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。     

GCr15轴承钢中TiN(C)析出行为热力学分析和研究

通过对TiN(C)生成热力学和动力学计算,分析研究了GCr15轴承钢(0.97％C、1.45％ Cr)凝固过程中TiN(C)夹杂的析出规律以及夹杂物长大的影响因素.研究表明,液相线温度以上,TiN不会析出,只有在液相线至固相线温度之间,当凝固百分数fs≥0.4～0.5,1694～1703 K时TiN析出;整个凝固过程中,TiC在凝固末端有少量析出,当fs≥0.87 ～0.92,1 633～1 643 K时,降低Ti、N含量能够显著降低TiN的析出温度和尺寸.冷却速率不会影响TiN的析出温度,但对夹杂长大也有较为明显的影响.控制析出TiN夹杂的条件为:[Ti]/％≤0.006、[N]/％≤0.004和较大冷却速率.     

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。     

过共析帘线钢中Ti夹杂的析出热力学与形成机制

过共析帘线钢中析出的含Ti夹杂对钢丝拉拔性能产生有害影响,研究钢中Ti夹杂的析出行为对夹杂物性质控制以及钢材质量提高具有重要意义.考虑夹杂物析出对凝固前沿溶质浓度和温度影响下,基于传统Ohnaka模型建立了相应的耦合模型并以此计算了92级过共析帘线钢中TiN夹杂的析出热力学.结果表明,耦合模型条件下TiN夹杂的析出时间...     

钢连铸过程的溶质微观偏析模型

建立了钢凝固过程包含δ/γ相变及MnS夹杂析出的溶质微观偏析模型。分析了钢种成分、MnS夹杂物析出及冷却速率对钢凝固过程高温力学性能的影响,模型计算结果与文献报道的实测零强度温度(ZST)和零塑性温度(ZDT)吻合良好。     

硫化锰对钢中Sb析出行为的影响

研究了钢中不同夹杂物对Sb的析出和高温氧化过程中富集行为的影响.Fe-1.5%Sb合金1100℃水冷试样中Sb在钢中主要析出位置是晶界.与单一的氧化物夹杂相比,硫化锰是更为有效的Sb异质形核核心,且Sb析出相成分组成接近于FeSb相.实验结果与二维错配度理论计算结果相一致.通过降低氧含量,钢中加入Ti变质硫化锰夹杂等方式,增加了MnS数量,使得更多的Sb在夹杂物上析出,从而减少钢中Sb的偏析和固溶量,改变Sb在钢中的析出位置.      

09CuPTiRE钢凝固过程中稀土与钛的相互作用

以09CuPTiRE钢为研究对象,建立钢液凝固过程中溶质偏析和夹杂物析出的耦合热力学模型.利用该模型,研究分析了09CuPTiRE钢凝固过程中稀土与钛的相互作用,得到以下结论:稀土能抑制09CuPTiRE钢中Ti3O5夹杂的析出,当RE含量为0.0045％时,Ti3O5夹杂完全消失;微量稀土有利于09CuPTiRE钢中TiN的析出,随着稀土加入量的增加,对TiN的析出起到抑制作用;钛能抑制09CuPTiRE钢中REN的析出,从而影响凝固过程中RES的析出行为.     

稀土处理C-Mn钢显微组织和夹杂物演化

对稀土处理C-Mn钢的夹杂物和显微组织进行分析,统计稀土处理C-Mn钢中针状铁素体形核核心尺寸,并将稀土处理钢在不同温度下淬火,研究稀土夹杂物生成和长大过程.实验结果表明:C-Mn钢加入少量稀土后钢中夹杂物从MnS＋硅铝酸盐夹杂转变为La₂O₂S＋LaAlO₃＋MnS＋硅铝酸盐夹杂,尺寸得到细化,显微组织也从马氏体＋贝氏体组织变成侧板条铁素体、针状铁素体和块状铁素体组织;稀土处理C-Mn钢中针状铁素体有效形核核心的尺寸集中在1~4μm,主要是在钢液中形成,冷却和凝固过程形成的数量较少;稀土夹杂物在钢液温度和冷却及凝固过程容易碰撞黏合长大,上浮从钢液中去除,MnS能在稀土夹杂物颗粒间析出.      

