Influence of Rare Earth on Property of Low Chromium Semi-Steel

The influence of rare earth( RE) content on mechanical properties and abrasion resistance of low chromium semi-steel was studied by means of metallographic examination,scanning electron microscopic examination and mechanical property test. The experiment results show that RE can improve the comprehensive properties,especially in combination with proper heat treatment. The optimum properties of low chromium semi-steel modified by RE of 0. 25 % could be obtained by normalization at 950 ℃ for 3 h. The main reason is the change in morphology and distribution of eutectic carbide and the precipitation of granular carbides.

Mechanical Property of Low Chromium Semi-Steel Grinding Ball Prepared by Cross Rolling

The preparing method,rolling technology and mechanical properties of low chromium semi-steel grinding ball by cross rolling were studied.The results show that when the low chromium semi-steel bar is forged from55mm to50mm,cross-rolled into grinding ball at 1 000-1 050℃,air cooled and tempered at 550℃for 2h,the best mechanical properties,especially the abrasive resistance under the action of hard abrasive,can be obtained.

Effect of RE on the Formation and Growth of Granular Carbides of Cast Semi-Steel in Heat Treatment Process

In heat treatment process,the effect of rare earth elements on the formation and growth of granular carbides in cast semi-steel and the growing mechanism of granular carbides were studied. The experimental results show that RE is helpful to the formation of granular carbides during high-temperature heat treatment process,but in following isothermal process,it has little effect on the growth of granular carbides. The feature of the growth of carbide proceeds is the size increment and the amount decrement of carbide particles,the volume fraction of carbides keeps constant. And the mathematical model of the growth rate of granular carbides is put forward.

Effect of Rare Earth Element on Formation and Propagation of Thermal Fatigue Crack in Low-Chromium Semi-Steel

The formation and growth of thermal fatigue crack in low-chromium semi-steel were investigated by means of optical microscope and scanning electron microscope, and the function of RE in low-chromium semi-steel was analyzed. The results show that the thermal fatigue cracks are mainly generated at eutectic carbides, and the cracks not only grow and spread but also join each other. RE can improve the eutectic carbide′s morphology, inhibit the generation and propagation of thermal fatigue cracks, and therefore promote the activation energy for the crack′s propagation, which is especially more noticeable in case of the RE modification in combination with heat treatment. The mathematical model of the crack propagation is put forward.

Low-Energy Multi-Impact Fracture Resistance of Cross Rolled Low Chromium Cast Semi-Steel Containing Rare Earth Grinding Ball

The low-energy multi-impact fracture resistance of the cross rolled low chromium cast semi-steel containing RE grinding balls was studied. Moreover, its damage mode was analyzed by means of metallographic examination, scanning electron microscopic examination and drop ball test. The results show that it can obtain extractive impact fracture resistance after proper heat treatment. More advantages were obtained for the ball worked in the condition of low-imp ductility act. The main reasons are the function of RE and the change in morphology of eutectic carbide network.

Study on Carburizing and Temperature Rising of the Semi-Steel Melt with Plasma Heating

Experiments were carried out on carburizing and temperature rising of the semi steel melt in a plasma induction furnace.Influence of many factors, such as power supply mode,position of the plasma torch and bottom blown gas stirring,on heating efficiency and melt temperature distribution was studied. Melt temperature could be effectively controlled by plasma heating,and carbon content of semi steel melt increased from 1.92 % to 4.58 %, and the utilization rate of carbon reached up to 61.57 % during carburizing of the melt.

Effect of Rare Earth Elements on Thermal Fatigue Property of Low Chromium Semi-Steel

The effect of rare earth elements on eutectic carbide′s morphology of low chromium semi steel in as cast state and after heat treatment was investigated, and accordingly, the thermal fatigue property of this material was studied. The results show that RE can improve the eutectic carbide′s morphology, inhibit the formation and propagation of thermal fatigue cracks, therefore, promote the thermal fatigue property, which is more noticeable in case of the RE modification in combination with heat treatment. The optimal thermal fatigue property can be obtained when treated with 0.2% RE modification as well as normalization at 950 ℃ for 3 h.

