Bo Lin He

Study on the Recrystallization Behaviour of Hot Deformed Austenite in GCr15 Bearing Steel

Along with the rapid development of the science and technology, the requirements of microstructure and properties for the bearing steel are more and more strict. The recrystallization behavior of hot deformed austenite in GCr15 bearing steel was systematically studied under the different deformation amount, deformation temperature and dwell time after rolling, the changes of microstructure and recrystallization percentage was analyzed. The research results show that the recrystallization behavior of hot deformed austenite in GCr15 bearing steel is more and more obvious as the deformation amount, deformation temperature and dwell time after rolling increase, the microstructure is more uniform, and the recrystallization percentage increases; When the deformation amount is 20%, the deformation temperature is 850°C and the dwell time after rolling is 10s, the recrystallization percentage is 32.09%, when the deformation amount is 45%, the deformation temperature is 950°C and the dwell time after rolling is 60s, the recrystallization percentage is 64.31%, comparing it to 32.09%, it increases 100.4%.

Influence of Ultrasonic Peening on Wear Resistance of U70 Rails

The surface of U70 rails was treated by ultrasonic peening method. Keeping the electric current 1.5 A, the amplitude 24 µm and the frequency 10000 HZ during the treatment, the peening duration was 10 min, 20 min, 40 min and 60 min respectively. The wear property, wear appearance, and structural appearance of specimens have been studied by M-2000 wear tester and 6360LA scanning electron microscope. Results show that ultrasonic peening treatment can significantly improve the wear resistance of U70 rails, and the longer the peening duration, the stronger the wear resistance. The wear mass loss of the specimen with 60 min treatment is only 27 % of the one untreated. The reason is that ultrasonic peening can form plastic deformation zones. The depth of plastic deformation zones increases with the peening duration. The depth of plastic deformation zones of the specimen with 60 min treatment is nearly 100 µm. Longer peening duration means severer plastic deformation. In the plastic deformation zone, ferrite is refined to smaller grains so that the matrix is strengthened.

Effect of Ultrasonic Impact Treatment on Corrosion Resistance of Welded Joints of 16MnR Steel

The weld seam and weld toe surface were treated by ultrasonic impact method. The contrast corrosion tests were performed in 3.5% NaCl aqueous solution both for the un-treated and treated joint. The experimental results indicate that the severe plastic deformation on the surface of weld seam and weld toe were formed by ultrasonic impact for different time, the maximum depth of the plastic deformation layer is about 300μm. Residual tensile stress in the surface of weld seam and weld toe can be changed to residual compressive stress by impact treatment, and the grain in the surface of welded joint could be refined. Compared to the un-treated joint, when the impact current is 1.2A and 1.5A, respectively, the corrosion rate of treated joint was reduced by 22.67%, 54.59%, 43.99% and 33.92%, 56.54%, 49.29%, respectively for 10, 20 and 30 min. treating. The corrosion resistance of welded joint has a certain relationship with the residual stress on the surface of welded joint. The ultrasonic impact treatment has distinct effect on the corrosion resistance of 16MnR welded joint.

Review of Status about the Effect of Ultrasonic Impact on Fatigue Properties of Welded Joints of Magnesium Alloy

The study on magnesium alloy has attracted attention at home and abroad. Status and development trend about the fatigue properties of welded joints of magnesium alloy were reviewed. The main problems and deficiencies were pointed out, and the recent developments focus was outlined. The development trend of improving the fatigue propeties and fatigue life was analyzed. The ultrasonic impact method can not only decrease the stress concentration coefficient and tensile residual stress of welded joint, but also refine the grain size of welded joints, even to compressive stress and nanograins. The method has put forward a new way for increasing fatigue properties and life of welded joint of magnesium alloy.

Effect of Air Oxidation Treated Carbon Fiber on Mechanical Properties of Carbon Fiber Reinforced Polyethylene Resin Composite

The composite of carbon fiber reinforced polyethylene resin was prepared by using a twin-screw extruder. The effect of carbon fiber oxidation treating on the mechanical properties of carbon fiber reinforced polyethylene resin composite was researched. The tensile fracture failure mechanism of composite was analyzed for both untreated and air oxidation treated specimen. The experimental results indicate that when carbon fiber content is equal, the tensile strength and the elastic modulus of air oxidation-treated carbon fiber-reinforced polyethylene composite are improved than that of the untreated. When the fraction of adding carbon fiber is 3.99%, compared with the pure polyethylene resin matrix, the tensile strength, elastic modulus is increased by 13.12% and 172.91%, respectively. Compared to the untreated carbon fiber reinforced polyethylene resin composite, the tensile strength and tensile modulus is increased by 4.71% and 13.14%, respectively.

