Effects of Finishing Rolling Temperature on the Microstructural Behavior for Fe-0.1C Steel as a Function of Niobium Content

2007 ◽  
Vol 26-28 ◽  
pp. 55-60 ◽  
Author(s):  
Nam Hyun Kang ◽  
Inae Park ◽  
Jong Won Jin ◽  
Sang Ho Byun ◽  
Young Jung Lee ◽  
...  
Keyword(s):  
Grain Size ◽  
Impact Toughness ◽  
Rolling Process ◽  
Controlled Rolling ◽  
Rolling Temperature ◽  
Microstructural Investigation ◽  
Niobium Content ◽  
Nb Content ◽  
Microstructural Behavior ◽  
The Impact

The demand to replace Fe-V steel with Fe-Nb steel is evolving because of high costs of raw vanadium material. For the mass production of Fe-Nb steel, the most critical barrier is a poor impact toughness comparing with that of Fe-V steel. This study covers a microstructural investigation for ferrite grain size to explain the strength and toughness results as a function of V and Nb contents. The steel samples were made of three different compositions, i.e., Fe-V steel (Fe-0.05V-0.001Nb), Fe-V-Nb steel (Fe-0.014V-0.03Nb), and Fe-Nb steel (Fe-0.003V-0.033Nb). Rolling temperature to initiate was 1150°C for the all experiments. However, rolling temperature to finish was set differently for two conditions; 950°C and 860°C. The rolling to 860°C decreased the grain size for the ferrite phase and increased the impact toughness rather than the case of 950°C. The Fe-V-Nb steel exhibited similar value of the impact toughness with that for the Fe-V steel because of the low rolling temperature to finish, i.e., 860°C. The whole replace of V with Nb decreased the impact toughness significantly, however some extent of V content remained with Nb content showed the comparable toughness to the Fe-V steel by optimizing the controlled rolling process.

Estimation of Impact Toughness Transition Temperatures of As-Quenched Steels

2018 ◽  
Vol 941 ◽  
pp. 498-503
Author(s):  
Sakari Pallaspuro ◽  
Antti J. Kaijalainen ◽  
Saara Mehtonen ◽  
Jukka I. Kömi ◽  
Zhi Liang Zhang ◽  
...  
Keyword(s):  
Grain Size ◽  
Low Temperature ◽  
Impact Toughness ◽  
Yield Strength ◽  
Rolling Temperature ◽  
Transition Temperatures ◽  
Finish Rolling Temperature ◽  
Finish Rolling ◽  
Low Temperature Toughness ◽  
The Impact

High strength and sufficient toughness are key requirements for modern high-performance structural steels. In an attempt to develop a suitable estimation of impact toughness transition temperatures for as-quenched steels, we investigated the determiners of low-temperature toughness with a group of thermomechanically rolled direct-quenched steels with varying martensite contents. These were produced by altering chemical composition, finish rolling temperature and reduction below the non-recrystallization temperature, i.e. austenite pancaking, and characterised in terms of microstructural constituents, grain size distributions, texture and fractography. Provided the finish rolling temperature is high enough to avoid the formation of granular bainite on subsequent cooling, high levels of austenite pancaking yield the best combinations of low-temperature toughness and strength by effectively refining the size of the coarsest grains and randomizing the texture. While absolutely no direct correlation is found within as-quenched steels between the impact toughness transition temperatures and yield strength alone, T28J and T50 do closely follow a dynamic reference toughness, i.e. the opening stress intensity factor defined by yield strength and the size of the coarsest grains in the effective grain size distribution. This parameter reflects the transition temperatures – the lower the temperature, the lower the reference toughness needed to cause a local brittle fracture. Finally, we show that the impact toughness transition temperatures T28J and T50 of as-quenched steels can be accurately estimated, irrespective of the test specimen orientation, by utilizing just the dynamic reference toughness and the fraction of {100} cleavage planes within ± 15° of the specimen notch plane.

