钛、锆脱氧对钢中夹杂物及组织的影响

通过采用锰铁、硅铁合金预脱氧,钛、锆单独或复合终脱氧的脱氧制度,研究了某低碳钢种脱氧后,钢中夹杂物的形貌、成分、尺寸分布情况。结果表明:采用Zr、Ti脱氧可以获得尺寸较小且数量较多的夹杂物粒子,加Ti后试样中的夹杂物主要为TixOy,Al2O3,MnS的复合夹杂;加Zr试样,钢中夹杂物主要为ZrxOy,SiO2,Al2O3,MnS系复合夹杂;复合添加Ti、Zr的试样,其夹杂物主要为ZrxOy,TixOy,SiO2,Al2O3,MnS复合夹杂物。Zr,Ti复合氧化物粒子能促进晶内针状铁素体形成。     

Mg-Al合金对钢液脱氧作用的试验研究

使用镁合金脱氧剂研究了ZG25钢液的脱氧行为,选取Al、Al-Mg、Mg-Al合金分别对钢液脱氧,对比脱氧后钢中夹杂物的变化情况.结果表明:含镁合金在对钢水脱氧的同时具有较强的脱硫能力;含镁合金终脱氧后夹杂物大多转化为复合夹杂物,其中Al2O3夹杂物主要转变为MgO·Al2O3,FeS和MnS等硫化物夹杂转变为MnS·MgS等复合硫化物夹杂.     

钙处理含硫20CrMo齿轮钢夹杂物析出研究

通过热力学计算控制钢中喂钙量,把钙处理20CrMo钢中Al2O3变性为低熔点的12CaO·7Al2O3上浮去除,从而使钢中夹杂物满足评级要求;并用Thermo-Calc软件模拟钢液凝固过程中CA6、CA、CA2钙铝酸盐及MnS夹杂物的析出情况.用SEM对轧材中纺锤状夹杂物进行分析,少量夹杂物内核颜色较深,为Al2O3、CaS等夹杂,外层包裹的夹杂颜色较浅,为MnS夹杂.说明凝固过程中钢液中先析出的Al2O3、CaS等复合夹杂可以被后析出的MnS捕获作为其核心.     

薄厚度板坯连铸机非稳态连铸坯中夹杂物分布

针对鞍钢股份有限公司薄厚度(200 mm)板坯连铸机生产的非稳态铸坯中夹杂物分布进行了研究.Factsage热力学计算结果表明,铸坯中的夹杂物类型主要为Al2 O3、TiN、Ti2 S3、MnS,及其复合夹杂物,该计算结果与夹杂物分析结果相符.在铸坯厚度方向上,内弧近表面侧的夹杂物类型主要为TiN,Ti2 S3和Al2...     

转炉生产20CrMnTi齿轮钢中夹杂物及相分析研究

分析研究了转炉生产20CrMnTi齿轮钢中夹杂物的种类、组成、数量和形态,发现钢中存在以Al2O3为主的氧化物、-αMnS、(Ti0.952Cr0.047)(C0.551N0.501)、Ti2CS和AlN等夹杂物;严格控制钢中[T.O]和[S]含量,可获得较低的夹杂物总量水平。     

超低氧钢中复合夹杂物形成的实验室研究

通过实验室真空感应炉试验,研究了超低氧条件下钢中复合非金属夹杂物的形成。研究发现:在含有一定硫的超低氧钢中高熔点氧化物夹杂很少,大部分为MnS。钢中Al2O3的尺寸较MgO-Al2O3系夹杂要大。以高熔点夹杂物为异质形核核心析出的MnS能显著提高钢材的疲劳寿命,此种复合夹杂物的形成与钢液成分、高熔点夹杂物的尺寸有关。     

超低氧钢中复合夹杂物形成的实验室研究简

 通过实验室真空感应炉试验,研究了超低氧条件下钢中复合非金属夹杂物的形成。研究发现：在含有一定硫的超低氧钢中高熔点氧化物夹杂很少,大部分为MnS。钢中Al2O3的尺寸较MgO-Al2O3系夹杂要大。以高熔点夹杂物为异质形核核心析出的MnS能显著提高钢材的疲劳寿命,此种复合夹杂物的形成与钢液成分、高熔点夹杂物的尺寸有关。     

国内外23CrNi3Mo钎具钢洁净度的差异

通过国内外23CrNi3Mo钎具钢的洁净度对比，找出在冶金环节上与国外钎具钢的差距，并对国外钎具钢中夹杂物的生成机理进行了理论热力学计算。结果表明，国外钎具钢的洁净度较高，易偏析元素砷、磷等含量远低于国内钎具钢；夹杂物的类型主要以单独的Mg Al O类夹杂物和Mg Al O外包裹MnS类夹杂物为主，夹杂物的尺寸主要为0～3 μm；纵截面上MnS夹杂物具有很明显的拉长现象，且具有很好的熔断效果，宽度为1 μm左右，纵横比为3～6。国内钎具钢中夹杂物主要为单独的Mg Al O类夹杂物和Mg Al O外包裹(Ca,Mn)S类夹杂物，尺寸以3～6 μm为主；纵截面上，单独的(Ca,Mn)S沿轧制方向几乎不变形。热力学计算表明，MnS类夹杂物的两次析出是导致Mg Al O类夹杂物的包裹率达到70%、复合类夹杂物尺寸较小的主要原因。     

