Accelerated Nano Super Bainite in Ductile Iron

MRS Advances ◽  
2018 ◽  
Vol 3 (45-46) ◽  
pp. 2789-2794
Author(s):  
Eric Jiahan Zhao ◽  
Cheng Liu ◽  
Derek O. Northwood
Keyword(s):  
Ductile Iron ◽  
Retained Austenite ◽  
Bainitic Ferrite ◽  
Isothermal Treatment ◽  
Strengthening Effect ◽  
Matrix Microstructure ◽  
Upper Bainite ◽  
Multi Phase ◽  
Step Heat Treatment ◽  
Kinetics Of

ABSTRACTA commercial unalloyed ductile iron has been developed to produce a multiphase matrix microstructure consisting of lenticular prior martensite, feathery upper bainite and a nano-scaled super bainite of lath bainitic ferrite and carbon-enriched film retained austenite. Multi-step heat treatment composed of austenizing, rapidly quenching and isothermally holding at low temperature have been developed. A tensile strength of more than 1.6 GPa, a hardness higher than HRC 54, and an elongation in excess of 5%, are achieved. This is attributed to a synergistic multi-phase strengthening effect. The developed nano super bainite exhibits a good balance between strength and toughness. The presence of martensite formed during the quenching prior to the isothermal treatment, accelerates the kinetics of subsequent nano super bainitic transformation by bainitic laths nucleating quickly at the martensite-austenite interfaces.

Isothermal Transformation, Microstructure and Mechanical Properties of Ausformed Low-Carbon Carbide-Free Bainitic Steel

2018 ◽  
Vol 941 ◽  
pp. 329-333 ◽  
Author(s):  
Jiang Ying Meng ◽  
Lei Jie Zhao ◽  
Fan Huang ◽  
Fu Cheng Zhang ◽  
Li He Qian
Keyword(s):  
Mechanical Properties ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Bainitic Ferrite ◽  
Isothermal Transformation ◽  
Bainitic Transformation ◽  
Isothermal Treatment ◽  
Bainitic Steel ◽  
Low Carbon ◽  
Microstructure And Mechanical Properties

In the present study, the effects of ausforming on the bainitic transformation, microstructure and mechanical properties of a low-carbon rich-silicon carbide-free bainitic steel have been investigated. Results show that prior ausforming shortens both the incubation period and finishing time of bainitic transformation during isothermal treatment at a temperature slightly above the Mspoint. The thicknesses of bainitic ferrite laths are reduced appreciably by ausforming; however, ausforming increases the amount of large blocks of retained austenite/martenisite and decreases the volume fraction of retained austenite. And accordingly, ausforming gives rise to significant increases in both yield and tensile strengths, but causes noticeable decreases in ductility and impact toughness.

scholarly journals The Effect of Stepped Austempering on Phase Composition and Mechanical Properties of Nanostructured X37CrMoV5-1 Steel

2015 ◽  
Vol 60 (1) ◽  
pp. 517-521
Author(s):  
S. Marciniak ◽  
E. Skołek ◽  
W. Świątnicki
Keyword(s):  
Mechanical Properties ◽  
Retained Austenite ◽  
Isothermal Annealing ◽  
Volume Fraction ◽  
Bainitic Ferrite ◽  
High Volume ◽  
Thin Layers ◽  
Strength Parameters ◽  
One Step ◽  
Step Heat Treatment

AbstractThis paper presents the results of studies of X37CrMoV5-1 steel subjected to quenching processes with a one-step and a two-step isothermal annealing. The TEM observation revealed that steel after one-step treatment led is composed of carbide-free bainite with nanometric thickness of ferrite plates and of high volume fraction of retained austenite in form of thin layers or large blocks. In order to improve the strength parameters an attempt was made to reduce the austenite content by use of quenching with the two-step isothermal annealing. The temperature and time of each step were designed on the basis of dilatometric measurements. It was shown, that the two-step heat treatment led to increase of the bainitic ferrite content and resulted in improvement of steel's strength with no loss of steel ductility.

