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By applying ferrite-martensite microstructural control, high-deformability linepipes of grade X70 have been developed. The steel with an acicular ferrite microstructure was intercritically heat-treated at 820°C for 10 min, followed by rapidly water cooling, in order to get a ferrite/martensite dual-phase microstructure. After aging at 200-250°C for 5-15 min, the microstructure and mechanical properties of the ferrite-martensite microstructural steel were studied. The pipe with a ferrite/martensite dual-phase microstructure exhibited a superior strain aging resistance aging at 200-250°C for 5-15 min. The yield ratios were below 0.77 and the pipe still exhibited continuous yielding behavior, meanwhile tensile strength, uniform elongation and impact toughness did not experience significant change. By intercritical annealing, carbides and carbonitride containing Nb and Ti precipitated out of the ferrite phase further, at the same time, solute carbon atoms could adequately diffused from the ferrite to the uniformly distributed austenite derived from the acicular ferrite initial microstructures, leading to the reduction of the amount of free carbon and nitrogen to pin the mobile dislocations in the ferrite phase, therefore, strain aging effects were not pronounced in the temperature and time range investigated. [ABSTRACT FROM AUTHOR]

High-strength, wear-resistant steel often suffers from delayed cracking after flame cutting. Delayed cracking can lead to extremely harmful sudden brittle fracture; therefore, it is necessary to study the formation of delayed cracking in high-strength steel. This work investigated the influence of TiN inclusions and segregation on the delayed cracking in NM450 wear-resistant steel by optical microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy and electron backscattered diffractometer methods. The results indicated that the delayed cracks originated from the segregation zones (SZs) containing multiple high-hardness segregation bands. The tensile strength of the SZ specimens was higher than that of non-segregation zone (NSZ) specimens, while the total elongation and reduction of area of the SZ specimens were relatively lower compared with the NSZ specimens. Therefore, the delayed cracking on the flame cutting surface of the NM450 steel plate was attributed to the existence of SZs that contain a high density of dislocations and considerable micro-sized TiN inclusions. [ABSTRACT FROM AUTHOR]

Abstract: The effect of B/Ti mass ratio on grain refining of the low-titanium aluminum produced by electrolysis was investigated by adding AlB master alloy to the melt of the low-titanium aluminum. The results show that the addition of titanium by electrolysis is an effective way of grain refining of aluminum, and addition of boron to the melt of the low-titanium aluminum can further increase the grain refining efficiency. And the best grain refining efficiency is obtained when the B/Ti mass ratio is 1:10. However, when the B/Ti mass ratio is 1:2.22 (the stoichiometric value for TiB2), the grain refining efficiency vanishes almost completely. It means that all of the solute titanium atoms in the melt of the low-titanium aluminum react with boron atoms that come from AlB master alloy to form TiB2 particles, and TiB2 particles have not grain refining ability. The grain refining efficiency seems to increase with addition of more boron to the melt after the B/Ti mass ratio exceeds 1:2.22. But the grain refining efficiency is very poor, and similar to that of pure Al refined by AlB master alloy. It further shows that TiB2 particles do not participate in grain refining, and that the excess boron atoms in the melt also cannot turn TiB2 particles into the effective nuclei for aluminum as the solute titanium atoms do. [Copyright &y& Elsevier]