Influence of hot-rolling conditions on texture development in deep-drawing steels

As the textures of deep-drawing sheet steels are important for certain material properties the purpose of this paper was to take a closer look at the hot-rolling, cold-rolling and annealing textures of different deep-drawing steel grades. Several Al-killed mild steels and vacuum-degassed Ti-IF steels have been hot rolled in the mill varying the finishing temperature (FT). After coiling, cold rolling and short-time annealing the textures at different thickness levels have been measured by means of (110)-pole figures and orientation distribution functions (ODFs). For both steel groups the textures at the surface of the hot strip exhibit a more or less pronounced shear type character. Towards the mid-thickness level (with lower FT more clearly) typical (cold-) rolling textures exist characterized by a strong {001}<110> orientation and in the Ti-IF steels additionally by a significant {112}<110> orientation density. In the case of high FT cold rolling and annealing lead to favourable {111}-textures where deep-drawing application is concerned. For the Al-killed steels lowering FT results in diffuse recrystallization textures whereas in the Ti-IF steels a sharp texture with near {223}<582> orientations can be observed which have not been known for these steels before. The results prove that the hot strip textures can be of great importance for the resulting annealing textures and the according material properties.     

The Effect of Recrystallization on Interphase Precipitation in Hot-Rolled Steel Sheet

Hot-rolled steel products with high strength and good formability are in demand for automobile body parts, particularly steels which can reduce weight without sacrificing vehicle safety. Recent studies have suggested that interphase precipitation (IP) hardening is a promising approach for obtaining excellent high strength and superior formability from low-alloy steels. However, the effects of hot rolling conditions and alloying elements on IP hardening have not been clearly determined. In this study, we sought to clarify the above effects by analyzing the recrystallization behavior during hot rolling. As a result of sample testing and analysis, it was determined that the recrystallization which occurs during hot rolling plays a critical role in enhancing the IP hardening of low-alloy steels.     

A study of the hot working behavior of Al-Mg alloy 5052 by hot torsion testing

The hot working behavior of commercial Al-2.5 wt pct Mg alloy 5052 was studied using hot torsion testing to simulate commercial hot rolling. The effects of homogenization time and temperature, and deformation temperature on the flow stress and hot ductility were carefully assessed. Microstructural characterizations and differential thermal analyses were performed to help explain the torsion data obtained. Significant variations in hot working behavior were noted for material machined from different regions of the commercial ingot studied. The constituent particles were found to play a significant role in determining the hot ductility of the alloy.     

Effect of Hot Band Annealing on Magnetic Properties in 3% Si Grain‐oriented Electrical Steels

Hot band annealing is known to be a prerequisite for good magnetic properties irrespective of manufacturing methods in grain‐oriented Fe‐3 wt.% Si electrical steels. In this study, the effects of hot band annealing on magnetic properties were investigated in 3% grain‐oriented electrical steels of low soluble AI contents and one‐stage cold rolling. Microstructure and precipitate distribution were compared with hot band annealing conditions. Secondary recrystallization behaviour with hot band annealing condition was also discussed.     

薄带连铸取向硅钢Goss晶粒二次再结晶过程的研究

研究了双辊薄带连铸Fe- 3%Si取向硅钢薄带在冷轧后二次再结晶过程中Goss晶粒的演化过程。结果表明：薄带连铸流程可以固溶较多的抑制剂元素，并且无需通过“γ→α”相变控制AlN的析出。铸带经过两阶段冷轧变形和高温退火后，可以获得完善且位向准确的Goss晶粒，B8值达到1. 92T以上。高温退火升温过程中，在抑制剂的作用下基体晶粒尺寸基本稳定，Goss晶粒在1035～1060℃范围内发生异常长大。长大方式为位向准确的Goss二次晶粒快速发生异常长大，吞并基体中稳定的初次晶粒，而后快速发生异常长大的二次晶粒继续吞并发展缓慢的Goss二次晶粒和一些尺寸较大的初次晶粒，最终完成全部二次再结晶过程。     