scholarly journals Effect of Carbon Content and Intercritical Annealing on Microstructure and Mechanical Tensile Properties in FeCMnSiCr TRIP-Assisted Steels

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1546
Author(s):  
Enzo Tesser ◽  
Carlos Silva ◽  
Alfredo Artigas ◽  
Alberto Monsalve
Keyword(s):  
Carbon Content ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Intercritical Annealing ◽  
Bainitic Ferrite ◽  
Ferrite Matrix ◽  
Polygonal Ferrite ◽  
Isothermal Treatment ◽  
Ferrite Steel ◽  
Mechanical Tensile

Four TRIP (Transformation Induced Plasticity) assisted steels, three TBF (TRIP Bainitic Ferrite) steels and one TPF (TRIP Polygonal Ferrite) steel, were manufactured from three different carbon contents (0.2, 0.3 and 0.4 wt.% C), to study the evolution of their microstructure and tensile mechanical properties in 15 mm thick plates. TBF steels were subjected to the same austenitization heat treatment and subsequent bainitization isothermal treatment. The TPF steel was subjected to an intercritical annealing and subsequent isothermal bainitization treatment. All were microstructurally characterized by optical, scanning electron and atomic force microscopy, as well as X-ray diffraction. Mechanically, they were characterized by the ASTM E8 tensile test and fractographies. For the TBF steels, the results showed that when the carbon content increased, there were an increase in volume fraction of retained austenite, of the microconstituent “martensite/retained austenite” and in the tensile strength; and a decrease in the volume fraction of bainitic ferrite matrix and elongation; with an improvement in TRIP behavior due to the increase in retained austenite. The TPF steel presented around 50% ductile polygonal ferrite developing better TRIP behavior than the TBF steels. The evolution of the fractographies was ductile to brittle for TBF steels with an increase in carbon content, and for TPF, the appearance of the fracture surface was ductile.

Influence of Multi-Step Austempering Temperature on Tensile Performance of Unalloyed Ductile Iron

2019 ◽  
Vol 803 ◽  
pp. 3-7
Author(s):  
Wei Ci Zhuang ◽  
Ying Ming Jiang ◽  
Wen Tao Zhou ◽  
Zhong Yang Liang ◽  
Derek O. Northwood ◽  
...  
Keyword(s):  
Ductile Iron ◽  
Isothermal Holding ◽  
Bainitic Ferrite ◽  
High Strength ◽  
Rapid Quenching ◽  
Air Cooling ◽  
Strengthening Effect ◽  
Multiphase Structure ◽  
Tensile Performance ◽  
Austempering Temperature

Austempered ductile iron (ADI) has been widely used in various industries due to its excellent combination of high strength, ductility and good wear resistance. The tensile behavior of an unalloyed commercial ADI with a multiphase structure designed by a novel multi-step austempering treatment is investigated. The developed austempering process consists of austenitizing at 890°C for 20min, then initial rapid quenching to 180°C, and isothermal holding at 190, 220, 250°Cfor 120min, and finally air cooling to room temperature. The optimum mechanical properties with an ultimate tensile strength of 1350MPa, a yield strength of 1090MPa, as well as an elongation of 3.5% is achieved at 220°C. This is attributed to a synergistic strengthening effect of multiphase structure including a prior martensite with fine needle bainitic ferrite and film retained austenite.

High Performance Unalloyed Ductile Cast Iron with Multiphase Structure

2019 ◽  
Vol 295 ◽  
pp. 43-48
Author(s):  
Wen Tao Zhou ◽  
Chen Yang ◽  
Xi Xi Cui ◽  
Zhong Yang Liang ◽  
Xuan Wang ◽  
...  
Keyword(s):  
Cast Iron ◽  
Retained Austenite ◽  
High Performance ◽  
Bainitic Ferrite ◽  
Rapid Quenching ◽  
Ductile Cast Iron ◽  
Fine Needle ◽  
Multiphase Structure ◽  
Matrix Microstructure ◽  
The Matrix

