Effects of yttrium on recrystallization and grain growth of Mg-4.9Zn-0.7Zr alloy

Recrystallization and grain growth in Mg-4.9Zn-0.7Zr and Mg-4.9Zn-0.9Y-0.7Zr alloys as a function of temperature on deformation were investigated with regards to hot rolling and annealing. The influence of yttrium addition on the microstructure was examined by X-ray diffraction （XRD）, optical microscopy （OM）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. The results indicated that yttrium addition promoted nucleation of recrystallization during hot rolling process. The grain size of Mg-4.9Zn-0.7Zr alloy samples grew significantly with annealing temperature （300-400 ℃） and holding time （0-120 min）, while the microstructure of the alloy with yttrium addition remained unchanged and fine. The activation energy of grain boundary migration for Mg-4.9Zn-0.9Y-0.7Zr alloy samples （56.34 kJ/mol） was higher than that for Mg-4.9Zn-0.7Zr （42.66 kJ/mol） owing to the pinning effect of Y-containing particles. The proposed growth models of recrysta/lized grains for the two studied alloys conformed well to E. Robert＇s grain-growth equation. Besides, the ultimate strength and yield strength of the alloys with yttrium addition were improved with good plasticity.     

Effect of Heating Rate on Microstructure Evolution and Magnetic Properties of Cold Rolled Non-Oriented Electrical Steel

The effects of heating rate (ranging from 50 to 300 ℃/s) during the final annealing process on microstructure evolution and magnetic properties of cold rolled non-oriented electrical steel were investigated. It was found that increasing heating rate increased the nucleation temperature and complete recrystallization temperature. At the same time, heating rate increasing could cause the substantially refined structures for the recrystallization grains and this grain refinement would decline when the heating rate was beyond 50 ℃/s. The recrystallization texture exhibited pronounced improvement with heating rate, such as the intensity decrease of 111ND (normal direction) fiber and the intensity increase of {110}001 Goss texture component. The texture improvement and grain size refinement caused by heating rate increasing resulted in complicated variation of the magnetic properties. The magnetic induction (B50) keeps increasing while heating rate increases from 15 to 300 ℃/s which is due to the recrystallized texture optimization caused by rapid heating. The core losses (P1.5/50) decrease while heating rate increases from 15 to 100 ℃/s; however, the core losses would increase when heating rate is higher than 100 ℃/s, which is caused by the mean grain size refinement after rapid heating annealing. The results indicate that recrystallization texture and the magnetic properties of the non-oriented electrical steel can be improved definitely by rapid heating during the final annealing treatment.     

Effect of Hf on Stress Rupture Properties of DD6 Single Crystal Superalloy After Long Term Aging

 The specimens of the second generation single crystal superalloy DD6 with different Hf contents were prepared in the directionally solidified furnace with a high temperature gradient. The long term aging of the specimens after full heat treatment was performed at 1040 ℃ for 800 h. The effect of Hf on the microstructure and stress rupture properties under 980 ℃/250 MPa of the alloy after long term aging was investigated. The results show that the γ′ coarsening and rafting and no topologically close packed phase (TCP) are observed in the microstructures of DD6 alloy with different Hf contents after aged at 1040 ℃ for 800 h. It indicates that DD6 alloy with different Hf contents all possesses good microstructure stability. With increasing Hf content the rupture life after long term aging turns shorter and the elongation represents the increasing first and decreasing afterwards. The fracture mechanism of the alloy with different Hf contents at 980 ℃/250 MPa all shows dimple model. The influence of the microstructures on the stress rupture properties of the alloy is also discussed.     

A study on hot deformation behaviour of alloy Monel K-500

Thermal simulation tests were conducted at different deformation temperatures and degrees by a Gleeble simulator.The results show that the alloy has higher resistance to deformation;with an increase of the deformation temperature,the alloy's flow stress and maximum value decrease;with an increase of the deformation degree,both the initial recrystallization temperature and the complete recrystallization temperature decrease sharply.When the deformation degree reaches 30%,60% and 80%,the initial recrystallization temperature is around 950℃,850℃ and 800℃,the complete recrystallization temperature is around 1 100℃,1 050℃ and 1 000℃ respectively.When the deformation temperature is higher than 1100℃,the deformation degree increases and the re-crystalized grains are significantly refined.The forging process parameters were established according to the regular pattern mentioned above.The microstructure of the bar forged in this pattern is uniform and the result is satisfying.     

