加热气氛对一种C-Mn-Si-Al高强钢选择性氧化的影响

为了研究局部露点技术在含铝高强钢上应用的潜力,采用热浸镀工艺模拟器研究了加热过程的露点温度对一种C-Mn-Si-Al高强钢选择性氧化的影响。加热过程中的露点温度设置为-10、-20和-50℃,而在保温过程中的露点温度为-50℃。采用SEM/EDS表征了退火后试样表面的氧化形貌和元素质量分数,使用GDOES分析了退火试样表层的元素深度分布,采用XPS分析鉴定了试样表面的氧化物种类。试验结果表明,使用-10℃露点温度加热时,试样表面氧化轻微,铝元素出现明显内氧化现象。随着加热过程露点温度降低到-50℃,试样表面出现较多富含锰和铝的氧化物。因此,加热过程中较高的露点温度可以抑制合金元素向外表面的富集,减少试样表面的氧化物数量。     

过时效工艺对C-Mn-Si高强钢表面选择性氧化的影响

 为了研究过时效过程露点调节技术在高强钢上的应用，采用热浸镀工艺模拟器研究了过时效工艺中气氛露点温度（－30、－10 ℃）和温度（250、350 ℃）对一种C-Mn-Si高强钢选择性氧化的影响，分别采用FE-SEM和EDS观察分析了试样表面形貌和化学成分，采用GDOES表征了试样表面的元素深度分布，采用XPS确定了氧化物种类。结果表明，高过时效温度（350 ℃）和高露点温度（－10 ℃），可显著抑制锰和硅在钢表面的选择性氧化，此时试样表面为无定型SiOx、无定型MnOx以及纯态锰。随着过时效温度和露点温度的降低，锰和硅在表面的富集明显增加，同时发现，露点温度对合金表面元素富集峰值的影响比过时效温度更显著。采用低过时效温度（250 ℃）和低露点温度（－30 ℃）时，试样表面出现大量富锰和硅的颗粒状氧化物，由晶态的Mn3O4和MnO2以及硅的非化学计量氧化物SiO1.49和SiO0.93组成。     

过时效段露点对双相钢表面色差的影响

 冷轧双相钢具有较高的抗拉强度和较低的屈强比,成形性能优异,被汽车工业广泛用于生产形状比较复杂的结构件。由于冷轧双相钢中含有较多的易氧化的合金元素如锰、硅等,因此在退火时容易出现表面色差缺陷。采用镀锌模拟器研究了退火的过时效段工艺对该缺陷的影响,分别采用扫描电镜和辉光放电光谱分析了冷轧双相钢试样的表面形貌以及元素分布。结果表明,过时效段的露点温度对表面合金元素的富集和氧化有显著影响,较高的过时效露点温度会导致出现明显的色差缺陷。     

先进高强钢选择性氧化及抗粉化性能

介绍了生产先进高强钢热浸镀锌板的重要性,论述了生产过程中出现选择性氧化的原因及合金化板产生粉化的原因.具体分析了保护气氛的露点、保护气氛的组成、退火温度及时间、合金元素的种类和含量对高强钢选择氧化的影响.并分析了合金化工艺及锌液成分对合金化镀层相结构及抗粉化性能的影响.     

590 MPa级冷轧低合金高强钢表面色差分析

随着汽车轻量化的要求,高强钢在汽车产业中应用越发广泛。针对在生产冷轧低合金高强钢的过程中遇到的色差不良问题,分析色差产生的原因:一是退火炉炉内气氛异常,导致铁元素氧化生成氧化色产生色差。这种情况通过降低退火炉氧气含量、降低露点、提高氢气浓度可以避免。另是高强钢的合金元素锰元素,因高温在钢板表面富集导致的色差,此种情况因钢板成分所致,较难避免。经实验分析,有色差钢板的拉伸性能、化学处理性能符合客户标准,但颜色差异会导致客户疑义,因此实际生产中应尽量避免色差问题。     

