Cold roll bonding of bimetallic sheets and strips

Abstract

The successful production of wide bimetallic sheets and strips by cold roll cladding depends on the technical solution of reduction of rolling load while still guaranteeing good bond quality. In the present paper, systematic experimental data on the cold roll cladding of aluminium–stainless steel, copper–stainless steel, and mild steel–stainless steel are correlated and the basic mechanism is discussed, aided by a scanning electron microscopy study of the separated interface. The effects of conventional rolling and cross-shear rolling (i.e. between rolls of differing peripheral speeds) on roll force and bonding strength are critically compared. It is found that use of the cross-shear cold rolling technique results in a significant reduction in rolling load for equal primary bonding strength and that the incorporation of an optimum final heat treatment considerably decreases the requirement on rolling.

MST/971     

Comparison of thermomechanical stresses produced in work rolls during hot and cold rolling of Cartridge Brass 1101

Thermomechanical stresses play an important role in defining the life of the work roll used in hot rolling process. In this research temperature dependent mechanical properties of cartridge brass are determined experimentally using high temperature compression tests at different temperatures and strain rates. Real life measurements are made from a brass rolling mill as input data for the simulation boundary conditions. Hot rolls are made of AISI H11 hot work tool steel. Temperature dependent mechanical properties of AISI H11 steel are used. Thermal and mechanical stresses produced in the work rolls during hot rolling process are predicted using a thermoplastic finite element approach in the ABAQUS Standard software. Hot rolling is compared with cold rolling to determine the effects produced on the work rolls. A criterion is introduced to compare the severity of stresses produced on the rolling surfaces in case of hot rolling and cold rolling based on the yield stress of the roller material for different temperatures. A method for separating thermal and mechanical stresses in the simulation is also described.     

Cold densification rolling of porous copper strip obtained directly from cuprous oxide perform

Abstract

The densification of porous copper strips obtained from the combined reduction and sintering of cuprous oxide preforms by cold rolling has been discussed. It has been shown that such strips, although containing a relatively large amount of porosity, exhibit no problems during cold rolling and, in general, have good workability. Although it is possible to subject the strip to cold rolling thickness deformations of the order of 75%, without any intermediate annealing, rolling with annealing after every 35–40% cold rolling reduction yields better results. The efficiency of densification and changes in the pore morphology during the cold rolling of the porous strip have also been discussed.

MST/670     

Evaluation of hot strip mill backup roll cladding

Abstract

A new cladding material based on the Fe–Cr–Mo–V–C alloy system, suitable for submerged arc welding, has been designed for the refurbishment of forged and cast backup rolls used in the finishing stands of hot strip rolling mills. The work undertaken includes mechanical analysis, mechanical testing, and microstructural characterisation. The mechanical analysis indicated the nature and level of stresses operating near the surface of rolls; mechanical testing allowed material performance to be anticipated. An optimal post-weld heat treatment procedure, which maximises strength while minimising material strain hardening, was subsequently chosen. The microstructure of the candidate cladding material is a mixture of lower bainite and martensite, containing a very fine distribution of molybdenum carbides. In situresults have shown that welded rolls outperform traditional rolls, as the amount of steel rolled per millimetre of cladding material is 40% higher than with forged rolls and double that obtained with cast rolls.     

Through thickness residual stresses in large rolls and sleeves for metal working industry

Abstract

There is little experimental knowledge about the initial state of through thickness residual stresses in rolls and sleeves for the steel rolling industry. This is surprising bearing in mind the impact that residual stress has on the performance of the roll and sleeve materials in the highly aggressive loading environments of the metal working industry. Previous work has been confined to measurement of very near surface residual stresses and numerical predictions of residual stress distributions. In the present paper through thickness residual stress measurements were carried out using a deep hole drilling technique on a series of rolls and sleeves representative of those used in the rolling industry. Different features of the manufacturing processes used in their production are shown to influence the magnitude and distribution of the residual stresses. It is also shown that the measurements can be used, together with a finite element analysis, to determine the volumetric distribution of the residual stresses.     

Cold roll bonding bond strengths: review

Abstract

Cold roll bonding (CRB), a well established and widely used manufacturing process, is a solid state bonding process to join similar and dissimilar metals. The present work offers a review of the CRB process and effective parameters on bond strength of cold roll bonded materials. The effects of different amounts of reduction in thickness, annealing treatment, initial thickness, rolling speed, rolling direction, friction coefficient and presence of particles between strips on bond strength were evaluated. It was found that higher reduction in thickness and friction coefficient, lower initial thickness, rolling speed and amount of particles were the important factors involved in improving bond strength. In addition, annealing treatment before and/or after the CRB process increased bond strength, while the effect of prerolling annealing was more pronounced. Finally, it has been indicated that bond strength of cold roll bonded fcc materials is stronger than that of the bcc and hcp materials.     

