Papers by Author: Hui Ping Ren

Abstract: It is significant theoretically to study the nucleation laws of the phase transformation products of the supercooled austenite. The different iron and steel materials were used to study the nucleation of pearlite, bainite and martensite by QUANTA-400 environmental scanning electron microscope and JEM-2100 transmission electron microscope. The results show that, from the high-temperature zone to the low-temperature zone, the nucleation of the transformation products of the supercooled austenite is a gradually evolutionary process from two-phase nucleation to single-phase nucleation. Pearlite nucleates in the austenitic grain boundary, bainite nucleates preferentially in the grain boundary and sometimes in the grain interior and martensite nucleates preferentially in the interface and generally in the grain interior. The preferential nucleation sites are the interface, and with the decrease of the transformation temperature, they gradually shift to the defects in the grain interiors, which accord with the general rules of the phase transformation nucleation.

Abstract: The original austenite grain size, the inclusions and the isothermal annealing microstructure of 20MnCrNi2Mo wear-resistant cast steel without and with Rare Earth were observed by metallographic microscope and QUANTA-400 environmental scanning electronic microscope. The effect mechanism of Rare Earth in 20MnCrNi2Mo wear-resistant cast steel was investigated. The results show that adding Rare Earth in 20MnCrNi2Mo wear-resistant cast steel can refine the original austenite grains. Meanwhile, it can reduce the inclusions size and change the inclusions shape from irregular to nearly spherical. In addition, the Rare Earth in 20MnCrNi2Mo wear-resistant cast steel can increase the amount of ferrite, reduce that of pearlite in the isothermal annealing microstructure and refine the microstructure of pearlite.

Abstract: The precipitation of copper during aging at 600oC in high-purity Fe-Cu alloy was examined by means of transmission electron microscopy (TEM).Nano-scale copper-rich clusters with a B2-like structure were observed during heat treatment. These micro structural features play an important role in precipitation strengthening. In addition, the precipitation process has been analyzed in terms of the evolution of microstructure by a Monte Carlo method. A description of the coherent precipitation of copper in iron, based on a vacancy diffusion mechanism, thermally activated jump frequencies and cohesive energy is discussed in order to deal with simultaneous precipitation of metastable and stable phases in Cu-containing steel during aging. This analysis gives an estimation of the precipitation dynamics, as well as the evolution of Cu precipitates across a wide range of temperatures.

Abstract: In this item, the low carbon steel hot sheets by compact strip production (CSP) technology were cold rolled and annealed in laboratory. texture evolution during the production process of CSP-cold rolled strip were investigated by means of the XRD. The results were as follows: After hot deformation of thin slab formed a strong γ- fibre orientation texture, the density of texture increase with the cold rolled reduction increased, especially for the negative texture {100}, in γ-fibre orientation cold rolling texture density has no significant change. Compared to the traditional process, hot rolled steel sheet has higher texture, cold-rolled steel sheet has the same texture, and after-annealing sheet has further higher texture in the CSP-cold rolling process. This study enables better understanding and control on the evolution of textures the cold-rolled steel sheet processed by CSP technique and provides theory support for exploiting the CSP the cold-rolling deep drawing steel sheet

Abstract: 0MnVTiNb, 12Cr1MoV, 20Cr2Ni4, 35CrMo, 40Cr, 42CrMo, 60Si2CrV and T8 steels and Fe-1.2C alloy were used to study the morphology and formation mechanism of martensite by metallographic microscope, QUANTA-400 environmental scanning electron microscope and JEM-2100 transmission electron microscope after they were austenized at different temperature and then quenched respectively. The results show that the martensite of low-carbon steel is lath martensite, the martensite of high-carbon steel is plate martensite, and the martensite of medium-carbon steel is the integrated microstructure of lath martensite and plate martensite. With the increase of carbon content, the morphology of martensite in steel evolves from lath shape to plate shape, the distribution of martensite slices changes from in parallel to with crossing angle, and the substructure evolves from high density dislocations and stacking faults to twin crystals. The martensite in steel can nucleate in the austenite crystal grain interior as well as along the austenite crystal grain boundary. It is proposed that the volumetric strain energy in martensite transformation is the essential reason of the different morphologies of martensite.

