scholarly journals Interactions Between Dynamic Softening and Strengthening Mechanisms During Hot Forging of a High-Strength Steel

2021 ◽  
Vol 7 ◽  
Author(s):  
Makarim Khan ◽  
Davood Shahriari ◽  
Mohammad Jahazi ◽  
Jean-Benoit Morin
Keyword(s):  
Electron Microscopy ◽  
Dynamic Recrystallization ◽  
High Strength Steel ◽  
True Strain ◽  
Hot Forging ◽  
High Strength ◽  
Actual Process ◽  
Dynamic Precipitation ◽  
Die Forging ◽  
Open Die Forging

Open-die forging is a critical step in the manufacture of large numbers of components used in the transportation and energy industries. Dynamic recrystallization, dynamic transformation, and dynamic precipitation take place during the hot deformation process and significantly affect microstructure conditioning, which ultimately influences the service properties of the component. In the present work, using a Gleeble 3800 thermomechanical simulator, the open-die forging of a large-size ingot made of a modified AISI 6140 medium carbon high-strength steel is investigated. Deformation temperatures ranging from 950°C to 1,250°C and strain rates ranging from 0.01 to 1 s−1, representative of the actual process, are considered in the analysis. The generated true stress–true strain curves are used as a basis for the development of a constitutive model predicting the occurrence of softening and strengthening phenomena as a function of thermomechanical conditions. The corresponding activation energy is determined to be about 374 kJ mol−1 and is compared against the values reported in the literature for other high-strength steels. Dynamic recrystallization kinetics is studied using the t50 model, and the influence of temperature and strain rate is quantified and discussed. The interaction between dynamic precipitation and dynamic recrystallization is discussed, and the deformation conditions under which such interactions occur are determined. The thermomechanical results are validated by microstructure examination, including laser confocal microscopy, field emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive spectroscopy. The present study focuses on reproducing the deformation cycle applied during the open-die forging process of a vanadium-containing high-strength steel used in the industry with special attention to the interaction between dynamic recrystallization and precipitation processes.

scholarly journals Analysis of Void Closure during Open Die Forging Process of Large Size Steel Ingots

2016 ◽  
Vol 716 ◽  
pp. 579-585 ◽  
Author(s):  
Nathan Harris ◽  
Davood Shahriari ◽  
Mohammad Jahazi
Keyword(s):  
Strain Rate ◽  
High Strength Steel ◽  
Volumetric Strain ◽  
High Strength ◽  
Material Model ◽  
Void Closure ◽  
Forging Process ◽  
Large Size ◽  
Die Forging ◽  
Open Die Forging

Large size forged ingots, made of high strength steel, are widely used in aerospace, transport and energy applications. The presence of internal voids in the as-cast ingot may significantly affect the mechanical properties of final products. Thus, such internal defects must be eliminated during first steps of the open die forging process. In this paper, the effect of in-billet void positioning on void closure throughout the ingot breakdown process and specifically the upsetting step in a large ingot size steel is quantitatively investigated. The developed Hansel-Spittel material model for new high strength steel is used in this study. The ingot forging process (3D simulation) was simulated with Forge NxT 1.0® according to existing industrial data. A degree of closure of ten virtual existing voids was evaluated using a semi-analytical void closure model. It is found that the upsetting process is most effective for void closure in core regions and central upper billet including certain areas within the dead metal zone (DMZ). The volumetric strain rate is determined and two types of inertial effects are observed. The dependence of void closure on accumulated equivalent deformation is calculated and discussed in relation to void in-billet locations. The original combination of information from both relative void closure and the volumetric strain rate provides a way to optimize the forging process in terms of void elimination.

Dynamically recrystallized austenitic grain in a low carbon advanced ultra-high strength steel (A-UHSS) microalloyed with boron under hot deformation conditions

2012 ◽  
Vol 1485 ◽  
pp. 143-148 ◽  
Author(s):  
I. Mejía ◽  
E. García-Mora ◽  
G. Altamirano ◽  
A. Bedolla-Jacuinde ◽  
J. M. Cabrera
Keyword(s):  
Grain Size ◽  
Hot Deformation ◽  
High Strength Steel ◽  
Picric Acid ◽  
True Strain ◽  
Research Work ◽  
High Strength ◽  
Low Carbon ◽  
Ultra High Strength Steel ◽  
Wide Range

ABSTRACTThis research work studies the dynamically recrystallized austenitic grain size (Drec) in a new family of low carbon NiCrCuV advanced ultra-high strength steel (A-UHSS) microalloyed with boron under hot deformation conditions. For this purpose, uniaxial hot-compression tests are carried out in a low carbon A-UHSS microalloyed with different amounts of boron (14, 33, 82, 126 and 214 ppm) over a wide range of temperatures (950, 1000, 1050 and 1100°C) and constant true strain rates (10−3, 10−2and 10−1s−1). Deformed samples are prepared and chemically etched with a saturated aqueous picric acid solution at 80°C in order to reveal theDrecand examined by light optical (LOM) and scanning electron microscopy (SEM). TheDrecis related to the Zener-Hollomon parameter (Z), and thereafter theDrecdivided by Burger's vector (b) is related to the steady state stress (σss) divided by the shear modulus (µ) (Derby model). Results shown that theDrecin the current steels is fine (≈ 23 μm) and almost equiaxed, and the recrystallized grain size-flow stress relationship observed after of plastic deformation is consistent with the general formulation proposed by Derby. It is corroborated that boron additions to the current A-UHSS do not have meaningful influence on theDrec.

