含钛低碳钢晶内铁素体形核机制研究

对含钛低碳钢的晶内铁素体（IGF）的形核机理进行研究,结果表明：含钛低碳钢中IGF的形核核心主要是外层包裹着MnS的Ti2O3复合夹杂物粒子,IGF形核过程是由应变诱导机制和贫Mn区机制的共同作用完成。     

钛夹杂物细化管线钢热影响区组织研究现状

阐明了钢中夹杂物（氧化物冶金技术）对焊接热影响区组织的影响,综述了钢中各种含钛夹杂物对晶内铁素体的形核机制的研究概况,包括钛脱氧、Ti- Mg复合脱氧、Ti- Nb- N复合脱氧、Ti- Al复合脱氧及Ti- Mn- Si复合脱氧等几项措施,探讨了在这些措施下,如何对铁素体的形成提供最佳条件。最后,对钛夹杂物细化管线钢焊缝组织研究的发展做出了展望。     

30 t转炉-钢包吹氩-连铸生产A级船板钢中的非金属夹杂

用电解法和扫描电镜（SEM）分析研究30t顶吹氧气转炉-钢包吹氩-150mm×1050mm板坯连铸工艺生产的A级船板钢（％：0．16C、0．21Si、0．50Mn、0．011P、0．027S）中的非金属夹杂的组成、尺寸、数量和分布。结果表明，A级船板钢中的夹杂物包括硅酸盐、铝硅酸盐、硫化物以及铝硅酸盐-硫化物复合夹杂物。钢水二次氧化及耐火材料外来夹杂抵消了吹氩去除夹杂物的冶金效果。增强中间包去夹杂能力可减少钢中大尺寸夹杂物。     

Fe-Si-B合金中非金属夹杂物的热力学分析

利用扫描电镜及能谱仪对Fe-Si-B合金中非金属夹杂物组成进行了分析，并研究了氧化物及硫化物夹杂在熔炼过程中的演变规律及其形成条件.研究结果表明：Fe-Si-B合金中夹杂物主要有Al、Si的氧化物，以及少量Ti、Mn的硫化物.经热力学计算，在1623 K下，熔炼初期主要为Al的氧化过程，当熔体中[Al]的质量分数降低至0.0022％后才发生Si的氧化；Ti及Mn的硫化物在1623 K下不能形成，需熔体分别冷却至1550和1310 K下才可形成.     

低碳钢快速凝固过程中针状铁素体在硫化物夹杂中的形核

细晶显微结构可以同时提高钢的强度和韧性。通过在夹杂物内形成细化的颗粒内针状铁素体形核可以使铁素体显微组织细化,因此,人们广泛关注该铁素体显微组织在冶金焊接性能和其它冶金领域的应用。由于在轧制工艺中有可能使细化显微组织减少,所以在带坯连铸和板坯连铸工艺中,细化铸态显微组织也同样非常重要。本文通过光学显微镜、扫描电子显微镜（SEM）和透射电子显微镜（TEM）,研究了在钢的快速凝固过程中,不加入任何特殊合金化元素,颗粒内针状铁素体在硫化物夹杂中形核的可能性,同时也通过背散射电子衍射（EBSD）分析,研究了针状铁素体的聚集取向。试验发现：试样中的氧化物夹杂和硫化物夹杂非常普及,而且仅观察到硫化物夹杂有助于针状铁素体的形核,此外详细讨论了针状铁素体在现有试样中形成的可能机理,那些区域可能是在夹杂物周围附近锰的消耗区和磷的富集区。     

钛脱氧钢中超细夹杂物内部结构和物相组成研究

在真空感应炉中采用了真空碳脱氧再加钛终脱氧的脱氧工艺冶炼出了与高级别管线钢成分接近的试样钢,对钛脱氧钢中超细夹杂物的外部形貌、尺寸、内部结构和物相组成等进行了研究。在扫描电镜下通过对金相试样和电解提取的夹杂物的研究表明,钢中夹杂物是Ti-O-Mn-S形成的尺寸为1~3μm的球形复合夹杂物。通过离子减薄后观察了夹杂物的内部结构,中心是Ti-O化合物,外围是Mn-S化合物;通过电子背散射衍射(EBSD)对夹杂物物相组成的分析表明,该复合夹杂物是有利于针状铁素体(IGF)形核的Ti2O3和在凝固过程中以Ti2O3为核心形核的MnS。     

