Corrosion reactions between structural heat-resistant steels and melted lead with additions

We investigate processes of physicochemical interaction between 20Kh13 ferritic steel and melted lead with metallic additions and study the influence of each addition (Ni, Co, Cr, Ti, Al, Si, and B) on the structure and properties of the steel after isothermal holding at 900°C for 100 h.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 3, pp. 65–69, May – June, 1994.     

Precipitation and hot deformation behavior of austenitic heat-resistant steels: A review

The austenitic heat resistant-steels have been considered as important candidate materials for advanced supercritical boilers, nuclear reactors, super heaters and chemical reactors, due to their favorable combination of high strength, corrosion resistance, perfect mechanical properties, workability and low cost.Since the precipitation behavior of the steels during long-term service at elevated temperature would lead to the deterioration of mechanical properties, it is essential to clarify the evolution of secondary phases in the microstructure of the steels. Here, a summary of recent progress in the precipitation behavior and the coarsening mechanism of various precipitates during aging in austenitic steels is made. Various secondary phases are formed under service conditions, like MX carbonitrides, M_(23)C_6 carbides, Z phase, sigma phase and Laves phase. It is found that the coarsening rate of M_(23)C_6 carbides is much higher than that of MX carbonitrides. In order to understand the thermal deformation mechanism, a constitutive equation can be established, and thus obtained processing maps are beneficial to optimizing thermal processing parameters, leading to improved thermal processing properties of steels.     

Influence of laser shock-wave treatment on the impact toughness of heat-resistant steels

The influence of irradiation in a transparent condensed medium on the impact toughness of heat-resistant steels is investigated. The irradiation of a specimen in front of a concentrator causes a substantial increase (up to a factor of two) in the impact toughness of 15Kh13_F steel. Using fractographic analysis, we established that the steel was fractured by the intragranular mechanism independently of the irradiation scheme. The increase in the impact toughness of the material after shock-wave treatment is justified.     

Hot-cracking of high-alloyed steels evaluated by wedge rolling test

We present a new methodology of determination of hot-cracking of metallic materials, which is based on laboratory application of the wedge rolling test and computer processing of the results obtained. The experiment was made with selected new types of high-alloyed free-cutting (ferritic and austenitic) steels. The initial specimens underwent an additional modification enabling easier development of cracks which consisted in milling out of the defined V-shaped notches on a side wall of a specimen. After taking specimens from the rolled material, we performed the metallographic analysis of microstructures by means of optical microscopy as well as a SEM analysis of the cracks. The resulting microstructure in the propagating crack vicinity was markedly influenced by this fracture. In the crack vicinity, a noticeable refinement of grains was observed due to the stress-induced recrystallization and occurrence of deformation zones that were pronounced by the rolled-out and stretched sulphides. As a rule, fractures were created by the ductile failure with visible pits, caused by tearing of sulphides from the material. Susceptibility of the studied steels to hot-cracking was evaluated and compared. __________ Translated from Problemy Prochnosti, No. 1, pp. 60–63, January–February, 2008.     

Influence of grain size on plastic anisotropy in low-carbon steels

Abstract

The plastic anisotropy of textured polycrystalline materials has often been described by the r-value – the ratio of the width and thickness strains. The measured –-values of low-carbon steels for larger grain sizes are found to agree reasonably well with values calculated by the authors on the basis of the Taylor theory. In steels with small grain sizes the absolute level of r-value is not predicted particularly well, but the variation with testing direction (planar anisotropy) is predicted well. Calculations showed that in all cases the instantaneous anisotropy parameter ρ as a function of strain, when extrapolated to zero strain, agreed with the value predicted from the measured texture. With small grain sizes a sudden drop in ρ was observed with increasing strain, this being complete within 2–3% of strain. The influence of grain size on the plastic anisotropy can be understood if it is assumed that the grain boundary resistance parameter K in the Hall–Petch relation depends on the contraction ratio – in a different way from the Taylor factor M(q). Measurements of the Hall–Petch constant in plane-strain compression support this view.

MST/84     

Influence of deformation on the transformation of austenitic stainless steels

Two commercial austenitic stainless steels of type 304 and 321 were deformed by reduction in thickness at room temperature or at liquid nitrogen temperature and subsequently annealed in the temperature range 473 to 1073 K. Microstructural changes were examined by electron microscopy. The deformation product in both the steels are different. An attempt has been made to correlate the mechanical properties with the microstructural changes.     

Influence of plastic deformation on occurrence of discontinuous precipitation

We have studied the effect of plastic deformation by compression on the occurrence of discontinuous precipitation in Al-30% Zn alloy after ageing at two different temperatures (348 and 423 K) has been studied. Optical microscope, scanning electron microscope, X-ray diffraction and differential scanning calorimetry were used for characterization.During ageing of undeformed alloy, the grain boundary of supersaturated solid solution represents the favorite site of precipitation by discontinuous mechanism. We found that the occurrence of discontinuous precipitation depends mainly on the degree of plastic deformation before ageing. The grain boundary act as reaction front and migrates in case of low degree of prior deformation.     

Influence of preliminary cyclic plastic deformation on crack resistance

The influence of preliminary (before crack origin) cyclic plastic deformation by tension-compression (R = _min/_max = –1 on the brittle fracture resistance of 15Kh2MFA heat resistant steel in two conditions was investigated. The preliminary loading was done at 293 K and the fracture at 123 and 293 K. It was established that in the case of relatively short preliminary deformation the change in static fracture toughness is caused by a change in yield strength as the result of the Bauschinger effect. However, with an increase in cyclic deformation the total irreversibly dispersed specific energy of inelastic deformation and the structural changes in the material are the determining factor. A physically based method is proposed for prediction of the influence of preliminary cyclic plastic deformation on the brittle fracture resistance of cyclically softening steels.Institute of Problems of Strength of the Academy of Sciences of the Ukrainian SSR, Kiev. Leningrad. Translated from Problemy Prochnosti, No. 11, pp. 14–20, November, 1989.     

Effect of previous plastic deformation on the resistance of chromium-manganese steels to cavitation erosion

The investigation described in this paper was concerned with austenitic chromium-manganese steels characterized by various resistances to the martensitic transformation during plastic deformation. It was established that the influence of previous plastic deformation on the resistance of these steels to cavitation erosion varies. In each case it is necessary to consider both the susceptibility of austenite to decomposition (accompanied by the formation of martensite and -phase) under the influence of cavitation and various phase and structural transformations taking place in the steel as a result of previous plastic deformation.