Jitai Niu

Analysis of the Mechanical Behavior, Creep Resistance and Uniaxial Fatigue Strength of Martensitic Steel X46Cr13

The article deals with the analysis of the mechanical behavior at different temperatures, uniaxial creep and uniaxial fatigue of martensitic steel X46Cr13 (1.4034, AISI 420). For the purpose of considering the aforementioned mechanical behavior, as well as determining the appropriate resistance to creep and fatigue strength levels, numerous uniaxial tests were carried out. Tests related to mechanical properties performed at different temperatures are presented in the form of engineering stress-strain diagrams. Short-time creep tests performed at different temperatures and different stress levels are presented in the form of creep curves. Fatigue tests carried out at stress ratios R=0.25 and R=−1 are shown in the form of S–N (fatigue) diagrams. The finite fatigue regime for each of the mentioned stress ratios is modeled by an inclined log line, while the infinite fatigue regime is modeled by a horizontal line, which represents the fatigue limit of the material and previously was calculated by the modified staircase method. Finally, the fracture toughness has been calculated based on the Charpy V-notch impact energy.

Mechanical Properties, Short Time Creep, and Fatigue of an Austenitic Steel

The correct choice of a material in the process of structural design is the most important task. This study deals with determining and analyzing the mechanical properties of the material, and the material resistance to short-time creep and fatigue. The material under consideration in this investigation is austenitic stainless steel X6CrNiTi18-10. The results presenting ultimate tensile strength and 0.2 offset yield strength at room and elevated temperatures are displayed in the form of engineering stress-strain diagrams. Besides, the creep behavior of the steel is presented in the form of creep curves. The material is consequently considered to be creep resistant at temperatures of 400 °C and 500 °C when subjected to a stress which is less than 0.9 of the yield strength at the mentioned temperatures. Even when the applied stress at a temperature of 600 °C is less than 0.5 of the yield strength, the steel may be considered as resistant to creep. Cyclic tensile fatigue tests were carried out at stress ratio R = 0.25 using a servo-pulser machine and the results were recorded. The analysis shows that the stress level of 434.33 MPa can be adopted as a fatigue limit. The impact energy was also determined and the fracture toughness assessed.

Effects of Al–8.5Si–25Cu–xY filler metal foils on vacuum brazing of SiCp/Al composites

ABSTRACT Rapidly solidified Al–8.5Si–25Cu–xY (wt-%, x = 0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5) foils were used as filler metal to braze Al matrix composites with high SiC particle content (SiCp/Al-MMCs), and the filler presented fine microstructure and good wettability on the composites. The joint shear strength first increased, then decreased and a sound joint with a maximum shear strength of 135.32 MPa was achieved using Al–8.5Si–25Cu–0.3Y as the filler metal. After Y exceeded 0.3%, a needle-like intermetallic compound, Al3Y, was found in the brazing seam, resulting in a dramatic decline in the shear strength of the brazed joints. In this research, the Al–8.5Si–25Cu–0.3Y filler metal foil was found to be suitable for the brazing of SiCp/Al-MMCs with high SiC particle content.

Structure and properties of welded joint of high-strength wear-resistant steel NM360

Present research studies the structure and properties of welded joint of high-strength wear-resistant steel NM360 by means of carbon dioxide arc welding with welding material GFM-70. The experimental result indicates that high-strength wear-resistant steel NM360 can be welded together with appropriate welding parameters. In the whole joint area, macroscopic defect such as pore, inclusion and crack does not appear. The joint tensile strength exceeds that of welding material GFM-70 at least 10.5%. The impact energy in each part of joint doubles that of base metal. Between the joint and base metal, there is coarse grain zone, fully recrystallised zone, incompletely recrystallised zone. The hardness in heat affected zone and near fusion line is quite large, which distributes in the range of 360–394 HV. The hardness of other area in joint is smaller than that of base metal NM360.

Significance of experimental data in the design of structures made from 1.4057 steel

This paper presents experimentally-obtained data which can be of importance in the design procedure of engineering components made of 1.4057 (X17CrNi16-2; AISI 431) steel. In this manner, uniaxialy tests related to determine material mechanical properties and short-time creep behavior were performed. Based on the mentioned tests, ultimate tensile strength, 0.2 offset yield strength and modulus of elasticity at low and elevated temperatures were determined. Also, creep behavior of considered steel was tested for selected temperatures and selected stress levels. According to experimentally determined Charpy impact energy an assessment of fracture toughness was made.

Elements Diffusion in Brazing Seam of High Volume Fraction SiCp/6063Al Matrix Composites

In this research, 6063 aluminum matrix composites containing 55–75% SiC particle reinforcing phase was selected as the parent metal and Al-Cu24-Si5-Zn2-Ti1 alloy metal was selected as the filler metal. After nickel plating of the parent metal, the brazing process is carried out on vacuum brazing furnace under the temperature of 565, 570, and 575 °C and holding for 10, 20, and 30 min. The interfacial microstructure is investigated by light optical microscopy (LOM) and scanning electron microscopy (SEM), and the element diffusion is analyzed by energy spectrum analysis (EDS). The result shows that the nickel plating layer on the surface of parent metal not only metalizes the SiC particle, but also participates in the diffusion process. The element distribution in the brazing seam is described exactly. Finally, the reason why finest crystalline grains and evenest distribution could be achieved under brazing temperature of 575 °C and holding for 30 min is analyzed.

Changes in the Material Properties of Steel 1.4762 Depending on the Temperature

Abstract This paper presents the experimental results and analysis of the behaviour of steel 1.4762 at different temperatures. Tensile mechanical properties and creep behaviour were determined using uniaxial tests. Charpy impact test was used to determine impact energies at different temperatures. The mentioned mechanical properties are displayed as engineering stress–strain diagrams while material resistance to creep is presented in the form of creep curves. Based on Charpy impact energy an assessment of fracture toughness is given. Experimental results show that the values of mechanical properties are continuously decreased by increasing the temperature. After the temperature of 623 K (tensile strength: 468 MPa; yield strength: 298 MPa) the decrease of the ultimate strength and yield strength is especially emphasized and the difference between them becomes smaller. The creep resistance is considered quite small, except at low stress levels.