钒 钛微合金钢的析出特征

采用透射电子显微镜对碳萃取复型样进行了观测。碳萃取复型样由不同轧制条件下热轧成10mm棒材的两种商用钒微合金钢和一种商用钛微合金钢制备。 钒或钛微合金钢中的铜含量约为0.13％时,即使钢中的锰含量大于1％,首先会生成硫化铜,而不生成硫化锰。在钛微合金钢中,除生成硫化铜外,还观测到Ti_4C_2S_2型的球状碳硫化钛。 对钒微合金钢使用透射电子显微镜显示出,在先共析铁素体中有很细小的析出物(≈5nm),经鉴别为M(C,N)型(M=V和Cr,V/Cr≈5)碳化物或碳氮化物。此外,还观测到一些较粗的颗粒(≈0.1μm,V/Cr>15时),可能是温度较高时,在奥氏体中生成的氮化钒或碳氮化钒。 在钛微合金钢中观察到粗大的氮化钛颗粒(>5μm)以及很细小的(≈5nm,Ti/Cr≈9)MC型(M=Ti和Cr)析出物,或较粗大的(≈0.1μm,Ti/Cr>30)碳化物颗粒。     

钛微合金钢中碳氮化钛固溶量及化学组成的计算与分析

根据相关热力学理论,提出了钛微合金钢中钛、碳、氮元素在奥氏体中的平衡固溶量及平衡沉淀析出的碳氮化钛的化学式系数的理论计算方法,对典型化学成分的钛微合金钢进行了理论计算并对计算结果进行了分析.结果表明,通常情况下在较高温度析出或未溶的碳氮化钛相当接近于TiN.     

钒微合金钢的热塑性

低碳低氮微合金钢通常表现出抗横向开裂性能,而碳含量较高的微合金钢则不然。讨论了碳含量质量分数为0.05%~0.6%的含钒微合金钢的热塑性研究和工业经验。在不同碳含量的情况下,只要[V][N]乘积不超过1×10-3,添加的钒就能降低钢对横向开裂的敏感性。铌和钒的结合增加了800~900℃临界矫直温度范围内的热塑性,这一改善得益于钒和铌复合加入减缓了动态析出过程。在含钛钢中,最初在高温下生成的Ti N具有促进Ti Nb(C,N)沉淀粗化和降低对塑性不利的细小Nb V(C,N)沉淀体积分数的额外作用。还介绍了TWIP钢热塑性的最新结果以及含钒微合金钢连铸的工业经验。     

钒和铌-钒低碳微合金钢的静态再结晶行为

采用MMS-300热力模拟试验机研究了钒和铌-钒微合金钢的静态再结晶规律,绘制了试验钢的静态再结晶软化率曲线,计算出试验钢的静态再结晶激活能并建立了静态再结晶动力学模型,结合沉淀析出物的微观形貌观察,分析了铌对钒微合金钢静态再结晶行为的影响规律。结果表明,铌-钒钢的静态再结晶激活能要显著高于钒钢,在800~950℃变形保温60 s以上的试验条件下,铌-钒钢发生了形变诱导析出,细小的碳氮化物弥散分布在位错及晶界上,使得软化率曲线在此范围内出现"平台",说明铌既限制了静态再结晶的发生,又阻碍了软化行为的进行。     

微钛处理对钒微合金钢组织与力学性能的影响

在承钢1780热连轧生产线上,轧制了钒微合金钢及钒钛复合微合金化钢,研究了微钛处理对钒微合金化钢微观组织与力学性能的影响.试验结果表明,钒微合金钢经微钛处理后生成了少量TiN析出物,其数量较少,晶粒细化效果有限;由于钛与氮的优先结合,减少了与钒结合的氮含量,降低了钒的析出量,导致微钛处理的钒微合金钢抗拉强度降低约54 ...     

