底吹氮气V-N微合金化研究

鉴于传统微合金化工艺所用钒氮合金具有成本高、能耗高、制备周期长等不足,提出了采用添加钒铁+底吹氮气的方式实现钢液快速增氮,从而达到V-N微合金化的目的。通过对不同底吹参数钢中氮含量的分析、珠光体组织表征和晶粒度评级、析出相诱导晶内铁素体形核机制分析,明确了在含钒钢液中底吹氮气可以实现快速增氮,氮含量随底吹时间的增加而提高,且氮含量越高越有利于晶粒细化、促进钢中V(C,N)的析出并使其分布更加弥散,证明添加钒铁+底吹氮气进行V-N微合金化是可行的。     

低碳铌钒微合金化铸钢的研究

文中叙及的是一种低碳铌钒微合金化铸钢的研究,主要说明的是热处理工艺;稀土一硅钙变质处理;钢的组织对钢的性能的影响.结果表明,该钢的优点是具有高强韧性及良好的焊接性能,因而很有应用潜力.     

HRB500E微合金化钢筋中钒的化合物析出行为

分析了HRB500E微合金化高强度钢筋中钒的氮化物、碳化物和碳氮化物分别在液相、凝固过程、奥氏体以及铁素体相中的析出热力学条件,并研究了它们在实验钢连铸或热处理过程中的析出规律。结果表明：实验钢中,钒的碳化物和氮化物在钢液中不析出。碳氮化钒(VC_xN_1-x)中的x值随温度降低而增大,即在高温平衡条件下析出富氮的碳氮化物,在全固溶温度1450 K下析出物为VC_0.03N_0.97。VN在1176～1448 K温度区间内在奥氏体相中析出,温度低于1176 K时,主要析出物为碳化钒或碳氮化钒。实验钢铁素体相中也观察到有钒的化合物析出,呈椭圆形,析出规律与热力学分析结果基本吻合。     

钒微合金化钢的热塑性探讨

利用 Gleeble-3800对钒微合金化钢的高温塑性进行了测定,并通过扫描电镜对不同温度下试验钢拉断后的断口形貌进行了观察分析。结果表明：随着温度降低,热塑性降低,断面收缩率降低,奥氏体化温度以上拉伸时,断口以深韧窝为主,部分韧窝底部分布着第二相粒子;但铁素体相变温度以下拉伸时,断口呈现沿晶断裂特征,断裂面上分布着浅而小的韧窝,降低了材料的热塑性;随着温度的升高,断面收缩率不断增加,试验钢在 850℃及其以上温度拉伸时的断面收缩率均大于 60%,在连铸坯生产时矫直温度不低于 850℃能够有效减少铸坯表面裂纹发生率,因此,在连铸坯生产时适宜的矫直温度应该不低于 850℃。     

中碳铌微合金化钢NbC的析出控制

对开坯+连轧生产出的大规格铌微合金化中碳圆钢的轧后NbC形态进行了研究分析。研究发现,中碳钢铌的质量分数为0.03%时,连铸凝固过程中会析出5 μm以上的碳化铌;钢坯轧制加热温度为1 250 ℃左右,高温段保温时间为4 h以上时,微米级碳化铌得到固溶。     

钒微合金化HRB400抗震钢筋的研制

介绍了承钢利用特有的钒资源优势研制生产抗震钢筋的过程。该钢筋按规格大小采用了不同的化学成分及加钒方法 ,并采用了合理的生产工艺参数 ,其研制成果在工业试验和工程应用中取得较好效果     

钒氮微合金化高强耐候钢开发研究

进行了450、550 MPa高强耐候钢的成分设计和冶炼,通过热膨胀试验并结合金相组织,分析了该高强度耐候钢的相变规律.利用光学显微镜、扫描电镜、透射电镜以及拉伸试验对该试验钢的组织结构、第二相粒子的析出行为以及力学性能进行了研究,分析了钒氮微合金化对高强耐候钢析出强化和细晶强化的作用.结果表明:在钒钢中添加氮元素不但增强了析出强化效果,而且还能细化晶粒,提高耐候钢的综合力学性能.     

