Effect Of Finish Rolling Temperature Research Articles

Effects of Finish Rolling Temperature on the Critical Crack Tip Opening Displacement (CTOD) of Typical 500 MPa Grade Weathering Steel

In this study, the effect of finish rolling temperature on the critical crack tip opening displacement (CTOD) of typical 500 MPa grade weathering steel was elucidated. The microstructures were observed via optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), and electron back-scattered diffraction (EBSD). The cryogenic fracture toughness and microstructures of steels were analyzed at different finish rolling temperatures (780–840 °C). The results show that a mixed microstructure, i.e., granular bainitic ferrite (GBF), polygonal ferrite (PF), and martensite/austenite (M/A), constituent was formed in each sample. With the decrease of the finish rolling temperature, the GBF content decreased, PF content increased, and the high angle grain boundary (HAGB) number fraction of the matrix increased. Furthermore, the fraction of M/A constituents was increased with reduced average size. The value of CTOD increased significantly from 0.28 to 1.12 mm as the finish rolling temperature decreased from 840 to 780 °C. Both the decrease of M/A constituents and the increase of HAGB increased the cryogenic (−40 °C) fracture toughness of the typical 500 MPa grade weathering steel.

Effect of Finish Rolling Temperature on the Texture and Fracture Resistance of Low-Carbon High-Strength Pipe Steels during Thermomechanical Treatment

Effect of Finish Rolling Temperature on the Texture and Fracture Resistance of Low-Carbon High-Strength Pipe Steels during Thermomechanical Treatment

Effect of Finish Rolling Temperature on Microstructure and Mechanical Properties of 500 MPa Grade Gantry Mounting Structural Steel

Effect of Finish Rolling Temperature on Microstructure and Mechanical Properties of 500 MPa Grade Gantry Mounting Structural Steel

Effect of finish rolling temperature on microstructure and mechanical properties of X80 pipeline steel by on-line quenching

A Ti–V microalloyed X80 seamless pipeline steel was prepared using on-line quenching and off-line tempering technology. The influence of finish rolling temperatures (FRTs∼950 °C and 900 °C) and tempering temperatures (600°C–700 °C) on microstructure and mechanical properties was investigated. Fully recrystallized austenite was formed at 950 °C FRT, but partially at 900 °C FRT. The quenched microstructure consisted of lath bainite, granular bainite, cementite and TiC precipitates. With the decrease in FRT, more granular bainite and strain-induced TiC precipitates were obtained in the quenched microstructure. The original quenched structure significantly impacted the subsequently tempered microstructure. The tempered microstructure was composed of polygonal ferrite, tempered bainitic laths, cementite and (Ti, V)C precipitates. As FRT decreased, the tempered microstructure exhibited more polygonal ferrite, smaller grain size and better precipitation characteristics of (Ti, V)C precipitates, simultaneously improving the strength and impact toughness. An ideal combination of the yield strength (∼632 MPa), tensile strength (∼707 MPa), impact value (∼249 J at −20 °C) and shear-fracture area (∼97% at −20 °C) was achieved at 900 °C FRT and 680 °C tempering temperature, which satisfied the API requirements of X80 pipe. Therefore, 900 °C FRT and 680 °C tempering temperature were suitable process parameters for on-line quenching technology to produce X80 seamless pipeline steel.

Effect of finish rolling temperature on microstructures and mechanical properties of 1000 MPa grade tempered steel plate for hydropower station

With the decreasing of finish rolling temperature, the microstructure of the hot rolled steel was changed from lath martensite to complex microstructures composed of lath martensite, ferrite, granular bainite and lath bainite, unrecrystallized prior austenite grains are the main reason for the formation of complex microstructures. After tempering, the steels are mainly composed of ferrite and cementite. For the steel with high finish rolling temperature, the proportion of high misorientation boundary is less, and it has rod-like precipitates with the length of 25−85 nm and punctate precipitates with the size of 4−16 nm, the intensities of {111}<110> and {001}<110> textures are enhanced. The experimental steel has the best combination with strength and toughness as yield strength of 996 MPa, tensile strength of 1023 MPa, total elongation of 19.1 %, impact value at -60 ℃ of 125 J. Grain refinement, higher density of dislocation, fine and dispersed precipitates could enhance the yield strength and tensile strength. Stronger intensity of {332}<113> texture and weaker intensity of {001}<110> texture could improve the impact toughness.

