Hot Rolling Conditions Research Articles

Study of Dry Sliding Wear Behavior of Hot-Rolled and Mushy-State Rolled Al-4.5Cu-5TiB2 In-Situ Composite with Analysis of Work Hardening and Subsurface Microstructure-Microtexture Evolution Using EBSD

The response of the Al-4.5 wt pct Cu-5 wt pct TiB2 in-situ composite in the as-cast, hot-rolled, mushy-state rolled, or pre-cold rolled mushy-state rolled conditions to dry sliding wear tests at 1 m/s linear speed under 20N load has been examined. Further, microstructures and chemical compositions were simultaneously studied by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively, whereas the microtexture was quantified by electron backscattered diffraction (EBSD) analysis. An effort has been made to understand the relationship of CuAl2 and TiB2 particle distribution, microtexture, and hardness obtained through the aforementioned rolling processes with wear rates and post-wear surface profile. Additionally, the amount and depth of work hardening as a result of wear has been correlated with the subsurface microtexture evolution. Among the investigated wear-tested samples, the pre-cold rolled mushy-state rolled composite (PCMRC) has shown the best wear resistance due to high hardness being contributed by the highest low-angle boundary (LABs; misorientation angles 15 deg due to considerable strain accumulation near TiB2 particles or particle-stimulated nucleation by dynamic recrystallization due to flash heat generation. Furthermore, a remarkable increase in the post-wear microhardness of the subsurface locations has been used to confirm that significant work hardening is caused by severe plastic deformation of the composite matrix during wear, which is in great coherence with the results of EBSD analysis.

Observation of grain growth in U-10Mo alloy

Both as-cast and homogenized wedge specimens of U-10wt%Mo (U-10Mo) alloy were thermomechanically processed in both cold and hot rolled conditions and annealed at 700 °C for periods lasting up to 2 h. The hot rolled samples had a net strain of 70% whereas the cold rolled ones were subjected to 30% strain. Annealed microstructures were examined using electron backscatter diffraction in order to estimate the completeness of recrystallization and grain size, and these were mapped as a function of strain. In as-cast samples, the stored energy with strain increases but in the homogenized samples the stored energy remains constant with strain. This is due to a difference in the initial microstructure (before deformation) of the homogenized samples.

Development and Microstructural Characterization of a New Wrought High Entropy Superalloy

In this study, a newly developed γ′ precipitation hardened high entropy superalloy (designated as HES-A1 hereafter) was produced and its microstructural features were characterized. The new alloy composition is based on the major elements of conventional IN718 alloy, however other elements were added or removed to minimize possible presence of δ (or γʺ) phase and increase the volume fraction of very fine γ′ precipitates instead. Broadening the hot working window, lower density, and avoiding the use of expensive elements were other considerations taken into account in the design of the new alloy. CALPHAD (CALculation of PHAse Diagrams) and PhaComp methods were used for the prediction of phases and their evolutions. The microstructure of the HES-A1 alloy in as-cast, homogenized, hot rolled, annealed and aged conditions were characterized using optical, scanning, and transmission electron microscopes as well as X-ray diffraction technique. The as-cast microstructure of HES-A1 contained 5.5% of Laves phase, which was reduced to less than 0.3% through the development of a homogenization treatment. Hot rolling with reductions up to 36% at 1015 °C did not produce any cracking, indicating a good forming potential for the new alloy. The application of double aging treatment, similar to the one for IN718 alloy, showed no presence of γʺ or formation of δ phase in the microstructure. HES-A1 has been designed with a higher Al/(Ti + Nb) ratio and higher proportion of Al + Ti + Nb so that it could be mainly strengthened by γ′ precipitation. The average size of monomodal γ′ precipitates was smaller than that observed in conventional alloys after similar treatments.