输电塔半刚性连接钢管构件轴压稳定性能研究

为了研究输电塔半刚性连接钢管构件的轴压稳定性能,对60根钢管试件进行了轴压试验,分析了其失稳破坏模式和稳定承载力,并与现行设计规范计算的承载力进行了对比;建立了半刚性连接钢管构件的有限元模型,经与试验结果对比验证后开展了参数分析,研究了初始转动刚度、径厚比、材料强度以及初始缺陷对半刚性连接钢管构件的稳定系数-长细比曲线的影响;基于有限元分析的结果提出了半刚性连接钢管构件的轴压稳定计算公式。研究结果表明:半刚性连接构件的试验稳定承载力均大于铰接构件的试验稳定承载力,在所有试验工况中两者的相对差距最小为5.6%;中国和美国现行设计规范计算得到的钢管构件稳定承载力总体偏保守,分别约为试验结果的0.78倍和0.89倍;影响半刚性连接钢管构件稳定承载力的主要因素为长细比、初始转动刚度以及边界条件;提出的半刚性连接钢管构件轴压稳定计算公式能准确地预测其稳定系数并具有良好的适用性,可为实际工程提供参考。

Influence of desulfurization slag containing oxides of vanadium and titanium on semi-steel pre-desulfurization

The desulfurization and resulfurization of slag containing oxides of vanadium and titanium(CaO–SiO_(2)–MgO–Al_(2)O_(3)–V_(2)O_(3)–TiO_(2)–FeO)in the pretreatment of semi-steel desulfurization at 1623 K were investigated.Based on the ionic structure theory of slag,it could be concluded that V_(2)O_(3) and TiO_(2) combined with(O_(2)–)to form complex anions including VO_(3)^(3–),TiO_(4)^(4–),etc.,which reduced the activity of(O_(2)–)and decreased the sulfur partition ratio(LS).And FeO enhanced the activity of[O]at the slag–metal interface,which decreased the desulfurization capacity of the slag.Compared to the binary basicity,the presented basicity expression containing V_(2)O_(3) and TiO_(2) described the relationship between LS and basicity more accurately.Considering the problems of dilute slag,a large amount of residual slag and much resulfurization in the slagging-off process after pretreatment,the effect of CaO+C-based slag modifier on the resulfurization,melting point and viscosity of the desulfurization slag was investigated.It was proposed that adding 5%–10%of the slag modifier to the desulfurization slag after desulfurization decreased the resulfurization effectively.And the added modifier adjusted the slag viscosity well,which helped to reduce iron loss and residual slag.

考虑初始缺陷的桥梁高大施工支架整体稳定性能研究

高大施工支架是大跨度复杂桥梁工程中常用的钢结构支撑系统。实际工程中由于受到高大施工支架加工安装误差、超限受力或不均匀受力等因素影响,因此钢结构施工支架存在节点连接不牢固、杆件弯曲变形等初始缺陷。为明确初始缺陷对桥梁高大施工支架整体稳定性能的影响规律,首先开展了桥梁高大施工支架的线性屈曲分析,进而探讨了节点半刚性、杆件初弯曲等初始缺陷对桥梁高大施工支架极限承载力的影响规律。为提高桥梁高大施工支架极限承载力的求解精度,引入刚度系数来衡量节点半刚性,综合考虑节点体对杆件计算长度的影响,并提出模拟节点三向六自由度的方法以简化计算。研究表明,结构的极限承载力与刚度系数相关,实际工程中应保障刚度系数在4以上。以第一阶整体屈曲模态作为结构初始几何缺陷时,缺陷对于结构的极限承载力和跨中平面外位移的影响更显著;以第二阶屈曲模态作为结构初始几何缺陷时,缺陷对于结构的边杆平面外位移的影响更显著。