Effect of Finish Rolling Temperature on Microstructure and Mechanical Properties of Low-Si Steel After Quenching and Nonisothermal Partitioning

The quenching and nonisothermal partitioning process has been found to achieve excellent combinations of strength and ductility through the retention of austenite in the microstructure. Therefore, in the present study, the effect of grain size on phase transformations and ensuing mechanical properties has been investigated. A low-Si and Al-free steel was finish rolled at different temperatures which was subsequently quenched to a constant temperature below Ms for the formation of martensite with remaining untransformed austenite. This was followed by slow cooling to room temperature to simulate the condition of nonisothermal partitioning of carbon from martensite to the austenite. The results show that there is not much change in the average grain size with variation in the finish rolling temperature, as well as, no measurable differences are observed in the microstructural features and retained austenite content. The microstructure shows the presence of martensite, carbides, and a small amount of retained austenite. However, in terms of mechanical properties, the finish rolling at a lower temperature of 900 °C lead to higher hardness and strength with comparable ductility in comparison to the sample which has been finish rolled at a relatively higher temperature (940 °C). The above results will thus be helpful in designing the industrial processing schedule for low-Si steel to achieve enhanced performance.

Effects of finish rolling temperature and yield ratio on variations in yield strength after pipe-forming of API-X65 line-pipe steels

Flattened plates often show the lower or higher yield strength than initial leveled plates because tensile and compressive strains are repeatedly experienced at outer and inner walls during the pipe-forming and flattening, but reasons for the yield-strength variation after the pipe-forming are not sufficiently verified yet. In this study, ten line-pipe steels were fabricated by controlling alloying elements and finish rolling temperatures (FRTs), and the yield strength of pipe-flattened steel plates was predicted by using cyclic simulation tests, based on competing contributions of Bauschinger effect (BE) and strain hardening (SH) effect quantified from yield drop (YD) and yield rise (YR) parameters, respectively. High-FRT-treated steels (H steels) showed the lower BE and the higher SH than low-FRT-treated steels (L steels), thereby resulting in the smaller yield-strength reduction. This lower BE in the H steels was caused by the lower total boundary density, while the higher SH was caused by the higher fraction of granular bainite. According to the SH analyses between the YR parameters obtained from cyclic simulation tests and the yield ratios obtained from ordinary tensile tests, the decrease in yield-strength reduction with decreasing yield ratio was not attributed to the increase in ordinary tensile SH but to the increase in YR parameter.

Effects of Finish Rolling Temperature and Deformation on Microstructural Evolution and Precipitation Behavior of Non‐quenched and Tempered Carbide‐Free Bainitic Steel

Double compression tests are carried out to investigate the microstructural evolution and precipitation behavior of Nb–Ti microalloyed carbide‐free bainitic steel under different finish rolling conditions. With decreasing finish rolling temperature and increasing finish rolling deformation, the area fraction of lath bainite (LB) and martensite (M) was increased, the width of bainitic ferrite lath was decreased, the dislocation density and the number fraction of high‐angle grain boundaries are raised. Meanwhile, the larger deformation and lower temperature reduce the amount of retained austenite (RA) and refine the precipitated particles, which benefit the performance further. Hence, the phase transformation strengthening, refinement strengthening, dislocation strengthening, and precipitation strengthening synergistically contribute to the increase in hardness with increasing deformation and decreasing temperature.

Influence of Finish Rolling Temperature on Microstructure and Mechanical Properties of a 19Cr1.5Mo0.5 W Ferritic Stainless Steel

A 444-type heat-resistant ferritic stainless steel containing 0.05 wt% Ce (rare earth element) and 2 wt% (Mo + W) was adopted as an experimental material to study the effect of finish rolling temperature on microstructure and texture evolution as well as on mechanical properties and formability. The rolling processes contain hot rolling at two different finish rolling temperatures (860 °C and 770 °C) and annealing, cold rolling and subsequent annealing. It was found that the microstructures after hot rolling and annealing could be refined by lowering finish rolling temperature. The resultant microstructures after cold rolling and annealing were hereditarily refined. Lowering finish rolling temperature can weaken α-fiber texture in hot-rolled or cold-rolled ferritic stainless steel strip, while γ-fiber texture in the final product was homogeneously strengthened. Additionally, enhanced mechanical property and formability in terms of strength and average plastic strain ratio could be obtained via decreasing finish rolling temperature.

