Effect of Hot Deformation and Cooling Rate on Phase Transformations in Low Carbon HN5MVNb Bainitic Steel

Deformations at temperatures 900 °C, 860 °C, 810 °C and 780 °C in the consecutive amounts 24%, 20%, 19% and 18.5% were applied to low carbon HN5MVNb bainitic steel using hot compression testing in dilatometer Bähr 805 followed by continuous cooling. The results show clearly that the kinetics of the austenite decomposition were depended on local equilibrium conditions between recovery, recrystallization and phase transformation processes for a given cooling rate. Bainite transformation was accelerated when sample was cooled after deformation at cooling rate 60 °C/s. At lower cooling rates than 5 °C/s down to 0.5 °C/s, bainite transformation was postpone when comparing its kinetics with those for non deformed steel. The bainitic transformation cannot be fitted to a single transformation mechanism owing to the formation of carbides. Different behavior was observed for austenite to ferrite transformation. Usually it was accelerated with consecutive deformations of the steel for all cooling rates used in experiments.

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Development of Precipitation Hardening Parameters for High Strength Alloy AA 7068

Materials ◽

10.3390/ma13040918 ◽

2020 ◽

Vol 13 (4) ◽

pp. 918

Author(s):

Julia Osten ◽

Benjamin Milkereit ◽

Michael Reich ◽

Bin Yang ◽

Armin Springer ◽

...

Keyword(s):

Heat Treatment ◽

Cooling Rate ◽

Maximum Yield ◽

High Strength ◽

Tensile Tests ◽

Age Hardening ◽

Scanning Calorimetry ◽

Cooling Rates ◽

Critical Cooling Rate ◽

Kinetics Of

The mechanical properties after age hardening heat treatment and the kinetics of related phase transformations of high strength AlZnMgCu alloy AA 7068 were investigated. The experimental work includes differential scanning calorimetry (DSC), differential fast scanning calorimetry (DFSC), sophisticated differential dilatometry (DIL), scanning electron microscopy (SEM), as well as hardness and tensile tests. For the kinetic analysis of quench induced precipitation by dilatometry new metrological methods and evaluation procedures were established. Using DSC, dissolution behaviour during heating to solution annealing temperature was investigated. These experiments allowed for identification of the appropriate temperature and duration for the solution heat treatment. Continuous cooling experiments in DSC, DFSC, and DIL determined the kinetics of quench induced precipitation. DSC and DIL revealed several overlapping precipitation reactions. The critical cooling rate for a complete supersaturation of the solid solution has been identified to be 600 to 800 K/s. At slightly subcritical cooling rates quench induced precipitation results in a direct hardening effect resulting in a technological critical cooling rate of about 100 K/s, i.e., the hardness after ageing reaches a saturation level for cooling rates faster than 100 K/s. Maximum yield strength of above 600 MPa and tensile strength of up to 650 MPa were attained.

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The Influence of Thermomechanical Controlled Processing on Bainite Formation in Low Carbon High Strength Steel

Materials Science Forum ◽

10.4028/www.scientific.net/msf.783-786.21 ◽

2014 ◽

Vol 783-786 ◽

pp. 21-26

Author(s):

Xiao Jun Liang ◽

Ming Jian Hua ◽

Anthony J. DeArdo

Keyword(s):

Mechanical Properties ◽

High Strength Steel ◽

High Strength ◽

Manganese Steel ◽

Low Carbon ◽

High Manganese ◽

Bainite Transformation ◽

High Manganese Steel ◽

Cooling Rates ◽

Controlled Processing

Thermomechanical controlled processing is a very important way to control the microstructure and mechanical properties in low carbon, high strength steel. This is especially true in the case of bainite formation, where the complexity of the austenite-bainite transformation makes the control of the processing important. In this study, a low carbon, high manganese steel containing niobium was investigated to better understand the roles of austenite conditioning and cooling rates on the bainitic phase transformation. Specimens were compared with and without deformation, and followed by seven different cooling rates ranging between 0.5°C/s and 40°C/s. The CCT curves showed that the transformation behaviors and temperatures are very different. The different bainitic microstructures which varied with austenite deformation and cooling rates will be discussed.