热处理工艺对铝硅镀层热成形钢组织性能的影响

为深入理解不同热处理工艺参数对铝硅镀层热成形钢组织性能的影响规律,主要研究了加热温度和保温时间对铝硅镀层热成形钢的硬度、微观组织、镀层厚度和镀层成分的影响。结果表明,当加热温度不大于 900 ℃ 时,铝硅镀层热成形钢的硬度随着保温时间的增加而增加;当加热温度大于 900 ℃ 时,铝硅镀层热成形钢的硬度随着保温时间的增加而下降。当加热温度为850~930 ℃,保温时间为 4、8 min 时铝硅镀层热成形钢的微观组织在模具淬火冷却过程中均转化成为马氏体。在相同加热温度下,铝硅镀层热成形钢合金层的厚度随着保温时间的增加而增大,当加热温度升高至 930 ℃ 时,镀层因氧化而挥发严重,导致镀层变薄,所以铝硅镀层热成形钢的加热温度应控制在 930 ℃ 以下。保温温度升高、保温时间增加导致元素扩散显著,聚集的硅元素含量和面积由于其不断向四周扩散而降低。同时铁元素大量扩散到镀层中,镀层中铁元素含量增加显著。高温下,镀层发生明显的氧化反应,氧化反应促进了微孔洞的形核和长大。     

镀锌DP780漏镀缺陷的成因分析与预防措施

为了解决热镀锌线生产高强度双相钢产品出现的表面漏镀问题,通过对缺陷的宏观与微观形貌以及成分进行分析,同时对漏镀的形成机理进行分析,确定影响表面漏镀的主要原因是双相钢中含有硅、锰等元素较多,容易发生选择性氧化,氧化物阻碍铁元素和锌液的铝热反应,形成漏镀。根据分析结果,采取提高炉区加热段露点和降低氢气含量的方法对漏镀进行预防。结果表明,同时提高炉区加热段露点和降低氢气含量能有效解决表面漏镀问题,取得了较好的实用效果,为进一步开发拓展更高级别镀锌双相钢提供了技术基础和理论依据。     

FeMnAlC TWIP钢加热过程中的氧化行为GD-OES研究

摘要：以成分（质量分数）为Fe-16%Mn-1.5%Al-0.6%C-0.11%Cr的TWIP钢为研究对象，采用模拟试验研究了加热过程中的氧化行为，使用GD-OES分析了加热温度和加热气氛中O2含量对表面元素深度分布的影响。结果表明，当TWIP钢在N2-0.05%（体积分数）O2的气氛中加热至550~700℃时，表面会形成Fe-Mn氧化层，次表层会形成贫锰层、脱碳层及内氧化层，各层厚度随加热温度升高而增大。在氧化性气氛中加热时，Al元素优先在次表层形成内氧化，少量的Cr元素在氧化层/基体界面上形成外氧化，表面氧化层中基本不含Al和Cr。当加热温度为650℃时，气氛中O2体积分数在0.025%~0.2%之间变化对氧化层厚度影响较小，均可获得厚度介于400~500nm的氧化层。由此可见，为获得TWIP钢合适的预氧化层厚度，同时减少预氧化层/基板界面位置的氧化物，直火加热出口温度控制比空燃比控制更重要。     

热镀锌线上炉内带钢表面选择性氧化的影响因素分析

对热镀锌线上带钢表面合金元素选择性氧化的几个主要影响因素进行分析,阐述了合金元素的选择性氧化不仅与露点有关,还与热处理的退火气氛和合金元素的组成成分有关,另外热处理过程的退火时间和保温时间也会影响合金元素的选择性氧化,从而影响镀锌的粘附性,进而影响带钢的镀锌性能.     

退火过程IF钢表面氧化膜形成及其电化学性能研究

IF钢具有低屈强比、高伸长率、良好的深冲性能和无时效性等优异性能,被广泛应用于汽车等制造产业中。研究表明,IF钢表面形成的氧化膜对其耐蚀性具有重要的作用。采用XPS、EBSD、XRD和电化学分析方法,研究了退火过程IF钢表面氧化膜形成及其电化学性能。结果表明,在退火过程中不同合金成分IF钢晶体织构发生显著变化,且合金成分Si和Mn元素存在着明显的迁移行为。对于高Mn含量的IF钢表面氧化膜富集了锰氧化物和硅氧化物,降低了氧化膜的致密性,进而降低了氧化膜的自腐蚀电位和电阻值,提高了的自腐蚀电流,导致其氧化膜耐蚀性能下降。     

