Guo Yuan

Deformation and damping behaviors of foamed Al-Si-SiCp composite

Abstract The tensile and compressive as well as damping behaviors of A356/20SiCp composite foams with different porosity and cell sizes, which were produced by a foaming route, have been studied. The tensile stress–strain curves of the composite foams show a quite low fracture elongation, and the compressive stress–strain curves demonstrate three distinct regions, i.e. the linear elastic region, the crushing collapse region and the densification region. The linear elastic region only appears at very low strain (

Effect of direct quenching and partitioning treatment on mechanical properties of a hot rolled strip steel

Three different online heat treatment processes were designed to study the effects on the mechanical properties of a 0.19C-1.6Si-1.6Mn (wt%) hot rolled strip steel. The microstructures were characterized by means of SEM, TEM, EPMA, and XRD. The mechanical properties were estimated by tensile tests. Results showed that a satisfying combination of strength and ductility could be obtained through the ferrite relaxation and direct quenching and partitioning process. Analysis was also focused on this process. The microstructure contained proeutectoid ferrite grains, martensite packets and blocky or interlath retained austenite, and also contained carbide-free bainite in the case of relatively high quench temperatures. The retained austenite fraction was increased through proeutectoid ferrite and partial bainite transformation, while the tensile strength was also consequently decreased. The most of retained austenite transformed to ferrite under deformation and the elongation was obviously improved.

Heat Transfer During Quenching by Plate Roller Quenching Machine

For plate quenching on a roller quenching machine, heat transfer process is investigated. According to the practical online experiment of plate center temperature, average heat transfer coefficient under different conditions and temperature fields are analyzed by numerical simulation. The results show that, at the water temperature of 15 °C, the instantaneous maximum quenching cooling rate is 17.6 °C/s for the plate of 50 mm in thickness in roller quenching process. In the temperature range of 400 — 850 °C, the maximum is 12. 1 °C/s. With the plate surface temperature decreasing, surface heat transfer coefficient increases at first, and reaches the maximum value of about 15 000 W/(m2 • K), and then decreases. The calculated heat transfer coefficients are applied to analyze plate temperature field of different thicknesses, and the difference between the calculated and measured temperature is less than 5%.

Microstructure and mechanical properties of economical dual phase wheel steels based on CSP line with later ultra fast cooling

Abstract To attain the economical wheel steels with high strength, the microstructure and properties of steel with microstructure consisting of ferrite and martensite were studied. The transformation behaviour of the economical wheel steels under continuous cooling condition and stepped cooling condition were researched and the 11·0-mm thickness wheel steel strips with simple chemical composition were developed on compact strip production (CSP) line with later ultra fast cooling (UFC) system. The results indicate that the dynamic continuous cooling transformation (CCT) curves of low carbon Mn–Cr steel is characterised by a large ferrite region, and the stepped cooling pattern is more beneficial to achieve ferrite–martensite microstructure than continuous cooling pattern. In order to obtain adequate polygonal ferrite matrix during stepped cooling process, the early cooling temperature should be controlled in the range of 700–660°C and the isothermal holding time should be ensured. The 11·0-mm thickness dual phase (DP) wheel steel strips are achieved on CSP line via control cooling technology based on later UFC system. Tensile strength increment of C–Mn–Cr steels can reach 130–170 MPa when the F-P microstucture is replaced by F-M microstucture. The wheel steel strips with tensile strength above 590 MPa, yield ratio under 0·62 and elongation above 28% have been used for wheel discs, whose weight achieve reduction of 16–22%.

An On-line Finite Element Temperature Field Model for Plate Ultra Fast Cooling Process

Taking the element specific-heat interpolation function into account, a one-dimensional (1-D) finite element temperature field model for the on-line control of the ultra fast cooling process was developed based on the heat transfer theory. This 1-D model was successfully implemented in one 4300 mm plate production line. To improve the calculation accuracy of this model, the temperature-dependent material properties inside an element were considered during the modeling process. Furthermore, in order to satisfy the real-time requirements of the on-line model, the variable bandwidth storage method and the Cholesky decomposition method were used in the programming to storage the data and carry out the numerical solution. The on-line application of the proposed model indicated that the deviation between the calculated cooling stop temperature and the measured one was less than ±15 °C.

