Direct Rolling Process Research Articles

Investigation on the microstructure and mechanical properties of 5356 aluminum alloy wire in continuous casting direct rolling process

Investigation on the microstructure and mechanical properties of 5356 aluminum alloy wire in continuous casting direct rolling process

Research on deformation behaviors at different temperatures of lean duplex stainless steel S32101 produced by direct cold rolling process

In this paper, the mechanical properties, work hardening characteristics and deformation mechanism of lean duplex stainless steel (LDSS) S32101 produced by direct cold rolling were studied under different temperature conditions. The yield strength (YS) and tensile strength (TS) of S32101 decreased with the increase of deformation temperature, while the elongation increased first and then decreased. The TS of S32101 at −70 °C was 1052.6 MPa, the elongation remained 57.2%, and the product of strength and elongation (PSE) was as high as 60.2 GPa·%, which was mainly due to the synergistic strengthening of transformation induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects in austenite at cryogenic temperatures. The efficiency of grain refinement at cryogenic temperature was improved by TRIP effect and deformation twins (DTs), indicating that it had the potential to be applied at low temperature (−70 ∼ −30°C). Moreover, the high density nanotwins and the strong interaction between the dislocation and nanotwin bundles also contributed to strain hardening at low temperatures and thus better comprehensive mechanical properties could be achieved.

Designing the heterogeneous microstructure via a direct warm rolling process to synergistically enhance the strength-ductility in a medium Mn steel

This work introduced a facile method for fabricating heterostructures in a medium Mn steel via a direct warm rolling process. The heavy warm rolling promoted the transformation of metastable austenite (∼12.2 vol%) into hard domain α’ martensite, which formed a heterogeneous microstructure with the untransformed γ (soft domain). After 600 °C re-annealing, the hard domain α’ re-reversed to α + γ, and the heterostructure disappeared. Compared to the homogeneous structure, the heterostructure exhibited the synergistic enhancement of strength-ductility (yield strength (YS): 782 → 1113 MPa; ultimate tensile strength (UTS): 1099 → 1304 MPa; total elongation (TEL): 20.8 % → 21.7 %). Quantitative analysis showed that the heterogeneous deformation induced (HDI) strengthening (∼261 MPa) was the primary contributor to the increased ΔYS (782 → 1113 MPa) value, rather than the traditional strengthening mechanisms. Transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) effect were the main deformation mechanisms of both homogeneous/heterogeneous structures. However, compared to the homogeneous microstructure, the heterogeneous structure possessed the more pronounced TRIP and HDI hardening effects as well as L-C locks, the cooperative effect of these three factors further improved the strain hardening ability to break through the strength-ductility trade-off dilemma.

Effects of Heat-Treatment and Cold-Rolling on Mechanical Properties and Impact Failure Resistance of New Al 6082 Aluminum Alloy by Continuous Casting Direct Rolling Process.

Al 6082 aluminum alloy has excellent corrosion resistance, strength, and formability. However, owing to the recrystallization effect of a hot working process, coarse grains form easily in this material, which reduces its strength and service life. The novel continuous casting direct rolling (CCDR) method can prevent the deterioration of this material. Thus, we used CCDR Al 6082 aluminum alloy as the research material in this study. By subjecting a CCDR Al 6082 aluminum alloy to heat treatment (T4 and T6) and cold rolling, the influence of recrystallization effect on its mechanical properties and on impact failure resistance were explored. The results demonstrated that the specimen subjected to T4 heat treatment had a higher elongation and that the specimen subjected to T6 heat treatment had a higher strength. After cold rolling, the hardness and strength of the specimens subjected to different heat treatments (coded T4R4 and T6R4) increased because of the work's hardening effect. Moreover, the elongations of both specimens decreased, but they were higher than the industrial standard (>10%). The strength of specimen T6R4 was higher (up to 400 MPa) than specimen T4R4. Moreover, relative to specimen T4R4, specimen T6R4 had greater tensile and Charpy impact failure toughness.

