常规热连轧超薄带钢生产技术研究

厚度小于1.5mm的超薄规格热轧产品可以实现"以热带冷",具有巨大的经济效益。常规热连轧超薄带钢生产技术一直是热轧生产技术研究的重点。全面分析了常规热连轧超薄规格带钢生产时的技术难点,针对该难点,通过研究和实践,总结出一整套超薄规格带钢生产技术,包括板形控制、精轧跑偏控制、全线带钢温度控制、辊道飞飘控制、轧制润滑技术、活套控制、设备精度维护、铁素体区轧制技术等。     

Design of Complex Sheet Metal Forming Processes: A New Computer Aided Progressive Approach

Ridge-buckle defects in cold rolled thin strip originate from the formation of ridges in hot rolled coil and corresponding ridges left in the strip following annealing, cold rolling and tempering. A numerical solution was developed to calculate three-dimensional stress distribution in a wound coil built up wrap-by-wrap and subsequent flatness change in the uncoiled product. The model takes into account both nonlinear compressible characteristic of interwrap layer and uneven strip profile, especially ridges, on the stress evolution during the coiling process. The sensitivity of ridge-buckle defects in cold rolled thin strip to ridges in hot rolled coil profile has been investigated in details. The results show that the ridge-buckle defects in tin plate are much dependent on the height, width and location of ridges in hot coil profile. The permissible tolerance of ridges in hot rolled coil, below which does not produce the ridge-buckle defects in subsequent cold rolling of thin strip, are recommended for different steel grades.     

On-line measurement of steel sheetr-value using magnetostrictive-type EMAT

An ultrasonic on-line system to measurer values in cold rolled steel sheets has been developed with electromagnetic acoustic transducers (EMATs). These EMATs are composed of meanderline coils and electromagnets and operate with the magnetostrictive mechanism. The EMAT instrument measures the propagation times of the fundamental symmetrical Lamb (S _o ) wave at a low frequency and relates them to ther values through a calibrated regression curve. Preliminary tests indicate that the on-line monitoring ofr is quite feasible with a standard deviation of 0.07 for various low carbon steel sheets; the thicknesses range from 0.5 mm to 2.5 mm. The measuring time is 20 msec per data. The liftoff is allowed to 5 mm with 2 mm thick sheet. Ther evaluation is independent of the line speed up to 325 m/min. These promising results promote installation of ultrasonicr-value measurement systems in steel production lines.     

Effects of aluminium powder content and cold rolling on foaming behaviour of xAlp/Al5Si4Cu4Mg/0.8TiH2 composites

Abstract

Aluminium foams were produced by applying powder metallurgy technology. The process began by making aluminium powder and mixing it with alloy powder (Al5Si4Cu4Mg) and foaming agent (TiH₂). The mix was compacted to the form of a billet by cold pressing and then it was hot extruded to a dense foamable strip, which was cold rolled to give 40% thickness reduction. The resulting precursor composites of both the extruded strip and the extruded plus rolled strip were then freely foamed without a mould at a constant temperature of 700°C for different foaming times. The effects of aluminium powder content and cold rolling on the foaming characteristics of the foamable composite strip were studied. It is noted that aluminium powder fibre in the extruded composite strip acts as a barrier to pore initiation and evolution due to the higher melting point of pure aluminium fibre than that of the alloy matrix. Cold rolling promotes foaming of the composite strip due to the TiH₂ cracking and debonding between TiH₂ particles and metal matrix. The morphological and microstructural evolution of composite foams was also investigated. The foaming mechanism can be described by the following sequence: cracklike pore nucleation between elongated powder fibres; ellipsoidal, spherical, and polygonal pore growth; and the collapse of pores as a result of coalescence.     

Infrared reflectance spectra of oxide films on aluminum-magnesium alloys

Infrared reflectance spectra of oxide films on hot rolled 3004 and 5182 aluminum alloy surfaces indicate the presence of two types of magnesium-doped aluminum oxide. Heating the samples to 350°C or more causes shifting and broadening of the 900 cm^?1 aluminum-oxygen absorption band for 3004 metal, and the appearance of a magnesium-oxygen absorption band at 670 cm^?1 in the reflectance spectra of both 3004 and 5182 metal.Reflectance spectra of the surfaces on cold rolled 3004 and 5182 metal show no absorption bands on unheated samples. However, results from time-temperature studies indicate that further oxidation of these samples is more rapid than in hot rolled samples. The oxides formed on cold and hot rolled 5182 metal are similar, while cold rolled 3004 metal initially forms an oxide which differs from that on hot rolled 3004 metal, exhibiting a broader absorption band at approximately 850 cm^?1.     

