重轨钢加热过程中MnS夹杂物形态

采用共聚焦激光扫描显微镜对重轨钢铸坯中MnS夹杂在连续升温过程中的变化进行了动态原位观察.结果表明,由于扩散和固溶影响,随温度的升高,MnS夹杂形态不断发生变化.当铸坯的加热温度为600 ～ 870℃或1150 ～ 1200℃时,有利于MnS夹杂的尺寸控制,过高的加热温度会引起MnS夹杂尺寸增大.     

取向电工钢中MnS粒子析出形核行为

采用场发射扫描电子显微镜观察了取向电工钢中MnS粒子在热变形及不同温度保温后的析出形核行为。以经典的形核率理论为基础,确定了MnS粒子形核析出的更准确潜在位置密度,进而建立了改进的MnS析出形核模型。研究结果表明,MnS粒子主要在晶界和位错上形核,MnS在900℃析出时粒子密度最大。随热变形后保温温度的升高,位错密度及相应的MnS位错形核密度降低。理论计算与实验观察的结果符合良好。     

M-EMS搅拌强度对钢轨钢MnS析出的影响研究

开展了M-EMS搅拌强度、硫质量分数对比工艺试验,采用Aspex分析了各工艺条件下钢轨特定位置MnS非金属夹杂的单颗粒长度尺寸及析出二维面积比例差异。结果表明：M-EMS搅拌强度越大,纯态较大尺寸的MnS非金属夹杂析出概率越大,复合态MnS非金属夹杂形核几率增加,同时也促进了较大尺寸的复合态MnS非金属夹杂形成;此外,硫质量分数较高的钢液更容易析出较大尺寸的纯态MnS非金属夹杂。降低钢液硫质量分数的基础上,增加形核质点并控制M-EMS搅拌强度可改善MnS非金属夹杂析出和分布。     

取向硅钢中MnS粒子形核析出的动力学计算与分析

利用热力学和动力学的相关理论计算分析了取向硅钢中MnS沉淀析出的动力学行为。计算分析结果表明,MnS粒子在取向硅钢中以在位错线上形核为主导,主要在铁素体中析出。在本文讨论的薄规格取向硅钢的合金成分下,计算出MnS的有效析出温度范围为850~1000 ℃,临界核心尺寸为0.4~0.8 nm,从开始析出到完全析出所需时间约30 s,建议热轧工序的终轧温度应控制在950 ℃,热轧板的正火时间应控制在5 min。     

夹杂物对15MnB钢冲击性能的影响

15MnB钢的化学成分和生产工艺决定了材料中极易出现MnS和TiN这两种夹杂物,研究了15MnB钢中S、Ti两种元素对夹杂物的产生及冲击性能的影响。设计不同S元素、Ti元素含量的15MnB钢,采用相同锻造、轧制及热处理工艺处理后,检测其冲击性能。采用光学显微镜观察试样的显微组织和夹杂物形貌,并用扫描电镜及能谱仪对夹杂物的化学成分进行检测。结果表明:S元素含量≤0.0029%,Ti元素含量≤0.03%时,15MnB钢的冲击性能最优;S元素含量≤0.0029%时,材料中形成的夹杂物数量少且尺寸小,15MnB钢的冲击性能稳定性随其含量减少而增强;Ti元素含量≥0.06%时,材料中会形成大量尺寸较大的TiN导致15MnB钢冲击性能大幅度降低。为了获得良好且稳定的冲击性能,建议企业在生产15MnB钢时严格控制夹杂物种类和等级,具体要求:D类(细系)≤1.0级、TiN≤0.5级,不应存在其他类型的夹杂物。     

The composition of the boundary region of MnS inclusions in stainless steel and its relevance in triggering pitting corrosion

Recently, controversy has arisen on the presence of a Cr-depleted zone around MnS inclusions in stainless steels and the relevance of such zones to pit initiation events. In the present work, we use a scanning Auger microscope (SAM) combined with simple pitting immersion tests to elucidate this question in more detail. The SAM analysis of 27 inclusions of a high S-containing DIN 1.4305 stainless steel indicated no Cr-depletion at the inclusion/matrix-interface with a lateral resolution of ±20 nm. A scanning electron microscope (SEM) characterization of the sample surface after an exposure to 10% FeCl₃ solution shows that pitting attack in all cases initiates at inclusion sites. Different pit initiation morphologies were observed (inside the inclusion, around the inclusion, mixed attack morphology). However, even the attack morphology “around an inclusion” cannot be ascribed to Cr depletion at the inclusion. Although in special cases (special composition or heat treatment history of the steel) a Cr-depleted may be induced at the matrix/inclusion-interface, the present work shows that this approach does not generally hold and therefore the presence of such a depletion zone cannot be the general explanation for pitting of stainless steels in the vicinity of inclusions.     

