Deformation banding and origins of rolling and annealing textures in low carbon and interstitial free steels

Abstract

This paper is dedicated to the memory of Professor Sir Robert Honeycombe, who examined the first author's PhD thesis on this subject in 1972. The paper reviews some of the very large improvements in the understanding of the formation of textures and microstructures in drawing quality steels in both their deformed and recrystallised states made since the 1970s, focusing in particular on deformation bending in interstitial free steels.     

Optimization of annealing cycle parameters of dual phase and interstitial free steels by multiobjective genetic algorithms

Data-driven models have been constructed for Dual Phase (DP) and Interstitials Free (IF) steels using an evolutionary approach. DP steel data are utilized from an existing database, while for the IF steels, data generated at an integrated steel plant have been used. The objective function for Ultimate Tensile Strength (UTS) and % elongation, created as data-driven models, is simultaneously optimized for an optimum strength-ductility balance and the results indicate the possibilities of developing steels with better mechanical properties than what are known to have been existing so far.     

Evolution of microstructure and texture in copper during repetitive extrusion-upsetting and subsequent annealing

The evolution of the microstructure and texture in copper has been studied during repetitive extrusionupsetting(REU) to a total von Mises strain of 4.7 and during subsequent annealing at different temperatures. It is found that the texture is significantly altered by each deformation pass. A duplex 001 + 111 fiber texture with an increased 111 component is observed after each extrusion pass,whereas the 110 fiber component dominates the texture after each upsetting pass. During REU, the microstructure is refined by deformation-induced boundaries. The average cell size after a total strain of 4.7 is measured to be ~0.3 μm. This refined microstructure is unstable at room temperature as is evident from the presence of a small number of recrystallized grains in the deformed matrix. Pronounced recrystallization took place during annealing at 200?C for 1 h with recrystallized grains developing predominantly in high misorientation regions. At 350?C the microstructure is fully recrystallized with an average grain size of only 2.3 μm and a very weak crystallographic texture. This REU-processed and subsequently annealed material is considered to be potentially suitable for using as a material for sputtering targets.     

高硅钢薄板退火过程中的织构演变

采用传统的轧制和退火工艺制备了0.30mm厚的6.5%（质量分数）Si高硅电工钢薄板,采用X射线衍射技术对退火过程中的再结晶织构进行了研究。冷轧高硅钢薄板700℃退火形成以{111}〈112〉为峰值的γ织构（〈111〉∥ND）和以{001}〈210〉为峰值的{001}织构;而900℃以上温度退火则形成强{001}〈210〉织构。进一步的研究表明是在晶粒长大过程中{001}〈210〉发展成为主要再结晶织构组分。     

Influence of B and Ti on hot ductility of high Al and high Al,Nb containing TWIP steels

Abstract

The addition of ～0·002%B and ～0·04%Ti as microalloying additions to improve the poor hot ductility and high risk of cracking on continuous casting of high Al containing twinning induced plasticity (TWIP) steels has been examined. Tensile specimens were either cast in situ or heated to 1250°C before cooling at 60 K min^?1 to test temperatures in the range 700–1100°C and strained to failure at 3×10^?3 s^?1. For tensile specimens reheated to 1250°C, the presence of B with sufficient Ti to combine with all the N improved ductility over the temperature range of 700–950°C, the reduction in area (RA) values being >40%. For the higher strength more complex high Al, TWIP steels having Nb present, there was no improvement in ductility with a similar B and Ti addition, when the average cooling rate after melting to the test temperature was 60 K min^?1. Reducing the cooling rate to 12 K min^?1 resulted in the RA values being close to the minimum required to avoid transverse cracking throughout the temperature range 800–1000°C. Using these additions of B and Ti, transverse cracking was found not to be a problem when continuously casting these high Al containing TWIP steels.     

Evolution of textures in hot rolled Nb - Ti and V - Nb microalloyed steels

Abstract

A considerable texture gradient in the through thickness direction was observed during hot rolling of Nb - Ti and V - Nb microalloyed steels. The most intense deformation texture for Nb- Ti steels was {113}〈110〉 at all depths, whereas for V - Nb steels the plane was shifted to {115}〈110〉 ; the angular difference between {113} and {115} is about a degree. The recrystallisation texture of austenite, {100}〈001〉 , transformed into {100} 〈011〉 component in the ferrite and indicated an increase in the intensity with increase in depth for both Nb - Ti and V - Nb steels. However, the intensity of this {100}〈011〉 texture was less for Nb - Ti steels compared to V - Nb steels at all depths. The reduced intensity of {100}〈011〉 texture in Nb -Ti steels is likely to be the reason for the superior formability and improved toughness of Nb - Ti steels as compared with V - Nb steels. The {100}〈011〉 type of texture has an undesirable effect on the edge formability of steels.     

