Development of Low Carbon Microalloyed Ultra High Strength Steels

2005 ◽  
Vol 500-501 ◽  
pp. 551-558 ◽  
Author(s):  
A. Ghosh ◽  
Brajendra Mishra ◽  
Subrata Chatterjee
Keyword(s):  
Room Temperature ◽  
High Strength Steels ◽  
High Strength ◽  
Low Carbon ◽  
Hsla Steels ◽  
Finish Rolling ◽  
Ultra High Strength Steels ◽  
Rolling Temperatures ◽  
Carbon Microalloyed ◽  
Carbon Concentrations

In the present study HSLA steels of varying carbon concentrations, alloyed with Mn, Ni, Cr, Mo, Cu and micro-alloyed with Nb and Ti were subjected to different finish rolling temperatures from 850oC to 750oC in steps of 50oC. The microstructure of the steel predominantly shows martensite. Fine twins, strain induced precipitates in the martensite lath along with e-Cu precipitates are observed in the microstructure. With an increase in carbon content the strength value increases from 1200MPa UTS to 1700MPa UTS with a negligible reduction in elongation. Impact toughness values of 20-26 joules at room temperature and −40oC were obtained in sub-size samples.

Local texture analysis of structure non-uniformity in low carbon high-strength steel after direct quenching

2020 ◽  
pp. 9-16
Author(s):  
A. A. Zisman ◽  
N. Yu. Zolotorevsky ◽  
S. N. Petrov ◽  
E. I. Khlusova ◽  
E. A. Yashina
Keyword(s):  
High Strength Steels ◽  
High Strength ◽  
Careful Analysis ◽  
Structural Features ◽  
Low Carbon ◽  
Orientation Data ◽  
Direct Quenching ◽  
Finish Rolling ◽  
Subsequent Quenching ◽  
Rolling Stage

The direct quenching of high-strength steels after hot rolling, which enables discard of the reheating operation, is economically efficient but necessitates a careful analysis of corresponding structural features. In particular, this treatment sometimes results in extended domains of coarse bainite decreasing the fracture toughness of steel. To reveal dependence of such effects on ausforming conditions, local textures of the parent γ-phase have been reconstructed from EBSD orientation data with allowance for the inter-phase orientation relationship. According to the obtained results, the unfavorable structural non-uniformity appears in the direct quenching due to excessive work hardening of austenite at the finish rolling stage; however, the structure and properties of steel can be improved by the reheating and subsequent quenching.

Mechanical properties and microstructure of low carbon ultra-high strength steels (UHSS) microalloyed with boron

2012 ◽  
Vol 1373 ◽  
Author(s):  
I. Mejía ◽  
A. García de la Rosa ◽  
A. Bedolla-Jacuinde ◽  
J.M. Cabrera
Keyword(s):  
Mechanical Properties ◽  
Research Work ◽  
High Strength Steels ◽  
High Strength ◽  
Tensile Tests ◽  
Low Carbon ◽  
Advanced High Strength Steels ◽  
New Family ◽  
Ultra High Strength Steels ◽  
Hot Rolled

ABSTRACTThe aim of this research work is to study the effect of boron addition on mechanical properties and microstructure of a new family of low carbon NiCrVCu advanced high strength steels (AHSS). Experimental steels are thermo-mechanically processed (TMP) (hot-rolled+quenched). Results show that the microstructure of these steels contains bainite and martensite, predominantly, which nucleate along prior austenite grain boundaries (GB). On the other hand, tensile tests reveal that the TMP steels have YS (0.2% offset) of 978 MPa, UTS of 1140 MPa and EL of 18%. On the basis of exhibited microstructure and mechanical properties, these experimental steels are classified as bainitic-martensitic complex phase (CP) advanced ultra-high strength steels (UHSS).

Influence of Boron on the Precipitation Kinetics in Advanced Ultra-High Strength Steels

2015 ◽  
Vol 1765 ◽  
pp. 91-96
Author(s):  
G. Altamirano ◽  
I. Mejía ◽  
A. Hernández-Expósito ◽  
J.M. Cabrera
Keyword(s):  
Stress Relaxation ◽  
High Strength Steels ◽  
High Strength ◽  
Relaxation Method ◽  
Low Carbon ◽  
Precipitation Kinetics ◽  
Austenite Recrystallization ◽  
Ultra High Strength Steels ◽  
Relaxation Curves ◽  
Kinetics Of

