scholarly journals Kinetics of Austenite Phase Transformations in Newly-Developed 0.17C-2Mn-1Si-0.2Mo Forging Steel with Ti and V Microadditions

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1698
Author(s):  
Mateusz Morawiec ◽  
Anna Wojtacha ◽  
Marek Opiela
Keyword(s):  
Cooling Rate ◽  
Retained Austenite ◽  
Theoretical Calculations ◽  
Bainitic Ferrite ◽  
High Strength ◽  
Granular Bainite ◽  
Transformation Kinetics ◽  
Austenitization Temperature ◽  
Kinetics Of

This work presents the results of phase transformation kinetics during continuous cooling in newly developed high strength low-alloy steel (HSLA). Initial theoretical calculations for the determination of heat treatment parameters were conducted. To determine the structural constituents formed due to the austenite decomposition the dilatometry approach was used. The material was cooled down from the austenitization temperature of 1000 °C with cooling rates between 0.1 °C/s to 60 °C/s. Then, light and scanning electron microscopy investigations were carried out. The microstructure after cooling at rates between 0.1 °C/s up to 1 °C/s is mainly ferritic with some fraction of granular bainite. Increasing the cooling rate led to formation of a higher fraction of bainitic ferrite. At 60 °C/s the microstructure was mainly bainite with some fraction of ferrite. To determine the presence of retained austenite, color etching using Klemm solution was used. The results show that the increase of cooling rate decreases the amount of retained austenite in the microstructure of the steel. Hardness measurements were made to determine the changes in the mechanical properties as a function of the cooling rate.

Effects of Retained Austenite Stability on Mechanical Properties of High Strength TRIP Steel

2012 ◽  
Vol 602-604 ◽  
pp. 287-293
Author(s):  
Zhi Feng Li ◽  
Ren Yu Fu ◽  
Qing Shan Li
Keyword(s):  
Mechanical Properties ◽  
Trip Steel ◽  
Retained Austenite ◽  
Mechanical Stability ◽  
High Strength ◽  
Tensile Tests ◽  
Transformation Kinetics ◽  
Austenite Stability ◽  
Kinetics Of ◽  
Strength And Ductility

Mechanical stability of retained austenite and its effect on mechanical properties of high strength TRIP steel were studied by means of OM, SEM, TEM, XRD, and mechanical testing after various heat treatments. Results revealed that the film-type retained austenite located between bainite laths with high carbon content showed gradual martensitic transformation with strain, demonstrating a good TRIP effect. Samples annealed at 800°C and held at 420°C showed an optimum value of strength and ductility product up to 18381.2MPa%. Transformation kinetics of the retained austenite were evaluated through tensile tests and fitted by the function y=0.86-0.86×exp(-Ax). The fitting results were good.

scholarly journals Effect of Quenching and Partitioning Temperatures in the Q-P Process on the Properties of AHSS with Various Amounts of Manganese and Silicon

2012 ◽  
Vol 706-709 ◽  
pp. 2734-2739 ◽  
Author(s):  
Hana Jirková ◽  
Ludmila Kučerová ◽  
Bohuslav Mašek
Keyword(s):  
Tensile Strength ◽  
Retained Austenite ◽  
Isothermal Holding ◽  
Bainitic Ferrite ◽  
High Strength Steels ◽  
High Strength ◽  
Experimental Program ◽  
Quenching Temperature ◽  
Quenching And Partitioning ◽  
Advanced High Strength Steels

The use of the combined influence of retained austenite and bainitic ferrite to improve strength and ductility has been known for many years from the treatment of multiphase steels. Recently, the very fine films of retained austenite along the martensitic laths have also become the centre of attention. This treatment is called the Q-P process (quenching and partitioning). In this experimental program the quenching temperature and the isothermal holding temperature for diffusion carbon distribution for three advanced high strength steels with carbon content of 0.43 % was examined. The alloying strategies have a different content of manganese and silicon, which leads to various martensite start and finish temperatures. The model treatment was carried out using a thermomechanical simulator. Tested regimes resulted in a tensile strength of over 2000MPa with a ductility of above 14 %. The increase of the partitioning temperature influenced the intensity of martensite tempering and caused the decrease of tensile strength by 400MPa down to 1600MPa and at the same time more than 10 % growth of ductility occurred, increasing it to more than 20%.

scholarly journals Effect of Two-Step Austempering Process on Transformation Kinetics of Nanostructured Bainitic Steel

Materials ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 166 ◽  
Author(s):  
Chunhe Chu ◽  
Yuman Qin ◽  
Xuemei Li ◽  
Zhinan Yang ◽  
Fucheng Zhang ◽  
...  
Keyword(s):  
Activation Energy ◽  
Energy Barrier ◽  
Bainitic Ferrite ◽  
Transformation Process ◽  
Transformation Rate ◽  
Bainitic Steel ◽  
Transformation Kinetics ◽  
Activation Energy Barrier ◽  
Quenching Process ◽  
Kinetics Of