Influence of silicon and tramp elements on the high-temperature oxidation of steel in direct casting and rolling processes

Influence of silicon and tramp elements on the high-temperature oxidation of steel in direct casting and rolling processes

Microstructure and corrosion resistance of commercial purity aluminum sheet manufactured by continuous casting direct rolling after ultrasonic melt pre-treatment

During the new continuous casting direct rolling (CCDR) process for manufacturing commercially pure aluminum sheet for foils, casting defects tend to arise as the raw material with huge mass flow rapidly solidifies under a high cooling rate, which generates negative effects on the formability of aluminum sheets and the performance of final foil products. Therefore, melt pre-treatment during continuous casting is very essential to improve the quality of the billet. In this study, multi-source ultrasonic field was employed to pretreat an Al melt during the continuous casting stage in a Hazelett CCDR strip production line. The Ti content distribution in the melt, the microstructure and corrosion behaviors of the rolled sheet with and without ultrasonic melt pre-treatment (UMPT) were investigated. The microstructure of the rolled sheet was refined due to the increased Ti content and uniformly distributed Al3Ti particles under UMPT. In addition, the morphology of the Fe-containing secondary phase was modified from an aggregated to a scattered structure, with reduced continuity. As a result, under the combined effects of the refined α-Al grains and secondary phase, the corrosion resistance of the rolled sheet was improved. The underlying mechanisms for the modifications of the microstructure and corrosion resistance after UMPT are also interpreted, which gives theoretical guidance on the practical applications of the ultrasound-assisted continuous casting in industrial production.

Tailoring retained austenite and mechanical property improvement in Al–Si–V containing medium Mn steel via direct intercritical rolling

Medium Mn steels are promising candidates for the third-generation advanced high strength steels. However, it shows a distinct limit of mechanical property under conventional hot-rolling and intercritical annealing procedures. Aiming at improving the combination of strength, ductility and toughness, the present study proposed a multi-alloyed design principle together with a direct intercritical rolling process. The results show that the microstructure of the hot rolled steel consisted of wide delta ferrite, lath martensite, twinned-martensite and coarse retained austenite with a low stability, corresponding to a product of strength and elongation (PSE) of 24.0 GPa% and an impact toughness of 13.8 J/cm2 at −40 °C. In contrast, the intercritical rolling produced a laminated microstructure containing thin delta ferrite, submicron recrystallized ferrite and retained austenite. The PSE and impact toughness at −40 °C simultaneously increased to 46.1 GPa% and 46.7 J/cm2, respectively, which was also much higher than the hot rolled steel subjected to low temperature and high temperature annealing. The significant enhancement of mechanical property was mainly attributed to the highest content and optimal stability of retained austenite caused by the submicron grain size, high density of dislocations, granular morphology, and elemental enrichment. The optimized austenite stability provided persistent transformation-induced plasticity (TRIP) effect for work hardening and damage resistance. Moreover, the nano-sized VC precipitates in the intercritical rolled steel played a significant role in reaching an ultrahigh yield strength of ∼1 GPa. This study not only provides a very simple pathway to improve the mechanical property of medium Mn steel, but also sheds light on the design and development of high-performance materials.

Simulation on the Direct Powder Rolling Process of Cu Powder by Drucker–Prager/Cap Model and Its Experimental Verification

For better clarifying the influence of processing factors on the forming quality of the direct powder rolling (DPR) process, finite element simulation based on the modified Drucker–Prager/Cap (DPC) model was established and the key physical parameters of the powder were confirmed by experimental measurements. Subsequently, the effect of the main factors in the DPR process, viz., powder gradation, rolling speed and rolling gap, on the density and morphology of a green sheet were discussed by using an orthogonal experiment design followed by experimental verification. The influence of DPR parameters on the density of the green sheet is examined by a range analysis, which can reflect the sensitivity of influencing factors to the forming quality of the green sheet. The larger the range value is, the more sensitive the influencing factor is. This suggests that the quality of the green sheet is mainly influenced by particle gradation. The results show that the density of the resulting DPR green sheet with optimal parameters is mainly 7.5~8.0 g/cm3, reaches 80% of the theoretical density, and the mechanical strength can also afford the transferring process of the green sheet for the next sintering craft. The methods for modeling, obtaining physical parameters and the numerical simulation results can be used to guide rapid formation of the metal sheet by using direct powder rolling craft.