Effects of oxygen content on microstructure and impact toughness of high heat input flux-cored wire weld metals

2018 ◽  
Vol 115 (4) ◽  
pp. 410
Author(s):  
Fengyu Song ◽  
Yanmei Li ◽  
Ping Wang ◽  
Fuxian Zhu
Keyword(s):  
Grain Size ◽  
Impact Toughness ◽  
Weld Metal ◽  
Oxygen Content ◽  
Heat Input ◽  
High Heat ◽  
Cored Wire ◽  
Weld Metals ◽  
High Heat Input ◽  
The Impact

Three weld metals with different oxygen contents were developed. The influence of oxygen contents on the microstructure and impact toughness of weld metal was investigated through high heat input welding tests. The results showed that a large number of fine inclusions were formed and distributed randomly in the weld metal with oxygen content of 500 ppm under the heat input condition of 341 kJ/cm. Substantial cross interlocked acicular ferritic grains were induced to generate in the vicinity of the inclusions, primarily leading to the high impact toughness at low temperature for the weld metal. With the increase of oxygen content, the number of fine inclusions distributed in the weld metal increased and the grain size of intragranular acicular ferrites decreased, which enhanced the impact toughness of the weld metal. Nevertheless, a further increase of oxygen content would contribute to a great diminution of the austenitic grain size. Following that the fraction of grain boundary and the start temperature of transformation increased, which facilitated the abundant formation of pro-eutectoid ferrites and resulted in a deteriorative impact toughness of the weld metal.

Effect of Grain Size and Meso-Texture on the Impact Toughness of Ti-Microalloyed Steel

2011 ◽  
Vol 702-703 ◽  
pp. 766-769 ◽  
Author(s):  
A. Ray ◽  
Debalay Chakrabarti
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Impact Toughness ◽  
Microalloyed Steel ◽  
Charpy Impact ◽  
Impact Testing ◽  
Grain Sizes ◽  
Matrix Strength ◽  
Charpy Impact Testing ◽  
The Impact

Charpy impact testing (over the transition temperature rage) on different samples of a Ti-microalloyed steel, having the same average-TiN particle size but different average-ferrite grain sizes, showed that in spite of the presence of large TiN cuboides, ferrite grain refinement can significantly improve the impact toughness, provided the meso-texture (i.e. the intensity of low-angle boundaries) and matrix strength can be restricted to low values.

Impact Toughness for PM HIP 316L at Cryogenic Temperatures

2016 ◽  
Author(s):  
Tomas Berglund ◽  
Martin Östlund
Keyword(s):  
Grain Size ◽  
Impact Toughness ◽  
Oxygen Content ◽  
Room Temperature ◽  
Hot Isostatic Pressing ◽  
Cryogenic Temperatures ◽  
Inclusion Content ◽  
Conventional Material ◽  
The Impact ◽  
Suggested Explanation

It is well known throughout the PM HIP (Powder Metallurgy Hot Isostatic Pressing) industry that PM HIPed 316L material in general exhibit higher strength than conventional 316L. However, previous studies have shown an uncharacteristic behavior in impact toughness properties at cryogenic temperatures compared to conventional forged material. The uncharacteristic behavior consists of unexpectedly large drop in impact toughness at cryogenic temperatures which is not seen in the same extent in conventional material e.g. forged 316L. With the recent code case approval for PM HIPed 316L material, this behavior can be seen as an uncertainty regarding the performance of the material and its use in nuclear applications can therefore become limited. The behavior and underlying mechanisms is yet to be explained in detail. One possible explanation is that it is caused by oxides in the material, of which a large amount originates from oxygen picked up by the very large surface area of the powder during the manufacturing process. The correlation between impact toughness at room temperature and oxygen content is often referred to. In this study the non-metallic inclusion content is correlated to the impact properties at −196°C (−321°F), and a suggested explanation for the behavior of PM HIP 316L/316LN vs. conventional 316L is presented. The size and number of inclusions constitutes a major difference between the PM HIPed and conventional material. The results show that the size of the inclusions is significantly smaller in the PM materials compared to the conventional material and as a consequence they are present in larger numbers in the PM materials. Furthermore, the results clearly show the correlation between inclusion content and the impact toughness at cryogenic temperatures. The correlation is not as clear at room temperature where the different materials behave more similar. The suggested explanation is further supported by literature on cryogenic properties of 316L/316LN, 316L weld material and PM HIP 316LN with greatly reduced oxygen content. The impact toughness testing was performed using instrumented test equipment capable of recording load vs. displacement during testing. From this data the crack propagation and crack initiation energy can be estimated. Furthermore, it is known that grain size can influence mechanical properties. In this study no clear relationship between impact toughness and grain size could be observed. However, a correlation between the grain size and the amount of inclusions in the material was observed. It was found that larger amounts of inclusions in the PM HIPed material are correlated to a finer grain size. The results indicate that the inclusion particles inhibit grain growth during the HIP and heat treatment process by pinning of grain boundaries.

