scholarly journals Effect of High Ti Contents on Austenite Microstructural Evolution During Hot Deformation in Low Carbon Nb Microalloyed Steels

Metals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 165 ◽  
Author(s):  
Leire García-Sesma ◽  
Beatriz López ◽  
Beatriz Pereda
Keyword(s):  
Microstructural Evolution ◽  
Hot Deformation ◽  
Solute Drag ◽  
Carbon Steels ◽  
Microalloyed Steels ◽  
Low Carbon ◽  
Grain Sizes ◽  
Austenite Recrystallization ◽  
Pancaked Austenite

This work has focused on the study of hot working behavior of Ti-Nb microalloyed steels with high Ti contents (> 0.05%). The role of Nb during the hot deformation of low carbon steels is well known: it mainly retards austenite recrystallization, leading to pancaked austenite microstructures before phase transformation and to refined room temperature microstructures. However, to design rolling schedules that result in properly conditioned austenite microstructures, it is necessary to develop models that take into account the effect of high Ti concentrations on the microstructural evolution of austenite. To that end, in this work torsion tests were performed to investigate the microstructural evolution during hot deformation of steels microalloyed with 0.03% Nb and different high Ti concentrations (0.05%, 0.1%, 0.15%). It was observed that the 0.1% and 0.15% Ti additions resulted in retarded softening kinetics at all the temperatures. This retardation can be mainly attributed to the solute drag effect exerted by Ti in solid solution. The precipitation state of the steels after reheating and after deformation was characterized and the applicability of existing microstructural evolution models was also evaluated. Determined recrystallization kinetics and recrystallized grain sizes reasonably agree with those predicted by equations previously developed for Nb-Ti microalloyed steels with lower Ti concentrations (<0.05%).

scholarly journals Role of Nb on Microstructural Evolution during Intercritical Annealing in Low-carbon Steels

2016 ◽  
Vol 56 (12) ◽  
pp. 2290-2297 ◽  
Author(s):  
Toshio Ogawa ◽  
Keiichi Sato ◽  
Hiroyuki Dannoshita ◽  
Kuniaki Maruoka ◽  
Kohsaku Ushioda
Keyword(s):  
Microstructural Evolution ◽  
Intercritical Annealing ◽  
Carbon Steels ◽  
Low Carbon ◽  
Low Carbon Steels

Deformation Induced Ferrite Transformation in Microalloyed Steels: Theory and Application

2007 ◽  
Vol 561-565 ◽  
pp. 2491-2508 ◽  
Author(s):  
Yu Qing Weng ◽  
Xin Jun Sun ◽  
Han Dong
Keyword(s):  
Plain Carbon Steel ◽  
Carbon Steels ◽  
Microalloyed Steels ◽  
Low Carbon ◽  
Ferrite Transformation ◽  
Ultrafine Grained ◽  
The Common ◽  
Microalloying Elements ◽  
Deformation Induced Ferrite Transformation

Deformation Induced Ferrite Transformation (DIFT), i.e. transformation occurs during deformation applied in the temperatures above Ar3, has received wider attention since it has been proved to be a very effective way to produce ultrafine grained ferrite in low carbon steels. Although numerous works have been done on this topic in the past decade, the systematic works on DIFT in microalloyed steel, especially on the role of microalloying elements are still lacking compared with those in plain carbon steel. In this paper, the common features of DIFT will reviewed firstly, then an attempt will be made to elucidate the role of microalloying elements (niobium and vanadium) in DIFT, and the application of DIFT technology in microalloyed steels will be presented finally.

Microstructural Evolution of Two Medium Carbon Microalloyed Steels during Hot Forging Process

2005 ◽  
Vol 500-501 ◽  
pp. 155-162 ◽  
Author(s):  
A. Al Omar ◽  
A. Chenaoui ◽  
Rachid Dkiouak ◽  
Jose María Cabrera ◽  
Jose Manuel Prado
Keyword(s):  
Microstructural Evolution ◽  
Hot Forging ◽  
Microalloyed Steels ◽  
Hollomon Parameter ◽  
Medium Carbon ◽  
Grain Sizes ◽  
Recrystallized Grain Size ◽  
Carbon Microalloyed ◽  
Hot Forging Process ◽  
Cyclic Dynamic

The main aim of the present investigation was to study the flow behaviour of two medium carbon microalloyed steels under hot forming conditions, and to analyse its microstructural evolution. The dependence of recrystallized grain size (Drec) on the Zener-Hollomon parameter Z shows a bimodal behaviour with transition from single to cyclic dynamic recrystallization. Also we observed that the variation of Drec normalized by Burgers vector (b) with sss normalized by shear modulus ( µ) shows the same bimodal behaviour cited above. The Derby’s universal equation cited in literature for recrystallized grain sizes was not followed; it seems that the presence of fine precipitated particles has a clear effect on this disagreement.

