重轨钢中MnS析出热力学和动力学分析

 采用无水有机溶液电解法分离提取重轨钢中的MnS夹杂物,采用扫描电镜观察铸坯内和钢轨中MnS夹杂物的三维形貌,并结合能谱仪分析其成分。铸坯被轧制成钢轨后,相应的MnS夹杂物都沿着轧制方向被轧制成长条状。基于热力学和动力学模型,分析重轨钢中MnS夹杂物析出行为以及在钢液凝固过程中锰元素和硫元素偏析的程度。热力学分析表明,MnS夹杂物在凝固末期凝固分数为0.94时开始析出,其析出量由初始[w([Mn])]和初始[w([S])]决定,且在凝固过程受到冷却速率的影响,对比发现,热力学的计算析出结果与Thermo-Calc和FactSage6.4的计算结果有较好的一致性;动力学分析表明,在钢液凝固过程增加冷却速率,凝固析出的MnS颗粒尺寸将减小。通过调整钢中[w([Mn])]和[w([S])]以及改变冷却速率,可以控制MnS的析出时机和形态,减小其对钢性能的有害影响。     

百米高速重轨钢中大型MnS夹杂的形成原因

大型MnS是引起百米高速重轨夹杂物超标和超声波探伤不合的重要原因.理论计算表明,对于U75V重轨钢,在凝固末期固相分率大于0.98时,MnS才能在液相中析出.利用扫描电镜配合能谱仪分别对铸坯和钢轨试样中Mns夹杂进行了研究.结果表明,铸坯边部是尺寸小于10 μm的球状MnS,中心为尺寸小于30 μm扇形或条状MnS,钢...     

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.     

20CrMnTiH齿轮钢凝固和冷却过程中非金属夹杂物的转变研究

非金属夹杂物的类型、数量、尺寸对齿轮钢的疲劳性能具有重要影响。为了明确20CrMnTiH齿轮钢在凝固和冷却过程中夹杂物的转变和析出行为,通过Aspex自动扫描电镜对齿轮钢连铸过程中非金属夹杂物的类型、数量、尺寸等进行系统分析。研究发现,中间包内钢液中氧化物夹杂的主要类型为Al_2O_3-CaO-MgO和Al_2O_3-CaO-CaS型,铸坯中氧化物夹杂的主要类型转变为Al_2O_3-MgO和Al_2O_3-CaS型。齿轮钢钢液在凝固和冷却过程氧化物夹杂中CaO向CaS转变,夹杂物的数密度降低,平均尺寸略有增加。通过热力学软件FactSage 7.1计算了中间包内钢液在凝固和冷却过程中夹杂物的形成和转变,对齿轮钢在凝固和冷却过程夹杂物的转变提供了理论依据。     

碳含量对帘线钢凝固析出TiN夹杂的影响

对含碳量(质量分数)分别为0.72%、0.82%和0.95%的帘线钢凝固析出TiN夹杂进行热力学研究,结果表明:碳含量对于不同强度级别的帘线钢中TiN夹杂的析出有着明显的影响.随着帘线钢碳含量增加,凝固前沿温度逐渐降低,析出TiN夹杂所需的氮钛活度积也逐渐下降.在相同的钢液初始Ti、N含量条件下,较高碳含量的帘线钢中析出的TiN夹杂尺寸会大于较低碳含量帘线钢中析出的TiN夹杂尺寸.为了控制超高强度级别的过共析帘线钢中TiN夹杂的析出对帘线钢加工性能的有害影响,必须通过冶炼工艺进一步降低钢液中的钛、氮含量.     

SWRH 92A帘线钢中异相形核TiN复合夹杂析出机制

摘要：高碳帘线钢中析出的非金属夹杂物如钛夹杂,对钢材疲劳强度影响巨大。系统分析过共析帘线钢中钛夹杂的析出行为对控制夹杂物形成及产品质量提升尤为重要。结合形核理论以及热力学耦合模型,对SWRH 92A帘线钢盘条存在的Al2O3 TiN复合夹杂物的形成机制进行了研究。结果表明：TiN夹杂在钢液凝固进程凝固分数约为0.866(温度为1457K)时开始析出;凝固前期Ti、N偏析比基本相当,然而当凝固接近结束时Ti的偏析比明显大于N,分别为6.059和2.367×10-6。TiN夹杂物形成过程中,其异相形核功小于均相形核功,异相形核半径大于均相形核半径,并且形核功与形核半径变化曲线在1457K时均达峰值。呈球形形态的Al2O3夹杂在TiN析出之前就已经析出,并且尺寸较小的Al2O3将被推动至凝固前沿被TiN捕获并以此为核心析出长大最终形成Al2O3 TiN复合夹杂。     