An unalloyed ductile cast iron with a multiphase structure is designed by a novel austempering process. The designed austempering treatment consists of initial rapid quenching to 180°C after austenizing at 890°C for 20min, and finally austempering at 220°C for 240min. A multiphase structure comprising lenticular/needle-like prior martensite, fine needle bainitic ferrite and film retained austenite is obtained. The excellent mechanical properties, with a tensile strength of 1530MPa and an elongation of 3.1% can be achieved by controlling the matrix microstructure of 12% prior martensite, 15% retained austenite with 1.64% carbon content, and 73% bainitic ferrite. This is mainly attributed to prior marteniste which can promote refinement of multiphase colonies.

Effect of Retained Austenite on Impact Toughness of the Multi-Phase Bainitic-Martensitic Steel

2014 ◽  
Vol 922 ◽  
pp. 298-303 ◽  
Author(s):  
José Alberto da Cruz ◽  
Jefferson José Vilela ◽  
Berenice Mendonça Gonzalez ◽  
Dagoberto Brandão Santos
Keyword(s):  
Retained Austenite ◽  
Room Temperature ◽  
Volume Fraction ◽  
Martensitic Steel ◽  
Bainitic Ferrite ◽  
Bainitic Transformation ◽  
New Class ◽  
Bainitic Steels ◽  
Si Content ◽  
Multi Phase

The new class of bainitic steels can present toughness at room temperature greater than traditional quenched and tempered martensitic steel. This is because the microstructure of steel with high Si content (≈1.5wt%) submitted to bainitic transformation is compose of fine plates of bainitic ferrite separated by retained austenite. The inhibition of cementite precipitation leads to the improvement of toughness. The presence of cementite facilitates the nucleation of cracks. Moreover, the blocks of retained austenite are undesirable. This morphology is rather unstable and tends to transform into hard and brittle untempered martensite under the influence of small stress, contributing to a low toughness. However, it was observed in this work that the greater the volume fraction of retained austenite, the greater is the toughness (10-24 J) for multi-phase steel. The values of toughness were independent whether the retained austenite is present on film or block forms. The decrease of toughness values was observed by the tempered samples after the bainitic transformation (10-14 J). This occurred because the blocks of retained austenite decomposed into carbides, martensite and/or bainite.

Thermo-Mechanically Processed Multi-Phase Ductile Iron: Microstructure Development

2010 ◽  
Vol 457 ◽  
pp. 199-204 ◽  
Author(s):  
Mohamed Soliman ◽  
Heinz Palkowski ◽  
Adel Nofal
Keyword(s):  
Ductile Iron ◽  
Deformation Process ◽  
Formation Temperature ◽  
Microstructure Development ◽  
Controlled Cooling ◽  
Ferrite Formation ◽  
Final Microstructure ◽  
Mn Content ◽  
Multi Phase ◽  
Kinetics Of

Using thermo-mechanical simulator equipped with dilatometry system, two ductile iron alloys with different Mn-content are processed by combining both, well defined deformation process and subsequent controlled cooling in a single processing chain to control the final microstructure. Accordingly, ductile irons with four different structrues are produced namely, martensite, ausferrite, martensite+ferrite and ausferrite+ferrite. Depending on the dilatometric measurments, the ferrite formation temperature-range has been defined for both alloys. Preferential transformation of austenite to ferrite at graphite nodules during cooling is observed. It is also observed that the formation of ferrite during cooling results in both decreased martensite start of the undecomposed austenite and accelerated kinetics of ausferrite formation.

scholarly journals Bainite Transformation-Kinetics-Microstructure Characterization of Austempered 4140 Steel

Metals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 236
Author(s):  
Jian G. Zhu ◽  
Xichen Sun ◽  
Gary C. Barber ◽  
Xue Han ◽  
Hao Qin
Keyword(s):  
Linear Trend ◽  
Bainitic Ferrite ◽  
Lower Bainite ◽  
Structure Evolution ◽  
Bainite Transformation ◽  
Solid Diffusion ◽  
Wide Range ◽  
Upper Bainite ◽  
Kinetics Of