稀土La和Ce对25CrMoVB钢夹杂物的影响

用扫描电镜及能谱仪观察和分析不同La和Ce含量的25CrMoVB钢中夹杂物形貌和成分。结果表明,随着加入La、Ce含量的增加,钢中的长条形MnS夹杂逐渐被改性,最终变成小尺寸球状的稀土硫氧化物;同时钢中的硅酸盐、氧化铝夹杂也被改性成稀土夹杂。但La、Ce加入过量时,钢中会出现较大尺寸的复合夹杂。     

0Cr14Mn21NiN奥氏体不锈钢的析出行为

采用Thermal-Calc热力学计算软件对0Cr14Mn21NiN奥氏体不锈钢C、Cr含量变化对试验钢碳化物析出热力学特征进行了计算。通过光学显微镜、扫描电镜、透射电镜等分析方法探讨了时效温度、保温时间、变形对试验钢析出行为的影响。结果表明:析出相主要是在晶界处产生的Cr₂₃C₆,试验钢析出敏感温度为750~850 ℃。在800 ℃下时效30 min的试验钢晶界处可以明显观察到析出相的产生,随保温时间的延长,析出相含量逐渐增多,尺寸变大,并逐渐向晶内生长。时效前的变形明显缩短了析出相的孕育时间,变形后保温1 min的试验钢晶界处可观察到较多析出相的产生,晶界明显变粗。     

Morphology and chemistry of oxide inclusions after Al and Ti complex deoxidation

The morphology and chemistry of oxide inclusions after various Al and Ti complex deoxidation sequences were investigated at 1600°C. Depending on the addition sequence of Al and Ti deoxidants and the holding time, the morphology and the chemistry were changed. In particular, when Ti was added prior to Al, spherical Al₂O₃ oxide inclusions with hollow holes were frequently observed, which is reported for the first time. On the other hand, when Al was added prior to Ti, Al₂O₃ inclusion formed. When Al and Ti were added simultaneously, Al−Ti−O oxide inclusion formed in the beginning and was transformed to Al₂O₃ inclusion. Based on the experimental results, the formation mechanism of the oxide inclusions after Al−Ti deoxidation was proposed. The nozzle clogging of Ti bearing Al killed steel was also discussed based on the experimental results.     

V-N微合金化CrSiMn系低合金铸钢中的析出行为

利用JMatPro热力学模拟软件对V-N微合金化CrSiMn系低合金铸钢进行了计算,得到了不同V含量铸钢的平衡相组成,着重研究了平衡状态下各析出相的析出行为。结果表明,在加热过程中,V含量的增加将增大铁素体向奥氏体的转变阻力;V含量对微合金化渗碳体及M₇C₃型碳化物的析出行为影响不大;V含量对氮化物及碳氮化物的析出有较大影响,当V含量由0增加至0.18%(质量分数)时,氮化物及碳氮化物的初始析出温度由734.2 ℃提升至1133.93 ℃,最大析出量(质量分数)由0.07%提升至0.24%。     

氧化物冶金钢CGHAZ中有益夹杂物的作用

运用物理模拟技术研究了氧化物冶金钢焊接热影响粗晶区(CGHAZ)中有益夹杂物对显微组织的影响;用透射电镜观察了诱导针状铁素体形核的夹杂物,并用能谱仪分析了有益夹杂物的化学成分.结果表明,氧化物冶金钢CGHAZ的有益夹杂物为MnO,TiOx,SiO2和Al2O3的氧化物复合物,或氧化物与MnS,CuS或(Mn, Cu)S构成的氧硫复合物,有益夹杂物的直径为0.2～0.6 μm.焊接过程中,氧化物冶金钢CGHAZ的有益夹杂物诱导针状铁素体多维形核并促进感生形核,CGHAZ针状铁素体互相连锁交织,晶粒明显细小,氧化物冶金钢CGHAZ的显微组织具有自身细化的能力.     

A particle population analysis in Ti- and Al- deoxidized Hadfield steels

A quantitative analysis of the amount, size and number of particles that precipitate in situ in titanium- and aluminium-treated Hadfield steel cast during pilot-scale experiments has been performed. SEM with EDS and automated particle analysis abilities was utilized for the analysis. Additionally, Thermo-Calc was used for thermodynamic calculations and Magma 5 for solidification and cooling simulations. Predicted particles sizes calculated with a model based on the Ostwald ripening mechanism were compared with the experimental data. The effect of solute availability, cooling rate and deoxidation practice on the particle population characteristics was determined. It was concluded that the amount, size and number of precipitating particles in Hadfield steel castings is possible to be controlled according to certain requirements by a careful selection of proper additives in proper amounts and also by the optimization of the casting process in aspects of deoxidation timing and control of the cooling rate of the castings.     