低硫微合金钢中MnS析出及晶内铁素体形成研究

采用真空感应炉冶炼Al-Si-Mn-Ti复合脱氧的低硫微合金钢,通过热力学计算对钢液凝固过程中Mn S析出规律进行分析,运用带X射线能谱分析仪的场发射扫描电镜对夹杂物形貌、尺寸和成分以及Mn S在复合氧化物上的析出形态进行分析。结果表明:Mn S的析出主要受液相中Mn、S含量和液相温度控制。Mn-Si,Mn-Ti,Al-Mn-Ti,Al-Mn-Si复合氧化物都能作Mn S析出的核心,Mn S在硅锰氧化物表面呈镶嵌状析出,在钛锰氧化物表面呈包裹状析出,还可溶解在铝钛锰和铝硅锰氧化物的内部。诱发IGF形核的复合夹杂物尺寸为2~3μm。     

非调质厚板材焊接热影响区晶内铁素体相变研究

研究了添加微量元素（Ti、V、Zr、Nb）低合金高强度钢焊接热影响区（HAZ）晶内针状铁素体（IGF）的形成机理，并采用TEM和EDS观察和分析HAZ中晶内针状铁素体形成核心的化学成分和结构及核心周边锰含量变化。结果表明：添加微量元素可有效阻止HAZ晶粒粗大化，抑制离异珠光体出现；HAZ中以ZrO2氧化物为核心形成的复合化合物ZrO2＋（Zr，Ti）2O5＋MnS＋V（C、N）＋NbN能有效促进IGF形成；复合化合物周围的MnS造成复合化合物周围约40nm的Mn贫化区，Mn贫化区锰含量大小与生成IGF量有良好对应关系。     

微量钛镁复合处理对低碳钢中夹杂物和组织的影响

对低碳钢进行钛镁复合处理,通过SEM-EDS和金相显微镜表征钢中夹杂物的特征(种类、尺寸、分布)和微观组织变化,探讨夹杂物诱导形核的可能机制。结果表明:钛镁复合处理后,钢中77%的夹杂物尺寸小于4μm,单位体积的夹杂物数量提高了48%;(Ti,Mg)Ox-MnS型复合杂物具有促进晶内铁素体形核的能力;贫Mn区是(Ti,Mg)Ox-MnS型复合夹杂物诱导晶内铁素体形核的可能机制。     

氧含量对硫系易切削钢切削性能的影响

研究了氧含量对硫系易切削钢中硫化物夹杂及对切削性能的影响。结果表明：在一定范围内,钢中氧含量越高越有利于改善切削性能,其原因是氧含量高时,钢中会形成大量的纺锤形（Mn、Fe）（S、O）复合夹杂物。在切削过程中,这类硫化物能割断基体的连续性,在刀具表面形成一层保护膜,从而降低刀具的磨损。实验室切削试验表明：w（O）=0．014％时,硫系易切削钢的切削性能优于45钢,能够获得理想的切削性能。     

Effects of Cerium Addition on Inclusions and Solidification Structure of a Low-Nickel Si–Mn-Killed Stainless Steel

The effect of cerium on inclusions and solidification structure of a low-nickel Si–Mn-killed stainless steel is studied using laboratory experiments. When the cerium content in steel increased from 0 to 250 ppm, modification sequence of inclusions is Si–Mn(–Al)–O and MnS → Ce–Si–Mn–O–S → Ce(–Si)–O–S → CeS and CeC₂. The number density and area fraction of inclusion first decrease with the increase in the cerium content and then increase due to the formation of CeC₂ inclusions when the cerium content is bigger than 150 ppm, which is precipitated in solid steel during solidification. When the cerium content increases from 0 to 250 ppm, the fraction of equiaxed grain zones of steel ingot first increases and reaches a maximum value when the cerium content is 54 ppm; then the fraction of equiaxed grain zones decreases with the increase of the cerium content. 2D lattice misfit calculations are performed and it is found that there are no heterogeneous nucleation cores in the steel without cerium during solidification. For the steel with cerium, Ce_4.67Si₃O₁₃, Ce₂O₂S, and CeS inclusions act as heterogeneous nucleation cores, increasing the fraction of the equiaxed grain zone. Bigger effective heterogeneous nucleation cores number density leads to a larger fraction of the equiaxed grain zone.     

Heterogeneous Nucleation of α-Al Grain on Primary α-AlFeMnSi Intermetallic Investigated Using 3D SEM Ultramicrotomy and HRTEM