碳化钒、碳氮化钒生产工艺条件的实验室研究

在碳热还原钒氧化物(V_2O_5)反应体系平衡组成计算的基础上,进行了实验研究工作,确定了制取碳化钒(V_2C)的生产工艺条件.采用正交设计方法,研究了对碳化钒的渗氮过程,制定出碳氮化钒的生产工艺条件。     

钒微合金钢的工艺、显微组织和性能(上)

钒元素最早作为一个重要的钢的合金元素,源自于钒钢回火后所得到的性能。由于透射电子显微镜的分辨率达到了～1 nm,以及选区电子衍射技术的进步,提升了对钒钢显微组织进行研究的兴趣。第二项及时的技术进步是控制轧制,特别是板、带产品控轧技术的开发。本概述的内容将包括以下几方面的历史背景,即淬火回火钒钢,等温时效时、常规控轧时和薄板坯直接装炉时的析出,以及提高钒微合金钢强韧性的进展。介绍钒钢显微组织的特征,特别是析出物化学成分的分析方法及技术的进步,由于70年代X-光能谱分析的运用,电子能损失谱的运用使得钒微合金钢中碳和氮的定量分析得以实现。当今,关于钒钢还存在许多矛盾的课题。这些课题包括有:钒碳化物均匀析出物的形核次序,这类形核是否是共格形核,钒析出物的化学成分,相间析出的形核机制,奥氏体中钒的碳氮化物形变诱导析出的重要性,相间析出和铁素体中的无序析出对屈服强度的贡献,以及工艺过程参数对性能的影响。对这些课题进行讨论,并将结合其它合金的长期研究,集中讨论热轧钒微合金钢。     

钒微合金钢的工艺、显微组织和性能(下)

钒元素最早作为一个重要的钢的合金元素,源自于钒钢回火后所得到的性能。由于透射电子显微镜的分辨率达到了~1 nm,以及选区电子衍射技术的进步,提升了对钒钢显微组织进行研究的兴趣。第二项及时的技术进步是控制轧制,特别是板、带产品控轧技术的开发。本概述的内容包括以下几方面的历史背景,即淬火回火钒钢,等温时效时、常规控轧时和薄板坯直接装炉时的析出,以及提高钒微合金钢强韧性的进展。介绍钒钢显微组织的特征,特别是析出物化学成分的分析方法及技术的进步,由于20世纪70年代X-光能谱分析的运用,电子能损失谱的运用使得钒微合金钢中碳和氮的定量分析得以实现。当今,关于钒钢还存在许多矛盾的课题。这些课题包括:钒碳化物均匀析出物的形核次序,这类形核是否是共格形核,钒析出物的化学成分,相间析出的形核机制,奥氏体中钒的碳氮化物形变诱导析出的重要性,相间析出和铁素体中的无序析出对屈服强度的贡献,以及工艺过程参数对性能的影响。对这些课题进行讨论,并将结合其它合金的长期研究,集中讨论热轧钒微合金钢。     

鞍钢钒、钛、铌微合金钢的应用与开发

对钒、钛、铌在钢中的微合金化作用作了全面阐述,并介绍了鞍钢在开发钒、钛、铌微合金钢方面所进行的工作及前景。     

一种钒氮微合金钢的静态再结晶行为

 通过双道次压缩试验,研究一种钒氮微合金钢道次间隔时间内在奥氏体区变形后的软化行为,采用应力补偿法计算静态再结晶的体积分数,并建立静态再结晶动力学模型。分析变形温度与间隔时间以及钒的析出物对静态软化行为的影响。结果表明,在高于900℃时进行第一道次变形,该钒氮微合金钢很快完成了静态再结晶;在850、800℃变形后的等温阶段,发生了形变诱导析出现象,使再结晶激活能增加,静态再结晶进程受到抑制,导致软化率曲线上出现了平台。     