Effect of the presence of alloying elements in interstitial-free and low-carbon steels on their surface composition after annealing in reducing atmospheres (dew point=−30 °C)

The X-ray photoelectron spectroscopy (XPS) method is used to study the outer surfaces of interstitial-free (IF) and low-carbon (LC) steels with different alloying element contents (P, Ti, Nb, and Mn) after annealing at temperatures of 805 °C and 705 °C, respectively, for 40 seconds in reducing atmospheres (dew point=−30 °C). The work discussed seeks to establish possible relationships between the bulk composition of the IF and LC steels and the contents of segregated alloying element observed by XPS on the surface of the annealed steels, as well as to establish the influence of the presence of a thin iron oxide film on the steel surface on the segregation and oxidation of the alloying elements. Despite the low Mn and Si bulk steel contents and the shortness of the annealing cycle, considerable enrichment of these elements on the surface is seen, mainly as manganese and silicon oxides. The formation of a MnO layer on the annealed steel surface seems to be related to the reduction of iron oxides and the increase in the metallic Fe content. Despite its low content in LC steels, carbon also seems to diffuse towards the annealed steel surface to reduce iron oxides.     

The Development of a Processing Window for the Continuous Galvanizing of a Mn–Cr–Si Martensitic Steel

Martensitic or complex phase steels are leading candidates for automotive impact management applications. However, achieving high strengths while obtaining high quality coatings via continuous galvanizing is a challenge due to cooling rate limitations of the processing equipment and selective oxidation of alloying elements such as Cr, Mn, and Si adversely affecting reactive wetting. The galvanizability of a Cr? Mn? Si steel with a target tensile strength above 1250 MPa was investigated within the context of the continuous galvanizing line. The continuous cooling transformation behavior of the candidate alloy was determined, from which intercritical and austenitic annealing thermal cycles were developed. The evolution of substrate surface chemistry and oxide morphology during these treatments and their subsequent effect on reactive wetting during galvanizing were characterized. The target strength of 1250 MPa was achieved and high quality coatings produced using both intercritical (75% γ) and austenitic (100% γ) annealing using a conventional 95%N₂–5%H₂, ?30°C dew point process atmosphere and 0.20 wt% dissolved (effective) Al bath, despite the presence of significant Mn and Cr oxides on the substrate surfaces. It is proposed that complete reactive wetting by the Zn(Al, Fe) bath was promoted by in situ aluminothermic reduction of the Mn and Cr‐oxides by the dissolved bath Al.     

Hot Dip Galvanizing Simulation of Interstitial Free Steel by Liquid Zinc Spin Coater: Influence of Dew Point on Surface Chemistry and Wettability

In order to establish the relationship between surface chemistry and wettability as a function of dew point, an attempt has been made to simulate the hot‐dip galvanizing process with an ‘in‐house’ built Liquid Zinc Spin Coater. Interstitial free (IF) steel was annealed at 820°C in N₂‐5%H₂ gas atmospheres with dew points of ‐79°C, ‐29°C and 0°C, respectively. The wettability tests were conducted at 470°C at low dew point of ‐79°C. Surface analyses prior to wetting were carried out by using X‐ray photoelectron spectroscopy (XPS) and Field Emission Scanning Electron Microscopy (FE‐SEM). As expected, external oxidation of Al was observed only at the low dew point. With increasing dew point the oxidation of Cr and Si becomes internal. The formation of manganese silicates was observed at all dew points. While sulphur was detected on the specimen surface after all annealing conditions, the segregation of P starts to be significant at dew point 0°C by forming Mn‐phosphates. Despite the surface oxides, specimens annealed at all dew points are in the wetting regime by liquid zinc. Investigations on the steel/zinc interface of IF steel by using the liquid zinc spin coater were successful.     

