Austenite Grain Refinement in Direct Charging Based Thermomechanical Processes

2012 ◽  
Vol 715-716 ◽  
pp. 711-718 ◽  
Author(s):  
J.M. Rodriguez-Ibabe ◽  
Beatriz López
Keyword(s):  
Mechanical Properties ◽  
Applied Strain ◽  
Microalloyed Steels ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Steel Grades ◽  
Near Net Shape ◽  
Thermomechanical Processes ◽  
Tailored Design ◽  
Kinetics Of

Thermomechanical processes based on direct charging routes combined with near net shape technologies have become one of the main industrial production routes. The singularity of the coarse as cast initial austenite grain size, combined with the limited total applied strain during hot working, requires a tailored design of the composition and deformation schedules in order to achieve the required mechanical properties. This becomes more and more complex as higher steel grades combined with thicker sections are incorporated into production. This paper reviews the role played by the interaction of dynamic-metadynamic-static recrystallisation and strain induced precipitation on achieving the finest and most homogeneous austenite microstructures as possible, prior to transformation in the case of Nb, Nb-Mo and Ti microalloyed steels. Special emphasis will be put on the relevance of the kinetics of combined postdynamic softening mechanisms before a complete stop of recrystallisation due to precipitation occurs.

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.

scholarly journals Prediction of As-cast Austenite Grain Size for Near-net-shape CC

2004 ◽  
Vol 90 (4) ◽  
pp. 198-205 ◽  
Author(s):  
Naotsugu YOSHIDA ◽  
Yoshinao KOBAYASHI ◽  
Kotobu NAGAI
Keyword(s):  
Grain Size ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Near Net Shape

Studies on Softening Kinetics of Niobium Microalloyed Steel Using Stress Relaxation Technique

2012 ◽  
Vol 715-716 ◽  
pp. 794-799 ◽  
Author(s):  
Cheng Liang Miao ◽  
Cheng Jia Shang ◽  
Guo Dong Zhang ◽  
Guo Hui Zhu ◽  
Hatem S. Zurob ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Microalloyed Steels ◽  
Distinct Advantage ◽  
Low Carbon ◽  
Shape Processing ◽  
Physically Based ◽  
Near Net Shape ◽  
Niobium Microalloyed Steel ◽  
Relaxation Curves ◽  
Kinetics Of

Stress relaxation was studied in a series of low carbon, high Mn microalloyed steels containing 0.012, 0.06 and 0.1 wt% Nb. The stress-relaxation curves were modeled using a physically-based model that takes into account the time evolution of precipitation, recovery and recrystallization as well as their interactions. The results confirm that high Mn-high Nb design can offer distinct advantage over the low-Mn design for the application of near net shape processing.

Effect of Pearlite Structure on the Mechanical Properties of Microalloyed Hypereutectoid Steels

2005 ◽  
Vol 500-501 ◽  
pp. 737-744 ◽  
Author(s):  
A.M. Elwazri ◽  
Steve Yue
Keyword(s):  
Mechanical Properties ◽  
Structural Evolution ◽  
Salt Bath ◽  
Austenite Grain Size ◽  
Boundary Area ◽  
Austenite Grain ◽  
Heat Treated ◽  
Hypereutectoid Steels ◽  
The Relationship ◽  
Different Levels

The relationship between mechanical properties and pearlite microstructure was investigated using various heat treatments on a hypereutectoid steels containing 1% carbon with different levels of vanadium and silicon. Specimens were heat treated at various temperatures ranging from 900 to 1200°C and transferred to salt bath conditions at 550, 580 and 620°C to examine the structural evolution of pearlite. The results show that the thickness of the cementite network increases with increasing reheat temperature. This is likely due to the larger austenite grain size reducing the grain boundary area available for proeutectoid cementite nucleation. It was found that the vanadium and silicon additions increased the strength of hypereutectoid steels through refinement of the microstructure and precipitation strengthening.

