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Title: Carbon Redistribution and Carbide Precipitation in a High-Strength Low-Carbon HSLA-115 Steel Studied on a Nanoscale by Atom Probe Tomography

Abstract

HSLA-115 is a newly developed Cu-bearing high-strength low-carbon martensitic steel for use in Naval structural applications. This research provides, for the first time, a comprehensive compositional analysis of carbon redistribution and associated complex phase transformations in an isothermal aging study of HSLA-115 at 823 K (550 °C). Specifically, we characterize carbon segregation at lath boundaries, grain-refining niobium carbonitrides, cementite, and secondary hardening M2C carbides, in addition to copper precipitation, by 3D atom probe tomography (APT). Segregation of carbon (3 to 6 at. pct C) is observed at martensitic lath boundaries in the as-quenched and 0.12-hour aged microstructures. On further aging, carbon redistributes itself forming cementite and M2C carbides. Niobium carbonitride precipitates do not dissolve during the austenitizing treatment and are inherited in the as-quenched and aged microstructures; these are characterized along with cementite by synchrotron X-ray diffraction and APT. Sub-nanometer-sized M2C carbide precipitates are observed after the formation of Cu precipitates, co-located with the latter, indicating heterogeneous nucleation of M2C. The temporal evolution of the composition and morphology of M2C carbides at 823 K (550 °C) is described using APT; their precipitation kinetics is intertwined with Cu precipitates, affecting the bulk mechanical properties of HSLA-115. Phase compositions determined by APTmore » are compared with computed compositions at thermodynamic equilibrium using ThermoCalc.« less

Authors:
; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
U.S. OFFICE OF NAVAL RESEARCH
OSTI Identifier:
1373785
Resource Type:
Journal Article
Resource Relation:
Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science; Journal Volume: 48; Journal Issue: 7
Country of Publication:
United States
Language:
ENGLISH
Subject:
36 MATERIALS SCIENCE

