高氮钒微合金钢中终轧温度和锰的综合作用

通过对高锰高终轧温度钢和低锰低终轧温度钢的力学性能测试、并观察其组织及其碳氮化物的析出,研究了Mn和终轧温度在高氮钒微合金钢中的综合作用.结果表明： 高锰含量可以弥补高的终轧温度对组织的不利影响,而高的终轧温度可以弥补高的锰含量对析出的不利作用;提高锰含量同时提高终轧温度比降低锰含量同时降低终轧温度有利于组织细化和析出.     

谈微合金化钢的控轧控冷技术

通过查阅大量参考文献,主要综述了控轧控冷技术的原理、特点及控制要素,并分析了控轧控冷对微合金钢的组织与性能的影响。     

精轧入口温度对Nb-V-Ti微合金钢组织的影响

在Gleeble-3800热模拟试验机上模拟了Nb-V-Ti微合金钢不同精轧入口温度的轧制和卷取过程,并观察了最终试样的显微组织。同时进行了多道次变形的模拟试验,通过平均流变应力分析了不同应变量下的未再结晶温度。结果表明,当精轧入口温度在未再结晶温度以上时,针状铁素体和多边形铁素体相对粗大;精轧入口温度在未再结晶温度以下时,随着精轧入口温度的降低,针状铁素体和多边形铁素体均逐渐细化。     

Effects of Rare Earth on Behavior of Precipitation and Properties in Microalloyed Steels

The influence of rare earths on the behavior of precipitation of 14MnNb,X60 and 10Mn V steels was studied by STEM, XRD, ICP and thermal simulation method. The main carbonitride precipitates are Nb(C, N), (Nb, Ti) (C, N) and V(C, N). In austenite RE delays the beginning of precipitation, and decreases the rate of precipitation. In ferrite RE promotes precipitation and increases the amount of equilibrium carbonitride precipitation. RE can make precipitates fine,globular and dispersed in the microalloyed steels. With the increase of the amount of RE in steel, the amount of precipitation increases. The promotion effect is weakened with excessive RE. RE has only little influence on the strength of microalloyed steel, but it can improve impact toughness effectively.     

Effect of Finishing Rolling Temperature on Microstructure and Mechanical Properties of Microalloyed TRIP Steels

Different samples of TRIP (transformation induced plasticity) steel obtained by two different hot-rolling schedules are investigated by using a SEM (scanning electron microscope). The microstructure is characterized by using an OM (optical microscope) for phase distribution and by EBSD (electron backscatter diffraction) for texture and phase mapping. ODF (orientation distribution function) graphs are used to investigate the effect of recrystallization behavior of the hot-deformed austenite on phase transformation during the controlled cooling process. The mechanical behavior is interpreted in terms of the strength of both hard and soft phases, in combination with the quantity, location and transformation kinetics of the mechanically induced martensite (TRIP effect). The results show that more austenite grains exist in the steels obtained at finishing rolling temperature (FRT) of 750 °C, which inherited the deformation structure after the hot-rolling process. The instantaneous n value (n_i) of those steels is kept high during a large range of strain before failure, while the tensile strength and total elongation of the steels with respect to the different finishing rolling temperatures do not show any significant differences.     

Thermomechanical Control of Microstructure and Precipitation in Vanadium Microalloyed Steel: Influence of Finish Rolling and Coiling Temperatures

Six hot compression tests are conducted using the Gleeble3500 thermomechanical simulator to investigate the microstructural evolution and precipitation behavior in low-C–Mn V-microalloyed steel. The specimens are subjected to hot isothermal compression deformation of 87%. The optical microscopy and transmission electron microscopy using carbon extraction replica method are used to characterize the microstructures and precipitation after the simulated thermomechanical controlled process and coiling. The results indicate that increasing the finish rolling temperature benefits the refinement of ferrite grains but has little influence on the refinement of the precipitates. It is also observed that lower coiling temperatures (CTs) promote the formation of fine precipitates. When the CT is 500 °C, the average precipitate size is found to be 86 nm. Furthermore, it is found that the CT significantly influences the nucleation sites of the precipitates inter alia, the matrix, interphase, grain boundaries, and dislocations. As expected, at higher CTs, nucleation is predominantly on the defects rather than the matrix.     