钒氮微合金化高强度钢的研究及应用

根据国内外钒氮合金微合金化技术的发展状况,综述了钒氮微合金化的优越性和在高强度钢中的强化机制,并概述了钒氮微合金化在高强度钢中的研究开发和应用状况。     

钒微合金化对TRIP钢组织和性能的影响

采用CCT-AY-Ⅱ型钢板连续退火机模拟分析了V元素添加对TRIP800钢组织性能的影响规律。采用SEM和TEM等微观分析方法观察含钒与不含钒TRIP的微观组织,利用XRD法测量了残留奥氏体量,实验室测量了其力学性能。结果表明,随着退火温度的升高,试验钢铁素体相比例降低,贝氏体相比例升高,且含钒TRIP钢中有V(C,N)析出。820℃保温时,试验钢均获得最佳的综合力学性能。V元素的添加增加了试验TRIP钢的抗拉强度,而降低了屈服强度,有效降低了TRIP钢屈强比。且含V TRIP钢瞬时加工硬化指数前期大于无V TRIP钢,后期则小于无V TRIP钢。     

低碳微合金钢碳氮析出物的Thermo-calc热力学分析

利用Thermo-calc热力学软件TCFE3数据库研究Nb-Ti、V-Ti、Nb-V-Ti低碳微合金钢中析出物的析出开始温度、给定温度的奥氏体成分,计算得到Nb-Ti低碳微合金钢中Nb、Ti碳氮化物的开始形成温度分别为1090和1400℃,最大摩尔分数分别为7.1×10-4、2.4×10-4,V-Ti低碳微合金钢中V、Ti碳氮化物的开始形成温度分别为800和1395℃,最大摩尔分数为2.1×10-3,1.5×10-4,Nb-V-Ti低碳微合金钢中Nb-V碳氮化物和Ti碳氮化物的开始形成温度分别为1070和1390℃,其碳氮化物最大摩尔分数分别为1.2×10-3、1.8×10-4。热力学软件的计算结果与有关文献的实验数据有较好的一致性。     

低碳微合金钢中Nb、V、Ti碳氮化物的回溶研究

采用透射电镜和X射线光谱技术,研究了低碳微合金钢中Nb、V、Ti的碳氮化物在不同温度保温1 h后的回溶行为.结果表明,低碳微合金钢中存在尺寸明显不同的两类析出,其中颗粒尺寸较大的在80 nm以上;这种颗粒的心部是(Nb,V,Ti)(C,N)相,而颗粒边缘为(Nb,Ti)(C,N)相;颗粒尺寸较小的在20 nm以下,其类型为(Nb,Ti)(C,N).两类析出物中Nb与Ti的原子比均随回溶温度的升高而减小.     

微合金化钢的动态再结晶及其显微组织的研究

应用Ｇｌｅｅｂｌｅ－１５００热模拟试验机测定了合金化钢在不轧温度下的真应力－真应变曲线,研究了终轧温度及微合金元素含量对动态再结晶的影响。研究结果表明,Ｖ、Ｎｂ可显著抑制微合金化钢轧制过程中形变奥氏体的动态再结晶,因此,在较高的终轧温度下,仍能得到细小而均匀的显微组织。     

Modeling of Work Hardening During Hot Rolling of Vanadium and Niobium Microalloyed Steels in the Low Temperature Austenite Region

This work extends the application of the well-established Estrin and Mecking (EM) work-hardening model in unstable low temperature austenite region. The interaction between work hardening, recovery and softening attributed to recrystallization and transformation to ferrite under dynamic conditions is considered. Experimental parameters were varied to study the effects of strain, strain rate and temperature during hot rolling in the low temperature austenite region. Hot compression tests were performed two microalloyed steels—one containing V and the other Nb—at strain rates between 0.1 and 10 s^?1 over a temperature range of 750-1000 °C. A model is presented that describes the influence of dynamic recovery on flow behavior in the unstable austenite region. The modified work-hardening model incorporates an additional fitting parameter to the EM model and is dependent on the recovery and softening rates. The new model improved prediction in the unstable austenite region, while the original EM model gave better correlation at relatively higher temperatures when dynamic recrystallization is dominant or at relatively lower temperatures when only dynamic recrystallization to ferrite was the softening mechanism.     