奥氏体化温度对低碳钢硼化物析出的影响

用电子显微镜和自射线方法观察了0.12C、0.06C-0.2Si-1.0Mn-0.0013N-0.0013B 低碳钢在不同热处理条件下,硼的形态变化.热轧钢板中的氮化硼多以硫化锰为核心析出.也观察到了不含硫化锰核的单纯氮化硼.加热温度高于1000℃时,氮化硼分解,只剩下硫化锰,其后若在950℃保温时,硫化锰等夹杂物的界面上再次析出氮化硼.氧化铝也是氮化硼再析出的核心.在硫化锰和氧化铝等非金属夹杂物界面上,氮化硼的优先析出行为是我们初次确认的,由此可知降低钢中的硫和氧,减少其夹杂物含量,从而减少夹杂物界面上的无效硼,即使加入少量硼也可提高钢的淬透性,改善钢的加工性和可焊性.     

Q345B钢直装轧制厚板冷弯裂纹分析

某钢厂Q345B钢供厚板轧制铸坯改直装轧制工艺后,轧制后钢板出现冷弯裂纹。通过对热装、直装轧制工艺的钢板金相组织、夹杂物、析出物进行研究,发现直装轧制工艺的钢板内的带状组织、MnS夹杂是冷弯裂纹产生的主要原因。另外直装轧制工艺钢板内析出物较少,不能充分发挥微合金元素的强化作用。带状组织产生的根本原因是连铸坯在凝固过程中碳和其他元素一起产生枝晶偏析,轧制过程中枝晶偏析逐渐转变成中间坯和成品钢板的带状偏析。硫化锰夹杂是在钢液凝固过程产生的,根据化学成分和硫化锰的形貌推断,这种均质呈带状分布的硫化锰夹杂是形成于用铝脱氧但又无其他过多合金元素的镇静钢中。通过控制硫含量、电磁搅拌、钢种成分微调等研究工作,目前直装轧制钢板内的条带状硫化锰夹杂已经减少,铸坯成分偏析也得到相应改善。     

Effect of Mn,Si and Mn‐Si Alloying on the Precipitation of Ultra‐fine Oxides in Fe during Solidification

The effect of Mn, Si and Mn‐Si alloying on the precipitation of oxide inclusions in Fe during solidification has been investigated. The results show that the inclusions precipitating during solidification are relatively small and distribute uniformly in Mn, SI and Mn‐Si alloyed steels. Most of the inclusions are nearly spherical. The maximum diameter of inclusions is only 3.3μm in the three types of alloyed steels. The average size of inclusions is 1.3μm, 1.2μm and 1.1μm in Mn, Si and Mn‐Si alloyed steels, respectively. The maximum amount of inclusions is 1.1×10⁵ per unit volume (mm^?3) in Mn alloyed steel and the minimum is 5.8×10⁴ per unit volume in Si alloyed steel. The volume fractions of the inclusions with Mn, Si and Mn‐Si alloying are 0.01%, 0.005% and 0.006%, respectively.     

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.     

202不锈钢中非金属夹杂物的形成机理

通过工业试验对202不锈钢进行系统取样,分析试样中夹杂物的变化特征,结合热力学计算,研究了202不锈钢中非金属夹杂物的形成机理。在进行硅锰脱氧后,LF精炼过程中钢液内以球型Ca?Si?Mn?O夹杂物为主。对于硅锰脱氧钢,钢液中残余铝质量分数为1×10?5时,可以扩大Mn?Si?O相图的液相区,但铝质量分数超过3×10?5会导致钢中容易形成氧化铝夹杂物并减小液相区。在连铸坯中以Mn?Al?O类夹杂物为主,相较于LF精炼过程试样,连铸坯试样中夹杂物的MnO和Al₂O₃含量明显增加,CaO和SiO₂含量明显减小,夹杂物个数则由LF出钢试样的5.5 mm?2增加到11.3 mm?2。结合热力学计算发现,凝固过程中会有Mn?Al?O夹杂物形成,这也使其成为连铸坯中主要的夹杂物类型。      

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.     

