Ti对中碳高锰钢奥氏体晶粒长大的影响

研究了Ti对中碳高锰钢在不同加热温度和保温时间下的奥氏体晶粒长大规律的影响。结果表明,随着加热温度的升高和保温时间的延长,含Ti钢的奥氏体晶粒长大速率明显较慢,且相同温度下其晶粒尺寸更为细小。含Ti钢中含有较多的纳米级Ti(C,N)粒子,Thermo-calc计算表明其完全固溶温度约1 450℃,当温度逐渐升高时,Ti(C,N)虽有部分固溶,但尺寸小于100 nm的粒子比例依然较高,起到了阻碍奥氏体晶界迁移的作用,因此高温下含Ti钢的奥氏体晶界迁移速率较慢。建立了含Ti钢的高温奥氏体晶粒长大模型:D_B=729.25t~(0.16)exp(-71 972.3/RT),根据拟合模型所得含Ti钢中的奥氏体晶界迁移能为72 k J/mol,大于不含Ti钢的45 k J/mol,同时生长指数n为0.16,而不含Ti钢为0.25,试验所得奥氏体晶粒尺寸与计算模拟值吻合较好。     

Ti对AH36粗化温度和奥氏体晶粒大小的影响

利用 Gleeble-15 0 0热模拟试验机 ,研究了 Ti含量对 AH3 6钢粗化温度的影响 ,同时利用二辊轧机研究了轧制温度、变形量对 AH3 6钢的奥氏体晶粒大小的影响。结果表明 :钛含量增加 ,钢的粗化温度提高 ,该钢合理的加热温度范围为12 0 0～ 12 5 0℃。在轧制温度一定时 ,变形量和钛含量增加 ,奥氏体晶粒尺寸减小。     

Austenite particle coarsening and delta-ferrite grain growth in model Fe–Al alloy

Abstract

The grain growth kinetics of delta-ferrite was investigated in a model Fe–Al alloy in which a small volume fraction of austenite particles is used to control grain growth. The specimens were heated to different temperatures in the two phase (delta-ferrite+austenite) region and held for times between 5 min and 288 h followed by water quenching. The coarsening kinetics of the austenite particles could be described both in terms of bulk (t^1/3) and grain boundary (t^1/4) diffusion. The growth of the delta-ferrite grains was dominated by the pinning effect of the austenite particles. When the particle pinning pressure was much larger than the driving force for grain growth, the growth of delta-ferrite grains was completely pinned. Under conditions in which the particle pinning force and the driving force for grain growth were comparable, ferrite grain growth occurred at a rate which is proportional to the rate of coarsening of the austenite particles. When the particle pinning force is smaller than the driving force, grain growth occurs at a rate which is lower than that expected without pinning.

On a examiné la cinétique de croissance de grain de ferrite delta dans un alliage modèle de Fe-Al dans lequel une petite fraction volumique de particules d’austénite est utilisée pour contrôler la croissance de grain. On a chauffé les échantillons à différentes températures dans la région à deux phases (ferrite delta + austénite) et on les a maintenus pour des durées allant de 5 minutes à 288 heures, puis on les a trempés à l’eau. On pourrait décrire la cinétique de grossissement des particules d’austénite tant en fonction de la diffusion volumique (t^1/3) que de la diffusion aux joints de grain (t^1/4). La croissance des grains de ferrite delta était dominée par l’effet d’épinglage des particules d’austénite. Lorsque la pression d’épinglage de particule était beaucoup plus grande que la force motrice pour la croissance de grain, la croissance des grains de ferrite delta était entièrement épinglée. Dans les conditions où la force d’épinglage de particule et la force motrice pour la croissance de grain étaient comparables, la croissance de grain de ferrite se produisait à une vitesse proportionnelle à la vitesse de grossissement des particules d’austénite. Lorsque la force d’épinglage de particule était plus petite que la force motrice, la croissance de grain se produisait à une vitesse plus faible que la vitesse sans épinglage.     