两种钛合金半穿甲战斗部侵彻单层钢靶性能试验研究

选取亚稳态β型TB17和高损伤容限α+β型TC4-DT两种高韧钛合金材料,对2种钛合金材料在高应变率条件下动态力学响应特性进行测试分析,并应用125 mm火炮发射装置开展2种钛合金半穿甲战斗部侵彻单层钢靶性能试验研究。结果表明,作为半穿甲战斗部的壳体材料,应选择屈服强度与冲击韧性匹配性好的钛合金,其中更应关注钛合金材料的塑性变形能力和抗冲击韧性;随着侵彻着角的增加,侵彻单层钢靶过程弹体头部侵蚀量及径向墩粗程度更严重,不利于弹体保持侵彻强度及装药安定性。

局部半包裹部分包覆钢-混凝土组合梁受弯性能试验研究

针对部分包覆钢-混凝土组合梁柱节点区域后浇筑混凝土不易密实的问题,研究了受拉侧混凝土对局部半包裹部分包覆钢-混凝土组合梁(局部半包裹PEC梁)受弯性能的影响,进行了2根不同构造的局部半包裹PEC梁的四点弯曲试验,模拟局部半包裹PEC梁负弯矩区受力状态,对其受弯性能、延性、破坏形式等展开分析。结果表明:局部半包裹PEC梁表现出良好的延性,挠度达到l_(0)/50时截面抗弯承载力并未下降。型钢主钢件、混凝土的应变沿截面高度方向大致呈线性变化,可引用平截面假定计算受弯承载力及刚度。局部半包裹PEC梁受拉侧混凝土对其极限承载力与破坏模式影响不大,在计算局部半包裹PEC梁柱节点受力时可不考虑受拉侧混凝土作用,节点后浇筑区域可采用半包裹填充,以加快施工进度。此外,对局部半包裹PEC梁进行建模,进行梁受弯过程的有限元分析,对比模拟结果与试验结果,二者荷载-挠度曲线吻合较好,误差均在10%以内。

半钢炼钢条件下转炉护炉技术探讨

钒钛磁铁矿经过高炉炼铁得到含钒铁水,转炉炼钢时利用碳与钒的选择性氧化,将铁水中的钒富集后进入炉渣,然后从钒渣中提取钒,是目前国内主流的提钒方法。含钒铁水的冶炼,转炉的成渣条件及渣相与常规铁水冶炼差异较大,对护炉技术提出挑战,因此掌握半钢炼钢条件下转炉护炉技术,在生产过程中才能不影响生产组织,保证一座提钒转炉对应两座半钢冶炼转炉的顺行。本文基于半钢炼钢条件下钒渣与钢渣的成分和岩相结构分析研究的基础上,总结了影响转炉护炉的主要因素,针对性的提出改进措施,在某厂半钢炼钢条件下,转炉护炉取得了较好的冶金效果。

不同连接节点的重型管道支吊架承载性能研究

随着装配式建筑的快速发展,装配式管道支吊架的应用范围越来越广,与传统焊接支吊架相比,装配式支吊架具有施工效率高、环境污染小等优势。目前针对装配式重型支吊架的设计规范及相关研究较为缺乏,因此针对不同连接方式的装配式重型支吊架展开足尺试验研究,结合数值仿真与理论分析,探究不同连接节点支吊架的破坏形态与承载能力。研究结果表明:不同节点的支吊架破坏形式均表现为横梁弯扭破坏,且符合极值点失稳特征;使用槽钢横梁及半槽型连接件的支吊架承载力明显低于采用端板连接的H型钢横梁支吊架,外伸竖向端板连接结构的承载力优于平齐竖向端板连接,也优于水平端板连接节点;在进行理论计算时,半槽型连接节点和外伸端板连接节点可采用半刚接模型计算,平齐端板连接节点可采用铰接模型计算,4种节点形式的支吊架整体稳定系数均高于规范计算数值,能够满足整体稳定性的要求。

