强磁场下奥氏体化温度对Fe-0．76％C钢先共析铁素体组织的影响

借助于光学显微镜研究12T磁场对Fe-0.76%C合金在不同奥氏体化温度下保温 30 min后以2 ℃/min冷却条件下先共析铁素体显微组织形貌变化.结果表明:在相同奥氏体化温度条件下,强磁场热处理样品中的先共析铁素体的面积分数和晶粒数量明显高于非磁场热处理样品中先共析铁素体的面积分数和晶粒数量.原因可归结为强磁场提高了先共析铁素体形核驱动力及强磁场使共析点向高碳高温方向移动.随着奥氏体化温度升高先共析铁素体晶粒沿着强磁场方向伸长的趋势明显越弱.奥氏体晶粒随着奥氏体化温度逐渐增大导致铁素体晶核之间的距离增大,从而造成奥氏体中的Fe原子向先共析铁素体晶粒扩散的距离增大的速度减慢所致.     

强磁场下保温时间对Fe-0.76%C钢先共析铁素体组织形貌的影响

 借助于光学显微镜研究了磁场（12 T）对Fe 0.76%C合金在807 ℃奥氏体化保温不同时间(10 min、30 min、60 min)后以2 ℃/min的冷速冷却后,先共析铁素体显微组织的形貌变化。结果表明：在相同奥氏体化保温时间下,经强磁场热处理样品的先共析铁素体的面积分数和晶粒数量明显高于无磁场热处理样品。这可归结为强磁场降低了先共析铁素体形核所需的驱动力。随着奥氏体化保温时间的延长先共析铁素体晶粒沿着强磁场方向伸长的趋势明显变弱。这主要是由于奥氏体晶粒随着奥氏体化保温时间的延长逐渐增大,导致铁素体晶核之间的距离增大,从而造成奥氏体中的Fe原子向先共析铁素体晶粒扩散的距离增大所致。     

强磁场下冷却速率对Fe-1.1％C合金中“反常”组织的影响

研究了强磁场下冷却速率对Fe-1.1％C钢中“反常”组织形貌及性能的影响.结果表明:强磁场下“反常”组织面积分数随冷却速率的增加而减小,这是由于快速冷却时原子扩散不能充分进行所致.在相同冷却速率条件下,经强磁场处理后样品与非磁场处理样品相比,“反常”组织面积分数明显增加,样品宏观硬度值下降.     

TiN析出对Fe-1．5％Mn-0．12％Ti-Si（〈1．1％）C（0．05％和0．15％）合金奥氏体晶粒大小的影响

为阐明非均匀分布的TiN粒子对抑制非稳定态下奥氏体晶粒长大的影响,Fe-1．5％Mn-0．12％Ti—Si（〈1．1％）-N（20～130ppm）-C（0．05％和0．15％）合金,在有Mg和无Mg脱氧条件下从1873K以50或5K／min的冷却速度冷却到1473K,然后淬火。检测了奥氏体晶粒大小分布与C、N和Si含量以及Mg脱氧和冷却速度的关系,发现在0．05％C时,均匀分布的TiN粒子抑制了γ晶粒的生长,没有观察到Si含量（0—1．1％）在给定C、N和Ti含量时对γ晶粒大小的影响。在Mg脱氧条件下,TiN＋MgO和TiN粒子数量是无Mg脱氧的2倍多,因此导致相似的γ晶粒大小。γ晶粒大小^-Dλ在0．05％C时随齐纳钉扎力的增加而减小,但在0．15％C时就并不如此。0．05％C50K／min冷速时的^-Dλ值比5K／min时的小,但0．15％C时^-Dλ值与冷却速度的关系是不同的,这可解释为0．05％C时,冷却速度降低,非均匀分布的TiN粒子数减少,但是0．15％C时,只有枝晶区域内的TiN粒子减少。     

退火温度对441铁素体不锈钢组织性能的影响

为探索超纯铁素体不锈钢热轧板材在退火过程中组织和力学性能的演变,对441进行了900～1 050 ℃的退火试验,利用OM、SEM和TEM表征了441在退火过程中显微组织的变化规律,并通过拉伸试验和冲击试验研究了退火温度对力学性能的影响.结果表明,随着退火温度升高,轧制组织发生再结晶,且晶粒逐渐长大.退火后441热轧板材...     

