scholarly journals The Impact of Retained Austenite on the Mechanical Properties of Bainitic and Dual Phase Steels

2022 ◽  
Author(s):  
Bogusława Adamczyk-Cieślak ◽  
Milena Koralnik ◽  
Roman Kuziak ◽  
Kamil Majchrowicz ◽  
Tomasz Zygmunt ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Transformation Temperature ◽  
Retained Austenite ◽  
Tensile Tests ◽  
Total Elongation ◽  
Isothermal Transformation ◽  
Bainitic Transformation ◽  
Bainitic Steel ◽  
Continuous Cooling

AbstractThis paper presents the microstructural changes and mechanical properties of carbide-free bainitic steel subjected to various heat treatment processes and compares these results with similarly treated ferritic–pearlitic steel. A key feature of the investigated steel, which is common among others described in the literature, is that the Si content in the developed steel was >1 wt.% to avoid carbide precipitation in the retained austenite during the bainitic transformation. The phase identification before and after various heat treatment conditions was carried out based on microstructural observations and x-ray diffraction. Hardness measurements and tensile tests were conducted to determine the mechanical properties of the investigated materials. In addition, following the tensile tests, the fracture surfaces of both types of steels were analyzed. Changing the bainitic transformation temperature generated distinct volume fractions of retained austenite and different values of mechanical strength properties. The mechanical properties of the examined steels were strongly influenced by the volume fractions and morphological features of the microstructural constituents. It is worth noting that the bainitic steel was characterized by a high ultimate tensile strength (1250 MPa) combined with a total elongation of 18% after austenitizing and continuous cooling. The chemical composition of the bainitic steel was designed to obtain the optimal microstructure and mechanical properties after hot deformation followed by natural cooling in still air. Extensive tests using isothermal transformation to bainite were conducted to understand the relationships between transformation temperature and the resulting microstructures, mechanical properties, and fracture characteristics. The isothermal transformation tests indicated that the optimal relationship between the sample strength and total elongation was obtained after bainitic treatment at 400 °C. However, it should be noted that the mechanical properties and total elongation of the bainitic steel after continuous cooling differed little from the condition after isothermal transformation at 400 °C.

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 Novel Approach of Nanostructured Bainitic Steels’ Production with Improved Toughness and Strength

Materials ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1220
Author(s):  
Peter Kirbiš ◽  
Ivan Anžel ◽  
Rebeka Rudolf ◽  
Mihael Brunčko
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Fine Structure ◽  
Retained Austenite ◽  
Bainitic Ferrite ◽  
High Hardness ◽  
Tensile Tests ◽  
Isothermal Transformation ◽  
Impact Testing ◽  
Bainitic Steels

The tendencies of development within the field of engineering materials show a persistent trend towards the increase of strength and toughness. This pressure is particularly pronounced in the field of steels, since they compete with light alloys and composite materials in many applications. The improvement of steels’ mechanical properties is sought to be achieved with the formation of exceptionally fine microstructures ranging well into the nanoscale, which enable a substantial increase in strength without being detrimental to toughness. The preferred route by which such a structure can be produced is not by applying the external plastic deformation, but by controlling the phase transformation from austenite into ferrite at low temperatures. The formation of bainite in steels at temperatures lower than about 200 °C enables the obtainment of the bulk nanostructured materials purely by heat treatment. This offers the advantages of high productivity, as well as few constraints in regard to the shape and size of the workpiece when compared with other methods for the production of nanostructured metals. The development of novel bainitic steels was based on high Si or high Al alloys. These groups of steels distinguish a very fine microstructure, comprised predominantly of bainitic ferrite plates, and a small fraction of retained austenite, as well as carbides. The very fine structure, within which the thickness of individual bainitic ferrite plates can be as thin as 5 nm, is obtained purely by quenching and natural ageing, without the use of isothermal transformation, which is characteristic for most bainitic steels. By virtue of their fine structure and low retained austenite content, this group of steels can develop a very high hardness of up to 65 HRC, while retaining a considerable level of impact toughness. The mechanical properties were evaluated by hardness measurements, impact testing of notched and unnotched specimens, as well as compression and tensile tests. Additionally, the steels’ microstructures were characterised using light microscopy, field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). The obtained results confirmed that the strong refinement of the microstructural elements in the steels results in a combination of extremely high strength and very good toughness.