含钛钢的奥氏体晶粒粗化与再结晶参数

研究了3种不同含Ti量(0.04%-0.16%Ti)钢奥氏体晶粒粗化温度及热轧后奥体再结晶的行为。在950-1200℃加热,含0.04%Ti钢奥氏体晶粒最小,其晶粒开始粗化温度在1 150℃以上。得出含Ti钢开始再结晶的临界形变率(ε_c)与原始奥氏体晶粒直径(D₀)、轧制温度(T)间定量关系。     

Al、Ti处理对低合金钢焊接粗晶区组织的影响

研究了Al、Ti处理对低合金钢焊接粗晶区组织的影响.研究发现:用Al处理时,钢中形成的夹杂物为Al的氧化物和细小的TiN.Al的氧化物和TiN不能促进晶内铁素体的形成,焊接粗晶区主要由粗大的晶界铁素体和平行排列的侧板条铁素体组成.用Ti处理时,钢中形成大量的Al、Ti、Mg、Ca复合氧化物夹杂,其颗粒大小为0.5～3.0 μm,同时还有一定量细小的Ti的氮化物.复合Ti的氧化物具有促进晶内针状铁素体形核的能力,焊接粗晶区主要由晶界铁素体、少量的侧板条铁素体和大量的晶内针状铁素体组成.随焊接热循环高温保温时间增长,晶界铁素体粗大,侧板条铁素体数量减少.相变区的冷却速度减慢,晶界铁素体数量增多,针状铁素体的尺寸显著增大.     

Austenite Grain Coarsening Behaviour in a Medium Carbon Si‐Cr Spring Steel with and without Vanadium

The austenite grain coarsening behaviour in a medium carbon Si‐Cr spring steel with and without vanadium was investigated by the thermal etching method. This method is efficient when the austenitization temperature is not lower than 900 °C. The average grain sizes on the surfaces of the samples determined by thermal etching vary little from those in the bulk as revealed by chemical etching. The austenite grain coarsening behaviour of the steel with vanadium can be classified in three temperature regimes. Below a critical temperature the vanadium addition is effective to impede grain growth and fine grains are observed. The austenite grain size was significantly smaller than in the steel without vanadium. In a medium temperature regime the steel with vanadium exhibits a bimodal grain size distribution. Above the dissolution temperature of vanadium carbides normal grain growth is observed. An equation was set up to predict the grain coarsening behaviour in the steel without vanadium. The results show how the austenite grain size, which is very important for the toughness and ductility of the spring steels, can be controlled by microalloying with vanadium.     

Effect of Ti on Austenite Grain Growth Behavior in High Carbon Steels

Austenite grain growth behavior of two high carbon steels was observed using Confocal l.aser Scanning Mi croscope （CLSM）. Apparent austenite grain sizes for different holding time under a series of temperatures were measured by employing linear intercept method. Experimental results showed that Ti bearing steel exhibited a much sluggish growth rate compared with Ti free counterpart, which was attributed to the pinning effect of Ti（C,N） nan oparticles with the size of 20 to 40 nm on austenite grain boundaries. Based on the research conducted by using Transmission Electron Microscope （TEM） observation and Thermo Calc calculation, Ti（C, N） was confirmed to be the dominant phase at elevated temperature. Some models were introduced to predict the grain sizes of both steels. By comparison, the results predicted by the modified Gladman equation are found to be closest to the experimental resuits, which could be employed to predict accurately the austenite grain growth of high carbon steels.     

Study on Austenite Grain Growth Law of Ultra-High Strength Hot-Stamped 22MnB5 Steel During Thin Slab Casting and Rolling Process

Clarifying the austenite grain growth law in the thin slab casting and rolling (TSCR) process can provide theoretical guidance for the control of austenite grain in the slab. Starting with the austenite nucleation during solidification process, the growth law of austenite grains is methodically studied throughout the TSCR continuous casting and soaking process. The results show that the austenite growth is not interrupted during the TSCR continuous casting and soaking process. The austenite grain growth in the continuous casting process accounts for more than 70% of the total growth. The growth rate of austenite in the continuous casting cooling process is always faster than that when reheated to this temperature. Compared with the holding temperature and holding time, the final size of austenite grains in the TSCR process slab is most affected by the continuous casting cooling rate. In addition, compared with the traditional process, the growth rate of austenite in TSCR process is faster at the end of soaking.     

