Materials Science Forum Vol. 762

Abstract: In this paper, based on the determination of the stress-strain relationship of sintered W-40wt.%Cu by upsetting tests, the hot extrusion process of the materials covered with a steel cup has been simulated by DEFORM. The effect of the thickness of steel cup, extrusion temperature and extrusion ratio on the extrusion process has been studied, so that a group of optimal parameters could be obtained which is useful to the experiment of powder compact by extrusion with cups.

Abstract: The multi-laminated Ti-(SiC_p/Al) composite was produced by hot press and subsequent hot roll bonding of Ti and SiC_p/Al foils. The microstructure evolution of the composite in reaction annealing was investigated by scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer (EDX) and X-ray diffractometer (XRD). The results show that after the reaction annealing at 1300°C for 3h, the Ti and SiC_p/Al foils were completely consumed and transformed into the TiAl composite with a microlaminated structure. The microlaminated microstructure of the composite is composed of Ti₃Al/(TiAl+Ti₅Si_3p)/Ti₅Si₃/duplex-phase (TiC+Ti₃AlC) layers. The reaction mechanism is elucidated by employing the reaction model.

Abstract: The nickel-based superalloy C263 is commonly used within Aeroengine manufacture for various casing components. FE weld simulation methods using the commercial code Sysweld2012 have been developed to attain better understanding of a pulsed TIG welding process. Test-plate welds are performed and cross-sectioned for metallographic analysis. The welds are modelled as steady-state, continuous welding heat sources. The heat sources used in the models considered a modified 3D conical distribution, and are best-fitted against the fusion-zone boundary measured in the cross-sections. A reasonable agreement between fusion zone boundaries for the modelled predictions and the experimental cross-sections was achieved, demonstrating that the pulsed TIG weld application can be reasonably modelled using a steady-state heating.

Abstract: A process model for electron beam (EB) welding with a variable thickness weld joint has been developed. Based on theoretical aspects and experimental calibration of electron beam focusing, welding parameters including beam power, focus current, working distance and welding speed were formulated in the heat source model. The model has been applied for the simulation of assembly of components in a gas turbine engine compressor. A series of metallographic weld sections with different welding thickness were investigated to validate the predicted thermal results. The workpieces were scanned both prior to-and after welding, using automated optical metrology (GOM scanning) in order to measure the distortion induced in the welding process. The measured result was compared with predicted displacement. This work demonstrates the attempts to improve the EB welding process modelling by connecting the heat input directly from the actual welding parameters, which could potentially reduce (or even remove) the need for weld bead calibrations from experimental observation.

Abstract: The paper presents a numerical and experimental approach for the quantification of the thermo-mechanical properties in multi-pass welds heat affected zone (HAZ) of low alloy steel S355J2+N. First, the characteristic temperature cycles for multi-pass welds were identified by FE temperature field simulations of welding. Based on the identified temperature cycles, the microstructure in the HAZ has been physically simulated with the simulation and testing system Gleeble 3500 to investigate the influence of multi thermal exposure on the thermo-mechanical properties. Thus, the thermo-mechanical material properties including thermal strain and temperature dependent stress strain behaviour as function of peak temperatures and cooling rates have been determined. These material properties were used to calibrate a developed model for numerical prediction of the material properties of multi-pass weld HAZ.

Abstract: In the present study, the investigation of weldability of new ultra-high strength - Weldox 1300 steel has been presented. The thermal simulated samples were used to investigate the effect of welding cooling time t_8/5 on the microstructure and mechanical properties of the heat affected zone (HAZ). In the frame of these investigation the microstructure was studied by the light (LM) and transmission electron microscopies (TEM). It has been shown that the microstructure of the Weldox 1300 steel is composed of tempered martensite, and inside the laths the minor precipitations mainly V(CN) and molybdenum carbide Mo₂C were observed. Mechanical properties of parent material were analysed by the tensile, impact and hardness tests. In details the influence of cooling time in the range of 2,5 - 300 s. on hardness, impact toughness and microstructure of simulated HAZ was studied by using welding thermal simulation test. The results show that the impact toughness and hardness decrease with the increase of t_8/5 under the condition of a single thermal cycle in simulated HAZ. The continuous cooling transformation diagrams (CCT-W for welding conditions) of Weldox 1300 steel for welding purposes was also elaborated. The steel Weldox 1300 for cooling time in the range of 2,5 - 4 s showed martensite microstructure, for time from 4 s to 60 s mixture of martensite and bainite, and for longer cooling time mixture of ferrite, bainite and martensite. The results indicated that the weldability of Weldox 1300 steel is limited and to avoid the cold cracking the preheating procedure or medium net linear heat input should be used.

Abstract: In this paper, the simulation heat affected zone (HAZ) continuous cooling transformation (SH-CCT) diagram of X100 pipeline steel was drew by using Gleeble 3500-HS thermal/mechanics simulation test machine, and the microstructure and properties of the HAZ of single-pass/double-pass welding were simulated and studied. The results show that the hardening trend of X100 pipeline steel weld coarse grain HAZ (CGHAZ) is significant when using the small welding heat input. To prevent the hardening of weld CGHAZ and reduce the cold cracking sensitivity, moderate heat input welding specification (between 12 and 18 kJ/cm) and weld preheating process (between 100 and 150°C) should be adopted. When appearing obvious embrittlement, the microstructure of double-pass weld intercritically reheated coarse grain HAZ (ICCGHAZ) of X100 pipeline steel is mainly upper bainite, the precipitation and the chain-like distribution of quantity more martensite-austenite (M-A) constituents in austenite grain boundaries is one of the main reasons leading to toughness deterioration. In conclusion, optimization control measures on the microstructure and properties of X100 pipeline steel weld HAZ are presented by above comprehensive analysis.

Abstract: Grain growth during welding and the level of impact toughness in thermally simulated high-temperature heat-affected zones were determined for a series of AOD-level laboratory melted 21% chromium ferritic stainless steels. The effects of niobium and titanium stabilizing elements on microstructure were evaluated by optical and scanning electron microscopy. Overall, grain growth was only slightly affected by the stabilizing element ratio. On a weight percent basis, niobium was the most effective for restricting the grain growth in the heat-affected zone either alone or in the presence of a small amount of titanium. The predominantly niobium-stabilized heats also had the highest impact toughness in both air-cooled and water-quenched conditions, differences in transition temperatures being up to 55 °C. However, all the simulated heat-affected zones fit into a narrow ductile-to-brittle transition temperature band width of 30 °C, even including variations in heat input. This was attributed to intense grain boundary precipitation, which occurred even with a low heat input.

Abstract: This study developed a thermodynamic model to investigate the quasi-steady thermal process of a wide thin steel workpiece irradiated with a moving Gaussian laser beam. Equations were established for the temperature distribution and the Ac1 and Ac3 boundaries. The temperature distributions for diverse thicknesses were compared with that for infinite thickness at different laser traverse speed. The lag of the peak temperature relative to the center of laser beam is found to be limited.

Abstract: A thermodynamic model was developed to describe the quasi-steady thermal process of a wide thin steel workpiece irradiated by a moving Gaussian laser beam. In this study, an experiment was done on six steels to verify this model. The calculated Ac₁ and Ac₃ depths and temperature cycles were compared with the measured results. For AISI 4340 steel, correction coefficients were applied to produce an empirical equation for temperature cycles above 488.4°C.