控轧控冷工艺条件下Nb—V钢碳氮化物的析出行为

本文通过热模拟实验和电子显微技术等方法,系统地研究了控轧控冷对铌钒钛复合微合金化低碳热轧钢板的铌、钒、钛碳氧化物的析出行为的影响,研究结果对开发高强度船体用钢板具有参考价值。通过研究表明,在奥氏体区和铁素体区都用Ni(C,N）析出,对Nb、V的析出起了诱导作用,并与Nb、V形成复杂的碳氮化物。在铁素体中主要以基体均匀沉淀析出和位错沉淀析出。     

一种Nb-Ti微合金钢微合金碳氮化物析出行为的研究

利用热模拟和TEM技术研究了Nb—Ti微合金钢中微合金碳氮化物的析出行为,研究结果表明,高温奥氏体区析出的微合金碳氮化物数量随变形量的增大而增加,尺寸随着变形温度的升高稍有增大。铁素体区析出的微合金碳氮化物尺寸比在形变奥氏体中析出的更为细小,数量随着保温时间的增加而增多,但尺寸变化不大;当温度较低的时候,微合金碳氮化物主要在位错线等晶内缺陷处析出。     

Effects of Rolling and Cooling Conditions on Microstructure and Tensile and Charpy Impact Properties of Ultra-Low-Carbon High-Strength Bainitic Steels

Six ultra-low-carbon high-strength bainitic steel plates were fabricated by controlling rolling and cooling conditions, and effects of bainitic microstructure on tensile and Charpy impact properties were investigated. The microstructural evolution was more critically affected by start cooling temperature and cooling rate than by finish rolling temperature. Bainitic microstructures such as granular bainites (GBs) and bainitic ferrites (BFs) were well developed as the start cooling temperature decreased or the cooling rate increased. When the steels cooled from 973 K or 873 K (700 °C or 600 °C) were compared under the same cooling rate of 10 K/s (10 °C/s), the steels cooled from 973 K (700 °C) consisted mainly of coarse GBs, while the steels cooled from 873 K (600 °C) contained a considerable amount of BFs having high strength, thereby resulting in the higher strength but the lower ductility and upper shelf energy (USE). When the steels cooled from 673 K (400 °C) at a cooling rate of 10 K/s (10 °C/s) or 0.1 K/s (0.1 °C/s) were compared under the same start cooling temperature of 873 K (600 °C), the fast cooled specimens were composed mainly of coarse GBs or BFs, while the slowly cooled specimens were composed mainly of acicular ferrites (AFs). Since AFs had small effective grain size and contained secondary phases finely distributed at grain boundaries, the slowly cooled specimens had a good combination of strength, ductility, and USE, together with very low energy transition temperature (ETT).     

The Influence of Hot Charging Conditions on Microstructure and Precipitation of High Strength Nb–Ti Complex Microalloyed Steels

A comprehensive microstructure analyses were conducted for hot charging processed Nb, Ti microalloyed steel, especially focusing on the evolution of microstructure and precipitation behavior. Hot charging process was simulated in the laboratory in the current research. Precipitation and microstructure in Ti–Nb microalloyed HSLA steels were investigated in different hot charging temperature conditions using transmission electron microscope (TEM), optical microscopy, analytical transmission electron microscopy, and energy dispersive spectroscopy (EDS). The results showed that the microstructure consists of fine and homogeneous lath bainite at 1000°C, lath bainite and granular bainite at 900°C. As the hot charging temperature decreased, there appeared a small fraction of proeutectoid ferrite along grain boundary at 800°C. The grain sizes in hot charging are coarse compared with that of 700°C due to the phase transformation didn't occur. The chemical composition of complex carbonitrides changes from Ti rich to Ti–Nb uniform with decreasing temperature.     