Microstructural examination of the Al-5.3Mg-2.4Si-0.6Mn-1.0Fe alloy in the die-cast condition revealed that a significant number of the primary α-AlFeMnSi intermetallic particles were found inside both the coarse α-Al dendrite fragments formed in the shot sleeve and the fine α-Al grains formed in the die cavity. The heterogeneous nucleation of α-Al phase on primary α-AlFeMnSi intermetallic particle was further investigated experimentally. 3-Dimension (3D) scanning electron microscopy ultramicrotomy revealed that the probability of finding at least one primary α-AlFeMnSi intermetallic particle inside each α-Al grain was almost 90 pct. The detailed microstructural analysis identified the primary α-AlFeMnSi intermetallic particle as the α-Al₁₂(Fe,Mn)₃Si composition with a body-centered cubic structure and a lattice parameter of a = 1.265 nm. It was found that the primary α-Al₁₂(Fe,Mn)₃Si intermetallic particle had a faceted morphology with {110} planes exposed as its natural surfaces. High resolution transmission electron microscopy further confirmed that the crystallographic orientation relationship between α-Al₁₂(Fe,Mn)₃Si intermetallic particle and α-Al phase was: [111]_α-AlFeMnSi//[110]_Al and (1 \( \overline{1} \) 0)_α-AlFeMnSi~6 deg from (1 \( \overline{1} \) 1)_α-Al, and the corresponding interface between two phases could be confirmed as a semi-coherent interface with a lattice misfit of 2.67 pct at 933 K (660 °C), which was considerably smaller than the theoretical limit (5.7 pct) for epitaxial nucleation. Finally, based on these experimental evidences and the epitaxial nucleation model, we concluded that the primary α-Al₁₂(Fe,Mn)₃Si intermetallic particles were both potent and effective nucleating substrates for the α-Al phase.     

Nucleation Behavior Analysis of Intragranular Acicu-lar Ferrite in a Ti-killed C-Mn Steel

By using a Gleeble 3500Dthermo-mechanical simulator,the nucleation behavior of intragranular acicular ferrites(IAF)was studied in a Ti-killed C-Mn steel.During continuous cooling transformation,the allotriomorphic ferrite(AF)and ferrite side plate(FSP)microstructures grew more rapidly with the temperature decreasing from800to 650℃,and the IAF microstructure was dominant within austenite grain with further cooling to 600℃.The diffusion bonding experiment and the effect of C,Mn and Si concentrations on the Ae3temperature by thermodynamic calculation confirm that Ti2O3itself absorbs neighboring Mn atoms to form Mn-depleted zone(MDZ),which promotes the nucleation of IAF microstructure effectively.High temperature holding tests indicate that the nucleation potential of IAF microstructure was lowered in the Ti-killed C-Mn steel when it was treated at high temperature(1 250℃)for a longer time,which is attributed to the saturated absorption degree of Mn atoms by titanium oxide.     

等温温度对低碳齿轮钢带状组织的影响

通过计算铁素体形核孕育期和形核率探讨了等温温度对带状组织的影响机理,并观察了齿轮钢SAE8822H(/%:0.22C、0.20Si、0.98Mn、0.60Cr、0.46Ni、0.36Mo)在管式炉经930℃10 min降至703～579℃等温1h空冷,或710～570℃等温处理2 h炉冷后钢中带状组织演变。结果表明,贫、富溶质区铁素体形核孕育时间差和铁素体形核率差异是造成等温转变时产生带状的原因;等温温度降低时,贫、富溶质区的孕育期时间差缩短,相对形核率减少,带状减轻;齿轮钢SAE8822H在570℃等温可使带状组织消失,这时相对形核率为6.3%。     

Heterogeneous nucleation of solidification of Si by solid AI in hypoeutectic Al-Si alloy

Melt-spun Al-3 wt pct Si with and without ternary additions of Na and Sr has been heat-treated above the Al-Si eutectic temperature in a differential scanning calorimeter to form a microstructure of Al-Si eutectic liquid droplets embedded in the α-Al matrix. During subsequent cooling in the calorimeter, the heterogeneous nucleation temperature for solidification of Si in contact with the surrounding Al matrix depends sensitively on the alloy purity, with a nucleation undercooling which increases with increasing alloy purity from 9 to 63 K below the Al-Si eutectic temperature. These results are consistent with Southin’s hypothesis that low levels of trace P impurities are effective in catalyzing Si nucleation in contact with the surrounding Al matrix. With a low Al purity alloy, 0.1 wt pct Na addition increases the Si nucleation undercooling from 9 to 50 K, 0.15 wt pct Sr addition does not affect the Si nucleation temperature, and 0.3 wt pct Sr addition decreases the Si nucleation undercooling from 9 to 3 to 4 K. The solidified microstructure of the liquid Al-Si eutectic droplets embedded in the Al matrix depends on the Si nucleation undercooling. With low Si nucleation undercooling, each Al-Si eutectic liquid droplet solidifies to form one faceted Si particle; however, with high Si nucleation undercooling, each Al-Si eutectic droplet solidifies to form a large number of nonfaceted Si particles embedded in Al. Formerly with the Oxford Centre for Advanced Materials and Composites, Department of Materials, Oxford University     

The kinetics of ferrite nucleation at austenite grain edges in Fe-C and Fe-C-X alloys