Mechanisms of Dynamic Recrystallization in Cu-Sn-P Alloy

2010 ◽  
Vol 654-656 ◽  
pp. 1267-1270 ◽  
Author(s):  
Hiromi Miura ◽  
Masato Watanabe ◽  
Takashi Shirai ◽  
Akihiko Ishibashi
Keyword(s):  
Grain Boundary ◽  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Boundary Migration ◽  
True Strain ◽  
Copper Alloys ◽  
Peak Stress ◽  
High Strength ◽  
Columnar Grains ◽  
Almost All

Dynamic recrystallization (DRX) behavior in a Cu-0.65Sn-0.025P (mass%) alloy (Cu-Sn-P), which had been newly developed for high strength copper tubes, was systematically investigated. For this purpose, an orientation-controlled bicrystal ( =28o); a model samples of the as-casted billet having coarse columnar grains, was hot deformed in compression at 1073 K at true strain rates from 2 x 10-3 s-1 to 2 x 10-1 s-1 in vacuum. Appearance of peak stress, where DRX sets in, was much delayed in Cu-Sn-P alloy compared with that in Cu and the other copper alloys. While nucleation of new grains preferentially took place at grain boundary, this tendency became more significant with decreasing strain rate. Almost all the new grains were annealing twins (3) formed behind the migrating grain boundary. The more preferential nucleation at grain boundary with decreasing strain rate could be, therefore, reasonably understood by easier and more extensive occurrence of grain boundary migration at lower strain rate.

scholarly journals Softening Characterization of 300M High-Strength Steel during Post-Dynamic Recrystallization

Metals ◽  
2018 ◽  
Vol 8 (5) ◽  
pp. 340 ◽  
Author(s):  
Rong Zeng ◽  
Liang Huang ◽  
Hongliang Su ◽  
Huijuan Ma ◽  
Yangfei Ma ◽  
...  
Keyword(s):  
Dynamic Recrystallization ◽  
High Strength Steel ◽  
High Strength

Structure formation of nitrogen-containing austenitic 04Kh20N6G11M2AFB steel. Part 1: Influence of deformation temperature and strain rate on the dynamic recrystallization

2019 ◽  
pp. 7-21
Author(s):  
O. V. Fomina ◽  
T. V. Vikhareva ◽  
V. V. Sagaradze ◽  
N. V. Kataeva
Keyword(s):  
Electron Microscopy ◽  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Deformation Temperature ◽  
High Strength ◽  
Steel Part ◽  
Corrosion Resistant ◽  
Rate Analysis ◽  
Transmission Electron ◽  
Weak Peak

The paper determines values of the deformation threshold necessary for the initiation and development of dynamic recrystallization in the investigated deformation temperature and strain rate. Analysis of diagrams shows that the deformation resistance increases with decreasing of temperature, while a weak peak is observed at temperature 1000–1200°C, when dynamic recrystallization starts. The structure of high-strength corrosion-resistant nitrogen-containing austenitic steel 04Kh20N6G11M2AFB after hot deformation with strain rate 0.1, 1.0 and 10 s-1  in the temperature range 900–1200°С has been studied by EBSD analysis and transmission electron microscopy.

scholarly journals Effect of Dynamic Recrystallization on the Transformed Ferrite Microstructures in HSLA Steel

Metals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 817 ◽  
Author(s):  
Ning Li ◽  
Wilasinee Kingkam ◽  
Renheng Han ◽  
Ming Tang ◽  
Hexin Zhang ◽  
...  
Keyword(s):  
Dynamic Recrystallization ◽  
Grain Boundaries ◽  
Electron Backscatter Diffraction ◽  
Boundary Migration ◽  
Hsla Steel ◽  
True Strain ◽  
High Strength ◽  
Transmission Electron ◽  
High Fraction ◽  
Backscatter Diffraction

The flow stress behavior of high-strength low-alloy (HSLA) steel at different true strains was studied using a hot compression test. The effect of dynamic recrystallization (DRX) on the transformed ferrite microstructures was investigated with electron backscatter diffraction (EBSD). The EBSD analysis indicated that the fraction of high-angle grain boundaries (HAGBs) and DRX increased with increasing true strain. The low-angle grain boundaries (LAGBs) were gradually transformed into HAGBs with increasing DRX degree. When the true strain was increased to 0.916, the fraction of HAGBs increased to 85% and the fraction of DRX increased to 80.3%. The relatively high fraction of HAGBs was related to the complete DRX. The dislocations and substructures in the tested steel at different true strains were characterized by transmission electron microscopy (TEM). TEM observation shows that the nucleation of the dynamically recrystallized grains occurred by the bulging of the original grain boundaries. The DRX nucleation mechanism of the HSLA steel is the strain-induced grain boundary migration mechanism.

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

Metals ◽  
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.

Sign in / Sign up

Export Citation Format

Share Document