Hot Deformation Behavior of Nickel-Based Superalloy GH4720Li

 The hot deformation characteristics of GH4720Li alloy were studied at the temperature of 1100-1170 ℃ and strain rate of 001-1 s-1 using Gleeble hot compression tests. True stress-true strain curves and deformation microstructures were investigated. Constitutive equation was established using the hyperbolic law. Processing map for hot working was also developed on the basis of the variations of efficiency of power dissipation with temperature and strain rate. The results show that dynamic recrystallization is the dominant softening mechanism during hot deformation. Fully recrystallized grain is obtained at strain of 07 above 1130 ℃, and coarsening occurs above 1150 ℃. The mean deformation activation energy is determined to be 512 kJ/mol. According to the low activation energy value, high dissipation efficiency parameter and fine recrystallized microstructure, 1130 ℃ is chosen as the hot working temperature for GH4720Li alloy.     

Properties and Microstructure of OneStep Cold Rolled Steel Strip for Shadow Mask

The effect of recrystallization annealing temperature on the properties and microstructure of onestep cold rolled steel strip for shadow mask was studied. The results showed that there was no yield point elongation when the tensile tests were performed on the samples for annealing temperatures ranging from 750 ℃ to 810 ℃. Moreover, increasing annealing temperature resulted in large grains, which was beneficial to the formability and magnetic property of steel strips. On the other hand, when the sample was annealed at 840 ℃, its microstructure showed ununiformity with 004% yield point elongation, which was not good for the function of the shadow mask. Therefore, the proper recrystallization annealing temperature was about 810 ℃ for the present steel strip for shadow mask.     

Hot Compression Behavior of AsCast Precipitation Hardening Stainless Steel

 High temperature deformation characteristics of a semiaustenitic grade of precipitation hardening stainless steels were investigated by conducting hot compression tests at temperatures of 900-1 100 ℃ and strain rates of 0001-1 s-1. Flow behavior of this alloy was investigated and it was realized that dynamic recrystallization (DRX) was responsible for flow softening. The correlation between critical strain for initiation of DRX and deformation parameters including temperature and strain rate, and therefore, Zener Hollomon parameter (Z) was studied. Metallographic observation was performed to determine the as deformed microstructure. Microstructural observation shows that recrystallized grain size increases with increasing the temperature and decreasing the strain rate. The activation energy required for DRX of the investigated steel was determined using correlations of flow stress versus temperature and strain rate. The calculated value of activation energy, 460 kJ/mol, is in accordance with other studies on stainless steels. The relationship between peak strain and Z parameter is proposed.     

Effect of Processing Condition on Texture and Drawability of a Ferritic Rolled and Annealed Interstitial-Free Steel

The processing conditions of the texture formation and deep drawability of a Ti-IF steel strip hot-rolled in ferritic region and subsequently annealed were investigated. The r-value increases with the decrease of reheating temperature, and finish rolling temperature and the increase of reductions in ferritic region. For lubricated ferritic rolling and annealing, the r-value is raised up to 1.75, and elongation rate is over 50% at the finish rolling temperature of 650 ℃, which is suitable for DDQ grade products. However, the r-value is below 1.0 in the case of unlubricated rolling. The X-ray diffraction was used to analyze the textural characteristic of samples. For samples subjected to lubricated rolling and annealing, the strong { 111 }//ND recrystallization texture is distributed homogeneously along the thickness direction, and the intensity of { 110} recrystallization texture is very low even in surface. However, for unlubricated samples, the {111} texture is distributed inhomogeneously and is weak along the thickness direction, and （110}//ND recrystallization texture is strong, which deteriorates the formability.     

Microwave strengthens decomposition of mixed rare earth concentrate: Microwave absorption characteristics

The potential application of microwave heating technology for processing the mixed rare earth concentrate was systematically investigated by analyzing the microwave absorption characteristics in this study. The complex permittivity was measured through resonant cavity perturbation method. The variations of permittivity, the loss factor, loss tangent and the penetration depth with the increasing temperature were investigated numerically. The results indicate that the permittivity increases as the temperature increases, and temperature has a pivotal effect on it. The mixed concentrate is high loss material at the temperature range from 600 to 800℃ according to theoretical analyses of loss tangent and penetration depth. The results of phase transition analysis prove that the variation of microwave absorption characteristics of mixed concentrate is caused by the changes of crystal and lattice structures.The reflectivity, loss factor and penetration depth of the mixed concentrate were also calculated, and the results indicate that processing the mixed concentrate by microwave heating is of high feasibility and industrial potential.     

Effect of Processing Condition on Texture and Drawability of a Ferritic Rolled and Annealed InterstitialFree Steel

The processing conditions of the texture formation and deep drawability of a TiIF steel strip hotrolled in ferritic region and subsequently annealed were investigated. The rvalue increases with the decrease of reheating temperature, and finish rolling temperature and the increase of reductions in ferritic region. For lubricated ferritic rolling and annealing, the rvalue is raised up to 175, and elongation rate is over 50% at the finish rolling temperature of 650 ℃, which is suitable for DDQ grade products. However, the rvalue is below 10 in the case of unlubricated rolling. The Xray diffraction was used to analyze the textural characteristic of samples. For samples subjected to lubricated rolling and annealing, the strong {111}∥ND recrystallization texture is distributed homogeneously along the thickness direction, and the intensity of {110} recrystallization texture is very low even in surface. However, for unlubricated samples, the {111} texture is distributed inhomogeneously and is weak along the thickness direction, and {110}∥ND recrystallization texture is strong, which deteriorates the formability.     

