Relationship between Oxygen Chemical Potential and Steel Cleanliness

To investigate inclusion formation in each step during steel making process, several samples were taken in different steps of the production of steel at Mobarakeh Steel Co of Esfahan to measure the oxygen chemical potential of the molten steel in each stage. The chemical compositions of the inclusions in samples were investigated by scanning electron microscope. The chemical composition of the slag was analyzed. With the use of thermodnamic calculations and chemical analysis of the melt, at the working temperature, the relationship between dissolved oxygen and other elements were determined. Finally, it was found that there is a close relationship between inclusions formed in each step with the oxygen partial pressure.

Synthesis of steel slag ceramics: chemical composition and crystalline phases of raw materials

Two types of porcelain tiles with steel slag as the main raw material （steel slag ceramics） were synthesized based on the CaO-A1203-SiO2 and CaO--MgO-SiO2 systems, and their bending strengths up to 53.47 MPa and 99.84 MPa, respectively, were obtained. The presence of anorthite, a-quartz, magnetite, and pyroxene crystals （augite and diopside） in the steel slag ceramics were very different from the composition of traditional ceramics. X-ray diffraction （XRD） and electron probe X-ray microanalysis （EPMA） results illustrated that the addition of steel slag reduced the temperature of extensive liquid generation and further decreased the firing temperature. The considerable contents of glass-modifying oxide liquids with rather low viscosities at high temperature in the steel slag ceramic adobes promoted element diffusion and crystallization. The results of this study demonstrated a new approach for extensive and effective recycling of steel slag.

Influence of chemical composition and cold deformation on aging precipitation behavior of high nitrogen austenitic stainless steels

The influence of chemical composition and cold deformation on aging precipitation behavior of 18Cr-16Mn-2Mo-I.IN （HNS-A）, 18Cr-16Mn-I.3N （HNS-B）, 18Cr-18Mn-2Mo-0.96N （HNS-C） and 18Cr-18Mn-2Mo-0.77N （I-INS-D） high nitrogen austenitic stainless steels was investigated. The results show that the ＂nose＂ temperatures and incubation periods of the initial time-temperature-precipitation （TTP） curves of aged HNSs are found to be 850 ℃, 60 s; 850 ℃, 45 s; 850 ℃, 60 s and 900 ℃, 90 s, respectively. Based on the analysis of SAD patterns, the coarse cellular Cr2N precipitate which presents a lamellar structure has a hexagonal structure of a=0.478 nm and c=0.444 nm. The Z phase corresponding to a composition of Fe36Cr^2Mo10, is determined to be a body-centered cubic structure ofa=0.892 nm. The precipitating sensitivity presents no more difference with the nitrogen content increasing from 0.77% to 0.96%, but exhibits so obviously that the cellular precipitates nearly overspread the whole field. The addition of Mo element can restrain the TTP curves moving left and down, which means decreasing the sensitivity of aging precipitation. With increasing the cold deformation, the sensitivity of precipitation increases obviously.

Effect of Shrinkage Reducing Agent and Steel Fiber on the Fluidity and Cracking Performance of Ultra-High Performance Concrete

Due to the low water-cement ratio of ultra-high-performance concrete(UHPC),fluidity and shrinkage cracking are key aspects determining the performance and durability of this type of concrete.In this study,the effects of different types of cementitious materials,chemical shrinkage-reducing agents(SRA)and steel fiber(SF)were assessed.Compared with M2-UHPC and M3-UHPC,M1-UHPC was found to have better fluidity and shrinkage cracking performance.Moreover,different SRA incorporation methods,dosage and different SF types and aspect ratios were implemented.The incorporation of SRA and SF led to a decrease in the fluidity of UHPC.SRA internal content of 1%(NSRA-1%),SRA external content of 1%(WSRA-1%),STS-0.22 and STE-0.7 decreased the fluidity of UHPC by 3.3%,8.3%,9.2%and 25%,respectively.However,SRA and SF improved the UHPC shrinkage cracking performance.NSRA-1%and STE-0.7 reduced the shrinkage value of UHPC by 40%and 60%,respectively,and increased the crack resistance by 338%and 175%,respectively.In addition,the addition of SF was observed to make the microstructure of UHPC more compact,and the compressive strength and flexural strength of 28 d were increased by 26.9%and 19.9%,respectively.