生产工艺对08Al钢冷轧薄板冲压性能影响的研究

通过冷轧及热处理试验，借助于三维取向分布函数（ＯＤＦ６织构分析，对０８Ａｌ钢冷轧薄板冲压性能进行了系统的研究，得出不同轧制工艺，再结晶退火制度，对０８Ａｌ冷轧薄板冲压性能的影响规律，为制订０８Ａｌ钢冷轧薄板的生产工艺制度提供了有利依据。     

Untersuchung des Einflusses von Prozessparametern in der Fertigstrasse auf die Tertiärzunderausbildung

Investigation of the influence of processing parameters during hot rolling on tertiary scale formation The permanent demand for a cost saving production of flat products of steel as well as the technical progress in the engineering established the basis for a substitution of cold rolled products by hot rolled products. Precondition is a systematic control of the inevitable oxidation of the strip during the entire hot rolling process. With the generation of appropriate scale properties at hot rolled strip, taking into account the required mechanical properties, a direct processing of hot strip without prior pickling, cold rolling and annealing could be possible. The knowledge of the influence of the processing conditions during hot rolling on the properties of tertiary scale, especially the thickness, the constitution and adherence is incomplete till now. That’s why influences on the oxidation and scale properties respectively during the hot rolling process starting from the finishing line to the coiling as well as consequences for the downstream process are discussed in this paper based on the results of laboratory hot rolling trials to the simulation of considerably processing parameters in the finishing line.     

Application of Radial Effective Thermal Conductivity for Heat Transfer Model of Steel Coils in HPH Furnace

The hot/cold rolled steel coil can be considered as a periodically laminated material composed of layers of steel strips and gas gaps in the radial direction. The conduction of steel, of gas, of contact points due to the surface roughness, as well as radiation have been included in a determination of the radial effective thermal conductivity. Based on the analysis of heat transfer mechanisms in radial coils, a new formula for the radial effective thermal conductivity has been derived, which depends not only on the temperature but also on the type of atmosphere gas, the surface characteristic of coils, strip thickness, and compressive stress. Using this effective conductivity, a detailed mathematical model has been developed to predict the temperature distribution of coils in a high performance hydrogen (HPH) furnace. The calculated annealing curves are in good agreement with experimental data.     

Effect of thermal ageing on microstructure,mechanical properties,and fracture behaviour of 50 % cold rolled duplex stainless steel (alloy 2507)

The paper deals with cold rolling and ageing on microstructure and mechanical properties of 2507 duplex stainless steel. Microstructure depicts acicular/Widmanstätten austenite and δ-ferrite with dissimilar volume fraction (∼0.55 for ferrite and ∼0.45 for austenite). Cold rolling and ageing at 950 °C, 1000 °C and 1050 °C result in equiaxed austenite for samples solution treated at 1040 °C and elongated at 1300 °C. By lowering ageing temperature from 1050 °C to 950 °C, structure becomes finer from ∼20 μm to <10 μm grain size. The sigma (σ) phase appears after ageing at 950 °C. Micro-hardness reveals maximum hardness for the hot rolled, solutionized (1040 °C) water quenched, and cold rolled (50 %) sample (380 HV_δF 100 and 430 HV_γ 100), whereas the tensile results reveal the hot rolled, solution treated (1300 °C, 1040 °C), cold rolled and aged at 950 °C samples show higher strength (yield strength=625 MPa, 567 MPa and ultimate tensile strength=892 MPa, 826 MPa) and lower ductility (23 %, 32 %) due to the σ-phase. The solution treated (1040 °C), cold rolled, aged at 1050 °C sample exhibits attractive strength and ductility combination (∼30 GPa %). Fractography supports the tensile results.     

On the formability of sheet steels

Formability of sheet steel in stamping operation primarily depends on strain hardening exponent (n), average plastic strain ratio ( ) and the maximum strain the material can undergo before the onset of localized necking. The formability parameters (n and ) and the forming limit diagrams have been evaluated for a variety of sheet steel products, extensively used for press forming of components of diverse shapes e.g. extra deep drawing quality auto-body sheets, high strength cold rolled sheets, LPG steel for gas cylinders, austenitic and ferritic stainless steels, etc. The effect of sulphide shape control on formability of hot rolled HSLA steel has also been studied. Additionally, the press performance of auto-body sheets and austenitic stainless steels have been monitored and evaluated at customer’s end for complete information on the formability.     

