scholarly journals Influence of Alloying Elements on the Dynamic Recrystallization of 4 wt.–% Medium Manganese Steels

Materials ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5178
Author(s):  
Alexander Gramlich ◽  
Hanne Schäfers ◽  
Ulrich Krupp
Keyword(s):  
Dynamic Recrystallization ◽  
Prior Austenite ◽  
Deformation Behaviour ◽  
Alloying Elements ◽  
Drag Effect ◽  
Flow Curves ◽  
Austenite Grain ◽  
Hot Deformation Behaviour ◽  
Manganese Steels ◽  
Prior Austenite Grain

The hot deformation behaviour of air-hardening martensitic forging steels (of type 1.5132) is presented. The newly developed steels are characterized through dilatometric tests as well as through microstructure analyses with LOM and SEM and hardness measurements. Additionally, the influence of alloying elements on the flow curves at high temperatures is discussed. It is demonstrated that the higher alloying content does not increase the equivalent stresses in comparison to the reference alloys and contrariwise reduces the offset for dynamic recrystallization at temperatures below 1100 ∘C. Furthermore, the effect of different alloying elements on the strain hardening behaviour during hot compression of 4wt.–% medium manganese steels is presented. It is shown that boron reduces the offset for dynamic recrystallization if present in solid solution, while the combined addition of titanium and niobium annihilates the solid drag effect on the prior austenite grain boundaries.

scholarly journals Effect of Heterogeneous Microstructure on Refining Austenite Grain Size in Low Alloy Heavy-Gage Plate

Metals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 132
Author(s):  
Shengfu Yuan ◽  
Zhenjia Xie ◽  
Jingliang Wang ◽  
Longhao Zhu ◽  
Ling Yan ◽  
...  
Keyword(s):  
Grain Size ◽  
Prior Austenite ◽  
Alloying Elements ◽  
Nucleation Density ◽  
Reversed Austenite ◽  
Austenite Grain Size ◽  
Heterogeneous Microstructure ◽  
Austenite Grain ◽  
Prior Austenite Grain Size ◽  
Prior Austenite Grain

The present work introduces the role of heterogeneous microstructure in enhancing the nucleation density of reversed austenite. It was found that the novel pre-annealing produced a heterogeneous microstructure consisting of alloying elements-enriched martensite and alloying-depleted intercritical ferrite. The shape of the martensite at the prior austenite grain boundary was equiaxed and acicular at inter-laths. The equiaxed reversed austenite had a K-S orientation with adjacent prior austenite grain, and effectively refined the prior austenite grain that it grew into. The alloying elements-enriched martensite provided additional nucleation sites to form equiaxed reversed austenite at both prior austenite grain boundaries and intragranular inter-lath boundaries during re-austenitization. It was revealed that prior austenite grain size was refined to ~12 μm by pre-annealing and quenching, while it was ~30 μm by conventional quenching. This is a practical way of refining transformation products by refining prior austenite grain size to improve the strength, ductility and low temperature toughness of heavy-gage plate steel.

scholarly journals A New Systematic Approach Based on Dilatometric Analysis to Track Bainite Transformation Kinetics and the Influence of the Prior Austenite Grain Size

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 324
Author(s):  
David San-Martin ◽  
Matthias Kuntz ◽  
Francisca G. Caballero ◽  
Carlos Garcia-Mateo
Keyword(s):  
Heat Treatment ◽  
Grain Size ◽  
Prior Austenite ◽  
Bainitic Transformation ◽  
Transformation Rate ◽  
Transformation Kinetics ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Prior Austenite Grain Size ◽  
Prior Austenite Grain

This investigation explores the influence of the austenitisation heat treatment and thus, of the prior austenite grain size (PAGS), on the kinetics of the bainitic transformation, using as A case study two high-carbon, high-silicon, bainitic steels isothermally transformed (TIso = 250, 300, 350 °C), after being austenised at different temperatures (γTγ = 925–1125 °C). A methodology, based on the three defining dilatometric parameters extracted from the derivative of the relative change in length, was proposed to analyse the transformation kinetics. These parameters are related to the time to start bainitic transformation, the time lapse for most of the transformation to take place and the transformation rate at the end of the transformation. The results show that increasing the PAGS up to 70 µm leads to an increase in the bainite nucleation rate, this effect being more pronounced for the lowest TIso. However, the overall transformation kinetics seems to be weakly affected by the applied heat treatment (γTγ and TIso). In one of the steels, PAGS > 70 µm (γTγ > 1050 °C), which weakly affects the progress of the transformation, except for TIso = 250 °C, for which the enhancement of the autocatalytic effect could be the reason behind an acceleration of the overall transformation.