Citation Formats

Jain, Divya, Isheim, Dieter, and Seidman, David N. Carbon Redistribution and Carbide Precipitation in a High-Strength Low-Carbon HSLA-115 Steel Studied on a Nanoscale by Atom Probe Tomography. United States: N. p., 2017. Web. doi:10.1007/s11661-017-4129-3.
Jain, Divya, Isheim, Dieter, & Seidman, David N. Carbon Redistribution and Carbide Precipitation in a High-Strength Low-Carbon HSLA-115 Steel Studied on a Nanoscale by Atom Probe Tomography. United States. doi:10.1007/s11661-017-4129-3.
Jain, Divya, Isheim, Dieter, and Seidman, David N. Tue . "Carbon Redistribution and Carbide Precipitation in a High-Strength Low-Carbon HSLA-115 Steel Studied on a Nanoscale by Atom Probe Tomography". United States. doi:10.1007/s11661-017-4129-3.
@article{osti_1373785,
title = {Carbon Redistribution and Carbide Precipitation in a High-Strength Low-Carbon HSLA-115 Steel Studied on a Nanoscale by Atom Probe Tomography},
author = {Jain, Divya and Isheim, Dieter and Seidman, David N.},
abstractNote = {HSLA-115 is a newly developed Cu-bearing high-strength low-carbon martensitic steel for use in Naval structural applications. This research provides, for the first time, a comprehensive compositional analysis of carbon redistribution and associated complex phase transformations in an isothermal aging study of HSLA-115 at 823 K (550 °C). Specifically, we characterize carbon segregation at lath boundaries, grain-refining niobium carbonitrides, cementite, and secondary hardening M2C carbides, in addition to copper precipitation, by 3D atom probe tomography (APT). Segregation of carbon (3 to 6 at. pct C) is observed at martensitic lath boundaries in the as-quenched and 0.12-hour aged microstructures. On further aging, carbon redistributes itself forming cementite and M2C carbides. Niobium carbonitride precipitates do not dissolve during the austenitizing treatment and are inherited in the as-quenched and aged microstructures; these are characterized along with cementite by synchrotron X-ray diffraction and APT. Sub-nanometer-sized M2C carbide precipitates are observed after the formation of Cu precipitates, co-located with the latter, indicating heterogeneous nucleation of M2C. The temporal evolution of the composition and morphology of M2C carbides at 823 K (550 °C) is described using APT; their precipitation kinetics is intertwined with Cu precipitates, affecting the bulk mechanical properties of HSLA-115. Phase compositions determined by APT are compared with computed compositions at thermodynamic equilibrium using ThermoCalc.},
doi = {10.1007/s11661-017-4129-3},
journal = {Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science},
number = 7,
volume = 48,
place = {United States},
year = {Tue May 09 00:00:00 EDT 2017},
month = {Tue May 09 00:00:00 EDT 2017}
}
  • The nature of precipitation and the solutionizing temperature of the precipitates are crucial factors in controlling the strength of high strength low alloy steels. Niobium, vanadium and titanium are the elements most commonly added to HSLA steels to produce fine precipitates and grain refinement. In addition to these, other alloying additions such as chromium, molybdenum and manganese are also made. Copper is added to provide age hardening. Addition of copper is accompanied by a proportional level of nickel in these steels. Such a complex scenario of alloying additions can influence the mass transfer kinetics as well as equilibrium precipitation. Therefore,more » steels of similar chemistry can exhibit different precipitation behaviour as has been already observed in some cases. Investigations made on the precipitation behaviour, in the austenitic range, of two steels are reported in this communication. The precipitates were studied for their morphology, size and chemistry. SEM along with EDX has been employed in characterizing these precipitates. A few TEM results have been included. The solutionizing temperatures of the precipitates were computed from thermodynamic models and compared with experimental observations.« less
  • The co-precipitation of Cu, M{sub 2}C (where M is any combination of Cr, Mo or Ti) and austenite (face-centered cubic) is characterized for 5 h isochronal aging times by synchrotron X-ray diffraction and three-dimensional atom-probe tomography for a high-strength low-carbon steel, BlastAlloy 160. High number densities, {approx}10{sup 23} m{sup 03}, of co-located Cu and M{sub 2}C preciptates were observed. Only small austenite volume percentages (<2.1%) were measured after aging at temperatures up to 625 C for 5 h.
  • Tailored metal alloy thin film-oxide interfaces generated using molecular beam epitaxial (MBE) deposition of alloy thin films on a single crystalline oxide substrate can be used for detailed studies of irradiation damage response on the interface structure. However presence of nanoscale phase separation in the MBE grown alloy thin films can impact the metal-oxide interface structure. Due to nanoscale domain size of such phase separation it is very challenging to characterize by conventional techniques. Therefor laser assisted atom probe tomography (APT) was utilized to study the phase separation in epitaxial Cr 0.61Mo 0.39, Cr 0.77Mo 0.23, and Cr 0.32V 0.68more » alloy thin films grown by MBE on MgO(001) single crystal substrates. Statistical analysis, namely frequency distribution analysis and Pearson coefficient analysis of experimental data was compared with similar analyses conducted on simulated APT datasets with known extent of phase separation. Thus the presence of phase separation in Cr-Mo films, even when phase separation was not clearly observed by x-ray diffraction, and the absence of phase separation in the Cr-V film were thus confirmed.« less
  • Tailored metal alloy thin film-oxide interfaces generated using molecular beam epitaxy (MBE) deposition of alloy thin films on a single crystalline oxide substrate can be used for detailed studies of irradiation damage response on the interface structure. However, the presence of nanoscale phase separation in the MBE grown alloy thin films can impact the metal-oxide interface structure. Due to nanoscale domain size of such phase separation, it is very challenging to characterize by conventional techniques. Therefore, laser assisted atom probe tomography (APT) was utilized to study the phase separation in epitaxial Cr{sub 0.61}Mo{sub 0.39}, Cr{sub 0.77}Mo{sub 0.23}, and Cr{sub 0.32}V{submore » 0.68} alloy thin films grown by MBE on MgO(001) single crystal substrates. Statistical analysis, namely frequency distribution analysis and Pearson coefficient analysis of experimental data was compared with similar analyses conducted on simulated APT datasets with known extent of phase separation. Thus, the presence of phase separation in Cr-Mo films, even when phase separation was not clearly observed by x-ray diffraction, and the absence of phase separation in the Cr-V film were confirmed.« less