Effects of Roughing on Finish Rolling Simulations in Microalloyed Strip Steels

The effects of a roughing pass in hot rolling simulations were assessed in VN and Nb-Ti steels. Continuous cooling phase transformation temperatures, flow curves, softening mechanisms (dynamic transformation DT and dynamic recrystallization DRX), and deformed microstructure morphologies were analyzed. The application of one or more roughing passes eliminates the effects of prior microstructural history and ensures that all stock material experiences equivalent hot working conditions and state of the microalloying elements. It has been shown that roughing in hot simulation has the following positive influences: (1) provide more reliable flow stress data; (2) give greater consistencies and accuracy in analysis of softening mechanisms giving three distinct regimes (DT regime at temperatures below 800 °C, DT/DRX inter-mode regime between 800 and 950 °C and DRX regime for temperatures above 950 °C for VN steel); (3) promotion of softening mechanisms as evidence by low critical strains (\(\varepsilon_{{{\text{c}}\,{\text{DT}}}}\) was within the range 0.08-0.12, while for finishing-only pass, the \(\varepsilon_{{{\text{c}}\,{\text{DT}}}}\) was in the range of 0.11-0.14 at \(\dot{\varepsilon } = 0.1\) s^?1); (4) for roughing and finishing schedules, DT was verified to occur at temperatures 117 and 133 °C above \(Ae_{3}\) for VN steel and Nb-Ti steel, respectively, compared to the F-only schedules which showed that DT can only occur at temperatures below the \(Ae_{3}\); (5) RF schedules promoted uniform microstructural morphologies compared to inhomogeneous microstructures realized in F-only schedules.     

钒对中碳非调质钢疲劳性能的影响

采用旋转弯曲疲劳实验研究了含钒的38MnVS钢与不含钒的38MnS钢在热锻态和退火态下的疲劳行为.结果表明,V元素主要通过析出强化和组织细化改善铁素体 珠光体型非调质钢的疲劳性能.在热锻态,V(C,N)呈细小弥散分布,与铁素体间具有特定位向关系,具有明显的析出强化和细化组织作用.铁索体的强化使得疲劳裂纹萌生和扩展的抗力提高,因而38MnVS钢的疲劳性能明显优于38MnS钢;在退火态,V(C,N)质点长大,与铁素体间失去共格关系,不再具有明显的析出强化作用,因而退火态38MnVS钢的疲劳性能明显低于热锻态,而与38MnS钢的疲劳性能相当.     

Nb-Ti微合金化超低碳低合金高强度钢中第二相的析出行为

研究了Nb-Ti微合金化超低碳低合金高强钢在控轧控冷及回火过程中含Nb和Ti相的析出行为及其与硬度的关系.结果表明,Nb-Ti微合金化超低碳低合金高强钢在控轧控冷驰豫过程及随后的回火过程中均有第二相析出,在变形过程中Nb(CxNy)相析出颗粒更为细小,在回火过程中Nb(CxNy)依附于TiN形核长大,600 ℃回火2 h后其硬度高于其它温度回火后的硬度.     

微合金V-N钢轧制工艺与显微组织

研究了含碳量和轧制工艺对低碳微合金V-N钢显微组织和性能的影响。对含碳量分别为0．20％和0．11％，但含氮量相同的两种V-N钢进行了不同工艺的轧制；对轧后试样进行了拉伸试验、显微组织分析以及晶粒大小的测定。试验结果表明，V-N钢中碳含量及轧制形变量对组织和性能具有明显的影响，试验钢中碳含量的增加及轧制形变量的增大均可使晶粒相对细小、钢的强度相应提高。     

Solid Solubility in Laser Cladding

Laser cladding techniques have recently enjoyed attention in preparing in-situ novel surface clad alloys with extended solid solution. Mass transport involved in this process is rather intriguing since it plays the major role in producing new materials without being restricted by equilibrium phase diagram. Although earlier work has identified convection as the dominant factor for homogeneous liquid metal composition, very little is understood about the solute redistribution at the solid-liquid interface under such non-equilibrium conditions. In this paper, a mathematical model is presented for determining the composition of extended solid solution formed due to rapid cooling in laser cladding. This model considers a diffusion mechanism for mass transport in a one-dimensional semi-infinite molten pool of the cladding material from which heat is removed by conduction through a one-dimensional semi-infinite solid substrate. The rate of solidification was obtained by modeling the cooling process as a composite medium heat transfer problem, and the discontinuity of the concentration field was simulated using a nonequilibrium partition coefficient. A non-similar exact solution for the mass transport equation was obtained using a set of similarity variables derived using Lie group theory.