Corrosion Mechanism of Alumina-magnesia Dry Materials for Smelting Manganese/chromium Steel in Coreless Medium Frequency Induction Furnaces

Alumina-magnesia dry materials are widely used in induction furnace linings, but they show different kinds of damage when melting different kinds of alloy steel. In this paper, the chemical composition, phase composition, and microstructure of the post-use dry materials for the working liners melting different kinds of steel were evaluated. Furthermore, the corrosion mechanism of the steel on the furnace lining materials was comprehensively analyzed. The findings reveal a significant ability of the Mn element in the molten steel to diffuse and penetrate into the refractories. Mn oxidizes to form MnO at the steel-refractory interface, and then forms a liquid phase with Al_(2)O_(3). The Cr element is dissolved into corundum and spinel of the refractories, resulting in lattice defects and structural damage of the materials. TiO2reacts with Al_(2)O_(3) to form Al_(2)TiO_(5), which plays a crucial role in preventing crack formation and propagation. Part of Ti4+dissolves into magnesia-alumina(MA), densifying the materials. TiO2also slows down the reaction between the Cr element and refractory components, further improving the corrosion resistance of the materials.

Review on the plastic instability of medium -Mn steels for identifying the formation mechanisms of Lüders and Portevin -Le Chatelier bands

Plastic instability,including both the discontinuous yielding and stress serrations,has been frequently observed during the tensile deformation of medium-Mn steels(MMnS)and has been intensively studied in recent years.Unfortunately,research results are controversial,and no consensus has been achieved regarding the topic.Here,we first summarize all the possible factors that affect the yielding and flow stress serrations in MMnS,including the morphology and stability of austenite,the feature of the phase interface,and the deformation parameters.Then,we propose a universal mechanism to explain the conflicting experimental results.We conclude that the discontinuous yielding can be attributed to the lack of mobile dislocation before deformation and the rapid dislocation multiplication at the beginning of plastic deformation.Meanwhile,the results show that the stress serrations are formed due to the pinning and depinning between dislocations and interstitial atoms in austenite.Strain-induced martensitic transformation,influenced by the mechanical stability of austenite grain and deformation parameters,should not be the intrinsic cause of plastic instability.However,it can intensify or weaken the discontinuous yielding and the stress serrations by affecting the mobility and density of dislocations,as well as the interaction between the interstitial atoms and dislocations in austenite grains.

Effect of rare earth and alloying elements on the thermal conductivity of austenitic medium manganese steel

The influence of different contents of Cr, Mo, and rare earth element(RE) additives on the thermal conductivity of austenitic medium manganese steel was studied and discussed. The results show that the addition of Cr in medium manganese steel can improved the ordering of C–Mn atomic clusters, so as to improve the steel's thermal conductivity. However, Cr will lead to precipitation of a great deal of carbides in medium manganese steel when its content is greater than 4wt%. These carbides would aggregate around the grain boundary, and as a result, the thermal conductivity is decreased. By the addition of Mo whose content is about 2wt%, spherical carbides will be formed, thus improving the thermal conductivity of the medium manganese steel. The interaction between rare earth elements and alloying elements will raise both the thermal conductivity and the wear-resisting property of medium manganese steel.

SiO_2 AS HETEROGENEOUS NUCLEI OF INTERGROWTH EUTECTIC IN MODIFIED AS-CAST MEDIUM MANGANESE STEEL

By calculation of thermodynamics,analysis of crystal structure and study of TEM and eletron probe,it is first discovered that SiO2 can be acted as one of the heterogeneous nu- clei for lamellar intergorowth eutectic(austenite and cementite)crystallizing in modified as-cast medium manganese steel.

Effect of RE-Modifier on Microstructure and Mechanical Property of High-Carbon Medium-Manganese Steel

The effect of RE-modifier on the microstructure and mechanical properties of high carbon-medium manganese steel has been investigated in present work.The results showed that the RE-modifier can refine the crystalline grain of high-carbon medium-manganese steel.The shape and distribution of carbides are improved and the columnar grains and phosphide in grain boundary are eliminated.Consequently,the impact toughness of the steel is increased by more than one time,compared with no addition of RE-modifier.

Plastic deformation wear in modified medium manganese steel

A medium manganese steel with high wear-resistance,strength and toughness has been produced with addition of a complex modifier (or refining agent) containing Nb,N,RE and Si-Ca. The results showed that the wear resistance,strength and toughness of the modified medium manganese steel are respectively 1.92 times,1.45 times and 3.63 times as high as that of the referenced unmodified medium manganese steel. The plastic deformation characteristic involved in the wear mechanism of the modified medium manganese steel was investigated by means of plastic-elasticity calculation and TEM electro-microscopy. The relationship between wear resistance and yield strength of the steel was established. Since the wear volume W is proportional to the square of the loading and to the numbers of the abrasives,and inversely proportional to the square of the yield strength of the materials,the wear resistance can be substantially improved by the enhancement of yield strength of the materials. The calculation results generally agreed with the experimental results.

