Comparison between the surface defects caused by Al_2O_3 and TiN inclusions in interstitial-free steel auto sheets

Al_2O_3 and TiN inclusions in interstitial-free(IF) steel deteriorate the properties of the steel. To decrease the defects of cold-rolled sheet, it is important to clearly distinguish between the degrees of damage caused by these two inclusions on the surface quality of the steel. In this study, a nanoindenter was used to test the mechanical properties of the inclusions, and the distribution and size of the inclusions were obtained by scanning electron microscopy(SEM). It was found that when only mechanical properties are considered, TiN inclusions are more likely to cause defects than Al_2O_3 inclusions of the same size during the rolling process. However, Al_2O_3 inclusions are generally more inclined to cause defects in the rolling process than TiN inclusions because of their distribution characteristic in the thickness direction. The precipitation of Al_2O_3 and TiN was obtained through thermodynamical calculations. The growth laws of inclusions at different cooling rates were calculated by solidification and segregation models. The results show that the precipitation regularity is closely related to the distribution law of the inclusions in IF slabs along the thickness direction.

Effect of continuous annealing temperature on microstructure and properties of ferritic rolled interstitial-free steel

In this report,the microstructure,mechanical properties,and textures of warm rolled interstitial-free steel annealed at four different temperatures(730,760,790,and 820°C)were studied.The overall structural features of specimens were investigated by optical microscopy,and the textures were measured by X-ray diffraction(XRD).Nano-sized precipitates were then observed by a transmission electron microscope(TEM)on carbon extraction replicas.According to the results,with increased annealing temperatures,the ferrite grains grew;in addition,the sizes of Ti_4C_2S_2 and Ti C precipitates also increased.Additionally,the sizes of Ti N and Ti S precipitates slightly changed.When the annealing temperature increased from 730 to 820°C,the yield strength(YS)and the ultimate tensile strength(UTS)showed a decreasing trend.Meanwhile,elongation and the strain harden exponent(n value)increased to 49.6%and 0.34,respectively.By comparing textures annealed at different temperatures,the intensity of{111}texture annealed at 820°C was the largest,while the difference between the intensity of{111}<110>and{111}<112>was the smallest when the annealing temperature was 820°C.Therefore,the plastic strain ratio(r value)annealed at 820°C was the highest.

Study on grain refinement of interstitial-free steel during continuous frictional angular extrusion

To explore the application of severe plastic deformation for grain refinement in steel production, a new method called continuous frictional angular extrusion （CFAE） was applied to refine the grain of interstitial-free steel. The deformation was carried out at room temperature and individual sheet specimens were processed in different number of passes. An overall grain size of 200nm was achieved after 8 passes and the proportion of high-angle boundaries to the total boundaries was more than 60%. Through the characterization of high resolution EBSD, X-ray diffraction （XRD） and hardness testing,this paper discussed the evolution of microstructures and textures during deformation and explored the development direction of the method.

Determination of CaO in Baotou Columbite and Steel Cinder with Flame Atomic Absorption Spectrometry

The determination of CaO content in columbite and steel cinder with flame atomic absorption spectrometry is studied. EDTA+TEA is used to eliminate the interferences, in HCI media,with La as releaser. The methods of sample treatment and the CaO in remainder undissolved in acids have been conducted. The result of the determination and recovery of CaO shows that the rate of recovery is 100% ～ 102 %, R. S.D<2 %.

Texture evolution during semicontinuous equal-channel angular extrusion process of interstitial-free steel

Semicontinuous equal-channel angular extrusion（ SC-ECAE） is a novel severe plastic deformation technique that has been developed to produce ultrafine-grain steels. Instead of external forces being exerted on specimens in the conventional ECAE,driving forces are applied to dies in SC-EACE. The deformation of interstitial-free（ IF） steel w as performed at room temperature,and individual specimens w ere repeatedly processed at various passes. An overall grain size of 0. 55 μm w as achieved after 10 passes. During SC-ECAE,the main textures of IF steel included { 111} ,{ 110} ,{ 112} ,{ 110} ,and { 110} At an early stage,increasing dislocations induce new textures and increase intensity. When the deformation continues,low-angle boundaries are formed betw een dislocation cell bands,w hich cause some dislocation cell bands to change their orientation,and therefore,the intensity of the textures begins to decrease. After more passes,the intensity of textures continues to decrease w ith high-angle boundaries,and the sub-grains in dislocation cell bands continuously increase. The present study reports the evolution of textures during deformation; these w ere examined and characterized using high-resolution electron backscattered diffraction（ EBSD） in a field emission scanning electron microscope. The mechanisms of texture evolution are discussed.

