Nb-Ti微合金钢碳氮化物的析出热力学模型及分析

以规则溶液亚点阵模型为基础,针对Fe-Nb-Ti-C-N系统,进行了热力学平衡计算。计算结果表明,高温阶段的析出相为TiN,微细的TiN强烈地抑制奥氏体晶粒长大;低温阶段的析出相以碳化物(NbTi)C为主,NbC和TiC是抑制奥氏体再结晶及再结晶后晶粒长大的主要因素。析出相形成元素Ti的增加引起其形核化学驱动力增大,并加快析出的动力学过程。     

控轧控冷时Nb-V微合金钢中碳氮化物的析出行为

研究了Ｎｂ（ＣＮ）,Ｖ（ＣＮ）在控轧控冷不同阶段的析出行为,探讨了各阶段析出物在钢中的作用。结果表明,轧后冷却制度对碳氮化物的析出有较大影响。     

Nb-Ti微合金钢中第二相析出的热力学计算

分析了Nb-Ti微合金钢在液相、凝固过程、奥氏体以及铁素体相中氮化物、碳化物和碳氮化物等第二相析出的热力学条件,计算了钛和铌的碳化物和氮化物在不同温度下的溶度积,由此得出微合金钢在不同相阶段的析出规律。计算结果表明,在该微合金钢中,氮化物、碳化物和碳氮化物不可能在液相中析出;TiC0.03N0.97和TiN在凝固过程中具备析出的热力学条件;在奥氏体相中,随着温度的降低,氮化物、碳化物及碳氮化物的析出顺序为:NbC0.75N0.25、NbC、TiC、NbN。     

Nb-Ti微合金钢热变形后组织演变及第二相粒子析出行为

利用GLEEBLE-2000对试验钢进行热模拟试验,并结合显微硬度测试,研究了一种Nb-Ti微合金钢热变形奥氏体的变形后冷却相变行为.利用JEM-2000FX电镜对碳膜萃取复型法获取的第二相析出物进行分析,从而对热变形后冷却相变中的第二相析出行为进行了研究,探讨了不同冷却速度对第二相析出的影响,结果表明,有大量弥散分布的细小粒子析出,析出相主要以Nb-Ti碳氮化物复合相形式存在,一般呈方形、椭圆形、圆形以及不规则形状,并且随着冷却速度的增加,第二相析出增多且变得细小.     

Nb-Ti微合金钢中的奥氏体晶粒长大行为研究

Nb、Ti是管线钢中常用的合金元素。主要通过热处理和喷碳处理等手段研究了合金元素Nb、Ti的含量及加热制度对再加热奥氏体晶粒长大的影响。试验结果表明:试验钢在再加热过程中,奥氏体晶粒尺寸随加热温度升高而增大;在常规含铌钢中,为获得较小的加热态奥氏体晶粒,钛的质量分数应控制在一定范围内(0.010%~0.015%),钛含量过高或过低都对晶粒细化有不利影响。此外,在钛含量相同的情况下,高铌钢奥氏体晶粒长大明显,高铌钢的最佳钛含量范围也与常规含铌钢的最佳钛含量不同。     

微合金管线钢的碳氮化物高温溶解与析出

结合无缝管线钢的生产实践,根据固溶度积公式和理想化学配比计算出各种微合金的全固溶温度.在连铸过程中,Nb、Ti、Al的析出将降低连铸坯的高温热塑性;在穿孔和连轧过程中,固溶的Ti、Nb、Al的碳氮化物将有效地阻止形变奥氏体再结晶,并诱导析出(Ti,Nb)(C,N);在定径终轧期间及终轧结束后,随着钢中N含量的增加,V的沉淀强化作用增强.     

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。     

Nb-Ti微合金钢力学性能的预报模型

根据Nb Ti高强度低合金钢 (0 0 8%～ 0 11%C ,0 0 1%～ 0 0 4 %Nb ,0 0 1%～ 0 2 3%Ti)板材实际生产数据 ,采用多元逐步线性回归 ,得出钢板屈服强度σs(MPa)和抗拉强度σb(MPa)的数学模型 :σs=2 94 0 1Wc+74 7 89WNb+10 2 1 0 9WTi- 0 17Tc+5 95 99;σb=135 6 73WNb+136 1 39WTi- 0 0 1b - 1 6 9h +44 2 4 3(Wc,WNb,WTi为成分质量分数 / % ;Tc 为卷取温度 ;b为成品板宽 ;h为成品板厚 )。同时建立了BP神经网络预报模型 ,两种模型均具有较好的预报精度 ,神经网络预测值与实测值之间的相对误差小于± 10 %。     

碳氮化物析出模型在Nb微合金船板钢连铸工艺中的应用

针对含铌微合金钢(D36船板钢,%:0.12～0.16C、0.25～0.45Si、1.25～1.45Mn、≤0.020P、≤0.010S、0.015～0.040Als、0.015～0.025Nb、≤0.009 0N)连铸过程裂纹敏感性大的问题,建立了Nb(C,N)和A1N在奥氏体中的析出模型,以分析板坯在850～1150℃矫直时Nb(C,N)和AlN析出对铸坯热塑性的影响。结果表明,含铌微合金钢中碳氮化物的析出方式主要是晶界和位错线形核,在950℃时Nb(C,N)的综合析出速度和AlN在晶界上的析出速度最大。因此,含铌微合金钢的矫直温度应大于950℃。     

