scholarly journals Rational Alloy Design of Niobium-Bearing HSLA Steels

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 413
Author(s):  
Rami A. Almatani ◽  
Anthony J. DeArdo
Keyword(s):  
Grain Refinement ◽  
Controlled Rolling ◽  
Coarse Grained ◽  
Low Carbon ◽  
Hsla Steels ◽  
Finish Rolling ◽  
Basic Studies ◽  
Linepipe Steels ◽  
Rough Rolling ◽  
Strength And Toughness

In the 61 years that niobium has been used in commercial steels, it has proven to be beneficial via several properties, such as strength and toughness. Over this time, numerous studies have been performed and papers published showing that both the strength and toughness can be improved with higher Nb additions. Earlier studies have verified this trend for steels containing up to about 0.04 wt.% Nb. Basic studies have shown that the addition of Nb increases the recrystallization-stop temperature, T5% or Tnr. These same studies have shown that with up to about 0.05 wt.% of Nb, the T5% temperature increases in the range of finish rolling, which is the basis of controlled rolling. These studies also have shown that at very high Nb levels, exceeding approximately 0.06 wt.% Nb, the recrystallization-stop temperature or T5% can increase into the temperature range of rough rolling, and this could result in insufficient grain refinement and recrystallization during rough rolling. However, the question remains as to how much Nb can be added before the detriments outweigh the benefits. While the benefits are easily observed and discussed, the detriments are not. These detriments at high Nb levels include cost, undissolved Nb particles, weldability issues, higher mill loads and roll wear and the lessening of grain refinement that might otherwise occur during plate rough rolling. This loss of grain refinement is important, since coarse grained microstructures often result in failure in the drop weight tear testing of the plate and pipe. The purpose of this paper is to discuss the practical limits of Nb microalloying in controlled rolled low carbon linepipe steels of gauges ranging from 12 to 25 mm in thickness.

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.

Grain Refinement by Rapid Transformation Annealing of Cold Rolled Low Carbon Steels

2005 ◽  
Vol 500-501 ◽  
pp. 771-778 ◽  
Author(s):  
P. Álvarez ◽  
C. Lesch ◽  
Wolfgang Bleck ◽  
Hélène Petitgand ◽  
Joachim Schöttler ◽  
...  
Keyword(s):  
Grain Refinement ◽  
Rapid Heating ◽  
Carbon Steels ◽  
Low Carbon ◽  
Steel Sheets ◽  
Hsla Steels ◽  
Mn Content ◽  
Cold Rolled ◽  
Equiaxed Grains ◽  
Rapid Transformation

A novel thermal treatment, rapid transformation annealing (RTA), has been applied to six different cold rolled low-carbon (LC) steel sheets with the aim of refining their microstructure. The process involves rapid heating to just above the austenite (g) to ferrite (a) transformation temperature and subsequent rapid cooling to room temperature. Grain sizes around 2 µm in two different Nb-Ti HSLA steels, 5 µm in a Ti-LC steel and 6 µm in a plain LC (0.037%C) steel have been produced using fast cooling rates (200°C/s). Non-equiaxed structures are obtained in a Nb-Ti HSIF steel and in a plain LC (0.135%C) (CM) steel due to their higher Mn content. However, very fine equiaxed grains (2 µm) are obtained by rapid intercritical annealing (RIA) in the CM steel. Irrespective of the microalloying concept, the grain growth of recrystallized a grains before their transformation was inhibited in CM and in both HSLA steels. This inhibition is connected with the overlapping of a recrystallization and a-g transformation processes which is essential in order to achieve extreme grain refinement either by RTA or RIA.