Effects of cooling rate and Al on MnS formation in medium-carbon non-quenched and tempered steels

The effect of Al on the morphology of MnS in medium-carbon non-quenched and tempered steel was investigated at three different cooling rates of 0.24, 0.43, and 200°C·s^-1. The formation mechanisms of three types of MnS were elucidated based on phase diagram information combined with crystal growth models. The morphology of MnS is governed by the precipitation mode and the growth conditions. A monotectic reaction and subsequent fast solidification lead to globular Type I MnS. Type II MnS inclusions with different morphological characteristics form as a result of a eutectic reaction followed by the growth in the Fe matrix. Type III MnS presents a divorced eutectic morphology. At the cooling rate of 0.24°C·s^-1, the precipitation of dispersed Type III MnS is significantly enhanced by the addition of 0.044wt% acid-soluble Al（Als）, while Type II MnS clusters prefer to form in steels with either 0.034wt% or 0.052wt% Als. At the relatively higher cooling rates of 200°C·s^-1 and 0.43°C·s^-1, the formation of Type I and Type II MnS inclusions is promoted, and the influence of Al is negligible. The results of this work are expected to be employed in practice to improve the mechanical properties of non-quenched and tempered steels.

TUDY OFSTRAIN INDUCED MARTENSITE TRANSFORMATION FOR A MEDIUM MANGANE SESTEEL

The distribution of Cand Mn atomsinthe austenitic matrix isheterogeneous,the Mn atoms tendtooccupythefirst neighbour position ofthe Catomsin theaustenite. During deforma tion thethreekindsof martensitearestraininduced , havinginternal magneticfield valuese qualto33 0T, 30 5Tand 28 2Trespectively, andthe martensiteisstraininduced firstin the austenitecontainingless Cand Mn atoms.

As-cast Medium Mn Steel with Nodular Carbide Modified by Y-base Heavy RE Compound

1.IntroductionMedium Mn steel was developed be-cause the wear resistance of Hadfield steel(Mn13)is poor under low or medium im-pact and extrusion abrasion[1-4].In theforegoing investigations[2-4]we found thatwith the increase of C content,theneedle-like and network carbide in mediumMn steel increased(as shown in Fig.1(a)and(c)).Although its wear resistance was largelyimproved,its impact toughness was greatlydecreased.In order to increase toughness,along-term high temperature heat-treatmentwas needed.But the treatment caused cracks

Influence of aging treatment on mechanical properties and wear resistance of medium manganese steel reinforced with Ti(C,N) particles

In this study,the hot rolled medium manganese steel containing titanium was solution treated at 1,000°C and followed by aging treatment at 500,550,and 600°C.The influence of aging treatment on mechanical properties and wear resistance of medium manganese steel reinforced with Ti(C,N)particles was investigated.It was found that the matrix of medium manganese steel was austenite.The austenite grain size was refined,and Ti(C,N)particles were precipitated after aging treatment.Compared to that of the as-hot rolled sample,the initial hardness of 500°C aged sample increased by 9.5%to 312.86 HV,whose impact energy was more than doubled to 148.5 J.As the aging temperature raised to 600°C,the initial hardness changed slightly.However,the impact energy dropped significantly to 8 J due to the aggregation of Mn at the grain boundaries.In addition,the main wear mechanisms of the samples were fatigue wear and abrasive wear.It was worth noting that 500°C aged sample exhibited the best wear resistance under a 300 N applied load,whose wear loss was just half of the as-hot rolled sample.The relationship between wear loss and mechanical properties indicated that the wear resistance of medium manganese steel was independent of the initial hardness.The large difference in the wear resistance was predominately due to the outstanding work hardening ability of 500°C aged sample,whose strengthening mechanisms were contributed from transformation induced plasticity(TRIP)effect,dislocation strengthening,twinning induced plasticity(TWIP)effect,and precipitation strengthening.

