Microstructure and Properties of Ultrafast Annealed High Strength Steel

2013 ◽  
Vol 753 ◽  
pp. 554-558 ◽  
Author(s):  
Roumen H. Petrov ◽  
Farideh Hajyakbari ◽  
Fernando Ramos Saz ◽  
Jurij Sidor ◽  
Maria Jesus Santofimia ◽  
...  
Keyword(s):  
Grain Size ◽  
Phase Transformation ◽  
High Strength Steel ◽  
High Strength ◽  
Deformation Texture ◽  
Point Of View ◽  
Structural Refinement ◽  
Cold Rolled ◽  
Ferrite Grain Size ◽  
Martensite Structure

The grain size, recrystallization, phase transformation and mechanical properties of a cold-rolled high-strength steel (HSS) are studied after annealing with high (~140°C/s) and ultra-high (~1500°C/s) reheating rate, followed by subsequent water quenching without isothermal soaking. By monitoring the hardness and microstructure, it was shown that the increase of the reheating rate from 140°C/s to 1500°C/s causes grain refinement from 5 µm to 1 µm in diameter and the final ferrite grain size depends significantly on the reheating temperature and reheating rate. It was observed that after an extreme reheating rate of ~1500°C/s the α-γ phase transformation starts before the completion of recrystallization in the recovered matrix. The crystallographic texture of the ultrafast reheated and water-quenched high-strength steel inherits the cold-rolled deformation texture with well pronounced RD and ND texture fibres, even after the α-γ-α′ phase transformations. It was found that the ultrafast reheating results in a very fine non-equilibrium ferrite-martensite structure with an excellent ultimate tensile strength of ~1400 MPa and an acceptable elongation at fracture. The observed data are very promising from industrial application point of view and open up possibilities for further structural refinement and alternative texture control.

Grain Refinement of a Cold Rolled TRIP Assisted Steel after Ultra Short Annealing

2012 ◽  
Vol 715-716 ◽  
pp. 661-666 ◽  
Author(s):  
Roumen H. Petrov ◽  
Jurij J. Sidor ◽  
Wlodzimierz Kaluba ◽  
Leo Kestens
Keyword(s):  
Grain Size ◽  
Grain Refinement ◽  
Steel Sheet ◽  
Intercritical Annealing ◽  
Austenite Formation ◽  
Rolled Steel ◽  
Structural Refinement ◽  
Cold Rolled ◽  
Short Annealing ◽  
Ferrite Grain Size

Recrystallization and austenite formation in a TRIP-assisted steel during conventional and ultra fast reheating for intercritical annealing are studied with the purpose to clarify the possibility for grain refinement. Partially recrystallized (or transformed) samples were prepared by reheating and water quenching to temperatures between 650 and 1050°C at reheating rates of 10, 50, and 3000 °C/s, respectively, without isothermal soaking from 95% cold rolled steel sheet with ferrite-pearlite microstructure. By monitoring the hardness and microstructure, it was shown that the increase of the reheating rate from 10 to 3000°C/s causes grain refinement from 5µm to 1µm in diameter and the final ferrite grain size depends significantly on both reheating temperature and reheating rate. It was observed that after an extreme reheating rate of 3000°C/s the α-γ phase transformation starts before the completion of the recrystallization. This opens up possibilities for further structural refinement and alternative texture control.

Development of Micro-Alloying Ultra-Fine Grain High Strength Steel Produced by EAF-TSCR

2011 ◽  
Vol 697-698 ◽  
pp. 474-478
Author(s):  
Ji Xiang Gao ◽  
Xin Ping Mao ◽  
L.J. Li
Keyword(s):  
Grain Size ◽  
Yield Strength ◽  
Continuous Casting ◽  
High Strength Steel ◽  
Raw Materials ◽  
High Strength ◽  
Strengthening Mechanism ◽  
Fine Grain ◽  
Ferrite Grain Size