Nucleation kinetics of proeutectoid ferrite allotriomorphs at the edges of austenite grains in Fe-C and Fe-C-X alloys, where X is successively Mn, Ni, Co, and Si, have been measured using a modification of the techniques previously developed to study nucleation at grain faces. Analysis of these data with classical heterogeneous nucleation theory has shown that ferrite nuclei formed at grain edges have low energy interphase boundaries. An equivalent conclusion was reached during our previous studies of ferrite nucleation at austenite grain faces. The influence of alloying elements on nucleation rates was also found to follow a pattern similar to that demonstrated for grain face nucleation. Formerly Graduate Student with the Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon University,     

The kinetics of martensite formation in small particles

The kinetics of martensite nucleation in “atomized” particles of Fe-24.2 Ni-3.6 Mn and Fe-22 Ni-0.49 C have been investigated as a function of particle size (10 to 140 μ) and reaction temperature. The dependence of particle fraction transformed on particle size indicates that martensite nucleates at surface or near-surface sites for the Fe?Ni?C powder and throughout the bulk for the Fe?Ni?Mn powder. It is shown that, in contrast to kinetic measurements on bulk samples where autocatalysis predominates, the present technique measures reaction rate due solely to the sites present initially. The measurements show that there is no detectable incubation time for nucleation and that the nucleation sites have a specific distribution of activation energies. A method for extracting the distribution from experimental measurements is given and the result is used to develop a revised equation for describing isothermal martensite formation. The isothermal kinetics of martensite formation in Fe-22 Ni-0.49 C are investigated despite the fact that such measurements are not possible in bulk samples because the alloy transforms by “bursting”. It is found that the apparent activation entropy for martensite nucleation is significantly higher for this alloy than for Fe-24.2 Ni-3.6 Mn. This suggests that the dislocation-dislocation interactions at the critical nucleation step are longer-range in the Fe?Ni?C alloy than in the Fe?Ni?Mn alloy.     

含Ca汽车控制臂用钢中复合硫化物控制机理

 汽车控制臂由于形状复杂,切削量大,部分汽车控制臂用钢在加入质量分数0.03%硫元素的基础上,又进一步添加了少量钙元素,希望将钢中常见的细长条状MnS转变为纺锤状(Ca, Mn)S以增加零件的切削性能。然而,硫质量分数为0.03%时,钙元素在钢液中的溶解度很低,冷却和凝固过程单一的纯(Ca, Mn)S生成量极少。因此,提出了利用钢液中生成的含CaO类的氧化物来诱导(Ca, Mn)S在其外围形核长大,形成大量双层结构复合硫化物的形貌控制机理。为了研究最佳双层结构复合硫化物形成机理,选取了3炉不同冶炼工艺的汽车控制臂用钢,利用带能谱分析的电子扫描显微镜观察了铸坯和轧材中典型复合硫化物形貌、成分特征,并手动测量了其尺寸,最后利用热力学软件FactSage计算了钢中夹杂物的生成行为。研究结果表明,当钢中不进行钙处理时,复合硫化物内部氧化物主要为Al₂O₃或低MgO比例的镁铝尖晶石,外围硫化物为纯MnS,轧制后成细长条状。当钢中进行钙处理后,可以得到两种不同类型的复合硫化物。一种内部氧化物中CaO组元含量较高,外围硫化物主要是高CaS比例的(Ca, Mn)S,基本不变形,成典型的D类或Ds类形貌;另一种核心氧化物中CaO组元低,外围硫化物主要是低CaS比例的(Ca, Mn)S,轧制后成纺锤状。控制钙处理后钢液氧化物中合适的CaO比例使得氧化物既具有高效的硫化物形核能力,又能促进合适CaS比例的(Ca, Mn)S在其外围生成,这是钢中得到大量纺锤状双层结构复合硫化物的关键。当钢中Ca/S比约为0.07时,外围硫化物中的钙元素质量分数为2%~5%最为理想。     

Formation of Intragranular Ferrite During Isothermal/Thermomechanical Processes in a Medium Carbon V-Ti-N Microalloyed Steel

For a V-Ti-N microalloyed steel with 0.34%C-1.54%Mn,intragranular ferrite (IGF) was obtained in both isothermal austenite decomposition processes and thermomechanical processes simulating the industrial seamless tubing manufacture process.Results show that with decrease of the isothermal temperature in range of 600℃ down to 450℃,not only the morphology of IGF changed from equiaxed to acicular,but also the equiaxed IGF and the acicular IGF were refined.More importantly,it is found that the amount of equiaxed ferrite increased significantly in the thermomechanical process sample water quenched from 550℃ after 800℃ deformation than that in the isothermally treated sample at 550℃ sample without hot deformation.It implies that appropriate controlled deformation with controlled cooling can significantly promote equiaxed IGF formation,and not solely rely on nucleation mechanisms related with inclusions.Hot deformation of austenite without dynamic and complete static recrystallization causes high energy regions,therefore further promotes the nucleation potency of IGF.