Applied Mechanics and Materials Vols. 670-671

Abstract: To solve the crack and fracture problem in blade made of K403 alloy, the samples of K403 are laser shock processed and then the microstructure, microhardness, residual compressive stress and surface roughness of the samples are tested. The test results show that some grains are observed refined in the grain boundary of shock region, the microhardness improves in a depth of 0.8mm from the surface and the surface microhardness improves 16%, a residual compressive stress which is more than 450MPa is developed in a depth of 1mm from the surface, and obvious changes of the surface roughness are not tested.

Abstract: The effect of heat treatment on transformation of residual austenite in bearing steel is studied, by adding the cryogenic treatment into the normal heat treatment process. The results indicate that the residual austenite content is decreased and the hardness is improved obviously, when putting the cryogenic treatment at -70°C or lower directly behind the quenching process. While when the tempering is added between quench and cryogenic treatment, the temperature of cryogenic treatment must be much lower than -70°C to offset the thermal stability of residual austenite, which is given by tempering.

Abstract: JG590 steel is one of high strength, low alloy and high toughness engineering machinery steels, and its tensile strength is not less than 590MPa. The fatigue failure is one of the main forms of the welding structure failure. This paper studies the influence of the ultrasonic treatment on welded joint fatigue performance. Through the experiments, the paper compares the fatigue performance on as-welded welding joint with the performance on ultrasonic impact treatment welding joint. The results show that the ultrasonic treatment reduces the stress concentration factor by improving the geometry of the toe of weld’ area. It transforms the welding residual tensile stress on the surface of the welded joint into compressive stress, and makes the surface of the toe of weld’ area hardening. The fatigue strength of welded joint is increased by 114%, and the fatigue life increased by 133~184 times.

Abstract: JB800 steel has grain boundary allotriomorphic ferrite and granular bainite (F_GBA/B_G), and it is a kind of high strength low alloy steels, which has simple produce procedure, lower cost and excelled property. The law of microstructure transformation in CGHAZ, hardness, and impact toughness in HAZ of JB800 steel were studied by means of thermal simulation. The test results show that under the general condition of welding process (t_8/5=5~50s), microstructure of CGHAZ is composed of mixture microstructure of Martensite and Bainite and with the increase of cooling rate, the content of Martensite will decrease, but that of Bainite will increase; when t_8/5 is 20s, CGHAZ zone have better impact toughness, which is composed of 95% Martensite and 5% Bainite. Therefore t_8/5 should be controlled at about 20s to get better impact toughness.

Abstract: The environment of fresh water has been changed greatly because of eutrophication, which made the corrosion behaviors of metals in this water become more and more complex. Presently, the study on the corrosion behaviors and mechanism of metals in eutrophic fresh water was very rare; therefore, we considered the research on this field was a very meaningful work. In this paper, the corrosion behaviors of three kinds of metal in eutrophic fresh water were studied by electrochemical methods, the influence of temperature, value of pH and dissolving oxygen content on the electrochemical corrosion behavior of three kinds of metals were investigated mostly.

Abstract: Nickel based alloys are well considered materials for uses in high temperature applications. Inconel 690 is the one of outstanding candidate with the superior properties. The aim of this report is to present the influence of water vapor on thermal oxide film. Inconel 690 was oxidized under dry and wet atmosphere at 900°C for 30 hours. The oxidized samples were characterized by SEM/EDS, Raman spectroscopy, and photoelectrochemical technique. The results illustrated that typical thermal oxides grown on alloy composed of Cr, Fe, Ni, in forms of Cr₂O₃, NiFe₂O₄, NiCr₂O₄, Fe₂O₃, Fe_2–xCr_xO₃ and/or solid solution of NiFe₂O₄−NiCr₂O₄. The presence of water vapor affected on oxide morphology, its stoichiometry, and also semiconducting behavior. Oxide film grown under water vapor atmosphere show the homogeneity. Water vapor promoted the predominated oxide of Cr₂O₃ with n−type semiconducting. Moreover the characterization revealed the effect of surface orientation on oxidation mechanism in case of sample which oxidized in oxygen atmosphere.

Abstract: Transformation induced plasticity (TRIP) steels is a kind of low-alloying high strength steel with good combination of strength and plasticity. To investigate the material behavior of TRIP steel, the multiscale simulation method was used in this paper. Through the investigation we can see that, multiscale simulation model of TRIP steel can be setup by combining finite element and microscope technology together, and the simulation results agree with the experimental results greatly. Both for uniaxial tension and biaxial tension, the micro stress distribution was unevenly for the difference of material behavior of bainite, ferrite and retained austenite, which create local stress concentration, and for uniaxial tension and biaxial tension, the stress distribution of biaxial tension was relative average, for the boundary condition biaxial tension was a kind of relative even boundary condition, the stress on different direction was balance.

Abstract: A new bulk amorphous alloy, Y₃₆Nd₂₀Al₂₄Co₂₀, with a diameter of 5 mm was successfully fabricated by the method of equiatomic substitution for the Y element in Y₅₆Al₂₄Co₂₀ amorphous alloy. The values of the supercooled liquid region ∆T_x(=T_x-T_g ), the reduced glass transition temperature T_rg (=T_g/T_l) and the parameter γ (=T_x/(T_g+T_l)) for Y₃₆Nd₂₀Al₂₄Co₂₀ bulk amorphous alloy are 60K, 0.605 and 0.415, respectively. The critical cooling rate of the Y₃₆Nd₂₀Al₂₄Co₂₀ bulk amorphous alloy was determined to be 40 K/s, providing an indication that this alloy has a high glass-forming ability.

Abstract: In this paper, experimental and finite element modeling methods were adopted to investigate the effects of microporosity on the tensile properties and fracture behavior of high-pressure die-casting (HPDC) AM50 alloy. By specimen-to-specimen fractographic analysis, the variability in tensile properties could be quantitatively correlated with the areal fraction of the porosity presented in the corresponding fracture surfaces by using a simple power law equation. Numerical models of synthetic microstructures with different pore sizes, areal fractions of pores and pore distributions were established. Based on the experimental and numerical simulation results, it could be concluded that the fracture will initially occur in the region where has the highest intensity of equivalent stress field (i.e., contains the most highly localized cluster of pores and shrinkage), and then, fracture crack will fast propagate through the adjacent regions which have the relatively high intensity of stress field.

Abstract: In chemical processing plants and petroleum refineries, the pressure vessels and pipelines suffered often from fire accidents and thus resulted in the metal materials were in overheating state. Elevated temperature could cause the changes in metallographic structure and have unfavorable effects on material mechanical properties. In order to understand better the influence laws of overheating on metallographic structures and material mechanical properties, the methods of theoretical analysis and experimental research were used and the effects of thermal exposure temperature, duration time and cooling rate on microstructure and mechanical properties of low-alloy steel 12MnNiVR, were studied systematically. In the paper, mechanical testing (hardness test) are carried out to understand changes in the mechanical properties that would be observed in the metal exposed to elevated temperatures during a fire accident. The study can provide basis data for the material properties database of metal material suffered from fire accident, and afford technical supports in the key technologies on fire damage FFS (Fitness-For-Service) integrity assessment.