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Fe-Mn-Al-Si-Sn合金的选择性氧化及部分相关系的研究

作者:完美论文网  来源:www.wmlunwen.com  发布时间:2019/9/3 10:00:23  

摘要:TWIP钢又称为孪晶诱导塑性钢 (Twinning induced plasticity),具有高强度和高塑性的同时,还拥有优异的能量吸收能力,被认为是一种理想的汽车车身用钢。但是在连续热浸镀锌的生产线(CAL)中, TWIP钢由于含有Mn、Si、Al等合金元素,在低露点下退火时,在钢板表面会发生选择性氧化,使锌液与钢板表面的润湿性变差。因此为了改善TWIP钢的可镀性,有必要对钢板表面选择性氧化行为进行深入的研究。

本文首先通过实验测定了Mn-Si-Sn和Mn-Al-Sn三元体系的相平衡关系,补充了Fe-Mn-Al-Si-Sn-O体系的部分热力学数据。通过实验并结合FactSage软件计算,对Fe-Mn、Fe-Mn-Si、Fe-Mn-Al、Fe-Mn-Al-Si、Fe-Mn-Al-Si-Sn TWIP钢模型合金的选择性氧化进行了研究。主要工作如下:

1、通过平衡合金法,结合X射线衍射仪(XRD)、扫描电镜与能谱仪(SEM-EDS)等检测手段,测定了Mn-Al-Sn三元合金相图450°C和800°C的等温截面。实验结果表明,Al-Mn-Sn 450°C等温截面具有10个三相区,Al在Mn3Sn、Mn3Sn2和MnSn2中的溶解度分别约为2.8、3.6和0.5 at.%。800°C等温截面有5个三相区,Al在Mn3Sn和Mn2-xSn中的固溶度约为3和3.1 at.%。在这两个温度下均不产生三元化合物。Al12Mn也被称为G相,在450°C下能够观察到它的稳定存在。

2、确定了Mn-Si-Sn 500°C的等温截面存在12个三相区:(1) α-Mn+β-Mn+R-Mn6Si, (2) R-Mn6Si + β-Mn + Mn3Sn, (3) R-Mn6Si + υ-Mn9Si2 + Mn3Sn, (4) υ-Mn9Si2 + Mn3Sn + Mn3Si, (5) Mn3Si + Mn3Sn + Mn2-xSn, (6) Mn3Si + Mn5Si3 + Mn2-xSn, (7) Mn2-xSn + Mn5Si3 + Mn3Sn2, (8) Mn5Si3 + Mn3Sn2 + MnSn2, (9) Mn5Si3 + MnSn2 + Liq., (10) Mn5Si3 + MnSi + Liq., (11) MnSi + Mn11Si19 + Liq. 和 (12) Mn11Si19 + Si + Liq.。未发现三元化合物的存在,并且Mn-Si二元系中存在争议的Mn5Si2相,在本实验中也未被观察到。

3、 通过FactSage软件计算并结合选择性氧化实验,对Fe-25Mn、Fe-25Mn-3Al、Fe-25Mn-3Si、Fe-25Mn-3Al-3Si、Fe-25Mn-3Al-3Si-xSn  TWIP钢模型合金的选择性氧化行为进行了研究。首先利用FactSage软件计算了初生氧化物相图,结果显示Fe-Mn-Al-Si-Sn的模型合金在发生选择性氧化时,氧化物形成的先后顺序为Al2O3、MnAl2O4、Mn2SiO4和MnO。采用了场发射扫描电镜(Fe-SEM)、能谱仪(EDS)、X射线光电子能谱分析(XPS)等检测手段,研究了不同氧压、温度和时间对模型合金选择性氧化的影响。发现随着氧压的升高,合金元素存在由外氧化到内氧化的转变过程。Sn元素在高温退火时,会富集到合金的表层附近,能够有效阻碍氧和合金的扩散,从而减少合金表面选择性氧化物的形成。

TWIP steel, also known as Twin induced plasticity steel, has high strength, plasticity and excellent energy absorption capacity. It is considered to be ideal automotive steel. However, in Continuous Hot Dip Galvanizing Production Line (CAL), Mn, Si and Al alloying elements will selective oxidize on the surface of TWIP steel at low dew point, and surface oxides will deteriorate the wettability of zinc to steel. Therefore, in order to improve the palatability of TWIP steel, it is necessary to study the selective oxidation behavior of steel.