AN INVESTIGATION OF CHEMICAL SHORT CRACK CHARACTERISTICS IN GC－4 HIGH－STRENGTH STEEL

A method of constant △K value is applied experimentally to investigatechemical short crack characteristics of GC-4 high-strength steel in 3.5%NaClsolution. Experimental results show that there is a critical point of crack geometry aon da / dN-a curve of the crack propagation at constant △K value. When the cracklength a < a , chemical short crack effect appears. The value of a is almost not af-fected by the loading frequency, stress ratio and △K level. The ratio of characteristiccrack propagation rate of chemical short cracks to that of long cracks is a weak func-tion of the loading frequency, stress ratio and △K level. Based on the analysis, the rela-tion between the short crack propagation rate and crack size is suggested.

Microstructure Analysis for Chemical Interaction between Cesium and SUS316 Steel in Fast Breeder Reactor Application

The objective of this study is to presume cesium corrosion process and its dominant factors in SUS316 steel, a fuel cladding material for fast breeder reactor application, based on both experimental results of cesium corrosion out-pile test and thermodynamic consideration. The cesium corrosion test was performed in simulated environment of high burn-up fuel pin. And main corrosion products in the specimen after the corrosion test were specified by TEM （transition electron microscopy） and SEM （scanning electron microscopy） in order to formulate a hypothesis of the cesium corrosion process. At the end of this study, it was found that the dominant factors of the corrosion process are the amount of cesium on the surface of the specimen, chromium content in the alloy, the supply rate of oxygen and temperature.

Physical and chemical performances of high Al steels

The effects of acid-soluble Al content on the physical and chemical performances of high Al steels were investigated. The results show that the distribution of acid-soluble Al in steel substrate is uniform. With increasing Al content, the strength and toughness of steels decrease a little but the hardness increases. The average yield strength and tensile strength are 425MPa and 570MPa, respectively, and the Rockwell hardness is 89.7. For non-Al steels the average oxidation rate is up to 0.421mg/(cm2·h) at 1373K. For high Al steels, when the mass fraction of Al is less than 5%, there is a thinner gray oxidized layer on surface and the oxidation rate is high; when the mass fraction of Al is more than 8.0%, the thin, close and yellow glossing film still exists, and the average oxidation rate is only 0.016mg/(cm2·h).

Fretting Wear Behavior of Medium Carbon Steel Modified by Low Temperature Gas Multi-component Thermo-chemical Treatment

The introduction of surface engineering is expected to be an effective strategy against fretting damage. A large number of studies show that the low gas multi-component （such as carbon, nitrogen, sulphur and oxygen, etc） thermo-chemical treatment（LTGMTT） can overcome the brittleness of nitriding process, and upgrade the surface hardness and improve the wear resistance and fatigue properties of the work-pieces significantly. However, there are few reports on the anti-fretting properties of the LTGMTT modified layer up to now, which limits the applications of fretting. So this paper discusses the fretting wear behavior of modified layer on the surface of LZ50 （0.48%C） steel prepared by low temperature gas multi-component thermo-chemical treatment （LTGMTT） technology. The fretting wear tests of the modified layer flat specimens and its substrate （LZ50 steel） against 52100 steel balls with diameter of 40 mm are carried out under normal load of 150 N and displacement amplitudes varied from 2 μm to 40 μm. Characterization of the modified layer and dynamic analyses in combination with microscopic examinations were performed through the means of scanning electron microscope（SEM）, optical microscope（OM）, X-ray diffraction（XRD） and surface profilometer. The experimental results showed that the modified layer with a total thickness of 60 μm was consisted of three parts, i.e., loose layer, compound layer and diffusion layer. Compared with the substrate, the range of the mixed fretting regime（MFR） of the LTGMTT modified layer diminished, and the slip regime（SR） of the modified layer shifted to the direction of smaller displacement amplitude. The coefficient of friction（COF） of the modified layer was lower than that of the substrate in the initial stage. For the modified layer, the damage in partial slip regime（PSR） was very slight. The fretting wear mechanism of the modified layer both in MFR and SR was abrasive wear and delamination. The modified layer presented better wear resistance than the substrate in PSR and MFR; however, in SR, the wear resistance of the modified layer decreased with the increase of the displacement amplitudes. The experimental results can provide some experimental bases for promoting industrial application of LTGMTT modified layer in anti-fretting wear.