The effect of Nb,V, N and Al on the creep rupture strength of 9–12 % Cr steel

The creep resistance of advanced chromium steels can be significantly increased due to precipitation of very small particles of vanadium nitride VN. The solubility and precipitation of VN, Nb(C,N) and AIN in austenite and ferrite was analysed using relevant solubility products. The calculated values of nitrogen in solid solution were used for assessment of creep rupture strength of chromium steel (mean considered chemical composition, mass contents in %: 0.18 C; 10.5 Cr; 1.0 Mo; 0.2 V; 0.07 Nb; 0.05 N; 0.01 Al). Increasing N mass contents from 0.03 to 0.07 % leads to increasing creep rupture strength in 100 000 h at 600°C of about 60 %. Lowering AI mass contents from 0.045 to 0.005 % produces higher creep rupture strength of about 30 %.     

碳氮化钒在奥氏体中析出的动力学模型

 采用应力松弛方法研究了钒氮微合金钢中V(C,N)在奥氏体区的等温析出行为,证实了动力学计算模型的模拟结果。结果表明,试验钢的析出 温度 时间(PTT)曲线呈典型的“C”形,本试验条件下析出开始时间最短的“鼻子”温度为850 ℃左右,与模型计算得到的820 ℃相差很小。钢中氮含量对PTT曲线形状有较大影响,随着氮含量的增加C曲线向左移动,这与模型计算结果非常吻合。     

Compositional and microstructural changes which attend reheating and grain coarsening in steels containing niobium

This work describes the effect of temperature on both the microstructure and composition of microalloyed steel austenite in the as-reheated condition. Four laboratory steels of similar C levels were analyzed in this investigation. Three steels had different Nb concentrations at con-stant N levels, and the fourth exhibited a difference in N concentration. The average prior-austenite grain size was determined using quantitative metallographic techniques as a function of reheat temperature. The corresponding amount of Nb in solution in austenite was determined from atom probe analysis. Results from this investigation indicate that at elevated temperatures, representative of typical reheating practice, a smaller amount of Nb is soluble in austenite than what would have been predicted from any existing solubility relation for NbC_x in austenite. The solubility of Nb and C in austenite for the low-N steels is described by the relation: Log [Nb][C] = 2.06 - 6700/T. Additionally, it is shown that undissolved NbC_x particles are present in austenite approximately 125 ‡C above the grain-coarsening temperature.     

Effect of V Precipitation on Continuously Cooled Sulfur-Lean Vanadium-Alloyed Steels for Long Products Applications

The acicular ferrite formation as decomposition product of S-lean V-alloyed austenite with high N content is studied in this article. A combination of thermodynamic models as well as some physical metallurgical principles was used to analyze the intragranular nucleation potency of V(C,N) precipitates. The designed thermomechanical and heat treatments ensure an almost homogeneous microstructure consisting of acicular ferrite for this N-rich laboratory cast steel. The results presented in this work demonstrate that, in the absence of sulfide inclusions, acicular ferrite is nucleated on V(C,N) precipitates.     

钒氮钢中晶粒细化研究

 采用Gleeble 3500热模拟试验机，在相同工艺条件下，对比研究了钒氮钢、钒钢以及碳锰钢的晶粒细化效果。结果表明，钒氮钢的晶粒细化效果最显著，铁素体的晶粒尺寸可达61 μm，这主要与在奥氏体区中析出的V(C，N)有关。奥氏体区析出的V(C，N)，不但可抑制奥氏体晶粒长大，同时还可以作为铁素体的形核核心，诱导晶内铁素体形成，大大增加铁素体形核率，从而提高了相变细化的比率。     

A Model for Precipitation Kinetics in Vanadium Microalloyed Steel

Small dispersoid particles inhibit recrystallization which is critical in controlling the grain structure of many high strength low alloy steels. A general kinetic model has been developed to predict precipitation of V(C, N) in vanadium microalloyed steels with a series of carbon and nitrogen contents. The solubility product and driving force of carbonitrides precipitated in austenite as well as the interfacial energy and other parameters can be evaluated to predict Nucleation rates-Temperature (NrT) and Precipitation-Time-Temperature (PTT) diagram. By using stress relaxation tests and fitting with Avrami equation, it is possible to draw PTT diagrams. The predictions of the model coincide with results of experimental investigation on V(C, N) precipitation in austenite. The nose temperature is around 850 ℃ obtained by experiment which is different from the prediction of the model and the difference is 30 ℃, and nitrogen has more effect on the shape of "C" curve of PTT diagram than carbon that makes "C" curve move leftward significantly.     

