Liu Xiang-hua

A three-dimensional finite element simulation of the vertical–horizontal rolling process in the width reduction of slab

Abstract A thermal coupling analysis is carried out by the full three-dimensional rigid–plastic finite element method to simulate vertical–horizontal rolling process during width reduction in the roughing stands of a hot strip mill. The slab shape, the spread and temperature as calculated are in good agreement with the experimental results in production mills, and the sectional distribution of temperature is given.

3-D rigid–plastic FEM analysis of the rolling of a strip with local residual deformation

Abstract A strip with longitudinal ribs is one type of new-shaped strip that has been developed in recent years. The main characteristic of the rolling of a strip with ribs is that there is local residual deformation on a normal flat, and it is a new forming process that has the deformation characteristics of both strip- and shaped-steel. Using the rigid–plastic FEM, the forming process is analyzed in this paper and the numerical results of the change of the rib height in the deformation zone and of quantities such as rib height, the separating rolling load and the spread ratio have been obtained, the result of calculation being in accordance with those of the experiment.

Three-dimensional thermo-mechanical finite element simulation of the vertical–horizontal rolling process

Abstract This paper presents a three-dimensional thermo-mechanical analysis of the vertical–horizontal rolling process utilised in the large width reductions of slabs in hot strip mills. The theoretical analysis is based on the utilisation of the finite element flow formulation to characterise the material flow, to predict the distribution of temperature and to estimate the roll separating force. The numerical predictions were verified by metal experiments performed at the hot strip mill unit of Bao Steels (China). The experimental work consisted of the monitorisation of the surface temperature and of the roll separating force for several rolled slabs. The theoretical distribution of stress obtained from the numerical simulation of the process is also analysed.

Self-Learning and Its Application to Laminar Cooling Model of Hot Rolled Strip

The mathematical model for online controlling hot rolled steel cooling on run-out table (ROT for abbreviation) was analyzed, and water cooling is found to be the main cooling mode for hot rolled steel. The calculation of the drop in strip temperature by both water cooling and air cooling is summed up to obtain the change of heat transfer coefficient. It is found that the learning coefficient of heat transfer coefficient is the kernel coefficient of coiler temperature control (CTC) model tuning. To decrease the deviation between the calculated steel temperature and the measured one at coiler entrance, a laminar cooling control self-learning strategy is used. Using the data acquired in the field, the results of the self-learning model used in the field were analyzed. The analyzed results show that the selflearning function is effective.

Analysis of the non-steady state vertical–horizontal rolling process in roughing trains by the three-dimensional finite element method

Abstract The vertical–horizontal rolling process is often used to accomplish width reduction so as to provide a synchronising operation between the continuous slab casting and hot rolling processes. Numerical simulation of the non-steady state deformation behaviour around the head and tail ends during this process is made by the full three-dimensional rigid–plastic finite element method. An explanation is provided in the theory for the ‘thin element technique’ at the inlet surface of velocity discontinuity. To deal with the interpolation of friction within a surface of an element contacting partly with the roll, a new term, so-called ‘pseudo shape function’, is presented and a related new equation formula is deduced. The calculated shape of the slab edge, the separating force and the rolling torque are consistent with those measured experimental ones for the model material lead.

DYNAMIC RECRYSTALLIZATION AND PRECIPITATION BEHAVIORS OF A KIND OF LOW CARBON V–MICROALLYED STEEL

By using thermo-mechanical simulator,OM and TEM,the dynamic recrystallization (DRX) and precipitation behaviors of a kind of low carbon V-microalloyed steel have been investigated at temperatures ranging from 900 to 1050℃and strain rates from 0.01 to 10 s~(-1).The activation energy (Qdef) for hot deformation of this kind of V-microalloyed steel was calculated to be 341.97 kJ/mol by regression analysis,while the apparent stress exponent(n) was calculated to be 4.24.The equation describing the hot working process was also obtained.The critical strain for DRX was accurately determined based on the P-J method and high order polynomial fitting between strain hardening rate and true stress,and mathematical models of critical strain and peak strain versus Z parameter were deduced.The dynamic precipitation behavior of V(C,N) particles at low strain rate was further investigated.The results show that with increasing the strain,the average size of V(C,N) particles increases and the size distribution of the precipitates become wide.The calculations of the driving force for recrystallization and pinning force show that once the dynamic recrystallization take place, the dynamic precipitation could not prevent dynamic recrystallization from occurring.

Forward and Backward Slip Models in MAS Rolling Process and Its On-Line Application

Based on the MAS rolling process in plate mill, the mathematical models of forward and backward slips of the wedges at plate head and tail were derived. According to the new model, the difference between the forward slip of the wedge and that of the normal part of the plate is obviously very small. The deviation is less than 2. 5% in general. Thus, in actual application, the forward slip of normal part of the plate can be used to calculate the length of rolled plate instead of the derived model. The rationality of this simplified method was confirmed with the application in Shougang 3 500 mm plate mill. The test results showed that the wedges of plate head and tail are symmetrical. The plate width deviation is greatly decreased by using the MAS method.

MICROSTRUCTURE, MECHANICAL PROPERTIES AND STRENGTHENING MECHANISMS OF A Cu BEARING LOW-CARBON STEEL TREATED BY Q&P PROCESS

A low carbon steel containing Cu addition was treated by Q&P process using a CAS- 200 continuous annealing simulator. The microstructure of the steel was characterized by means of SEM, EBSD, XRD and TEM and its mechanical properties were investigated by tensile testing at room temperature. Cu-rich precipitates formed during the Q&P process were observed as spherical particles in martensitic laths and are 9 nm to 20 nm in diameter. According to the Orowan mechanism, those fine particles may have a contribution to the yield strength of the steel about 134 MPa. Also observed are three different morphologies of the retained austenite phase in the test steel, i.e. thin film-like, fine granular and blocky, formed at different locations. The test steel has a good comprehensive mechanical properties, of which the product of tensile strength and elongation, the tensile strength and the total elongation are as high as 21.2 GPa·%, 1326 MPa and 16%, respectively. The excellent combined properties can be attributed to the effect of transformation induced plasticity (TRIP) caused by the retained austenite.

Static recrystallization behavior of a martensitic heat-resistant stainless steel 403Nb

A static recrystallization behavior between the rolling passes of a martensitic heatresistant stainless steel 403Nb has been studied by OM, TEM and double-hit thermomechanical simulator to explore the efiects of deformation temperature, strain rate, strain and the prior austenite grain size. The results show that increases of deformation temperature and strain rate and strain can promote the static recrystallization of 403Nb steel. Static recrystallization also proceeds faster when the prior austenite grain size is smaller. Microstructural observation indicates that the volume fraction of static recrystallization increases with prolonged interval of the rolling passes. Straininduced precipitation can lead to an appearance of a platform in the kinetic curve of static recrystallization. Difierent from the conventional micro-alloying steel, the strain-induced precipitates in 403Nb steel during hot rolling are carbides containing Nb and Cr.

Derivation of Simplified Models of Plan View Pattern Control Function for Plate Mill

The plan view pattern control theoretical models were simplified. Under the condition of constant volume for the plan view pattern compensation, the relation between the thickness and the length can be simplified to the linearity in the segment for the plan view pattern control function. The compensation volume can be dispersed for easy calculation. By comparing the model calculation result with the actual result, it was concluded that the simplified model can be used for the online control process.