Hot ductility of high Al TWIP steels containing Nb and Nb-V

The hot ductility of B-Ti-Nb-high Al (1.5%Al) containing TWIP steels having Ti/N ratios mainly in excess of 3.4/1 was obtained. After soaking at 1250°C, the tensile specimens were cooled at 12 or 60°C?min^?1 to the test temperature and then strained to failure at 3?×?10^?3?s^?1. Ductility was always good (reduction of area >40%), independent of Ti/N ratio or cooling rate. The good ductility is due to B segregation strengthening the grain boundaries and the low S level (0.005%S) limiting the volume fraction of MnS inclusions and restricting AlN precipitation to the matrix. Increasing the cooling rate, higher N levels and Nb resulted in a small improvement in ductility. An addition of V to the Nb-containing steels caused a slight deterioration in the hot ductility.     

Application of electron backscattered diffraction and crystal orientation mapping to recrystallisation studies in high strength interstitial free steels

Abstract

Electron backscattered diffraction (EBSD) has been demonstrated to be a valuable tool in gathering data to aid in the understanding of microstructural development in a variety of materials. A high strength interstitial free steel has been studied using the capabilities of a modern EBSD system, particularly by use of the crystal orientation mapping facility. Grain boundary characteristics have been determined and used to develop an understanding of the recrystallisation process. Little evidence in favour of the oriented growth theory has been found. It is proposed that the nucleation process during annealing is critical in controlling the fully annealed texture.     

高强度钢板BR1500HS热成形微观结构和力学性能研究

以BR1500HS高强度钢为研究对象,采用金相显微镜、显微硬度仪和万能拉伸实验机对比分析了其热成形前后的微观组织和力学性能,同时得到了试样在不同冷却速度时的时间-温度曲线图,即马氏体转变曲线。分析结果表明,高强钢BR1500HS室温条件下其微观组织为90F+10B,其屈服强度、抗拉强度分别为462,627 MPa;而经热成形后的微观组织最好为98M+1B+1F,最大硬度、抗拉强度值分别为501.2HRV、1 633.69 MPa,与此同时,得硬度、抗拉强度值排序情况与组织中马氏体含量排序情况基本吻合。马氏体转变曲线表明,BR1500HS的马氏体转变温度范围为375~325℃,其转变发生在保压冷却时间为15~25s区间,且当冷却速率值超过40℃/s时,马氏体转变进行得较为充分。     

Influence of microstructure and load ratio on cyclic fatigue and final fracture behavior of two high strength steels

The results of a recent study aimed at understanding the conjoint influence of load ratio and microstructure on the high cycle fatigue properties and resultant fracture behavior of two high strength alloy steels is presented and discussed. Both the chosen alloy steels, i.e., AerMet® 100 and PremoMet™ 290 have much better strength and ductility properties to offer in comparison with the other competing high strength steels having near similar chemical composition. Test specimens were precision machined from the as-provided stock of each steel. The machined specimens were deformed in both uniaxial tension and cyclic fatigue under conditions of stress control. The test specimens of each alloy steel were cyclically deformed over a range of maximum stress at two different load ratios and the number of cycles to failure recorded. The specific influence of load ratio on cyclic fatigue life is presented and discussed keeping in mind the maximum stress used during cyclic deformation. The fatigue fracture surfaces were examined in a scanning electron microscope to establish the macroscopic mode and to concurrently characterize the intrinsic features on the fracture surface. The conjoint influence of nature of loading, maximum stress and microstructure on cyclic fatigue life is discussed.     

Influence of V and Ti on hot ductility of Nb containing steels of peritectic C contents

Abstract

The hot ductility of in situ melted tensile specimens of Ti–Nb containing steels having C contents in the peritectic C range 0·12–0·17% with and without V has been examined over the temperature range 700–1000°C. An improved testing regime for simulating the continuous casting process was used, which takes into account both primary and secondary cooling conditions. For the Nb containing steels, the ductility improved in the temperature range 750–850°C as the Ti/N ratio increased. However, ductility at 800°C was still below the 35–40% reduction in area values required to avoid transverse cracking. This was attributed to the copious precipitation of sub 40 nm NbTi(CN) precipitates along the grain boundaries and finer precipitates within the grains. Adding V to the Ti–Nb containing steels resulted in significantly improved ductility with reduction in area values at 800°C in excess of 45%. This improvement was due to a decrease in the fraction of fine particles, and in accord with this better ductility, transverse cracking of industrial slabs was avoided.     

高Nb-TiAl合金的凝固组织与力学性能研究

研究了Al含量变化对高Nb-TiAl合金的凝固组织与力学性能的影响.结果表明:随着Al含量的增加,TiAl合金晶粒尺寸呈增加趋势;当Al含量为45.7%时,凝固过程中局部区域发生包晶转变,使晶粒尺寸显著增大;室温及700℃高温拉伸强度随着Al含量的增加而呈增加的趋势,但发生包晶转变致使室温及700℃高温拉伸强度下降约200MPa;Al含量对延伸率不敏感,持久性能随Al含量的增加呈增加趋势.为控制铸锭凝固后的组织与力学性能,尽量避开包晶转变区,合金中Al含量应低于45.7%.     