Intercritical and subcritical spheroidization of 10B38 cold heading steel

For the production of bolts by cold forging, the hardenable steel has to be in a soft and ductile state. The Cold Heading Quality Steel is achievable by a spherodization heat treatment on the hot rolled material. The scope of this study is a boron bearing medium carbon steel which has many promising properties as bolting material. The experimentations covered two different initial conditions before the spheroidization heat treatment: hot rolled (ferrite-pearlite microstructure) and quenched (martensitic microstructure). In combination, two spheroidization procedures were considered too: subcritical and intercritical heat treatments. Intercritical heat treatment process included heating to 750 °C , holding for 2 h and then cooling to 715 °C and then holding for 12 h. In the subcritical heat treatment proess, the materialwas heated to 715 °C , holding for 12 h followed by cooling in the furnace. To assess the cold formability, a special notched tensile test was employed and the results were supported with metallographic and microhardness measurements. For both subcritical and intercritical heat treatment, higher levels of spheroidizatin were achieved with the quenched samples compared with the hot rolled condition. On the other hand the subcritical heat treatment resulted in higher levels of spheroiization. A practical equation is developed which relates the failure strain of notched tensile specimens with pearlite content and the hardness of the 10B38 steel.

Microstructural development and mechanical properties during hot rolling and annealing of an automotive steel combining TRIP/TWIP effects

This research was carried out in order to study the variations of microstructure and mechanical properties of 9 wt% Mn steel, which was produced by ingot casting, hot rolling and intercritical annealing (IA). Thermodynamic simulation of the corresponding phase diagram for the experimental composition allowed to select a suitable intercritical annealing temperature of 680 °C. After this step, we found a microstructure composed by lamellar ferrite within an austenite matrix. Austenite content was 47% for the hot rolled sample, while it was 36% and 52% for two and 6 h of intercritical annealing, respectively.Unfortunately, austenite phase started to coarsen at 6 h and ferrite lamellas were also fragmented, causing an important hardness and elongation reduction. Mechanical properties were measured comparing hot rolling samples vs. annealed samples at 680 °C for 2 h. We found that an excellent combination of UTS (ultimate tensile strength) of 1200 MPa, an elongation of almost 60% and an impact energy of 55 J could be obtained after IA for 2 h. These results, with the exception of UTS, significantly exceeded the values displayed by hot rolling condition and were associated with the stability of austenite which increased during annealing. Finally, we demonstrated that only TRIP (transformation induced plasticity) effect was present in the hot rolled sample during tension testing, in contrast with the annealed sample in which austenite content only diminished 12%, which indicates that TWIP (twinning induced plasticity) effect was also effective.

Microstructure and Texture Control in Cold Rolled High Strength Steels

Formability had been important property of metals which is attributed to the texture development during thermomechanical processing particularly during hot rolling and cold rolling. In the present paper, the high strength steels with different carbon and manganese composition have been hot rolled above and below of austenite recrystallization temperature and followed by fast cooling up to different coiling temperature to get hot bands with different texture and two phase microstructure consisting ferrite with pearlite, bainite and martensite. Subsequently, these hot bands were cold rolled with 80 percent under plain strain condition. The microstructure of cold rolled sheets samples were analyzed using scanning electron microscope and showed the cold rolled microstructure with strong pancaked of two phase which was carried from the hot rolling. Cold rolled texture in ferrite pearlite microstructure is completely replaced by new texture components from hot rolled condition without the effect of Tnr. Hot rolled texture was retained in ferrite-bainite and martensite microstructure with the effect of Tnr. Increase in alloy chemistry weakens the texture intensity in ferrite pearlite/bainite microstructure. Whereas increase in alloy chemistry strengthens the texture intensity in ferrite martensite microstructure.

The Influence of Hot‐Rolling Conditions on the Content and Morphology of Retained Austenite in Ultra‐High Strength Bainitic Steel and Its Mechanical Properties

Bainitic steel with retained austenite belongs to the family of multi‐phase steels, which exhibit high strength combined with high deformability due to their special microstructural composition. In this contribution, the microstructural conditions of the hot‐rolled bainitic steel are presented and characterized as a function of the chromium content and the hot‐rolling conditions. In particular, the aim of this study is to understand the influence of hot rolling conditions and of Cr content on retained austenite morphology for a Cr containing, carbide‐free bainitic steel. The mechanical properties are largely controlled by the multi‐phase microstructure. A high degree of deformability is evaluated unlike to the large amount of retained austenite islands in the microstructure. The morphology of the retained austenite is described as blocky‐type, which questions previous findings on retained austenite in literature. In this work, the best ratio between tensile strength (1340 MPa) and total elongation (22%) is found for blocky retained austenite while the island size do not measure more than 2 μm. These results are found for steel with a Cr‐content of 0.9% and after hot rolling (finish rolling temperature >970 °C) with a coiling temperature of 450 °C.

