Papers by Keyword: Thick Plate

Abstract: The effect of thermomechanical controlled processing (TMCP) strain and finishing temperature on the microstructure of as-rolled and air-cooled 50mm thick Nb-Ti-V-Ni microalloyed steel plate was investigated through laboratory simulations, incorporating variations in reheating, roughing and finishing practices. Laboratory simulations produced microstructures similar to those observed in industrial rolling owing to comparable total strain in the TMCP region. Larger total strains in the TMCP region promoted sub-grain formation and increased nucleation site density, leading to grain refinement. Recrystallisation was completely suppressed at the commencement of finishing in all TMCP schedules due to sufficiently lower starting temperatures. The extent of recrystallisation during finishing depended on the finishing temperature: i) partial softening after finishing above 910°C and ii) complete recrystallisation below 910°C due to substantial accumulated strain. Finishing below 910°C produced finer polygonal ferrite and pearlite microstructures. Microstructure and mechanical properties were fairly consistent when the finishing temperature was between 925 and 950°C. However, the sub-zero impact toughness can be significantly improved by employing lower finish temperatures or applying larger total TMCP strains. Interrupted accelerated cooling at 5°C/s after finishing significantly refined the microstructure.

Abstract: Two types of side dams for a semi-continuous caster, a thin steel plate and a deformable fence, were developed and tested. The semi-continuous caster equipped with deformable side dam fences was found to be superior. The deformable side dam fences were set between the substrate and the roll. Molten metal was solidified by the lower substrate and the upper roll. A 10-mm-thick 1200 aluminum alloy plate was cast at 1 m/min. The deformable side dam fences were effective at providing plate reduction and ensuring a flat upper surface.

Abstract: The microstructure and properties of rolled AZ31 magnesium alloy sheet with the change of normal position were investigated by electronic universal testing machine, ZEISS optical microscopy and scanning electron microscopy. The tensile test results showed that the mechanical properties of sample selected at the depth of 8mm, which is 2/5 of the whole thickness counting from rolling plane are closest to the properties for whole sheet. Microstructure characterization indicated that a large number of tiny grains are distributed around the large grains. The majority of these grains are equiaxed grains, and the few twins could be observeded. The fracture mechanism was ascribed to mixed ductile and brittle fractures.

Abstract: As part of a collaborative program to develop advanced manufacturing processes for next-generation hydraulic turbines, this study investigated the technological challenges for joining 25-mm thick martensitic stainless steel (MSS) plates using tandem and hybrid laser-arc welding. Although candidate materials for the intended application typically include wrought AISI 415 and cast CA6NM, a martensitic 410 stainless steel (SS) was especially selected in this study due to its greater crack sensitivity. A narrow-gap groove was designed to minimize the amount of 410NiMo filler metal required to fill the groove using a multi-pass single-sided welding technique. All the welding trials were performed using a 5.2 kW fiber laser. The root-pass quality was characterized in terms of weld bead geometry, defects and microstructure. The main technical challenges observed for the root pass were lack of penetration, lack of fusion and cracking, as detailed in this work.

Abstract: A 60mm Q345 rigid thick plate with V groove welding connection was modeled in order to simulate the welding residual stress by finite element method. Both element birth and death technique and double ellipse heat source model were introduced to simulate the welding process. The welding thermal field and residual stress of thick steel plate were analyzed by finite element simulation software ANSYS.Then the thermal field and residual stress distribution were visually demonstrated. The result shows that the thermal field shaped like a spindle during welding period and the residual stress at the mid-section in lateral, longitudinal and thickness direction of the welding joint is lower than the stress at the surface of the welding connection.

Abstract: In this work, there are presented overviews of theoretical and numerical models for defining the stress-strain state in the cross section of moderately thick and thick composite plates in case of bending. Layered composite plates are constructed by combination of layers of various materials and geometrical characteristics, wherein each of them has got a bearing capacity in previously defined directions. By applying Equivalent Single-layer Laminate Theory (or ESL theory) these layers' problems cannot be solved successfully. That is the reason to apply contemporary theories of plates, in literature known as Layerwise theories. At the end of this work, there are given numeric examples of applying Partial Layerwise Theory.

Abstract: Pre-stress shot peen forming is a metal forming process widely used in aeronautical industry. The test parts of 7150 Al alloy of different thickness were pre-stress shot peen formed. The deformation rule of those parts was investigated by means of changing the peening coverage. The results show that the radius of curvature of the parts will enhance gradually with increasing of the plate’s thickness. In addition, enhancing peening coverage could raise the deformation in the case of that the thickness and peening parameters are unchanged. Furthermore, the minimum radius of curvature of the 8mm plate after saturation pre-stress shot peen forming could reach 499mm.

Abstract: Stress relief on thick and large welded components is greatly needed in various applications, such as large oil transporting pipes and offshore oil platforms. Vibration stress relief (VSR) is an relatively new method for this purpose. The efficiency of this method is a key subject, especially when the components are extremely large and it is difficult to trigger sufficient vibration amplitude in the structures. In this study, additional heating on the area near the weld line was used to promote the efficiency of VSR. Both VSR and thermal-vibration compound stress relief (TVCSR) were used to 50mm thick DH 36 steel welded plates. The Longitudinal and transverse stresses near the weld lines before and after the treatments were investigated. Comparing to VSR, the TVCSR was more effective in decreasing the residual stress. Effects of additional heating was discussed.

Abstract: The mechanical property, fracture toughness and fatigue behavior of T7451 Al-Zn-Mg-Cu alloy thick plates in different orientations and with various thicknesses were investigated by means of tensile, fatigue and plain strain fracture toughness testing. And the microstructures and fracture morphologies were analyzed with optical microscopy and scanning electron microscopy. The results showed that the samples in longitudinal (L)-transversal (T) orientation possessed better mechanical property, fracture toughness and fatigue resistance than that in T-L orientation. Fractography and optical microanalysis clearly demonstrated that the feature of recrystallized grains is the decisive factor for this anisotropy. On the other hand, values of strength and fracture toughness decreased with the increase of plate thickness, but their fatigue crack growth rate became slower. Combined with the fractography analysis, the increase of recrystallization degree and the coarser grains in the thicker plate should be the main reason for the detrimental to the strength and toughness properties since the main fracture mechanism changes from ductile transgranular fracture to intergranular failure. However, these coarse recrystallized grains play an advantageous role for fatigue resistance from crack deflection and closure perspectives.

Abstract: Multi-point forming (MPF) is an advanced flexible manufacturing technology for three-dimensional sheet metal forming. The substance of MPF is replacing the conventional solid dies by a set of discrete punches called punch group. Due to the discrete contacts between the workpiece and punches, the dimple defects occurred, which are inevitable and particular for MPF. In this study, the analysis of the deformation features of the dimple defects was implemented. The dynamic explicit finite element method was chosen to implement the simulation of MPF process. The influencing factors of the surface defects were researched. The relevant experiment was implemented, and it verified that the forming defects decreased with the increasing of the thickness of metal plate and the objective surface curvature radius.