As-cast Strip Research Articles

Simple route to produce excellent mechanical properties of 9Mn steel with heterostructure induced by pre-existing austenite with sub-rapid solidification

Medium-Mn steels have garnered significant interest due to their unique combination of high strength and exceptional ductility. However, a high Mn content inevitably causes the macro-segregation of Mn, which can significantly compromise the mechanical properties. This study effectively prevented the formation of Mn macro-segregation by employing the sub-rapid solidification. It resulted in the distribution of Mn micro-segregation bands within dendritic gaps in Fe-9Mn-2Si-0.5Al-0.1C steel. Mn micro-segregation bands results in a high proportion of pre-existing austenite (γpre) with small size and suitable stability in the as-cast strip, forming a lamellar structure with alternating distribution of lath martensite and austenite on the micrometer scale. The as-cast strip necessitates only basic simple hot rolling control without the need for any tempering treatment to achieve excellent mechanical properties comparable to conventional lengthy processes (ultimate tensile strength (UTS) of 1762 MPa, total elongation (TE) of 20 %, and product of strength and elongation (PSE) up to 35 GPa%). Utilizing this structure as a foundation, a simple austenite reverse tempering (ART) treatment can lead to additional enhancements in comprehensive mechanical characteristics with the UTS of 1529 MPa, TE of 25 % and PSE of 38 GPa%.

Sheet Forming of Roll Cast Aluminum Alloy for Die Casting

This study explored the capability of sheet forming of JIS ADC12 aluminum alloy, commonly used for die casting. Despite the poor ductility of ADC12, we attempted to improve this property by applying rapid solidification through an unequal diameter twin roll caster. A strip with a thickness of 3.7 mm was cast at a speed of 20 m/min. The as-cast strip was then cold rolled and annealed to investigate its sheet-formability by deep drawing, three-roll bending and V-bending. This research also investigated the elements of ADC12 that contribute to poor ductility, with a focus on the impact of Mg, Cu, Fe, and Zn during the deep drawing process.

Reduction of Surface Cracking for Al-4.6%Mg Strips Cast Surface Using an Unequal-Diameter Twin-Roll Caster by Back-Dam Plate with Lip

Cracks occur on the surface of Al-Mg strips cast using a high-speed twin-roll caster. Surface cracking of the as-cast strip decreases with decreasing roll load. However, the difficulty of roll casting increases as the roll load is decreased because the strip becomes brittle and is easily broken because the strip is not completely solidified. In the present study, an unequal-diameter twin-roll caster, which is capable of high-speed casting, was used with a lip attached to a back-dam plate in an attempt to decrease surface cracking without deceasing the roll load. The thickness of the solidified layer was found to decrease as the length of the solidified region decreased. The thickness of the solidified layer at the center of the width direction of a strip on the lower roll decreased by shortening the solidification length by a lip attached to a back dam-plate. The solidified layer at the edges was thicker than that inside the cast strip. The thickness of semisolid metal inside the cast strip increased more than that at the edges of the roll bite. The roll load at the width of the lip decreased. The effect of the lip length on surface cracks was investigated.

Microstructure, properties and deformation mechanism of HCCM horizontal continuous casting Cu–Ni–Co–Si alloy strip during cold rolling

Cu-1.3 wt%Ni-1.0 wt%Co-0.9 wt%Si-0.1 wt%Mg alloy strip with 10 mm in thickness produced by heating-cooling combined mold (HCCM) horizontal continuous casting was cold rolled. Microstructure evolution and mechanical properties of the cold-rolled alloy strips with different reduction were studied, and the deformation mechanism was clarified. The results showed that the continuous casting strips had axial columnar grain with main <001> orientations and straight small angle grain boundaries, the elongation after fracture was up to 25.0%, which can be directly processed by large deformation cold rolling, and the maximum cumulative cold deformation was up to 99%.When the reduction was 40% and 60%, the dislocation bands crossed each other and shear bands formed, and the alternating distribution of soft/hard oriented grains were conducive to improve the deformation coordination ability of micro-region under high strain. When the deformation exceeded 80%, deformation twins formed and the twins had strong interaction with the shear band and grain boundaries, resulting in strong shear and rotation of the local grains. The tensile strength and hardness increased from 464 MPa to 137HV of the as-cast strip to 629 MPa and 208HV with reduction 90%, respectively, while the elongation decreased from 25.0% to 4.1%. These results can lay a foundation for the development of compact method for producing high performance Cu–Ni–Co–Si alloy strips.

