[en] In this paper, the development status of titanium microalloyed high strength steels is comprehensively introduced, and the precipitation behaviors of titanium, including the strain-induced precipitation and interphase precipitation of nano-sized carbides, are illustrated in detail. Moreover, the future trend of titanium microalloying technology is also discussed, which provides insightful suggestions for not only the prospective developments but also the potential industrial applications of these titanium microalloyed steels. (topical review)

No abstract available

[en] The paper demonstrates that the fatigue strength of the high-strength steels investigated depends in the first line on their tensile strength and not on the microstructure, that at increasing stress concentration factor α_k the gain in endurable fatigue strength is reduced by higher tensile strength, and that stress concentration factors higher than 2.5 should be avoided for several reasons. A concept for estimating the life of components subjected to dynamic stress is presented on the basis of the knowledge acquired. The resulting design S-N-curves are also presented. (orig.)

[en] Hydrogen induced cracking (HIC) was studied phenomenologically and the effect of microstructure on HIC was discussed for the steels having two different levels of nonmetallic inclusions. Steels having different microstructures were produced by thermomechaincally controlled processes (TMCP) from two different heats which had the different level of nonmetallic inclusions. Ferrite/pearlite (F/P), ferrite/acicular ferrite (F/AF), ferrite/bainite (F/B) were three representative microstructures for all tested steels. For the steels with higher level of inclusions, permissible inclusion level for HIC not to develop was different according to steel microstructure. On the contrary, HIC occurred also at the martensite/austenite (M/A) constituents regardless of steel microstructure when they accumulated to a certain degree. It was proved that M/A constituents were easily embrittled by hydrogen atoms. Steels having F/AF is resistant to HIC at a given actual service condition since they covers a wide range of diffusible hydrogen content without developing HIC

[en] Results of the experimental study of 15X2NMFN steel performed with the aim to determine a role of breaks in the cyclic loading under plane stressed state at room temperature are discussed. It is shown that recovery in the process of cyclic loading under uniaxial pulsating tension increases durability of the studied steel while in the case of pulsating internal pressure the effect of loading breaks on the durability is not discovered

[en] The oil and gas industry of Alberta, Canada use coiled tubing made from high strength low alloyed steel (HSLA) to extract oil from reservoirs deep beneath the earth's surface. The repeated use of the coiled tubing in down-hole wells results in fatigue failure of the tube material. In order to repair the coiled tube, a section of tubing is fusion welded using tungsten inert gas welding onto the remaining tube steel. However, the fusion weld often fails within the weld region and therefore, alternative joining methods need to be explored to minimize detrimental changes at the joint region. In this study transient liquid phase (TLP) bonding is used with the aid of metal interlayers based on the Ag-Cu and Ni-P systems. These interlayers form a liquid at the melting point and the gradual diffusion of alloying elements into the joint and the diffusion of elements out of the joint region induces isothermal solidification whilst the joint is held at the bonding temperature. The TLP bonding behaviour of the HSLA steel as a function of bonding parameters was investigated and the quality of the joint region determined using metallurgical techniques (light and scanning electron microscopy, energy dispersive spectroscopy) and mechanical testing. (author)

[en] The very strong steel 21 CrMoNiV 57 showed the following crack propagation behaviour in the threshold range: - The threshold value decreased with increasing R value as expected. - Regardless of the R ratio and the threshold value reached, the hysteresis effect was found during subsequent increase in load, even if there was no crack closing (R=0.7=R_eff). - The ΔK range in which the crack could not spread, lay 25% to 38% above the threshold value reached. - According to metallurgical investigations, the cause of the hysteresis effect lay in the fact that the crack stops at micro-structural obstacles. This also leads to relaxation of the ΔK and ΔK_eff concept. (orig.)

[en] The general desire by the power reactor process makers to increase power rating and their efforts to involve more advanced thermal behaviour and fuel handling facilities within the reactor vessels are accompanied by an increase in both pressure vessel dimensions and various difficulties in giving practical solutions of design materials and fabrication problems. In any section of this report it is emphasized that difficulties and problems already met with will meet again in the future vessels but then in modified forms and in many cases more pertinent than before. As for the increase in geometrical size it can be postulated that with use of better materials and adjusted fabrication methods the size problems can be taken proper care of. It seems likely that vessels of sufficient large diameter and height for the largest power output, which is judged as interesting in the next ten year period, can be built without developing totally new site fabrication technique. It is, however, supposed that such a fabrication technique will be feasible though at higher specific costs for the same quality requirements as obtained in shop fabrication. By the postulated use of more efficient vessel material with principally the same good features of easy fabrication in different stages such as preparation, welding, heat treatment etc as ordinary or slightly modified carbon steels the increase in wall thickness might be kept low. There exists, however, a development work to be done for low-alloy steels to prove their justified use in large reactor pressure vessels

[en] Abstracts: The phase transformation behavior during continuous cooling of low-carbon (LC) Boron-treated steels was studied. Furthermore, the influence of combining Boron with Nb or Ti or V on transformation kinetics was investigated. Additions of Boron to LC steels have a strong influence on the ferrite transformation. By adding 30 ppm Boron to a Boron-free reference alloy the suppressing effect on the ferrite transformation is most pronounced, whereas 10 ppm Boron has almost no effect and 50 ppm Boron the same effect as 30 ppm Boron. Thereby the critical Boron concentration for transformation kinetics in this alloying concept is 30 ppm. The combination of Boron with Ti shifts the phase fields to shorter times and increase the ferrite start temperature, whereas the combination of B+V and B+Nb only affects the ferrite start temperature. Hardness values are mostly influenced by the presence of Boron and strongly depend on the cooling rate

[en] Kinetics of reversible temper brittleness of chromium-nickel-molybdenum steel with bainite structure was investigated by constructing isothermal diagrams. It is shown that brittle fracture resistance in nonembrittled state embrittlement rate and degree are sufficiently lower, as compared to martensite structure. Peculiarities of effect of molybdenum and strength level of tempered structure on embrittlement characteristics were studied, as well as peculiarities of fracture and segregation processes in the case of temper brittleness of bainite