Direct Rolling Process Research Articles

The Evolution of Microstructure during Thin Slab Direct Rolling Processing in Vanadium Microalloyed Steels.

The evolution of microstructure during a simulation of the thin slab direct rolling process has been studied on two low carbon steels, microalloyed with V-N and V-Ti-N. The steels were examined using optical microscopy, analytical transmission electron microscopy (TEM) and energy dispersive X-ray (EDAX).After the 4th rolling pass, in a five pass schedule, the initial coarse austenite grain size (≈1 mm) was reduced to about 50 μm in Steel V-N and 22μm in Steel V-Ti-N. The average ferrite grain size in the final strip was slightly smaller in Steel V-Ti-N (4.8-6.6 μm) than in Steel V-N (5.3-7.2 μm). For Steel V-N, VN was only observed after 1 050°C equalization, but it was not found after 1 200°C and 1 100°C equalisation. For Steel V-Ti-N, V-Ti(N) particles formed during casting and during equalization for all the equalization temperatures (1 200°C, 1 100°C and 1 050°C). AlN particles precipitated in Steel V-N only during 1 050°C equalization and were often associated with MnS or MnS and VN. No AlN was detected in Steel V-Ti-N. Fine V containing precipitates (<10 nm) were observed in the final strip for both of the steels, but the frequency of the fine particles was lower in Steel V-Ti-N than in Steel V-N. The fine precipitates in the final strip make a major contribution to dispersion strengthening. High strength (LYS≈460-560 MPa) with good toughness and good ductility were achieved in the steels, which are competitive to similar products made by conventional controlled rolling. However, the addition of Ti to the V-N steel decreased the yield strength due to formation of V-Ti(N) particles in austenite, which reduced the amounts of V and N available for subsequent V rich fine particle precipitation in ferrite.

Hot strength and hot ductility of titanium alloys—a challenge for continuous casting process

Abstract Hot workability of Ti-6Al-2Sn-4Zr-2Mo, Ti-10V-2Fe-3Al, Ti-15V-3Cr-3Sn-3Al and NiTi have been examined up to the melting point, and compared with those of Ti-6Al-4V and carbon steels. Titanium alloys do not show any embrittlement in zone II, which is the best region of hot rolling. The embrittlement occurs just below the β transus temperature. Based on these results, it is suggested that titanium alloys can be successfully produced by the continuous casting and hot direct rolling processes if cast material passes the unbending point at temperature above β transus in order to avoid the embrittlement in zone III. Since the strength level of titanium alloys in the β region is very low, it is also easier to unbend the strand. Hot direct rolling immediately after the casting is also an effective method for obtaining good product shapes free from surface oxidation and also has substantial cost benefits.

溶湯直接圧延法によるＡｌ‐Ｃｕ超塑性合金薄板の製造

In order to clarify the possibility of simple and novel process to produce superplastic thin sheet, melt direct rolling of Al–Cu alloys was investigated. Sound strips of Al–6%∼20%Cu alloys were successfully produced from molten state by the melt direct rolling process. 47%∼64% of rolling reduction was applied to the materials during melt direct rolling. Fine θ (Al2Cu) particles were distributed in the deformed matrix, though the distribution of θ phase was quite inhomogeneous through thickness location in the melt direct-rolled strips: θ (Cu) concentrated near the surface to show inverse segregation. The Al–Cu melt direct-rolled strips were provided for tensile tests at 520°C. Although elongation of the Al–6%–15%Cu melt direct-rolled strips was not large and hardly depended on strain rate, elongation of the Al–20%Cu strip largely depended on strain rate and showed the maximum value of 354% at a strain rate of 4.2 × 10−3s−1. At the strain rates where large elongation appeared, the strain rate sensitivity (m-value) reached up to 0.32. It could be concluded that it is possible to produce the supelplastic sheets of Al–20%Cu directly from molten state by means of the melt direct rolling.

Model experiments for the determination of the heat-transfer coefficient and transition thermal analysis in the direct rolling process

Abstract The direct rolling process of steel is characterized by two rotating water-cooled rolls receiving a steady supply of molten metal that solidifies onto the rolls. A solidification analysis of the molten metal considering phase transformation and thermofluids is performed using the finite-difference method with curvilinear coordinates to reduce computing time. An enthalpy–specific-heat method is used to handle relaxation of latent heat during the phase change. The computed flow field is used to analyze solidification in the molten metal. The temperature distribution in the cooling roll is obtained using a two-dimensional finite-element method, because of the complex roll shape due to the cooling holes in the rolls and secure improvement in the accuracy of the calculation results. The energy equation of the cooling roll is solved simultaneously with the conservation equation of the molten metal in order to consider heat transfer from the molten metal. The calculated roll temperature is compared to experimental results and the heat-transfer coefficient between the cooling roll surface and the cast material is also determined from comparison of the measured roll temperature and the calculated roll temperature.

