مجله مهندسی ساخت و تولید ایران
سال هشتم شماره 12 (اسفند 1400)

Duplex stainless steel 2205, famous for its excellent combination of high corrosion resistance and good mechanical properties, is widely used in the industrial fields in different temperature ranges, and can be a suitable alternative to austenitic or ferritic stainless steels. In the present study, the hot compression tests were performed to identify the hot and warm working behavior of duplex 2205 stainless steel and the effect of temperature, strain rate and strain parameters on its flow stress. Cylindrical specimens with a diameter of 8 mm and a height of 12 mm at temperatures of 600, 700, 800, 900, 1000, 1100 °C and strain rates of 0.3, 0.1, 0.01, 0.001 s-1 were compressed to a strain of 0.6. The constitutive equations were used to predict the mechanical behavior and flow stress analysis of this steel, and finally the modified dynamic materials model and strain rate sensitivity(m) maps were used to indicate the best temperature and strain rate ranges for hot and warm working of this alloy. The strain rate sensitivity(m) maps showed the hot and warm stable workability of duplex 2205 stainless steel is in three domains with 800 °C temperature and 0.3 s-1 strain rate, 1050 ˚C temperature and 0.001 s-1 strain rate and 1050 ˚C temperature and 0.001 s-1 strain rate.

15-5 PH steel is a stainless steel with a martensitic base that increases in hardness, hardness and strength with the aging process. The high hardness and low thermal conductivity of this steel cause severe wear of the tool and high cutting force and increase the roughness of the workpiece surface. The common method in the production of parts of this material is machining in solution (dissolution) with a maximum hardness of 35HRC.Then, in order to increase the strength, hardening operations are used. In this paper, in order to analyze the effect of hardening heat treatment on the machinability of this steel, two very common heat treatments H900 and H1150 were performed on the mentioned steel and the turning results in each operation were compared with the turning results in solution mode.Lathe force was measured during the process using a dynamometer and surface roughness of the parts after turning. The results showed that the best conditions in terms of reducing lathe force and surface roughness are obtained in H1150 mode. A comparison between turning in the H900 and solution modes also shows that, although the average turning force in the H900 mode is approximately 22% higher than the solution mode.But the average surface roughness, in the H900 mode, is 17% higher than the solution mode. In addition, turning in the H900 mode reduces defects such as lateral slippage of the workpiece material and plowing by the tool compared to lathe turning.

In this paper, a new structure of an electromagnetic flow meter capable of measuring the velocity profile in a rectangular channel is presented. Common electromagnetic flowmeters measure the average velocity and are not capable of detecting velocity profiles in the cross-section of the channel. An array electromagnet with the ability to control the magnetic field across the channel is used to measure the velocity profile. The dimensions of the rectangular channel are 6 × 150 mm2 and the magnetic field is created by five coils with a low carbon iron core with a wire diameter of 0.3 mm. 20% NaoH solution with a conductivity of 4 S/m is used as the fluid passing through the flowmeter. An electromagnetic arrayed flowmeter is fabricated and experimentally tested in a closed path. Three-dimensional simulations of flowmeter including magnetic field, fluid velocity and induced current at the electrodes are performed in the finite element software COMSOL.The arrayed electromagnetic flow meter is experimentally and numerically investigated when the magnetic field was uniform and the array is also activated separately. Also, the parabolic and linear inlet flow profiles, with speed changes from 0 to 10 liters per minute, are applied to the inlet and the flowmeter output signal is recorded. The experimental and simulation results have a good fit (mean error 16%) and show the successful performance of the array flowmeter in measuring the channel cross-sectional velocity profile.

The hot deformation behavior of materials has considerable complexity due to its dependence on the strain, strain rate, and temperature changes. Therefore, the prediction of material behavior is very important in these conditions. Various constitutive equations have been developed to predict the deformation behavior of materials at elevated temperatures, one of the most important of which is the Johnson-Cook equation. To develop a suitable constitutive equation that can accurately predict the behavior of the material, various tests such as tensile, compressive, and torsion tests are used. Due to the lack of frictional limitation, the torsion test can apply much higher deformation or strain than the compression and/or tensile tests. Therefore, in this study, the hot working behavior of 304 austenitic stainless steel was investigated using the hot torsion test and the Johnson-Cook constitutive equation was developed for it. For this purpose, experiments have been performed at the temperature range of 800-1000 ̊C and strain rate of 0.001-1 s-1 and high strain up to about 3. The results showed that flow stress decreases significantly with increasing temperature and decreasing strain rate. In places where the strain is sufficiently applied and the deformation temperature is high, dynamic recrystallization is observed in the microstructure while due to the strain difference along the sample radius, the microstructure of the deformed part is not nuniform along the radius. The developed Johnson-Cook equation was compared with the experimental results which were observed to have acceptable accuracy in predicting the hot deformation behavior of the studied steel.

The shunting effect in resistance spot welding (RSW) occurs due to the side electrical current created through the previous spot welds. In creation of alternating welding points, the quality of subsequent welding points is affected by a side electric current due to electro-thermal changes. This shows that the analysis of the effect of the side current is important for achieving cognition of how different parameters affect this process. Therefore, the dimensions of the welding nuggets, the metallurgical structures and the mechanical strength of the welding points are affected by the changes in the electric current and the temperature distribution caused by this current. The amount of this current depends mostly on factors such as distance, number and size of previous spot welds. In this study, experimental research was performed to investigate the shunting effect on the tensile-shear strength of RSW spot welds in aluminum alloy 2219 sheets. The most important factor in shunting (welding distance) together with welding current and time was investigated by three design of experiment factor (DOE) within the welding range to achieve a statistical model based on tensile-shear strength results. An experimental regression model was derived. Results show that increasing the welding current or distance increases the tensile-shear strength of the joints.

In the present paper, gas turbine blade made of Inconel 939 superalloy creep behavior under rotation and thermal stress which is obtained from thermoelastic analysis is studied. Four models including Larson-Miller, Orr-Sherby-Dorn, Manson-Hoferd, and Minimum Commitment Method are used for creep analysis and their results are compared. At the first step, material constants of these four models are obtained by curve fitting of experimental results provided by COST-50. Then with use of these temperature dependent material constants, finite element model is created and stress due to temperature distribution and blade rotation is determined. Temperature range of blade is obtained from 1050 K to 1200 K. Because obtained von- Mises stress is below the yield stress of Inconel 939 at above temperature range, viscoelastic creep analysis is done by ABAQUS creep subroutine. Obtained results show that Larson-Miller and Minimum Commitment Method predict lower creep rate and creep strain relative to two other models. Also analysis results show that creep is more important at points with higher temperature.