Crystallographic Reconstruction Study of the Effects of Finish Rolling Temperature on the Variant Selection During Bainite Transformation in C-Mn High-Strength Steels

The effect of finish rolling temperature on the austenite-(γ) to-bainite (α) phase transformation is quantitatively investigated in high-strength C-Mn steels using an alternative crystallographic γ reconstruction procedure, which can be directly applied to experimental electron backscatter diffraction mappings. In particular, the current study aims to clarify the respective contributions of the γ conditioning during the hot rolling and the variant selection during the phase transformation to the inherited texture. The results confirm that the sample finish rolled at the lowest temperature [1102 K (829 °C)] exhibits the sharpest transformation texture. It is shown that this sharp texture is exclusively due to a strong variant selection from parent brass {110} \( \left\langle {1\bar{1}2} \right\rangle \) , S {213} \( \left\langle {\bar{3}\bar{6}4} \right\rangle \) and Goss {110}〈001〉 grains, whereas the variant selection from the copper {112} \( \left\langle {\bar{1}\bar{1}1} \right\rangle \) grains is insensitive to the finish rolling temperature. In addition, a statistical variant selection analysis proves that the habit planes of the selected variants do not systematically correspond to the predicted active γ slip planes using the Taylor model. In contrast, a correlation between the Bain group to which the selected variants belong and the finish rolling temperature is clearly revealed, regardless of the parent orientation. These results are discussed in terms of polygranular accommodation mechanisms, especially in view of the observed development in the hot-rolled samples of high-angle grain boundaries with misorientation axes between 〈111〉γ and 〈110〉γ.     

钒微合金钢在薄板坯连铸连轧工艺过程中微观组织的演变

利用光学显微镜、透射电镜(TEM)和X射线能量散射仪(EDAX),对V-N和V-Ti-N两种低碳微合金钢在薄板坯连铸连轧工艺中微观组织的演变进行了检验.在5道次轧制过程中的第4道次轧制后,V-N钢的晶粒尺寸由原始粗大的晶粒(≈1mm)减小到约50μm,V-Ti-N钢减小到22μm.V-Ti-N钢最终平均铁素体晶粒尺寸为4.8～6.6μm,略小于V-N钢的晶粒尺寸(5.3～7.2μm).V-N钢仅在1050℃均热之后观察到了VN第二相,而在1200℃和1100℃均热后没有发现VN存在.V-Ti-N钢在浇铸和均热期间(1200℃、1100℃和1050℃),V-Ti-N颗粒已经形成.而V-N钢仅在1050℃均热期间才析出AlN颗粒,并与MnS或MnS和VN复合析出有关.在V-Ti-N钢中没有检测到AlN.在两种钢的最终产品中均发现了含V的细小析出物(小于10nm),但在V-Ti-N钢中出现的频率比V-N钢低,最终板材中的细小析出物对弥散强化起主要作用,可以获得良好韧性、良好延展性的高强度性能(LYS≈460～560MPa),与常规控制轧制生产的类似产品相比,具有一定的竞争性.但V-N钢中加入Ti后,降低了屈服强度,这是由于奥氏体中形成了V-Ti(N)颗粒,减少了可在铁素体中形成富V细小析出物的V、N量的结果.     

Effects of Nitrogen Content and Austenitization Temperature on Precipitation in Niobium Micro-alloyed Steels

The influences of nitrogen content and austenitization temperature on Nb(C,N)precipitation in niobium micro-alloyed steels were studied by different methods:optical microscopy,tensile tests,scanning electron microscopy,transmission electron microscopy,physicochemical phase analysis,and small-angle X-ray scattering.The results show that the strength of the steel with high nitrogen content is slightly higher than that of the steel with low nitrogen content.The increase in the nitrogen content does not result in the increase in the amount of Nb(C,N)precipitates,which mainly depends on the niobium content in the steel.The mass fraction of small-sized Nb(C,N)precipitates(1-10nm)in the steel with high nitrogen content is less than that in the steel with low nitrogen content.After austenitized at 1 150 ℃,a number of large cuboidal and needle-shaped particles are detected in the steel with high nitrogen content,whereas they dissolve after austenitized at 1 200 ℃ and the Nb(C,N)precipitates become finer in both steels.Furthermore,the results also show that part of the nitrogen in steel involves the formation of alloyed cementite.     