Optimum shape design techniques of direct roller under thermal load and rolling force in the direct rolling process of molten materials considering solid fraction

Rolling force in the direct rolling (or in the twin-roll strip continuous casting) process of semi-solid material has been computed using the rigid-viscoplastic finite-element method. Temperature distributions for calculations of rolling force and roll deformation are obtained from thermofluid analysis. Three-dimensional roll deformation analysis has also been performed using the commercial package ANSYS. From the results, the behavior of the metal flow, the rolling force and the roll deformation have been investigated according to the process conditions of semi-solid direct rolling.

A coupled solidification analysis of materials and cooling roller in direct rolling process

A computer program has been developed to analyze the two-dimensional unsteady conservation equations for transport phenomena in the pool region with semi-solid materials containing the cooling roll of direct rolling (or twin-roll strip continuous casting). The solidification phenomena of the semi-solid metal are investigated considering phase transformation. The energy equation of the cooling roll is solved simultaneously with the conservation equations of the semi-solid metal to consider heat transfer through the cooling roll. The finite difference method and the finite method are used in the analysis of the pool region and the cooling roll, respectively, to reduce computing time and to improve the accuracy of calculation. The assumption of viscous flow and Darcy's flow are used for the calculation of the flow and the temperature fields of the semi-solid metal. In the present study, the influences of the solid fraction and the casting speed are investigated from the points of view of the possibility of fabrication and roll design.

A continuous fabrication of Al 2O 3 short fiber reinforced aluminium composites by direct rolling process

The importance of high strength, wear resistance, thermal stability, and lightweight materials have attracted much interest in the development of the manufacturing process of metal matrix composites (MMCs). Problems in the rolling process are damage to fibers and a reduction of strength by the debonding of interface as well as defects on the surface and internal imperfection in the fabricated composites sheet. Therefore, a roll experiment of semi-solid materials containing short fiber was carried out in this study to fabricate an MMCs sheet. The composites slurry containing Al{sub 2}O{sub 3} short fiber was fabricated with mixing techniques in order to manufacture a composites sheet. Also, the possibility of strip fabrication for direct rolling was investigated for semi-solid materials containing short fiber. The mechanical properties for the composites sheet were also investigated.

Results of hot direct rolling operation

Kwangyang No.2 continuous caster, which is designed for Hot Direct Rolling (HDR) process, has started its operation in November 1990.

Surface cracking mechanism of continuously cast low carbon low alloy steel slabs

The present state of understanding of surface cracking in low C low alloy steel slabs in the continuous casting (CC) and direct rolling (DR) processes is outlined. Hot cracking of the CC slab surface can be explained in terms of carbide and/or nitride precipitation behaviour. In addition to γ grain boundary precipitation, the matrix strengthening owing to dynamic precipitation and the existence of softer layers along the boundaries such as grain boundary allotriomorphs of ferrite or precipitate free zones play animportant role in intergranular ductile fracture. The origin of hot cracking during the DR process lies also in the precipitation of carbides and/or nitrides, and is not related to the severe embrittlement caused by a similar mechanism with dynamic precipitation of sulphides, which is observed usually in the high strain rate deformation after reheating at higher temperatures. Furthermore, a well known effect of C on hot cracking susceptibility in both CC and DR processes, attaining a maximum in the range 0·10–0·15 wt.–%C, is found to arise mainly from γ grain growth during solidification in the mould. Some methods to prevent surface cracking are also discussed.MST/1226

Effect of thermo-mechanical history on surface cracking of as-cast low carbon low alloy steel slabs.

Surface cracking and the effect of predeformation on the cracks of low alloy steel slabs in the continuous casting and the direct rolling processes have been studied by means of hot bending tests simulating the processes using as-cast thin slabs. Two kinds of cracks, i.e., fine transverse cracks in microalloyed steels and severe cracks in low Mn steels, are easily simulated by the deformation in low temperature γ region, if the deformation conditions are suitably controlled. They are markedly suppressed by the slight predeformation at certain conditions on the slab surface during cooling to the bending temperature. These results can consistently be explained in terms of precipitation behavior of carbonitride or sulfide. Suppression of the cracks due to the predeformation is caused by nucleation and coarsening of the precipitates by the deformation, and does not result from γ grain refinement by recrystallization due to the predeformation.

冷延鋼板用アルミキルド鋼の連続鋳造・熱間圧延直結工程におけるAlNの析出挙動

冷延鋼板用アルミキルド鋼の連続鋳造・熱間圧延直結工程におけるAlNの析出挙動

熱延における直送圧延対応技術

In NKK Fukuyama Works, Hot Direct Rolling (HDR) process on No. 5 continuous casting machine and No. 2 hot strip mill is operated for the purpose of the saving of the energy and the materials, and the manpower. In the hot strip mill, the process is maintained by the technology of the prevention of temperature going down such as the heat insulating cover, the induction heater, and the technology of the schedule free rolling and the equalize of the product ability between the continuous casting and the hot strip mill, and the new computer system which controls these. By the achievement about each technology, the large quantities of production by HDR is operated stably, and the effect of the improvement about the quality is obtained.

