钛精粉氧化过程中物相转变

采用热重分析和恒温实验法研究了攀枝花钛精粉氧化过程中相的存在形式及其转变规律.X射线衍射结果和微观形貌分析表明:温度低于500℃,钛精粉未发生氧化反应;600℃时产生Fe₂Ti₃O₉和TiO₂相,其和原相Fe₂O₃相衍射峰强度均随温度的升高而增强;900℃时,Fe₂Ti₃O₉相完全转变为Fe₂TiO₅相,且随温度的升高,TiO₂相和Fe₂O₃相衍射峰强度逐渐减弱;在整个氧化过程中存在四个化学反应,其与烧结作用相互关联,使得氧化产物表面形成较多孔隙,变得凹凸不平且疏松.     

一水硬铝石矿-氢氧化钠体系微波焙烧相变规律

以饱和氢氧化钠溶液为添加剂,利用微波加热对一水硬铝石矿进行焙烧处理.考察微波焙烧温度和氢氧化钠添加量对一水硬铝石矿-氢氧化钠体系相变规律的影响,并对微波加热和常规加热得出的焙烧产物做物相结构的比较.利用X射线衍射分析和扫描电子显微镜技术对熟料的物相结构和微观形貌进行分析.结果表明微波加热促进氢氧化钠快速并充分的与一水硬铝石矿反应.与常规加热相比,微波加热在更低的温度下能生成更多铝酸钠物相.微波加热后的熟料疏松多孔,有利于后续溶出处理.     

Phase transformation of stainless steel during fatigue

Transformation of austenite during cyclic loading was studied in AISI 301 and 304 alloys whose stability was adjusted by heat treatment and temperature changes. Fatigue life was determined under controlled strain amplitude tension-compression conditions. The amount of transformation to α’ (bcc) martensite was continuously indicated magnetically during testing, and the α’ and ∈ (hcp) phases were observed metallographically at failure. It was found in room temperature testing that at strain amplitudes in excess of 0.4 pct the formation of α’ (bcc) martensite was detrimental to the fatigue life. At 200°F (366 K) the fatigue life of an unstable alloy was increased, while in a completely stable austenitic alloy (20Cr, 6Ni, 9Mn), the life at 200°F (366 K) was less than that at room temperature for the same cyclic strain amplitude. The differing effect of temperature on life of these two types of alloy is attributed to the alteration of the austenite stacking fault energy and the relative free energies of the α’ (bcc), ∈ (hcp) and γ (fcc) phases in the unstable alloys. It has been observed that within the standard composition ranges of the two 300 series stainless steel grades there can be marked differences in the degree of transformation resulting from cyclic loading. This has the implication that for fatigue applications modifications in the specifications for the different grades of stainless would be advantageous.     

Phase transformation of stainless steel during fatigue

Transformation of austenite during cyclic loading was studied in AISI 301 and 304 alloys whose stability was adjusted by heat treatment and temperature changes. Fatigue life was determined under controlled strain amplitude tension-compression conditions. The amount of transformation to α’ (bcc) martensite was continuously indicated magnetically during testing, and the α’ and ∈ (hcp) phases were observed metallographically at failure. It was found in room temperature testing that at strain amplitudes in excess of 0.4 pct the formation of α’ (bcc) martensite was detrimental to the fatigue life. At 200°F (366 K) the fatigue life of an unstable alloy was increased, while in a completely stable austenitic alloy (20Cr, 6Ni, 9Mn), the life at 200°F (366 K) was less than that at room temperature for the same cyclic strain amplitude. The differing effect of temperature on life of these two types of alloy is attributed to the alteration of the austenite stacking fault energy and the relative free energies of the α’ (bcc), ∈ (hcp) and γ (fcc) phases in the unstable alloys. It has been observed that within the standard composition ranges of the two 300 series stainless steel grades there can be marked differences in the degree of transformation resulting from cyclic loading. This has the implication that for fatigue applications modifications in the specifications for the different grades of stainless would be advantageous. Formerly a Research Assistant     

Phase transformation effects during hip of TiAl

The densification of titanium aluminide powders during hot isostatic pressing has been measured in situ by an eddy-current sensor. The samples were found to experience enhanced densification as they transformed from an initial metastable α₂ structure to an equilibrium structure consisting mostly of the γ phase. The temperature at which the enhanced densification occurred corresponded closely to the temperature at which an exotherm is observed by differential thermal analysis. Evaluation of several possible explanations for this enhanced densification indicates that it is most probably the result of transformation plasticity.     