The two-step austempering process has been reported to be an effective method to accelerate the bainitic transformation process by introducing martensite (Q-M-B). However, in this study, it was found that the Q-M-B process reduced the incubation time, but the transformation duration remained nearly unchanged. The notably reduced activation energy barrier for nucleation of bainitic ferrite on the preformed martensite should be responsible for the reduced duration time of the Q-M-B process. A process that both of the two steps were above, Ms (Q-B-B), has been demonstrated to increase transformation rate and improve the amount of bainitic ferrite, which probably results from the additional hysteresis free energy provided by the first quenching process.

scholarly journals Study on Phase Transformation in Hot Stamping Process of USIBOR® 1500 High-Strength Steel

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1119 ◽  
Author(s):  
Pengyun Zhang ◽  
Le Zhu ◽  
Chenyang Xi ◽  
Junting Luo
Keyword(s):  
Phase Transformation ◽  
High Strength Steel ◽  
Hot Stamping ◽  
High Strength ◽  
Transformation Kinetics ◽  
Martensite Content ◽  
Cct Curve ◽  
Stamping Process ◽  
Quenching Process ◽  
Kinetics Of

Based on the Kirkaldy-Venugopalan model, a theoretical model for the phase transformation of USIBOR® 1500 high strength steel was established, and a graph of the phase transformation kinetics of ferrite, pearlite, and bainite were plotted using the software MATLAB. Meanwhile, with the use of the software DYNAFORM, the thermal stamping process of an automobile collision avoidance beam was simulated. The phase transformation law of USIBOR® 1500 high-strength steel during hot stamping was studied through a simulation of the phase transformation during the pressure holding quenching process. In combination with the continuous cooling transformation (CCT) curve, the cooling rate of quenching must be greater than 27 °C/s to ensure maximum martensite content in the final parts, and the final martensite content increases as the initial temperature of the sheet rises.

scholarly journals Development of Precipitation Hardening Parameters for High Strength Alloy AA 7068

Materials ◽  
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.

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

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.

Transformation kinetics of retained austenite in the tensile Lüders strain range in medium Mn steel

2019 ◽  
Vol 169 ◽  
pp. 1-5 ◽  
Author(s):  
Jiawei Ma ◽  
Haiting Liu ◽  
Qi Lu ◽  
Yong Zhong ◽  
Li Wang ◽  
...  
Keyword(s):  
Retained Austenite ◽  
Strain Range ◽  
Transformation Kinetics ◽  
Medium Mn Steel ◽  
Mn Steel ◽  
Kinetics Of

Development of Laminar Flow Cooling of Ultra-High Strength Ferrite-Bainite Dual Phase Steel

2012 ◽  
Vol 184-185 ◽  
pp. 940-943
Author(s):  
Wei Lv ◽  
Di Wu ◽  
Zhuang Li
Keyword(s):  
Tensile Strength ◽  
Ultimate Tensile Strength ◽  
Laminar Flow ◽  
Hot Rolling ◽  
Retained Austenite ◽  
High Strength ◽  
Total Elongation ◽  
Granular Bainite ◽  
Dual Phase ◽  
Dp Steel

In the present paper, controlled cooling in different ways was performed using a laboratory hot rolling mill in ultra-high strength hot rolled ferrite-bainite dual phase (DP) steel. The results have shown that the final microstructures of DP steel comprise ferrite, bainite and a small amount of retained austenite and martensite. DP steel has a tensile strength ranging from 1010 to 1130MPa and yet retains considerable total elongation in the range of 14–17%. The addition of Mn and Nb to DP steel leads to the maximum ultimate tensile strength, yield strength and the product of ultimate tensile strength and total elongation due to the formation of retained austenite and granular bainite structure. Laminar flow cooling after hot rolling results in a significant increase in the quantity of ferrite and bainite due to the suppression of pearlite transformation, and as a result, the present steel possesses high strengths and good toughness.

Atomic Scale Investigation of Solutes and Precipitates in High Strength Steels

2013 ◽  
Vol 762 ◽  
pp. 14-21 ◽  
Author(s):  
Peter Hodgson ◽  
Subrata Mukherjee ◽  
Hossein Beladi ◽  
Xiang Yuan Xiong ◽  
Ilana B. Timokhina
Keyword(s):  
Retained Austenite ◽  
Thermomechanical Processing ◽  
Bainitic Ferrite ◽  
High Strength Steels ◽  
High Strength ◽  
Atom Probe ◽  
Atomic Scale ◽  
Isothermal Hold ◽  
Local Defects ◽  
Lower Carbon

Two steels, ferritic, high strength with interphase precipitation and nanobainitic, were used to show the advances in and application of atom probe. The coexistence of the nanoscale, interphase Nb-Mo-C clusters and stoichiometric MC nanoparticles was found in the high strength steel after thermomechanical processing. Moreover, the segregation of carbon at different heterogeneous sites such as grain boundary that reduces the solute element available for fine precipitation was observed. The APT study of the solutes redistribution between the retained austenite and bainitic ferrite in the nanobainitic steel revealed: (i) the presence of two types of the retained austenite with higher and lower carbon content and (ii) segregation of carbon at the local defects such as dislocations in the bainitic ferrite during the isothermal hold.

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