装配式冷弯厚壁型钢半刚性梁-柱节点抗震性能试验研究

冷弯型钢在装配式结构中应用具有天然的优势,为了扩展冷弯厚壁型钢结构的使用范围,克服冷弯厚壁钢的缺点,设计6个新型分层装配式“十字型”梁-柱节点,进行循环加载试验,对梁-柱节点的破坏模式、初始刚度、骨架曲线、等效黏滞阻尼系数、能量耗散系数、割线刚度、滞回曲线和关键部位应变分布进行研究,主要得到以下结论:通过螺栓和节点板的滑移,半刚性节点具有一定的耗能能力。增设高强螺栓可以提高梁柱节点的承载力,初始刚度和耗能能力也得到提高,避免梁端与连接板孔壁承压。增加可更换节点翼缘板,对梁-柱节点的破坏模式没有明显影响,承载能力、耗能能力、初始刚度分别得到较大提高。

西十高铁汉江特大桥主桥设计

西十高铁汉江特大桥主桥为主跨420 m的梁桁组合结构双塔斜拉桥,采用半飘浮体系。主梁采用钢桁加劲PC箱梁,梁高3.0 m,桥面全宽17 m。PC箱梁采用C55混凝土,单箱四室等高截面,加劲桁采用渐变三角桁式,材质为Q370qE钢,桁高9.4 m。斜拉索采用标准抗拉强度1770 MPa的镀锌平行钢丝,双索面扇形布置。桥塔采用花瓶式钢筋混凝土框架结构,塔高186.5 m,基础采用∅3 m的钻孔灌注桩,按长短桩设计。结构受力分析结果表明:该桥力学性能指标均满足相关规范要求,整体刚度性能优越,具有良好的颤振稳定性,设置的风嘴能有效抑制涡激振动,采取加劲钢桁上弦杆灌注混凝土、延迟铺轨时间等措施能有效控制主梁的收缩徐变,桥面线形满足铺设无砟轨道的要求。

脉冲电流对轧辊用AD180高碳半钢材料力学性能及组织的影响

为分析电流处理对轧辊材料的影响规律,通过改变电流密度和处理时间来调整AD180高碳半钢的微观组织和力学性能。使用万能拉伸试验机对电流处理后的试样进行单轴拉伸实验,并对试样进行SEM断口截面分析和EBSD微观表征,研究其力学性能和微观组织的变化规律。拉伸结果表明,在电流密度11.88 A·mm-2、通电5 min时,试样的综合性能最好,屈服强度提高6.5%,抗拉强度提高12.1%,伸长率提高了25.4%。通过断口截面分析发现,拉伸试样均为脆性断裂,未通电试样存在大量孔洞缺陷,而合适的电流密度和通电时间可以促进试样内部孔洞缺陷的“愈合”,其中,电流密度为11.88 A·mm^(-2)、通电5 min时,试样断口上的缺陷最少。EBSD微观表征结果表明,脉冲电流使试样在较低温度下发生了再结晶,细化了晶粒。由此可见,脉冲电流可以改善试样内部的组织结构和治愈微缺陷,提高其综合力学性能。

加强筋位置对半穿甲战斗部侵彻多层钢靶性能影响研究

为了研究加强筋位置对半穿甲战斗部侵彻多层钢靶性能的影响,通过试验及数值仿真,研究了加强筋在弹体轴向不同位置处的2种半穿甲战斗部,以一定速度(710 m/s)、着角(20°)侵彻8层钢靶的弹道偏转、弹孔尺寸、余速的差异。研究结果表明:加强筋位置由弹尖向质心位置逼近时弹道偏转角减小、弹孔长轴减小、穿甲能力提升;弹道偏转角增量与靶间距呈正相关关系;弹道偏转角、侵彻余速、弹头侵蚀量及弹孔仿真结果与试验实测值最大偏差为8.82%,仿真与试验结果符合较好。研究结果可为半穿甲战斗部方案设计提供参考。