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Cu Precipitation Behaviors and Microscopic Mechanical Characteristics of a Novel Ultra-Low Carbon Steel

Materials ◽

10.3390/ma13163571 ◽

2020 ◽

Vol 13 (16) ◽

pp. 3571

Author(s):

Mingxue Sun ◽

Yang Xu ◽

Tiewei Xu

Keyword(s):

Cooling Rate ◽

Young’S Modulus ◽

Vickers Hardness ◽

Young's Modulus ◽

Low Carbon Steel ◽

Carbon Steels ◽

Precipitation Strengthening ◽

Low Carbon ◽

Cooling Rates ◽

The Matrix

We studied the effect of Cu addition on the hardness of ultra-low carbon steels heat treated with different cooling rates using thermal simulation techniques. The microstructural evolution, Cu precipitation behaviors, variations of Vickers hardness and nano-hardness are comparatively studied for Cu-free and Cu-bearing steels. The microstructure transforms from ferritic structure to ferritic + bainitic structure as a function of cooling rate for the two steels. Interphase precipitation occurs in association with the formation of ferritic structure at slower cooling rates of 0.05 and 0.2 °C/s. Coarsening of Cu precipitates occurs at 0.05 °C/s, leading to lower precipitation strengthening. As the cooling rate increases to 0.2 °C/s, the interphase and dispersive precipitation strengthening effects are increased by 63.9 and 50.0 MPa, respectively. Cu precipitation is partially constrained at cooling rate of 5 °C/s, resulting in poor nano-hardness and Young’s Modulus. In comparison with Cu-free steel, the peak Vickers hardness, nano-hardness and Young’s Modulus are increased by 56 HV, 0.61 GPa and 55.5 GPa at a cooling rate of 0.2 °C/s, respectively. These values are apparently higher than those of Cu-free steel, indicating that Cu addition in steels can effectively strengthen the matrix.

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Mechanism of Cementite Spheroidization from Different Initial Microstructures in Fe-0.65C-2.33Mn Alloy

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.815.107 ◽

2019 ◽

Vol 815 ◽

pp. 107-113

Author(s):

Li Ma ◽

Tao Jia ◽

Xiu Hua Gao ◽

Run Ni

Keyword(s):

Electron Microscopy ◽

Cooling Rate ◽

Local Equilibrium ◽

Lamellar Spacing ◽

Initial Structure ◽

Equilibrium Conditions ◽

Transmission Electron ◽

Spheroidizing Annealing ◽

Carburizing Process ◽

Scanning Electron

The spheroidization mechanism from different initial microstructures during spheroidizing heat treatment was studied in Fe-0.68C-2.33Mn alloy. Two types of initial microstructures, i.e. pearlite and martensite, were obtained by varying the cooling rate. The microstructure and property evolution during spheroidizing annealing was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The DICTRA software, assuming local equilibrium conditions, was used to simulate the carburizing process of different initial microstructures through different cooling rate. The results indicate that the spheroidization mechanism of cementite was related to the initial microstructures and the smaller lamellar spacing of pearlite inhibited the coarsening of cementite, resulting in the size of cementite smaller than that of martensite as the initial structure.

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Influence of Chromium Content and Prior Deformation on the Continuous Cooling Transformation Diagram of Low-Carbon Bainitic Steels

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.835.58 ◽

2020 ◽

Vol 835 ◽

pp. 58-67

Author(s):

Mohammed Ali ◽

Antti J. Kaijalainen ◽

Jaakko Hannula ◽

David Porter ◽

Jukka I. Kömi

Keyword(s):

Cooling Rate ◽

Hot Deformation ◽

Laser Scanning ◽

Chromium Content ◽

Bainitic Ferrite ◽

Granular Bainite ◽

Low Carbon ◽

Cooling Rates ◽

Continuous Cooling Transformation ◽

Continuous Cooling

The effect of chromium content and prior hot deformation of the austenite on the continuous cooling transformation (CCT) diagram of a newly developed low-carbon bainitic steel has been studied using dilatometer measurements conducted on a Gleeble 3800 simulator with cooling rates ranging from 2-80 °C/s. After austenitization at 1100 °C, specimens were either cooled without strain or given 0.6 strain at 880 °C prior to dilatometer measurements. The resultant microstructures have been studied using laser scanning confocal microscopy, scanning electron microscopy and macrohardness measurements. CCT and deformation continuous cooling transformation (DCCT) diagrams were constructed based on the dilatation curves, final microstructures and hardness values. Depending on the cooling rate, the microstructures of the investigated steels after cooling from the austenite region consist of one or more of the following microstructural components: lath-like upper bainite, i.e. bainitic ferrite (BF), granular bainite (GB), polygonal ferrite (PF) and pearlite (P). The proportion of BF to GB as well as the hardness of the transformation products decreased with decreasing cooling rate. The cooling rate at which PF starts to appear depends on the steel composition. With both undeformed and deformed austenite, increasing the chromium content led to higher hardenability and refinement of the microstructure, promoting the formation of BF and shifting the ferrite start curve to lower cooling rates. Prior hot deformation shifted the transformation curves to shorter times and higher temperatures and led to a reduction in hardness at the low cooling rates through the promotion of ferrite formation.

