X120管线钢中含镁夹杂物对形变奥氏体及γ-α相变的影响

 对微镁处理X120管线钢轧制工艺进行热模拟,发现含镁夹杂物可以在形变奥氏体细化与再结晶时起到形核核心的作用,同时晶界夹杂物还有晶内铁素体诱导的双重作用。含镁夹杂物还可以在小于20µm甚至10µm的形变奥氏体内直接诱导晶内铁素体形核,部分夹杂物也有在形变奥氏体内间接诱导晶内铁素体形核的作用。     

Al对稀土处理C-Mn钢连续冷却组织转变的影响

研究Al预脱氧对Ce处理钢夹杂物和显微组织的影响,利用热力学计算、带能谱的扫描电镜和DIL805A热膨胀仪检测进行了对比研究。得到如下结论:Ce处理后钢中的主要夹杂物从MnS转变为Ce2O2S+MnS,Al脱氧能使Ce处理钢中夹杂物转变为CeAlO3+Ce2S3+MnS。Ce处理C-Mn钢连续冷却过程有利于获得晶内铁素体的冷速为2~8℃/s。Al脱氧能改变诱导晶内铁素体形核的核心夹杂物种类,诱导铁素体形核的能力降低,且Al能够使Ce处理钢连续冷却组织转变(CCT)曲线向左上方移动,促进铁素体在晶界形核,不利于Ce处理后晶内铁素体的形成。Al脱氧Ce处理C-Mn钢在冷速为2~5℃/s时,由于夹杂物核心成分的改变与Al合金化作用导致晶内铁素体含量较未用Al脱氧Ce处理钢少。     

钛-镁处理对低碳钢夹杂物和组织的影响

通过实验室对低碳钢进行钛-镁处理研究,利用BX51M金相显微镜观察钢的微观组织,以JSM-6510LV扫描电镜为平台,利用SEM-EDS研究钢中夹杂物的形貌、成分,探讨MnS的析出与贫锰区机制之间的内在关联性,澄清MnS在诱导形核现象中的作用。结果表明:经过钛-镁处理后,钢的晶粒得到明显细化; Ti-Mg-Al复合夹杂物能够通过诱导晶内铁素体形核细化晶粒; MnS的存在与晶内铁素体的形成之间没有直接联系。     

20MnSi中夹杂物对针状铁素体形成的影响

 通过热模拟试验对20MnSi连续冷却过程中的相变规律进行了测定,通过电石、硅钙线脱氧及热处理得到了含有晶内针状铁素体试样,利用显微硬度仪对针状铁素体聚集区进行了显微硬度的测定,利用光学显微镜对晶内针状铁素体进行了形貌观察,利用扫描电镜和能谱仪对诱导针状铁素体生成的夹杂物的性质进行了分析。结果表明,20MnSi中可以形成晶内针状铁素体的冷却速度范围为5～20 ℃/s;能够诱发针状铁素体组织形核的夹杂物主要为MnS夹杂,其次为MnO·SiO2和MnS·SiO2夹杂,并且3类夹杂物的尺寸主要在小于3 μm的区间内;MnS夹杂促进针状铁素体形核是由应力-应变能和惰性界面能等原因共同造成的;高温加热和等温保温有利于使贫锰区减弱或消失,不利于针状铁素体的形成;高熔点夹杂物有利于诱导针状铁素体的形核,复合夹杂物和镶嵌存在的夹杂物可以为针状铁素体的形核提供多个合适的形核区,有利于促进多个针状铁素体的同时形核、长大。     

X120管线钢镁铝尖晶石对形变奥氏体及γ→α相变的影响

对微镁处理X120管线钢轧制工艺进行热模拟,发现镁铝尖晶石可以在形变奥氏体细化与再结晶时起到形核核心的作用,同时晶界夹杂物还有晶内铁素体诱导的双重作用。镁铝尖晶石还可以在晶粒粒径小于50μm甚至10μm的形变奥氏体内直接诱导晶内铁素体形核,部分夹杂物也有在形变奥氏体内感生形核的作用。     

