Cyclic low-temperature cracking resistance of structural steels and welded joints in metal structures

The results are presented of investigations into 09G2S, 10KhSND, St20, VSt.3sp, and St-38-b2 (East Germany) steels and welded joints to determine cyclic cracking resistance at temperatures of +20 and –70°C taking into account the nature of the loading cycle of metal structures in lifting machines.Translated from Problemy Prochnosti, No. 10, pp. 8–11, October, 1990.     

Cyclic crack resistance of ferritic-pearlitic steels and their weld joints

The cyclic crack resistance of ferritic-pearlitic steels and their weld joints is determined. On the basis of an analysis of our own and literature data a method of evaluation of the endurance of welded structures in the area of multicycle fatigue is proposed. The endurance limit _e, the parameter K_th ^*, and other parameters have been introduced into this method. The concepts of repairless structures and safely damaged structures are proposed.Translated from Problemy Prochnosti, No. 7, pp. 25–30, July, 1991.     

Fracture toughness and crack growth resistance of pressure vessel plate and weld metal steels

Compact tension specimens were used to measure the initiation fracture toughness and crack growth resistance of pressure vessel steel plates and submerged are weld metal. Plate test specimens were manufactured from four different casts of steel comprising: aluminium killed C-Mn-Mo-Cu and C-Mn steel and two silicon killed C-Mn steels. Weld metal test specimens were extracted from five weld joints of Unionmelt No. 2 weld metal. The welds were of double V butt geometry having either the C-Mn-Mo-Cu steel (three weld joints) or one particular silicon killed C-Mn steel (two weld joints) as parent plate. On the upper shelf, a multiple specimen test technique was used to obtain crack growth data which were analysed by simple linear regression to determine the crack growth resistance lines and to derive the initiation fracture toughness values for each test temperature. These regression lines were highly scattered with respect to temperature and it was very difficult to determine precisely the temperature dependence of the initiation fracture toughness and crack growth resistance. The data were re-analysed, using a multiple linear regression method, to obtain a relationship between the materials' crack growth resistance and toughness, and the principal independent variables (temperature, crack growth, weld joint code and strain ageing).     

Static and cyclic crack resistance of 22K-type steels

The data on the cyclic and static crack resistance of 22K-type steel used in large-diameter pipelines of nuclear power plants with RBMK-100 reactors are generalized. The data on the fatigue crack growth rate at 20 and 350°C for R = 0.1–0.7 and fracture toughness are presented. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 4, pp. 54–58, July–August, 2006.     

The cold resistance of weld joints of several construction steels after impulse loading

Experimental studies have been carried out on the effects of explosion treatment on a number of strength characteristics and the brittle-ductile transition point found in weld joints made of two tube steels. The choosen regime of explosion treatment did not significantly change the values of these characteristics. However, by changing the investigated strength and deformation characteristics, it has been shown possible to estimate the effectiveness of weld joint explosion treatment on tube steels.Translated from Problemy Prochnosti, No. 8, pp. 22–26, August, 1992.     

The influence of properties of metal and temperature on cyclical crack resistance of power-plant steels

The cyclical crack resistance of power-plant steels is studied. The influence of metal condition (properties) within a specific steel grade on the characteristics of cyclical crack resistance is analyzed. It is shown that, at a room temperature, i.e., in the range of viscous-brittle transition, the cyclical crack resistance of steel decreases with the increase in its tendency to the brittle state. With increasing temperature from room to 300–320°C, the cyclical crack resistance steel decreases, and for state-specific conditions, the degree of fatigue crack growth correlates with the level of yield strength decrease at the same temperature. Taking this into account, the approach to approximation of the kinetic cyclical crack resistance diagram is experimentally proved by a generalized dependence invariant to temperatures in the range 20–300 (320)°C.     

