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     

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.     

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.     

Microstructure and texture evolution in hot rolled AA 3004 aluminium alloy

Abstract

The evolution of microstructure and texture in industrially hot rolled AA 3004 aluminium alloy has been studied. Specimens were subjected to isothermal annealing treatments and the recrystallisation kinetics was determined via measurement of changes in hardness at surface and centre locations. Metallographic examination of specimens was performed using electron channelling contrast. With the aid of an image processor, the Mg₂Si precipitate count and size distributions were obtained. A significant increase in the number of precipitates was observed to occur after the completion of recrystallisation. Quantitative texture analysis was performed on the tapered specimens to characterise the through thickness effect. The quantity of cube texture component was shown to be higher at the surface than at the centre location and decreased with increasing exit temperature of the hotband.

MST/1564     

Deformation behaviour of Al–Cu–Li alloy containing T1 precipitates

In the present work, a systematic investigation of crystallographic texture evolution and strain hardening behaviour was undertaken to comprehend the deformation behaviour in the presence of T₁ (Al₂CuLi) precipitates. Characteristic texture components symbolising multiple slip condition such as Copper and S were observed upon rolling which is in contrast with other Al alloys containing shearable precipitates. Strain hardening ability was also observed to be remarkably high in the presence of T₁ precipitates. The texture and strain hardening results are compared with another age hardenable Al alloy (Al–Mg–Si alloy) containing shearable precipitates to clearly bring out the difference in the nature of T₁ precipitates.     

Control of annealing texture and earing in non-hardenable aluminium alloys

Abstract

Factors affecting textures in non-hardenable aluminium alloys are considered on the basis of published results and some new experimental results. Emphasis is placed on conditions relevant to industrial scale rolling and annealing of sheet products. The most commonly observed texture components in these alloys are summarised, together with available evidence regarding their origins. Hot rolling conditions have a powerful effect on subsequent annealing textures, which is attributed to the microstructural state of the material before cold rolling. This can influence the relative frequency of different nucleation mechanisms. Heat treatment of the hot rolled band can also bring about marked changes in texture and earing for the same reason. The effect of cold rolling reduction on texture is complex and depends on the initial microstructure; increasing reduction promotes an increasingly heterogeneous substructure. The main impurity in these alloys is iron, which plays several different roles in controlling texture and earing level. Iron, both in solid solution and as coarse precipitates, can weaken the cube texture and promote 45° earing tendency. However, fine scale precipitation in the deformation substructure before recrystallisation may contribute to a strengthening of the cube texture. For high contents of iron and heavy rolling reductions, where continuous recrystallisation occurs, the rolling texture is retained or may even become strengthened. Influences of silicon, manganese, and magnesium are also discussed.

MST/1295     

Effect of texture evolution on tensile properties of Al–Ni eutectic alloy fabricated by equal channel angular pressing

Abstract

The present study investigated in detail the effect of texture evolution on the mechanical properties of an Al–5·7 wt-%Ni eutectic alloy, which was subjected to severe plastic deformation by the equal channel angular pressing (ECAP) technique. The ECAP procedure was carried out using two strain introduction methods, route B_C and route A, at a temperature of 298 K and a pressing rate of 0·33 mm s^?1. The as pressed microstructures were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results indicated that the Al–Ni eutectic alloy specimens after ECAP processing by route B_C and route A methods had very different microstructures, which strongly affected the tensile properties of the specimens. It was demonstrated that after ECAP processing by route B_C, fine Al₃Ni particles of ～300 nm were homogeneously dispersed in the aluminium matrix, and the specimens showed no clear anisotropy in tensile properties. After ECAP processing by route A, however, eutectic textures containing α-Al and Al₃Ni fibrous dispersoids had a highly anisotropic distribution and were demonstrated to have significantly anisotropic tensile properties. Based on the experimental results, the fracture mechanism during tensile testing of the Al–Ni eutectic alloy using different strain induction methods is discussed.     