红土镍矿选择性还原焙烧过程中的相变转化

针对传统选矿方法难以回收低品位红七镍矿中有价金属镍的问题,采用选择性还原焙烧法研究了不同焙烧温度以及不同焙烧时间条件下红土镍矿(Ni品化为1.49%)中发生的微观结构变化以及相变转化.通过X射线衍射、扫描电镜及X射线能谱分析等测试手段分析表明,在不同焙烧温度及不同时间条件下经选择性还原后的红土镍矿中,镍氧化物逐渐被还原成镍铁合金相,铁氧化物主要转变成浮氏体相,硅酸盐主要以橄榄石形式存在.最后通过还原焙烧磁选试验证实,还原剂为烟煤,添加剂为NCS,两者用量分别为原矿质量的2%和7%,在1200℃条件下焙烧50min,磁选分离得到镍铁产品中镍品位为9.78%,镍的回收率为92.06%,镍铁回收率差为62.51%,实现了红土镍矿中镍铁的选择性还原.     

38MnSiVS非调质钢的相变模型

 对于热轧非调质钢棒材,轧后相变组织对最终产品的力学性能有着重要影响。为了准确预测38MnSiVS非调质钢棒材热轧后的组织演变和性能,利用热膨胀与定量金相方法,在Gleeble-3500热模拟机及Dil805淬火变形膨胀仪上分别测定了试验钢动态连续冷却转变(CCT)和动态等温转变(TTT)曲线。研究分析了冷却速率对试验钢相变及珠光体片层间距的影响,基于Esake and Pietrzyk和Zener and Hillert模型,分别建立了铁素体晶粒尺寸d_α、珠光体片层间距S_P关系式。结合动态等温转变曲线数据和Scheil叠加原理对铁素体体积分数进行了理论计算,为实际热轧生产中的组织性能控制提供理论依据。     

铜渣煤基直接还原过程中的铁物相转变

采用直接还原工艺回收铜冶炼渣中的铁,对不同温度下铁物相的转化以及金属铁颗粒的长大规律进行分析。通过对铜渣进行配料造球-煤基直接还原焙烧-弱磁选处理,得到了直接还原铁精矿指标随时间及温度的变化。结果表明,在焙烧温度1 300℃,焙烧时间30 min的条件下得到了TFe质量分数为91.55%、金属化率为92.99%及回收率为82.99%的铁精矿。对不同还原温度下铁精矿分析表明:1 050、1 100、1 150℃均生成了金属铁,但还原度及TFe含量较低。1 200℃时发现有Fe₂C₅及SiC相的生成,形成的CaSiO₃·FeSiO₃液相影响了还原过程。1 250℃时生成了Fe₃C,但Fe₂SiO₄会与CaO形成低熔点矿物。1 300℃时精矿中含有大量金属铁,但也形成了低熔点化合物,增加了后续处理的难度。金属铁颗粒首先出现在矿物颗粒失氧而产生的裂纹及孔洞的边缘,金属铁小颗粒被大颗粒吸收并聚结长大,金属铁经过斑点状-蠕虫状-仙人掌状的转变最后...     

镍沉降渣深度还原过程中的相变特征

通过化学成分、光学显微镜、X射线衍射、扫描电镜能谱分析等测试手段,分析了镍沉降渣矿物成分和嵌布特点和沉降渣深度还原过程中物相的转变特征,结果表明,渣的物相由铁镁橄榄石和玻璃质组成.渣中主要有用成分铜镍铁硫化物嵌布粒度微细,分布无规律,回收困难.经深度还原,沉降渣逐渐转变为镁黄长石、含镍金属铁、辉石、钙霞石、钠闪石、石英等新的矿物成分,加热至1300℃,还原产物物相组成稳定,镁黄长石和含镍金属铁相对含量最高.还原时间也是影响还原效果重要因素,含镍金属铁相对含量随还原时间的增加而增长,120 min时相对含量最高.热力学分析表明,镍沉降渣深度还原过程中主要发生的反应为铁镁橄榄石与氧化钙作用生成镁黄长石和FeO,FeO被C和CO还原为金属铁.金属硫化物与CaO和C通过氧化还原作用,生成的金属铜和镍溶于金属铁中,产生的CaS与硅酸盐一起析出.     