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Kinetics and Mechanisms of Formation of Al-Ni Intermetallics

MRS Proceedings ◽

10.1557/proc-81-135 ◽

1986 ◽

Vol 81 ◽

Author(s):

J. A. Patchett ◽

G. J. Abbaschian

Keyword(s):

Cooling Rate ◽

Nucleation And Growth ◽

Primary Phase ◽

Peritectic Temperature ◽

Cooling Rates ◽

Fault Density ◽

Metastable Extension ◽

Mechanisms Of Formation ◽

Free Growth ◽

Kinetics Of

AbstractThe effects of cooling rate and composition on the nucleation and growth kinetics of NiAl, Ni2Al3, and NiAl3 intermetallics were studied for alloys containing 25 and 31.5 ht.% Ni. Fgr the former composition, the peritectic regction Ni Al + Liquid → NiAl3 was studied over cooling rates from 20 to 105 K/s. For the latter composhtion, the reaction NiAl + Liquid → Ni2Al3 was studied at cooling rates ranging form 10 to 600 K/sec. The amounis of constituent phases are shown to depend on the cooling rate, and for the peritectic phases, on the surface area of the primary phase. The nucleation of Ni2Al3 and NiAl3, and the ordering of the aluminum-rich NiAl were also examines uding trans ission electron microscopy. Cooling the NiAl + liquid below the peritectic temperature results in a metastable extension of NiAl with a high dislocation and stacking fault density, followed by the epitaxial nucleation and almost dislocation-free growth of Ni2Al3 In contrast, the nucleation of the NiAl3 on Ni2Al3 occurs directly witgoud the formationof an intermediate region.

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Achieving the Dual Phase Structure in Low Alloyed Steel with Slow Cooling Rate

Materials Science Forum ◽

10.4028/www.scientific.net/msf.575-578.1117 ◽

2008 ◽

Vol 575-578 ◽

pp. 1117-1122

Author(s):

Tarja Jäppinen ◽

Seppo Kivivuori

Keyword(s):

Cooling Rate ◽

Phase Structure ◽

Steel Wire ◽

Optical Microscope ◽

Carbon Steels ◽

Alloying Elements ◽

Dual Phase ◽

Low Carbon ◽

Slow Cooling ◽

Cooling Rates

In steel wire processing it is difficult to reach a homogenous structure throughout the cross-section of the wire particularly in greater diameters. One alternative for producing a homogenous structure is to find a cooling path with a wide transformation temperature range. Fully austenite steel wire rolled at high temperatures can be decomposed into ferritic-martensitic dual phase structure using relatively slow cooling rates. Test materials were low alloyed low carbon steels with variations in alloying elements. Gleeble-1500 thermomechanical simulator was utilised to study the effect of cooling rate on decomposition of austenite after deformation. The microstructures were studied with an optical microscope. In certain low alloyed steels slow cooling rates eliminate the bainite transformation and instead martensite is formed. The final microstructure depends mainly on the carbon content but also on the amount of other alloying elements and their effects on the austenite phase.

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Effect of Austempering below and above Ms on the Microstructure and Wear Performance of a Low-Carbon Bainitic Steel

Metals ◽

10.3390/met12010104 ◽

2022 ◽

Vol 12 (1) ◽

pp. 104

Author(s):

Zhirui Wei ◽

Haijiang Hu ◽

Man Liu ◽

Junyu Tian ◽

Guang Xu

Keyword(s):

Impact Toughness ◽

Low Carbon Steel ◽

Total Elongation ◽

Bainitic Steel ◽

Low Carbon ◽

Bainite Transformation ◽

Wear Performance ◽

Isothermal Temperature ◽

Considerable Impact ◽

Fresh Martensite

The microstructure and wear performance of a low-carbon steel treated by austempering below and above martensite start temperature (Ms) were investigated. The results show that the bainite, fresh martensite (FM) and retained austenite (RA) were observed in samples austempered above Ms. Except for the three above phases, the athermal martensite (AM) was also observed in samples austempered below Ms. The bainite transformation was accelerated and finer bainite was obtained due to the AM formation in samples austempered below Ms. In addition, the strength and hardness were improved with the decrease of the isothermal temperature and time, whereas the total elongation decreased with the increasing isothermal time and the decreasing isothermal temperature. Moreover, the materials austempered below Ms exhibited better wear performance than the ones treated above Ms, which is attributed to the improved impact toughness by the finer bainite and the enhanced hardness by AM. The best wear resistance was obtained in the samples austempered at 300 °C below Ms for 200 s, due to the highest hardness and considerable impact toughness.

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