Initial weldability study on Al0.5CrCoCu0.1FeNi high-entropy alloy

The weld solidification behavior, segregation tendency, phase formation, and cracking susceptibility of Al0.5CoCrCu0.1FeNi high-entropy alloy (HEA) were investigated. The AlCoCrCuFeNi alloy system has received wide attention due to its high temperature stability and strength retention. Characterization of the as-melted, heat-treated, and hot-rolled and heat-treated alloy conditions was performed and compared to thermodynamic CALPHAD-based calculations. Autogenous gas tungsten arc (GTA) and laser beam welding was done on the different alloy conditions. Microstructural changes in the fusion zone and heat-affected zone (HAZ) were investigated by optical microscopy and micro-hardness. Hot cracking susceptibility was evaluated using the cast pin tear test (CPTT). The fusion zone solidification microstructure of Al0.5CoCrCu0.1FeNi alloy consists of primary face centered cubic dendrites and interdendritic body centered cubic phase that forms at the end of solidification. GTA welding results in the partial dissolution of the interdendritic phase in the high-temperature HAZ, adjacent to the fusion boundary. Welding on the heat-treated alloy leads to HAZ softening due to the dissolution of strengthening nano-sized precipitates. No solidification cracking or HAZ liquation cracking was observed. Laser welding did not result in a drop in hardness or significant microstructural changes in the HAZ. The CPTT results correspond well with the predicted solidification temperature range (141 K) for Al0.5CoCrCu0.1FeNi alloy and its overall good weldability that was observed in the present work.

The Impact of Strain Aging on the Mechanical Properties of Steel 37KhGF

Abstract—The impact of the strain aging effect on the structural behavior and viscoplastic properties of steel 37KhGF in hot-rolled condition and after in heat treated condition and special strengthening treatment involving the imposition of a small plastic deformation (e = 2%) and artificial aging at 250°C for 1 h was studied. The quantitative evaluation of the contribution of the strengthening mechanism and strain aging effect to the yield point was performed.

Evolution of Texture during Hot Rolling of a New Magnesium Alloy

High-strength wrought magnesium alloys are one of the sought-after materials in the automotive sector owing to the demands for weight reduction in the automobiles due to fuel economy and CO2 emission. However, because of low room temperature strength and formability of Mg alloys, only a few applications in wrought form have been explored with these materials. In the present investigation, a high strength, good ductility and low cost wrought magnesium alloy with Mg-Sn-Zn composition have been developed and subjected to conventional wrought processing. Hot rolling was carried out at 350°C without homogenization and after homogenization at 300°C and 330°C. The phase stability, microstructure and texture of the alloy has been investigated for as-cast, homogenized and hot rolled conditions. The compositional and microstructural characterization was carried out by Electron Probe Micro-analysis (EPMA) and optical microscopy respectively. Texture evolution was investigated by X-ray diffraction method. A strong (0002) basal texture develops after hot rolling without homogenization. The (0002) basal texture has been weekend by splitting of poles and double peak distribution when hot rolling was carried out after homogenization.

Effect of hot Rolling and Cooling Conditions on the Microstructure, MA Constituent Formation, and Pipeline Steels Mechanical Properties

Two types of pipeline steels differentiated by the content of aluminum and silicon are produced during the pilot plant test with varying rolling temperature and accelerated cooling rate. Microstructures, MA constituent morphology, and mechanical properties of such materials are compared using digital and electron microscopy, tensile, and Charpy impact tests. Results show that low finishing rolling temperature stimulates MA constituent refinement. Cooling rate increase leads to MA constituent amount increase and refinement. Alloying with aluminum significantly stabilizes austenite and leads to MA constituent amount and size increase. Higher MA constituent amount has in most cases positive effect on plasticity without strength and impact toughness degradation.