Effect of cooling rate on the order degree, residual stress, and room temperature mechanical properties of Fe-6.5wt.%Si alloy

The top side-pouring twin-roll casting (TSTRC) process was used to prepare a 100 × 1.7 mm non-oriented Fe-6.5 wt% Si alloy as-cast strip. The as-cast strip is directly rolled at 700 °C into 0.4 mm without the intermediate hot rolling step. This paper discusses the effects of different cooling rates in furnace cooling, air cooling, oil quenching, and water quenching on the order degree, residual stress, room temperature mechanical properties, and cold-rolled processing properties of Fe-6.5wt.%Si alloy after annealing of warm-rolled sheets are systematically investigated. Meanwhile, the effects of order degree, residual stress, and grain boundary element segregation on the mechanical properties were analyzed. The results show that as the cooling rate increases, the order degree of the Fe-6.5 wt% Si alloy decreases and the maximum residual tensile stress increases. The fracture modes of the furnace cooling, air cooling, and oil quenching samples are through-crystal disintegration fracture, and the fracture mode of the water quenching samples is an along-crystal fracture. The oil-quenched samples exhibit good room temperature plasticity due to the relatively low order degree and residual tensile stresses in the Fe-6.5wt.%Si alloy. Oil quenching improves the room temperature plasticity and cold rolling properties of Fe-6.5wt.%Si alloy warm rolled sheets, reduces edge cracks, and offers greater room temperature cold rolling processibility of the Fe-6.5wt.%Si alloy warm rolled sheets.

Strip Casting of Al-4.7%Mg with Impurity Fe Using a Single Roll Caster with a Scraper

Fe was added to Al-4.7%Mg to make model alloys of recycled Al-Mg alloy. The effect of Fe addition on the mechanical properties of the Al-4.7%Mg strip cast using a single-roll caster equipped with a scraper was investigated. The added Fe content was 0.2, 0.4, 0.6, and 0.8%. The as-cast strip cast at 30 m/min was cold rolled down to a thickness of 1 mm thick annealed to conduct a tensile test and a cup test. The as-cast strip could be cold rolled without cracking. The tensile stress and the 0.2% proof stress were only slightly affected by the addition of Fe. The elongation gradually decreased as the Fe content increased. When the Fe content was 0.8%, the elongation in the casting direction was 27.7%. The limiting drawing ratio did not deteriorate until the Fe content was 0.4%. When the Fe content was 0.4% and 0.8%, the limiting drawing ratios were 2.0 and 1.7, respectively.

Alleviating segregation and enhancing tensile properties of Inconel 718 superalloy by twin-roll casting and two-stage cold rolling

A novel processing route involving twin-roll casting and two-stage cold rolling was proposed to manufacture Inconel 718 alloy. Due to the sub-rapid solidification rate (412.5 °C/s) of as-cast strip, the element segregation can be alleviated and the growth of Laves phase was effectively suppressed. It was also observed that the dissolution of Laves phases during subsequent homogenization was significantly accelerated because of their refined size. The corresponding homogenization time can be shortened from dozens of hours to 1 h. Additionally, the non-uniform microstructure of cold-rolled and annealed samples caused by coarse grains from homogenization treatment can be eliminated by two-stage cold rolling method. Furthermore, a large amount of granular δ phases precipitated during intermediate annealing. After double aging treatment, the final products exhibited an excellent combination of strength and elongation. The ultimate tensile strength when deformed at room temperature and at 650 °C were about 1475 and 1120 MPa, and the corresponding total elongation were ∼ 15% and ∼ 22%. These results indicated that the twin-roll casting was a promising route to produce Inconel 718 alloy.