A quantitative atom probe study of the Nb excess at prior austenite grain boundaries in a Nb microalloyed strip-cast steel

2012 ◽  
Vol 60 (13-14) ◽  
pp. 5049-5055 ◽  
Author(s):  
Peter J. Felfer ◽  
Chris R. Killmore ◽  
Jim G. Williams ◽  
Kristin R. Carpenter ◽  
Simon P. Ringer ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Prior Austenite ◽  
Cast Steel ◽  
Atom Probe ◽  
Austenite Grain ◽  
Strip Cast ◽  
Prior Austenite Grain

Nb segregation at prior austenite grain boundaries and defects in high strength low alloy steel during cooling

2017 ◽  
Vol 115 ◽  
pp. 165-169 ◽  
Author(s):  
Xianglong Li ◽  
Ping Wu ◽  
Ruijie Yang ◽  
Shoutian Zhao ◽  
Shiping Zhang ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Alloy Steel ◽  
Prior Austenite ◽  
High Strength ◽  
Low Alloy Steel ◽  
Austenite Grain ◽  
Prior Austenite Grain

Cavitation control in steels of high residual element content

1980 ◽  
Vol 295 (1413) ◽  
pp. 305-305 ◽  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Prior Austenite ◽  
Low Alloy Steels ◽  
Boundary Zone ◽  
Austenite Grain ◽  
Alloy Steels ◽  
Austenite Grain Boundary ◽  
Prior Austenite Grain ◽  
Transverse Boundary

The cavitational mode of failure of prior austenite grain boundaries in bainitic creep-resisting low alloy steels is now well established as a principal factor in the high incidence of cracking problems which has developed on modern power plant in recent years. The microstructural features dominating the cavitation process at the reheat temperature in a ½CMV bainitic steel of high classical residual level have been determined. The prior austenite grain boundaries become zones of comparative weakness ca . 1 pm thick at 700 °C and are incapable of sustaining significant shear loads. Deformation is therefore initiated by a relaxation of load, through a process of prior austenite grain boundary zone shear, from inclined to transverse boundaries such that a concentration of normal stress develops across the latter. The overall deformation is thereafter determined by cavitation of the transverse boundary zones, the necessary inclined boundary displacements being accommodated by further grain boundary zone shear. Transverse boundary cavitation is shown to be an essentially time-independent process of localized ductile microvoid coalescence resulting from the plastic deformation of the boundary zone.

Fatigue Performance of Low Pressure Carbonitrided 20MnCr5 and SAE 8620 Steel Alloys

2021 ◽  
Author(s):  
Larissa Vilela Costa ◽  
Vincent Lelong ◽  
Dennis Beauchesne ◽  
Robert L. Cryderman ◽  
Kip O. Findley
Keyword(s):  
Retained Austenite ◽  
Prior Austenite ◽  
Endurance Limit ◽  
Fatigue Testing ◽  
Surface Hardness ◽  
Low Pressure ◽  
Austenite Grain Size ◽  
Steel Alloys ◽  
Austenite Grain ◽  
Prior Austenite Grain

Abstract Low pressure carbonitriding and pressurized gas quenching heat treatments were conducted on four steel alloys. Bending fatigue tests were performed, and the highest endurance limit was attained by 20MnCr5+B, followed by 20MnCr5, SAE 8620+Nb, and SAE 8620. The differences in fatigue endurance limit occurred despite similar case depths and surface hardness between alloys. Low magnitude tensile residual stresses were measured near the surface in all conditions. Additionally, nonmartensitic transformation products (NMTPs) were observed to various extents near the surface. However, there were no differences in retained austenite profiles, and retained austenite was mostly stable against deformation-induced transformation to martensite during fatigue testing, contrasting some studies on carburized steels. The results suggest that the observed difference in fatigue lives is due to differences in chemical composition and prior austenite grain size. Alloys containing B and Nb had refined prior austenite grain sizes compared to their counterparts in each alloy class.

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.

scholarly journals Exploring the Difference in Bainite Transformation with Varying the Prior Austenite Grain Size in Low Carbon Steel

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 988 ◽  
Author(s):  
Liangyun Lan ◽  
Zhiyuan Chang ◽  
Penghui Fan
Keyword(s):  
Grain Size ◽  
Prior Austenite ◽  
Low Carbon Steel ◽  
Low Carbon ◽  
Bainite Transformation ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Austenite Grains ◽  
Prior Austenite Grain Size ◽  
Prior Austenite Grain

The simulation welding thermal cycle technique was employed to generate different sizes of prior austenite grains. Dilatometry tests, in situ laser scanning confocal microscopy, and transmission electron microscopy were used to investigate the role of prior austenite grain size on bainite transformation in low carbon steel. The bainite start transformation (Bs) temperature was reduced by fine austenite grains (lowered by about 30 °C under the experimental conditions). Through careful microstructural observation, it can be found that, besides the Hall–Petch strengthening effect, the carbon segregation at the fine austenite grain boundaries is probably another factor that decreases the Bs temperature as a result of the increase in interfacial energy of nucleation. At the early stage of the transformation, the bainite laths nucleate near to the grain boundaries and grow in a “side-by-side” mode in fine austenite grains, whereas in coarse austenite grains, the sympathetic nucleation at the broad side of the pre-existing laths causes the distribution of bainitic ferrite packets to be interlocked.

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