New comprehension on the microstructure, texture and deformation behaviors of UNS S32101 duplex stainless steel fabricated by direct cold rolling process

The effect of cold deformation on the detailed microstructure evolution, texture development and deformation behaviors/mechanisms of UNS S32101 duplex stainless steel (DSS2101) during the direct cold rolling process was investigated. The results showed that throughout the cold deformation process, the negative texture of {001}<110> component was nonexistent in deformed ferrite, and most texture components were mainly concentrated on α/γ-fibers. Detwinning in austenite was substantial responsible for the reorientation in {111}<112> towards {111}<110> of γ-fiber in ferrite rather than martensite transformation. Austenite texture were composed of {110}<100> Goss and {110}<115> Goss/Brass components at heavy deformation (50% and 70%). The refinement and deformation behavior in ferrite was attributed to microbands (MBs) subdivision and dislocation activities, whilst that of austenite mainly occurred through twinning, strain induced detwinning (SID) and strain induced martensite (SIM).

New Comprehension on the Microstructure, Texture and Deformation Behaviors of Uns S32101 Fabricated by Direct Cold Rolling Process

New Comprehension on the Microstructure, Texture and Deformation Behaviors of Uns S32101 Fabricated by Direct Cold Rolling Process

Study on Microstructure, Mechanical Properties and Erosion Characteristics of Al-Si Alloy Manufactured by Continuous Casting Direct Rolling Process

Al-Si alloys exhibit promising wear resistance, thus being mainly employed to weld Al alloy parts and processed into components of equipment. During the new continuous casting direct rolling (CCDR) process, the raw material gradually cools and solidifies, simultaneously plastically deformed. Hence, the materials manufactured through the CCDR process presented an unparalleled microstructure. The experimental results indicated that the strength of the CCDR Al-Si alloy can be increased through cold rolling. A two-stage heat treatment (solid solution and aging treatment) was introduced to improve the ductility and satisfy the industrial application. Furthermore, the erosion wear characteristics and fracture mechanism of the CCDR Al-Si alloy dominated by the ductility were confirmed. Both cold rolling specimens (FR) and those with heat treatment (FRH) showed greater wear resistance than as-manufactured (F). The FR specimens exhibited greater wear resistance owing to a higher Al matrix strength at a lower impact angle; on the other hand, at a higher impact angle, the FRH specimens with a softer Al matrix presented better wear resistance due to the formation of a lip structure to reduce material removal. The TEM results confirmed that the nanoscale grains formation was induced in the erosion-affected region and affected the Si concentration. Conclusively, the heat-treated CCDR Al-Si alloy possessed excellent erosion resistance and workability, which can serve as a reference processed as wear-resistant mechanical parts.

Rolling parameters, microstructure control, and mechanical properties of powder metallurgy Ti–44Al–3Nb-(Mo, V, Y) alloy: The impact of rolling temperatures

Flow softening behavior, microstructure evolution and hot working parameters of powder metallurgy Ti–44Al–3Nb-(Mo, V, Y) alloy were systematically studied by isothermal hot compression. Based on the analysis of processing maps and the corresponding microstructure, power dissipation efficiency peak occurred at two domains, which were associated with dynamic recrystallization (DRX) and super-plasticity. Pile-up of high density dislocation and a large number of twins were the primary deformation mechanisms at low temperature and high strain rate. As the temperature increases, fine DRX grains promote the movement and rotation of grain boundary, the softening of β phase and the transformation of β→α/α2+γ above 1200 °C improve the deformation capacity of the alloy significantly. Crack-free TiAl sheets were successfully obtained by direct hot rolling process at 1080 °C and 1220 °C. The corresponding microstructure and mechanical properties were analyzed. The sheets rolled at 1080 °C was characterized by near γ (NG)+β0 microstructure with a streamline along the rolling direction, while duplex (DP)+β0 microstructure appeared to be the main microstructure at rolling temperature of 1220 °C. The as-rolled sheet exhibits excellent mechanical properties at 800 °C. The sheet rolled at 1080 °C exhibits 320 MPa yield strength and 468 MPa ultimate tensile strength with 142% elongation. The yield strength, ultimate tensile strength, and elongation of the as-rolled sheet are 446 MPa, 586 MPa, and 3.0%, respectively, when rolled at 1220 °C. The excellent ductility of the sample rolled at 1080 °C is attributed to formation of fine DRX grains due to consumption of twins and substructure under tensile stress, which promote grain boundary slip. Lamellar colonies with fine interlamellar spacing and α2 laths formed at 1220 °C can effectively prevent dislocation motion, resulting in a significant increase in the strength of the alloy.