Effect of Σ3 grain boundaries on microstructure and properties of oriented Fe-6.5 wt%Si in twin-roll strip casting

Oriented Fe-6.5 wt%Si alloy with excellent magnetic properties was prepared by twin-roll strip casting (TRSC). We studied the abnormal Σ3 grain boundaries in the as-cast strip. The experimental results demonstrated that the Σ3 grain boundary (GB) in oriented Fe-6.5 wt%Si steel had a good thermal stability, which could refine the microstructure by inhibiting growth of structure in as-cast strip. Moreover, the Σ3 GB in Fe-6.5 wt%Si as-cast strip could improve the toughness of matrix and restrain the propagation of cracks, which was beneficial to its plastic working. The Σ3 GB was relatively stable during warm rolling and could be inherited partly after annealing. At the same time, the low migration rate of Σ3 GB in primary recrystallization structure could stabilize the matrix and help to obtain the abnormal growth of Goss grains. The finished Fe-6.5 wt%Si steel had excellent magnetic properties, B800 and P10/50 were 1.76 T and 0.59 W/kg, respectively.

Effect of test temperature on tensile behavior of Fe-6.5wt.%Si alloy as-cast strip

The non-oriented Fe-6.5wt.%Si alloy as-cast strip is prepared by the top side-pouring twin-roll casting (TSTRC) process and the solidification structure of the as-cast strip is a uniform fine equiaxed grain structure. This paper studied the mechanical properties, fracture morphology, ordered phase morphology, and types of Fe-6.5wt.%Si alloy as-cast strips at different temperatures. The results show that the yield and tensile strength of the as-cast strip decreased gradually with the increase of tensile temperature, and the elongation after fracture increased gradually. The temperature rise prevented the formation of cleavage cracks, and the temperature rise is an effective method to improve the plasticity of Fe-6.5wt.%Si alloys. Concurrently, the ambient temperature is the main factor determining the tensile mechanical properties of Fe-6.5wt.%Si alloy at medium temperature. When the stretching temperature exceeds 500 °C, the Fe-6.5wt.%Si alloy has apparent plastic deformation ability. The Fe-6.5wt.%Si alloy exhibits excellent elongation when the stretching temperature is 700 °C. The serration fluctuations that appear on the 400 °C stretch curve should be attributed to the Portevin-Le Chatelier (PLC) effect caused by the reordering of the antiphase domains and the deformation-induced disorder. The Fe-6.5wt.%Si alloy as-cast strip is directly subjected to warm-rolling without the hot-rolling. When the warm-rolling is performed at the temperature of 700 °C, there are almost no cracks at the edge of the plate, the edge cracks are effectively controlled, and the surface quality of the warm-rolled sheet is fine. The obtained 700 °C warm-rolled sheets were cold-rolled at room temperature, and after recrystallization annealing, the sample had good comprehensive magnetic properties. Suppose the TSTRC-warm rolling-cold rolling-annealing process prepares the Fe-6.5wt.%Si alloy cold-rolled sheet. In that case, the production efficiency will be significantly improved, the process flow will be shortened, and the goal of energy-saving and emission reduction will be achieved.