scholarly journals Influence of Prior Martensite on Bainite Transformation, Microstructures, and Mechanical Properties in Ultra-Fine Bainitic Steel

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 527 ◽  
Author(s):  
Hui Guo ◽  
Xianying Feng ◽  
Aimin Zhao ◽  
Qiang Li ◽  
Jun Ma
Keyword(s):  
Mechanical Properties ◽  
Retained Austenite ◽  
Bainitic Ferrite ◽  
Growth Direction ◽  
Bainitic Transformation ◽  
Bainitic Steel ◽  
Bainite Transformation ◽  
Multiphase Microstructure ◽  
Microstructures And Mechanical Properties ◽  
The Impact

A multiphase microstructure comprising of different volume fractions of prior martensite and ultra-fine bainite (bainitic ferrite and retained austenite) was obtained by quenching to certain temperatures, followed by isothermal bainitic transformation. The effect of the prior martensite transformation on the bainitic transformation behavior, microstructures, and mechanical properties were discussed. The results showed that the prior martensite accelerated the subsequent low-temperature bainite transformation, and the incubation period and completion time of the bainite reaction were significantly shortened. This phenomenon was attributed to the enhanced nucleation ratio caused by the introduced strain in austenite, due to the formation of prior martensite and a carbon partitioning between the prior martensite and retained austenite. Moreover, the prior martensite could influence the crystal growth direction of bainite ferrite, refine bainitic ferrite plates, and reduce the dimension of blocky retained austenite, all of which were responsible for improving the mechanical properties of the ultra-fine bainitic steel. When the content of the prior martensite reached 15%, the investigated steels had the best performance, which were 1800 MPa and 21% for the tensile strength and elongation, respectively. Unfortunately, the increased content of the prior martensite could lead to a worsening of the impact toughness.

scholarly journals Controlling the Content and Morphology of Phase Constituents in Nanobainitic Steel Containing 0.6%C to Obtain the Required Ratio of Strength to Plasticity

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 658
Author(s):  
Jarosław Marcisz ◽  
Bogdan Garbarz ◽  
Aleksandra Janik ◽  
Władysław Zalecki
Keyword(s):  
Mechanical Properties ◽  
Phase Composition ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Total Elongation ◽  
Isothermal Transformation ◽  
Effect Of Temperature ◽  
Isothermal Heat Treatment ◽  
Dilatometric Studies ◽  
Kinetics Of

The phase composition of nanobainitic steel 0.56–0.60%C, 1.68–1.95%Mn, 1.58–1.80%Si, 1.30–1.47%Cr, 0.57–0.75%Mo is described in this paper. The phase composition is controlled in order to obtain diversified mechanical properties for specific applications, such as armor plates. The effect of temperature and time of isothermal heat treatment on both the microstructure and the mechanical properties of the steel were determined. Dilatometric studies, as well as measurements of volume fraction and size distribution of retained austenite were carried out. Analysis of the kinetics of isothermal transformation in the temperature range of 200–225 °C for times of up to 144 h were also carried out, and the parameters of the production process of the steel were determined. A microstructure consisting of nanolathy carbideless bainite and blocky and lathy retained austenite, providing tensile strength of at least 2000 MPa, yield strength of at least 1300 MPa, and total elongation of at least 10% has been found.

scholarly journals The Effect of Heat Treatment on Microstructure and Mechanical Properties of Cast Bainitic Steel Used for Frogs in Railway Crossovers

2017 ◽  
Vol 62 (4) ◽  
pp. 2147-2151 ◽  
Author(s):  
S. Parzych
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Cast Steel ◽  
Pearlitic Steel ◽  
Strength Properties ◽  
Tensile Yield Strength ◽  
Bainitic Steel ◽  
Microstructure And Mechanical Properties