Application of Queuing Theory in Production Efficiency of Direct Rolling Process of Long Product

Based on the mathematical method of queuing theory, the queuing model of billets in the direct rolling process of the long product was established, which represented the conveying process of billets at the casting and rolling interface. Using the billets queuing model, the influence of different steel quantity, length, speed and other factors on the average waiting time of a single billet in the direct rolling production process was analyzed. Combined with the temperature drop of billets, the optimal average waiting time for a single billet was determined. The method improved the conveying connection efficiency of the casting-rolling interface and the direct rolling rate of billets.

Effect of alloying additions on work hardening, dynamic recrystallization, and mechanical properties of Ti–44Al–5Nb–1Mo alloys during direct hot-pack rolling

There is significant gap in the understanding of the effect of alloying elements, particularly V and B, on the dynamic recrystallization (DRX) behavior, and the corresponding microstructure evolution in Ti–44Al–5Nb–1Mo-(V, B) alloys during uniaxial hot compression. In this regard, we have studied here the relationship of work hardening rate (θ) and critical strain of dynamic recrystallization (εc) on strain, deformation parameters. The θ values showed typical dynamic recrystallization characteristics, and were sensitive to temperature and strain rate. Deformation mechanism involving twinning-dislocation interactions and phase transformation contributed to characteristics of θ. DRX occurred in Ti–44Al–5Nb–1Mo–2V-0.2B alloys even at higher rolling speed and at ambient temperatures over a wide range, which implied a wider processing window during the direct hot-pack rolling process. Crack-free sheets were directly obtained from the as-HIPed alloys at 1250 oC with rolling speeds of 0.3 m/s, and 10%–20% reduction per pass. Their microstructure, high-temperature tensile properties and fracture mechanisms are discussed. As rolling progressed, Ti–44Al–5Nb–1Mo alloy was characterized by residual lamellae with locally dissolved α2 laths, broadening γ laths, and fine sub-grains. Dislocation-induced DRX and phase transformation of α2/γ lamellae were the primary deformation modes. In contrast, on the addition of V and B, deformation twinning was activated. Multi-phase microstructure was characterized by equiaxed grains of ~ 5–20 μm. The as-rolled sheets of both the alloys exhibited superior performance at 800 oC. Ti–44Al–5Nb–1Mo alloy showed a higher ultimate tensile stress of ~689 MPa, while superior ductility of greater than 75% was obtained for Ti–44Al–5Nb–1Mo–2V-0.2B alloy. The microstructure with different degree of dynamic recrystallization contributed to various aspects of high-temperature tensile properties.

Modified wear behavior of selective laser melted Ti6Al4V alloy by direct current assisted ultrasonic surface rolling process

Ti6Al4V alloy samples prepared by selective laser melting were treated by three different post-treatments: namely heat-treatment, ultrasonic surface rolling process (USRP) and direct current assisted ultrasonic surface rolling process (DC-USRP). Wear behaviors were evaluated using a block-on-disc rig under lubrication conditions. Results showed that the DC-USRP treated sample exhibited the lowest wear rate of 1 × 10−6 mm3 N−1 m−1, compared to that of the as-built (4 × 10−5 mm3 N−1 m−1), heat-treated (2 × 10−5 mm3 N−1 m−1) and USRP-treated samples (5 × 10−6 mm3 N−1 m−1). Consistent with changes in the wear rate, the friction coefficient was also gradually reduced. The as-built and heat-treated samples showed severe abrasive wear and delamination, while the USRP and DC-USRP treated samples displayed only mild abrasive wear. The improved wear resistance of the USRP and DC-USRP treated samples was attributed to the modified lubrication mechanism, increased hardness and compressive residual stress. Moreover, the wear resistance of the DC-USRP treated samples decreased with the increasing depth from the surface due to the effect of gradient work hardening.

