Compact Strip Production Technology Research Articles

Comprehensive Study of CaO–SiO2‐Based MgO/Li2O‐Modified Mold Flux System for the Casting of Peritectic Steels

It is a challenge to produce peritectic steels through compact strip production (CSP) technology, due to the large volume shrinkage during the initial solidification of peritectic steels and dramatic thermodynamics variation caused by the significant improvement of casting speed. Herein, two mold fluxes are developed to meet the demands for producing peritectic steels by CSP technology. The results show that the developed mold flux MF‐2 achieves the balance between the heat transfer control and mold lubrication, by increasing the CaO/SiO2 ratio to a particular point at 1.25 and the addition of Li2O content. The oxides of CaO and Li2O act as network breakers that will provide more O2− ions to depolymerize the original silicate structure, which in turn promote the mold flux crystallization capability and an effective heat transfer control. Meanwhile, the system viscosity of MF‐2 is lowered; also a good flow fluidity and break temperature are achieved to guarantee an appropriate mold lubrication behavior. In addition, the further addition of Li2O could lower the melting temperature to ensure a certain thickness of liquid layer as well. Therefore, MF‐2 shows the best overall performance and could be applied to industrial operations.

Study on High-Temperature Mechanical Properties of SPHC Steel Produced by CSP Technology

The high-temperature mechanical properties of SPHC steel produced by compact strip production (CSP) process were tested on Gleeble thermal simulator under different temperature conditions. The results show that: at the strain rate of 1×10-3s-1,the SPHC steel has three brittleness temperature zones within the range from 650°C to 1200°C;the percentage reduction of area of the tested steel are all above 60% within the range from 950°C to 1150°C,thus the steel has good high temperature plasticity; the percentage reduction of area decreases rapidly when the testing temperature is under 900°C and the minimum percentage reduction of area is only about 41.78% at 800°C.

Effect of nano-sized precipitates on the crystallography of ferrite in high-strength strip steel

For strip steel with the thickness of 1.6 mm, the yield and tensile strengths as high as 760 and 850 MPa, respectively, were achieved using the compact strip production technology. Precipitates in the steel were characterized by scanning and transmission electron microscopy to elucidate the strengthening mechanism. In addition, intragranular misorientation, Kernel average misorientation, and stored energy were measured using electron backscatter diffraction for crystallographic analysis of ferrite grains containing precipitates and their neighbors without precipitates. It is found that precipitates in specimens primarily consist of TiC and Ti4C2S2. Ferrite grains containing precipitates exhibit the high Taylor factor as well as the crystallographic orientations with {012}, {011}, {112}, or {221} plane parallel to the rolling plane. Compared with the intragranular orientation of adjoining grains, the intragranular misorientation of grains containing precipitates fluctuates more frequently and more mildly as a function of distance. Moreover, the precipitates can induce ferrite grains to store a relatively large amount of energy. These results suggest that a correlation exists between precipitation in ferrite grains and grain crystallographic properties.

EFFECTS OF Ti AND Mn CONTENTS ON THE PRECIPITATE CHARACTERISTICS AND STRENGTHENING MECHANISM IN Ti MICROALLOYED STEELSPRODUCED BY CSP

As an advanced manufacturing technology to produce hot rolled strips,compact strip production(CSP) process was developed at the end of the last century and has been widely applied due to its high efficiency and low cost.Compared with the traditional technology,the advantages of CSP technology benefit from the refinement of austenitic grains and precipitation strengthening in the steels.This is because cooling rate is higher during the solidification of slab and the direct charging slab temperature is also higher in the CSP process,resulting in much higher solute contents in the solid solution before hot rolling than expected by the experiences from traditional steel production. Therefore,the Ti microalloyed steels produced by the CSP process exhibit good performance and have drawn much attention to Ti precipitate behavior and strengthening mechanism.However,the influence of alloying element Mn on the Ti microalloyed steels produced by CSP.especially the synergistic effect of Mn and Ti,was rarely reported.Therefore,in this work the microstructure and precipitate characteristics of two Ti microalloyed steels with different Ti and Mn contents produced by the CSP process were studied by electron backscatter diffraction(EBSD) technology and high resolution transmission electron microscope(HRTEM).The results show that the steel with higher Ti and Mn contents has a higher fraction of small-angle grain boundaries.Furthermore,the weight fraction of TiC precipitates with particle size smaller than 10 nm increases significantly,from 7.6%in the lower Ti and Mn steel to 26.1%in the higher Ti and Mn steel.However,the amount of Fe_3C precipitates decreases markedly. In addition,the strengthening mechanism analysis of the two tested steels shows that grain refinement strengthening and dislocation strengthening make great contribution to the yield strength,while the precipitation strengthening is the primary reason for the difference in the strength between two tested steels.