Effect of Microstructure on Post-Rolling Induction Treatment in a Low C Ti-Mo Microalloyed Steel

Cost-effective advanced design concepts are becoming more common in the production of thick plates in order to meet demanding market requirements. Accordingly, precipitation strengthening mechanisms are extensively employed in thin strip products, because they enhance the final properties by using a coiling optimization strategy. Nevertheless, and specifically for thick plate production, the formation of effective precipitation during continuous cooling after hot rolling is more challenging. With the aim of gaining further knowledge about this strengthening mechanism, plate hot rolling conditions were reproduced in low carbon Ti-Mo microalloyed steel through laboratory simulation tests to generate different hot-rolled microstructures. Subsequently, a rapid heating process was applied in order to simulate induction heat treatment conditions. The results indicated that the nature of the matrix microstructure (i.e., ferrite, bainite) affects the achieved precipitation hardening, while the balance between strength and toughness depends on the hot-rolled microstructure.

Effect of hot rolling conditions on the nitride precipitation process in low carbon steel strips

The nitride precipitation process plays an important role in the final mechanical and aging behaviour of low carbon steels in hot rolled state as well as in cold rolled and annealed state. The nitride precipitation process is investigated in an indirect manner: instead of measuring the amount of nitrogen compounds, the free nitrogen content of the samples was measured using a special thermomechanical treatment and a thermoelectric power tester. It was found, that the free nitrogen content in a steel strip strongly depends on three main factors: on the position in strip transverse direction, on the coiling temperature and on the cooling method at the run-out table of the hot rolling mill.

Comparison of Fatigue Properties for Alloy EP708 Specimens Prepared by Selective Laser Melting and Hot Rolling

Structure and fatigue resistance tests of EP708 alloy specimens prepared by selective laser melting (SLM) and subjected to strengthening heat treatment and hot isostatic pressing (HIP), combined with heat treatment compared with hot-rolled heat-treated specimens, are studied. It is shown that the use of the HIP process significantly reduces specimen porosity obtained by the SLM method for EP708 alloy, and it also increases cyclic endurance. Test specimens prepared by the SLM method, after heat treatment and after HIP and heat treatment, as well as those hot-rolled and heat-treated, withstand 2·106 cycles during the first stage of loading at 340 MPa. With a subsequent increase in the load to 380 MPa, the best cyclic durability is shown by specimens in a hot-rolled heat-treated condition. In this case, specimens after HIP and heat treatment show a reduction of twice the cycle time from the hot-rolled specimens, and the specimens obtained by the SLP method given heat treatment have an operating cycle an order of magnitude lower than for hot-rolled specimens. The SLM-specimens after HIP and heat treatment have characteristics comparable with hot-rolled heat-treated specimens for fatigue resistance required by the standard documents for products made of alloy EP708.

Effect of deformation mode, dynamic recrystallization and twinning on rolling texture evolution of AZ31 magnesium alloys

Abstract In order to obtain quantitative relationship between (0002) texture intensity and hot rolling conditions, conventional rolling experiments on AZ31 magnesium alloys were performed with 20%–40% reductions and temperatures within the range of 300–500 °C. Shear strain and equivalent strain distributions along the thickness of the rolled sheets were calculated experimentally using embedded pin in a rolling sheet. Rolling microstructures and textures in the sheet surface and center layers of the AZ31 alloys were measured by optical microscopy (OM), X-ray diffractometry (XRD) and electron back scatter diffraction (EBSD). Effects of the rolling strain, dynamic recrystallization (DRX) and twinning on the texture evolution of the AZ31 alloys were investigated quantitatively. It is found that the highest (0002) basal texture intensities are obtained at a starting rolling temperature of 400 °C under the same strain. Strain–temperature dependency of the (0002) texture intensity of the AZ31 alloy is derived.