ABSTRACTIn the present work, the stress relaxation method was employed to determine the influence of B addition on the kinetics of strain-induced precipitation and its interaction with the static austenite recrystallization. For this purpose, the behavior of two low carbon advanced ultra-high strength steels was analyzed during stress relaxation tests at different temperatures and constant pre-strain rate. The precipitation start (Ps) and finish (Pf) times were determined from the relaxation curves and then the corresponding precipitation-time-temperature diagrams were constructed for each steel. Transmission Electron Microscopy was used to determine the chemical nature and evolution of precipitation. In general, the results show that the addition of B retards the austenite recrystallization, tends to accelerate the precipitation kinetics of carbonitrides and leads to a finer and denser distribution of precipitates. These results are discussed in terms of the driving force for the nucleation of precipitation, which in turn is controlled by the degree of supersaturation of microalloying element and as a function of B segregation and B-vacancy complexes to dislocations and grain boundaries.

scholarly journals Modeling of Precipitation Hardening during Coiling of Nb–Mo Steels

Metals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 758 ◽  
Author(s):  
Jean-Yves Maetz ◽  
Matthias Militzer ◽  
Yu Chen ◽  
Jer-Ren Yang ◽  
Nam Goo ◽  
...  
Keyword(s):  
Electron Backscatter Diffraction ◽  
Bainitic Ferrite ◽  
High Strength Steels ◽  
High Strength ◽  
Carbon Steels ◽  
Age Hardening ◽  
Precipitation Strengthening ◽  
Low Carbon ◽  
Coiling Temperature ◽  
Hsla Steels

Nb–Mo low-alloyed steels are promising advanced high strength steels (AHSS) because of the highly dislocated bainitic ferrite microstructure conferring an excellent combination of strength and toughness. In this study, the potential of precipitation strengthening during coiling for hot-strip Nb–Mo-bearing low-carbon steels has been investigated using hot-torsion and aging tests to simulate the hot-rolling process including coiling. The obtained microstructures were characterized using electron backscatter diffraction (EBSD), highlighting the effects of Nb and Mo additions on formation and tempering of the bainitic ferrite microstructures. Further, the evolution of nanometer-sized precipitates was quantified with high-resolution transmission electron microscopy (HR-TEM). The resulting age hardening kinetics have been modelled by combining a phenomenological precipitation strengthening model with a tempering model. Analysis of the model suggests a narrower coiling temperature window to maximize the precipitation strengthening potential in bainite/ferrite high strength low-alloyed (HSLA) steels than that for conventional HSLA steels with polygonal ferrite/pearlite microstructures.

Effect of the Root Gap on the Structure and Properties of High Strength Steel S700MC Welds

2021 ◽  
Vol 890 ◽  
pp. 201-208
Author(s):  
Nikolay Ferdinandov ◽  
Danail Gospodinov ◽  
Mariana Ilieva ◽  
Rossen Radev
Keyword(s):  
High Strength Steels ◽  
High Strength ◽  
Pressure Vessels ◽  
Coarse Grained ◽  
Carbon Equivalent ◽  
Welding Parameters ◽  
Low Carbon ◽  
Negative Effect ◽  
Ultra High Strength Steels ◽  
Time Required

Nowadays, the use of high strength (HS) and ultra-high strength steels (UHS) increases, notably in welded constructions. These steels are mainly exploited in heavy loaded welded constructions such as bridges, cranes and excavators, in pressure vessels, vehicles, ships, drilling rigs etc. working at room or lower temperatures. As the welded constructions have specific requirements, the development of high strength and ultra-high strength steels imposes the need for research on the factors influencing their weldability. Among the possible negative implications are: cold cracks formation, softening of the heat affected zone, brittleness in the coarse grained zone. When complying with the generally accepted rules for welding, HS and UHS are readily welded by all conventional welding methods. Recommendations for welding of steels after normalization, thermo-mechanical treatment and quenching and tempering are given in the standard EN 1011 -1, 2. The use of thermo-mechanically treated (hot-rolled) steels with low carbon equivalent, such as S700MC, allows reduction in time required for welding as the preheating temperature is lowered or even preheating is not necessary. A more pronounced negative effect on the weld quality has the presence of different defects. S700MC can be welded by all conventional methods, and a reduction in the softened zone can be achieved by using appropriate welding parameters. Joint preparation for welding of HS and UHS steels is described in the standards EN ISO 9692-1:2013 and EN ISO 9692-2:2001. Nevertheless, the root gap is often the closing part in constructions and does not comply with the standard recommendations. That is why the effect of the root gap on welds has to be researched. The present work introduces results of a research studying the effect of the root gap on the structure and some mechanical and technological properties of S700MS welds, welded by submerged arc welding.