Effect of auto-tempering on the cold roll-ability of medium-Mn steel

ABSTRACT

Recently, medium-Mn steels have attracted attention for high-strength automotive components. However, because they exhibit martensitic microstructure at room temperature, low cold roll-ability is concerned so that annealing or tempering is often performed before cold rolling. Therefore, we investigated whether cold roll-ability can be improved by adjusting coiling condition in the hot rolling process. For comparison, some specimens were water-quenched or air-cooled after hot rolling. While the water-quenched specimen revealed cracks at ～30% cold reduction, air-cooled and coiling-simulated specimens at high reductions above ～68%. This is because the latter had lower and wider ranged hardness values compared to the former due to partial auto-tempering occurring after coiling. The higher coiling temperature caused higher cold roll-ability probably due to the active recovery of austenite.

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

Assessment of surface bonding strength in Al clad steel strip using electrical resistivity and peeling tests

Abstract

Aluminium clad steel strip successfully combines the surface properties of an aluminium alloy coating with the satisfactory mechanical properties of the steel substrate. The production of Al clad steel strip by rolling, however, is a more efficient and economical approach compared with other processes. In this investigation, trilayer strips of aluminium/steel/aluminium were produced using the cold roll bonding technique. The bonding strength between the layers and the electrical resistivity of the samples were measured using a peeling test and four point probe test, respectively. The effects of reduction of thickness, the friction condition between the outer layer and rolls, and the rolling velocity on the bonding strength and electrical resistivity of the samples were assessed. Finally, it is shown that the resistivity test can be used as a non-destructive test for the evaluation of the quality of bonding between the layers of aluminium clad steel strip.     

Influence of transformation induced recrystallisation on hot rolling textures of low carbon steel sheet

Abstract

A series of hot rolling textures of steel sheet with different compositions and hot rolling parameters have been compared. The observed hot rolling textures all belonged to a limited number of different types. These types seemed to depend on the composition, the hot rolling parameters, and the local deformation mode. The influence of these hot rolling textures on the properties of commercial sheet steels after cold rolling and continuous annealing is critically evaluated. For steels with a low content of high temperature precipitates, the texture and microstructure after intercritical hot rolling often appeared to be the result of a transformation induced recrystallisation process with a specific nucleation mode. Understanding of the nature of this type of recrystallisation may facilitate an improvement in the material properties by optimisation of the hot rolling texture.

MST/1327     

Role of Friction in Cold Ring Rolling

1. Introduction Cold ring rolling is a main technology used to manu- facture various precise seamless ring shape parts. It has been increasingly used in many industrial fields such as bearing, machine, automobile, petrochemicals, aeronau- tics, astronautics and atomic energy because of its many technical superiorities such as considerable saving in en- ergy and material cost, high quality, high efficiency, and low noise, etc. To research and develop advanced precise cold ring rolling technolog…     

Morphology and microstructure of Alp/SiCp composite powder prepared using a stone mill

Abstract

Aluminium based metal matrix composite powder was prepared using a stone mill. Elemental powders of pure aluminium and SiC particle reinforcement were milled in a horizontal stone mill at a constant rotation. Two different mill gaps were employed to investigate the distribution of SiC particles embedded in the aluminium matrix. In each case, 1 ton h^-1 of Al_p/SiC_p composite powder was produced. The shape of the aluminium particles changed from ligamental to spherical and the angular faceted SiC particles became more spherical in form. Morphological and microstructural observations revealed that the advantages of using a stone mill to produce composite powder were that it provided well distributed SiC particles and good bonding between matrix and reinforcement. The mixing mechanism of the stone mill can be described as follows: shear deformation of aluminium particles and embedding of the SiC into the aluminium flakes, rolling and cold welding of the Al/SiC composite flakes to form rolls, and fracture of the composite rolls into spherical particles. Hot extrusion improved the distribution of the SiC particles in the matrix.     

Relaxation effect of pulse current on Ti50·0Ni50·0 structure during rolling

Abstract

Using transmission electron microscopy and differential scanning calorimetry, the microstructure and martensitic transformation of the Ti_50·0Ni_50·0 alloy after cold rolling and after rolling with a pulse current were compared. A structural relaxation effect was observed in the alloy during rolling with current. The effect is manifested in the more slow kinetics of the structure formation and less intensive suppression of martensitic transformations at rolling with current compared to cold rolling with some deformation degrees.     

Drag coefficients for a sphere rolling down an inclined channel

Abstract

Forces acting on a sphere rolling down an inclined smooth or rough channel include submerged weight of the sphere, fluid drag, fluid lift, and rolling resistance from the channel bed. When the acting forces are in equilibrium, the sphere rolls down the inclined channel with a terminal velocity. The steady movements of such a sphere rolling down smooth and rough channel beds with the terminal velocity are studied through laboratory experiments and a simplified theoretical analysis. A method is proposed to evaluate the rolling resistance that consists of collision and friction parts of resistance. The coefficients of rolling resistance and the drag coefficients are determined by regression analysis with experimental data. The relationships of the drag coefficients and the Reynolds numbers for a sphere rolling over smooth and rough channel beds are also obtained. It is found that at the same Reynolds number, the drag coefficient for a sphere rolling down a rough bed is larger than that for a sphere down a smooth one, and that both are much larger than that of a sphere in the free fall.     