Phase transformation and stabilization of a high strength austenite

An investigation of the phase transformation and the austenite stabilization in a high strength austenite has been made. An Fe-29Ni-4.3Ti austenite age-hardened byγ′(Ni₃Ti) precipitates showed a further increase of strength after martensitic and reverse martensitic phase transformations. The stability of ausaged austenite as well as ausaged and transformation-strengthened austenite was improved significantly through an isothermal treatment at 500°C. TheM _s temperature of the strengthened austenite was restored to nearly that of annealed austenite while the austenite was hardened toR _c 41 through precipitation and phase transformations. The observed austenite stabilization is attributed to the formation of G.P. zones or short-range order of less than ∼10? size. Formerly with University of California, Berkeley     

Phase transformation and stabilization of a high strength austenite

An investigation of the phase transformation and the austenite stabilization in a high strength austenite has been made. An Fe?29Ni?4.3Ti austenite age-hardened by γ′(Ni₃Ti) precipitates showed a further increase of strength after martensitic and reverse martensitic phase transformations. The stability of ausaged austenite as well as ausaged and transformation-strengthened austenite was improved significantly through an isothermal treatment at 500°C. TheM _s temperature of the strengthened austenite was restored to nearly that of annealed austenite while the austenite was hardened toR _C 41 through precipitation and phase transformations. The observed austenite stabilization is attributed to the formation of G.P. zones or short-range order of less than ～10Å size.     

Phase transformation of TRIP-aided multiphase steel during continuous cooling

The phase transformation characteristics of a high-strength TRIP-aided multiphase cold-rolled steel during continuous heating at different cooling rates were studied by means of dilatometry,and the critical temperatures were also determined.The samples were fully austenitized at 1 050 ℃ and then cooled at different cooling rates ranging from0.5 ℃/s to 100 ℃/s.The continuous cooling transformation(CCT)curves were obtained for the experimental steel.The experimental results showed that a high cooling rate depressed the formation of ferrite and pearlite and promoted the formation of bainite and martensite,leading to a higher hardness.A large amount of martensite in high-strength TRIP-aided multiphase cold-rolled steel can be obtained at cooling rates in excess of 50 ℃/s.The experimental results provide guidelines for cooling control and heat treatment in real steel production.     

Phase transformation in an Fe-10.1Al-28.6Mn-0.46C alloy

The microstructure of an (α + γ) duplex Fe-10.1Al-28.6Mn-0.46C alloy has been investigated by means of optical microscopy and transmission electron microscopy (TEM). In the as-quenched condition, extremely fine D0₃ particles could be observed within the ferrite phase. During the early stage of isothermal aging at 550 °C, the D0₃ particles grew rapidly, especially the D0₃ particles in the vicinity of the α/γ grain boundary. After prolonged aging at 550 °C, coarse K’-phase (Fe, Mn)₃AlC precipitates began to appear at the regions contiguous to the D0₃ particles, and —Mn precipitates occurred on the α/γ and α/α grain boundaries. Subsequently, the grain boundary β-Mn precipitates grew into the adjacent austenite grains accompanied by a γ→ α + β-Mn transition. When the alloy was aged at 650 °C for short times, coarse. K-phase precipitates were formed on the α/γ grain boundary. With increasing the aging time, the α/γ grain boundary migrated into the adjacent austenite grain, owing to the heterogeneous precipitation of the Mn-enrichedK phase on the grain boundary. However, the α/γ grain boundary migrated into the adjacent ferrite grain, even though coarse K-phase precipitates were also formed on the α/γ grain boundary in the specimen aged at 750 °C.     

Phase transformation in an Fe-9.0AI-29.5Mn-1.2Si alloy

The microstructure of an (α + γ) duplex Fe-9.0Al-29.5Mn-l.2Si alloy has been investigated by means of transmission electron microscopy. In the as-quenched condition, extremely fine D0₃ particles were formed within the ferrite matrix by a continuous ordering transition during quenching. After being aged at 550 °C, the extremely fine D0₃ particles existing in the as-quenched specimen grew preferentially along (100) directions. With increasing the aging time at 550 °C, a (Si, Mn)-rich phase (designated as “L phase”) began to appear at the regions contiguous to the D0₃ particles. The L phase has never been observed in various Fe-Al-Mn, Fe-Al-Si, Fe-Mn-Si, and Mn-Al-Si alloy systems before. When the as-quenched specimen was aged at temperatures ranging from 550 °C to 950 °C, the phase transformation sequence occurring within the (α + D0₃) region as the aging temperature increases was found to be (α + D0₃ + L phase) → (α + D0₃ + A13 β-Mn)→ (B2 + D0₃ + A13 β-Mn)→ (B2 + A13β-Mn)→ (α + A13 β-Mn)→ (α +γ)→α.     

溶胶-凝胶自燃合成掺杂纳米二氧化钛的相变

以TiCl₄为前驱体,采用溶胶-凝胶自燃合成的方法制备了同时掺杂Ce³⁺,Fe³⁺,Zn²⁺的纳米TiO₂粉体．用X光衍射法对粉体的相组成进行了表征．用正交试验研究方法考察了Fe/Ce、（Fe+Ce）/Ti、柠檬酸/Ti（物质的量的比）、煅烧温度、煅烧时间等对产物相组成的影响。结果表明,柠檬酸/Ti,煅烧温度,（Fe+Ce）/Ti对产物相组成具有显著影响。