超低碳钢钢中夹杂物的研究

为控制超低碳钢中的簇状夹杂物,对超低碳钢中的夹杂物和与全氧含量的关系进行了研究.钢中的夹杂物主要是Al2O3夹杂和Al2O3-TiN复合夹杂,独立夹杂物尺寸大部分小于10 μm.铸坯中w(TO)小于0.003 0%时,钢中仍存在簇状Al2O3夹杂;Al2O3簇状夹杂物与铸坯中全氧含量没有直接关系,所以钢中的全氧含量不能完全代表钢中夹杂物的水平.钢中的簇状Al2O3夹杂物与RH脱碳结束活度氧有关,要控制超低碳钢中簇状Al2O3夹杂物必须稳定生产工艺,减少RH加铝升温,使RH脱碳结束活度氧保持在一定范围.     

含Zr低合金高强度钢中夹杂物的特性

用电子探针研究了含Zr低合金高强度钢中夹杂物的形貌、大小及分布等特性。结果表明 ,钢样中的夹杂物为圆形 ,呈分散分布 ,其组成系含ZrO2 的复合夹杂物 ,而且MnS依附此复合夹杂物成核和长大。钢中添加少量Zr可明显改善夹杂物形态和分布 ,从而改善钢的强度和韧性     

Pitting corrosion behavior of cerium treated HSLA steel induced by sulfide inclusions in 3.5 wt% NaCl solution

Pitting corrosion behavior of Ce treated HSLA steels induced by sulfide inclusions in 3.5 wt% NaCl solution was investigated with potentiodynamic polarization and immersion corrosion test.The results show that Ce added steels exhibit better pitting corrosion resistance with lower corrosion current density and bigger pitting potential compared with steel without Ce,which is mainly attributed to optimized characteristics of spherical Ce-oxysulfide inclusions with less number density,smaller average size and lower pitting corrosion susceptibility.The spherical Ce₂O₂ S inclusions precipitated on the surface of CeAlO₃ inclusions in the Ce added steels induce pits with bigger opening mouth and shallow depth,reducing their tendency of extension to go deeper due to occlusion corrosion battery in the pitting holes.Furthermore,corrosion inhibitor Ce(OH)₃ generated by Ce₂O₂ S hydration can weaken electrochemical corrosion of the matrix micro-region around the pits.To avoid harmful bigger inclusions,Ce content in steels should be regulated within reasonable range,0.015 wt% Ce in present steels effectively modified inclusions to acquire the best pitting corrosion resistance of the steels.     

Experimental and DFT study on cerium inclusions in clean steels

To provide insights into deforming Ce-O-S-Al inclusions in steels and improving the mechanical properties,the evolution process of such harmful inclusions in clean steels was investigated by thermodynamic calculation,metallographic examination and first-principles calculation in this paper.For the tested IF steel,the thermodynamic analysis results are consistent with the calculated formation enthalpy.After Ce addition,the inclusions are transformed from Al₂O₃and TiN-Al₂TiO₅-Al₂O₃to Ce2O₃,Ce₂O₂S,CeAlO₃,TiN-Al₂TiO₅-Ce₂O₃and TiN-Al₂TiO₅-Ce₂O₂S composite inclusions,which can be confirmed by metallographic examination.The elastic constants were calculated,and the bulk modulus,Young's modulus,shear modulus and Poisson's ratio were evaluated by the Voigt-Reuss-Hill(VRH)approximation.All inclusions except Ce₂O₃show apparent brittleness.TiN,Al₂O₃,Al₂TiO₅and CeAlO₃present much higher hardness than iron matrix,while the hardness of Ce2O₃or Ce₂O₂S is close to that of iron matrix.The thermal expansion coefficients of Ce₂O₃and CeAlO₃are close to that of iron matrix,whereas,Ce₂O₂S inclusion has largely different thermal expansion coefficient from iron matrix and may deteriorate the steel performance at higher temperatures.The relatively small differences between Ce inclusions and iron matrix in terms of hardness,toughness,brittleness,and thermal expansion coefficient can explain the improvement of the mechanical properties of the tested steel.     

Inclusion behaviour in aluminium-killed steel during continuous casting

The inclusion behaviour during continuous casting were investigated in ultra low carbon (ULC) and high strength low alloy (HSLA) steels. From tundish to cast slabs, the total oxygen (T.O) content decreased from 19 to 12?ppm, 12 to 11?ppm in ULC steel and HSLA steel, respectively. The number density of inclusions in ULC decreased by about 40%, while it kept almost constant in HSLA steel during casting. A simple calculation on the T.O removal agreed well with the measured value, which showed that T.O removal was much larger through mould flux absorption than nozzle attachment. The T.O removal in ULC steel is substantially higher than that of HSLA steel due to the fact that alumina particles in ULC steel tend to agglomerate easier than calcium aluminates in HSLA steel, which facilitates inclusion removal to the mould powder.     