The static and dynamic low-temperature crack-toughness performance of seven structural steels

To properly describe the crack-toughness behavior of steels in a quantitative manner, a study was undertaken to establish the effects of strain rate and low temperature on the K_ic values of seven structural steels. Steels having room-temperature yield strengths ranging from 40 to 250 ksi-ABS-C, A302-B, HY-80, A517-F, HY-130(T), 18Ni(180), and 18Ni(250) steels-were evaluated for static and dynamic loading over the range of temperatures for which K_ic values were attainable.

The results indicate that for the ABS-C, A302-B, HY-80, and A517-F steels, an increase in strain rate of approximately six orders of magnitude caused a decrease in the K_ic values measured at the same test temperatures. No significant effect was observed for the HY-130T and 18NI(250) steels. However, the most significant effect of the increased strain rate was the increase in the threshold temperature below which plane-strain behavior occurred.

When all steels — except the 18Ni(180) maraging steel, for which insufficient valid data were obtained were compared on the basis of equivalent critical flaw-size behavior, the crack-toughness performance in terms of _ic/σ_ys for dynamic loading could be separated into three groups. The HY-80 and HY-130(T) steels were best, the ABS-C, A302-B, and A517-F steels were intermediate in performance, and the 18Ni-(250) maraging steel was the poorest. These groupings of performance prevailed over a relatively wide range of test temperatures. As a means of accounting for the differences in strain rate, the K_ic/σ_ys values for all steels investigated were plotted in terms of the rate-temperature parameter, Tln A/ε, which superimposed most of the static crack-toughness performance data into these same levels of performance. In addition, the results of the investigation substantiated the interpretation that the nil-ductility-transition temperature measured in the drop-weight test is the upper limit of dynamic plane-strain crack-toughness behavior for 1-in.-thick plates.

In general, the results of the present investigation provide a quantitative comparison of the plane-strain crack-toughness performance of 1-in.-thick plates of seven structurel steels under both static and dynamic loading conditions. Because of the increase in temperature range over which K_ic behavior occurs with increased strain rate, dynamic loading can be an especially significant factor in the performance of structural steels, particularly those having yield strengths less than approximately 140 ksi.     

Investigation of the thermodynamic criterion of crack resistance of steels

The article shows the validity of the previously proposed criterion K_Ic = K_Ic ^* + _0.2iK_Ic/_0.2 (K_Ic is reduced crack resistance, _0.2i is internal component of yield strength _0.2) for a wide range of body-centered cubic metals such as iron—carbon alloys (cast iron; low-, medium-, and high-strength carbon and alloy steels). It examines the relationship between this criterion and energy and force concepts of the fracture micromechanism. Existence of a common temperature dependence of the effective yield strength component in ferrite—pearlite carbon and alloy steels in the annealed, normalized, and heat-treated states is established. It is shown that the fraction of effective stress In the total yield strength, i.e., _0.2 ^*/_0.2 controls crack resistance K_Ic over a wide range of temperatures and deformation rates. For impact strength KCV, linear dependences of KCV — KCV/_0.2 and KCV-KCV/HB are observed In the zone of transition temperatures and cold brittleness threshold. A correlation equation connecting KCV and K_Ic over the indicated range is obtained. An applied software package has been worked out for computer-aided prediction of crack resistance and impact strength.Translated from Problemy Prochnosti, No. 8, pp. 14–22, August, 1993.     

Effect of copper on the cyclic crack resistance and heat resistance of graphitic steels

We study the effect of copper content (0.05–3.45 mass %) on the structure of the matrix and graphitic phase of graphitic steels (GS) annealed for globular perlite. It has been established that the effect of copper content on the physicomechanical characteristics of GS is ambiguous. An increase in the copper content up to 2.3–2.9% is accompanied by an increase in the characteristics of thermal conductivity, strength, cyclic crack resistance, and heat resistance. The thermal conductivity of GS grows with increase in the copper content (if it is more than 3%), but the mechanical characteristics fall. Thus, the heat resistance of GS is mainly determined by their crack resistance.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 3, pp. 109–112, May–June, 2004.