Program (Grant Number DMR-1121262). Additional instrumentation at NUCAPT was supported by the Initiative for Sustainability and Energy at Northwestern (ISEN).
Publisher Copyright:
© 2016, The Minerals, Metals & Materials Society and ASM International.
PY - 2016/4/1
Y1 - 2016/4/1
N2 - The microstructure of a new martensitic high-strength steel (Fe-0.40C-3.81Ni-1.31Cr-1.50Si-0.75Mn-0.52Mo-0.51Cu-0.30V) with high fracture toughness is characterized by transmission electron microscopy and atom probe tomography (APT). MC, M6C, and M23C6 precipitates form inside the martensitic lath matrix. The fracture toughness is insensitive to the dissolution of M23C6 precipitates at austenitizing temperatures above 1164 K (891 °C). APT reveals that solute segregation at the prior austenite grain boundaries (PAGB) is not uniform, with C, Mo, Si, Ni, and/or P enrichment varying at different areas of the PAGB. Si depletion is detected in the same area as the highest C enrichment. Carbon also segregates at lath boundaries. Segregation of C indicates the presence of retained austenite films at both PAGB and lath boundaries. Regions enriched in C up to 10 pct were found within the laths; however, no regions were enriched to the level expected of cementite or ε-carbide. The observed C distribution and high fracture toughness indicates that the tempering behavior is significantly different than that observed in 300M steel. The effect of Si, Ni, and Cu on the formation and stabilization of the regions of C enrichment and retained austenite require further study, as it may be key to the increased toughness.
AB - The microstructure of a new martensitic high-strength steel (Fe-0.40C-3.81Ni-1.31Cr-1.50Si-0.75Mn-0.52Mo-0.51Cu-0.30V) with high fracture toughness is characterized by transmission electron microscopy and atom probe tomography (APT). MC, M6C, and M23C6 precipitates form inside the martensitic lath matrix. The fracture toughness is insensitive to the dissolution of M23C6 precipitates at austenitizing temperatures above 1164 K (891 °C). APT reveals that solute segregation at the prior austenite grain boundaries (PAGB) is not uniform, with C, Mo, Si, Ni, and/or P enrichment varying at different areas of the PAGB. Si depletion is detected in the same area as the highest C enrichment. Carbon also segregates at lath boundaries. Segregation of C indicates the presence of retained austenite films at both PAGB and lath boundaries. Regions enriched in C up to 10 pct were found within the laths; however, no regions were enriched to the level expected of cementite or ε-carbide. The observed C distribution and high fracture toughness indicates that the tempering behavior is significantly different than that observed in 300M steel. The effect of Si, Ni, and Cu on the formation and stabilization of the regions of C enrichment and retained austenite require further study, as it may be key to the increased toughness.
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U2 - 10.1007/s11661-016-3325-x
DO - 10.1007/s11661-016-3325-x
M3 - Article
AN - SCOPUS:84961286717
SN - 1073-5623
VL - 47
SP - 1517
EP - 1528
JO - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
JF - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
IS - 4
ER -