冷轧压下率和再结晶退火温度对Ti-IF钢织构和成型性能的影响

采用背散射衍射技术(EBSD)研究了3.13 mm热轧板的冷轧压下量(65%~80%)和再结晶退火温度(660~780℃)对0.64~1.10 mm Ti-IF钢冷轧板(/%:0.02C、0.01Si、0.10Mn、0.013P、0.011S、0.064 Ti、0.028Al、0.002 0N)的织构和成型性能应变硬化指数(n)、塑性应变比(r)的影响。结果表明,Ti-IF钢冷轧板在冷轧压下率为75%时{111}织构含量最大,成型性能最佳;在740℃以下再结晶退火时材料{111}<110>织构含量高,高于740℃时材料{111}<112>织构含量高;在660~780℃再结晶退火随温度增高,材料{111}织构含量增加,成型性能提高。     

Recrystallization of deep drawing columbium (Nb)-treated interstitial-free sheet steels

The softening response after isochronal annealing of cold-rolled, Cb-treated, vacuum decarburized-deoxidized, interstitial-free steels was investigated by hardness measurements, tension tests, and optical and transmission electron microscopy. Softening after annealing, following cold reduction, occurs by recovery-recrystallization and a reduction in precipitation hardening due to the coarsening of CbC precipitates. The recrystallization start temperature increases markedly with increasing amounts of Cb in solid solution in ferrite. Fine CbC precipitates retard recrystallization to a much lesser degree, and their effects can be eliminated by coarsening prior to cold reduction. Recrystallization initiates at free surfaces. Partially recrystallized structures consist of two layers of recrystallized matrix separated by an unrecrystallized zone. The recrystallized layers thicken with increasing temperature or time. This phenomenon is an inherent characteristic of these steels and not a result of external influences.     

Recrystallization of deep drawing columbium (Nb)-treated interstitial-free sheet steels

The softening response after isochronal annealing of cold-rolled, Cb-treated, vacuum decarburized-deoxidized, interstitial-free steels was investigated by hardness measurements, tension tests, and optical and transmission electron microscopy. Softening after annealing, following cold reduction, occurs by recovery-recrystallization and a reduction in precipitation hardening due to the coarsening of CbC precipitates. The recrystallization start temperature increases markedly with increasing amounts of Cb in solid solution in ferrite. Fine CbC precipitates retard recrystallization to a much lesser degree, and their effects can be eliminated by coarsening prior to cold reduction. Recrystallization initiates at free surfaces. Partially recrystallized structures consist of two layers of recrystallized matrix separated by an unrecrystallized zone. The recrystallized layers thicken with increasing temperature or time. This phenomenon is an inherent characteristic of these steels and not a result of external influences.     

Cu-Ni-Si-P合金冷加工硬化及再结晶温度的研究

为全面掌握Cu-Ni-Si-P合金的加工特性及再结晶的退火制度，并指导产业化生产，对Cu-Ni-Si-P合金的冷加工特性展开研究，且通过对不同厚度退火后试样进行抗拉强度、延伸率的测试和组织观察，确定出新型Cu-Ni-Si-P合金的再结晶退火制度.试验结果表明，Cu-Ni-Si-P合金具有明显的加工硬化特征；合金的抗拉强度随加工率的增大，呈先快速增大后趋于平稳的趋势，而延伸率和导电率，则呈现相反的变化规律；变形量越大，则相应的开始再结晶温度越低；综合优化出Cu-Ni-Si-P合金在80 %加工率的再结晶退火温度制度为460 ℃×1 h.      

