Effect of austempering treatment on the microstructure and mechanical properties of 0.4C–1.5Si-1.5Mn TRIP-aided bainitic ferrite steel

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.

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

Materials Express ◽

10.1166/mex.2020.1846 ◽

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.

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Effect of Heat Treatment on Microstructure and Mechanical Properties of High-Strength Steel for in Hot Forging Products

Metals ◽

10.3390/met11050768 ◽

2021 ◽

Vol 11 (5) ◽

pp. 768

Author(s):

Moonseok Kang ◽

Minha Park ◽

Byoungkoo Kim ◽

Hyoung Chan Kim ◽

Jong Bae Jeon ◽

...

Keyword(s):

Mechanical Properties ◽

Heat Treatment ◽

High Strength Steel ◽

Fracture Behavior ◽

Hot Forging ◽

Bainitic Ferrite ◽

High Strength ◽

Austenitizing Temperature ◽

Microstructure And Mechanical Properties ◽

The Difference

High-strength steel is widely used in hot forging products for application to the oil and gas industry because it has good mechanical properties under severe environment. In order to apply to the extreme environment industry requiring high temperature and high pressure, heat treatments such as austenitizing, quenching and tempering are required. The microstructure of high-strength steel after heat treatment has various microstructures such as Granular Bainite (GB), Acicular Ferrite (AF), Bainitic Ferrite (BF), and Martensite (M) depending on the heat treatment conditions and cooling rate. Especially in large forged products, the difference in microstructure occurs due to the difference in the forging ratio depending on the location and the temperature gradient according to the thickness during post-heat treatment. Therefore, this study attempted to quantitatively analyze various phases of F70 high-strength steel according to the austenitizing temperature and hot forging ratio using the existing EBSD analysis method. In addition, the correlation between microstructure and mechanical properties was investigated through various phase analysis and fracture behavior of high-strength steel. We found that various microstructures of strength steel depend on the austenitizing temperature and hot forging ratio, and influence the mechanical properties and fracture behavior.

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Microstructure and mechanical properties of CuNiMo austempered ductile iron

Journal of Mining and Metallurgy Section B Metallurgy ◽

10.2298/jmmb0401011e ◽

2004 ◽

Vol 40 (1) ◽

pp. 11-19 ◽

Cited By ~ 6

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.

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Effect of Multi-Step Austempering Treatment on the Microstructure and Mechanical Properties of a High Silicon Carbide-Free Bainitic Steel with Bimodal Bainite Distribution

Metals ◽

10.3390/met11122055 ◽

2021 ◽

Vol 11 (12) ◽

pp. 2055

Author(s):

Mattia Franceschi ◽

Alvise Miotti Bettanini ◽

Luca Pezzato ◽

Manuele Dabalà ◽

Pascal J. Jacques

Keyword(s):

Mechanical Properties ◽

Silicon Carbide ◽

Mechanical Response ◽

Bainitic Ferrite ◽

Single Step ◽

Isothermal Treatment ◽

Bainitic Steel ◽

Microstructure And Mechanical Properties ◽

Single Temperature ◽

High Silicon

The effect of multi-step austempering treatments on the microstructure and mechanical properties of a novel medium carbon high silicon carbide-free bainitic steel was studied. Five different isothermal treatment processes were selected, including single-step isothermal treatments above martensite start temperature (at 350 °C and 370 °C, respectively), and three kinds of two-step routes (370 °C + 300 °C, 370 °C + 250 °C, and 350 °C + 250 °C). In comparison with single-step austempering treatment adopting a two-step process, a microstructure with a bimodal-size distribution of bainitic ferrite and without martensite was obtained. Bainitic transformation was studied using dilatometry both for single-step and two-step routes and the specimens were completely characterised by electron microscopy (SEM and TEM), X-ray diffraction (XRD) and standard tensile tests. The mechanical response of the samples subjected to two-step routes was superior to those treated at a single temperature.

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The Effect of Twice Thermal Cycle on the Microstructure and Mechanical Properties of Coarse Grain Region in X80 Pipeline Steel

Materials Science Forum ◽

10.4028/www.scientific.net/msf.898.749 ◽

2017 ◽

Vol 898 ◽

pp. 749-752

Author(s):

Shuo Li ◽

Xiao Jiang Guo ◽

Ye Zheng Li ◽

Yong Li Sui ◽

Zong Bin You

Keyword(s):

Mechanical Properties ◽

Grain Size ◽

Impact Toughness ◽

Thermal Cycle ◽

Pipeline Steel ◽

Bainitic Ferrite ◽

Peak Temperature ◽

Coarse Grain ◽

X80 Pipeline Steel ◽

Microstructure And Mechanical Properties

Based on the multi-pass welding characteristics of X80 pipeline steel, the influence of twice thermal cycle on the microstructure and mechanical properties of coarse grain region in X80 pipeline steel was investigated. The thermal cycles of weld coarse grain region with different peak temperature for the second thermal cycle were simulated with the Gleeble-3500 thermal/mechanical simulator. The Charpy impact absorbed energy for toughness was measured, and the corresponding optical micrographs and electron micrographs were systematically investigated to study the effect of the peak temperature on microstructure and impact toughness in the coarse grain region. The results of simulated experiment showed that the microstructure in heat affected zone of coarse grain region is granular bainitic and bainitic ferrite. When the peak temperature of the second thermal cycle is 800°C, the types of microstructure and the grain size of original austenite have no change. However, it forms network microstructure with chain structure in grain boundary and the reduction of toughness may be affected by the M–A constituents. With the peak temperature of 1000°C, the micro structure is composed of granular bainitic and a little bainitic ferrite. In this case, the grain size of austenite can be significantly fined, being helpful to increase the impact toughness.

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