Precipitation Strengthening in a Low Carbon Nb-Microalloyed Steel

2005 ◽  
Vol 500-501 ◽  
pp. 481-488 ◽  
Author(s):  
D.Q. Bai ◽  
F. Hamad ◽  
J. Asante ◽  
S. Hansen
Keyword(s):  
Mechanical Properties ◽  
Microalloyed Steel ◽  
High Strength Steels ◽  
Aging Treatment ◽  
High Strength ◽  
Precipitation Strengthening ◽  
Microalloyed Steels ◽  
Low Carbon ◽  
Nb Microalloyed Steel ◽  
Carbon Microalloyed

Among modern weldable high strength steels, low carbon microalloyed steels have been widely used for linepipe, construction, and automobile industries. One of the major technical components to successfully produce these steels is to effectively use precipitation strengthening. In the present paper, the effect of an aging treatment on the microstructure and mechanical properties of a low carbon Nb-microalloyed steel is analyzed.

In Situ Characterisation of Austenite/Ferrite Transformation Kinetics and Modelling of Interphase Precipitation Inter-Sheet Spacing in V Microalloyed HSLA Steels

2016 ◽  
Vol 879 ◽  
pp. 356-362 ◽  
Author(s):  
Samuel Clark ◽  
Yong Jun Lan ◽  
Vit Janik ◽  
Arjan Rijkenberg ◽  
Seetharaman Sridhar
Keyword(s):  
High Strength ◽  
Isothermal Transformation ◽  
Precipitation Reaction ◽  
Low Carbon ◽  
Interphase Precipitation ◽  
Hsla Steels ◽  
High Level ◽  
Carbon Microalloyed ◽  
New Generation

A new generation of low-carbon microalloyed High Strength Low Alloy (HSLA) steels has been developed to utilize a combination of single-phase ferritic microstructures and optimized interphase precipitation to provide high level strength and exceptional formability. The interphase precipitation reaction is a transient process lending itself strongly to take advantage of in-situ characterization techniques. The austenite/ferrite interface kinetics during isothermal transformation at 1003 K is measured using HT-CSLM, the pre-exponential effective mobility constant was found to be mobility 0.822 (m J)/(mole s). The V interphase precipitation is characterised using TEM at isothermal transformation temperatures of 923 and 973 K as having inter-sheet spacing of 22±7 and 32±9 nm respectively. Interphase precipitation inter-sheet-spacing is simulated using a revised Quasi-Ledge model and qualitatively predicts the observed trends observed for inter-sheet spacing. The results of in-situ characterisation and modelling suggest that it is possible to optimize the strengthening potential of the precipitation processes by controlling the thermal processing of microalloyed HSLA.

scholarly journals Comprehensive Analysis of the Microstructure and Mechanical Properties of Friction-Stir-Welded Low-Carbon High-Strength Steels with Tensile Strengths Ranging from 590 MPa to 1.5 GPa

2021 ◽  
Vol 11 (12) ◽  
pp. 5728
Author(s):  
HyeonJeong You ◽  
Minjung Kang ◽  
Sung Yi ◽  
Soongkeun Hyun ◽  
Cheolhee Kim
Keyword(s):  
Mechanical Properties ◽  
Tensile Test ◽  
Joint Strength ◽  
Solid Phase ◽  
Welding Process ◽  
High Strength Steels ◽  
High Strength ◽  
Low Carbon ◽  
Friction Stir ◽  
Welding Processes

High-strength steels are being increasingly employed in the automotive industry, requiring efficient welding processes. This study analyzed the materials and mechanical properties of high-strength automotive steels with strengths ranging from 590 MPa to 1500 MPa, subjected to friction stir welding (FSW), which is a solid-phase welding process. The high-strength steels were hardened by a high fraction of martensite, and the welds were composed of a recrystallized zone (RZ), a partially recrystallized zone (PRZ), a tempered zone (TZ), and an unaffected base metal (BM). The RZ exhibited a higher hardness than the BM and was fully martensitic when the BM strength was 980 MPa or higher. When the BM strength was 780 MPa or higher, the PRZ and TZ softened owing to tempered martensitic formation and were the fracture locations in the tensile test, whereas BM fracture occurred in the tensile test of the 590 MPa steel weld. The joint strength, determined by the hardness and width of the softened zone, increased and then saturated with an increase in the BM strength. From the results, we can conclude that the thermal history and size of the PRZ and TZ should be controlled to enhance the joint strength of automotive steels.

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