钛处理钢凝固后夹杂物的析出行为

 利用扫描电镜和能谱分析研究了钛处理钢凝固结束后钢中夹杂物的形貌、组成和尺寸分布,并考查了加钛前后钢中夹杂物行为变化。研究表明通过钢液加钛处理,凝固结束后钢中夹杂物主要为以含钛复合氧化物为核心、外包硫化锰的复合质点,它们尺寸较小(2~3 μm),形状为球形,不易受力变形,可望成为钢中铜弥散化非均质形核的有效质点。     

碱土钡元素对重轨钢夹杂和性能影响的研究

用Fe-Ba-Al-Si合金处理U_(71)Mn钢液,可以减少钢中夹杂物总量。钡能改变夹杂物的形态,并能获得细小的、均匀分布的球状夹杂;夹杂物主要是Al_2O_3与变态的(Ca、Mn)S结合成的复相夹杂,减少了单相存在的Al_2O_3;钡能缩减或消失夹杂物的长度,特别是对Al_2O_3簇状夹杂物的长度;钡在钢中溶解度极小,对钢的机械性能未见不良影响而能改善钢的冲击韧性。     

含铈304不锈钢夹杂物改性及耐腐蚀性能优化

 通过在304不锈钢中加入不同含量的铈,研究了铈处理前后钢中夹杂物的变化,并借助于腐蚀失重试验及电化学试验,分析了不同含量的铈处理后钢中夹杂物性质变化对304不锈钢耐腐蚀性能的影响。研究结果表明,未加铈的不锈钢中主要为MnS夹杂及复合氧化物夹杂,夹杂物的平均尺寸为8.6 μm,而钢的自腐蚀电位仅为-348.52 mV。加入稀土铈后,夹杂物逐渐改性成球状或椭球状的含铈夹杂物,平均尺寸有所降低,而不锈钢耐腐蚀性则有所提高。当铈质量分数达到0.012%时,钢中MnS夹杂全部改性成球状含铈夹杂,不锈钢自腐蚀电位高达-311.25 mV,耐腐蚀性能最好。继续增加稀土铈含量,钢中夹杂物的形状变得不规则,尺寸也有所增加,导致不锈钢耐腐蚀性能降低。     

含钡合金对冷镦钢脱氧的试验研究

在250kg感应炉上对冷镦钢进行了含钡合金脱氧的试验研究。试验中钡系合金主要选取SiAlBaCa和SiAlBaCaSr及用于钙处理的SiCa、SiCaBa包芯线。选用FeSiAl作为对比脱氧剂，考察了钡系合金脱氧的全氧含量，脱氧产物的分布、尺寸和形貌，探讨了钡系合金脱氧和对夹杂物的变质作用的机理。试验中发现，含钡合金用于钢液脱氧，可获得较低的氧含量，其脱氧产物易于上浮且速度很快，钢中的夹杂物形态发生改善呈球形，而且均匀分布于钢中。     

Effects of cerium addition on solidification structure and mechanical properties of 434 ferritic stainless steel

Effects of Ce refiners on the solidification structure and the mechanical property of ferritic stainless steel were investigated, the corresponding mechanisms were also discussed. The results showed that the solidification of the ferritic stainless steel was remarkably refined with 0.011 wt.% Ce and 0.023 wt.% Ce refiners. Ce played a great role of inclusion modification and the shape and size of the inclusions were changed by adding Ce. And after adding rare earth Ce, great amounts of high-melting point rare earth Ce inclusions(Ce_2O_3 and Ce_2O_2S) were formed. The fracture mode of 434 ferritic stainless steel was typical cleavage fracture, however, the ductility and the toughness of ferritic stainless steel was remarkably enhanced with 0.011 wt.% Ce and 0.023 wt.% Ce refiner. But the solidification structure and the mechanical property of 434 ferritic stainless steel could not be improved with 0.034 wt.% Cerefiner.     

Twin roll strip casting of low carbon steels

Abstract

Strip casting of low carbon steels has been investigated using a laboratory twin roll machine with copper rolls. The following grades have been studied: a deep drawing low carbon (LC) steel, a LC steel with titanium addition, and a high strength low alloy (HSLA) grade. The casting behaviour of these steels has been examined, and the observed surface defects classified. Defects are most pronounced for the LC grade and significantly less for the HSLA steel and the LC steel with titanium addition. The as cast structure has been analysed. It can be modified by post-cast treatment, e.g. by normalisation or in line rolling. The mechanical properties of cold rolled and annealed strip materials and their textures are presented. Satisfactory sheet properties can be achieved both as hot band and as cold rolled sheet when adequate treatment steps are applied. Consequences for strip casting applications and future research are discussed.