The effect of finish rolling temperature and tempering on the microstructure, mechanical properties and dislocation density of direct-quenched steel

A unique batch tempering treatment for industrial scale direct-quenched steel coils has been studied using laboratory simulations. The tempering treatment was non-isothermal with slow heating to 570 °C and slow cooling to simulate the tempering of large steel coils. The paper presents the effect of finishing rolling temperature (FRT) relative to the non-recrystallization temperature (TNR) and the effect of long time tempering on the microstructure, dislocation density and mechanical properties of direct-quenched coiled strips. Conditioning austenite below the recrystallization stop temperature resulted in a finer effective grain size distribution, which correlated strongly with the impact toughness of the final product. Furthermore low finish rolling temperature resulted in partially ferritic microstructures while higher finishing rolling temperatures led to mixtures of bainite and martensite. Dislocation densities determined with TEM and XRD showed somewhat different trends regarding the effect of tempering: intra-lath dislocation density, as measured with TEM, showed a statistically significant drop in only one case, while XRD analysis indicated a drop in all cases. Furthermore, no significant correlation between finishing rolling temperature and dislocation density existed in XRD studies. The XRD results indicate that the decrease in dislocation density corresponds to about 100 MPa lower dislocation strengthening. However, precipitation hardening and potential internal micro stress relief compensates this as yield strength remains unchanged or even increases during tempering.

Microstructure–mechanical property relationship in hot-rolled high-Al-low-Si dual-phase steel

ABSTRACTIn this study, the effect of finish rolling temperature and coiling temperature on the microstructure and mechanical properties of high-Al-low-Si dual-phase (DP) steels is explored. Two different finish rolling temperatures (850 and 790°C) and three different coiling temperatures (200, 250 and 300°C) were studied. The results indicated that all the different processing conditions led to ferrite-martensite DP microstructure. With the decrease in finish rolling temperature, the volume fraction of ferrite was increased and martensite content was decreased. When the coiling temperature was increased to 300°C, autotempered martensite was obtained, which led to the softening of martensite and decrease in tensile strength and strain hardening ability, but higher post-necking elongation. Moreover, the nanoscale Nb-based carbides played a crucial role in refining the microstructure of hot-rolled high-Al-low-Si DP steel. EBSD (Electron Backscattered Diffraction) analysis revealed that the ferrite grains were fine, and decrease in finish rolling temperature and coiling temperature led to an increase in low-angle boundaries. When the finish rolling temperature was decreased to 790°C and coiling temperature was decreased to 200°C, the steel had excellent mechanical properties with tensile strength of 885 MPa, uniform and total elongation of 16.0 and 25.94%, respectively, and the product of tensile strength and total elongation was 20 264 MPa%. The improvement of strength and plasticity can be attributed to the fraction of ferrite and martensite, precipitation of NbC, fine microstructure.

The Effects of Finish Rolling Temperature and Niobium Microalloying on the Microstructure and Properties of a Direct Quenched High-Strength Steel

AbstractThis paper comprehends the effects of finish rolling temperature (FRT) and Nb-microalloying on the microstructural evolution and resultant properties of a low carbon direct quenched steel in the yield strength category of ≥900 MPa. Results indicate that a decrease in FRT close to Ar3temperature significantly influenced the microstructure following phase transformation, especially at the subsurface (~50-400 μm) of the rolled strip. On decreasing the FRT, the subsurface microstructure revealed a fine mixture of ferrite and bainite obviously as a result of strain-induced transformation, whereas the structure at the centreline remained essentially martensitic. Further, Nb-microalloying promoted the formation of ferrite and bainite even at higher FRTs, thus influencing the mechanical properties. The microstructures of the hot-rolled strips were further corroborated with the aid of CCT diagrams.