Study of strength properties of semi-finished products from economically alloyed high-strength aluminium-scandium alloys for application in automobile transport and shipbuilding

Abstract The results of a study on the strength of rolled products from aluminium alloys doped with scandium under various processing conditions of hot and cold rolling are presented. The regularities of metal flow and the level of strength of deformed semi-finished products from aluminum-scandium alloys are established, depending on the total degree of deformation and the various modes of single reduction during rolling. It is shown that when using one heating of a cast billet to obtain high-quality semi-finished products, the temperature during the rolling process should not be lower than 350-370°, and the total degree of deformation does not exceed 50-60%. It was found that the semi-finished products from alloys with a content of scandium in the range 0.11-0.12% in the deformed state had elevated values of ultimate tensile strength and yield strength of the metal, which allows them to be recommended for industrial production of sheet metal products.

Influence of phase composition and microstructure on mechanical properties of hot-rolled Ti-χZr-4Al-0.005B alloys

The effects of phase composition and microstructure evolution on mechanical properties of hot-rolled Ti-χZr-4Al-0.005B alloys (abbreviated as, TχZAB with χ = 0, 10, 20, 30, and 40 wt%) were investigated by means of theoretical calculations, optical microscopy, scanning electron microscopy, and transmission electron microscopy. The as-prepared TχZAB alloys showed an excellent combination of the tensile strength and ductility features. For example, the hot-rolled T40ZAB alloy displayed the ultrahigh tensile strength of 1535 MPa at 6.06% elongation. As Zr content increased, the fracture morphologies revealed typical transitional processes from dimple to quasi-cleavage fracture surfaces. The theoretical calculations agreed well with results from X-ray diffraction, where examined alloys showed only α/α′ crystal phases. Under the same hot-rolled condition, the microstructure evolved from distorted (or broken) lamellar α phase to crisscross acicular α′ martensite phase as the Zr content increased. Finally, in search for ideal structural titanium alloys, phase composition and microstructure and relationship with mechanical properties were examined and discussed.

Hot Deformation Behavior of Al-Cu-Li-Mg-Zn-Zr-Sc Alloy in As-Cast and Hot-Rolled Condition

The results of physical simulation of hot compression of semi-finished products, selected from a cast ingot and hot-rolled plate from aluminum-lithium alloy V-1461, in the temperature range of 400-460°C and strain rates of 1-60 s-1are presented. It is established that at a constant strain rate the flow stresses decrease with increasing test temperature, an increase in the strain rate leads to an increase in flow stresses at a constant temperature. The parameters of the hot deformation rheological model, including the Zener-Hollomon parameter and the hyperbolic sine law, are determined. It is established that the parameters of the rheological model for the cast and hot-rolled state differ insignificantly.

Microstructure, texture and mechanical properties of hot rolled and annealed Ni-Fe-W and Ni-Fe-W-Co matrix alloys

Present work describes microstructure, texture and mechanical properties of hot rolled and annealed matrix Alloys (Ni-29Fe-18W (A1), Ni-29Fe-18W-5Co (A2), Ni-29Fe-18W-10Co (A3) and Ni-10Fe-30W-16Co (A4)). These alloys exhibit single fcc γ phase in hot rolled and annealed condition. The lattice constant and hardness values of A1 and A4 are smallest and largest among all the alloys, respectively. Microstructures of all the alloys display equiaxed grains along with annealing twins. The overall grains are quite fine in alloy A4 in comparison to those of the other alloys. The overall textures of hot rolled and annealed samples of all the four alloys are weak exhibiting low to moderate values of in plane anisotropy and anisotropy index. The strength of the alloy A1 is smallest while A4 displays both highest strength and maximum ductility. The flow curves of all the alloys exhibit two slopes at low and high strain regimes, respectively and follow Ludwigson constitutive equation. The differential curves of all the alloys shows three typical stages of work hardening. Dislocation controlled strain hardening occurs in all the three stages of these alloys and slip is the predominant deformation mechanism during tensile testing.

Effect of Hot-rolling Conditions on Texture and R-value of 16%Cr Ferritic Stainless Steel

Effect of Hot-rolling Conditions on Texture and R-value of 16%Cr Ferritic Stainless Steel