Static and dynamic low-temperature crack resistance of the steels and weld joints of the metal structures of load lifting machines

The results are given of experimental investigations of the static and dynamic low-temperature crack resistance of 1OKhND, St-38-b2, 09G2S, St20, and VSt3sp steels and weld joints of the metal structures of load lifting machines in the 203–293 K range of outdoor temperatures. The ductile-to-brittle transition temperatures are given. The temperature relationships of mechanical properties and stress intensity factors in static K_c, dynamic K _c ^d , and cyclic loading K_fc are established. The results may be used in calculations of residual strength and residual life of metal structures with cracks.Translated from Problemy Prochnosti, No. 5, pp. 29–34, May, 1991.     

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.     

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).     

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.     

Relationship between the structure and ductile fracture resistance of ferritic-pearlitic structural steels

Conclusions The nucleation in structural steels of regions of ductile failure whose main micromechanism is the formation, development, and coalescence of microvoids is usually linked with nonmetallic inclusions, and the cracking resistance _c ^d with their dimensions, form, composition, number and the nature of distribution.According to the results of metallographic and fractographic examination, the region of microfailure in the two-phase (ferrite-pearlitic) steels with a high volume proportion of the second phase (V_SP=18–38%) is represented by the second structure component (pearlite). The fracture toughness is determined in this case by its volume fraction and particle size h_SP in accordance with the simple empirical relation . Hardening of the second structural component, which increases the mechanical characteristics and impact toughness of the metal, has almost no effect on cracking resistance _c ^d .The effect of the nonmetallic inclusions on the resistance of the steel to ductile fracture is reflected in the relationship with the special features of the microstructure. At the volume fraction V_SP=18–38% the role of uniformly distributed single and separate clusters of nonmetallic inclusions (sulfides, oxides) of the globular and slightly elongated form is not significant when their dimensions and h_SP are comparable and the volume fraction of the nonmetallic inclusions V_NI exceeds 0.12%. Even a very large reduction of the number of inclusions (V_NI=0.004%) has no marked effect on the cracking resistance _c ^d . Only when V_SP reaches 9.2% ductile failure can be initiated by globular aluminum oxides (V_NI=0.012%, maximum size 8m) at a higher value of _c ^d in comparison with that predicted on the basis of this relation.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 3, pp. 88–94, May–June, 1992.     

Calculation of threshold and critical characteristics of ferritic-pearlitic steels

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 27, No. 4, pp. 77–81, July–August, 1991.     

Calculated evaluations of the threshold characteristics for ferritic-pearlitic steels

On the basis of modern physical concepts of the process of formation of the prefailure zone and rules of the change in microcleavage resistance during deformation within the limits of the deformation theory of plasticity relationships of the threshold criteria of fracture to the standard mechanical properties _t, _0.2, and _K were obtained analytically. It was shown that the resistance to crack advance in ferritic-pearlitic steels is determined by the strain hardening exponent. A method of analytical determination of the constant relating the two basic threshold characteristics K_th and _th was developed.Translated from Problemy Prochnosti, No. 4, pp. 50–56, April, 1992.