合金元素对取向硅钢高温组织中奥氏体含量的影响

利用金相显微镜、扫描电镜等试验设备,研究了取向硅钢在850~1 300℃温度区间的高温组织,分析了奥氏体含量与合金成分、温度之间的关系,以及合金元素在奥氏体、铁素体中的分布情况。结果表明:不同成分的取向硅钢在1 100~1 200℃之间奥氏体相含量最多,且随着奥氏体稳定化元素含量增加,最大奥氏体相含量对应温度升高。取向硅钢中奥氏体含量与碳含量之间存在近似线性关系。     

Austenite Grain Refinement and Isothermal Growth Behavior in a Low Carbon Vanadium Microalloyed Steel

The austenite grain refinement through control of the grain growth during reheating process after thermomechanical controlled process(TMCP)in a vanadium microalloyed steel was achieved.The formation of ultra-fine grained austenite was attributed to the high density of austenite nucleation at the ferrite/martensite structure and to the inhibition of austenite growth by(Ti,V)C particles at the relatively low reheating temperature.Corresponding with the precipitation behavior of(Ti,V)C with temperature,the growth behavior of austenite in the vanadium microalloyed steel could be divided into two regions.At lower reheating temperature,austenite grains grew slowly,and ultra-fine grained austenite smaller than 5μm was successfully obtained.By contrast,the austenite grains grew rapidly at high temperature due to the dissolution of(Ti,V)C particles.According to the measured and predicted results of austenite growth kinetics,two models were developed to describe the growth behavior of austenite grains in two different temperature regions,and the apparent activation energy Qappfor grain growth was estimated to be about 115 and 195kJ/mol,respectively.     

含铝高速钢中奥氏体非均匀长大的机制

M2AI和M2高速钢经一次和二次淬火后,奥氏体晶粒和未溶碳化物的定量研究表明,在高温r/f比值相同的条件下,由于淬火前原始组织的差别,可发生正常(均匀)和异常(非均匀)两类长大。根据异常粗晶形成初期的组织观察,提出了“连续-非连续”再结晶模式和“合并—推移”式的生长机制。提出了减轻或消除M2AI钢混晶的工艺原则。     

机械球磨作用下Al/Ti混合粉末的组织和热稳定性

为探索一种制备高综合性能Al-Ti基金属间化合物的新方法，研究了机械球磨方法制备的Al-10％Ti(质量分数)混合粉末的组织和热稳定性。结果表明：在球磨作用下，Al、Ti粉末的颗粒尺寸得到有效细化，并且球磨时间越长，Al／Ti粉末储备能量越大，生成Al-Ti金属间化合物所需的反应激活能越低，内能的增加和扩散能力的提高是由于机械球磨导致了大量的晶格缺陷；经90h球磨的粉末在660℃下经6h热处理后生成Al3Ti，还有少量的Al2Ti，Al5Ti2生成。     

Process Control for Structure of Martensite/Austenite Islands of 15.3 mm X100 Pipeline Steel in BX Steel

This paper mainly studies the influence of deformation amount and cooling rate,which existed in X100 pipeline steel rolled at 2300mm rolling mill in BX STEEL,on morphology,size relations and distribution of M/A islands of steel plate structure.Experimental results show that structures of M/A islands are homogenized and refined under the conditions of appropriately increasing the deformation amount in non-recrystallization region on basis of rational deformation amount in recrystallization region and cooling rate after deformation,respectively.Finally,according to the actual situation of 2300mm hot rolling mill,this paper gives rational deformation amount and cooling rate used to obtain ideal structure of M/A islands.     