Dissolution of Nb(C,N) in mild steel during annealing

A formula for the solubility products of Nb and C in mild steel containing small amount of Ti which has been annealed in the austenitic region for 90s is presented. This solubility product gives closer agreement than that calculated from Smith's formula based on long-term annealing. Fine ferrite grains were achieved by dissolving Nb(C,N) into the matrix during annealing due to the increased supercooling during the austenite → ferrite transformation.     

Effects of second-phase particles on coarsening of austenite in 0.15 Pct carbon steels

The effects of second-phase particles formed by the addition of vanadium, nitrogen, and aluminum on the austenite grain coarsening behavior of 0.15 pct carbon steels were studied. The oxidation and etching technique has been adopted to reveal the prior austenite grain boundaries. The specimens were austenitized at intervals of 50°C within the range of 900°C to 1150°C under high vacuum (<10⁻⁴ torr) for half an hour, toward the end of which they were oxidized for about one minute by introducing oxygen at about 250 mm Hg to reveal the grain boundaries, and then quenched into iced water. The variation of prior austenite grain size with temperature in these steels indicates that vanadium carbonitride, V(C, N), is much more effective in austenite grain refinement than vanadium carbide, VC, at all temperatures. The effect of vanadium carbonitride in austenite grain refinement is more or less the same as that of aluminum nitride. AlN, at temepratures below 1000°C, but this effect of vanadium carbonitride in austenite grain refinement decreases with increasing temperature. Above 1000°C, aluminum nitride is a much better grain refiner than vanadium carbonitride. The presence of the V (C, N) and AlN particles in the same steel causes moderate grain growth of austenite. MD. Mohar Ali Bepari, formerly with the Department of Metallurgy, The University of Sheffield, Sheffield, England, is Associate Professor of Department of Metallurgical Engineering, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh.     

中锰马氏体NM500钢奥氏体晶粒长大行为

 中锰马氏体耐磨钢是一种新型的低成本高性能耐磨钢,揭示钢中奥氏体晶粒长大行为,并建立精确的预测模型,对其组织和性能的调控至关重要。利用Gleeble-3500型热模拟试验机、金相显微镜和透射电子显微镜等设备,系统研究了中锰马氏体NM500钢在不同加热温度和保温时间下的奥氏体晶粒长大行为,探讨了微合金第二相对奥氏体晶粒长大行为的影响。研究结果表明,加热温度对试验钢中奥氏体晶粒长大的影响明显大于保温时间,且试验钢中奥氏体晶粒长大行为受基体中V(C,N)粒子析出行为的影响,其可分为两个阶段。当加热温度小于950 ℃时,试验钢中存在大量未溶的纳米级球状和短棒状V(C,N)粒子,能够有效地钉扎奥氏体晶界,奥氏体晶粒长大缓慢;但当加热温度不低于950 ℃时,试验钢中V(C,N)粒子大量溶解和粗化。其中,加热温度为950 ℃、保温时间为60 min时,试验钢中V(C,N)粒子的体积分数仅为0.041%,平均粒径增大至45.78 nm。其对奥氏体晶粒的钉扎作用显著减低,且随着温度升高,原子扩散速度加快,奥氏体晶粒快速长大。基于Beck模型,建立了试验钢中奥氏体晶粒等温长大动力学模型,计算得到低温及高温阶段试验钢中奥氏体晶粒长大表观激活能分别为66.561 kg/mol和170.416 kJ/mol,且奥氏体晶粒的理论计算值与实测结果吻合较好。