scholarly journals Local Characterization of Precipitation and Correlation with the Prior Austenitic Microstructure in Nb-Ti-Microalloyed Steel by SEM and AFM Methods

Metals ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 636 ◽  
Author(s):  
Lena Eisenhut ◽  
Jonas Fell ◽  
Christian Motz
Keyword(s):  
Electron Microscopy ◽  
Prior Austenite ◽  
Thermomechanical Processing ◽  
Electron Backscatter Diffraction ◽  
Grain Structure ◽  
Austenite Grain ◽  
Reconstruction Methods ◽  
Local Characterization ◽  
Prior Austenite Grain

Precipitation is one of the most important influences on microstructural evolution during thermomechanical processing (TMCP) of micro-alloyed steels. Due to precipitation, pinning of prior austenite grain (PAG) boundaries can occur. To understand the mechanisms in detail and in relation to the thermomechanical treatment, a local characterization of the precipitation state depending on the microstructure is essential. Commonly used methods for the characterization, such as transmission electron microscopy (TEM) or matrix dissolution techniques, only have the advantage of local or statistically secured characterization. By using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques, both advantages could be combined. In addition, in the present work a correlation of the precipitation conditions with the prior austenite grain structure for different austenitization states could be realized by Electron Backscatter Diffraction (EBSD) measurement and reconstruction methods using the reconstruction software Merengue 2.

scholarly journals Characterization of Coarse-Grained Heat-Affected Zones in Al and Ti-Deoxidized Offshore Steels

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1096
Author(s):  
Henri Tervo ◽  
Antti Kaijalainen ◽  
Vahid Javaheri ◽  
Satish Kolli ◽  
Tuomas Alatarvas ◽  
...  
Keyword(s):  
Prior Austenite ◽  
Electron Backscatter Diffraction ◽  
Coarse Grained ◽  
Grain Coarsening ◽  
Austenite Grain ◽  
The Matrix ◽  
Backscatter Diffraction ◽  
Prior Austenite Grain ◽  
Deoxidation Practice

Deterioration of the toughness in heat-affected zones (HAZs) due to the thermal cycles caused by welding is a known problem in offshore steels. Acicular ferrite (AF) in the HAZ is generally considered beneficial regarding the toughness. Three experimental steels were studied in order to find optimal conditions for the AF formation in the coarse-grained heat-affected zone (CGHAZ). One of the steels was Al-deoxidized, while the other two were Ti-deoxidized. The main focus was to distinguish whether the deoxidation practice affected the AF formation in the simulated CGHAZ. First, two different peak temperatures and prolonged annealing were used to study the prior austenite grain coarsening. Then, the effect of welding heat input was studied by applying three cooling times from 800 °C to 500 °C in a Gleeble thermomechanical simulator. The materials were characterized using electron microscopy, energy-dispersive X-ray spectrometry, and electron backscatter diffraction. The Mn depletion along the matrix-particle interface was modelled and measured. It was found that AF formed in the simulated CGHAZ of one of the Ti-deoxidized steels and its fraction increased with increasing cooling time. In this steel, the inclusions consisted mainly of small (1–4 μm) TiOx-MnS, and the tendency for prior austenite grain coarsening was the highest.

Effects of Processing Parameters on Microstructure Development in X70 Pipeline Steel

2010 ◽  
Vol 654-656 ◽  
pp. 298-301 ◽  
Author(s):  
A. Al Shahrani ◽  
Thomas Schambron ◽  
Ali Dehghan-Manshadi ◽  
James G. Williams ◽  
Elena V. Pereloma
Keyword(s):  
Low Temperature ◽  
Prior Austenite ◽  
Thermomechanical Processing ◽  
Pipeline Steel ◽  
Processing Parameters ◽  
Grain Structure ◽  
Microstructure Development ◽  
Austenite Grain ◽  
Low Temperature Toughness ◽  
Prior Austenite Grain

Achieving fine and uniform grains is the most effective way to enhance strength and toughness, which are required properties for pipeline steels. Steels microalloyed with Nb can exhibit a mixed grain structure, which can deteriorate low temperature toughness. In this work the effects of the thermomechanical processing parameters on the prior austenite grain structure before ferrite transformation have been investigated.

The Grain Boundary Embrittlement and De-Embrittlement Mechanism in Age Hardenable Fe-Ni-Ti Steels

2006 ◽  
Vol 118 ◽  
pp. 469-474 ◽  
Author(s):  
Min Saeng Kim ◽  
Yoon Uk Heo ◽  
Hu Chul Lee
Keyword(s):  
Electron Microscopy ◽  
Fracture Surface ◽  
Grain Boundary ◽  
Vickers Hardness ◽  
Prior Austenite ◽  
Aging Treatment ◽  
Austenite Grain ◽  
Grain Boundary Embrittlement ◽  
Prior Austenite Grain ◽  
Boundary Embrittlement