钢中硫化锰夹杂控制的机理分析与工业实践

钢中MnS夹杂的控制是一个涉及到包括冶炼、凝固、加热和轧制过程等多工序，需要多变量协同控制的系统工程。详细论述了国内外MnS夹杂的研究现状，阐述了不同元素、热处理和轧制工艺对MnS夹杂的影响机理；整理总结了当前MnS夹杂的工艺控制措施，通过采用合适的脱氧工艺提高凝固前沿氧含量、降低精炼渣碱度、采用合适的钙处理工艺、采用低碱度中间包覆盖剂、提高二冷水量加强冷却、降低电磁搅拌强度等方式能够有效地控制MnS夹杂形貌、尺寸和数量。近年来，针对MnS夹杂的变性处理和弥散化分布等控制难点，提出了一些新思路，即向钢液中添加Mg、Ca-Mg、Zr、Ce、Te等元素能够有效控制钢中MnS夹杂形貌、尺寸和数量。     

镁处理对1215易切削钢中夹杂物的影响

 1215易切削钢中硫化物夹杂不仅影响钢的切削性能,对钢性能的各向异性以及产品质量问题也有重要影响,对钢中硫化物夹杂的调控是改善产品品质的重要途径。采用镁处理技术,对钢中硫化物夹杂的形态、大小和分布进行调控,解析镁对夹杂物的改质影响。通过高温熔炼试验,冶炼不同镁含量的钢锭,采用光学显微镜、扫描电镜及小样电解技术对钢中夹杂物的二维及三维形态和分布进行分析,并结合热力学计算解析夹杂物改质机制。研究表明,镁具有较强的脱氧能力,可改变钢中硫化物形态和分布。钢中镁质量分数从0增加至0.000 6%、0.001 7%,夹杂物形态首先从Ⅰ类球形、椭球形转变至Ⅱ类沿晶分布的簇状、串链状、珊瑚状,然后再转变为多面体形或不规则块状的的Ⅲ类硫化物。镁质量分数进一步增加至0.002 7%,镁对夹杂物的形态、尺寸、分布影响不再显著。钢中的MnS在熔融液态中不会析出,主要在凝固过程固液两相区析出,其析出温度为1 502.0 ℃,对应的凝固分率为0.409。凝固过程中部分MnS会以钢中氧化物夹杂为异质形核点析出,形成内部氧化物、外部硫化物的复合夹杂。钢中Al₂O₃经镁改质转变成为更加细小弥散分布的MgO·Al₂O₃,改质后夹杂物不易聚集长大,成为更多的MnS析出异质形核点,从而促进了MnS析出,夹杂物整体数量密度增大,平均等效直径减小。     

帘线钢凝固过程夹杂物生成热力学及工业实践

 非金属夹杂物是影响帘线钢拉拔性能的重要因素之一,为了研究帘线钢中夹杂物的生成及转变机理,使用ASPEX自动扫描电镜观察分析了帘线钢工业生产过程中不同碱度条件下从钢液到铸坯中非金属夹杂物的转变现象,并使用FactSage7.0热力学计算软件对非金属夹杂物的转变机理进行了讨论。在高碱度条件下,钢液中非金属夹杂物主要类型为低熔点的CaO-SiO₂-Al₂O₃-MnO,铸坯中非金属夹杂物的CaO和MnO含量有所降低,同时SiO₂含量有所增加。在低碱度炉次中,钢液中非金属夹杂物主要为较高熔点的SiO₂-MnO-CaO类型,Al₂O₃含量较低。连铸坯中非金属夹杂物的SiO₂含量与钢液相比有所增加,同时MnO含量降低。热力学计算结果表明,帘线钢凝固和冷却过程中的非金属夹杂物转变由夹杂物自身的相转变和析出、非金属夹杂物和钢液间的化学反应以及溶解氧和钢基体化学成分的反应3方面原因造成。热力学计算结果较好地解释了帘线钢工业生产中钢液和铸坯中非金属夹杂物成分和形貌的转变,为帘线钢中非金属夹杂物的控制提供参考。     

硫含量对重轨钢中非金属夹杂物的影响

摘要：实际生产过程中由于原料和操作控制不精确,钢中硫含量和非金属夹杂物波动较大,严重影响钢的洁净度。为了准确控制重轨钢中硫化锰等非金属夹杂物的尺寸、形态和数量,在实验室开展了硫含量对重轨钢中非金属夹杂物的影响研究。钢中硫质量分数增至70×10-6、110×10-6、140×10-6后随炉冷却,采用全自动夹杂物分析仪对钢中非金属夹杂物进行统计,获得了硫含量与钢中非金属夹杂物成分、尺寸、形态和数量的关系。结果表明,钢中夹杂物大部分为以氧化物为形核核心的复合型MnS;随着硫含量的升高,复合型MnS、MnO-SiO2和MgO-Al2O3-SiO2-CaO型夹杂增多,CaO-SiO2和MgO-CaO-SiO2夹杂减少;夹杂物平均尺寸随硫含量的升高而增大,且不同尺寸的夹杂物均有所增加,尺寸为2~10μm增多最明显;硫质量分数为(70~140)×10-6的钢液凝固过程液相中都能单独析出MnS,且硫含量越高,MnS析出越早,含量越多。     