A comparative corrosion study of titanium strips produced by wrought and direct powder rolling processes

Titanium is a light metal that has a high strength to weight ratio compared to steel. It has good corrosion resistance and is biocompatible. However, due to its high costs, its use has been limited mainly to the aerospace and medical industries. Direct powder rolling (DPR), a powder metallurgy (PM) method, is being developed with the aim of reducing the cost of producing titanium flat mill products. Critical to the success of the DPR produced products will be their ability to match or exceed the properties and performance behaviour of the equivalent products produced by wrought metallurgy. Titanium strips that are 89 % and 98 % dense were produced by DPR and their corrosion behaviour was compared to the wrought produced titanium strips. The corrosion tests were carried out in 1.75 wt.%, 2.0 wt.% and 3.5 wt.% NaCl solutions kept at 23 °C using potentiodynamic polarization. The polarization curves showed that the wrought strips were the most corrosion resistant, followed by the DPR-98 % then the DPR-89 %. The influence of pores on the corrosion behaviour was high, therefore, effort needs to be made to reduce the pores of the DPR samples.

Properties of Rolled AZ31 Magnesium Alloy Sheet Fabricated by Continuous Variable Cross-Section Direct Extrusion

Rolling is currently a widely used method for manufacturing and processing high-performance magnesium alloy sheets and has received widespread attention in recent years. Here, we combined continuous variable cross-section direct extrusion (CVCDE) and rolling processes. The microstructure and mechanical properties of the resulting sheets rolled at different temperatures from CVCDE extrudate were investigated by optical microscopy, scanning electron microscope, transmission electron microscopy and electron backscatter diffraction. The results showed that a fine-grained microstructure was present with an average grain size of 3.62 μm in sheets rolled from CVCDE extrudate at 623 K. Dynamic recrystallization and a large strain were induced by the multi-pass rolling, which resulted in grain refinement. In the 573-673 K range, the yield strength, tensile strength and elongation initially increased and then declined as the CVCDE temperature increased. The above results provide an important scientific basis of processing, manufacturing and the active control on microstructure and property for high-performance magnesium alloy sheet.

More than 25 Years of Experience in Thin Slab Casting and Rolling Current State of the Art and Future Developments

Industrial thin slab casting and direct rolling processing started more than 25 years ago with the world's first compact strip production (CSP®). Since that time, CSP® and competing thin slab casting and direct rolling concepts have been developed to a standard process for hot strip production. Typical features of this process are the homogeneous structural and mechanical properties all along the strip. The product range covers low carbon, as well as medium and high carbon steel grades comprising IF, HSLA, API, electrical, and AHSS multiphase steel grades. Hot strip from thin slab can be easily further processed to cold rolled and/or surface treated strip. A special feature is thin hot strip that may substitute cold rolled strip. Today, process and material developments, for example, go for rise in productivity, thinner gauge hot strip, as well as thicker line pipe and 3rd generation AHSS grades combining higher strength and ductility. The quality- and product-related advantages of thin slab casting and direct rolling technology are explained in this contribution at the example of the CSP® process.

Effect of Rolling Process on Microstructure and Properties of 95CrMo Drill Steel

In order to improve the strength and toughness of 95CrMo steel and explore a short flow process, a direct rolling process was employed, and the effect of finishing rolling process on microstructure and mechanical properties was investigated. The results show that, with the decrease of finishing rolling temperature, inter-lamellar spacing increases, the strength as well as hardness has a general increase, and secondary cementite is distributed uniformly but represents a remarkable decrease in size. Based on Hall-Petch type equation, an effective relationship of yield strength and pearlite structure parameters was established. The correlation coefficients between the measured and calculated strength were more than 0. 95, which indicated a high reliability of the relationship. By analyzing the individual strength contributions of pearlite structures, yield strength was found to have a more great dependence on pearlite inter-lamellar spacing than colony size.

Study of the Structural Properties and Segregation of Alloying Elements in Strips from the TRC Line

Twin roll casting (TRC) technology is becoming increasingly popular because of the opportunity to receive aluminum strips which may serve as input for direct cold rolling processes. Furthermore, these strips have a favourable combination of mechanical and electric properties as well as dimensional tolerances. TRC line strips show segregation of alloying elements and structure providing a combination of casting structure and wrought alloy. As part of this study, the structure of the strips from the TRC line has been analyzed as well as the segregation of the alloying elements.