Papers by Keyword: Warm Rolling

Abstract: To attain the aim of weight reduction and safety improvement of vehicles, some high strength steel sheets have been developed and investigated. TRIP-aided steel sheets with transformation-induced plasticity (TRIP) of the retained austenite have high strength and ductility, and excellent hydrogen embrittlement resistance. In previous study, as high strength TRIP-aided steel for forging parts, the volume fraction of retained austenite in the TRIP-aided steel could be increased by hot forging with austempering. Similarly, our research group reported that the thermomechanical process of hot rolling following by austempering could also increase the amount of retained austenite in the TRIP-aided steel sheet. The tensile properties and formabilities of TRIP-aided steel sheet subjected to the thermomechanical rolling just before austempering possess obvious advantages compared with those of TRIP-aided steel sheet without thermomechanical rolling process (with only austempering). These excellent mechanical properties may be caused by the finely dispersed retained austenite and refined bainitic ferrite and/or martensite brock by thermomechanical rolling process.

Abstract: In the present study, Fe-0.2C-1.2Si-10.3Mn-3.4Al-0.33V multiphase steels were prepared by two different processing including intercritical annealing and warm rolling plus heat treatment. The microstructure changes induced by working processes and their effects on mechanical properties were investigated. By establishing the yield strength contribution model of each phase, the contribution of various strengthening mechanisms to the yield strength of each phase is calculated. The calculated results suggest that warm rolling plus heat treatment process improves the grain boundary strengthening, solid solution strengthening, precipitation strengthening and dislocation strengthening of each phase, and improves the yield strength.

Abstract: The UNS S32205 duplex stainless steel was warm rolled at 600°C with 60 and 80% of thickness reduction. The microstructure was characterized by optical, scanning and transmission electron microscopy, X-ray diffractometry and EBSD. The corrosion resistance was evaluated by electrochemical behavior in the chlorine ion environment using potentiodynamic polarization measurements. The tensile strength reached 1185 MPa and 1328 MPa, after warm rolling with 60 and 80%, respectively. In steel as-supplied, hot rolled and annealed, the tensile strength was 774 MPa. Ferrite microtexture presented the α-fiber and the rotated cube component, while the austenite enhanced the brass, copper, and cube components to a lesser extent. The substructure was characterized by intense formation of tangles and forests of dislocations and discrete subgrains in the ferritic phase and by planar gliding of dislocations and formation of dense dislocations walls in the austenite. Despite the existence of a certain similarity among the values of pitting potentials obtained for all samples, the number of pits observed was higher in the as-received sample, followed by the samples with 60 and 80% reduction. These results draw attention to innovative routes in the industrial production of duplex stainless steel of this class, even considering ductility lost. Keywords: Warm rolling; Mechanical strength; Texture; Substructure; Corrosion resistance

Abstract: In the present investigation the rolling response, microstructure and texture evolution of four Mg alloys during multi-pass warm rolling were evaluated. The nominal composition of the base alloy (alloy-1) was Mg-3Al-1Zn. The alloy-2, 3 and 4 were developed by separate additions of non-rare earth elements Ag and In, and a master alloy 85Ag15In (wt.%) to make target compositions Mg-3Al-1Zn-0.5x, (x = Ag ,In, AgIn). Samples from all four alloys were subjected to multi-pass warm rolling at 300 °C to accumulative reductions of 50, 75 and 90% with 8 minutes inter-pass annealing. For all four alloys, crack free sheets of less than 1 mm thickness were produced successfully with true strain corresponding to 90% reduction. The as-cast microstructures revealed second phase particles at grain boundaries and grains interiors for all alloys. A slight scatter in the size of the deformed grains was observed for alloy-1, 2 and 3 after rolling reductions of 50, 75 and 90%. However, a sustained decrease in grain size with increasing the rolling reductions was only observed in alloy-4, despite inter-pass annealing. XRD macro-texture results of alloy-2 and 3 presented very strong basal texture showing almost concentric contours around normal direction (ND). Such strong sheet texture is attributed to a preferential alignment of basal planes parallel to the sheet surface. On the other hand alloy-1 and alloy-4 revealed a weaker texture with basal poles spread more towards transverse direction (TD) as compared to rolling direction (RD) and may be due to the activation of some <c+a> non-basal slip and twinning in addition to basal slip under the same processing parameters.

Abstract: The deformation microstructures and mechanical properties of an austenitic stainless steel subjected to warm plate rolling were studied. The warm rolling was carried out at 300°C to different total true strains of 0.5, 1, 2 or 3. The structural changes during warm rolling were characterized by the elongation of original grains towards the rolling direction and the development of spatial network of strain-induced high-angle boundaries leading to the evolution of ultrafine-grained microstructure at sufficiently large strains. The grain refinement was assisted by the development of deformation twinning. After straining to 3, the transverse grain size decreased down to 220 nm in the warm rolled samples. The warm plate rolling resulted in significant strengthening. The microhardness increased from 2910 MPa to 4192 MPa with increase in the total strain from 0.5 to 3. Correspondingly, the yield strength approached 1005 MPa after warm rolling to a total strain of 3.