Thermodynamic Evaluation of Inclusions Formation and Behaviour in Steels during Casting and Solidification

For demanding applications high steel cleanliness and strictly controlled inclusions are required. Primary inclusions are formed during steel treatments in the ladle. Most of these are removed to the ladle slag or on the lining. However, the rest of the inclusions still remain through the successive process stages, and additionally new inclusions are formed during casting and solidification due to decreasing thermodynamic solubility of oxygen in the steel at lower temperatures, reactions with surrounding slag, refractory materials and eventual contact with air. Inclusions formation and transformation are simulated by thermodynamic calculations in the steel/inclusions/slag system taking into account the solidification phenomena. In this paper inclusions in Si/Mn‐deoxidised steel and Al‐deoxidised Ca‐treated steels are contributed. Calculations are compared with experimental results from steel plants.     

Basic Research on Precipitation and Control of BN Inclusions in Steel

The influencing factors on precipitation and the suitable controlling conditions of BN inclusions were not reported until now, although it has been proven that BN could improve the cutting performance of steel. The precipitation and control of BN inclusions have been investigated in detail in this article. First, the precipitation behaviors of main inclusions in steel have been investigated by theoretical calculation, especially those of BN inclusions. Then, the directional solidification and heat treatments were applied to study the precipitation of BN inclusions realistically, and the microstructures of steels under different cooling rates have been analyzed. The variation laws of size, distribution, and area ratio of BN inclusions were discussed under conditions of quantitative control of chemical composition and cooling rate of steel. The variation laws and the main influencing factors of precipitation of BN inclusions in steel have been obtained and the suitable controlling conditions have been proposed. Finally, it is validated with a cutting experiment that the cutting performance and the chip-breaking performance of steel have been greatly improved by BN inclusions precipitated in the suitable control conditions.     

镁处理对430铁素体不锈钢夹杂物形成和凝固组织的影响

试验研究了0.000 5%～0.001 2%Mg对60 kg真空感应炉熔炼的430铁素体不锈钢(/%:0.04C、0.25～0.32Si、0.28～0.38Mn、16.5～16.9Cr)夹杂物形成和凝固组织的影响。结果表明,430钢液中添加镁合金后,钢中形成平均粒径更小,数量密度更大的含MgO复合夹杂物;镁合金的加入可以改善430钢的凝固组织,且浇铸温度越低,改善效果越明显,在1 580℃浇铸时,等轴晶率由常规钢的30.8%提高至镁处理钢的88.5%,相应等轴晶尺寸由1 741.6μm降至945.3μm。含MgO夹杂物与δ相二维错配度极小,可作为430钢有效异质形核剂,促进等轴晶的形成,抑制柱状晶的生长,细化凝固组织。     

20CrMnTi齿轮钢中TiN夹杂物的特征与分布

为了研究含钛齿轮钢中TiN夹杂物的析出与控制,利用扫描电镜对20CrMnTi齿轮钢两个端淬试样中TiN夹杂的分布与形貌进行了观察,通过夹杂物自动分析系统统计了试样中TiN夹杂的尺寸、数量,建立了数学模型,对试样中TiN夹杂的析出与长大进行了计算。结果表明,较高钛含量的试样凝固过程中TiN析出更早,析出量也更大,由于析出了更多数量的TiN夹杂,从而使得析出TiN夹杂的最终尺寸更小,当TiN夹杂的数量密度由37.28增加为58.65个/mm2时,TiN平均尺寸由2.33减小为1.49 μm。通过在凝固过程中为TiN夹杂提供充足数量的氧化物颗粒作为析出核心,提高异质形核率,从而增大TiN的析出数量,就可以降低析出TiN的整体尺寸,这为含钛齿轮钢中TiN夹杂物的控制提供了一种新的思路。