凝固过程重轨钢中MnS粒子形核与长大动力学分析

利用经典形核理论和扩散控制长大模型计算分析了重轨钢中MnS粒子析出的动力学行为,计算结果表明,MnS粒子在重轨钢凝固过程以均匀形核和晶界形核为主,主要在凝固末期析出。在设定的重轨钢成分下,计算出MnS的有效形核温度为1 634K,即Mn、S实际浓度积等于平衡浓度积。降低S的质量分数小于5.0×10-5能够推迟MnS接近固相线析出,而对MnS的长大半径影响较小;提高冷却速率从0.14K/s到1.45K/s,连铸坯内柱状晶区中MnS的长大半径比中心等轴晶区的大1个数量级,但对MnS的析出时机无影响。S元素是MnS在凝固过程中粗化长大的控制性环节,在凝固过程冷却速率对MnS粒子长大半径起着决定性的作用。     

Genetic Analysis for Large TiN Inclusions in Wire Rod for Tire Cord Steel of SWRH82A

The law of element segregation of Ti, N, Mn and S, and the sequence of selective precipitation of TiN and MnS inclusions during solidification of molten steel of SWRH82A are studied on the basis of thermodynamics. The origin of large TiN inclusions which affect the titanium inclusions point penalty in SWRH82A wire rod is analyzed based on the research on the distribution characteristics of MnS and large size of TiN inclusions observed on metallographic specimen of SWRH82A steel wire rod. The solidification segregation ratio of Ti is far more than that of N, and the solidification segregation ratio of S is far more than that of Mn. In the range of cooling rate of the continuous casting production, the cooling rate of solidification has little effect on the segregation ratios of Ti, N, Mn and S. MnS inclusions will precipitate earlier than TiN inclusions during solidification of the molten steel of SWRH82A. The large TiN inclusion which is wrapped by MnS in the SWRH82A wire rod may be foreign inclusions and it is not precipitated product during solidification in the molten steel of SWRH82A.     

车轴钢铸锭中MnS的生成、长大、熟化规律分析

 为降低大尺寸MnS夹杂物引起的车轴磁粉探伤不合格率,利用第二相析出理论以及铸锭凝固数值模拟计算相结合,计算分析了车轴钢铸锭中MnS生成、长大、熟化规律。计算结果显示,MnS形核核心尺寸与熟化过程尺寸增加均为纳米级,凝固过程MnS的长大决定凝固完成时MnS粒子直径,理论计算得到车轴钢铸锭竖直中心线上冒口、中心、底部位置对应的MnS长大后尺寸分别为156.35、107.37和94.96 μm,中心处MnS尺寸为连铸工艺条件下的2倍,与实际检测结果相符。钢锭凝固过程缓慢是MnS易于长大的直接原因,显著区别于连铸过程。在现有工艺条件下,为控制车轴钢模铸钢MnS尺寸,关键在于降低钢液硫质量分数以及控制硫偏析。控制车轴成品中MnS夹杂物不超过1.5级,需降低钢液中w([S])至0.004 3%以下。     

A Coupled Thermodynamic Model for Prediction of Inclusions Precipitation during Solidification of Heat-resistant Steel Containing Cerium

A coupled thermodynamic model of inclusions precipitation both in liquid and solid phase and microsegregation of solute elements during solidification of heat-resistant steel containing cerium was established.Then the model was validated by the SEM analysis of the industrial products.The type and amount of inclusions in solidification structure of 253 MA heat-resistant steel were predicted by the model,and the valuable results for the inclusions controlling in 253 MA steel were obtained.When the cerium addition increases,the types of inclusions transform from SiO2 and MnS to Ce2O3 and Ce2O2S in 253 MA steel and the precipitation temperature of SiO2 and MnS decreases.The inclusions CeS and CeN convert to Ce2O3 and Ce2O2S as the oxygen content increases and Ce2O3 and CeN convert to Ce2O2 S,Ce3S4,and MnS as the sulfur content increases.The formation temperature of SiO2 increases when the oxygen content increases and the MnS precipitation temperature increases when the sulfur content increases.There is only a small quantity of inclusions containing cerium in 253 MA steel with high cleanliness,i.e.,low oxygen and sulfur contents.By contrast,a mass of SiO2,MnS and Ce2O2 S are formed in steel when the oxygen and sulfur contents are high enough.The condition that MnS precipitates in 253 MA steel is 1.2 w[O]+w[S]0.01%and SiO2 precipitates when 2 w[O]+w[S]0.017%(w[S]0.005%)and w[O]0.006%(w[S]0.005%).     