Characterization of 17-4PH stainless steel powders produced by supersonic gas atomization

17-4PH stainless steel powders were prepared using a supersonic nozzle in a close-coupled gas atomization system. The characteristics of powder particles were carried out by means of a laser particle size analyzer, scanning electron microscopy （SEM）, and the X-ray diffraction （XRD） technique. The results show that the mass median particle diameter is about 19.15 prn. Three main types of surface microstructures are observed in the powders： well-developed dendrite, cellular, and cellular dendrite structure. The XRD measurements show that, as the particle size decreases, the amount of fcc phase gradually decreases and that of bcc phase increases. The cooling rate is inversely related to the particle size, i.e., it decreases with an increase in particle size.

Microstructure simulation of rapidly solidified ASP30 high-speed steel particles by gas atomization

In this study, the microstructure evolution of rapidly solidified ASP30 high-speed steel particles was predicted using a simulation method based on the cellular automaton-finite element （CAFE） model. The dendritic growth kinetics, in view of the characteristics of ASP30 steel, were calculated and combined with macro heat transfer calculations by user-defined functions （UDFs） to simulate the microstructure of gas-atomized particles. The relationship among particle diameter, undercooling, and the convection heat transfer coefficient was also inves- tigated to provide cooling conditions for simulations. The simulated results indicated that a columnar grain microstructure was observed in small particles, whereas an equiaxed microstructure was observed in large particles. In addition, the morphologies and microstructures of gas-atomized ASP30 steel particles were also investigated experimentally using scanning electron microscopy （SEM）. The experimental re- suits showed that four major types ofmicrostructures were formed： dendritic, equiaxed, mixed, and multi-droplet microstructures. The simu- lated results and the available experimental data are in good agreement.

Enrichment characteristic of carbon atoms in solid-liquid zone of high carbon steel under different directional solidification rates

To reveal the formation mechanism and main influencing factors of C-segregation in high carbon steel under different solidification rates(40,80,160,200 and 320μm·s^(-1)),the enrichment characteristics of carbon atoms in the solid-liquid zone of Fe-0.61%C steel were studied using a zone melting liquid metal cooling apparatus and electron probe microanalysis.The relationships among micro-segregation of carbon atoms,solid-liquid interface morphology and solidification rate were fully discussed.The results show that large dendrite spacing and a slow-moving dendritic interface create less resistance and more time for the migration of interdendritic carbon atoms to liquid zone.This results in the continuous enrichment of carbon atoms in liquid zone,further expands the solid-liquid temperature range,prolongs the solidification time of molten steel,and causes the formation of carbon micro-segregation at the solidification end as the solidification rate is 40μm·s^(-1).Conversely,abundant and elongated secondary dendrite arms with small spacing seriously impede the diffusion of interdendritic carbon-rich molten steel to liquid zone.As a result,there is only obvious dendrite segregation,but little difference in the carbon content along the solidification direction as solidification rate exceeds 200μm·s^(-1).

Possibility of utilizing water-atomized Fe-Ni-Mo steel powder as base materials for warm compaction process

Water atomized Fe Ni Mo steel powder, was utilized as base powder for designing powder mixtures for warm pressing. The warm pressing and sintering behaviours of the powder mixtures were studied. The results show that, compared with the pressing at room temperature, the green density gain by warm pressing is within a range of 0.10 0.19 g/cm 3 and reduction in spring back is 30% 40% of the ambient, and maximum green density of 7.32 g/cm 3 at 735 MPa is obtained as the graphite mass fraction is 0.8%. It was found that sintered densities of the compacts were reduced slightly due to releasing of elastic stress stored in the compacts during sintering. The warm pressing of steel powders gives evidence for substituting the traditional double pressing and double sintering process.

Producing micro-droplet of dilute sulphuric acid on pure iron surface and observing its corrosion behaviour by atomic force microscopy

A simple method was presented to produce a micro-droplet of sulphuric acid on a pre-selected micro-zone on a pure iron surface with the tip of an AFM cantilever. The three-dimensional shape of the droplet was imaged with the AC non-contact mode of the AFM, and the liquid/solid interface was observed in situ during corrosion using the contact mode. The substrate surface beneath the droplet was lowered by approximately 19 nm after 3.6 ks of adhesion. This method has important implications for experimental studies of micro-zone corrosion or lubrication.