In this paper, phase equilibrium relationships of the Mn-Si-Sn and Mn-Al-Sn ternary systems have been measured by experiments. Partial thermodynamic data of Fe-Mn-Al-Si-Sn-O ternary systems have been supplemented. Selective oxidation of Fe-Mn, Fe-Mn-Al, Fe-Mn-Si, Fe-Mn-Al-Si and Fe-Mn-Si-Sn model alloys was studied by experiments and relevant thermodynamic calculation. The main work is as follows:

1. Isothermal cross sections of the Al-Mn-Sn ternary system at 450°C and 800°C were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Experimental results show that there are 10 three-phase regions in the isothermal section of the Al-Mn-Sn at 450°C and 5 three-phase regions in the isothermal section of 800°C. No ternary compound was found at these two temperatures. The Mn3Sn2 which is stable at low temperate was confirmed at 450°C. The solubilities of Al in Mn3Sn, Mn3Sn2 and MnSn2 are about 2.8, 3.6 and 0.5 at.% respectively. The stable existence of high temperature phase Mn2-xSn was confirmed at 800°C. The solubility of Al in Mn3Sn and Mn2-xSn is about 3.1 at. %. Al12Mn, also known as G phase, can also be observed at 450 °C.

2. There are 12 three-phase in the isothermal section of Mn-Si-Sn at 500 °C: (1) α-Mn+β-Mn+R-Mn6Si, (2) R-Mn6Si + β-Mn + Mn3Sn, (3) R-Mn6Si + υ-Mn9Si2 + Mn3Sn, (4) υ-Mn9Si2 + Mn3Sn + Mn3Si, (5) Mn3Si + Mn3Sn + Mn2-xSn, (6) Mn3Si + Mn5Si3 + Mn2-xSn, (7) Mn2-xSn + Mn5Si3 + Mn3Sn2, (8) Mn5Si3 + Mn3Sn2 + MnSn2, (9) Mn5Si3 + MnSn2 + Liq., (10) Mn5Si3 + MnSi + Liq., (11) MnSi + Mn11Si19 + Liq. and (12) Mn11Si19 + Si + Liq. No ternary compound exists in the system. The controversial Mn5Si2 phase has not been observed in this experiment.

3. The selective oxidation behavior of Fe-25Mn, Fe-25Mn-3Al, Fe-25Mn-3Si, Fe-25Mn-3Al-3Si, Fe-25Mn-3Al-3Si and Fe-25Mn-3Al-3 Si-xSn model alloys was studied by FactSage software calculation and selective oxidation experiments. The primary oxidation phase diagram calculated by FactSage software show that the order of oxide formation is is Al2O3, MnAl2O4, Mn2SiO4 and MnO when selective oxidation occurs in Fe-Mn-Al-Si-Sn model alloys. The effects of oxygen pressure, temperature and time on selective oxidation of model alloys were studied by FE-SEM, EDS, XPS, etc. With the increase of oxygen pressure, alloying elements have a transition process from external oxidation to internal oxidation. Sn enriches near the surface of the alloy during high temperature annealing, which can effectively hinder the diffusion of oxygen and alloy, and reducing the selective oxide on the surface of the alloy.

关键词:Fe-Mn-Al-Si-Sn;相平衡;选择性氧化;TWIP钢

Fe-Mn-Al-Si-Sn; phase equilibrium; selective oxidation; TWIP steel

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