Study on the Corrosion inhibitor and Fog Suppressor for Chemical Pickling of Iron and Steel

A new type of corrosion inhibitor and fog suppressor composed of Nitrogen-containing alkaloid,water-soluble butadiene lower polymer, and inorganic electrolyte has been investigated by gravimetric and electrochemical method. Effects or this chemicals on pickling rate and hydrogen penetration into iron and steel material in 50～150 g/L HCI or/and H2SO4 solutions at 20～70℃ temperature were examined. The amount of acid fog escaping from the surface of air-liquid was determined by chemical titration. The results indicate that the efficiency of inhibition and suppression depends on film properties by which mean a barrier film on the interface of bare mild steel/solution or an unsolvable liquid membrane as hydrophibic effect.In present work the film-forming mechanism by in situ and chemistry-mechanics effect is also discussed.

A Feedforward Controller to Regulate the Chemical Composition of Molten Steel in a Continuous Casting Tundish

A feedforward controller for the automatic regulation of chemical composition of molten steel in the tundish of a continuous casting machine is proposed in this work. The flow of molten steel inside the tundish is modeled as a distributed parameter system, and the resulting partial differential equation is transformed into a set of ordinary differential equations by means of the finite differences technique. From the above set and using a proper boundary condition, a feedforward control law is synthesized. No experimental tests are reported, however, the dynamic performance of the controller is illustrated by means of numerical simulations.

Effects of Chemical Composition and Cooling Process on Structures and Properties of Direct-Quenched Steels

The microstructures and mechanical properties of a series of direct-quenched steels containing,in weight percent,from 0.05 to 0.20 carbon,0.20 to 0.40 silicon,1.10 to 1.70 manganese and at least one microalloying element of vanadium,niobium,titanium and boron have been investigated.After controlled rolling,these steels were cooled in spray water to 400,300 and 200℃,respectively and then cooled in still air.Comparison of the Charpy V-notch impact toughness of direct-quenched steels without subsequent tempering was made with that of direct-quenched steels tempered at 600℃.It is found that an attractive combination of strength and toughness is achived by means of direct-quenching.There exists two types of microstructures in accordance with carbon equivalent.Lath martensitic microstructure is obtained for C>0.4%,granular bainitic microstructures for C.< 0.35%and mixtures of martensite and bainite for C,.in the range of 0.35— 0.40%.The effect of interrupted quenching temperature on microstructure is not significant for low C.steel,but interrupted quenching temperature has a strong effect on microstructure for high C,.steel.

Corrosive Behavior and Physic-Chemical Characterization of Filtration Tanks

Most drinkable water supplied to the public in Mexico City comes from deep wells which extract water from the subsoil. Before being distributed, it is treated in steel filtration tanks. This water must be subject to evaluation through physic-chemical and bacteriological analyses in order to determine its quality. However, doubts always remain over the influence of the components of this water on the corrosive behavior of the filtration tanks. In light of this, this article studies the physic-chemical characterization values of water and presents the results. This has also enabled the analysis of the corrosion speed of filtration tanks components, boilers and water-cooled systems, where incrustations in pipes, obstructions and loss of heat transfer efficiency occur, rendering drinkable water bad tasting and, after some time, causing pitting corrosion although this type of corrosion only causes serious problems in the long term.

激发材料对碱性钢渣替代水泥早期强度规律研究

以碱性钢渣为研究对象,在机械粉磨基础上,采用化学激发方式探究碱性钢渣替代水泥早期强度变化规律;研究不同种类、掺量化学激发剂对钢渣活性的作用,利用XRD、SEM对钢渣替代水泥的水化产物进行分析。结果表明:机械粉磨能够有效改善钢渣粒径中的粗颗粒和细颗粒含量,优化颗粒级配,最佳粉磨时间为20 min;化学激发能够在机械粉磨上进一步提高钢渣胶凝活性,当早强剂掺量为2.0%、芒硝掺量为3.0%、氢氧化钠掺量为1.0%、钢渣掺量为25%时效果最佳;钢渣替代水泥主要水化产物是方解石(CaCO_(3))、氢氧钙石(Ca(OH)_(2))、硅酸二钙(Ca_(2)SiO_(4))和C-S-H凝胶,微观组织呈现纤维网状结构,为力学性能的提高奠定了基础。

H13热作模具钢表面强化层耐磨性能研究进展

H13钢被广泛用于铝合金、镁合金等金属的热挤压模和压铸模,服役环境恶劣,常规处理淬、回火后,耐磨性严重不足,易导致热疲劳裂纹的产生,从而影响模具使用寿命和产品质量。对H13热作模具钢表面进行强化是提高耐磨性及服役寿命的有效手段。综述了国内外关于H13热作模具钢表面强化的研究现状及进展,并对H13模具钢表面改性技术发展方向做出展望。