Temperature Equalization by the Radiative Converter for a Slab in Continuous Casting Direct Rolling

This paper reports the experimental results on heat transfer performance of a newly suggested temperature equalizer with the radiative converter for a slab in the continuous casting direct rolling process. The present temperature equalization is based on the effective energy conversion method between gas enthalpy and thermal radiation using a porous media. The model temperature equalizer used is about one fifth of the actual one its dimensions. To simulate the continuous casting direct rolling process in the experiment, the uniformly preheated model slab was first cooled by thermal radiation, and subsequently fed into the temperature equalizer. By measurements of transient slab temperatures, it is proved that the radiative converter equalizes the slab temperature quickly owing to local heating of the slab edge. Furthermore, estimation of the overall energy balance in the temperature equalizer demonstrated that efficient temperature equalization is feasible if the available energy flowing out of it is recovered.

スケジュールフリー圧延技術を駆使した新世代連鋳-熱延直結プロセス

スケジュールフリー圧延技術を駆使した新世代連鋳-熱延直結プロセス

低炭素低合金鋼の鋳造まま材の表面割れに及ぼす熱加工履歴の影響

Surface cracking and the effect of predeformation on the cracks of low alloy steel slabs in the continuous casting and the direct rolling processes have been studied by means of hot bending tests simulating the processes using as-cast thin slabs. Two kinds of cracks, i.e., fine transverse cracks in microalloyed steels and severe cracks in low Mn steels, are easily simulated by the deformation in low temperature γ region, if the deformation conditions are suitably controlled. They are markedly suppressed by the slight predeformation at certain conditions on the slab surface during cooling to the bending temperature. These results can consistently be explained in terms of precipitation behavior of carbonitride or sulfide. Suppression of the cracks due to the predeformation is caused by nucleation and coarsening of the precipitates by the deformation, and does not result from γ grain refinement by recrystallization due to the predeformation.

Surface cracking mechanisms of low carbon low alloy steel slabs

The present state ofunderstanding ofsurface cracking oflow carbon low alloy steel slabs in the continuous casting (CC) and the direct rolling (DR) processes are outlined. Hot cracking ofCC slab surfaces can be explained in terms of carbonitride precipitation behaviour. In addition to y grain boundary precipitation, the matrix strengthening due to dynamic precipitation and the existence ofsofter layers along the boundaries such as ferrite or precipitation-free zones (PFZs) play an important role for intergranular ductile fracture. Hot cracking during the DR process can also be explained by a similar mechanism with dynamic sulphide precipitation, although the strain rate region in the ductility trough is much larger than in the CC process. Furthermore, a well-known effect ofcarbon on hot cracking susceptibility in both CC andDR processes can be explained mainly in terms of γ grain growth during the solidification process in the mould. Some methods to prevent surface cracking are also discussed.

直送圧延用高速スラブ連鋳機の操業

The slab caster No.5 was put into operation in September, 1984 at NKK Fukuyama Works, which was directly connected with the hot strip mill No.2 for the purpose of Hot Direct Rolling Process (HDR). To realize the HDR this caster is provided with various automatic facilities and with several characteristics on operation such as mentioned below. (1) For high speed casting (over 2.0 m/min); low viscosity mold powder (lithium being added), nonsinusoidal oscillation, and mold copper plate, etc. (2) For high temperature slab discharging; heat insulating apparatus, secondary cooling with width control system, and slab edge heater. (3) For improvement of surface and inner quality of slab; accurate mold level control, optimum design of immersion nozzle, air mist cooling, etc. By these newly developed techniques the monthly production by the HDR process was increased up to 100 thousand tons of steel. This report describes the new facilities and the operation technologies developed for this HDR process.

Development of Hot Slab Surface Defect Detecting Device

Nippon Steel developed a high-accuracy hot slab surface defect detecting device utilizing the high resolving power of photographs as a means of quality assurance in the hot charge rolling and hot direct rolling processes. The first device was installed in the slabbing mill at Muroran Works. It performs the photographing of slab surfaces automatically and at high speed to present inspection images of slab surfaces to the inspector. In addition to serving for quality assurance, this device contributes largely to yield improvement by giving instructions on the amount of scarfing to the hot scarfcr and quality improvement by quickly feeding back information on defects to the steelmaking process.

Method for manufacture of aluminium sheet and sintered high-density aluminium laminate by direct power rolling process : Suzuki, Y. (Agency of Industrial Science & Technology) US Patent 4 045 857 (6 September 1977)

Method for manufacture of aluminium sheet and sintered high-density aluminium laminate by direct power rolling process : Suzuki, Y. (Agency of Industrial Science & Technology) US Patent 4 045 857 (6 September 1977)