雾化射流对42CrMo钢车削断屑性能影响的实验研究

金属加工过程中,切屑周期性断裂有利于切削过程的稳定进行,实现高质高效加工。雾化射流是一种重要的冷却方式,把压缩空气与切削液混合并断续喷射形成雾状。与切削液溢流冷却相比,雾化射流射出的小液滴渗透性更好,冷却介质能更准确地施加到刀具前刀面和切屑内表面位置。为了探究雾化射流对42CrMo钢车削断屑性能的影响,采用三种冷却方式(干切削、切削液溢流及雾化射流)和两种进给量(0.15mm/r, 0.18mm/r)进行车削实验,对切屑的宏观长度、卷曲半径、切削力和刀—屑接触长度进行观测。在相同的进给量下,采用雾化射流冷却方式可以获得更短的切屑宏观长度、更小的切屑卷曲半径、更小的切削力、更短的刀—屑接触长度以及更小的切屑内表面粗糙度。

长时效期BH钢的烘烤硬化性能及其机理研究

采用万能材料试验机、TEM/EDS、3DAP,分别对时效3个月和6个月的超低碳烘烤硬化钢(钢号HC180B)进行力学性能测试和组织、析出相表征,并分析了烘烤硬化过程中的元素偏聚行为。结果表明,与时效3个月相比,钢板在时效6个月后仍具有优异的力学性能,展示出良好的抗时效性。TEM和3DAP分析显示,退火冷轧板中仅有C原子在晶界处轻微偏聚,B、Mn、Nb、Ti均匀分布在钢中;2%预拉伸变形后,这些元素在相同晶界处表现出不同程度的偏聚现象,TiN多呈矩形优先在晶界大量析出,NbC则少量析出;进一步烘烤后,C、B、Mn、Nb、Ti在晶界处的偏聚现象更为显著且连续,NbC呈椭球形大量析出。析出相与位错、晶界的交互作用显著提升了钢板的烘烤硬化性能。

X80管线钢内壁旋杯喷涂涂层厚度均匀性研究

石油天然气多采用管道进行输送,管道内壁的腐蚀是其主要失效形式,对管道内壁添加涂层可以提高管道耐腐蚀性能。对X80管线钢内壁高速旋杯离心喷涂开展工艺实验,研究了喷涂关键参数包括旋杯转速、行进速度、旋杯外径、喷涂压力对涂层平均厚度及涂层均匀性的影响规律和原因。而后对喷涂工艺参数进行系统性优化,得到最佳的工艺参数组合。实验结果表明,涂层平均厚度主要由旋杯转速、喷涂压力、行进速度以及旋杯外径决定,涂层的均匀性主要由旋杯转速以及喷涂压力决定。当旋杯转速为25000r/min、喷涂压力为0.2MPa、行进速度为0.9m/min、旋杯外径为32mm时,涂层均匀性最佳,涂层的平均厚度为450.3μm,涂层厚度标准差值为3.3μm。

钢晶粒度的截距直接测量法

针对钢产品中双相或多相组织平均晶粒度难以评定的问题,以单相组织无间隙原子钢为试验对象,采用图像处理软件对单视场内截距测量数量进行确定,开发了一种采用截距直接测量法测量平均晶粒度的新方法,并将该方法应用于DH590、38MnVS、400E钢等含双相或多相组织材料的平均晶粒度评定。结果表明:截距直接测量钢产品平均晶粒度的方法简便可行、检验效率高、出错率低;测量结果与GB/T 6394—2017中截点法的测量结果基本一致;截距直接测量法既适用于单相组织平均晶粒度的测量,也适用于双相或多相组织平均晶粒度的测量。

电感耦合等离子体原子发射光谱法测定核级316不锈钢中痕量铈

提出了电感耦合等离子体原子发射光谱法(ICP-AES)测定核级316不锈钢中痕量铈的方法。取0.100 0 g样品于烧杯中,加入15 m L现配体积比为1∶3∶4的硝酸-盐酸-水混酸溶液,置于150℃电热板上消解30 min,完全溶解后加入5 m L 30%(质量分数)过氧化氢溶液,恒温3 min后取下冷却至室温,用水定容至100 m L。设置仪器射频功率为1 150 W,雾化气流量为0.45 L·min^(-1),测量铈元素在404.076 nm分析谱线处的响应强度,基质匹配法定量。结果表明:铈的质量浓度在100 mg·L^(-1)以内与对应的响应强度呈线性关系,检出限(3s)为0.000 4%。4个样品精密度试验所得测定值的相对标准偏差(n=10)均小于5.0%。按照标准加入法进行回收试验,回收率为95.5%~103%;采用GH56(屑样)铁镍基标准物质进行准确度验证,测定值与认定值基本一致。