中锰钢热轧与冷轧退火工艺下组织与性能差异综述

中锰钢作为第三代先进高强钢的代表,由于其优异的力学性能已成为一个研究的热点。同一种中锰钢经过不同的轧制和热处理产生不同的微观组织进而导致其力学性能存在差异。因此,研究不同的热加工工艺下其微观组织与力学性能之间的关系至关重要。本文综述了中锰钢在热轧和冷轧退火工艺下的组织演变,重点阐述了微观组织与静拉伸力学性能、抗氢脆性能、低温冲击韧性之间关系方面的研究进展,并对提高中锰钢各种力学性能的方法进行了比较,最后对中锰钢未来的强韧性研究和发展方向进行了展望。

中锰钢棘轮行为的细观有限元模拟

基于微观形貌构建含铝中锰钢二维代表性体积元(RVE)模型,同时引入马氏体相变演化方程,采用Mori-Tanaka均匀化方法构建了奥氏体和马氏体组合相的本构模型,对试验钢在单轴拉伸和不同工况下(平均应力为50 MPa,应力幅分别为700,710 MPa)的棘轮行为进行了细观有限元模拟。结果表明:所建立的均匀化本构模型可以较好地反映马氏体相变对试验钢力学性能的影响,基于RVE模型模拟组织演变具有一定的准确性;马氏体相变会使试验钢的单轴拉伸中发生明显强化,并会使奥氏体和铁素体之间出现应力交替现象;当平均应力为50 MPa、应力幅为700 MPa时,考虑与不考虑马氏体相变模拟的棘轮应变演化曲线几乎重合;当平均应力为50 MPa、应力幅为710 MPa时,不考虑马氏体相变模拟的棘轮应变增长率明显高于考虑相变时。

10Mn5中锰钢电阻点焊接头的显微组织与力学性能

采用不同焊接工艺参数对2 mm厚10Mn5中锰钢板进行电阻点焊试验,以确定可焊性窗口,检测了接头的微观组织与力学性能。结果表明:在360 ms的焊接时间内,该钢种的可焊性工艺窗口宽度为1.5 kA。接头熔核区组织为马氏体,热影响区组织为铁素体、奥氏体和马氏体,母材为铁素体和奥氏体;熔核区平均硬度约390 HV0.2,母材硬度约225 HV0.2,热影响区硬度由近熔核侧至近母材侧逐渐降低;飞溅前接头最大拉剪力和正拉力分别为26.6和9.2 kN,失效模式均为界面断裂;接头拉剪试验时为脆性韧性-断裂,十字拉伸试验时则以脆性断裂为主。

高碳中锰耐磨钢凝固过程溶质微观偏析模型

通过定向凝固、电子探针(EPMA)、Factsage等多种实验与理论计算相结合的手段对中锰耐磨钢凝固过程溶质元素微观偏析行为进行了系统研究.研究表明在定向凝固试验中当拉速为50μm·s-1时,中锰钢的二次枝晶间距平均值为59.77μm;中锰钢凝固过程组织转变为L→L+γ→γ属于奥氏体凝固模式,无包晶反应的发生,也无铁素体相及其他相的出现;中锰钢定向凝固过程中Mn、Cr在枝晶间的含量明显高于枝晶内,表明Mn、Cr元素发生了明显的正偏析行为;通过对各特征参数求解,构建了中锰钢溶质元素微观偏析模型,发现中锰钢定向凝固过程中Mn元素偏析指数与Brody–Flemings模型符合较好,而Cr元素偏析指数与Clyne–Kurz模型分布较为一致.

热处理对热轧Fe-0.4C-10Mn-1.8Al-0.6V钢组织及力学性能的影响

研究了新型热轧Fe-0.4C-10Mn-1.8Al-0.6V中锰钢的组织和力学性能。结果表明,随着退火时间从30 min增加到60 min,由于稳定性下降导致残余奥氏体体积分数降低,板条状马氏体逐渐转变为针状马氏体。由于变形阶段不连续TRIP效应的发生,拉伸曲线呈锯齿状。随着退火时间的延长,实验钢的屈服强度、抗拉强度及总伸长率均降低。实验钢在800℃进行30 min退火后具有良好的力学性能,屈服强度为670 MPa,抗拉强度为1230 MPa,总伸长率为18.3%。

Development and microstructure characterization of BG110E high-strength expansion pipe

The BG110E high-strength expansion pipe was developed using medium manganese steel and subjected to a two-phase zone heat treatment process.Mechanical properties and microstructure analysis results have proven that the BG110E expansion pipe exhibits uniform elongation of more than 19%.Moreover,after undergoing expan-sion deformation,its strength,toughness,and plasticity are found to meet the stringent requirements of the P110 pipe.The microstructure of this high-strength expansion pipe,which has a strength of 110 ksi(1 ksi=6.895 MPa),consists of tempered martensite,ferrite,retained austenite,and granular bainite.The propotion of retained austenite reaches up to 12%,ensuring high plasticity and the occurrence of the transformation-induced plasticity effect during the deformation process.Consequently,it enhances the coordinated deformation ability between different phases,which significantly improves the internal yield pressure of the BG110E high-strength expansion pipe in turn.