Recrystallization of Single Crystal Nickel-Based Superalloy

A series of experiments of investigating the recrystallization of single crystal DD3 superalloy were carried out. The threshold temperature for recrystallization and the effect of annealing temperature on recrystaUization were studied. The results show that the threshold temperature for recrystallization of the shot-peened DD3 samples is be-tween 1 000 ℃ and 1 050℃ under the condition of annealing for 2 h, and the recrystallization depth increases with the rise of the annealing temperature. Below 1 150 ℃, the recrystallization depth increases slowly with the tempera-ture climbing, while above 1 150 ℃, the recrystallization depth increases quickly with the rise of the temperature. The solution of the γ' phase is a critical factor of the recrystallization behavior of DD3 superalloy. In addition, the ki-netics and microstructural evolution of recrystallization at 1 200 ℃ were also studied. It is found that the recrystalli-zation progresses rapidly at 1 200℃ through the growth of fully developed recrystallized grains, and the recrystalli-zation process on the shot-peened surface is similar to that of wrought materials, including nucleation of reerystalliza-tion, growth of new grains into the matrix, and growth of new grains by swallowing up each other.     

Surface recrystallization of a single crystal nickel-base superalloy

The recrystallization behavior of a single crystal nickel-base superalloy was investigated by shot peening and subsequent annealing. Two kinds of recrystallization microstructures, which are intensively dependent on the annealing temperature, are shown in the nickel-base superalloy after shot peening and subsequent annealing. Surface recrystallized grains are obtained when the superalloy is anparticles occurs. Cellular recrystallization is observed after annealing at lower temperatures. Cellular structures induced by high diffusivity of the shot-peened alloy annealed at 1050℃ accords with the Johnson-Mehl-Avrami-Kolmogorov equation. The low Avrami exponent is caused by the inhomogeneous distribution of stored energy, the decreasing of stored energy during recovery, and the strong resistance of boundary migration yb γ' particles.     

IF钢罩式退火过程中再结晶组织与织构的演变

研究了IF钢(/%:0.005C、0.02Si、0.16Mn、0.011P、0.004S、0.042Als、0.061Ti、0.003 1 N)0.8 mm冷轧板在500～800℃退火时的再结晶组织及织构,采用X射线衍射技术结合微观组织观察分析了IF钢罩式退火过程中{111}再结晶织构形成机制和显微组织演变规律。结果表明,随退火温度的升高,再结晶数量逐渐增多,640℃为实验钢实际再结晶温度,同时{111}再结晶织构强度亦逐渐增大,{111}取向的晶粒主要在再结晶过程中形成,并在{111}取向晶粒长大过程中,γ纤维织构之间也发生相互转化,主要由{111}〈112〉织构转变为{111}〈110〉织构。     

薄带连铸取向Fe-6.5％Si钢形变热处理过程组织演化

设计并利用双辊薄带连铸工艺制备出取向Fe- 6. 5%Si钢铸带，研究了热处理工艺对铸态、形变和初次再结晶组织、织构及析出物的影响规律。结果表明，铸带退火可以促进铸态组织中的柱状晶长大，同时增加200nm以下MnS- AlN或MnS- NbN复合析出物的面密度。随着铸带退火温度升高，冷轧组织中变形带宽度以及带内剪切带长度增加，初次再结晶织构中{111}〈112〉组分增强，{110}〈001〉晶粒所占比例增大。铸带退火有助于改善冷轧板高温退火过程中的二次再结晶行为，提升产品磁性能。     

柱状晶组织高硅电工钢二次再结晶的形成机理

  二次再结晶的发生会显著改变电工钢带材的组织和织构，进而影响其磁性能。以柱状晶组织高硅电工钢冷轧带材为研究对象，研究了不同退火方法对试样组织和织构的影响，明确了二次再结晶的发生条件、形成机理和控制方法。研究结果表明，柱状晶组织高硅电工钢冷轧试样发生二次再结晶的温度区间为850～1 000 ℃，在900 ℃退火可获得最大的晶粒尺寸。二次再结晶的形成是由于初次再结晶后试样的组织形成了织构抑制作用，小角度晶界抑制晶粒正常长大，大角度高能晶界迁移率高，具有大角度晶界的晶粒以取向长大方式发生二次再结晶。当退火温度高于1 000 ℃时，升温和冷却速率大于5 ℃/min可以有效抑制二次再结晶的发生。     

低温高磁感取向硅钢高温退火过程高斯晶粒的演变

对低温加热工艺生产的以AlN为主抑制剂的高磁感取向硅钢高温退火过程进行中断实验,借助电子背散射衍射技术对高温退火过程中高斯晶粒的演变进行了研究.在升温过程中高斯晶粒平均尺寸先减小再增大.800℃时取向分布函数图出现高斯织构组分,但强度很弱,高斯晶粒偏离角在10o以上;900℃时高斯晶粒平均生长速率超过其他晶粒;950~1000℃时高斯晶粒异常长大,偏离角3o~6o;在1000℃之前高斯取向晶粒相比于其他晶粒没有尺寸优势.      