2507超级双相不锈钢中第二相的析出行为

利用OM、SEM和EBSD等研究了经1100 ℃保温30 min固溶的热轧超级双相不锈钢(SDSS)2507在不同时效温度(750~1000 ℃)及时间(1~240 min)下的第二相析出行为。结果表明,固溶态SDSS 2507的微观组织主要是铁素体和奥氏体。在750～1000 ℃时效处理后有σ相和χ相析出。时效温度较低时,χ相从铁素体相析出且稳定存在。随着时效温度的升高,σ相主要通过α→σ+γ₂共析反应生成,随着时效时间的延长,组织中亚稳态χ相溶解并促进σ相析出。另外,时效温度也会影响第二相形貌:高温时效时(＞950 ℃),析出相形貌主要为片状σ相和γ₂相,低温时效时析出物主要呈颗粒状。由第二相析出行为及第二相的TTT曲线可知,热轧变形使SDSS 2507第二相形核的孕育期缩短,析出速度提高,析出敏感温度约为950 ℃。     

P590L连铸过程C、N化物析出行为

为研究微合金钢连铸过程C、N化物析出行为,以P590L微合金钢铸坯为研究对象,通过用碳膜萃取复型方法从拉伸试样中萃取析出物,使用JEM2100透射电镜观察试样中的第二相析出物,系统检验分析了微合金元素Ti、Nb的析出行为规律,分析了温度对析出物数量和尺寸影响规律,以及析出物对热塑性的影响趋势。试验表明,1 100℃时出现少量70nm以上的方形TiN和Ti-Nb复合析出物,在1 100~1 000℃有Nb(C,N)析出,随着温度的降低析出物数量增加,尺寸减小而且更加弥散,热塑性随析出物数量的增加而降低。     

FeTiP相在高强IF钢热轧过程中析出行为的研究

利用电阻炉、Gleeble热模拟试验机和透射电镜,分析了高强IF钢中FeTiP相在热轧过程的析出行为.结果表明,高强IF钢连铸坯中心位置存在少量的FeTiP相析出物,但经过加热和长时间保温,析出物可完全回溶;在热轧过程中,轧制温度范围内的应变诱导析出物主要为TiS相、Ti4C2S2相和TiC相,难以捕捉到明显的FeTi...     

00Cr12NiNbTi不锈钢热轧中析出行为

对00Cr12N iNbTi铁素体不锈钢进行加热、粗轧、精轧及卷取过程的模拟实验,应用扫描电镜、透射电镜、化学相分析及热模拟等方法对试样中析出物进行了定性定量分析。结果表明:加热到1140℃,保温0、45和90 m in后,粒子主要为TiN,Ti的固溶率为66.3%,N的固溶率为1.3%;从粗轧到精轧,微米级的小颗粒减少,大颗粒增多,颗粒平均尺寸由1.8μm增大到3.2μm,有聚集长大现象;在热轧过程中微米级粒子形貌为方形或球形,基本保持稳定;纳米级的(Nb,Ti)C颗粒在精轧阶段开始析出,卷取保温及缓冷至室温过程中大量析出,多分布于晶界及晶内处,在较高温度下卷取会析出较多的纳米级(Nb,Ti)C颗粒。     

Si、Mn元素对热成形钢连续冷却转变行为影响

以Gleeble-2000型热力模拟试验机为平台,结合热膨胀切线法和求导法,确定了不同成分热成形钢各冷却速度下的相变行为。研究了新开发热成形钢中Si、Mn元素对静态连续冷却转变行为的影响,Si使中温贝氏体转变曲线向右下方移动,Mn稳定奥氏体组织的能力非常强,抑制铁素体、贝氏体中高温转变,可显著增加钢的淬透性。另外,利用金相分析检测方法对不同冷却速度下的显微组织和硬度变化进行了观察和分析,绘制了连续冷却转变曲线,用于指导热成形试验的工艺参数制定。     

低碳低硫微合金化钢硫化物析出规律分析

利用热力学计算和Schiel凝固方程对于硫化物的析出进行计算模拟,最后利用金相组织证实MnS的析出规律.结果表明钢中MnS析出物是在钢凝固温度以下,锰及硫在晶界处偏析富集,[Mn][S]反应平衡发生移动而生成的.热力学计算和Schiel方程得出析出量随着温度的降低而逐渐增加.最后结合金相组织能谱,说明MnS,CaS共生出现,且温度降低MnS析出量增多.     

加热温度对高硫车轮钢夹杂物化学冶金的影响

研究了高温加热对高硫车轮钢中MnS+Al2O3复合夹杂物结构与形态的影响。通过采用扫描电子显微(SEM)技术对高硫车轮钢中夹杂物的类型及尺寸进行了分析统计。结果表明：加热温度为1 300 ℃时,MnS回溶对MnS+Al2O3复合相的包裹效果没有产生显著地破坏作用。而当加热温度升至1 350 ℃后,由于大量的硫化物回溶,使不少氧化物夹杂物直接暴露于钢基体,破坏高硫钢中MnS＋Al2O3复合相的包裹效果。在含硫车轮钢的热加工过程中,应该尽量降低处理温度（低于1 300 ℃）来降低MnS回溶对全包裹Al2O3复合夹杂物的破坏作用。     

Nucleation of phase transformations at intragranular inclusions in steel

The control of phase transformation nucleation in steel by inclusions has attracted considerable attention for a few decades. The potency as a transformation catalyst appears to depend on the species of ~nclusions and so, they may not simply act as an inert heterogeneous nucleation site. The formation of a solute depletion zone in surrounding austenite and the provision of nucleation sites which can form low energy nucleuslinclusion interfaces are considered to be a principal mechanism. These are discussed on the basis of simple models and available experimental data to relate nucleation potency with thermodynamic and other material properties of inclusions.