Electron Microscope studies of the microstructures in as-quenched and aged HSLA-100 production steels and correlation with mechanical properties

1991 ◽  
Vol 49 ◽  
pp. 582-583
Author(s):  
A.G. Fox ◽  
V.R. Mattes ◽  
S. Mikalac ◽  
M.G. Vassilaros
Keyword(s):  
Mechanical Properties ◽  
High Strength ◽  
Low Carbon ◽  
Austenite Grain Size ◽  
Solid Solution Strengthening ◽  
Austenite Grain ◽  
Microstructure And Mechanical Properties ◽  
Hsla Steels ◽  
Carbonitride Precipitation ◽  
Strength And Toughness

Because of their excellent weldability, high strength low alloy (HSLA) ultra low carbon bainitic (ULCB) steels are finding increasing applications in ship and submarine construction. In order to achieve the required strength and toughness in ULCB HSLA steels it is necessary to control chemical composition and thermo-mechanical processing very carefully so that the desired microstructure and mechanical properties can be achieved. For instance HSLA 100 ULCB steel (nominal yield strength 100 ksi) used by the U.S. Navy in shipbuilding applications can derive its strength and toughness from the following sources:- (1) solid solution strengthening (2) small prior austenite grain size derived from niobium carbonitride precipitation at austenite grain boundaries (3) dislocation substructure and (4) from copper precipitates (in aged alloys). The object of the present work is to correlate the microstructure and mechanical properties of production batches of HSLA 100 in the quenched and aged conditions. Because many of the salient features of these microstructures are submicron in size it was found necessary to use SEM and TEM.

Influence of Rolling Temperature and Cooling Rate on Microstructure and Properties of Pipeline Steel Grades

2012 ◽  
Vol 706-709 ◽  
pp. 2710-2715 ◽  
Author(s):  
V. Carretero Olalla ◽  
Roumen H. Petrov ◽  
Philippe Thibaux ◽  
Martin Liebeherr ◽  
P. Gurla ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Process Parameters ◽  
Pipeline Steel ◽  
Hsla Steel ◽  
Rolling Temperature ◽  
Air Cooling ◽  
Strong Impact ◽  
Hsla Steels ◽  
Finish Rolling ◽  
Strength And Toughness

Thermo-mechanical control processing (TMCP) is a powerful tool for development of high strength low alloy (HSLA) steels. The understanding of the effect of process parameters on the microstructure of these steels is a key aspect for the optimization of their mechanical properties. The influence of the rolling temperatures and the cooling conditions on the texture, strength and toughness of HSLA steel was investigated. Two stage controlled rolling (roughing and finishing) was carried out on a laboratory rolling mill. Four different compositions were rolled by maintaining same roughing conditions but varying the process parameters of the finish rolling, namely, start finish rolling temperature (SFRT), finish rolling and cooling temperatures. Subsequent to rolling, two different cooling routes were used, namely, air-cooling (AC) and accelerated water cooling (ACC). For the ACC route, the plates were subsequently heat treated to simulate coiling. The microstructure and texture obtained before and after each TMCP schedule were characterized quantifying the phases, grain size and texture by means of EBSD and XRD and associated with the mechanical properties. It was found that SFRT has a strong impact on both strength and toughness if the material was air-cooled. Plates rolled at lower temperature showed better strength and toughness than ones rolled at high temperature in both air-cooling and ACC due to grain refinement. However, for the material that was processed through ACC and coiling simulation, the strength increased without any substantial effect on the toughness. These results provide an interesting insight on the industrial processing of HSLA steels.

Grain refinement and formation of ultrafine-grained microstructure in a low-carbon steel under electropulsing

2002 ◽  
Vol 17 (8) ◽  
pp. 2105-2111 ◽  
Author(s):  
Yizhou Zhou ◽  
Wei Zhang ◽  
Baoquan Wang ◽  
Guanhu He ◽  
Jingdong Guo
Keyword(s):  
Carbon Steel ◽  
Grain Refinement ◽  
Low Carbon Steel ◽  
Coarse Grained ◽  
Low Carbon ◽  
Experimental Conditions ◽  
Ultrafine Grained ◽  
The Relationship ◽  
Ultrafine Grained Microstructure ◽  
A Current

High current electropulsing was applied to a low-carbon steel in the solid state. The relationship between grain size and experimental conditions was revealed. It was found that the ultrafine-grained (UFG) microstructure could be formed when electric current density, heating rate, and cooling rate all were high. The UFG samples prepared by applying electropulsing were free of porosity and contamination, and had no large microstrain. Also, their tensile strength was dramatically enhanced over that of their coarse-grained counterparts, without a decrease in ductility. The mechanism for grain refinement and formation of the UFG microstructure was discussed. It is proposed that the effect of a decrease in thermodynamic barrier and enhancement of nucleation rate in a current-carrying system cannot be neglected.

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