Abstract This work deals with the effect of heat treatment on a microstructure and mechanical properties of a selected cast steel assigned as a material used for frogs in railway crossovers. Materials used nowadays in the railway industry for frogs e.g. Hadfield cast steel (GX120Mn13) or wrougth pearlitic steel (eg. R260) do not fulfil all exploitation requirements indicated in the UIC (International Union of Railways) Decision No. 1692/96 in terms of train speed that should be reached on railways. One of the possible solution is using a cast steel with bainitic or bainitic-martensitic microstructure that allows to gain high strength properties the ultimate tensile strength (UTS) of 1400 MPa, the tensile yield strength (TYS) of 900 MPa and the hardness of up to 400 BHN. The tested material is considered as an alternative to Hadfield cast steel that is currently used for railway frogs. Results of an experimental analysis of the effect of conducted heat treatment on a microstructure, the volume fraction of retained austenite and mechanical properties of bainitic steel, are shown in this paper. It was found that, the heat treatment leads to a stabilization of retained austenite in grain boundaries area of the primary austenite. Additionally, the heat treatment according to the variant #3 results with an almost 3-times higher impact toughness to that exhibited by material subjected to the other treatments.

Microstructure and mechanical properties of a high-carbon bainitic steel containing Si/Al by different heat treatment processes

2020 ◽  
Vol 10 (11) ◽  
pp. 1932-1940
Author(s):  
Sufyan Naseem ◽  
Enzuo Liu ◽  
Xuefei Huang ◽  
Weigang Huang
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Electron Microscope ◽  
Retained Austenite ◽  
Bainitic Ferrite ◽  
Bainitic Steel ◽  
Boundary Misorientation ◽  
Treatment Processes ◽  
Microstructure And Mechanical Properties ◽  
The Impact

The present study aims to investigate the microstructure and mechanical properties of 0.79 C wt% bainitic steel containing Si and Al by three heat treatment processes: austempering and tempering (B-T), two-step austempering (2S-A) and the austempering-quenching-partitioning (AQP). The optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM) and electron backscatter diffraction (EBSD) were employed to analyze the microstructure of samples. The results demonstrate that the sample subjected to the AQP process exhibited a multiphase microstructure with martensite, filmy retained austenite (RA) and fine bainitic laths. The AQP sample evidenced a high tensile strength of 1705 MPa, yield strength of 1254 MPa, a better total elongation of 16.6%, product of strength and elongation (PSE) of 28 GPa% and the impact toughness of 33 J among all heat treatment processes. The higher strength and toughness could be ascribed to the fine bainitic ferrite as well as an appropriate amount of filmy retained austenite. A fraction of martensite that was formed during the quenching step at 110 °C possibly divided the untransformed austenite into small areas, which could refine the microstructure. EBSD analysis showed that the AQP sample exhibited a higher proportion (64%) of boundary misorientation angle greater than 15° than that of the 2S-A. These high angle boundaries can improve the toughness of steel.

scholarly journals Enhanced Strength and Ductility by Introducing Nanobainitic Ferrite in Bainitic Steel Used in Sports Equipment

Metals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 2007
Author(s):  
Han Meng ◽  
Zhenjun Hong ◽  
Yu Li ◽  
Xiaoshuai Jia ◽  
Zhihua Yin
Keyword(s):  
Mechanical Properties ◽  
Retained Austenite ◽  
Bainitic Ferrite ◽  
Total Elongation ◽  
Bainitic Steel ◽  
Bainitic Steels ◽  
Cottrell Atmosphere ◽  
The Stability ◽  
Strength And Ductility ◽  
Enhanced Stability

The mechanical properties of carbide-free bainitic steels used in sports equipment were investigated. The nanobainitic ferrite was introduced in bainitic steel to enhance the stability of blocky retained austenite (RA). The blocky RA formed in bainitic austempering process was coarse and led to poor mechanical properties. By introducing the nanobainitic ferrite into blocky RA, the yield strength was improved remarkably, which was increased from 706 to 1180 MPa. Furthermore, the total elongation was almost twice the value compared to the traditional bainitic treatment. The improved mechanical properties were attributed to the enhanced stability of blocky RA. Furthermore, the increased carbon content in RA derived from the carbon dissolved in bainitic ferrite and the carbon trapped in dislocation or Cottrell atmosphere.

scholarly journals On the Q&P Potential of a Commercial Spring Steel

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1612
Author(s):  
Markus Härtel ◽  
Alisa Wilke ◽  
Sebastian Dieck ◽  
Pierre Landgraf ◽  
Thomas Grund ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Electron Backscatter Diffraction ◽  
Tensile Tests ◽  
Spring Steel ◽  
Process Window ◽  
Compression Tests ◽  
Process Step