V析出对针状铁素体转变的影响

本文研究N与V结合成V（C,N）析出时对奥氏体分解成针状铁素体的影响。通过2种不同N含量的C—Mn—V钢,在2种不同奥氏体化温度,即不同奥氏体晶粒尺寸下的连续冷却转变图（CCT）,分析了V（C,N）在晶内析出的形核能。结果表明,奥氏体分解成针状铁素体,必须具备2个条件：首先,奥氏体内须有一定量的V（C,N）析出;第二,用先共析铁素体在奥氏体晶界形成而不形成贝氏体。第二部分研究奥氏体等温分解时,析出物对针状铁素体形成动力学的影响。     

退火温度对铁素体不锈钢Y0Cr17SiS组织和性能的影响

热轧状态下的铁素体不锈钢Y0Cr17SiS综合性能较差,不能满足加工使用要求,需进行退火处理,研究了退火温度750℃、800℃、850℃、900℃对Y0Cr17SiS钢Φ11 mm热轧材的组织和性能的影响.结果表明,经900℃2 h空冷退火,Y0Cr17SiS钢组织均匀、无析出物产生,抗拉强度为510 MPa,断后延伸...     

Fe-0：5％C合金自由枝晶的长大—二三维相区模拟和LKT模型

采用带有稀薄-界面-限制参数的三维相区模型研究了Fe-0．5％C合金的自由枝晶长大过程。在不同过冷度条件下,确定了枝晶长大速度和顶端曲率半径,然后估算了合金的稳定性参数。将用相区模拟得到韵枝晶长大速度与那些通过稳定性参数LKT模型得到的结果相比较,稳定性参数为0．05,结果表明两者吻合性较好。同时讨论了LKT模型在实践应用的有效性。     

Fe基块体非晶合金的结构转变及其对力学性能的影响

通过铜模吸铸法制备了尺寸不小于2 mm的块体非晶合金Fe45Co7Cr14Mo10Y2B6C15,采用热处理的方式实现非晶合金的结构转变过程,通过组织形貌观察及热力学分析表征非晶合金的结构变化,并且就非晶合金的结构转变对压缩强度及硬度的影响进行了探讨。试验结果表明:非晶合金的结构转变受热力学和动力学因素共同影响;而晶化相的存在会对力学性能产生影响,含部分晶化相的非晶合金硬度升高,压缩强度下降。     

Influence of magnetic field on the kinetics of proeutectoid ferrite transformation in iron alloys

The kinetics of proeutectoid ferrite transformation in Fe-C base alloys in a strong magnetic field (7.5 T) were studied. The transformation kinetics were accelerated at temperatures not only below but also significantly above the Curie temperature. The free energy and equilibrium ferrite/austenite phase boundaries in applied magnetic fields were calculated using the reported experimental magnetic susceptibility and Weiss molecular field theory. The persistence of magnetic field effects above the Curie temperature can be attributed to the rapidly diminishing difference in relative stability between ferrite and austenite toward the Ae ₃ temperature of iron.     

磁场对镍基Ni-Mn-Ga铁磁合金相变温度影响的热力学分析

通过测量磁化曲线、电阻-温度关系和热分析等手段,研究了磁场对镍基铁磁合金试样Ni-Mn-Ga相变的影响.结果表明：在磁场作用下相变温度升高了约1.5 K,具有明显的磁场影响特征.利用马氏体相变热力学理论,研究了磁场对镍基铁磁合金化学自由能和非化学自由能与温度的变化关系,建立了其作用的数理模型,并与实验结果比较后基本吻合.     