On the influence of the chromium content on the evolution of rolling textures in ferritic stainless steels

The crystallographic hot and cold rolling textures of various ferritic stainless steels with 10.5–16.5 wt% Cr content were investigated by use of quantitative texture analysis. The hot-rolled specimens revealed a texture gradient through the sheet thickness. In the centre layers they revealed a cold-rolling type texture (-fibre) and close to the surface layers a strong Goss orientation. The texture maximum as well as the through-thickness texture gradient of the hot-rolled specimens increased with the Cr content. During cold rolling the textures inherited from the hot rolling process sharpened in the centre layers and decreased in the sub-surface layers. The hot band textures from which this inhomogeneity proceeded were explained in terms of the strong through-thickness profile of the shear strains. The fact that the textures were not randomized by phase transformation during hot rolling was attributed to the elevated Cr content which stabilizes the ferritic regime.     

Effect of nish rolling temperature on static recrystallisation in hot bands of electrical steel containing 1·3% silicon

Abstract

The effect of the finish rolling temperature (FRT) on recrystallisation behaviour in hot bands of an electrical steel containing 1·3%Si was investigated. Four sequential passes of hot rolling were carried out on the 1·3%Si electrical steel, with finish rolling temperatures ranging from 980 to 700°C, followed by isothermal annealing at 720°C. The experimental results showed that when Ar ₁ <FRT <Ar ₃, fine equiaxed subgrains formed at the boundaries between deformed and non-deformed grains in a necklacelike arrangement, and strain induced boundary migration (SIBM) was the main mechanism corresponding to the formation of recrystallisation nuclei for steels finish rolled below Ar ₁. However, the study also demonstrated that when FRT <(Ar ₁­100 K), a second nucleation mechanism, i.e. subgrain growth, became active in recrystallisation, this resulted in an increase of nucleus density. Steels in which SIBM was the dominant mechanism of recrystallisation possessed the largest grain size, and strongest textures with major component {100}〈110〉.     

Microstructural development during cold deformation and recrystallisation of 2014 AI–AI2O3 particulate composite

Abstract

The recrystallisation behaviour has been studied in a cold worked 2014 Al–Al₂O₃ particulate reinforced composite which was heat treated to produce two markedly different initial matrix microstructures. The composite was cold deformed to a reduction of either 30 or 50% and then annealed for various times at temperatures in the range 100–500°C. The microstructural development during recrystallisation was studied using optical and transmission electron microscopy (TEM). The recrystallisation kinetics were monitored via hardness measurements and the results correlated with the microstructural analysis. It was observed that the kinetics and temperature of recrystallisation were dependent on the original heat treatment. A detailed TEM investigation indicated that nucleation occurs preferentially at individual and clustered Al₂O₃ particles, but the progress of recrystallisation was controlled by the distribution of dispersoid particles in the matrix. Recrystallisation proceeded rapidly in the composite containing large stable dispersoids. In contrast, when precipitation occurred during annealing, recrystallisation was severely retarded and was controlled by the fine precipitate dispersion.

MST/1566     

Annealing behaviour of dilute aluminium alloys following hot deformation

Abstract

The microstructure and texture of three dilute aluminium alloys after hot deformation and annealing was assessed; In particular, the influence of deformation temperature, strain rate, and strain on the annealed texture was examined, as well as the effect of alloy composition. The microstructures of the commercially pure materials studied (Al, Al+1%Mn and Al+1%Mg) varied in the volume fraction of coarse intermetallic particles, the type of dispersoid present, and the level and type of solute in solid solution. Furthermore, the initial stages of recovery and recrystallisation were studied in detail for one of the alloys (commercially pure Al). It was found that the main recrystallisation texture component was the cube and its strength, as well as the recrystallised grain size, depended strongly on the deformation strain. The deformation strain rate and temperature, and the alloy composition also strongly influenced the grain size and cube texture strength. These results are discussed in the context of current theories for cube nucleation within cube bands in the hot deformed microstructure. The present work was carried out as part of a wider research programme, partially supported by the European Union (Brite/Euram funded), to develop micromechanical models to describe the evolution of microstructure and texture during hot deformation and annealing of aluminium alloys.