终轧温度对低合金铌钛贝氏体钢组织和性能的影响

 采用光学显微镜、透射电子显微镜（TEM）、EDS能谱分析仪和拉伸冲击试验机,研究了终轧温度对TMCP(thermo-mechanical controlled processing)低合金铌钛贝氏体钢组织和性能的影响。结果表明：随着终轧温度的降低,强度和韧性先升高后降低。终轧温度为815 ℃时,由于冷却前温度已降低到奥氏体-铁素体两相区,在晶界形成大量先共析铁素体,造成了强度和韧性的下降。终轧温度为870 ℃时,得到细小的板条贝氏体＋少量的马氏体组织,在贝氏体板条上有30～50 nm的Nb、Ti析出相弥散分布,获得了最优异的性能,其屈服强度为805 MPa,抗拉强度为1 005 MPa,－20 ℃冲击功的平均值为197 J。     

热轧温度参数对Nb-Ti和Nb-V微合金钢力学性能的影响

 设计了650 MPa级的Nb Ti和Nb V微合金钢的化学成分。采用正交实验方法考察了加热温度、终轧温度和终冷温度对这2种钢力学性能的影响。实验结果表明,加热温度和终冷温度是影响Nb Ti和Nb V钢力学性能的主要因素。2种钢的伸长率与屈服强度以及屈强比与屈服强度之间都具有明显的相关关系。     

Improvement of Grain Size and Dome Height of Microalloyed Steels Using Taguchi Method Based on Grey Relational Grade in Controlled Rolling

An efficient approach was introduced for improving the condition of major controlled rolling process parameters of roughing, finishing and coiling temperatures and optimizing these parameters to obtain minimum grain size and maximum dome height simultaneously. Taguchi method combined with grey relational analysis was applied to achieve optimum grain size and dome height during controlled rolling process. For this purpose, four levels for the above temperatures were chosen and sixteen experiments were conducted based on orthogonal array of Taguchi method. Based on Taguchi approach, signal-to-noise (S/N) ratios were calculated and used in order to obtain the optimum levels for every input parameter. Analysis of variance revealed that finishing and coiling temperatures have the maximum effect on the grain size and dome height of microalloyed steels. The confirmation tests with the optimal levels of parameters indicated that the grain size and dome height of controlled rolled microalloyed steels can be improved effectively through this approach.     

20MnSi钢筋热连轧及轧后分级控冷过程温度变化模拟

 建立温度计算模型针对22 mm和28 mm规格20MnSi棒材热连轧及控制冷却过程温度场进行了计算机模拟分析,获得了棒材精轧及轧后分级控冷过程的温度变化规律。对轧制圆钢和螺纹钢筋不同条件下成品道次温度变化特点进行了研究。研究结果是,轧制22 mm和28 mm规格20MnSi螺纹钢筋时的终轧温度比轧制相同规格圆钢时显著升高。轧制螺纹钢筋时精轧末道次轧材表层形成螺纹出现较大的局部应变量和应变速率,由此产生大量变形热是终轧钢筋表层急速升温的根本原因。与轧制圆钢相比,为完成同等控冷效果及有效控制轧后组织性能,20MnSi螺纹钢筋精轧后第1水冷段的换热系数明显较高,因此需要相应采用较大的冷却水量。     

Modeling of Strain-Induced Precipitation Kinetics and Evolution of Austenite Grains in Nb Microalloyed Steels

Considering the effect of strain and chemical composition onprecipitation behavior, new models for the start and end time of Nb（C,N） precipitation in austenite under the conditions of different temperatures and strains have been investigated for Nb microalloyed steel. The value of n in the precipitation kinetic equation has been determined by using the available experimental data in literature, which indicated that n is a constant and independent of temperature. The values of the start and end time of the predicted precipitation are compared with the experimental values. Calculated results are in good agreement with the experimental results. Also, the evolution of austenite grains before ferrite transformation is simulated by taking the effect of precipitation into consideration. The measured austenite grain size is in good agreement with predicted one prior to ferrite transformation.