Hot Rolled Strip Re-reddening Temperature Changing Law during Ultra-fast Cooling

Temperature deviation between surface and the center of hot rolled strip is formed during ultra-fast cooling (UFC). Surface temperature would rise when temperature deviation goes up to an extent, and strip re-reddening phenomenon will appear. Strip re-reddening affects the stability of strip microstructure, property and temperature control precision. Thus, it is necessary to conduct research on re-reddening temperature changing law to improve strip property and temperature control precision. Strip temperature trends for various strip thicknesses and ultra-fast cooling rates were obtained by numerical calculation method. Re-reddening temperature, temperature deviation between surface and center, and boundary layer position changing law were obtained. By comparison, some conclusions were obtained: UFC re-reddening temperature and laminar cooling (LC) re-reddening temperature were linear to ultra-fast cooling rate respectively. Ultra-fast cooling rate affected UFC re-reddening temperature greatly, but it had little effect on LC re-reddening temperature. Equations which were used to calculate UFC re-reddening temperature, LC re-reddening temperature and maximum temperature deviation were obtained. The position of boundary layer stayed in 1/4 strip thickness.

The Development and Application of the Hot-Rolled Plate Ultra-Fast Cooling Equipment

The ultra-fast cooling technical is a newly developed thermal technical in recent years for the hot-rolled steel plate. The key to develop the ultra-fast cooling equipment are the design of the nozzle structure and the cooling process. The heat exchange mechanism of the jetting impingement heat transfer mode was illustrated during ultra-fast cooling process for the hot-rolled steel plate in this paper. The flow field characteristics and the cooling technological process during the plate ultra-fast cooling process were simulated. And the newly-developed ultra-fast cooling equipment for the hot-rolled plate and its application were also introduced in this paper.

Development of Cooling Process Control System for Backward UFC in CSP

Backward Ultra-fast cooling (UFC) plays a key role in low-cost dual-phase steels production. Cooling process control system for backward UFC was developed to meet the process requirements. Basing on basic theory of heat transfer, cooling control model was established to accomplish temperature calculation. To deal with the influence of technological conditions fluctuations an adaption system, including self-learning function and feedback function was proposed to intelligently realize temperature correction. The developed cooling strategy can achieve diversified cooling path control. The controlling of significant technological parameters, including cooling rate and air cooling time for dual-phase steels, was also accomplished. Furthermore, flexible and diversified UFC strategies were developed aiming at high temperature precision and low temperature deviation control in thickness direction. The system has been applied successfully in dual-phase steel production with high stability and reliability. The precision of medium temperature (MT) can be controlled within ±10°C, and the UFC delivery temperature (UFC-T) can be limited within ±30°C of the target values.

Effects of Processing Variables on Microstructure and Yield Ratio of High Strength Constructional Steels

The process of “controlled rolling+relaxation+ultra fast cooling (UFC)” for high strength constructional steel with low yield ratio was presented. Microstructure and corresponding relationship with low yield ratio were investigated. The results showed that the constructional steels with multiphase microstructure of bainitic ferrite, martensite-austenite (M-A) and lath bainite were obtained through the creative process. The grain size decreased with the decrease in finish rolling temperature, which enhanced the strength by the grain refinement strengthening. The proper relaxation treatment promoted the bainitic ferrite lath width and the formation of blocky M-A constituent. In addition, both the tensile and yield strength increased with the decrease in finish rolling temperature and UFC final temperature, but the yield strength increased more significantly than tensile strength, which caused the increase in yield ratio. By using the process of “controlled rolling+relaxation+ultra fast cooling”, the excellent comprehensive mechanical properties of 780 MPa grade constructional steels of 12 –40 mm in thickness were achieved.

Analysis on the Influencing Factors of Heat Transfer for the Slot Nozzle Convection Impact in Rolled Strip Preposition Ultra-Fast Cooling

The aim of this work is to optimize process design parameters of the hot rolling steel strip preposition ultra-fast cooling (UFC) system, and improve the stability and uniformity of micro heat transfer during the high strength cooling process of hot rolling strip. According to the technology and equipment feature of the pre-UFC system for a factory, the convective heat transfer process of single nozzle and strip in UFC system was studied numerically by the fluid-structure interaction finite element method (FEM). The influence of different parameters on the slot impinging jet heat transfer coefficient was obtained, such as jet angle, the jet velocity, the slot nozzle width and water temperature. The results show that on the ultra-fast cooling process of the strip in the initial temperature of 850 °C and thickness of 8 mm, the global average heat transfer coefficient can be increased with the increase of jet velocity, and decrease of the cooling water temperature. The jet angle and the slot nozzle width have minimal effect on it for the whole heat transfer zone. The local average heat transfer coefficient first increased and then decreased with the increase of jet angle and slot nozzle width at the jet impingement location.