Alloying Effects on Reverse Transformation to Austenite from Pearlite or Tempered Martensite Structures

2010 ◽  
Vol 638-642 ◽  
pp. 3400-3405 ◽  
Author(s):  
Goro Miyamoto ◽  
Zhao Dong Li ◽  
Hirokazu Usuki ◽  
Tadashi Furuhara
Keyword(s):  
Decomposition Reaction ◽  
Reverse Transformation ◽  
Transformation Kinetics ◽  
Tempered Martensite ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Cr Addition ◽  
Alloying Effects ◽  
Kinetics Of ◽  
Martensite Structure

Reverse transformation has been frequently used to refine austenite grain size for refining ferrite, pearlite and martensite structures. However, kinetics and microstructure change during reverse transformation to austenite has not been examined systematically compared with the austenite decomposition reaction. Therefore, alloying effects of 1mass% Mn, Si and Cr on reverse transformation kinetics from pearlite and tempered martensite structures in Fe-0.6mass%C alloys were investigated in this study. Vickers hardness of all the specimens increases with increasing holding time at 1073K because reversely-formed austenite transforms to martensite by quenching. In the reverse transformation from pearlite structure, the kinetics of reverse transformation is hardly changed by the Mn addition while Si and Cr additions delay it. Kinetics of reverse transformation from tempered martensite structure becomes slower than from the pearlite structure in all the alloys. In particular, retarding effect by the Cr addition is most significant among those elements.

scholarly journals Effect of Heat Treatment on Microstructure and Mechanical Properties of New Cold-Rolled Automotive Steels

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1414
Author(s):  
Fei Huang ◽  
Jian Chen ◽  
Zhangqi Ge ◽  
Junliang Li ◽  
Yongqiang Wang
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Testing Machine ◽  
Second Phase ◽  
Isothermal Heat Treatment ◽  
Austenitizing Temperature ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Microstructure And Mechanical Properties ◽  
Cold Rolled

The effect of austenitizing temperature and aging treatment on the microstructure and mechanical properties of two new cold-rolled automotive steel plates (20Mn2Cr and 20Mn2CrNb) was investigated by using isothermal heat treatment, optical microscope, scanning electron microscope, microhardness tester, and tensile testing machine. The results show that as the austenitizing temperature increased, the original austenite grain sizes of both steels increased. The original austenite grain size of 20Mn2CrNb was smaller than that of 20Mn2Cr. The microhardness of 20Mn2CrNb gradually decreased with increasing aging temperature, while the hardness of 20Mn2Cr varied irregularly. The mechanical properties of 20Mn2Cr were better than those of 20Mn2CrNb under the same heat-treatment process. The effect of heat treatment on microstructure and mechanical properties was related to the martensite content, dislocation density, and precipitation of second-phase particles.

Influence of Ti on Static Recrystallization in Near Net Shape Steels

2005 ◽  
Vol 500-501 ◽  
pp. 131-138 ◽  
Author(s):  
M. Arribas ◽  
Beatriz López ◽  
J.M. Rodriguez-Ibabe
Keyword(s):  
Carbon Steel ◽  
Static Recrystallization ◽  
Plain Carbon Steel ◽  
Carbon Steels ◽  
Low Carbon ◽  
Low Carbon Steels ◽  
Austenite Grain ◽  
Near Net Shape ◽  
Austenite Grain Growth ◽  
Kinetics Of

This study analyzes the recrystallization behaviour of Ti microalloyed low carbon steels processed by near net shape technology. Faster solidification rates associated with this technology allows for a finer precipitation of TiN particles that are very effective in controlling austenite grain growth during hot working. Furthermore, these small precipitates are shown to be able to retard ecrystallization compared to the kinetics of a plain carbon steel.

Analysis of a Thixo-Lateral Forged Spindle from LTT C45, LTT C38 and LTT 100Cr6 Steel Grades

2014 ◽  
Vol 217-218 ◽  
pp. 347-354 ◽  
Author(s):  
Jokin Lozares ◽  
Zigor Azpilgain ◽  
Iñaki Hurtado ◽  
Iñigo Loizaga
Keyword(s):  
Mechanical Properties ◽  
Current Trend ◽  
Research Work ◽  
Raw Material ◽  
Key Factor ◽  
Steel Grades ◽  
Near Net Shape ◽  
Net Shape Forming ◽  
Near Net Shaping ◽  
Net Shaping

Due to the current trend in prices of raw material and their sources, near net shaping of mechanical components will become a key factor for the companies to get the desired competitiveness. Semisolid metal (SSM) forming is one of those near net shape forming techniques revealing a high potential to reduce material as well as energy consumption compared to conventional process technologies. Thus, the aim of this research work is to demonstrate the above by manufacturing a steel commercial automotive spindle by thixo-lateral forming from three different steel grades. The starting material, the microstructure and mechanical properties are analysed along the article. Material savings of 20% have been reported together with a substantial decrease of the forming forces. In addition, great mechanical properties have been achieved which brings the process closer to the desired final industrial application.

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