Analysis of Influence of Aqueous Mediums on Cyclic Crack Resistance of Steels

Three variants of physical models of crack growth during corrosion fatigue destruction of steel are proposed: energy model, model of hydrogen embrittlement, and model of anodic dissolution of metal in crack tip. It is mentioned that the anodic model is more preferable for quantitative analysis. Using variant calculations, good agreement of this model with experimental results is demonstrated. The dominating role of local anodic dissolution is revealed as the main mechanism activating fatigue destruction of moderate strength carbon and low alloy steels in an aqueous corrosion medium.     

Enhancement of the Cyclic Crack Resistance of Graphitic Steels

We study the influence of silicon (1.0–2.5%), copper (0.5–1.5%), and aluminum (0.05–0.25%) on the structure of the matrix and graphitic phase of annealed graphitic steels (GS) containing 1.6% of carbon. We have established that, for such GS, one can achieve simultaneous enhancement of strength, plasticity, and cyclic crack resistance, which are optimal for steel of the following chemical composition (in mass %): C–1.6, Si–1.0, Cu–0.5, and Al–0.25. We also have discovered some microfractographic features of the fatigue fracture of graphitic inclusions in GS, differing from those in high-strength cast irons.     

Cyclic Crack Resistance of Austenitic Steels for Equipment of Nuclear Power Plants

We investigate the influence of the mode of thermal treatment, the structure and properties of a material, the direction of propagation of cracks, temperature, and the parameters of a loading cycle and a corrosion-active medium on the cyclic crack resistance of chromium–nickel austenitic stainless steels of a Du-500 pipeline, the main gate valve G33 Du-500, and the header of a PGV-1000U steam generator. We show that water with high parameters, the stress ratio, and the temperature have the strongest effect on the growth rate of cracks. By using metallographic and electron-fractographic methods, we revealed specific features of fatigue fracture of steels in air and water with high parameters. On the basis on these data and a generalization of the well-known results, we propose the rated dependences for the determination of the growth rate of fatigue cracks. These dependences are compared with the rated curves of the M-02-91 normative documentation and the ASME Code and recommended for their correction.     

Influence of Microstructure on the Strength and Cyclic Crack Resistance of Cast Irons

We study the influence of microstructure of high-strength cast irons of ferritic, ferritic-pearlitic, and pearlitic classes on the characteristics of strength and cyclic crack resistance and establish the relationship between the characteristics of strength and cyclic crack resistance and the chemical composition and microstructural parameters of the matrix and graphite inclusions of high-strength cast irons. Indeed, the ultimate strength _u = 750–850 MPa, fatigue threshold K _th = 8–10 MPa , and cyclic fracture toughness K _fc = 50–60 MPa are guaranteed by the pearlitic matrix and the following parameters of the graphite phase: the content of graphite f _p 10%, the degree of its spheroidization of about 95%, the size of globules d _gl 20–50 m, and the distance between them 40–70 m, obtained in high-strength cast irons containing (wt.%): 3.2–3.5 C, 1.9–2.5 Si, 0.35–0.4 Mn, and 0.05 Mg.     

Surface Cracking of Steels in the Process of Cyclic Deformation in Aqueous Media

We study the conditions of surface cracking of steels for pipelines of power-generating equipment subjected to cyclic deformation in aqueous media. A new parameter is proposed for the evaluation of the corrosion fatigue of materials, namely, a certain characteristic level of stresses within the limits of the loading cycle ( = _s ) above which the deformed surface undergoes noticeable electrochemical activation. A model scheme of the surface corrosion-fatigue cracking regarded as a result of the synergetic action of cyclic stresses and electrochemical processes is proposed. A criterion of initiation of a surface crack of length a relating the characteristic stress _s to the maximum stress in a cycle _max, the strength of corrosion current I _cor, and the constants of electrochemical dissolution of the metal on the deformed surface is established. On this basis, we propose an engineering estimate for the period of initiation of surface corrosion-fatigue cracks.     

模拟海洋大气环境下Cu和Cr对耐候钢耐腐蚀性能的影响

过去,合金元素对耐候钢海洋环境中的耐蚀性影响缺乏详细的论讨.选取Q235和5种不同Cu和Cr含量的耐候钢,在0.5%的NaCl溶液中模拟海洋大气环境进行周期浸润试验.研究结果表明:在Cl-存在的环境中,在碳钢的基础上单独添加Cr(0～3.0%)或单独添加Cu(0.25%～0.50%)都不能使钢的耐蚀性有显著的提高.单独提高耐候钢中Cr的含量,有助于抑制其在腐蚀初期的腐蚀速度,但对后期的腐蚀发展趋势不利;单独提高Cu的含量,有助于延缓腐蚀后期的发展趋势.当同时提高耐候钢中的Cu和Cr含量时,可使耐候钢得到较佳的耐大气腐蚀性能.XRD分析结果表明,合金元素对外锈层的成分影响不大,其主要大气腐蚀产物为γ-FeOOH,Fe3O4,γ-Fe2O3和少量α-FeOOH.     

On Experimental Procedure Development for Evaluating the Effect of Biaxial Loading on the Static Crack Resistance Characteristics of Reactor Vessel Steels

Strength of Materials - According to modern normative documents, the loading of postulated cracks in reactor vessels and standard specimens during crack resistance tests has a number of...