Abstract: The solid solution of the second phase particle and austenite grain growth behavior of the high niobium-containing RE steel was studied by mathematical calculation and extraction replica technique. The purpose of the study was to investigate the effects of Rare Earth La on austenite grain growth and propose an empirical equation for predicting the austenite grain size of RE steel. Austenite grain grows in an exponential law with the increase of heating temperature, while approximately in a parabolic law with the increase of holding time. Results show that the RE steel has good anti-coarsening ability at elevated temperatures. When soaking temperature is lower than 1250°C , AGS and growth rate are small for high niobium steel, but soaking temperature is lower than 1220°C , AGS and growth rate are small for RE steel. RE La can promote solid solution of second-phase particles Nb(C, N), the solution temperature decrease 30°C than high niobium steel.

Abstract: The mechanism responsible for the formation of recrystallization texture is still disputed although recrystallization texture has long been a subject of research. This is mainly related to the complexity of recrystallization itself .The mechanism of recrystallization microtexture Cold-rolling low carbon sheet steel based on CSP was investigated by the electron back scatter diffraction(EBSD) was investigated. In addition, the origin of nuclei with specific orientations was studied. The results showed that the formation of recrystallization texture is explained by oriented nucleation and the nucleis show around 50% frequency of 15–60°misorientation with their surrounding deformed matrices. Deformed γ-fibre texture components increase more rapidly during the early stage of recrystallization. In contrast, the deformed α-fibre components, such as {001}<110> components disappear rather rapidly early stage of recrystallization and {112}<110> components increases rapidly late stage of recrystallization and grains growth. By microcosmic orientation distribution analyse find that the new {011}<100> grains are nucleated within shear bands in the deformed {111}<112> grains, New {111}<112> grains are nucleated within deformed {111}<110> grains and new {111}<110> grains originated in the deformed {111}<112> grains .

Abstract: The precipitate behavior of copper in the high purity structural steel was investigated by means of transmission electron microscope (TEM), and aging hardening mechanism was investigated based on the corresponding phase transformation mechanism. The results show that lots of Cu rich clusters exist in supersaturated ferrite matrix in solid solution, which evolve to B2-like structure during aging. It is found that the hardening in the initial stage is controlled by the coherency relationship of the B2-like structure with matrix that forms the obstacle of the dislocation motion, while the decrease in hardness after the peak is attributed to the loss of coherency, which should highly likely be the dominant reason of aging hardening in Cu bearing high purity steels.

Abstract: The precipitation of copper during aging at 650oC within ferrite in high-purity Fe-1.03wt%Cu steel was examined by transmission electron microscopy, and the influence of precipitation particles on property of experimental steel was investigated. The microstructure and the corresponding diffraction patterns of different zone axis were analyzed. Nano-scale copper-rich clusters with B2-like structure and high density dislocation around precipitate was observed during either solution treatment or aging. Nano-scale metastable precipitates and high density around them were found to play the most important role for increasing steel strength.

Abstract: Six kinds of Al-Zn-Mg-Cu alloys, modified with nickel and zirconium, have been produced by rapid solidification using spray deposition(the Osprey process). The effect of nickel on the structures, mechanical properties of ultrahigh strength aluminium alloy is studied, and the probable maximum of mechanical properties is predicted. There are three nickel-rich phases, Al3Ni2, Al7Cu4Ni and MgNi2, forming in 1%Ni alloy, its ultimate tensile strength(UTS) increased with increasing extrusion ratios significantly while maintaining high levels of ductility, Futhermore, the extruded bars show enhancing more clearly than extruded plates in UTS and ductility. The content of Ni should decreased with increasing of Zn and Zr, and the highest properties(UTS=832MPa, Elongation=7.5%)are attained in 0.20Zr＋0.30Ni (wt%)alloy. In addition, the size, the shape and the homogeneous distribution of zirconium-rich phase produced in solidification is the key to effecting the mechanical properties of materials when Zr content is 0.2~0.5％.