Abstract: In the work, we studied the regularities and mechanisms of microstructure formation in binary TiNi alloys with 50.2 and 50.8 at.% Ni under warm abc pressing with a stepped decrease in strain temperature (873, 673, 623, and 573 К) and isothermal (723 К) multipass caliber rolling. In the TiNi alloy with 50.2 at.% Ni at all abc pressing stages, microstructures inhomogeneous in grain size were formed due to faster dynamic recrystallization and hence faster formation of finer grains and subgrains in strain localization bands compared to microvolumes bounded by these bands. After final abs pressing at 573 К with a total true strain е = 7.7, a microstructure composed of submicro-and nanocrystalline grains and subgrains was found. In the TiNi alloy with 50.8 at. % Ni subjected to warm rolling, three stages of grain structure evolution were revealed. At the first stage with low strains, the average grain size ‹d› increased due to collective dynamic recrystallization. At the second and third rolling stage, the average grain size ‹d› decreased steeply due to discontinuous and continuous dynamic recrystallization. On rolling at е = 2.0, a microstructure composed of micro-and submicrocrystalline grains was formed. An algorithm was proposed for estimating the critical strain for the onset of dynamic recrystallization from dependences of grain sizes on true strain. The sequences and temperatures of martensite transformations from a cubic В2 phase to rhombohedral R and monoclinic В19′ martensite phases were studied depending on the strain accumulated in abc pressing and rolling.

Abstract: The 6.5wt%Si composite plate, which contains three layers and the middle one is about 10wt% ferrosilicon alloy, is fabricated by clad casting and conventional thermomechanical processes. Experimental results reveal that the high silicon composite plate could get lager plastic deformation on the traditional rolling mill. Microstructure of different stages such as hot rolling, warm rolling and heat treatment are observed by optical microscope. Defects appeared in core layer of 6.5wt% high silicon composite plate could be eliminated in the diffusion annealing process. The values of iron loss are investigated at different frequencies which thickness of these homogenous thin sheets are near 0.3-0.5mm. Measurement results of 6.5wt%Si alloy samples produced by chemical vapor deposition (CVD) and powder rolling processing (DPR), and 3wt%Si grain oriented steel are compared with samples prepared by laminar composite technique.

Abstract: 6.5wt% high silicon electrical sheet is hard to be obtained through conventional different rolling processes due to its remarkable brittleness at room temperature and appearance of ordered phases in the alloy substrates, especially it has very excellent soft magnetic properties. In this study, 6.5wt%Si three-layer composite panels were prepared by advanced technology of laminar composite. The defects, bonding strength, and distribution of elements of the coating and core layers are analyzed by the photographs of metallographic phase and SEM. Experimental results show that the high silicon composite plate could carry out lager plastic deformation on the traditional hot mill after the inner layer which is10%Si ferrosilicon alloy was coated. The defects generated during hot deformation were reduced and uniform distribution of elements were achieved through proper diffusion annealing process. This article provides a short process method to produce 0.3-0.5mm 6.5wt%Si thin sheet.

Abstract: Amorphous alloys have many superior properties such as high tensile strength,anticorrosion and easy soft-magnetism, but few amorphous alloys have been used as final productsbecause they lack plasticity at room temperature. Thus, we have developed a new amorphous alloyrolling method. Although the amorphous alloy was brittle at room temperature, it has deformedplastically by semisolid rolling under hydraulic stress. After being subjected to ultrarapidcooling-thermal spraying, amorphous alloy strips were rolled with a ditch roll in the viscoelasticregion below the glass transition temperature. Using this rolling method, we successfully preformedstrips for use in fuel cell separator. This rolling technique is based on the principle of stress-inducedstructural relaxation under hydraulic stress.

Abstract: Microstructure and microtexture evolution during batch annealing of warm-rolled Ti-IF steel sheets were investigated in this paper. It was founded that α fiber texture and the relatively weak γ fiber texture were formed in warm-rolled and air-cooled Ti-IF steel sheets. In the early stage of recrystallization, the {111} recrystallization texture was formed from the deformed {111} grains in warm-rolled Ti-IF steels. In the later stage of recrystallization, the α fiber texture was consumed and the γ fiber texture in recrystallized grains was further developed. The main recrystallization texture characteristics of warm-rolled Ti-IF steel sheets had been decided in the early stages of recrystallization, and the oriented nucleation mechanism played a leading role in the formation of recrystallization texture in warm-rolled Ti-IF steel sheets.