Two-Sublattice Thermodynamic Model on Carbonitride Precipitation in Microalloyed Steels Bearing Nb-V-Ti

Based on the two sublattice model of the regular solution,one being metal atom sublattice and another being interstitial atom sublattice,a thermodynamic model for the precipitates of niobium carbonitride,vanadium carbonitride and titanium carbonitride was established to study the starting-temperature of precipitates and the austenite compositions at given temperature in a low carbon steel.The calculation results show that starting-temperature of the precipitation of niobium carbonitride,vanadium carbonitride and titanium carbonitride are 1100℃,920℃ and 1340℃,respectively,the mole fraction of carbonitride precipitates is 8.65×10-4 in the 0.053C-0.0028N-1.28Mn-0.008S-0.031Al-0.046Nb-0.008Ti0.029V-Fe steel.When the N content is from 0.0028% to 0.0056%,the starting-temperature of the precipitation of the titanium carbonitride changes from 1340℃ to 1430℃.And the C content is from 0.053% to 0.07%,the startingtemperature of the precipitation of the titanium carbonitride hardly changes,but the atomic fraction of niobium in the carbonitride obviously increases.     

中碳铌微合金钢的应变诱导析出行为

通过应力松弛法验证了修正后的DS析出模型,得到了中碳铌微合金钢的应变诱导析出规律,结果表明:修改后的DS模型由于考虑了Si、Mn元素对碳氮化物应变诱导析出的影响,得到的PTT曲线与试验测得的曲线基本吻合,可用于Si、Mn含量较高的铌微合金钢应变诱导析出行为的预测;对于本试验用钢,PTT曲线具有典型的C型特征,鼻子温度在900℃左右,并且,随着应变速率的增大,PTT曲线左移,析出孕育期缩短。     

连铸过程铌钛微合金钢中第二相复合析出模型

针对连铸过程铌钛微合金钢中第二相在固液两相区和奥氏体内的复合析出行为,通过近似处理建立了多元第二相复合析出的热力学模型,并利用模型研究了X80,E36,J55钢中第二相的析出行为。结果表明:在凝固过程不同的Ti/N摩尔比对液相中Ti,C,N元素的变化影响显著,先析出的第二相对后析出的第二相影响显著,成分高低的差异不但导致第二相析出量的不同,而且也导致析出相种类的不同,碳氮化物在析出的过程中C,N元素摩尔分数的变化受析出温度和钢中元素含量的影响。     

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.     

Numerical Analysis of the Nb(C,N) Precipitation Kinetics in Microalloyed Steels

Precipitation kinetics of Nb(C,N) in microalloyed steels is crucial for the achievement of favoured steel properties. Therefore, numerous experimental studies have been performed in the past and various theoretical models have been developed to describe Nb(C,N) precipitation. However, the experimental data is sometimes contradictory and even the thermodynamic data for NbC solubility in austenite have a large scatter. In this paper, experimental results on the Nb(C,N) and NbV(C,N) precipitation kinetics in deformed and undeformed austenite are reviewed. Based on these data and with the precipitation kinetics module of the software package MatCalc, computer simulations are performed. The predicted interfacial energy of precipitates is adjusted to match the observed kinetics. A comparison between experimental information and simulation, i.e. time ‐ temperature ‐ precipitation (TTP) diagrams, is drawn and discussed. The results of the computer simulations using modified interfacial energies are in good agreement with the experiments.     

Influence of cooling rates on the precipitation behavior and microstructure of Nb-Ti microalloyed steel

Influence of different cooling rates on the microstructure and the precipitation behavior of Nb-Ti microalloyed steel was investigated by CSLM,OM,SEM and EDS. The results show that the precipitation process of carbonitrides can be in-situ observed by CSLM,and with the increase of the cooling rate,the distribution of precipitates changes from along the austenitic grain boundaries to within the grains. With the increase of the cooling rate,the proeutectoid ferritic film becomes smaller and smaller and then disappears,and the original austenitic grains become finer and finer. In order to obtain non-film like proeutectoid ferrites or non-chain like precipitates along the austenitic grain boundaries and finer austenitic grains,the cooling rate should be at least 5℃/s.     

Influence of Finishing Cooling Temperature and Holding Time on Nanometer-size Carbide of Nb-Ti Microalloyed Steel

The nanometer-size carbides formed in ferrite matrix of Nb-Ti microalloyed steel at different finishing cooling temperatures and holding time have been investigated.The characteristics of nanometer-size carbides in ferrite were observed by transmission electron microscopy,and mechanical properties of ferrite were detected by a nanohardness tester.The results showed that interphase precipitation and diffusion precipitation were observed at different finishing cooling temperatures,and the interphase precipitation was planar and curved.Sheet spacing of interphase precipitation increased with the increase of finishing cooling temperature and changed a little when holding for 50-1 000s.Interphase precipitation shows higher nano-hardness at 640℃ compared with diffusion precipitation at 600℃,and the contribution of interphase precipitation to the mechanical properties of ferrite was larger than that of diffusion precipitation.