Galvanizing and Galvannealing Behavior of CMnSiCr Dual-Phase Steels

Alloying elements, such as Mn, Mo, Si, and Cr, are commonly used to enhance the strength of advanced high-strength steels. Those elements also play an important role in the hot-dip galvanizing (GI) and galvannealing (GA) process. In this study, two kinds of CMnSiCr dual-phase steels were galvanized and galvannealed using a hot-dip simulator to investigate the effect of the alloying elements on the microstructure of the GI and GA coatings. The results showed that the dual-phase steels had good galvanizability because no bare spots were observed and the Fe-Zn phases were readily formed at the interface. However, the alloying reaction during the GA process was significantly hindered. XPS analysis showed that external oxidation occurred under an extremely low dew point [213 K to 203 K (?60 °C to ?70 °C)] atmosphere during the annealing prior to hot dipping. However, most of the oxides were reduced during the GI process. After the GI process, the Al was present as solid solutes in the Fe-Zn phase, suggesting that the Fe-Zn phase was formed from the transformation of the Fe-Al inhibition alloy. Meanwhile, the solubility of Si in the ζ phase was extremely low. With continued GA reaction, the ζ phase transformed into the δ phase, which contained approximately 1.0 at.pct Si. The Si also diffused into the Zn layer during the GA reaction. Hence, the ζ phase did not homogeneously nucleate at the steel substrate/Zn coating interface, but was found at the area away from the interface. Therefore, the Fe-Zn phases on the CMnSiCr dual-phase steels were relatively non-uniform compared to those on interstitial-free steel.     

Galvanizability of Complex Phase High Strength Steel

Complex phase (CP) steels have very high ultimate tensile strengths, resulting from the use of specific alloying elements, which improve the hardenability but cause difficulties when applying a zinc coating by means of continuous hot‐dip galvanizing. The galvanizability of a cold rolled 1000MPa complex phase steel was investigated by monitoring the surface chemistry before dipping and evaluating the quality of the zinc coatings applied by a laboratory hot‐dipping simulator. Two steel compositions with different Cr levels were used. The influence of the most important production parameters, the annealing temperature and the dew point of the annealing atmosphere, was investigated. Both steel compositions were galvanizable, but both the surface appearance and zinc coating adhesion were improved when low Cr contents were used. At a low dew point of ‐30°C, Cr, Mn and Si segregated to the surface and the presence of Mn₂SiO₄ could be demonstrated. At high dew point of +10°C, less oxides were present at the steel surface. There was no effect of the annealing temperature on the coatability.     

连退板浅表层的富集元素表征

为了研究连退板表层元素富集行为及相互作用,借助扫描电镜、辉光放电光谱仪、光电子能谱仪和透射电镜等技术手段对铝镇静钢和双相钢连退板表层中的富集元素进行了详细地表征与分析。结果表明,铝镇静钢连退板表面的主要富集元素有O、Mn和Al;而双相钢连退板表面的主要富集元素有O、Mn和Si。沿着浅表层深度分析可知,对于合金元素含量较高的双相钢,沿浅表层富集更深,富集深度约为50 nm;而合金元素含量较低的铝镇静钢,富集深度仅约为25 nm。综合分析不难发现,相对于铝镇静钢,双相钢添加了Si元素以后在其表面优先富集Si元素并同时形成了Si的氧化物,从而导致Al元素的富集及氧化物的形成受到了抑制。     

Selective Oxidation and Surface Segregation in High Strength Steels during Short Term Annealing in H2‐N2 ‐ Influence of B on Surface Chemistry

In order to achieve appropriate mechanical properties, new high strength steels aimed for the car industry have to be alloyed with solution strengthening elements. The annealing treatment undergone on cold rolled sheets induces the selective oxidation of alloying elements such as Al, Mn, Si and Cr. The formed oxides exhibit a poor wetting by the Zn bath during hot dip galvanising, thus deteriorating the properties of the zinc coating. While surface‐segregating elements get oxidised, they interact with each other through the formation of spinels and/or mixed oxides during annealing and oxides which have a deleterious effect on wetting can be formed. The formation of (Mn, B) oxide was observed on alloys containing even very small amounts of B and this oxide is almost not wetted at all by Zn. Boron is added to interstitial‐free steels to improve the cold work embrittlement, by replacing phosphorus at the grain boundaries. In this paper, the selective oxidation of steels with and without B, in 5 vol. % H₂‐N₂ atmosphere at 820°C and different dew points was investigated. We found a very strong effect of segregation and oxidation of B on Si and S segregation and oxidation behaviour.