Papers by Author: Si Hai Jiao

Abstract: Abaqus software is used to simulate the deformation behavior of typical steel materials during the shearing process, and to analyze the displacement change of the materials during the shearing process, and to study the main causes of the steel plate shear cracks. The results show that the mechanical properties of the steel, especially the uniform elongation of the steel plate, are important factors affecting the shear crack. At the same time, the room temperature tensile curves of several typical steels are measured. The corresponding relationship between the curve characteristics and the shear cracks is in agreement with the simulation results. Keywords: shear crack, simulation, mechanical properties, uniform elongation

Abstract: To obtain a low cost, environmentally friendly and effective lubricant, a novel nanoTiO₂ additive oil-in-water (O/W) lubricant for hot steel rolling has been developed. Based on the contact angle, tribological and hot rolling tests, the performance of the nanoTiO₂ additive O/W lubricants was evaluated and discussed. The results show that the strongest adhesion force between the nanoTiO₂ additive O/W lubricant and the work roll is obtained after addition of 4% nanoTiO₂ additive in the 1% O/W lubricant. The nanoTiO₂ nanoparticles can reduce coefficient of friction (COF) and rolling force, and enhance the surface quality of the hot-rolled product. The lubrication mechanism of nanoTiO₂ additive O/W-based lubricant has been proposed.

Abstract: The dry sliding wear behaviour of the full pearlite in a novel bimetal consisting of low carbon steel and hypoeutectoid steel has been studied by means of pin-on-disc type wear tests at room temperature. Thermomechanical treatments were performed on the bimetallic samples to obtain different interlamellar spacings. It was found that interlamellar spacing decreased with an increase in plastic strain to a great extent initially and followed by a lower extent of decrease. This decrease not only increases the hardness and strain hardening capacity of the fully pearlitic microstructure, but also is in favor of stabilizing the friction coefficient during sliding process. The observations of wear tracks show that delamination dominated the wear process when interlamellar spacing is higher than 200 nm, while pronounced oxidational wear occurred with interlamellar spacing below 200 nm.

Abstract: The high carbon steel (HCS)/low carbon steel (LCS) laminated composite made by centrifugal casting technology was subjected to hot compression tests on Gleeble 3500 thermomechanical simulator in a range of temperatures (800-1100 ^oC) and strain rates (0.02-10 s^-1). The hot-working behavior of the laminate was characterised by analysing the flow stress-strain curves and constructing the processing map based on dynamic materials model via superimposing efficiency of power dissipation and flow instability maps. The safe and unsafe processing conditions were identified in the processing map which was validated by microstructural examinations. Banded microstructure and micro-shear cracks occurred in the unsafe domains were responsible for the flow instability, while dynamic recrystallisation in stable domains with high efficiency of power dissipation imparted a good workability to the laminate. The optimum hot-working parameters were determined to be: (i) 800-1050 ^oC and 0.02-0.04 s^-1, (ii) 800-1045 ^oC and 2.5-10 s^-1 and (iii) 1050-1100 ^oC and 0.02-2.5 s^-1.

Abstract: A high carbon steel (HCS) and low carbon steel (LCS) bimetal was fabricated by centrifugal composite casting. Two different thermomechanical treatments (TMT1 and TMT2) were employed to improve the mechanical properties of the bimetal. TMT1 process includes 60% of overall reduction by hot compression with temperatures of 1100 and 800 ^oC, respectively. While TMT2 process involves 60% of overall reduction using the two-step deformation method, which is a combination of non-isothermal compression cooling from 1100 to 800 ^oC and isothermal compression at 800 ^oC. The flow stress behavior, microstructural evolution and microhardness variation were analysed. Experimental results show that both TMT processes contributed to the improvement in mechanical properties resulting from a refinement of the grain size and an increase of density of pearlitic lamella in HCS layer. However, TMT2 process gave a better efficiency and a more significance in improvement of properties with the evidence of the same overall reduction leading to a higher microhardness.

Abstract: This investigation attempts to improve the wear resistance of low chromium white cast iron (LCCI) by thermomechanical treatment. The thermomechanical treatment of the brittle LCCI with crack-free was successfully carried out by bonding it with a ductile low carbon steel firstly. Afterwards the dry sliding wear behavior of as-cast (LCCI-A) and thermomechanically processed (LCCI-B) samples was studied using a pin-on-disc apparatus under different test conditions. The microstructural examination shows that the refined supercooled austenite and plenty of secondary carbides in LCCI-B replaced the original microstructure of martensite and retained austenite with network carbide in LCCI-A. This significant evolution is beneficial to form and stabilise the oxide layer on the substrate, which makes the oxidational wear rather than abrasive wear or delamination dominating the wear process so that the improvement of the wear resistance of LCCI was achieved by hot working.

Abstract: The relatively higher alloy content of AHSS leads to complex transformation behavior after finishing rolling and the transformation is unable to complete just after coiling, which causes some extent of deformation due to the transformation dilation. In the present study, low strain rate deformation was performed at γ/α temperature zone after the sample was deformed to simulate the deformation and transformation interaction after coiling by using Gleeble 3800 thermo-mechanical simulator. All the flow stress curves display a sharp decrease after certain strain when deformation temperatures below 750°C. The interaction between deformation and transformation is used to explain the phenomena.

Abstract: The bubble structures, fishscaling resistance, adhesion and its mechanism of vitreous enamel to low carbon steels were evaluated by microscopic methods. The results show that the microalloying elements deteriorates the adhesion but suppress the fishscaling tendency, the enamel-steel interface adhesion could be explained as mainly the mechanical interlocking and chemical bonding during the firing process; the lower carbon substrate causes higher proportion of bigger bubbles in the enamel layer and subsequently causes the lower fishscaling susceptibility.

Abstract: Contact friction is of crucial importance for the accurate modelling, optimum design and control of industrial rolling processes. Hot rolling tests were carried out to investigate the deformation of oxide scale and friction during hot rolling of stainless steel 304L. The morphology of oxide scale layer and the surface roughness transfer under the conditions of hot rolling were obtained. The friction condition at the roll-strip interface was determined.