强磁场对铁基合金相变温度和显微组织的影响

The effect of a high magnetic field up to 30 T on phase transformation temperature and microstructure of Fe-based alloys has been reviewed. A high magnetic field accelerates ferrite transformation, changes the morphology of the transformed microstructures and increases the As and A1 temperature. In a magnetic field of 30 T, the A1 temperature increases by about 37.1℃ for Fe-0.8C, the A3 temperature for pure Fe increases by about 33.1 ℃. The measured transformation temperature data are not consistent with calculation results using Weiss molecular field theory. Ferrite grains are elongated and aligned along the direction of magnetic field in Fe-0.4C and Fe-0.6C alloys by ferrite transformation, but elongated and aligned structure was not found in pure Fe, Fe-0.05C alloy and Fe-1.5Mn0.11C-0.1V alloy.     

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.     

Formation mechanism of bainitic ferrite in an Fe-2 Pct Si-0.6 Pct C alloy

The bainite transformation at 723 K in an Fe-2 pct Si-0.6 pct C alloy (mass pct) was investigated with transmission electron microscopy (TEM) and quantitative metallography to clarify the growth mechanism of the ferritic component of bainite. In early stages of transformation, the bainitic ferrite was carbide free. The laths of bainitic ferrite within a packet were parallel to one another and separated by carbon-enriched retained austenite. The average carbon concentration of the bainitic ferrite was estimated to be 0.19 mass pct at the lowest, indicating that the ferrite was highly supersaturated with respect to carbon. The laths did not thicken during the subsequent isothermal holding, although they were in contact with austenite of which the average carbon concentration was lower than the paraequilibrium value. In the later stage of transformation, large carbide plates formed in the austenite between the laths, resulting in the decrease in the carbon concentration of the austenite. Subsequently, the ferrite with a variant different from the initially formed ferrite in the packet was decomposed for the completion of transformation. The present results indicate that the bainitic ferrite develops by a displacive mechanism rather than a diffusional mechanism. Formerly Graduate Student, Kyoto University, Kyoto 606-01, Japan This article is based on a presentation made at the Pacific Rim Conference on the “Roles of Shear and Diffusion in the Formation of Plate-Shaped Transformation Products,” held December 18-22, 1992, in Kona, Hawaii, under the auspices of ASM INTERNATIONAL’S Phase Transformations Committee.     

Formation and annealing behavior of nanocrystalline ferrite in Fe-0.89C spheroidite steel produced by ball milling

Nanocrystalline ferrite formation by ball milling in Fe-0.89C spheroidite steel and its annealing behavior have been studied through microstructure observations and microhardness measurements. It was found that at the early stage of ball milling, the dislocation density increases and dislocation cells form due to plastic deformation. At the middle stage of ball milling, a layered nanocrystalline structure forms near the surface of the powder by localized severe deformation. The microhardness of nanocrystalline ferrite (10 GPa) is much higher than that of work-hardened ferrite (4 GPa). Together with the nanocrystallization of ferrite, the dissolution of cementite was observed. At the final stage of ball milling, equiaxed nanocrystalline ferrite forms from layered nanocrystalline ferrite by increasing the local misorientation. By annealing the milled powders, recrystallization was observed in the workhardened ferrite region, while in the nanocrystalline ferrite region, a slow grain growth was observed instead of recrystallization.     

连续冷却过程中铁素体相变温度的模拟

以传统的形核理论为基础,考虑了变形的影响,研究了奥氏体-铁素体相变的等温相变孕育期,采用Scheil的可加性法则计算了SS400钢在变形和未变形条件下的铁素体相变实际转变温度（Ar3）,并与实测值进行了对比,结果表明：计算的Ar3与实测的Ar3吻合良好,从而进一步表明该相变孕育期模型的准确性．