Influence of Strain Path on Microstructure Evolution of Low Carbon Steels

2010 ◽  
Vol 638-642 ◽  
pp. 3418-3423 ◽  
Author(s):  
K. Muszka ◽  
Lin Sun ◽  
Bradley P. Wynne ◽  
Eric J. Palmiere ◽  
Mark W. Rainforth
Keyword(s):  
Strain Path ◽  
Processing Parameters ◽  
Carbon Steels ◽  
Microalloyed Steels ◽  
Precipitation Process ◽  
Nucleation Density ◽  
Low Carbon ◽  
Dynamic Recrystallisation ◽  
Important Processing ◽  
Strain Path Change

Changes in strain path represent one of the most important processing parameters that characterise hot metal forming processes. In the present study, the effect of strain path change on dynamic recrystallisation, strain-induced precipitation processes and phase transformation behaviour in plain carbon and Nb-microalloyed steels was investigated. To assess the effect of strain-path change, forward/forward and forward/reverse torsion tests were conducted. It has been shown that the strain reversal delays the dynamic recrystallisation kinetics whereas its effect on strain-induced precipitation process of Nb(C,N) is rather negligible. Also the onset of austenite-ferrite transformation is delayed; its products however doesn’t change significantly. This can be due to the fact that ferrite nucleation density plays the second order role compared to the geometry of deformation.

Formation of Ultrafine Grained Low Carbon Steels via Martensite Deformation and Annealing

2006 ◽  
Vol 15-17 ◽  
pp. 750-755 ◽  
Author(s):  
H. Azizi-Alizamini ◽  
Matthias Militzer ◽  
Warren J. Poole
Keyword(s):  
Uniform Elongation ◽  
Carbon Steels ◽  
Grain Structure ◽  
Initial Structure ◽  
Low Carbon ◽  
Low Carbon Steels ◽  
Fine Grain ◽  
Ultrafine Grained ◽  
Kinetics Of

Recently, there has been a large interest in the development of low carbon steels with ultra fine grain structure using lean chemistries. Although these steels typically have superior strength, the lack of work hardening capability limits the uniform elongation and thus the formability of these kinds of steels. It has been reported by Tsuji and co-workers (2002) that straining of martensite as an initial structure can yield an ultra fine grain structure with good combination of strength and ductility. However, the detailed mechanism of the grain refinement has not yet been clarified. In the present work, the annealing behavior of a low carbon martensitic structure with and without deformation at room temperature has been systematically studied. It is proposed that the process of concurrent softening due to recovery and recrystallization and precipitation of carbides is different for the deformed and undeformed materials. Further, preliminary results have been found on the role of substitutional alloying elements such as Mo or Cr on the kinetics of the softening processes.

scholarly journals New Technology to Produce 1 GPa Low Carbon Microalloyed Steels from Cast Strip

Metals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 662 ◽  
Author(s):  
Andrii Kostryzhev ◽  
Olexandra Marenych
Keyword(s):  
Mechanical Properties ◽  
Global Economy ◽  
New Technology ◽  
Carbon Steels ◽  
Thin Strip ◽  
Microalloyed Steels ◽  
Accelerated Cooling ◽  
Low Carbon ◽  
Elongation To Failure ◽  
Carbon Microalloyed

Global economy requires steel with further increasing mechanical properties and simultaneously decreasing price. In mass manufacturing three major methods can be used to increase strength: (i) increase microalloying element additions (increases cost), (ii) decrease deformation temperature and (iii) increase cooling rate after high temperature processing (both can be challenging for equipment). Thin strip casting is an effective way to reduce cost as it brings a reduction in number of deformation passes and shortens the production line. However, the mechanical properties can be missed due to insufficient microstructure development. In this article, we investigate a recently proposed technology based on Austenite Conditioning followed by Accelerated Cooling and Warm Deformation (AC2WD). Two low carbon steels microalloyed with either 0.012Ti or 0.1Mo-0.064Nb-0.021Ti (wt.%) were subjected to three processing modifications of the AC2WD-technology with two, one or no deformation of cast microstructure in the austenite temperature field. The Ti- and MoNbTi-steels exhibited 685–765 MPa and 880–950 MPa of the yield stress, 780–840 MPa and 1035–1120 MPa of tensile strength, and 20–30% and 22–24% of elongation to failure, respectively. The nature of strengthening mechanisms associated with the AC2WD-technology is discussed on the basis of detailed microstructure characterisation.

scholarly journals Interaction between Microalloying Additions and Phase Transformation during Intercritical Deformation in Low Carbon Steels

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1049 ◽  
Author(s):  
Unai Mayo ◽  
Nerea Isasti ◽  
Jose M. Rodriguez-Ibabe ◽  
Pello Uranga
Keyword(s):  
Rolling Process ◽  
Bearing Steel ◽  
Phase Region ◽  
Carbon Steels ◽  
Transformation Model ◽  
Microalloyed Steels ◽  
Low Carbon ◽  
Electron Backscattered Diffraction ◽  
Two Phase ◽  
Line Pipe

Heavy gauge line pipe and structural steel plate materials are often rolled in the two-phase region for strength reasons. However, strength and toughness show opposite trends, and the exact effect of each rolling process parameter remains unclear. Even though intercritical rolling has been widely studied, the specific mechanisms that act when different microalloying elements are added remain unclear. To investigate this further, laboratory thermomechanical simulations reproducing intercritical rolling conditions were performed in plain low carbon and NbV-microalloyed steels. Based on a previously developed procedure using electron backscattered diffraction (EBSD), the discretization between intercritically deformed ferrite and new ferrite grains formed after deformation was extended to microalloyed steels. The austenite conditioning before intercritical deformation in the Nb-bearing steel affects the balance of final precipitates by modifying the size distributions and origin of the Nb (C, N). This fact could modify the substructure in the intercritically deformed grains. A simple transformation model is proposed to predict average grain sizes under intercritical deformation conditions.

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