Evaluation of changes in X-ray elastic constants and residual stress as a function of cold rolling of austenitic steels

Abstract

Austenitic steels rapidly attain high mechanical strength when subjected to cold working. The heterogeneous plastic deformation produced in cross section of the specimen, development of preferred orientation and martensitic transformation contribute to the occurrence of residual stress in cold worked steels. AISI 304 and 316 steels were cold rolled at room temperature from 10% up to 70% deformations in steps of 10%. The formation and sigmoidal growth of martensite caused by cold rolling (CR) 304 steel was studied by X-ray diffraction. The residual stresses generated were evaluated in both the austenite and martensite phases using sin² ψ technique. The accurate determination of residual stress by X-ray diffraction requires experimental determination of X-ray elastic constants for both the austenite and martensite phases. The changes in X-ray elastic constants as a function of CR of 304 and 316 steels were measured and their effect on residual stress values was established. The results show that tensile stress was generated initially on cold working in the austenite phase in both steels and in the dominant martensite phase in 304 steel, which decreases, passes through zero and becomes compressive at higher deformations. X-ray elastic constants were found to decrease in all cases and a maximum reduction of 15% was found.     

冷轧辊剥落原因分析

Cr3锻钢冷轧工作辊在冷处理过程中，辊身端部发生剥落。通过化学成分、显微组织和断口形貌的检验分析，认为电渣重熔时钢锭内部产生的夹渣使得轧辊在淬火过程中形成裂纹，在随后的冷处理时裂纹失稳扩展造成轧辊剥落。     

Microstructure and texture of aluminium alloys 3105 and 3015 during cold rolling and annealing

Abstract

The microstructure and texture of industrially produced hot bands of direct chill (DC) cast AA 3105 and continuous cast (CC) AA 3015 during cold rolling and annealing have been studied. The textures were determined using an X-ray diffraction technique and then analysed using orientation distribution functions. The Copper, Brass, and S texture components were the major deformation texture components for both the DC and CC materials after the same cold rolling process. After an annealing process, the Cube component was found to be the major recrystallisation texture component for AA 3105 DC material. In contrast, it was difficult to obtain the Cube texture component in AA 3015 CC material after cold rolling followed by annealing. Instead, the P orientation {011} 〈566〉 with Euler angles of (?₁,Φ,? ₂) = (60°,45°,0°/90°) was found to be the major recrystallisation texture component of the AA 3015 CC material.     

Effect of temperature on microstructure and texture of rolled Ni–9·3 at-%W alloy

Abstract

In the present paper, the microstructure and texture of cold rolling and warm rolling Ni–9·3 at-%W alloy were investigated by electron backscatter diffraction technique. It is found that warm rolling will reduce the deformation twins and transfer the rolling texture from brass type to copper type. The forming mechanism of rolling microstructure and texture of Ni–9·3 at-%W alloys as well as the temperature effects was discussed.     

3D coupled thermo-mechanical FE analysis of roll size effects on the radial–axial ring rolling process

Radial–axial ring rolling is an advanced but complicated incremental metal forming technique with multi-factors coupling interactive effects. During the radial–axial ring rolling process, the deformation and thermal behaviors of the ring mainly occur in the roll passes which are constituted by rolls. So, the rolls sizes have enormous influence on the quality of the rolled ring as well as the stability of the process. In this paper, the ranges of rolls sizes and forming parameters are reasonably determined at first, then a 3D elastic–plastic and coupled thermo-mechanical FE model of radial–axial ring rolling is developed using the dynamic explicit code ABAQUS/Explicit, and its reliability is verified theoretically and experimentally. Based on the valid 3D FE model, the size effects of rolls on the radial–axial ring rolling process are investigated. The research results provide valuable guidelines for the design and optimization of the rolls sizes in the actual radial–axial ring rolling production.     

Roping phenomena in ferritic stainless steels

Abstract

The mechanism of roping in two ferritic stainless steels (type 18·2 and type 430) has been studied. The effects of structure, substructure, and texture are considered in relation to hot and cold process parameters and results obtained from deep drawn cups and tensile specimens. The mechanism of roping is shown to result from differential yielding under tension, caused by heterogeneous bands of material which are developed during the hot rolling schedule. It is shown that small dispersions of austenite can prevent this banding effect.

MST/335     

Effective cooling of work rolls in strip rolling

Abstract

An examination has been made of the effectiveness of roll cooling as applied to strip rolling, taking into account practical considerations such as the spray location and positioning, coolant flowrate, and rolling temperature. It is indicated by the results that, for cold rolling, the most effective cooling can be achieved by commencing spray cooling at the exit side of the roll gap and by providing a large spray contact angle. However, for hot rolling, cooling should commence at least 45° from the roll gap exit and a high spray flux density with relatively small spray contact angle is more appropriate.

MST/642