Texture Evolution during the Cold Rolled Low Carbon Steel Sheet under CSP Technology

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

Finite Element Analsysis of Deformation during Continuopus Rolling on CSP

In this paper, the CSP (compact strip production) technology was studied with the aid of elastic-plastic and thermal-mechanical coupled FEM using commercial software ABAQUS. The distribution and change of temperature, stress and strain field in rolling process were analyzed. In the view of boundary conditional influence on temperature, some factors such as thermal exchange between the work-roll and the thin slab, plastic deforming quantity of heat, cooling flux, convection and radiation heat exchange were considered during simulation. The results show contact heat conduction and deformation heat are the main factors that influence the temperature change of the thin slab. A good agreement was found between the predicted and the experimental data.

Analysis of flow field and temperature distribution in compact strip production casting process

A three-dimensional finite difference model has been formulated, using the commercial code CFX4, to describe the fluid flow and heat transfer in the funnel mould and secondary cooling segment of the compact strip production (CSP) casting process. Through simulation and computation with the established simulation model, influences of the factors such as casting speed, casting superheat, immersion depth of submerged entrance nozzle, amount of cooling water in the secondary cooling segment on flow field and temperature field in the funnel mould and secondary cooling segment of CSP technology were analysed.

Comparison and analysis of dislocation density, morphology and evolution in microstructure of low-carbon steel produced using different technologies

Three kinds of specimens were produced from hot strips of similar composition and same thickness (nominal gauge 4.0 mm) but produced using different technologies, and the dislocation density of these strips was quantitatively measured by positron annihilation technique test. The dislocation morphology and evolution in microstructure of each pass for producing the 1.9 mm hot strip using CSP (compact strip production) technology were observed under an H-800 transmission electron microscope; its density was also quantitatively measured using the positron annihilation technique test, and the factors influencing the dislocation density during the production process were analyzed. The experimental results show that the dislocation density in the microstructure produced using CSP technology is higher than that in the microstructure produced using conventional technology. This result was discussed and confirmed on the basis of the finite element simulation and the theory relevant to dislocations.

High strength microalloyed CMn(V–Nb–Ti) and CMn(V–Nb) pipeline steels processed through CSP thin-slab technology: Microstructure, precipitation and mechanical properties

Compact strip production (CSP) technology is an important upcoming processing route to produce low cost microalloyed high strength pipeline steels that meet the API standards. Hot strips of CMn(VNbTi) and CMn(VNb) steel grades with fine-grained ferrite–pearlite microstructure and small volume fraction of lower transformation product (non-polygonal ferrite: acicular ferrite/bainite) were produced using CSP technology with high strength and excellent low-temperature toughness up to −60 °C. For strip thicknesses between 6 and 12.5 mm, yield strength levels of up to 590 MPa and tensile strength levels up to 680 MPa were achieved. The CMn(VNb) steel exhibited outstanding notch-toughness in the range of 200 and 400 J/cm 2, in spite of its higher yield strength (∼100 MPa or greater) over the CMn(VNbTi) steel. The precipitates present in CMn(VNbTi) and CMn(VNb) steels were characterized in terms of morphology, size and chemistry, and crystallography. The microalloying elements, Ti, Nb, and V form M 4C 3 type of carbides in the ferrite matrix of both the steels. The multi-microalloying approaches of CMn(VNbTi) and CMn(VNb) results in the formation of duplex and triplex carbonitrides, respectively. The results of the development effort are described.