Abstract: The metallurgical revolution of increased supply and decreased cost followed three stages: 1) coke use in the blast furnace, 2) puddling process for wrought iron (WI) and 3) Bessemer or Siemens processes for steel. The second gave rise to the conversion from wooden (iron-reinforced) machines to iron machines such as railroad engines, ships and long-span bridges, all hot-riveted. The self-made mechanical engineers raised the precision, scale and speed of mechanical shaping technology; this was transferred from WI to ingot steel with little difficulty for the same products with increased strength. Accurately measured mechanical properties of WI and steel were related for the first time to microstructure and processing by David Kirkaldy to improve Clyde-built ships and to propel metallurgy from artisanal to science-based.
Abstract: Recrystallisation/precipitation interaction in four steels having Nb, V, Ti, and Al, respectively, as microalloying elements has been studied by means of hot torsion tests. Remarkable differences were found in the results obtained for each steel. Nb and V-microalloyed steels presented long inhibition plateaus, but the steel with Al displayed a very short plateau. Finally the steel with Ti did not show plateau. This means that Nb and V precipitates (nitrides and carbides) can inhibit the static recrystallization but this does not happen for Al and Ti (which form nitrides). The difference between activation energies allows to predict the efficiency of different precipitates to strengthen the austenite during hot rolling. RPTT diagrams showed the interaction between both phenomena, along with the strain induced precipitation kinetics and precipitate coarsening. It is found that AlN particles nucleate and grow faster than NbCN or VN.
Abstract: Austempered ductile iron (ADI) is a very attractive material for applications where high strength, good ductility, wear resistance and fatigue strength are required. Thus, it offers design engineers an alternative to steel and aluminium alloys. ADI essentially is a cast ductile iron that undergoes a specially designed austempering heat treatment, which creates a microstructure of high carbon austenite and bainitic ferrite along with graphite nodules. The final proportion of these phases (and thus the mechanical properties) depends on the phase transformation kinetics which is strongly affected by composition, as-cast microstructure and heat treatment parameters (austempering).
ADI samples were austempered (heat treated) and the phase transitions were analysed after interrupted austempering. The phase fractions (austenite, ferrite, martensite, etc.) and their relation to bulk properties, like electrical resistivity, magnetic properties and mechanical properties (e.g. strength, hardness), and others were measured using optical and electron microscopy, X-ray and neutron diffraction, Mössbauer spectroscopy, and micro hardness measure¬ment. This combination of complementary techniques allows the correlation of the phase transition kinetics with the resulting properties.
Abstract: Reverse transformation has been frequently used to refine austenite grain size for refining ferrite, pearlite and martensite structures. However, kinetics and microstructure change during reverse transformation to austenite has not been examined systematically compared with the austenite decomposition reaction. Therefore, alloying effects of 1mass% Mn, Si and Cr on reverse transformation kinetics from pearlite and tempered martensite structures in Fe-0.6mass%C alloys were investigated in this study. Vickers hardness of all the specimens increases with increasing holding time at 1073K because reversely-formed austenite transforms to martensite by quenching. In the reverse transformation from pearlite structure, the kinetics of reverse transformation is hardly changed by the Mn addition while Si and Cr additions delay it. Kinetics of reverse transformation from tempered martensite structure becomes slower than from the pearlite structure in all the alloys. In particular, retarding effect by the Cr addition is most significant among those elements.