长材轧机热轧钢筋类产品生产概述

结合国家标准对长材轧机热轧钢筋类产品的生产工艺、产品特点等进行解读,并介绍高强螺纹钢筋的几种生产工艺。可供工程技术人员、产品用户等理解各类热轧钢筋的生产工艺、产品特点等。

三元固废掺和料耦合机理分析和活化

为实现铁尾矿固废材料的再生利用,提高工业固废利用率,利用陶瓷粉和钢渣组成三元固废掺和料(铁尾矿-陶瓷粉-钢渣)并耦合活化。通过对铁尾矿进行不同时间的机械研磨,加入不同活化剂进行化学活化来提高铁尾矿的活性。采用差热-热重(DTA-TG)分析、扫描电镜(SEM)等方法研究三元掺和料的耦合活化和机械-化学活化机理。结果表明,适当增加铁尾矿研磨时间可以提升掺和料体系的活性指数,Na2SiO3活化剂对掺和料体系活性提升最显著。在三元掺和料体系中,铁尾矿、陶瓷粉主要起填充作用,而钢渣中活性CaO、硅酸二钙(C2S)和硅酸三钙(C3S)成分可以参与水化反应生成较多水化产物,从而提升后期强度,复掺时活性指数均满足普通型Ⅱ级掺和料使用标准,最高活性指数可达88.29%,具备制备三元复合掺和料的潜力。

异常生产状态下钢包顶吹工艺研究与应用

针对马钢65 t转炉出钢后到站钢水钢包透气砖气量小或无底吹,无法保证钢水成分和温度均匀性,以及出钢后到站钢水温度低于工艺要求目标范围下限,无法满足铸机正常浇注对钢水温度要求的问题,通过向钢包顶吹氩气搅拌,实现均匀钢水成分和温度的目的,通过向钢包顶吹氧气,同时加入SiFe和SiMn合金,利用氧气与发热元素Si和Mn反应放热,实现低温钢水在线快速提升温度的目的。生产实践表明:采用硅铁合金(含硅72.5%)和硅锰合金(含硅18.64%、含锰66.6%)作为发热剂,氧气压力为1.2 MPa,流量为1200 Nm^(3)/h,吹氧时间为5 min时,平均升温速率为3.55℃/min,钢中发热元素Si和Mn的平均烧损率分别为0.014%/min和0.022%/min。钢包顶吹工艺为转炉平稳高效冶炼提供重要保障,取得了良好的使用效果。

利用电化学和显色检测法分级评估316L不锈钢钝化膜完整性

针对核电和航天工程不锈钢设备服役在高温高盐海洋环境中钝化和损伤的质检评估,提出显色检测图像分析钝化膜完整性分级的方法。以不同钝化及其损伤状态的316L不锈钢为研究对象,通过显色检测的红色色度图像分析与电化学腐蚀行为检测,建立显色色度与耐蚀性的关系,并获得分级范围。结果表明,显色色度随钝化膜损伤程度增加而增大,随自钝化时间的延长而减小;二次局部损伤在直方图中具有双峰特征;色度百分比和面积百分比呈现双对数线性二阶段特征;动电位极化和阻抗表明,点蚀电位和界面反应阻抗随损伤程度的增加而减小;耐蚀性随显色色度的增加而下降;最终获得了316L不锈钢钝化膜完整性的三个色度等级范围。这可为不锈钢钝化膜质检分级评估提供理论基础。

火电机组用耐热钢高温耐腐蚀性能研究进展

从火电机组用耐热钢的发展历程出发,综述了新型耐热钢高温耐腐蚀性能的研究现状,并分别从腐蚀原理、化学成分、腐蚀环境和腐蚀防护等方面对耐热钢耐腐蚀性能的影响进行阐述;最后对火电机组用耐热钢高温耐腐蚀性能现有研究成果进行分析总结,并对未来研究方向以及发展趋势进行了展望。

高锰钢表面耐磨蚀镀层研究

研究了不同化学镀工艺对高锰钢镀层组织和性能的影响。得出化学镀Ni-P的最佳参数为:NiSO_(4)·6H_(2)O质量浓度30 g/L;NaH_(2)PO_(2)·H_(2)O质量浓度35 g/L;pH值4.7。非晶态Ni-P镀层致密,厚度约25μm。镀层硬度由330 HV提高到600 HV以上,磨损体积减少。镀层的腐蚀电流密度从基体的8.51 mA/cm^(2)降低到1.82 mA/cm^(2)。镀层明显提高了高锰钢基体的表面硬度、耐磨性能和耐腐蚀性能。