scholarly journals Development of Intermediate Cooling Technology and Its Control for Two-Stand Plate Rolling

2016 ◽  
Vol 2016 ◽  
pp. 1-9
Author(s):  
Fei Zhang ◽  
Wei Yu ◽  
Tao Liu
Keyword(s):  
Steel Plate ◽  
Cooling System ◽  
Chromatic Aberration ◽  
Rolling Process ◽  
Controlled Rolling ◽  
Plate Surface ◽  
Plate Rolling ◽  
Intermediate Cooling ◽  
Rolling Efficiency ◽  
The Impact

In a plate rolling production line, thermomechanically controlled processing is critical for plate quality. In this paper, a set of intermediate cooling equipment of a two-stand plate mill with super density nozzles, medium pressure, and small flow is developed. Based on a simplified dynamic model, a cooling control scheme with combined feedforward, feedback, and adaptive algorithms is put forward. The new controlled rolling process and the highly efficient control system improve the controlled rolling efficiency by an average of 17.66%. The proposed intermediate cooling system can also effectively inhibit the growth of austenite grain, improve the impact toughness and yield strength of Q345B steel plate, reduce the formation of secondary oxide scale on the plate surface and the chromatic aberration of the plate surface, and greatly improve the surface quality of the steel plate.

Effect of Rolling Process on Impact Toughness in High Strength Low Carbon Bainitic Steel

2015 ◽  
Vol 816 ◽  
pp. 743-749 ◽  
Author(s):  
Xiao Long Yang ◽  
Xiao Dong Tan ◽  
Yun Bo Xu ◽  
Zhi Ping Hu ◽  
Yong Mei Yu ◽  
...  
Keyword(s):  
Impact Toughness ◽  
Ductile Fracture ◽  
Cleavage Fracture ◽  
Charpy Impact ◽  
High Strength ◽  
Rolling Process ◽  
Bainitic Steel ◽  
Low Carbon ◽  
Austenite Recrystallization ◽  
The Impact

Based on TMCP and UFC technology, the microstructures and impact toughness of low carbon bainitic steel were studied in this paper. The bainite morphology and fracture surfaces of Charpy impact specimens were observed by SEM, and mechanical properties of bainitic steel were measured by tensile and impact test. The results showed that the yield and tensile strengths of steel were 804MPa and 1015MPa, and elongation was 15.7% when the rolling was finished in the austenite recrystallization region. The steel rolled below Tnr temperature obtained tht yield strength of 930 MPa, tensile strength of 1090 MPa and elongation of 16.2%. However, the impact toughness was deteriorated in the steel rolled above Tnr temperature while the excellent impact toughness existed in the steel rolled below Tnr temperature. The impact toughness of steel rolled below Tnr temperature was 140J at-60°C, while the impact toughness of 15J at the same temperature was obtained for the steel rolled above Tnr temperature. The large cleavage fracture region on the fracture surface occured with the decrease of tested temperature in the steel rolled above Tnr temperature and inevitably reduced the impact toughness, while the main ductile fracture existed in the steel rolled below Tnr temperature at the same temperature. The rolling process of steel can strongly affect impact toughness of low carbon bainitic steel. Hence, the different rolling processes can adjust the occurrence of cleavage fracture and ductile fracture in order to improve the impact toughness.

Research Regarding the Development of Manufacturing of Electrical Welded Pipes from Micro-Alloy Steel with Good Weldability and Toughness

2015 ◽  
Vol 1128 ◽  
pp. 261-268 ◽  
Author(s):  
Petru Simion ◽  
Vasile Dia ◽  
Gabriela Hrițuleac ◽  
Ioan Hrițuleac ◽  
Corneliu Munteanu
Keyword(s):  
Experimental Research ◽  
Mechanical Characteristics ◽  
Phosphorus Content ◽  
Weld Seam ◽  
Maximum Level ◽  
Rolling Process ◽  
Niobium Content ◽  
Second Stage ◽  
Hot Rolled ◽  
The Impact