Abstract: One of noble grain refinement methods to attain ferrite grain size of around 1m in plain C-Mn steel has been so-called super short interval multi-pass rolling (SSMR) process, which is characterized by finish-rolling above Ae3, extreme short interpass time and then rapid cooling. The transformation mechanisms are demonstrated by the microstructural observation of an fcc Ni-Fe model alloy and C-Mn steels. In the Ni-Fe alloy hot-rolled by SSMR, equiaxed and cellar array of dislocation walls with low and high angle misorientations are observed in shear directions without recrystallization. The average spacing between the dislocation walls in the Ni-Fe alloy is in good agreement with the ferrite grain size of the C-Mn steel by SSMR process. On the other hand, in the C-Mn steel quenched to bypass ferrite transformation, the fine ferrite nuclei have been identified along intra-granular shear directions in the quenched martensite. It is concluded that the dislocation substructure in heavily deformed austenite by SSMR process have high potency as inherited ferrite nucleation
Abstract: In this study, Zr, Ti and TiC-based cermet specimens were prepared, and their friction and wear properties in various gas atmospheres were examined. The Zr specimens exhibited the lowest friction coefficients and the smallest volume change in the H2 gas atmosphere. This reason would have been due to the formation of the -type Zr hydride, which has a layered crystal structure. The Ti specimens exhibited similar friction and wear properties, although the TiC-based cermet specimens containing small amount of Mo, Ni and W exhibited the lowest friction coefficients in air, not in the H2 gas atmosphere. The low friction coefficients of the cermet specimens in air is likely to have been due to the formation of the low friction Mo oxides and W oxides.
Abstract: Changes in strain path represent one of the most important processing parameters that characterise hot metal forming processes. In the present study, the effect of strain path change on dynamic recrystallisation, strain-induced precipitation processes and phase transformation behaviour in plain carbon and Nb-microalloyed steels was investigated. To assess the effect of strain-path change, forward/forward and forward/reverse torsion tests were conducted. It has been shown that the strain reversal delays the dynamic recrystallisation kinetics whereas its effect on strain-induced precipitation process of Nb(C,N) is rather negligible. Also the onset of austenite-ferrite transformation is delayed; its products however doesn’t change significantly. This can be due to the fact that ferrite nucleation density plays the second order role compared to the geometry of deformation.
Abstract: The temperature dependence of austenite nucleation behavior within lath martensitic structure was investigated in an ultralow carbon 13%Cr-6%Ni martensitic stainless steel partially reversed at (austenite + ferrite) two phase region. The shape and nucleation site of the reversed austenite grains were varied depending on the reversion temperature; fine acicular austenite grains frequently formed along the lath boundaries at a temperature lower than 915 K, while the granular ones tended to nucleate mainly on the prior austenite grain boundaries at a higher temperature. In order to explain the temperature dependence of nucleation site transition, the difference in energetics of austenite nucleation between the lath boundary and the prior austenite grain boundary was discussed on the basis of the classical nucleation theory and FEM analysis. The calculation of the changes in interfacial energy and elastic strain for austenite nucleation suggested that the lath boundary acts as more preferential nucleation sites for austenite rather than the prior austenite grain boundary to reduce the increment of elastic strain when the reversion temperature is low.
Abstract: Behavior of the selective growth of Goss grains in grain-oriented electrical steel was investigated by controlling the heating rate in secondary recrystallization annealing．It was clarified that the important factors on the selective growth of Goss grains were the frequency and the mobility of grain boundary. It was demonstrated that boundaries having misorientation angle between 30 degree and 35 degree had the greatest influence on the selective growth, and the change of crystal orientation of secondary recrystallized grains expected by analyzing the change of primary recrystallized texture during secondary recrystallization annealing showed good agreement with the experimental result.
Abstract: With prices for metal resources such as nickel and molybdenum soaring, there is a heightened sense of crisis concerning resource scarcity. While Type304, the most common stainless steel, offers excellent corrosion resistance, its price is affected significantly by the cost of nickel because of its 8% nickel content. The stainless steel that has the same corrosion resistance as that of Type304 and does not contain nickel and molybdenum has been required. JFE Steel Corporation has developed a new 21%Cr-0.4%Cu stainless steel, the world’s first ferritic stainless steel, which offers equivalent corrosion resistance to Type304 while containing absolutely no nickel or molybdenum, two rare metals. The newly developed steel contains 21% chromium with the addition of 0.4% copper. The development of the steel is based on a new discovery that the passive films of stainless steels could be strengthened by the synergy effect of high chromium content and copper addition. Copper addition enriches the chromium content in passive films after field exposure. Newly developed 21%Cr-0.4%Cu stainless steel is adopted for many applications as a substitution for Type304, including commercial kitchenware, building materials and industrial machinery. The steel is expected to be a new standard of a ferritic stainless steel as a substitution for Type304.