晶内铁素体及其组织控制技术研究概况

介绍了晶内铁素体的组织特点以及晶内铁素体组织对钢材力学性能的影响,得出晶内铁素体能显著提高钢的冲击韧性。详细阐述了晶内铁素体的形核机理,分析表明目前晶内铁素体形核机理仍不够完善,尚未形成统一的机制。同时介绍了钛氧化物、MnS、稀土氧化物等促进晶内铁素体形核的夹杂物,指出含Ti复合夹杂物是理想的晶内铁素体形核核心。最后分析了夹杂物尺寸、冷却速度对晶内铁素体形核的影响,并简述了一些晶内铁素体组织控制技术,结果表明Ti-B 处理、Ti-Mg处理效果优于单独的Ti处理。     

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。     

非调质中碳钢晶内铁素体形核影响因素的研究

研究了非调质中碳钢晶内铁素体形核的影响因素。运用金相显微镜和扫描电子显微镜等设备,从夹杂物的尺寸、分布和种类三方面探究其对晶内铁素体形核长大的作用,进一步为高质量洁净钢冶炼提供理论依据。试验结果表明,夹杂物成分为Al2O3、Ti N、VN等时最佳诱导等轴型铁素体的尺寸为2~4μm;等轴型铁素体包裹夹杂物的分布最有利于铁素体的生长;Mn S析出于Ti N表面非常有助于诱发晶内铁素体。     

氧化物冶金技术应用及进展

氧化物冶金是利用钢中细小非金属夹杂物诱导晶内铁素体形核细化晶粒的新技术。应用氧化物冶金技术已成功开发出了高强度高韧性的非调质钢和低碳钢。文章讨论了氧化物冶金类型钢的显微组织特征,分析了钢中非金属夹杂物的性质和晶内铁素体的形核机理,简述了氧化物冶金技术的应用前景。利用钢中细小的氧化物,通过促进晶内针状铁素体形核明显改善焊接热影响区的组织,成为大线能量焊接用钢有效的技术途径。     

Ce/Ce-Zr夹杂物诱导高强船板钢中针状铁素体形核行为的研究

研究了FH40高强船板钢经稀土合金化处理后夹杂物诱发铁素体的变化行为,利用扫描电子显微镜（SEM）和能量衍射谱（EDS）等手段观察分析了钢中稀土夹杂物的形貌特征以及诱发形成IAF的行为机制。研究结果表明：经Ce或Ce-Zr复合处理后,稀土复合夹杂物形状得到球化,且均能诱发针状铁素体形成;单独Ce处理形成的Al-Ce-O+MnS夹杂物诱导针状铁素体行为可用贫Mn区机制和惰性基底机理解释,而Ce-Zr复合处理形成的CeZr-O+MnS夹杂物诱导针状铁素体行为只能用贫锰区机制解释。     

Effect of sulfur content on the microstructure and toughness of simulated Heat-Affected zone in Ti-Killed steels

Four Ti-killed steels were made to study the specific influence of sulfur on the inclusion, microstructure, and toughness of a simulated heat-affected zone (HAZ). The HAZ toughness was mainly determined by the volume fraction of intragranular acicular ferrite (IAF) which was closely related to the supercooling required to initiate austenite to ferrite transformation. The extent of supercooling was strongly influenced by the composition of grain boundary and inclusions. Sulfur addition up to 102 ppm caused a segregation of sulfur to the grain boundaries and a change of inclusion phase from predominantly Ti-oxides to Ti-oxysulphides and MnS. This behavior, in turn, suppressed the formation of polygonal ferrite and promoted the formation of IAF. Further addition of sulfur elevated transformation temperature and promoted the formation of polygonal ferrite due to the refinement of grain size and the increase of grain boundary associated inclusions. A methodology was proposed to evaluate the intragranular nucleation potential of inclusions, and the results showed that Ti-oxysulphides possessed better nucleation potential for IAF than Ti-oxides and MnS. With the lowest transformation temperature and most effective nuclei, the best HAZ toughness can be obtained at sulfur content of 102 ppm due to the achievement of the maximum volume fraction of IAF.     