The effect of finish rolling temperature on the microstructure and properties of non-quenched and tempered Bainite steel

Abstract Non-quenched and tempered steel has excellent properties, and the production process of it is energy-saving, low-cost and eco-friendly. With these advantages, non-quenched and tempered steel attracts more attentions and has been widely used in recent years. Existing non-quenched and tempered micro alloyed steel is roughly divided into three categories: ferrite-pearl steel, bainite steel and martensitic steel. The strength and toughness of bainite steel is better than ferrite-pearlite steel, but less research of bainite steel has been done, especially its rolling process. In this paper, the effect of finish rolling temperature on the microstructure and properties of bainite non-quenched and tempered steel is studied. The results show that with different finish rolling temperature, the mechanical property of bainite steel has distinctions, along with the phase composition, the morphology and distribution of lath bainite, the amount of retained austenite, the difference between grain boundary orientations, recovery and recrystallization phenomena, and phase relation of lath bainite and parent phase. When finish rolling temperature is high (870°C), the ductility and toughness of bainite steel sample is better than others while the strength is lower. The amount of lath bainite is about 85%, which is the highest among the samples, and the width of lath bainite is small. With finish rolling temperature decreases, the strength of bainite steel sample increases at the cost of toughness. The diffusion of carbon atoms is slowed down due to the lower temperature, and as a result, the stability of austenite decreases, and martensite phase transformation occurs in the following cooling process. The portion of high-angle grain boundaries decreases as the finish rolling temperature decreases, while the phase relation of lath bainite and parent phase remains the same.

Effect of Finish Rolling Temperature on the Microstructure and Tensile Properties of Nb–Ti Microalloyed X90 Pipeline Steel

The relationship between microstructure and tensile properties of an Nb–Ti microalloyed X90 pipeline steel was studied as a function of finish rolling temperature using a Gleeble 3500 simulator, an optical and scanning electron microscope, electron back scattered diffraction (EBSD), a transmission electron microscope (TEM) and X-ray diffraction. The results indicate that the microstructure is primarily composed of non-equiaxed ferrite with martensite/austenite (M/A) constituent dispersed at grain boundaries for the specimens with different finish rolling temperatures. With a decrease in the finish rolling temperature, the yield strength increases, following a significant increase in the grain refinement strengthening contribution and dislocation strengthening contribution, although the precipitation strengthening contribution decreases. The increasing yield ratio (YR) shows that the strain hardening capacity declines as a result of the microstructure evolution when decreasing the finish rolling temperature.

Microstructural Characteristics with Various Finish Rolling Temperature and Low Temperature Toughness in Hot Rolled Nb–Ti Ferritic Steel

In order to investigate the effects of finish rolling temperature on the microstructural characteristics and fracture mechanism of Nb–Ti ferritic steel, the samples with various finish rolling temperature have been observed by optical microscopy, scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. The results indicated that both ferrite grain size and volume fraction of (Nb,Ti)C precipitates decreased with the decreasing finish rolling temperature, but the size of (Nb,Ti)C precipitates changed little with the finish rolling temperature. All of these factors caused the yield strength, tensile strength and elongation remained similar. However, the low temperature toughness was significantly influenced by the finish rolling temperature. Based on the observation results of fracture surface of samples tested at −40°C, the fracture type of steels with finish rolling temperature of 940°C and 910°C was brittle, while the fracture of steel with finish rolling temperature of 880°C was ductile. At last, the crack initiation and propagation mechanism is elucidated in details. At −40°C, both intergranular cracks and transgranular cracks existed in the steels finish rolled at 940°C and 910°C, and only microvoides were observed in the steel finish rolled at 880°C with high toughness.

Effect of Finish Rolling Temperature on Direct Quenched Low Alloy Martensite Properties

The mechanical properties of direct quenched low alloy martensite steel can be altered considerably through control of the austenite condition prior to quenching. This can be done by varying the finish rolling temperature during hot rolling. The two main aspects to be taken into account are the prior austenite grain size and the accumulated strain due to rolling in the non-recrystallization regime. It is shown that rolling in the non-recrystallization regime increases the strength, but reduces the impact toughness. Increasing the accumulated strain, however, results in increasing the impact toughness for the same strength. Strain accumulation increases the forces during hot rolling and as such imposes a practical limit to the maximum strain that can be accumulated in the austenite. The current work illustrates the optimized combination between strength, impact toughness and processability of a direct quenched low alloy martensitic steel.