轻质中锰钢局部变形带的研究现状

轻质中锰钢是第三代先进高强钢的代表,在变形过程中由于C、Mn、Al等合金元素的存在其可动位错经历被固溶原子和C-Mn原子团钉扎和脱扎的过程,从而在应力-应变曲线上呈现出吕德斯(Lüders)带和Portrvin-Le Chatelier(PLC)带这两种最典型的局部变形带,导致材料表面质量降低,对后续加工使用不利。目前,消除Lüders带和PLC带引起的表面缺陷的常用方法是在成形前对材料施加小的预应变或者调控材料的组织。然而这种方法只适用于经历小Lüders带应变和PLC效应的材料,因此寻求一种更为有效的延迟或消除Lüders带与PLC带的方法显得极其重要。本文从发生机理入手,讨论预应变、退火温度、退火时间等工艺和合金元素对上述两种局部变形带的影响,进而从晶粒尺寸、组织形貌、位错密度等微观角度总结减弱或加剧二者的具体机制,并着重解释不同成分与热处理工艺对C-Mn原子团形成、移动速率和与位错交互时间的影响以及抑制局部变形带的形成与拓展的作用。随后根据已有研究提出的不同解决方案,结合上述宏观与微观影响因素,展望了未来该领域研究的发展。

轧制回火工艺对Q690ZM中厚板组织性能的影响

通过控制轧制、在线淬火和临界区逆转变回火处理,中锰钢的最终组织为回火马氏体和亚稳态残余奥氏体,但是回火温度和时间对中锰钢内部元素扩散、组织演化、残余奥氏体含量及稳定性、力学性能有很大的影响。由于Q690ZM中锰钢与传统热轧中锰钢相比采用更低的合金含量,极大地降低了成本,但为了能够满足强度要求,研究了其组织和力学性能的变化规律,以及强韧化机理,采取合适的轧制及回火工艺,最终满足工程机械用钢标准。

载荷对中锰钢耐磨性能的影响

采用UMT TriboLab摩擦磨损仪测试了冶炼工艺流程为电炉-精炼-模铸-粗轧-精轧-控冷-成品的中锰耐磨钢在不同载荷下的摩擦磨损性能,并利用白光干涉仪定量表征了摩擦磨损后样品表面磨痕的形貌,测量了摩擦断面的深度曲线。结果表明:随着试验载荷的增加,摩擦系数呈先升高后降低的变化规律,当载荷达到30 N时,摩擦系数达到最高值0.82;当载荷压力较小时(10 N),随着时间的延长,摩擦系数呈现逐渐变小的趋势;磨痕深度随着载荷的增加而增加,但与载荷增加不呈线性关系,载荷为10~30 N时磨痕深度显著增加,当载荷超过30 N后,磨痕深度的增加值逐渐减小,磨痕深度增加值不随载荷的增加而增加,呈现先升高后降低的现象,说明增加载荷后摩擦磨损机制发生了改变;不同载荷下磨痕的三维形貌分析结果表明,当载荷较小时,其磨损形式为梨沟磨损,其磨损机制为磨粒磨损,当载荷增加时,磨损形式为沟槽磨损,磨损机制转变为黏着磨损。

Effect of Al content on the reaction between Fe-10Mn-xAl(x=0.035wt%,0.5wt%,1wt%,and 2wt%)steel and CaO-SiO_(2)-Al_(2)O_(3)-MgO slag

The effect of Al content(0.035 wt%,0.5 wt%,1 wt%,and 2 wt%)on the composition change of steel and slag as well as inclusion transformation of high manganese steel after it has equilibrated with Ca O-Si O_(2)-Al_(2)O_(3)-Mg O slag was studied using the method of slag/steel reaction.The experimental results showed that as the initial content of Al increased from 0.035 wt%to 2 wt%,Al gradually replaced Mn to react with Si O_(2)in slag to avoid the loss of Mn due to the reaction;this process caused both Al_(2)O_(3)in slag and Si in steel to increase while Si O_(2)and Mn O in slag to reduce.In addition,the type of inclusions also evolved as the initial Al content increased.The evolution route of inclusions was Mn O→Mn O-Al_(2)O_(3)-Mg O→Mg O→Mn O-Ca O-Al_(2)O_(3)-Mg O and Mn O-Ca O-Mg O.The shape of inclusions evolved from spherical to irregular,became faceted,and finally transformed to spherical.The average size of inclusions presented a trend that was increasing first and then decreasing.The transformation mechanism of inclusions was explored.As the initial content of Al increased,Mg and Ca were reduced from top slag into molten steel in sequence,which consequently caused the transformation of inclusions.