Twin-Roll Casting of Al-4.8%Mg Alloy with Added Fe

Fe (0.2, 0.4, 0.6, and 0.8 %) was added to roll-cast Al-4.8%Mg alloy to create a model of recycled Al-4.8%Mg and its effect was investigated. An unequal-diameter twin-roll caster was used. The roll speed was 20 m/min. An as-cast strip was cold-rolled down to 1 mm and annealed. Its mechanical properties were then evaluated. The surface condition of the as-cast strip was not influenced by the Fe content. The thickness of the as-cast strip decreased with increasing Fe content. The tensile strength and 0.2% proof stress increased with Fe content up to 0.4%Fe and then decreased. When 0.8% Fe was added to Al-4.8%Mg, the tensile strength and 0.2% proof stress became higher than those for Al-Mg. Elongation and the limiting drawing ratio gradually decreased with increasing Fe content. When 0.8% Fe was added, elongation in the lateral direction was 19.6% and the limiting drawing ratio was 1.7.

Effect of Casting Condition on Ripple Mark and Surface Crack of Roll-Cast Al-Mg Alloy

Effect of casting conditions on ripple mark and surface crack of as-cast Al-4.7%Mg strip was investigated. A vertical type high speed twin roll caster was used. A casting speed was 30 m/min. Casting conditions were tip-shape of a back-dam plate, gap between a roll and the back dam plate and texture on the roll-surface. The texture on the roll-surface was useful to reduce the ripple mark. In bending test conducted to investigate surface crack of as-cast strip, the texture on the roll surface was effective to the reduce the crack. The position of the crack was not coin side with the position of the ripple mark. This result shows that there is no correlation between the ripple mark and the ductility or the strength of as-cast strip. Small roll load was effective to reduce the crack and degree of the ripple mark. Effect of the roll load on the ripple mark was discussed including solidification delay and seepage of Magnesium.

Role of Hot Rolling in Microstructure and Texture Development of Strip Cast Non-Oriented Electrical Steel

In this study, the effect of the hot-cold rolling process on the evolution of the microstructure, texture and magnetic properties of strip-cast non-oriented electrical steel was investigated by introducing hot rolling with different reductions. The results indicate that hot rolling with an appropriate reduction, such as the 20% used in this study, increases the shear bands and {100} deformed microstructure in the cold roll sheet. As a result, in our study, enhanced η and Cube recrystallization texture and the improved magnetic induction were obtained. However, hot rolling with excessive reduction (36–52%) decreased the shear bands and increased the α-oriented deformation microstructure with low stored energy. It enhanced the α recrystallization texture and weakened the η texture, resulting in a decrease in the magnetic induction. In addition, hot rolling promoted the precipitation of supersaturated solid solution elements in the as-cast strip, thereby affecting the subsequent microstructure evolution and the optimization of its magnetic properties.

The microstructure of high manganese TWIP steels produced via simulated direct strip casting

Three TWIP steels based on the composition Fe-23Mn-3Si-3.3Al with different carbon concentrations were examined. The alloys were produced by rapid solidification in an experimental apparatus designed to simulate direct strip casting conditions. Examination of the driving force for solidification for this alloy showed the preference for BCC and FCC solidification were very close for this composition, within 10% of one another. This factor combined with the high undercooling resulted in the change in the primary solidified phase. Chemical analysis of the as-cast strip showed inter-dendritic segregation of Si and Al, but negligible segregation of Mn. A simple heat treatment was sufficient to chemically homogenise all alloys and produce microstructures comprising a fully austenitic structure, consistent with thermodynamic predictions.

Effect of rolling reduction on microstructure, texture and magnetic properties of twin-roll casting non-oriented 6.5 wt% Si electrical steel