The strengthening and grain boundary embrittlement in an age hardenable Fe-20.4Ni-2.8Ti ternary alloy were investigated. The Vickers hardness and tensile properties were evaluated using a Vickers hardness and tensile tester and the precipitation behavior during aging treatment was observed by transmission electron microscopy (TEM). The fracture surface was observed using low voltage field emission scanning electron microscopy (FE-SEM). The alloy showed typical aging hardening curves with a single aging peak near 640 HV, but was found to undergo severe grain boundary embrittlement from the initial stages of aging treatment. Many fine particles were observed at the grain boundary fracture surface. These particles were identified as η-Ni3Ti precipitates nucleated at the prior austenite grain boundaries. When the aging time was extended, austenite nucleated at the interface of the matrix and η-Ni3Ti precipitate. With the formation of the austenite, the tensile ductility was recovered. It was concluded that the precipitation of the η-Ni3Ti intermetallic particles at the prior austenite grain boundaries and formation of the austenite are the main causes of embrittlement and subsequent de-embrittlement in aging of this alloy.

Strengthening Mechanisms in Low Carbon Lath Martensite as Influenced by Austenite Conditioning

2018 ◽  
Vol 941 ◽  
pp. 574-582
Author(s):  
S.C. Kennett ◽  
George Krauss ◽  
Kip O. Findley
Keyword(s):  
Grain Size ◽  
Dislocation Density ◽  
Prior Austenite ◽  
Thermomechanical Processing ◽  
Lath Martensite ◽  
Weight Percent ◽  
Low Carbon ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Prior Austenite Grain

Low carbon lath martensitic microstructures are used in various steel products requiring high strength and toughness. These microstructures are conventionally produced through re-austenitizing and quenching followed by low or high temperature tempering. It is also possible to produce lath martensite through direct quenching immediately following thermomechanical processing. In this study, deformation below the austenite recrystallization temperature before quenching to form martensite was simulated through laboratory scale Gleeble processing of a 0.2 weight percent carbon ASTM A514 steel microalloyed with up to 0.21 weight percent niobium. Thermomechanical processing generally increases the dislocation density of the as-quenched martensite, which is sensitive to the austenite grain size before thermomechanical processing. The hardness of the thermomechanically-processed steels is generally greater than steels austenitized at comparable temperatures without deformation; this hardness difference is attributed to the increase in dislocation density and increased lath misorientation in the thermomechanically-processed conditions. The hardness is generally independent of prior austenite grain size for the thermomechanically processed conditions in contrast to conventionally austenitized and quenched conditions, which have a Hall-Petch correlation with austenite grain size. The strength increase of the thermomechanically processed conditions compared to the conventionally austenitized and quenched conditions is maintained after tempering. However, there is a larger drop in strength for small prior austenite grain sizes for both conventionally austenitized and quenched and thermomechanically processed steels. Overall, the strength of these lath martensitic steels can be directly related to dislocation density through a Taylor hardening model.

scholarly journals Microstructure of Z-Phase Strengthened Martensitic Steels: Meeting the 650°C Challenge

2016 ◽  
Vol 879 ◽  
pp. 1147-1152 ◽  
Author(s):  
Fang Liu ◽  
Masoud Rashidi ◽  
John Hald ◽  
Lutz Reißig ◽  
Hans Olof Andrén
Keyword(s):  
Electron Microscopy ◽  
Atom Probe Tomography ◽  
Prior Austenite ◽  
Atom Probe ◽  
Martensitic Steels ◽  
Austenite Grain ◽  
Transmission Electron ◽  
Governing Factor ◽  
The Impact ◽  
Prior Austenite Grain

We studied three series of Z-phase strengthened steels using scanning electron microscopy, transmission electron microscopy, and atom probe tomography to reveal the detailed microstructure of these steels. In particular, the phase transformation from M(C,N) to Z-phase (CrMN) was studied. Carbon content in the steels is the governing factor in this transformation. The impact toughness of some test alloys was rather low. This is attributed to the formation of a continuous W-rich film along prior austenite grain boundaries. Cu and C addition to the test alloys changed Laves phase morphology to discrete precipitates and improved toughness dramatically. BN particles were found in some steels. Formation of BN is directly linked to the B concentration in the steels.

Microstructural Characterization of Creep Damaged 11Cr-3.5W-3Co Steel

2006 ◽  
Vol 118 ◽  
pp. 475-478 ◽  
Author(s):  
C.S. Kim ◽  
S.I. Kwun ◽  
Bong Young Ahn ◽  
Seung Hoon Nahm ◽  
Seung Seok Lee
Keyword(s):  
Prior Austenite ◽  
Microstructural Characterization ◽  
Martensite Lath ◽  
Square Root ◽  
Petch Relation ◽  
Softening Behavior ◽  
Austenite Grain ◽  
Lath Width ◽  
Prior Austenite Grain

The effects of the precipitate and martensite lath on the softening behavior have been investigated for 11Cr-3.5W-3Co steel during creep at 700. During creep, the precipitate on the PAG (prior austenite grain) boundaries and martensite lath boundaries coarsened. The recovery of dislocation density and an increase of martensite lath width took place. It is shown that the inverse of the size of the precipitates and the inverse of the square root of the martensite lath width have a linear relation with the Vickers hardness, which corresponds to the Hall-Petch relation and particle looping mechanism.

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