Microstructural Characterization of Spray Formed FGH4095 Superalloy During Hot Deformation

 In order to study the hot workability and to optimize the processing parameters for spray formed FGH4095 superalloy, thermal compression tests for spray formed FGH4095 superalloy have been finished by using a Gleeble 1500 thermal simulated test machine at the strain rates of 0. 01-10. 0 s-1 and temperatures of 1050-1140 ℃. The effects of strain rate and deformation temperature on the true stress-true strain curves and microstructure evolution were investigated. The results show that the generation of dynamic recrystallization (DRX) depends sensitively on deformation temperature. When the temperature was lower than 1080 ℃, long and narrow necklace grains were shown in the microstructure. When the temperature increased to 1140 ℃, new recrystallization grains were generated. The size and shape of γ′ precipitates in the grains have a very important effect as factors of hindering sufficient migration of dislocations on plastic deformation. The result of thermal processing map is in accord with the microstructure observation, and the best material thermal processing temperature is above 1128 ℃.     

2Cr12NiMo1W1V超临界汽轮机叶片用耐热钢的热变形行为

 为了解决2Cr12NiMo1W1V耐热钢在锻造过程中晶粒粗大和组织不均匀的问题，利用Gleeble-3800热模拟试验机，在变形温度为1 000～1 200 ℃、应变速率为0.01～10 s－1、变形量为70%的条件下，研究和分析了2Cr12NiMo1W1V耐热钢的高温塑性变形和动态再结晶行为。结果表明，该耐热钢的真应力-应变曲线具有动态再结晶特征。再结晶晶粒尺寸随着变形温度的增加或应变速率的降低呈增加趋势，在变形温度为1 150～1 200 ℃，应变速率为0.01 s－1时，晶粒尺寸急剧增加。在真应力-应变曲线的基础上，建立了材料热变形本构方程，其热激活能为453.74 kJ/mol。根据峰值应力绘制了合金的热加工图并获得在各加工条件下的效率值，合金的最佳热加工区间为变形温度为1 000～1 150 ℃、应变速率为0.1～1 s－1以及变形温度为1 060～1 125 ℃、应变速率为0.1～10 s－1。     

不同退火工艺下TWIP钢微观组织及力学性能演变

摘要：以在650℃温轧的Fe-24Mn-2Al-1Si-0.05C TWIP钢为研究对象，通过金相显微镜(OM)、扫描电镜（SEM）、透射电镜（TEM）、室温拉伸等实验手段，研究温轧TWIP钢在回复退火、部分再结晶退火、高温短时退火以及高温退火等不同退火工艺下其微观组织及力学性能的演变。结果表明，随着退火工艺的改变，实验钢的微观组织由回复退火时包含高密度位错、形变孪晶等的变形晶粒逐渐向高温退火时的无畸变再结晶晶粒转变；而部分再结晶退火时，实验钢的微观组织由未再结晶区的变形晶粒和细小的再结晶晶粒混合组成。随退火工艺的改变，实验钢拉伸前、后的硬度变化趋势为先下降然后基本不变最后上升；实验钢的变形机制逐渐由位错滑移为主向孪生滑移为主转变。     

FGH96合金双道次热变形及其热加工图

采用Gleeble-1500热模拟试验机对FGH96合金进行双道次真应变量为0.6＋0.6和0.3＋0.9的等温间断热压缩试验,研究了变形温度为1050~1125℃、变形速率为0.001~0.1 s-1时合金的热变形行为和组织演变.热变形过程中合金发生了再结晶,第一道次较小的真应变量减轻了合金的开裂.当第一道次真应变量小时,随着温度和变形速率的上升,合金道次间再结晶软化率增加.不同应变量以及不同道次真应变量均对合金热加工图产生明显影响.在相同变形条件下,当能量耗散率随应变量的增加而下降时,合金中组织由细晶向粗晶转变,反之则由粗晶向细晶转变;当能量耗散率不随应变量的变化而变化时,能量耗散率低于20%的合金中出现大量的不完全再结晶组织,能量耗散率高于35%的合金中出现细小完全再结晶组织.