Compact Strip Production Line Research Articles

Microstructures and Mechanical Properties of Low Carbon Steel Hot Rolled in Ferrite Region Based on CSP Line

In this paper, the effect of ferrite region rolling on the microstructure and properties of steel plate heat commercial (SPHC) steel produced by compact strip production (CSP) process was studied in detail. Comparing ferrite rolled sheet with austenite rolled sheet, it was found that the average ferrite grain size of low carbon steel sheet rolled in ferrite region increased from 10.6 to 27.6 µm and the dislocation density was slightly reduced from 1.79 × 1011 to 8.9 × 1010 cm−2. The yield strength of ferrite rolled sheet is 92 MPa lower than that of austenite rolled sheet. The theoretical calculation and experimental results indicates that the coarsening of grains contributes to the 70% reduction of yield strength of ferrite rolled sheet, and the reduction of dislocation density and other strengthening factors account for about 30%. Texture analysis results by electron backscattered diffraction (EBSD) shows that the growth of {001} <110> and {112} <110> component in the texture of ferrite rolled sheet lead to the reduction of and Δr.

Improvement in continuously variable crown work roll contour under CVC cyclical shifting mode

A method of calculating the continuously variable crown work roll contour and the relevant constraint conditions under CVC cyclical shifting mode are proposed. The finite element model is built to calculate the roll gap crowns and the adjustment coefficients of bending force for different strip widths. Improvement in the continuously variable crown work roll contour has been implemented on the 1800-mm compact strip production line. This has resulted in the shifting stroke for the main strip width increasing by 30 %, the work roll wear being more uniform and the strip cross-section shape being better. The qualified rate of strip crown has risen from 98 to 99.5 %, and the qualified rate of strip head flatness has increased from 80 to 91 %.

Effects of auto-tempering on microstructure and mechanical properties in hot rolled plain C-Mn dual phase steels

In this paper, the behavior of auto-tempering in hot rolled plain C-Mn dual phase steels was investigated. The steels with thickness of 11mm were fabricated on the compact strip production line and coiled at 150°C and 260°C, respectively. The auto-tempering in the steel with coiling temperature of 260°C caused the softening of ferrite and martensite and the reduction in hardness difference between these two phases, ultimately led to the decrease in tensile strength and strain hardening ability and the increase in post-necking elongation. The Charpy impact test results indicated that the toughness of auto-tempered steel was superior to the non-tempered steel. When the tensile test or impact test was conducted on the auto-tempered steel, both ferrite grains and tempered martensite islands were readily elongated as fibrous structure. The acquired fibrous structure could inhibit the formation of microvoids and propagation of cracks in tensile test, and delayed the tensile fracture. In addition, the fibrous structure could inhibit the propagation of main crack during impact test, whereas induced the branching cracks, leading to high impact energy.

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

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%.

Research on Distribution of the Trace of Boron in Hot-Rolling and Annealing Low Carbon Steels in a Compact Strip Production Line

Research on Distribution of the Trace of Boron in Hot-Rolling and Annealing Low Carbon Steels in a Compact Strip Production Line

Surface inclusions and their evolution on strip rolled on CSP line and in following cold rolling process

Hot and cold rolled strip samples with surface defects such as black pockmark, sliver and central cracking were collected from a compact strip production line followed by cold rolling. Microstructures and chemical compositions of the strip with defects were studied by scanning electronic microscopy and energy dispersive X-ray spectroscopy. Four typical types of defects on strip including surface spherical mould powder entrapment, centre spherical mould powder entrapment, surface linear mould powder entrapment and centre linear mould powder entrapment were studied by hot and cold rolling experiment in laboratory. It was observed that spherical mould powder entrapment was transformed into the surface black pockmark after the hot rolling and cold rolling process. Centre spherical mould powder entrapment led to central fracture in the hot and cold rolling process. Surface linear mould powder entrapment resulted in sliver and centre linear mould powder entrapment led to severe sliver.

Scale Accretion on Homogenization Furnace Rollers in Compact Strip Production Mills and Its Densification Mechanism

SEM, EDS, XRD, ICP-AES and DTA were used to analyze the densification mechanism of the scale accretion on homogenization furnace rollers in compact strip production line. It was discovered that the accumulated scale was composed of many layers. A thin outer layer was relatively loose and thick inner layers were hard and densified. There were great differences in phase types between the loose and the densified layers. The loose layer was composed of mainly Fe 2 O 3 with minor Fe 3 O 4 . However, the densified layers consisted of FeO and Fe 3 O 4 ; FeO was formed on billets at high temperatures, which was transformed to Fe 3 O 4 at low oxygen partial pressure. Owing to the weight of the billet, the picked-up scale became densified. A great amount of wustite Fe (1-x) O in a shape of star was discovered distributing dispersedly in the scale accretion, resulting in a higher strength of it. Additionally, the minor residual elements of low melting point, such as Mg, As, Cu from billet and sulfur from burning gas were melted, resulting in an acceleration of the densification process. On the contrary, the outer surface layer of the scale accretion was partly changed to Fe 2 O 3 by the oxygen in the furnace in blow-off process, leading to a loose-layer.

Microstructural research on hot strips of low carbon steel produced by a compact strip production line under different thermal histories

Coupons with the same composition and thickness (4.0 mm nominal gauge) obtained from hot strips of low carbon steel underwent a series of investigations to analyze the microstructural characteristics and mechanisms responsible for their differences in mechanical properties. Two different industrial technologies were adopted, although the strips used in this research were produced on the same Compact Strip Production (CSP) line. One of the strips was produced with a routine γ→α CSP thermal history, but the other with a γ→α→γ* conventional thermal history. The only difference between them was that one technology had a α→γ* thermal history. Different specimens of both types of strips were prepared for metallographic observation, tensile tests, electron back-scattered diffraction tests and positron annihilation technique tests. Experimental results showed that the differences in mechanical properties could be ascribed to dissimilarities not only in the grain size and textural components but also in dislocation density.