Surface Nanocrystallization of U70 Rail Steel Treated by Ultrasonic Impact

The ultrasonic impact treatment on U70 raill steel was carried out under different technology by using HJ-II ultrasonic impact machine. The electric current was 1.5 A, the amplitude was 24 µm and the impact frequency was 10000 HZ during the treatment, the peening duration was 60 min. The influence of impact on microstructure was observed with the scanning electron microscope of 6360LA type and high resolution transmission electron microscope of JEM-2100 type, and the hardness of impacted surface was also researched before and after impact treatment. The wear resistance was tested by using M-2000 type wearing machine. The experimental results indicate that the surface strength of rail steel can be improved evidently by using ultrasonic impact treatment. The surface microstructure of the rail steel could be refined to nanoscale and the hardness and wear resistance of impact layer were significantly improved through the ultrasonic impact technology. Compared to the specimen without treatment, its surface hardness was increased 26.4%, and the wear resistance was increased 40.63%. The depth of plastic deformation zones of the specimen with 60 min treatment is nearly 100µm. In the plastic deformation zone, ferrite is refined to nanoscale grains so that the matrix is strengthened.

Finite Element Calculation about Stress Concentration Coefficient of Welded Butt Joints Based on the ABAQUS

Stress concentration coefficient of welded joints has a crucial influence on mechanical properties of welded structures. Geometrical parameters of welded joints seriously affect the stress concentration coefficient. In order to increase the mechanical properties and using safety of welded structures, it has great significance for reducing stress concentration coefficient and improving the mechanical properties of welded structures by researching and improving the geometry of welded joints . In this paper, the effect of weld toe inclination angle θ and weld edge transition arc radius r on the stress concentration coefficient of welded butt joints were analyzed by using ABAQUS finite element program, and the change rule of stress concentration coefficient with the variation of the two parameters was also researched. The calculation results indicate that reducing weld toe inclination angle or increasing transition arc radius can effectively decrease the stress concentration coefficient of welded butt joints, so as to improve the mechanical properties of welded structures. For the safe use of welded structures, the true weld edge transition arc radius r should be greater than 3mm, and weld toe inclination angle θ should be smaller than 30°.

The Effect of QPQ Salt-Bath Nitriding on Microstructure and Wear Resistance of 4Cr5MoSiV1 Steel

In this paper, 4Cr5MoSiV1 steel is dealt with by QPQ salt-bath nitriding at 520°C, 540°C, 560°C and for 2h、4h、6h, respectively. The treated surface microstructure was analyzed by using SEM. The depth of nitriding layer, scratch hardness and wear-resistance were tested for QPQ salt-bath nitriding technology. The corrosion resistance was tested in the 5%NaCl water by using spraying method. The experimental results indicate that with increasing the temperature and the nitriding time, the depth of nitriding layer, scratch hardness and wear-resistance of 4Cr5MoSiV1 steel were increased greatly. Comparing with the untreated specimen, its hardness enhances 196.73%, wear resistance enhances 349.65%, anti-corrosion enhances 943.10%. The die hardness, wear resistance and the corrosion resistance can be greatly improved by using the QPQ salt-bath nitriding technology.

Reliability Calculation of Welded Pressure Pipe with Circumferential Crack Based on 3-D Elastic-Plastic SFEM

In this paper, the reliability of welded pressure pipe with circumferential surface crack was calculated by using three dimensional stochastic finite element method. This method has overcome the shortcomings of conservative results in safety assessment with deterministic fracture mechanics method. The calculation of reliability was based on three dimensional elastic-plastic stochastic finite element program which was developed by ourselves. The effects of variables such as fracture toughness, bending moment and the depth of the circumferential surface crack on the structure reliability were also discussed. The calculation results indicate that the crack depth has great effect on the reliability of the welded pipe. When the mean value of the crack depth is changed from 3mm to 7mm, the failure probability of the welded pipe will change from 10-8 to 10-2. The bending moment also has great effect on the reliability of the welded pipe. When the mean value of moment is changed from10000 N.m to 15000 N.m, the failure probability of the welded pipe increases dramatically for the same circumferential crack depth. Irrespective of the changing of moment, the pipe has higher reliability if the crack depth is less than 5mm(a/t<0.5, t is the thickness of the pipe). The method has put forward a new way for safety assessment of welded pipe with circumferential surface crack.

Research of Microstructure and Properties of the 4Cr14Ni14W2Mo Steel with QPQ Salt-Bath Nitriding

The wear-resistance, corrosion resistance, hardness can be greatly increased by using low temperature QPQ complex salt-bath treatment. And it is a new strengthening method without distortion in the treating process. The surface of 4Cr14Ni14W2Mo steel was treated using this method. The microstructure and depth of the treated surface for the steel were analyzed using SEM. The sliding wear resistance was tested on the M-2000 tester and the micro-hardness was tested using 401MVA microscopy hardness tester. The corrosion resistance was tested in the 5%NaCl water by using spraying method. The experimental results indicate that a certain depth of white layer and diffusion layer of the steel can be obtained by using low temperature QPQ complex salt-bath treatment. The nitriding compound layer with high hardness, superior wear resistance and stable microstructure, can also be obtained on the surface of the parts. The highest hardness in the surface is HV0.11012. The surface hardness is 2.8 times higher than that of inner part. The depth of white layer is from 10 to 12μm. The experimental results and applied results show that the low temperature QPQ complex salt-bath treatment has many advantages, such as fast nitriding speed, uniform heating, short process time, low treating temperature, small distortion, high production rate, low cost, stable nitriding quality no pollution and so on.