Three-dimensional Numerical Simulation and Experimental Analysis of Austenite Grain Growth Behavior in Hot Forging Processes of 300M Steel Large Components

The microstructure models were integrated into finite element (FE)code,and a three-dimensional (3D) FE analysis on the entire hot forging processes of 300M steel large components was performed to predict the distri-butions of effective strain,temperature field and austenite grain size.The simulated results show that the finest grains distribute in the maximum effective strain region because large strain induces the occurrence of dynamic re-crystallization.However,coarse macro-grains appear in the minimum effective strain region.Then,300M steel forg-ing test was performed to validate the results of FE simulation,and microstructure observations and quantitative analysis were implemented.The average relative difference between the calculated and experimental austenite grain size is 7.5 6%,implying that the present microstructure models are reasonable and can be used to analyze the hot forging processes of 300M steel.     

Interaction of Hydrogen and Retained Austenite in Bainite／Martensite Dual-Phase High Strength Steel

SymbolList　　DA———Apparentdiffusioncoefficient;　　DL———Latticediffusioncoefficient;　　EaD———Diffusionactivationenergyofhydrogeninnormallattice ;　　EaT———Trapactivationenergy ;　　EB———Trapbindingenergy ;　　ES———Saddlepointenergy ;     

铝、钛、钒和铌对中碳钢奥氏体晶粒度的影响

对6炉微合金化高氮L45钢进行了长时间(1800s)加热时和快速(50℃/s)短时间(5s)加热时奥氏体晶粒长大试验。测定了奥氏体晶粒平均截线长度。在萃取复型透射电镜照片上利用图象分析仪测定了1^#、3^#和6^#钢样中微细析出相的尺寸分布。利用透射电镜能谱仪分析了微细析出相的化学成分。还探讨了铝及微合金化元素钛、钒和铌与加热温度对高氮中碳钢奥氏体晶粒度的影响机制。     

新型Mn Cr齿轮钢的动态再结晶及晶粒细化

采用Gleeble 1500热模拟试验机研究了一种新型Mn-Cr齿轮钢在不同条件下的动态再结晶行为及晶粒尺寸的变化规律,确定了该Mn-Cr齿轮钢的再结晶激活能为378.6 kJ/mol,应力指数为7.08(相对于峰值应力)或6.2(相对于稳态流变应力).Z因子唯一地决定着稳态动态再结晶的晶粒尺寸,二者之间为幂指数关系.Z因子通过影响稳态流变应力,进而影响形变储存能来改变再结晶的晶粒尺寸.     

Modeling of Cell/Dendrite Transition During Directional Solidification of TiAl Alloy Using Cellular Automaton Method

 Solute diffusion controlled solidification model was used to simulate the initial stage cellular to dendrite transition of Ti44Al alloys during directional solidification at different velocities. The simulation results show that during this process, a mixed structure composed of cells and dendrites was observed,where secondary dendrites are absent at facing surface with parallel closely spaced dendrites, which agrees with the previous experimental observation. The dendrite spacings are larger than cellular spacings at a given rate, and the columnar grain spacing sharply increases to a maximum as solidification advance to coexistence zone. In addition, simulation also revealed that decreasing the numbers of the seed causes the trend of unstable dendrite transition to increase. Finally, the main influence factors affecting cell/dendrite transition were analyzed, which could be the change of growth rates resulting in slight fluctuations of liquid composition occurred at growth front. The simulation results are in reasonable agreement with the results of previous theoretical models and experimental observation at low cooling rates.     

Synthesis and characterisation of Ti6Al4V/xTa alloy processed by solid state sintering

ABSTRACT

This work investigates the effect of Ta particle addition into a Ti6Al4V alloy processed by solid state sintering. The volume fraction of Ta ranged between 0 and 30?vol.-%. The sintering kinetics of powder mixes are evaluated by dilatometry. Sintered materials are characterised by SEM and XRD, and their mechanical properties are obtained from microhardness and compression tests. Sintering behaviour and final microstructure are affected by Ta particles, which slow down the densification, lower the temperature of α-to-β phase transition and stabilise the β phase. Mechanical properties, as microhardness, Young’s modulus and yield stress, depend on the microstructure reached after sintering and on the residual porosity. An equation expressing the Young’s modulus of Ti6Al4V/xTa alloy as function of x and porosity is proposed and validated. The materials with at least 20?vol.-% of Ta exhibited a high strength to modulus ratio, which is suitable for orthopaedic implants.