Bainite transformation is a kinetic process that involves complex solid diffusion and phase structure evolution. This research systematically studies the bainite transformation of austempered 4140 steel in a wide range of isothermal temperatures, in which four bainite phases structures were generated: upper bainite; mixed upper bainite and lower bainite; lower bainite and mixed lower bainite and martensite. The kinetics of bainite transformation has been described with a linear trend using an Avrami n-value. It was found that the bainitic ferrite sheaves grow with widthwise preference. The sheaves are stable when half-grown and are variable in length, due to austenite size limit or soft/hard impingement, or autocatalytic nucleation, or these conditions combined. The full-grown upper/lower bainite sheaves were found to be 1.9 μm/1.2 μm in width under the conditions of this study. Each individual bainite sheave is lath-like instead of wedge-like. The upper bainite sheaves mostly appear as broad-short-coarse lath, while the lower bainite sheaves appear as narrow-long-fine lath. The overall bainite transformation activation energy ranges from 50–167 kJ/mol.

scholarly journals Microstructure and mechanical properties of CuNiMo austempered ductile iron

2004 ◽  
Vol 40 (1) ◽  
pp. 11-19 ◽  
Author(s):  
Olivera Eric ◽  
Marina Jovanovic ◽  
Leposava Sidjanin ◽  
Dragan Rajnovic
Keyword(s):  
Mechanical Properties ◽  
Ductile Iron ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Bainitic Ferrite ◽  
Austempered Ductile Iron ◽  
X Ray Diffraction ◽  
Microstructure And Mechanical Properties ◽  
Cast Ductile Iron

Microstructure and mechanical properties of Cu, Ni and Mo alloyed cast ductile iron have been investigated after austempering. Samples were austenitised at 860oC for 1h and then austempered at 320oC and 400oC in the interval from 0,5 to 5h. The X-ray diffraction technique and the light microscopy were utilized to investigate the bainitic transformation, while tensile and impact tests were performed for characterization of mechanical properties. By austempering at 320oC in the range between 2 and 5h, a microstructure typical for austempered ductile iron was produced, i.e. a mixture of free bainitic ferrite and highly carbon enriched retained austenite. The characteristic of the whole range of austempering at 400oC is the appearance of martensitic structure. The maximum impact energy (133 J) coincides with the maximum value of volume fraction of retained austenite that was obtained after 2,5h of austempering at 320oC. The appearance of martensite during austempering at 400oC is the main cause for much lower tensile properties than at 320oC.

Influence of the Austempering Temperature on the Microstructure and Crystallography of a Carbide-Free Bainitic Steel

2011 ◽  
Vol 172-174 ◽  
pp. 797-802 ◽  
Author(s):  
Jean Christophe Hell ◽  
Moukrane Dehmas ◽  
Guillaume Geandier ◽  
Nathalie Gey ◽  
Sebastien Allain ◽  
...  
Keyword(s):  
Retained Austenite ◽  
Volume Fraction ◽  
Bainitic Ferrite ◽  
High Energy ◽  
Isothermal Transformation ◽  
Bainitic Transformation ◽  
Bainitic Steels ◽  
Austempering Temperature ◽  
Kinetics Of

We elaborated two carbide-free bainitic steels with different microstructures through specific heat treatments and alloy design. EBSD analysis was used to point out major differences in these microstructures. In-situ characterizations of the bainitic transformation were performed by high energy synchrotron diffraction to go further into the study of each phase characteristics. The elaborated microstructures exhibited various phase fractions of bainitic ferrite, retained austenite and blocks of martensite and retained austenite. Moreover, the volume fraction of retained austenite increased with higher austempering temperatures. On the other hand, the austempering temperatures showed a strong influence on the kinetics of the bainitic transformation. Isothermal transformation under Ms showed a two stage transformation which led first to the formation of self-tempered martensite and then to bainitic ferrite. Furthermore, the evolution of the austenitic cell parameter showed enrichment in carbon ruled by diffusional mechanisms.

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