MST/3376     

Texture homogeneity and stability in severely warm-rolled and annealed ultrafine pearlite

The evolution of microstructure and texture was investigated in a severely warm-rolled ultrafine pearlitic steel. The steel was 95% warm-rolled at 600°C and annealed at 700°C for different time intervals. The spheroidisation of cementite initiated after 30% reduction and completed beyond 70% reduction. The 95% warm-rolled steel showed elongated as well as ultrafine equiaxed ferrite grains. Texture inhomogeneities were evidenced by the presence of Goss component ({011} <100>) on the surface originating due to surface shear and diffuse texture at the interior. Formation of equiaxed microstructure after annealing through continuous recrystallisation resulted in the retention of the surface Goss component. However, the Goss component was destroyed beyond annealing for 180?minutes due to the abnormal growth of other grains.     

Textures of ferritic stainless steels

Abstract

Whereas much research has been carried out on the texture development of Fe–Si steels or low carbon steels, very little attention has been given to the texture formation and investigation of the underlying mechanisms in Fe–Cr steels. Ferritic stainless steels containing between 11 and 17%Cr establish an important group of alloys owing to their good mechanical behaviour and corrosion resistance. Various industrial problems, such as roping or optimisation of deep drawability, can be tackled by means of quantitative texture analysis. Therefore, fundamental aspects concerning the inhomogeneity of the hot and cold rolled band, the origin of Goss texture after annealing, and selective particle drag during recrystallisation of alloys with finely dispersed Nb and Ti carbonitrides have been discussed.

MST/1678     

Development of microstructure in cast Mg–AI–rare earth alloys

Abstract

The microstructures and age hardening behaviours of a series of Mg–Al–rare earth (RE) alloys that had been either pressure die cast or permanent mould cast were investigated by SEM and analytical TEM. Two types of phases, Al₄MM and Al₁₂Mg₁₇, were found in the as cast alloys and no pseudoternary Mg–Al–RE phases were present. The Al₄MM phase was thermally stable during solution treatment at temperatures as high as 500°C, whereas Al₁₂Mg₁₇ partially dissolved in the α-Mg matrix during solution treatment at 420°C. No rare earth containing precipitates formed during heat treatment of the investigated alloys but two types of Al₁₂Mg₁₇ precipitation took place. Colonies of discontinuous precipitation containing alternate lamellae of α-Mg and Al₁₂Mg₁₇ formed preferentially in regions α-Mg with high aluminium content. Spheroidisation and coarsening of the discontinuous precipitates occurred after aging at 200°C. Continuous precipitation of Al₁₂Mg₁₇ also occurred and these precipitates had a rodlike morphology and grew in preferred crystallographic directions.

MST/3382     

The influence of sulphur content on the static recrystallisation of cold worked low carbon aluminium-killed strip steels

The static recrystallisation (SRX) after cold work was studied in four low carbon Al-killed steels with varying sulphur content ranging from 2 to 140 ppm. The sulphur had an indirect but significant effect on the SRX behaviour by the presence of coarse MnS particles on which the AlN precipitated heterogeneously during coiling after hot rolling. The mean size of the AlN/MnS compound particles was generally too coarse to be effective for Zener-pinning of moving boundaries during recrystallisation thereby rendering the AlN ineffective in influencing the SRX process. In the low sulphur content steels, however, with virtually no MnS present, very fine AlN nucleated homogeneously in the matrix or heterogeneously on grain boundaries or dislocations during coiling, with size often less than 30 nm in diameter. These AlN particles were more effective in Zener-pinning of dislocations and moving recrystallisation fronts, thereby retarding the start of SRX by up to 100 times at low coiling temperatures of about 600 °C.     