Over the last years heat treatment concept of “quenching and partitioning” (Q&P) has reached popularity for its ability to precisely adjust material properties to desired values. Mostly, Q&P process are applied on tailor-made materials with high purities or prototype alloys. The research in hand presents the whole routine of how to investigate the potential of a commercial 0.54C-1.45Si-0.71Mn spring steel in terms of Q&P heat treatment from lab scale in dilatometer measurements to widely used inductive heat treatment on larger scale. In order to obtain the small process window for this material we were focusing on the interplay of the formed microstructure and the resulting mechanical properties in hardness measurements, compression tests as well as tensile tests. After full austenitizing, three different Q&P processing routes were applied. Microstructural analyses by optical microscopy, Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD) exhibit a condition with 6.4 % and 15 % volume fraction of fine distributed retained austenite. Interestingly, the 15 % of retained austenite developed during the partitioning heat treatment. Contradictory to our expectations, tensile and compression testing were showing that the 6.4 % condition achieved improved mechanical properties compared to the 15 % retained austenite condition. The remarkable conclusion is that not only volume fraction and fine distribution of retained austenite determines the potential of improving mechanical properties by Q&P in commercial alloys: also the process step when the retained austenite is developing as well as occurring parallel formation of carbides may strongly influence this potential.

scholarly journals Effects of Heat Treatment on Morphology, Texture and Mechanical Properties of a MnSiAl Multiphase Steel with TRIP Behavior

2018 ◽  
Author(s):  
Alvaro Salinas ◽  
Alfredo Artigas ◽  
Juan Pérez-Ipiña ◽  
Felipe M. Castro-Cerda ◽  
Nelson F. Garza-Montes-de-Oca ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Retained Austenite ◽  
Room Temperature ◽  
Single Phase ◽  
Intercritical Annealing ◽  
Tensile Tests ◽  
Temperature Homogenization ◽  
Cold Rolled ◽  
Multiphase Steel

: The effect that the microstructure exerts on the TRIP phenomenon and on the mechanical properties in a multiphase steel was studied. Samples of an initially cold-rolled ferrite-pearlite steel underwent different intercritical annealing treatments at 750 °C until an equal fractions of austenite/ferrite was reached; the intercritical treatment was followed by isothermal bainitic treatments before cooling the samples to room temperature. Samples in the first treatment were heated  directly to the intercritical temperature, whereas other samples were heated to either 900 or 1100 °C to obtain a fully homogenized, single phase austenitic microstructure prior to the conducting the intercritical treatment. The high temperature homogenization of austenite resulted in the decrease in its stability, so a considerable austenite fraction transformed into martensite by cooling to room temperature after the bainitic heat treatment. Most of the retained austenite transformed during the tensile tests, and as a consequence, the previously homogenized steels showed the highest UTS. In turn, the steel with a ferritic-pearlitic initial microstructure, exhibited higher ductility than the other steels and texture components that favor forming processes.     

The Optimization of the Isothermal Transformation Dwell of the ADI Obtained at Transformation Temperature of 380 °C

2007 ◽  
Vol 567-568 ◽  
pp. 337-340
Author(s):  
Klára Hanzlíková ◽  
Stanislav Vĕchet ◽  
Jan Kohout ◽  
Josef Zapletal
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Ductile Iron ◽  
Transformation Temperature ◽  
Isothermal Transformation ◽  
Mixture Composition ◽  
Austempered Ductile Iron ◽  
Treatment Conditions ◽  
Static Mechanical ◽  
Static Mechanical Properties

The structure of austempered ductile iron (ADI) matrix and consequently its mechanical properties are influenced by the heat treatment conditions, above all by the temperature and dwell length of isothermal transformation. The paper is focused on deeper understanding the interrelation between matrix mixture composition and static mechanical properties of ADI in dependence on the isothermal transformation dwell. Practical aim of the paper is to find the optimal isothermal transformation dwell range for ADI isothermally transformed at the temperature of 380 °C with emphasis on the level of static mechanical properties in tension. Microstructure and mechanical properties changes that proceed during isothermal transformation are observed and evaluated for the transformation dwells of 2, 5, 10, 25, 60, 120, 270, and 540 minutes.

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