In this study, an as-cast strip of non-oriented 6.5 wt% Si electrical steel with an equiaxed structure was fabricated by twin-roll strip casting and then treated by hot and warm rolling with different reductions, and annealing. The results showed that the as-cast microstructure was gradually pancaked and then underwent dynamic and static recrystallization as the hot rolling reduction exceeded 52%. The subsequent warm rolling brought about shear bands in part of the deformed grains. The texture evolution in the multiple rolling routes basically conformed to the classical gain-orientation rotating paths. The {001}∼{118} 〈110〉, {223} 〈110〉 and {111} 〈110〉 texture components were intensified after warm rolling. A decreased hot rolling reduction accompanied by an increased warm rolling reduction raised the number of shear bands in the warm rolled sheets and decreased the annealing grain size. An improper combination of hot and warm rolling reductions tended to make the γ nuclei gain the superiority in number through grain-boundary or shear-band nucleation, leading to the prevalence of the γ annealing texture. By comparison, an alternative rolling regime adopting moderate hot (∼50%) and warm rolling (∼70%) reductions promoted the oriented nucleation of λ, {114} 〈48¯1〉 and many other non-γ nuclei in shear bands of the {223} 〈110〉 deformed grains which had already acquired a high volume fraction in the warm rolled sheet. Consequently, mixed λ, α* and γ annealing textures were formed, giving rise to enhanced magnetic properties. The combined oriented nucleation and oriented growth mechanism was responsible for the overall evolutions of the annealing textures.

Thin-gauge non-oriented silicon steel with balanced magnetic and mechanical properties processed by strip casting

Thin-gauge non-oriented silicon steel with high strength was successfully processed using strip casting. Texture evolution and strengthening mechanism via nanoscale Cu-rich precipitates were studied to fundamentally understand the balanced combination of magnetic properties and mechanical properties. Coarse equiaxed grains with average size of ∼190 μm and relatively random texture were formed in the as-cast strip, which contributed to the inhomogeneous deformation, resulting in high density of shear bands. Exact Cube was retained from the initial Cube texture and new Goss was formed during the heavy rolling process in the 0.20 mm cold rolled sheet, which promoted relatively strong Cube and Goss texture after recrystallization annealing. The 0.20 mm annealed sheet exhibited high magnetic induction of 1.709 T, which corresponds to the high texture factor of 0.5. The total iron losses were significantly reduced with decrease in thickness, and the P1.5/50, P1.0/400, and P1.0/1000 in 0.20 mm sheet were as low as 2.63, 15.17 and 55.63 W/kg, respectively, which showed a good match between magnetic induction and iron loss. During the aging process, both the magnetic induction and total iron loss exhibited relatively good stability. With increase in aging time, the yield strength first rapidly increased and then slightly decreased. In 0.20 mm sheet, peak yield strength of ∼630 MPa was obtained on aging at 550 °C for 90–120 min. The key mechanism of precipitation strengthening was attributed to the difference in modulus and coherency strain associated with high density of nanoscale precipitates of ∼5 nm. The study revealed that the nanoscale Cu-rich precipitates can be adopted as effective approach to increase the yield strength over ∼100 MPa without deteriorating iron loss in thin-gauge non-oriented silicon steel by strip casting, which guaranteed the balance of magnetic properties and mechanical properties to meet the requirements of high-speed motor.

Effects of Nozzle and Roll on Surface Condition of Al-1%Si Strip Cast Using Vertical type High Speed Twin Roll Caster

When a strip of Al-Si alloy with an Si content of 1% was cast using a vertical-type high-speed twin-roll caster, cracks form in its surface. The effects of the pouring method, the shape and position of the nozzle, and the roll surface texture on surface crack formation were evaluated with a roll caster. The rolls were made of a copper alloy, and the roll speed was 30 m/min. The as-cast strips were bent to investigate the degree of crack formation, and the outer surface of the strips was observed without magnification and with a stereomicroscope to determine the influence of the pouring method, the shape and position of the nozzle, and the roll surface. A roll machined to form V-shaped grooves 0.4 mm deep on the surface of the strips was most useful for reducing surface cracking. Changing the shape of the nozzle tip was second-most effective. There was a clear correlation between the roll surface condition and surface cracking in the Al-Si strip.