Hot working and recrystallization of as-cast 317L

Stress-strain behavior and microstructure evolution during hot working of as-cast austenitic stainless steel alloy 317L is investigated by uniaxial compression of cylindrical specimens at a strain rate of 1 s⁻¹ over the temperature range 1000 °C to 1150 °C and up to a strain of one. The measured flow curves show little strain hardening, attributed in part to the high stacking fault energy (SFE) of the alloy. Dynamic recrystallization is not observed. Static recrystallization is observed to nucleate within the austenite matrix in the dendrite cores at dislocation microbands and in austenite immediately adjacent to a vermicular microconstituent, composed primarily of sigma and austenite and, occasionally, some delta ferrite. The recrystallization kinetics of 317L are retarded compared to as-cast 316L steel. The relatively sluggish recrystallization behavior is attributed in part to the higher SFE of 317L, which favors recovery over recrystallization, and in part to gradients in chemical composition and SFE, not found in 316L, in the dendritic microstructure. Thus, in the austenite near the interphase boundary, with high SFE, recovery initially replaced recrystallization, in contrast to recrystallization in the austenite more distant from the boundary. The recrystallization kinetics of both as-cast 317L and 316L were relatively slow compared to wrought stainless steels of comparative grain size and SFE, presumably due to the crystallographic texture and associated relatively low flow stress in the former materials. A kinetic model for recrystallization in as-cast 317L is developed and utilized to simulate evolution of the first cycle of recrystallization during various thermal-mechanical treatment schedules typically employed during primary breakdown of as-cast material.     

冷轧冲压用钢SPHC热轧工艺研究

SPHC作为冷轧冲压用钢的原料,要求良好的冲压成型性,拉伸和弯曲性能以及较低的屈服强度,主要通过控制AlN在热轧过程中的固溶和析出,在随后的退火再结晶过程中促进γ纤维织构(<111>∥ND)的发展从而获得良好的冲压性能。退火工艺不同,热轧工艺也有所不同,对罩式退火,采用"三高一低"温度制度,对于连续退火,则采取低温加热、高温终轧以及高温卷取的工艺制度。     

1750mm冷连轧精冲钢的连续退火工艺

连续退火工艺制度是精冲钢冷连轧生产过程中的重要环节,对其成品组织性能有着极其重要的影响。在实验室进行轧制润滑试验研究,设计了多种连续退火工艺方案,采用CAS- 300连续退火试验机模拟连续退火试验,确定了C15/2精冲钢的再结晶温度为550℃。针对不同规格冷连轧精冲带钢,通过拉伸试验和显微组织鉴定,给出了适用于冷连轧生产实践的连续退火工艺制度。结果表明,退火后试样的屈服强度控制在(310±20)MPa,抗拉强度小于450MPa,伸长率大于30%,获得了良好综合力学性能的精冲钢组织。该研究完全满足工业生产实践的需求,对精冲钢冷连轧生产退火工艺研究具有重要意义。     

Development and Application of On-Line Solution Annealing Process for 304 Austenitic Stainless Steel

After hot rolling, 304 austenitic stainless steel requires a solution annealing treatment to prevent intergranular corrosion and eliminate work hardening effects. Compared to traditional offline processes, on-line solution annealing offers advantages in terms of cost and time savings. However, both recrystallization behavior and M₂₃C₆ carbide precipitation behavior are significantly influenced by the cooling process after rolling, which poses conflicting requirements. This study investigates the precipitation behavior of M₂₃C₆ carbides and the recrystallization softening behavior during the continuous cooling process of hot-rolled samples. The kinetics equations are derived using the Scheil's additivity rule. The temperature profiles in different regions of the plate are studied using finite element analysis. A practical approach for online solution annealing is proposed and applied in industrial testing.     

Effect of aluminum nitride formation on the recrystallization of Fe-0.06 pct Al single crystals

Single crystals of Fe-0.06 pct Al containing i) less than 0.001 pct N and, ii) 0.008 pct N were cold-rolled 70 pct and annealed under simulated box-annealing conditions. Crystals having (111) [άrc211] and (001) [110] stable-end orientations after rolling were investigated. Optical and electron microscopy, both replication and thin-foil techniques, and X-ray transmission experiments were used to follow recrystallization behavior, aluminum nitride precipitation behavior, and texture development during annealing. In the (111) [άrc211] Fe-0.06 pct Al crystals the presence of nitrogen had no obvious effect on the recovered structure but did retard the start of recrystallization. Once recrystallization started, however, it proceeded at least as rapidly in the nitrogen-containing crystals as in the nitrogen-free crystals. Recrystallization was complete in these crystals before the detection of A1N precipitates by electron microscopy. The recrystallization texture of both the nitrogen-free and nitrogen-doped crystals was predominantly (110) [001], the normal recrystallization for crystals having a (111) [211] as-rolled orientation. The (001) [110] crystals did not recrystallize during annealing. In these crystals, however, the presence of nitrogen had a marked effect on recovery characteristics. Low-angle boundary cell formation was retarded to much higher temperatures and occurred only after the aluminum nitride precipitate, which formed at temperatures in excess of 1100°F, had begun to coarsen. The implication of these single-crystal results for texture development in box-annealed aluminum-killed sheet steels is discussed. It is proposed that in aluminum-killed steels the first components to recrystallize, the (lll)-oriented grains, grow at an “uninhibited” rate during their last stage of recrystallization (new grain growth), whereas, in as-rolled grains of other orientations recovery and new grain nucleation proceed at a retarded rate. This results in a larger volume of (lll)-oriented grains in box-annealed aluminum-killed steel as compared with other sheet grades not containing aluminum.     