Obtaining welded pipes with a superior toughness and plasticity of weld seam is strictly related to the properties of steel utilized in manufacturing welded pipes and firstly to its weldability. As a consequence, experimental research has been focused on obtaining steel with a lower equivalent carbon content but presenting high toughness and plasticity properties. In order to compensate for the decreased mechanical strength of the steel caused by reducing the carbon and manganese contents, in the first stage micro-alloying has been applied with niobium (0.040-0.055 % wt. Nb) to a construction steel, with a reduced content of carbon and manganese. The results of the mechanical characteristics obtained on hot rolled coil were good, but in the cold rolling process of pipes, the toughness characteristics have decreased excessively due to severe cold working characteristics of this steel. The second stage of experimental research has utilized microalloying with titanium (0.015-0.025 % wt. Ti), simultaneously with reducing the niobium content to a maximum level of 0.030% wt. Nb. Also, in order to reduce the cold brittleness of the steel, the maximum phosphorus content has been limited to 0.010 % wt. It was obtained excellent results with respect to the material toughness (evaluated by the impact test on KV specimen), the toughness value going up from 30-40 Joules to 150-180 Joules, while maintaining the excellent results previously obtained for steel weldability as well as the overall mechanical characteristics.

Improvement on Impact Toughness of Cold Formed S420 Steel by Direct Quenching

2021 ◽  
Vol 1016 ◽  
pp. 648-653
Author(s):  
Antti Kaijalainen ◽  
Juho Mourujärvi ◽  
Juha Tulonen ◽  
Petteri Steen ◽  
Jukka I. Kömi
Keyword(s):  
Grain Size ◽  
Tensile Strength ◽  
Impact Toughness ◽  
Yield Strength ◽  
Uniform Elongation ◽  
Cold Deformation ◽  
Strength Level ◽  
Cold Forming ◽  
Direct Quenching ◽  
The Impact

The aim of this work is to study the effect cold forming rate (CFR) on the mechanical properties and microstructure of a conventional TMCP and a direct-quenched steel in 420 MPa strength level. The microstructure was characterized using FESEM-EBSD. Tensile properties and Charpy-V impact toughness were determined. As the CFR increased, the yield and tensile strength raised quite linearly with both steels. Yield strength values increased from 450 MPa (as-rolled material) to 700 MPa (25 % CFR). However, tensile strength increased less compared to yield strength. Uniform elongation decreased linearly till about 10 % CFR and total elongation till about 15 – 20 % CFR. The impact values decreased quite linearly in -40 °C and -60 °C test temperature when the cold forming rate increased. In longitudinal direction (L-T) the impact values were at high level at -40 °C and -60 °C with both steels with all CFR. In transverse direction (T-L) the impact results were lower. Impact energies were enhanced by direct quenching compared to conventional steel in every CFR stage. EBSD results showed no major difference between steels in the grain sizes in generally. However, cold forming decreased the grain size and increased low-angle grain boundaries in correlation with increasing CFR. Small size of the coarsest grains (d90%) usually indicate better toughness, however in this case the impact values were decreased even with smaller grain size as cold deformation occurs. On the other hand, the strength level increased with forming rate. Therefore, a brief discussion of the microstructural features controlling the impact toughness is given.

Microstructure–Property Relationship in 22mm Thick X80 Coil Skelp

2010 ◽  
Author(s):  
M. Liebeherr ◽  
N. Bernier ◽  
D. Le`bre ◽  
N. Ilic´ ◽  
D. Quidort
Keyword(s):  
Grain Size ◽  
Impact Toughness ◽  
Electron Backscatter Diffraction ◽  
Bainitic Ferrite ◽  
Hot Strip Mill ◽  
Low Carbon ◽  
Welded Pipe ◽  
Hot Rolled ◽  
Backscatter Diffraction ◽  
The Impact

The progress in the development of heavy gauge X80 linepipe steel on coil at ArcelorMittal was recently rewarded with a 6000 ton commercial order for the production of 21.6mm wall thickness spiral welded pipe. The further product development is concentrating on the improvement of the impact toughness at low temperatures. Research is currently focussing on the relationship between the mechanical properties and the microstructure of the steels. In the present study, two industrially hot rolled X80 steels with thickness 21.6mm were investigated. The steels had the same chemical composition but were processed with different parameter sets in the hot strip mill. The two resulting low-carbon bainitic microstructures were composed predominantly of quasi-polygonal ferrite and globular bainitic ferrite / bainitic ferrite, respectively. Emphasis of the microstructure and property characterisation was laid on through-thickness gradients of grain size, hardness, texture, impact toughness and tensile properties. Accordingly, the materials were characterised at different positions in the thickness. Grain size and texture were determined by means of Electron Backscatter Diffraction (EBSD). Sub-size Charpy as well as sub-thickness tensile test specimens were taken at different positions in the cross section. The results show that the link between microstructure and properties is not at all obvious. The influence of mean grain size, grain size distribution and texture is discussed in detail.

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