Evolution of microstructure and crystallographic texture during recrystallisation of high-strength sheet steel

Ultra-low carbon steels possess an attractive combination of mechanical properties namely drawability and strength that is suitable for automotive applications. A high-strength variant of the material containing large amounts of manganese and phosphorous has been produced in the laboratory. The main objective of the present work was to study the microstructural evolution after recrystallisation, below and above the critical phase transformation temperatures of the steel. Crystallographic texture of ferrite was found to intensify with increasing the annealing temperature; surprisingly even beyond the upper transformation temperature. The texture measurement data obtained with the electron backscatter diffraction and X-ray diffraction matched very well with each other. The steel recorded an impressive strength–drawability balance mainly due to solid solution strengthening and favourable γ-fibre texture.     

热处理工艺对高强高导铜合金组织级性能的影响

本研究利用多道次等径角挤压工艺制备了超细晶Cu-Cr-Zr合金棒,在450 ℃人工时效4h后,获得最佳综合性能:抗拉强度610 MPa,断裂延伸率12.5%,硬度199 HV,电导率77%IACS。通过EBSD技术和TEM分析,揭示了该工艺条件下合金主要的强化机制:超细晶组织贡献了260.6 MPa,析出相强化贡献了149 MPa,加工硬化效果为163.9 MPa。相比于等径角挤压试样,析出相取代了固溶原子,强化效果显著提高;而位错密度降低,加工硬化效果显著降低。     

Effect of high temperature annealing on texture and microstructure on an AISI-444 ferritic stainless steel

AISI 444 is a Mo-alloyed ferritic stainless steel which presents good naphthenic corrosion resistance, making it attractive for applications in petroleum refining plants; however, good formability is also important. To achieve good formability with this alloy the annealing process is crucial. The annealing temperature in ferritic stainless steel is usually around 850 °C, which falls in the range of sigma phase precipitation. A means to avoid this precipitation is to anneal at temperatures around 1000 °C followed by rapid cooling. Annealing at high temperatures can cause grain growth and carbide or nitride precipitation which can result in a reduction of room temperature toughness. In this paper, the rolling and recrystallization textures of AISI 444 steel were studied in samples cold rolled with different thickness reductions (30%, 60%, 80% and 90%) followed by annealing at 955, 980 and 1010 °C. Aspects of grain size and carbide precipitation after annealing were characterized using EBSD and AFM. The material drawability was analyzed through strain rate or Lankford (r) coefficients calculated from texture results.     

Influence of P on hot ductility of high C,Al, and Nb containing steels

Abstract

Hot ductility curves for high carbon Nb and Nb free steels have been determined immediately after casting at two P levels, ~0.01% and ~0.045%. High strain rates of 0.1-0.55 s^-1 were generally used but some limited low strain rate testing at 7 × 10^-3 s ^-1 was carried out on Nb containing steels. Nb containing steels showed, as expected, worse ductility than the Nb free steel but high P level was detrimental to ductility for both steels and ductility in general was very poor. Failure was intergranular with the presence of films of a P rich phase at the boundaries in the case of the Nb free steels and in addition to this, in Nb containing steel there was a Nb rich phase. The films were thicker and more continuous in the higher P steels. It is suggested that the P rich films are probably the low melting point phase Fe₃P or Fe₃(Mn)P, which can remain liquid down to temperatures as low as 950°C. Some back diffusion of P into the grain interior is possible if the strain rate is reduced and/or at high testing temperatures during the 5 min hold prior to testing. This allowed some improvement in ductility to occur in the lower P containing steels by reducing the amount of the low melting point phase at the boundaries.     

Evolution and stability of texture during thermomechanical processing of Ti-24Al-11Nb alloy

The evolution of basal texture during thermomechanical processing of Ti-24Al-11Nb alloy has been studied as a function of different processing variables like hot rolling temperature, amount of deformation, cooling conditions etc. The stability of the deformation texture during post-rolling annealing and during theα ₂→β→α ₂ phase transformation cycle was also investigated. Unrestricted rolling of primaryα ₂ to maximum thickness reduction at the lowest rolling temperature has been found to be most favourable for obtaining a good basal texture. Texture of transformed (secondary)α ₂ is generally non basal when the transformation takes place from deformedβ. Rolling texture does not seem to change during annealing leading to recrystallization. Theα ₂→β→α ₂ phase transformation cycle does not change the starting basal texture and a starting non basal texture also does not give rise to basal texture due to this treatment.     

Si和Nb对高强热轧高扩孔钢组织和性能的影响

为了研究Si和Nb对高强热轧高扩孔钢板显微组织、力学性能和扩孔性能的影响,在CSP连轧线上进行了3种成分试验钢的热轧试制,并对试验钢在扩孔过程中裂纹的形成和扩展行为进行了分析.研究表明:3种成分热轧钢板的显微组织均由铁素体和贝氏体组成,钢板的抗拉强度均高于610 MPa,伸长率大于24.5%,扩孔率高于104%;Si含量的增加,提高了组织中铁素体的含量,钢板的强度、伸长率和扩孔率得到提高;Nb含量的增加,细化了钢板的组织,钢板的强度和扩孔率增加明显,伸长率变化不大;试验钢在扩孔过程中裂纹主要沿铁素体和贝氏体的晶界处扩展,部分裂纹穿过铁素体晶粒.