Study on the effects of Ti micro-addition on the characteristics of MnS inclusions in rail steel

Laboratorial study was carried out to reduce the rates of sulphide inclusions in rail steel. Rail steel was re-melted in an induction furnace with the addition of titanium to 0.0098wt%. The cast ingot was then sampled and inclusions were carefully inspected on the morphology, composition, elastic moduli etc. of sulphide inclusion. The obtained results indicated that sulphides were mostly spherical shapes before/after the addition of Ti. Number density of inclusions with sizes not more than 10µm increased while the larger ones decreased. Compositions of sulphides were converted from MnS to Mn-Ti-S with [Ti] addition. SEM-mapping of the sulphides indicated that Ti distributed in the whole Mn-Ti-S inclusions. Moreover, Ti-enrich regions and Mn-enriched regions were not overlapped but mainly complementary. The measured elastic moduli of MnS and Mn-Ti-S sulphides were 27.3GPa and 34.7GPa, respectively, indicating a rise of about 7GPa against the rise of [Ti] content from 0.0018wt% to 0.0098wt%.     

Effect of sulfur content on non metallic inclusions of heavy rail steel

Due to the inaccurate control of raw materials and operation in the actual production process, the sulfur content and non-metallic inclusions in the steel fluctuate greatly, which seriously affects the cleanliness of steel. To accurately control the size, shape and quantity of non-metallic inclusions such as manganese sulfide in heavy rail steel, the effect of sulfur content on non-metallic inclusions in heavy rail steel was studied in the laboratory. To investigate the changes of the number and morphology of non-metallic inclusions in steel under different sulfur contents, the sulfur content of test steel was increased to 70×10-6, 110×10-6 and 140×10-6, respectively. During the experiment, the test steel was heated and melted in a tubular furnace according to a certain heating rule, and then cooled naturally in the furnace. Subsequently, the non metallic inclusions in steel were scanned by automatic inclusions analyzer, and the relationship between sulfur content and the composition, size, form and quantity of non-metallic inclusions in steel was obtained. The results indicate that most of the inclusions in the steel are composite MnS with oxides as nucleating cores. With the increase of sulfur content, the quantity density of composite MnS, MnO-SiO2 and MgO-Al2O3-SiO2-CaO inclusions increase, while the CaO-SiO2 and MgO-CaO-SiO2 inclusions decrease. The average size of inclusions increases with the increase of sulfur content, and the number of inclusions with different sizes also increases, especially for inclusions with sizes of 2-10μm which increase obviously. During solidification, MnS can be separated from molten steel with sulfur content of (70-140)×10-6. In addition, the higher the sulfur content is, the earlier MnS inclusions precipitate and the more the MnS content is.     

20MnCr5齿轮钢氧含量控制及其对钢的疲劳性能影响

提出了100 t EAF-LF-VD-CC-CR全流程控制齿轮钢氧含量的工艺措施;研究了0.00053%～0.00145%氧含量20MnCr5齿轮钢的旋转弯曲疲劳性能、断口和夹杂物尺寸。结果表明,钢中总氧含量越高,最大夹杂物尺寸也越大,疲劳强度越低,当[O]≤0.0010%时,随[O]降低,疲劳强度升高幅度较小;试验钢在表层不产生疲劳裂纹的临界夹杂物尺寸为21μm,距表面深度30～430μm的浅层区域为相对安全区域,其中的夹杂物很难引起疲劳开裂。     

非调质钢F45MnVS热顶锻裂纹分析和改进工艺措施

非调质钢F45MnVS的生产流程为50 t UHP EAF-LF-VD-260 mm×300 mm,180 mm×220 mm坯连铸-Φ20~Φ160 mm材轧制。根据显微组织分析,热顶锻裂纹由块状和片状MnS和附着的Al₂O₃-MnO-FeO复合氧化物引起,通过控制钢中Al 0.010%~0.030%,电弧炉终点[C]≥0.20%,终点[P]≤0.025%,[Mn]/[S]＞20,LF精炼渣碱度≥3.0,VD后软吹氩时间≥12 min,保证钢中硫分布均匀;中间包钢水过热度20~30℃,控制连铸拉速防止MnS偏析;控制终轧温度850~1000℃,轧后冷速2~4℃/s等工艺措施,使钢中夹杂物主要为长条状MnS,热顶锻试验无裂纹和其他缺陷,全部合格。