Effect of cold rolling on microstructure and texture evolution in strip casting Fe-36%Ni invar alloy foil

A new processing route including strip casting, cold rolling and annealing was proposed to manufacture the 0.05 mm-thick Fe-36%Ni invar alloy foil. The as-cast strip had coarse columnar austenite grains and pronounced {100}<0vw>fiber texture due to the high melt superheat during strip casting. The severe cold rolling in one-stage cold rolling route led to inhomogeneous deformed microstructures and strong copper-type textures. The striking features were the absence of Cube texture ({001}<100>) in the 0.05 mm-thick cold rolled strip and the appearance of {001}<310>texture after annealing, differing from the results that sharp Cube texture was normally the unique annealing texture in case of severe cold rolling. By contrast, two-stage cold rolling route led to the sharp Cube texture after final annealing even the cold rolling reduction was as high as 92.9%. The different microstructures prior to final cold rolling may be responsible for the evolution of Cube and {001}<310>texture in various routes.

The influence of Zener drag on recrystallization behaviour of twin-roll cast AA8079 alloy after homogenization

Intermediate annealing is a crucial step of aluminum foil production. The as-cast material hardens during rolling and an annealing step is required at intermediate gauges to soften the material and restore its ductility. Generally, fine recrystallized structure could assure sufficient ductility for further rolling and processing. Recrystallization of the material during intermediate annealing can be controlled by a microstructure tailored during homogenization. Recrystallization behaviour of a twin-roll cast aluminum alloy AA8079 was studied. The as-cast strip was homogenized at 420 °C and 580 °C and rolled down to two different thicknesses. Evolution of microstructure of rolled materials during a model intermediate annealing was studied, and Zener drag and particle stimulated nucleation were determined as mechanisms controlling recrystallization.

Characterization of AA6111 aluminum alloy thin strips produced via the horizontal single belt casting process

ABSTRACT In this research, AA6111 aluminum alloy strips, 250 mm wide and ~6 mm thick, were produced via the horizontal single belt casting process. The strip microstructure was analyzed using optical and scanning electron microscopy, and the measured average grain size was 90 μm. This is significantly smaller than the average grain size of the products produced via direct chill (DC) casting route (i.e., 231 μm). An analysis of intermetallic compounds was also conducted using energy dispersive spectroscopy. These were observed to be distributed within and along the grain boundaries and are enriched in Mg, Si, and Cu. The shear punch test was performed to determine the ultimate tensile strength of the cast strip, which was observed to be 280 MPa. This value is significantly higher than the strength documented in the literature for DC cast products. A 3D profilometer was used to determine the top and bottom surface roughness of the as-cast AA6111 strips. The strip top surface was found to lie within 120 μm range, whilst the bottom surface roughness was less than 30 μm.

Microstructure and mechanical properties of a Fe–28Mn–9Al-1.2C-(0, 3, 6, 9)Cr austenitic low-density steel

In this work, the effects of Cr addition on microstructure, carbide formation and mechanical properties of Fe–28Mn–9Al-1.2C-xCr (x = 0, 3, 6, 9) strips fabricated under a near-rapid solidification condition are investigated. It is found that Cr addition makes as-cast strips present a nonlinear evolution on yield strength, i.e. firstly reduces and then increases beyond that of Cr-free strip, and the total elongation of as-cast strips clearly decreases. The evolution is related to precipitation reduction of κ-carbides, increased dislocation density, and formation of Cr23C6 instead of κ-carbides in 9Cr strip with Cr addition. Annealing at 550 °C for 5 h enhances yield strengths of all strips due to more carbide precipitations. An observed unusual phenomenon is that after annealing, Cr-free strip shows lower total elongation than the as-cast strip, while all Cr-containing strips show higher total elongation due to reduction of dislocations. Formation of Cr23C6 carbides at austenite grain boundaries is a reason for the lowest ductility of as-cast and annealed strips containing 9 wt% Cr. Analysis in 0Cr and 6Cr strips indicates that both slip bands and dislocations contribute to ductility of this austenitic low-density steel.