Effect of preheat treatment on ingot structure and recrystallisation of brass component of rolling texture in hot rolled AA 5182

Abstract

Two different preheating treatments were used to vary the Al₆ Mn dispersoid characteristics in AA 5182. High temperature followed by slow cooling produced coarse, needlelike dispersoids which allowed rapid recrystallisation following hot rolling, whereas a low temperature preheat produced afine dispersion of low aspect ratio particles which retarded recrystallisation. Long, unrecrystallised bands persisted in the hot rolled material subected to the low temperature preheat even after holding for 24 h at the final pass temperature. Micro-orientation determinations within the bands showed that they were predominantly of the brass (Bs) orientation, {110}〈112〉, confirming the results of X-ray bulk texture analyses. The results are considered conclusive evidence of the widely reported higher resistance to recrystallisation of the Bs orientation compared with other orientations in rolled high stacking fault energy fcc metals. The Bs oriented bands could be removed by annealing at a temperature substantially greater than that experienced in the final hot rolling pass.

MST/1475     

Effects of hot deformation and accelerated cooling on microstructural evolution of low carbon microalloyed steels

Abstract

Using a Gleeble 1500 hot simulator, the effects of hot deformation parameters and accelerated cooling conditions on the microstructural characteristics of low carbon microalloyed steels were investigated by means of compression tests. It was found that the grain refinement effect of single pass reduction in the recrystallisation or unrecrystallisation temperature ranges is weaker than that of two pass reduction in the recrystallisation and unrecrystallisation temperature ranges. However, four pass deformation in the recrystallisation and unrecrystallisation temperature ranges could result in rather fine grained microstructures and, when coupled with moderately high cooling rate, partially acicular ferrite microstructure could be obtained. With the increase of cooling rate, the microstructure becomes finer and the content of acicular ferrite increases. Under similar deformation and cooling conditions, the specimens with relatively high carbon content have more refined microstructures.     

Deformation microstructure and texture in hot worked aluminium alloys

Abstract

Three non-heat-treatable aluminium based materials (AA 1050, AA 1050+1%Mn, and AA 1050+1%Mg) were deformed by plane strain compression (strains of 0·5 to 2, strain rates of 0·25 to 25 s^?1) at elevated temperature (300 to 500°C). The resulting microstructures and textures were studied using optical and back scattered electron microscopy and neutron diffraction. Trends in the development of the deformation microstructure and texture with deformation parameters were noted. It was found that the amount of cube texture in the deformed material decreases as the strain increases. The Zener–Hollomon parameter is not suitable for describing the evolution of cube texture during hot deformation in AA 1050. The addition of 1%Mn or 1%Mg to AA 1050 has little effect on the trends of texture development during hot working. The subgrain size in these alloys decreases with increasing Zener–Hollomon parameter, but the strain has little effect. The misorientation between neighbouring subgrains appears to be approximately independent of deformation parameters in the range of deformation conditions studied.

MST/3472     

Microstructure and tensile properties of as extruded and as aged Mg–Al–Zn–Mn–Sn alloy

The effect of 0–4 wt-% Sn addition on the microstructure and tensile properties of AZ80 alloys was investigated. The results indicated that Mg₂Sn particles were barely formed during the extrusion process until the content of Sn is >2 wt-%. The dislocation density in alloys after extrusion declined with the addition of Sn due to the promotion of dynamic recrystallisation after adding Sn. In aging treatment, Mg₁₇Al₁₂ precipitates were promoted by Sn and the phases distributed uniformly at low density level of dislocation. The AZ80-2 wt-% Sn alloy possessed the excellent tensile properties in as extruded and as aged state.     

Influence of particles on recrystallisation textures and microstructures of aluminium alloy 3103

Abstract

The evolution of recrystallisation textures in the commercial aluminium alloy 3103 has been investigated by means of a three-dimensional orientation distribution function (ODF) analysis. The global texture measurements were supplemented by local texture measurements by means of the electron backscattering pattern (EBSP) technique in SEM and optical microscopy, inparticular grain size measurements. The evolution of recrystallisation textures was determined by the competition between particle stimulated nucleation (PSN) and nucleation from cube bands. Precipitated particles were found to have a higher retarding effect on the nucleation from deformation zones around particles than on the nucleation from cube bands. The result of this is a strong cube texture and a large grain size in cases of a strong precipitation reaction. This phenomenon has also been discussed theoretically in terms of a semiquantitative model.