Evolution of Through-Thickness Texture in Ultra Purified 17%Cr Ferritic Stainless Steels

 Texture inhomogeneity usually takes place in ferritic stainless steels due to the lack of phase transformation and recrystallization during hot strip rolling, which can deteriorate the formability of final sheets. In order to work out the way of weakening texture inhomogeneity, conventional hot rolling and warm rolling processes have been carried out with an ultra purified ferritic stainless steel. The results showed that the evolution of through-thickness texture is closely dependent on rolling process, especially for the texture in the center layer. For both conventional and warm rolling processes, shear texture components were formed in the surface layers after hot rolling and annealing; sharp α-fiber and weak γ-fiber with the major component at {111}<110> were developed in both cold rolled sheet surfaces, leading to the formation of inhomogeneous γ-fiber dominated by {111}<112> after recrystallization annealing. In the center layer of conventional rolled and annealed bands, strong α-fiber and weak γ-fiber textures were formed; the cold rolled textures were comprised of sharp α-fiber and weak γ-fiber with the major component at {111}<110>, and inhomogeneous γ-fiber dominated by {111}<112> was formed after recrystallization annealing. By contrast, in the centre layer of warm rolled bands, the texture was comprised of weak α-fiber and sharp γ-fiber, and γ-fiber became the only component after annealing. The cold rolled texture displayed a sharp γ-fiber with the major component at {111}<112> and the intensity of γ-fiber close to that of α-fiber, resulting in the formation of a nearly homogeneous γ-fiber recrystallization texture in the center layer of the final sheet.     

The effect of thermomechanical history upon the microstructure and magnetic properties of nonoriented silicon steels

A study has been conducted to evaluate the effect of hot rolling conditions on precipitation behavior of MnS and AIN, microstructure, texture, and subsequent magnetic properties of nonoriented silicon steels. TEM work showed that MnS particles act as nucleating sites for dissolved A1N by providing an interface on which to precipitate. It was established that for the steels studied, a decrease in reheat temperature and a corresponding increase in coiling temperature resulted in an improved texture and, subsequently, better final magnetic properties. These results were explained based upon the effect of steel composition and hot rolling history on recrystallization behavior in the hot band and continuously annealed strip. This paper is based on a presentation made at the symposium “Physical Metallurgy of Electrical Steels” held at the {dy1985} annual AIME meeting in New York on February 24–28, {dy1985}, under the auspices of the TMS Ferrous Metallurgy Committee.     

Recrystallization Behavior of a Heavily Deformed Austenitic Stainless Steel During Iterative Type Annealing

The study describes evolution of the recrystallization microstructure in an austenitic stainless steel during iterative or repetitive type annealing process. The starting heavily cold deformed microstructure consisted of a dual phase structure i.e., strain-induced martensite (SIM) (43 pct in volume) and heavily deformed large grained retained austenite. Recrystallization behavior was compared with Johnson Mehl Avrami and Kolmogorov model. Early annealing iterations led to reversion of SIM to reversed austenite. The microstructure changes observed in the retained austenite and in the reverted austenite were mapped by electron backscatter diffraction technique and transmission electron microscope. The reversed austenite was characterized by a fine polygonal substructure consisting of low-angle grain boundaries. With an increasing number of annealing repetitions, these boundaries were gradually replaced by high-angle grain boundaries and recrystallized into ultrafine-grained microstructure. On the other hand, recrystallization of retained austenite grains was sluggish in nature. Progress of recrystallization in these grains was found to take place by a gradual evolution of subgrains and their subsequent transformation into fine grains. The observed recrystallization characteristics suggest continuous recrystallization type process. The analysis provided basic insight into the recrystallization mechanisms that enable the processing of ultrafine-grained fcc steels by iterative type annealing. Tensile properties of the processed material showed a good combination of strength and ductility.     