Effect of SiMg alloy on inclusions and microstructures of 16Mn steel

Abstract

The effects of cooling methods and Mg content on the inclusions and microstructures of 16Mn steel were observed, and the mechanism of intragranular ferrite nucleation induced by Mg containing inclusions is discussed. The results show that trace amounts of Mg in steel can induce intragranular ferrite nucleation. With increasing Mg content, the percentage of intragranular ferrite increases, while the optimum Mg content is ～0·0048 wt-%. The appropriate cooling methods are furnace cooling to 1473 plus water cooling and water cooling. The lattice disregistry among MgAl₂O₄, MgO and ferrite–Fe phase is very small, and there is a Si enriched zone on the inclusions, which both contribute to the nucleation of intragranular ferrite.     

Influence of Prior Austenite Deformation and Non-Metallic Inclusions on Ferrite Formation in Low-Carbon Steels

Effects of prior austenite deformation and non-metallic inclusions on the ferrite nucleation and grain refinement of two kinds of low-carbon steels have been studied. The ferrite nucleation on MnS and V(C,N) is observed. The combination of thermomechanical processes with adequate amounts of non-metallic inclusions formed in low-carbon steels could effectively refine the grain size and the microstructure. Ferrite nucleated on the single MnS or V(CN) inclusions and complex MnS+V(C,N) inclusion. The proper addition of elements S and V could effectively promote the formation of ferrite and further refinement of ferrite grains.     

Influence of Prior Austenite Deformation and Non-Metallic Inclusions on Ferrite in Low Carbon Steels

 Abstract Effects of prior austenite deformation and non-metallic inclusions on the ferrite nucleation and grain refinement of two kinds of low carbon steels have been studied. The ferrites nucleation on MnS and V(C,N) is observed. The combination of thermal-mechanical processes with adequate amounts of non-metallic inclusions formed in low carbon steels could effectively refine the grain size and the microstructure. Ferrite nucleated on the single MnS or V(C,N) inclusions and complex MnS+V(C,N) inclusion. The proper addition of elements S and V could effectively promote the formation of ferrite and further refinement of ferrite grains.     

硫含量对中碳非调质钢中硫化物及组织的影响

利用真空感应炉冶炼了不同硫含量的中碳非调质钢,研究了S含量对非调质钢中硫化物形态分布及显微组织的影响．结果表明:在0．025％~0．065％范围内,随S质量分数的增加,非调质钢中硫化物的数量增多,偏聚分布现象加重;晶内铁素体比例随之升高,组织得到细化．通过热力学计算及相图信息研究了硫化物的类型转变．S含量增加时第Ⅲ类MnS在凝固末期以离异共晶形式较早析出,剩余液相中的S在凝固结束时以共晶形式析出为第Ⅱ类MnS．单独MnS以及MnS-V（C,N）复合硫化物均可作为晶内铁素体的有效形核核心,促进铁素体的生成．      

Upper acicular ferrite formation in a medium-carbon microalloyed steel by isothermal transformation: Nucleation enhancement by CuS

The isothermal transformation vs time of a medium-carbon microalloyed steel at 450 °C, following austenitization at 1250 °C for 45 minutes, has been investigated using optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). At short times, the fine microstructure of acicular ferrite is nucleated at MnS inclusions, which are covered by a shell of a hexagonal CuS phase. The special orientation between MnS and the CuS crystals of this shell enables the formation of a low-energy interface between the ferrite and the inclusion with, at the same time, the ferrite satisfying one of the 24 variants of the orientation relationship into the Bain region with austenite. As the treatment times are increased, the increase in the volume fraction of acicular ferrite being formed raises the carbon concentration of the austenite, such that some retained austenite instead of martensite is observed for these intermediate treatment times. This retained austenite transforms to ferrite plus carbides at long treatment times, resulting in a final microstructure of acicular ferrite, very similar in nature to those encountered in the case of upper bainite formation.