Flatness measurement system based on a nonlinear opticaltriangulation technique

This paper describes the development of a flatness measurement system, integrated in the control process of a hot strip mill in the steel industry. The objective of the system is to calculate flatness indexes for every rolled strip, comparing the length of its lateral profiles with the central length. The reconstruction of the profiles is based on a nonlinear triangulation technique. Images of laser spots over the steel strip, at high temperature and high speed, are sampled every two milliseconds at five different points and are processed online in order to calculate height displacement values of the strip, so that final flatness indexes for the steel strip can be calculated. The measurement method developed introduces an innovative geometry in the disposition of the optic elements which increases the measurement range of the system without reducing its accuracy. It also includes a tracking system to compensate for the effects of lateral displacements of the strip. The flatness measurement system has been implemented using a heterogeneous distributed computer system     

Microstructural control by secondary processing of strip cast low carbon steel

Abstract

The secondary processing of low carbon steel strip produced by twin roll casting was investigated to examine its effect on microstructural development and mechanical properties. The as cast microstructure is predominantly acicular ferrite with regions of bainitepearlite and polygonal ferrite. Deformation at temperatures below Ar1 produces a heterogeneous microstructure with regions of moderately deformed acicular ferrite adjacent to highly deformed regions containing shear bands. Cold rolled and warm rolled steels show similar behaviour to conventional hot band in that dynamic recovery during warm rolling results in sluggish recrystallisation and produces a coarse final grain size. However, the initial as cast microstructure recrystallises at a slower rate than conventional hot band and produces a weaker recrystallisation texture. This can be attributed to the heterogeneous microstructure of the as cast strip such that, after rolling, nucleation occurs within shear bands and more ill defined sites, which results in nucleation of randomly oriented grains thereby producing a weak final texture. It was found that austenitising the as cast strip followed by rolling in the vicinity of Ar3 produces a uniform distribution of equiaxed, ultrafine ferrite UFF grains throughout the thickness of the strip. The production of UFF by twin roll casting and subsequent rolling represents a simple processing route for the production of fine grained low carbon sheet steel products.     

Thin-slab casting: New possibilities

Changes in the IT industry are known to proceed at a scorching pace. In sharp contrast, the rate of development in the steel industry is generally slow. Nonetheless, the unpact of recenr technical development on the steel industry has been quite significant. The production chain from iron ore to final rolled steel is a long one and the shortening of this length has long been the endeanvour of scientists and engineers. The initial development came in the form of speeding up the process of steelmaking by reducing the slow open-hearth process (8 h tap-to-tap time with the 45 min tap-to-tap time of the Basic Oxygen Furnace (BOF) process. Significant development thereafter have been in the process of continuous production of billets and blooms from liquid steel thereby doing away with the large blooming mills needed for rolling ingots. For a fairly long time after the stabilition of continuous casting, hot rolling involved reheating thick (200–250mm) slabs and reducing them in a hot strip mill. The advent of thin-slab casters has made even these large hot strip mills redundant. The new installations produce thin slabs (50–70mm) that are directly nil led hin strip without the need of an intermediate furnace for raising the stock temperature; the so-called cunnel furnace prior to the rolling stands serving only to equalise stock temperatures. Additionally, what started as a step for reducing investment in hot rolling has in fact, given new opportunity for direct hot rolling of thickneses that were, for long, considered to be feasible only through the cold-rolling route. This article discusses the slow but steady encroachment of hot-rolled sheets into the domain of strip thicknesses hitherto produced by cold rolling and tries to show how the development of thin-slab casters has allowed this process to be accelerated. A techno-economic analysis of thin-slab casting: been presented along with the benefits that arise when a thin-slab caster is linked to the blast furnace and basic oxygen route of steel making.     

Recrystallisation textures in cold rolled low carbon steel containing ferritic and bainitic microstructures

Abstract

Low carbon steel strip was heat treated to generate four different starting microstructures (fine and coarse polygonal ferrite, acicular ferrite and bainite) for investigating their influence on texture development during cold rolling and annealing. The starting materials were cold rolled to 50–90% reduction and annealed for various times in the temperature range 853–953 K. The resultant microstructures and textures were examined mainly by electron backscatter diffraction and X-ray diffraction. The initial microstructure strongly influenced the crystallographic rotation paths during cold rolling, whereby high strain deformation generated strong {223}〈110〉 texture components in the polygonal ferritic microstructures, whereas a strong {001}〈110〉 texture was produced in the acicular/bainitic microstructures. Subsequent annealing generated, to varying degrees, the classic {111}〈uvw〉 (γ-fibre) recrystallisation texture in all materials. Unexpectedly, coarse polygonal ferrite produced the strongest γ-fibre recrystallisation texture after 70–90% cold rolling reduction. Based on arguments involving the effect of carbon in solution, initial grain size and deformation textures on recrystallisation texture development, it was shown that a strong γ-fibre texture can indeed be generated in coarse polygonal ferrite.     