重量法-电感耦合等离子体原子发射光谱法联用测定无取向硅钢磷酸盐体系环保涂层液中二氧化硅含量

二氧化硅是无取向硅钢环保涂层液的核心成分,其含量直接影响硅钢涂层的固化工艺及涂层产品的磁性能。因此为保证涂覆过程的顺利进行,对涂层液中二氧化硅含量的检测是十分必要的。通过在样品中分别加入硝酸、过氧化氢及高氯酸,置于电热板上进行消解处理,处理后的样品经酸溶、过滤步骤,以重量法计算沉淀中二氧化硅的含量,采用电感耦合等离子体原子发射光谱(ICP-AES)法测定滤液中可溶性硅含量,则样品中二氧化硅含量为重量法和电感耦合等离子体原子发射光谱法测定结果的合量。从而建立了重量法-电感耦合等离子体原子发射光谱法联用测定无取向硅钢磷酸盐体系环保涂层液中二氧化硅含量的方法。讨论了样品前处理用消解酸及消解温度、滤液中可溶性硅及含量、ICP-AES仪器检测时的元素干扰。结果表明,检测结果的相对标准偏差(RSD,n=12)在0.76%~1.1%,加标回收率在97.0%~104%。方法可广泛应用于各检测部门对无取向硅钢磷酸盐体系环保涂层液中二氧化硅含量的监控。

不锈钢双极板涂层-TiO_(2)薄膜的导电耐腐蚀行为研究

为了提高燃料电池金属双极板的导电耐腐蚀性,本文采用原子层沉积(ALD)工艺,在不锈钢316L上制备了TiO_(2)纳米薄膜,对比了不同加热温度以及基板加热与否时薄膜的导电耐腐蚀性能。结果表明,当加热250℃且基板不加热时,0.84 V恒电位腐蚀24 h,双极板涂层-TiO_(2)薄膜的电流密度最小,为1×10^(-10)A/cm^(2),且腐蚀前后接触电阻相对较小,导电和耐腐蚀性能均表现优异。通过XPS分析腐蚀前后薄膜表面的成分结构,发现二氧化钛保持了较稳定的结构,接触电阻增大主要源于表面C的氧化。

原子吸收法测定钢铁废水中的重金属及影响因素分析

本文主要研究了石墨炉原子吸收分光光度法测定钢铁废水中的Cd、Pb、Cu三种重金属含量及其影响因素。该方法准确、高效、检出限低,解决了传统化学方法操作繁琐、分析周期长的弊端。

Effect of Silicon Content on Thermodynamics of Austenite Decomposition in C-Si-Mn TRIP Steels

Some numerical models such as central atoms model （CAM） and superelement model were used to simulate the thermodynamics of austenite decomposition in the Fe-C-Mn-Si TRIP （transformation induced plasticity） steels. Thermodynamic calculations were carried out under a para-equilibrium （PE） condition. The results show that certain silicon content can accelerate the polygonal ferritic transformation and increase the volume fraction and stability of retained austenite by retarding the precipitation of carbides during the bainitic transformation.

Corrosion behavior and mechanism of the automotive hot-dip galvanized steel with alkaline mud adhesion

The corrosion behavior and mechanism of hot-dip galvanized steel and interstitial-free （IF） substrate with alkaline mud adhesion were investigated by scanning electron microscopy （SEM）, X-ray diffraction （XRD）, electrochemical impedance spectroscopy （EIS）, and linear polarization. The results show that non-uniform corrosion occurs on the galvanized steel and IF substrate during 250 h with the mud adhesion. The corrosion products on the galvanized steel are very loose and porous, which are mainly ZnO, Zn5（OH）8C12·H2O and Zn（OH）2, and Fe-Zn alloy layer with a lower corrosion rate is exposed on the galvanized steel surface; however, the corrosion products on IF substrate are considerably harder and denser, whose compositions of rust are mainly FeOOH and Fe3O4, and several pits appear on their surface. The results of continuous EIS and linear polarization measurements exhibit a corrosion mechanism, that is, under activation control, the charge transfer resistances present different tendencies between the galvanized steel and IF substrate; in addition, the evolution of linear polarization resistances is similar to that of charge transfer resistances. The higher contents of dissolved oxygen and Cl^- ions in the mud play an important role in accelerating the corrosion.