Crystallographic Reconstruction Study of the Effects of Finish Rolling Temperature on the Variant Selection During Bainite Transformation in C-Mn High-Strength Steels

The effect of finish rolling temperature (FRT) on the austenite- () to-bainite () phase transformation is quantitatively investigated in high-strength C-Mn steels. In particular, the present study aims to clarify the respective contributions of the conditioning during the hot rolling and the variant selection (VS) during the phase transformation to the inherited texture. To this end, an alternative crystallographic reconstruction procedure, which can be directly applied to experimental electron backscatter diffraction (EBSD) mappings, is developed by combining the best features of the existing models: the orientation relationship (OR) refinement, the local pixel-by-pixel analysis and the nuclei identification and spreading strategy. The applicability of this method is demonstrated on both quenching and partitioning (Q&P) and as-quenched lath-martensite steels. The results obtained on the C-Mn steels confirm that the sample finish rolled at the lowest temperature (829{\deg}C) exhibits the sharpest transformation texture. It is shown that this sharp texture is exclusively due to a strong VS from parent brass {110}<1-12>, S {213}<-3-64> and Goss {110}<001> grains, whereas the VS from the copper {112}<-1-11> grains is insensitive to the FRT. In addition, a statistical VS analysis proves that the habit planes of the selected variants do not systematically correspond to the predicted active slip planes using the Taylor model. In contrast, a correlation between the Bain group to which the selected variants belong and the FRT is clearly revealed, regardless of the parent orientation. These results are discussed in terms of polygranular accommodation mechanisms, especially in view of the observed development in the hot-rolled samples of high-angle grain boundaries with misorientation axes between <111> and <110> .

Promotion of texture weakening in magnesium by alloying and thermomechanical processing. II: rolling speed

In the first part of this two-part paper, the effect of increasing Ce in solid solution on the recrystallization and texture evolution of four Mg–Zn–Ce sheets was investigated in the as-deformed and annealed state. In this second part, the effect of rolling speed on the microstructure and texture development of these alloys is evaluated. The effect of rolling speed on the recrystallization and texture evolution of four Mg–Zn–Ce sheets was investigated at as-deformed and different stages of annealing. The deformation microstructure was obtained through two stages that can be characterised as rough rolling and finish rolling. To study the effect of finish rolling temperature, one rolling pass with a 65 % reduction in thickness was performed at 300 and 450 °C and at rolling speeds of 15 and 1000 m/min. The results showed that by increasing the rolling speed, more secondary and compression twins were activated, which leads to the formation of more numerous local shear bands and a more uniform microstructure. Annealing secondary twins (S-twins) and their vicinity were observed to be the preferential sites for nucleation, and it seems that recrystallization on S-twins contributes to basal texture weakening. Therefore, an increasing number of such twins increase the texture weakening. In this way, the combination of these RE additions and HSR resulted in a weaker deformed and annealed texture.

The Effect of Finish Rolling Temperature on Microstructure and Mechanical Properties of Vanadium Containing Ferritic Stainless Steel

In this paper, the influence of finish rolling temperature during hot rolling on microstructure and mechanical properties of ferritic stainless steel containing vanadium was investigated. It showed that with the rolling temperature increasing, the tensile strength and hardness value fell down, while the value of ductility rising and less precipitates appearing. If the finish rolling temperature was set too high, the grain would get coarsened and the α-fiber get strengthened, which had an adverse effect on the formability and wrinkle resistance of the production sheet. 850°C was a reasonable finish rolling temperature.

Microstructure and texture evolution of MgZnCe magnesium alloys sheets and associated restoration mechanisms during annealing

The texture evolution in four MgZnCe alloys was compared to that of Mg3Al1Zn (AZ31) alloy following rolling and subsequent isothermal annealing. All the as-cast and homogenized alloys were rolled through two stages that can be characterized as rough rolling and finish rolling, respectively. To investigate the effect of finish rolling temperature, one finish rolling pass with 65% reduction in thickness was performed at 300°C and 450°C. Of the studied compositions, the Mg1Zn1Ce, which had the highest Ce/Zn ratio, showed the weakest as-rolled texture and homogenous shear banding/twinning. Changing the Zn content changed particle size and, in alloys subject to texture weakening, the static recrystallization mechanism altered. On annealing, the maximum intensity of basal pole figures decreases as recrystallization progresses. The Mg1Zn1Ce (with the highest Ce/Zn), texture weakening is maintained even after full recrystallization, when grain coarsening occurs. However, in the Mg4Zn1Ce and AZ31 alloys, texture strengthening occurs when grain coarsening occurs, and the double split basal peak is replaced by a single peak. In these two alloys, grain coarsening is also accompanied by a bimodal grain size whereas in the Mg1Zn1Ce alloy, the grain coarsening leads to a uniform grain size. It is concluded that the differences between the Ce bearing alloys are related to Zn; increasing Zn decreases the solubility of Ce, which can influence the texture changes.