Effect of process variables on tensile properties of ingot processed versus strip cast iron aluminides

Abstract

The effects of cold rolling and subsequent heat treatment are reported for ingot cast-hot rolled and strip cast iron aluminides (23–29 at.-%Al). Partially recrystallised microstructures obtained by hot rolling at 800°C gave higher strength and elongation to fracture than hot rolling at 1000° C. Elongation increased and proof strength decreased in proceeding from DO₃ to mixed B2 + DO₃ and to B2 order as a result of heat treatment following cold rolling. Variability in the properties of strip cast material was associated with casting defects such as laps, but the best properties were comparable with those of ingot processed material. The detrimental effects of tensile specimen preparation by spark erosion are discussed.     

Medium carbon steel deep drawing: A study on the evolution of mechanical properties,texture and simulations,from cold rolling to the end product

Medium carbon steels are mostly used for simple applications; nevertheless new applications have been developed for which good sheet formability is required. This class of steels has an inherent low formability. A medium carbon hot rolled SAE 1050 steel has been selected for this study. It has been cold rolled with reductions in the 7–80% range. Samples have been used to assess the cold work hardening curve. For samples with a 50 and 80% thickness reduction, an annealing heat treatment has been performed to obtain recrystallization. The material has been characterized in the “as received”, cold rolled and annealed conditions, using several methods: optical microscopy, X-ray diffraction (texture), Vickers hardness and tensile testing. The 50% cold rolled and recrystallized material has been further studied in terms of sheet metal formability and texture evolution during the actual stamping of a steel toecap that has been used to validate the finite element simulations.     

Influence of crystallographic textures on tensile properties of 316L austenitic stainless steel

Role of cold rolling texture on the tensile properties of the cold rolled and cold rolled and annealed AISI 316L austenitic stainless steel is described here. The solution-annealed stainless steel plates were unidirectionally cold rolled to 50, 70 and 90% of reduction in thickness. The cold rolled material was annealed at 500–900 °C annealing temperatures. X-ray diffraction technique was employed to study the texture evolution in cold rolled as well as cold rolled and annealed conditions. The texture components that evolved were translated into slip transmission number ‘λ’ and Schmid factor ‘μ’. These two parameters were correlated with the tensile properties of the material. The tensile properties were evaluated under all processing conditions. Softening of the cold rolled material was observed after annealing with increasing annealing temperatures. From the stress–strain curves, strain hardening coefficient ‘n’ and strain hardening rate ‘θ’ were determined. It was found that the effect of texture on tensile behaviour could be understood clearly by strain hardening rate. Out of the two parameters, ‘n’ and ‘θ’, strain hardening rate was found to be more sensitive to type of texture in the material.     

Recrystallization behaviour and tensile properties of Al-added medium-Mn-steel at different deformation-annealing conditions

The role of recrystallisation on structure–property relationship in Al-added medium-Mn steel was investigated at different stages of thermo-mechanical processing comprising of hot forging (HF), hot rolling (HR), cold rolling (CR) and intermediate annealing. The CR-annealed specimens have exhibited faster recrystallisation kinetics than HF-annealed and HR-annealed conditions, as reflected by the higher Avrami exponent (～1.28) and requirement of minimum annealing temperature-time (1073K-50?min) for complete recrystallisation. The specimen cold rolled and annealed at 1073?K for 3?min (CR-1073K-3?min annealed) has exhibited excellent tensile properties owing to the co-existence of deformed and recrystallised grains. Further, the refinement of ferrite grains, lower austenite aspect ratio and higher volume fraction of γ-fibre of ferrite phase are responsible for better strength–ductility combination in the CR-1073K-3?min annealed specimen.

This paper is part of a Thematic Issue on Medium Manganese Steels.     

带钢表面黑斑缺陷分析

采用扫描电镜及能谱等手段对热轧带钢和冷轧带钢表面产生黑斑的原因进行了分析。结果表明:酸洗热轧带钢表面黑斑主要是氧化铁,冷轧带钢表面黑斑主要是热轧带钢氧化铁经退火后被还原产生的还原铁。