Hot working and recrystallization of As-Cast 316L

Stress-strain behavior and microstructure evolution during hot working of as-cast austenitic stainless steel alloy 316L were investigated by uniaxial compression of cylindrical specimens at a strain rate of 1 s⁻¹ over the temperature range 1000 °C to 1150 °C and up to a strain of one. The measured flow curves showed monotonic hardening, indicating that dynamic recrystallization was not important in microstructural evolution. Static recrystallization was observed to nucleate preferentially at the delta ferrite-austenite interphase boundaries. The recrystallization kinetics of the as-cast material was compared to a relatively fine-grained wrought 316L material and found to be somewhat slower. However, the difference between the two material conditions was not nearly as great as previously reported for as-cast and wrought 304L alloy. The difference in behaviors between 316L and 304L is attributed to the relatively large amount and vermicular morphology of the delta ferrite phase in the 316L, resulting in a relatively fine effective grain size, compared to the existing coarse columnar structure, and concomitant enhancement of recrystallization. Compared to wrought 316L, the recrystallization rate of the as-cast material was relatively sluggish, despite a relatively fine effective grain size. The difference is associated with the 100 orientations of the columnar grains with respect to the compression axis, producing a soft orientation and a reduced rate of accumulation of dislocation density in the substructure. Also, compared to wrought 316L, the recrystallization rate of the as-cast material tends to decrease with time, the drop occurring concurrently with spheroidization and dissolution of the ferrite. It is suggested that (1) movement of the delta ferrite-austenite interphase boundary during spheroidization may poison incipient recrystallization and (2) dissolution of delta ferrite can locally enrich the austenite matrix in Mo and Cr, raising the local stacking fault energy and lowering grain boundary mobility to favor recovery over recrystallization in the vicinity of the ferrite-austenite boundary. A kinetic model for recrystallization was developed and used to simulate evolution of the first cycle of recrystallization during various thermal-mechanical treatment schedules typically employed during the primary breakdown of as-cast material.     

Interaction between deformation,recrystallization and precipitation in niobium steels

The present study was undertaken in order to establish the extent to which niobium (columbium) inhibits recovery and recrystallization of microalloyed austenite while present as solute on the one hand, and as carbonitride precipitates on the other. Three steels were used; the first was an HSLA steel containing 0.054 pct Nb, 0.05 pct C and 0.92 pct Mn. The second was prepared by treating the first in wet hydrogen at 1100°C so as to reduce the C and N content to about 10 ppm by wt. The third material was a plain carbon steel containing 0.055 pct C and 0.41 pct Mn. The isothermal recovery and re-crystallization of these materials, after an interval of hot working, was studied by means of interrupted compression tests. Samples were prestrained at 10^-2 and 10^-1s^-1 at 900, 950 and 1000°C to natural strains of 0.10 and 0.25, and held isothermally prior to reloading. The results obtained in this way, indicate that 0.56 pct of substitutional solute can give rise to an order of magnitude decrease in the rate of recrystallization. When precipitation of Nb(CN) takes place either during deformation or in strained aus-tenite the mean precipitate size is ∼ 20 nm. The presence of such particles inhibits both static recovery and recrystallization; the magnitude of the effect being dependent on the volume fraction of precipitate. When the volume fraction reaches about 0.02 pct, static recrystallization is completely suppressed for the present prestraining conditions. This paper is based on a presentation made at a symposium on “Precipitation Processes in Structural Steels” held at the annual meeting of the AIME, Denver, Colorado, February 27 to 28, 1978, under the sponsorship of the Ferrous Metallurgy Committee of The Metallurgical Society of AIME.