Showing papers on "Microalloyed steel published in 1988"

On the formation of duplex precipitate phases in an ultra-low carbon microalloyed steel

Abstract: The formation of duplex carbonitride precipitates in an ultra-low carbon Ti-Nb steel, either isothermally annealed or controlled rolled after a high temperature solutionizing treatment, has been studied experimentally and the relative phase stabilities of the precipitate and matrix phases, over the temperature range of the experiments, have been calculated. The austenite and ferrite phases were modelled using the Redlich-Kister-Muggianu interpolation formula and the (TiXNb1−X)(C1−YNY) phases, which were assumed to be stoichiometric, using the Hillert-Staffansson formalism. Two possible ways in which the duplex precipitates could have been formed were explored: Equilibrium phase separation within a (TiXNb1−X(C1−YNY) phase or two-step precipitation, the low-temperature precipitate being nucleated on a precipitate which had been formed earlier at a higher temperature. Comparison of the experimental and theoretical results clearly indicates that both the duplex precipitates formed by precipitation in austenite in specimens double-annealed at 1250C and 900C and those formed by controlled rolling specimens to 700C from a solution temperature of 1050C were formed by two-step precipitation processes.

Effects of thermomechanical processing on the microstructure and mechanical properties of a Ti-V-N steel

Abstract: Based on studies of austenite deformation behavior and continuous-cooling-transformation behavior of a Ti-V microalloyed steel by cam plastometer and quench-deformation dilatometer, respectively, plate rolling schedules were designed to produce (i) recrystallized austenite, (ii) unrecrystallized austenite, (iii) deformed ferrite + unrecrystallized austenite. The effects of austenite condition and cooling rate on the final microstructure and mechanical properties were investigated. To rationalize the variation in final ferrite grain size with different thermomechanical processing schedules, it is necessary to consider the kinetics of ferrite grain growth in addition to the density of ferrite nucleation sites. The benefit of dilatometer studies in determining the optimum deformation schedule and cooling rate for a given steel is domonstrated. A wide range of tensile and impact properties results from the different microstructures studied. Yield strength is increased by increasing the amount of deformed ferrite, bainite, or martensite, and by decreasing the ferrite grain size. Impact toughness is most strongly influenced by ferrite grain size and occurrence of rolling plane delaminations.

Process for producing rolling bearing elements from a microalloyed steel

Abstract: In a process for producing rolling bearing elements from a microalloyed steel, the rolling bearing elements are hardened only on their running track surfaces. To enable the process to be used particularly economically in spite of hot-forming and subsequent machining of the rolling bearing elements, these are hot-formed at 900 to 1200@C and cooled from the hot-forming heating pass under control, so that a fine perlite microstructure is formed. The rolling bearing elements are then machined and finally, for surface-hardening, heated partially inductively, austenitised and quenched in oil, salt or water.

Microanalysis of nonoriented P containing silicon steel

Abstract: Texture determination, Si, P distribution, and microstructural analyses were made for the nonoriented P containing silicon steel (DW1) by x‐ray diffractometer (XRD), electron probe microanalyzer (EPMA), and transmission‐electron microscope (TEM), respectively. DW1 is a new electrical steel designed by WISCo. It contains about 0.05% Si and 0.11% P [L. He, D. Fei, and P. Liu, in the Second International Conference on the Physical Metallurgy of Electrical Steel, New York, 1985 (unpublished)]. The textures were measured for samples decarburization‐annealed at different temperatures such as 710, 750, 820, and 860 °C. According to the ratio of (100) and the magnetic properties of DW1, we found that the optimum result was obtained at 820 °C. It was found from the result of EPMA measurements that the distribution of Si and P is homogeneous without any grain boundary segregation. The microstructure shows that coarse precipitates of AlN an MnS were present in the hot rolled strip and remained in the strip after 102...

Influence of accelerated cooling on the microstructure and mechanical properties of a microalloyed steel

Abstract: The effect of accelerated versus late cooling of microalloyed steels with finishing temperatures in the range 1143 to 1203K on the microstructure and mechanical properties has been investigated. The steel used in this investigation was a Nb microalloyed steel with a nominal composition O.1%C, 0.07%Nb, l.O%Mn, and 0.2%Si. The slabs were rolled on a hot strip mill using a controlled rolling practice and the cooling practice of the strip was controlled by the rolling speed and the cooling pattern. The results indicate that the finest ferrite grain size was obtained when the steel was rolled under the conditions of 1203K finishing temperature and delayed cooling practice. However the highest strength was obtained in the steel with the same finishing temperature but cooled early. The increase in strength was due to dispersion strengthening by fine Nb(CN) precipitates. Extensive grain boundary cementite formation was also noted in these steels while pearlite formation was mostly suppressed. No evidence of Nb(CN) precipitation during the austenite to ferrite transformation or in the ferrite was observed. This is suggested to be due to the suppression of the precipitation reaction by the fast cooling rate.