Based on the characteristics of raw materials in EAF-TSCR, the composition of VN micro-alloyed was designed, the processes of the steelmaking, continuous casting, soaking, rolling, cooling were controlled, and at last the VN Micro-alloying high strength steel with ultra-fine grain was developed. The ferrite grain size of the steel reaches 3.0 to 4.0 microns, and the yield strength of which reaches 550MPa. Besides, the steel processes good toughness, cold formability and weldability. In the end, the strengthening mechanism of the ultra-fine steel was discussed.

scholarly journals Overview of HSS Steel Grades Development and Study of Reheating Condition Effects on Austenite Grain Size Changes

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 1988
Author(s):  
Tibor Kvackaj ◽  
Jana Bidulská ◽  
Róbert Bidulský
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
High Strength Steel ◽  
Single Phase ◽  
Hsla Steel ◽  
High Strength ◽  
Strength Properties ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Steel Grades

This review paper concerns the development of the chemical compositions and controlled processes of rolling and cooling steels to increase their mechanical properties and reduce weight and production costs. The paper analyzes the basic differences among high-strength steel (HSS), advanced high-strength steel (AHSS) and ultra-high-strength steel (UHSS) depending on differences in their final microstructural components, chemical composition, alloying elements and strengthening contributions to determine strength and mechanical properties. HSS is characterized by a final single-phase structure with reduced perlite content, while AHSS has a final structure of two-phase to multiphase. UHSS is characterized by a single-phase or multiphase structure. The yield strength of the steels have the following value intervals: HSS, 180–550 MPa; AHSS, 260–900 MPa; UHSS, 600–960 MPa. In addition to strength properties, the ductility of these steel grades is also an important parameter. AHSS steel has the best ductility, followed by HSS and UHSS. Within the HSS steel group, high-strength low-alloy (HSLA) steel represents a special subgroup characterized by the use of microalloying elements for special strength and plastic properties. An important parameter determining the strength properties of these steels is the grain-size diameter of the final structure, which depends on the processing conditions of the previous austenitic structure. The influence of reheating temperatures (TReh) and the holding time at the reheating temperature (tReh) of C–Mn–Nb–V HSLA steel was investigated in detail. Mathematical equations describing changes in the diameter of austenite grain size (dγ), depending on reheating temperature and holding time, were derived by the authors. The coordinates of the point where normal grain growth turned abnormal was determined. These coordinates for testing steel are the reheating conditions TReh = 1060 °C, tReh = 1800 s at the diameter of austenite grain size dγ = 100 μm.

EFFECT OF GRAIN SIZE ON THE ELECTRON WORK FUNCTION OF Cu AND Al

2004 ◽  
Vol 11 (02) ◽  
pp. 173-178 ◽  
Author(s):  
WEN LI ◽  
D. Y. LI
Keyword(s):  
Grain Size ◽  
Phase Transformation ◽  
Grain Boundary ◽  
Work Function ◽  
Electron Work Function ◽  
Deformation Texture ◽  
Kelvin Probe ◽  
Surface Conditions ◽  
The Mean ◽  
Sophisticated Instrument

The Kelvin probe is a sophisticated instrument which is very sensitive to changes in surface conditions, such as deformation, texture, phase transformation and contamination. Efforts have been made to use this technique to diagnose wear. In this study, the effect of the grain boundary (GB) on the electron work function (EWF) was examined with the aim of investigating the contribution of changes in grain size to total changes in the EWF during wear. Copper and aluminum were studied as examples. It was demonstrated that the EWF dropped in the vicinity of GB's and the mean EWF decreased as the grain size decreased. The mechanism responsible for the changes in the EWF with respect to the GB is discussed.

