Strength and Fracture Mechanism of an Ultrafine-Grained Austenitic Steel for Medical Applications

In this paper, we study the corrosion-resistant austenitic steel Fe-0.02C-18Cr-8Ni for medical applications. The microstructure and mechanical properties (tensile mechanical properties, torsional strength, impact toughness, and static and cyclic crack resistance) under different types of loading of the steel are investigated. The results are compared for the two states of the steel: the initial (coarse-grained) state and the ultrafine-grained state produced by severe plastic deformation processing via equal-channel angular pressing. It is demonstrated that the ultrafine-grained steel 0.08C-18Cr-9Ni has essentially better properties and is very promising for the manufacture of medical products for various applications that experience various static and cyclic loads during operation.

Investigation of the fatigue crack growth rate in heatresistant nickel alloys

The results of tests on the FCGR (fatigue crack growth rate) of compact specimens of eccentric tension using a crack opening (COD) sensor under conditions of an asymmetric loading cycle R=0.1 at room and elevated temperatures are presented. The relationship between the conditions of force loading of preliminary growth of the initial fatigue crack is considered. The values of the effective stress intensity factor Keff were obtained, which is an important estimate for interpreting the observed character of crack growth. A comparison of the properties of the cyclic crack resistance of the VZh175-ID alloy with the properties of foreign analogues Rene 88DT, Inconel 625 SLM and domestic ones - EP741NP, EK151-ID is presented. The influence of the test temperature on the growth rate is shown. The hypothesis about the linear dependence of the parameters of the Paris equation is tested.

MODELS OF PHYSICALLY SHORT AND MACROSCOPIC CRACK DEVELOPMENT AND THEIR APPLICATION FOR TIN BASED BABBIT

The stages of fatigue crack development are analyzed. The well-known models of physically short cracks and generalized models describing some stages are shown. A perspectivity of a statistical generalized model offered is shown. The parameters obtained of a cyclic crack resistance of tin-based babbit are presented.

CRACK RESISTANCE OF CENTRIFUGAL-CAST STEAM P I P E S MADE OF STEEL 1 5 K h l M l F

Significance of assessing the characteristics of crack resistance of centrifugal-cast (CFC) tubes made of steel 15KhlMlF is substantiated. The characteristic features of the metal under study are considered along with the methodology of crack resistance tests. Three modifications of the metal of the CFC pipes in the initial state, that differ in the degree of developed segregational heterogeneity, and two modifications of the metal with almost the same degree of structural heterogeneity, which differ in the running time as a part of the operating equipment are studied. It is shown that a decrease in the intensity of the segregational damage of the metal structure has almost no effect on the level of the strength characteristics, but is accompanied by an increase in the plastic properties and toughness of the metal. We present the results of studying crack resistance of centrifugal-cast pipes (steel 15KhlMlF) under static, cyclic and prolonged static loading in conditions of high-temperature creep. It is shown that an increase in the degree of structural heterogeneity of the CFC steel adversely affects the characteristics of static crack resistance and cyclic crack resistance as well, but to a far lesser extent and has little if any effect on the crack resistance of the CFC steel at creep. Cyclic crack resistance slightly decreases with increase of the operating time of the metal in functioning pipelines, whereas the characteristics of the prolonged static crack resistance get worse significantly. It is shown that welded joints of the CFC pipelines have a substantially lower crack resistance under creep conditions compared to the base metal. Statistical processing of the experimental data is used to get kinetic diagrams of cyclic and prolonged static crack resistance of 15X1M1F CFC-steel in creep conditions. The results of practical applications of the obtained crack resistance characteristics of the metal of the CFC pipes are demonstrated with a focus on the problems of ensuring the reliable operation of the steam pipelines of thermal power plants at the end of their service lifetime.

Analysis of Methodological Framework for Computer Strength Justification of Steel Structures at Operating NPP Units

Over the last decade, new national regulatory documents on the design and assessment of the technical state of building structures, in particular steel ones, have been put into force in Ukraine to replace relevant former USSR regulations. The experience of applying new national regulatory documents indicates certain incorrect provisions, which can potentially cause catastrophic consequences in case of failure of steel building structures of corresponding facilities and(or) hazardous production capacities. The paper presents the analysis of Ukrainian regulations to check compliance of available methodologies for computer strength justification of steel structures. It is established that current regulatory documents of Ukraine do not contain a description of methodologies and procedures (formulae) with regard to calculations of steel structures on resistance to brittle fracture and cyclic crack resistance. The analysis of a number of publications was performed to define methods for the calculation of steel structures to check endurance, cyclic crack resistance and resistance to brittle fracture.

Low and high cycle fatigue of heat resistant steels and nickel based alloys in hydrogen for gas, steam turbines and generators applications

It has been established that, at some region of hydrogen pressure and strain rate exists a maximum influence of hydrogen on the plasticity, low cycle fatigue and cyclic crack resistance of Ni-Co alloys and high nitrogen steels. The drop of plasticity of the dispersion-hardening materials within the temperature range of intense phase transformations is caused by the localization of strains on the grain boundaries due to the intense redistribution of alloying elements in the boundary regions. Moreover, the increase in plasticity observed at higher temperatures is caused both by partial coagulation of hardening phases and possible dissolution of small amounts of finely divided precipitations. The effect hydrogen on short-term strength and plasticity, high- and low-cycle durability of 15Cr12Ni2MoNMoWNb martensitic steel, 10Cr15Ni27Ti3W2BMo austenitic dispersion-hardened steel, heat resistant 3,5NiCrMoV rotor steel, 04Kh16Ni56Nb5Mo5TiAl and 05Kh19Ni55Nb2Mo9Al Ni-base superalloys in range of pressures 0–30 MPa and temperatures 293–1073 K was investigated. In the case of 15Cr12Ni2MoNMoWNb steel and 04Kh16Ni56Nb5Mo5TiAl alloy the dependence of low-cycle durability (N) and characteristics of plasticity (δ and φ) on the hydrogen pressure consists of two regions. In the first region (low pressures), the N, δ and φ abruptly drops, and in the second, the negative action of hydrogen becomes stable or decrease negligibility.