Capability of martensitic low transformation temperature welding consumables for increasing the fatigue strength of high strength steel joints

2020 ◽  
Vol 62 (9) ◽  
pp. 891-900
Author(s):  
Jonas Hensel ◽  
Arne Kromm ◽  
Thomas Nitschke-Pagel ◽  
Jonny Dixneit ◽  
Klaus Dilger
Keyword(s):  
Residual Stress ◽  
Phase Transformation ◽  
Fatigue Strength ◽  
High Strength Steel ◽  
Transformation Temperature ◽  
Fatigue Cracks ◽  
High Strength ◽  
Filler Material ◽  
Phase Transformation Temperature ◽  
Filler Materials

Abstract The use of low transformation temperature (LTT) filler materials represents a smart approach for increasing the fatigue strength of welded high strength steel structures apart from the usual procedures of post weld treatment. The main mechanism is based on the effect of the low start temperature of martensite formation on the stress already present during welding. Thus, compressive residual stress formed due to constrained volume expansion in connection with phase transformation become highly effective. Furthermore, the weld metal has a high hardness that can delay the formation of fatigue cracks but also leads to low toughness. Fundamental investigations on the weldability of an LTT filler material are presented in this work, including the characterization of the weld microstructure, its hardness, phase transformation temperature and mechanical properties. Special attention was applied to avoid imperfections in order to ensure a high weld quality for subsequent fatigue testing. Fatigue tests were conducted on the welded joints of the base materials S355J2 and S960QL using conventional filler materials as a comparison to the LTT filler. Butt joints were used with a variation in the weld type (DY-weld and V-weld). In addition, a component-like specimen (longitudinal stiffener) was investigated where the LTT filler material was applied as an additional layer. The joints were characterized with respect to residual stress, its stability during cyclic loading and microstructure. The results show that the application of LTT consumables leads to a significant increase in fatigue strength when basic design guidelines are followed. This enables a benefit from the lightweight design potential of high-strength steel grades.

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.

Model for Predicting the Recrystallized Ferrite Grain Size after Annealing of Cold-Rolled Automobile Body Sheet Steels

2018 ◽  
Vol 2018 (10) ◽  
pp. 968-972
Author(s):  
A. A. Vasilyev ◽  
S. F. Sokolov ◽  
P. S. Zhitelev ◽  
D. F. Sokolov ◽  
N. G. Kolbasnikov ◽  
...  
Keyword(s):  
Grain Size ◽  
Sheet Steels ◽  
Automobile Body ◽  
Cold Rolled ◽  
Ferrite Grain Size

Grain Refinement and Mechanical Properties of a Metastable Austenitic Fe-Cr-Ni-Mn Alloy

2005 ◽  
Vol 475-479 ◽  
pp. 43-48 ◽  
Author(s):  
Yunqing Ma ◽  
Jae Eun Jin ◽  
Young Kook Lee
Keyword(s):  
Grain Size ◽  
Work Hardening ◽  
High Strength ◽  
Austenitic Steels ◽  
Nano Materials ◽  
Fundamental Research ◽  
Cold Rolled ◽  
Austenite Grains ◽  
Hot Rolled ◽  
Conventional Rolling

A lot of works for developing the structural nano-materials have been performed all over the world in recent years. Severe deformation techniques like HPT, ECPA and ARB have been applied to different materials such as Al, Cu, Ti and several steels. Such techniques greatly reduced the grain size and improved the yield and tensile strengths. However, the elongation of the materials is greatly decreased due to the small amount of work hardening, and these techniques do not seem suitable for the mass production. Therefore, this study has been carried out as a fundamental research for developing austenitic steels with high strength and good elongation using a conventional rolling and annealing processes. Fe-0.1%C-10%Cr-5%Ni-8%Mn alloy was melted, homogenized, hot rolled, and cold rolled at room temperature to transform γ austenite to α ’ martensite. After that, the specimens were annealed just above its reverse transformation finish temperature (Af) to obtain the fine reversed austenite grains. The grain size of the metastable austenitic steel was successfully refined to less than 200nm by repeating rolling and annealing processes. The resultant nanocrystalline material shows not only high strength but also large elongation because the work hardening ability is enhanced by the strain-induced martensitic transformation during the tensile test.

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