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.

Effect of Boron on Delayed Fracture Resistance of Medium-Carbon High Strength Spring Steel

The delayed fracture behavior of medium carbon high strength spring steel containing different amounts of boron （0. 000 5%, 0. 001 6 %） was studied using sustained load delayed fracture test. The results show that delayed fracture resistance of boron containing steels is higher than that of conventional steel 60Si2MnA at the same strength level and it increases with the increase of boron eontent from 0. 000 5% to 0. 001 6%. The delayed fracture mode is mainly intergranular in the boron containing steels tempered at 350℃, which indicates that the addition of boron does not change the fracture character. However, the increase of boron content enlarges the size of the crack initia tion area. Further study of phase analysis indicates that most boron is in solid solution, and only a very small quantity of boron is in the M3 （C, B） phase.

Multiphase microstructure formation and its effect on fracture behavior of medium carbon high silicon high strength steel

This work investigated the evolution of multiphase microstructure and impact fracture behavior of medium carbon high silicon high strength steel subjected to the austempering treatment at 240,360,and400℃.The results show that martensite,bainite,and retained austenite(RA)are the main microstructural phases.The austempering treatments at 360 and 400℃ caused the formation of carbon-poor ferrite in the matrix,and the transformation of ultrafine bainite into coarse lath bainite and granular bainite,respectively.Thick filmy RA was distributed between bainite laths.The polygonal martensiteaustenite islands and blocky RA formed along the grain boundaries.The average carbon concentration in the matrix decreased with the temperature increase,while the impact toughness initially increased and then dropped with temperature.The quasi-cleavage brittle fracture dominated the impact fracture mechanism of the sample austempered at 240℃ by forming tearing surfaces and tearing steps.The microcracks disappeared in the RA on the prior austenite grain boundaries.On the other side,the fracture surface of the sample austempered at 360℃ exhibited ductile fracture with deep dimples and brittle fracture with cleavage river patterns.The polygonal martensite-austenite islands or blocky RA constrained the microcracks.After austempered at 400℃,the brittle fracture was dominant,showing river patterns,and the microcracks propagated through the granular bainite without any resistance.

中高碳钢碳含量稳定性控制生产实践

结合中高碳钢生产特点,通过对炼钢冶炼过程全流程分析,找出影响碳含量波动的影响因素,识别出关键工艺控制点,制定了控制转炉终点氧含量、降低出钢温度、减少连铸增碳、稳定班组操作差异等措施,实现中高碳钢碳含量的稳定控制,为炼钢厂生产高质量产品奠定了基础,也为炼钢生产成本降低作出了积极贡献。

转炉终渣低全铁控制研究和应用

借鉴国内外学者对降转炉终渣全铁和炉渣脱磷的研究,结合120 t转炉生产实际,对40Cr钢进行了终渣低全铁控制实验。实验本着“前期渣早化,提高冶炼前期渣脱磷率,过程渣化透不返干”的原则,枪位由三段式优化为五段式,通过终点低枪位搅拌,在促进金—渣界面反应和促进脱磷反应的同时,加速降低渣中FeO的含量,在满足终点磷钢种要求的同时,达到降低渣中全铁的目的。实验结果表明:渣中w(TFe)平均为13.59%,较实际生产降低了2.50%。脱磷率平均为92.4%,较实际生产提高了2.8%。通过炉渣矿相分析,验证了降低渣中FeO,可以促进渣中磷的富集、固磷相C_(2)S的生成、长大。工业推广应用后,转炉终渣全铁控制在14.6%,实现了中高碳钢转炉终渣高拉碳低磷低全铁控制,取得了良好的效果。

降低中高碳钢脱碳层工艺技术研究

针对中高碳钢表面脱碳层产生原因、对产品质量影响、工艺影响因素进行了系统性分析,识别了加热温度、保温时间和炉内气氛等重点因素,并在生产中对不同工艺参数条件下脱碳层深度变化规律进行了研究,提出了有效的工艺改进措施,实现中高碳钢脱碳层深度的稳定控制,满足高质量产品要求,解决了行业共性技术难题,为同类型钢铁企业技术革新具有很好的借鉴推广意义。

Influence of Vanadium on Fracture Splitting Property of Medium Carbon Steel

The fracture splitting property of medium carbon steel 37MnSiS microalloyed with V up to 0. 45% was investigated by using simulated fracture splitting test,for the development of new crackable medium carbon steel to manufacture high performance connecting rod. Conventional high carbon steel C70S6 was used for comparison. The results show that the volume fraction of both ferrite and V-rich M（ C,N） particles increases,and the pearlite interlamellar spacing decreases with increasing V content,which in turn results in gradual increase of strength and decrease of ductility and impact energy. The fracture splitting property of the tested steel could be improved significantly due to the increase of V content mainly through the precipitation hardening mechanism of fine M（ C,N） precipitates. The fraction of brittle cleavage fracture in the crack initiation area increases noticeably with increasing V content and full brittle cleavage fracture surface could be obtained when V content was increased to 0. 45%. It is concluded that medium carbon steel with V content higher than about 0. 28% possesses not only comparable or even higher mechanical properties with those of conventional steel C70S6,but also excellent fracture splitting property,and therefore,is more suitable to fabricate high performance fracture splitting connecting rod.

Mechanism of Cracking Resistance of Hardfacing Specimens of Steel 5CrNiMo Improved by Rare Earth Oxide

The cracking morphology of the hardfacing specimens taken from steel 5CrNiMo was observed. Meanwhile, the residual stress fields were measured and simulated. Based on experiment mentioned above, the improved structure and modified inclusion in hardfacing metal with rare earth （RE） oxide were analyzed. The results show that, the hardfacing crack is initiated from the coarse dendritic crystal grain boundary, inclusions and coarse austenite grain boundary in the HAZ and propagated by the residual stress existing in the center of the hardfacing metal and HAZ. The primary columnar grain structure can be refined by adding RE oxide in the coating of the electrode. The inclusion in the hardfacing metal can be modified as well. Meanwhile, if the martensite transformation temperature is decreased, the largest value of the residual tensile stress in the dangerous region can be reduced.

Effect of RE oxide on growth dynamics of primary austenite grain in hardfacing layer of medium-high carbon steel

The flux cored wires with different rare earth oxide additions for hardfacing the workpieces of medium-high carbon steel were developed. The microstrucmre of the hardfacing layer was observed using the optical microscopy. The average dimension of primary austenite grains in hardfacing layer was measured by image analyzer. The primary austenite grain growth activation energy and index were calculated according to Sellars＇s mode and Beck formula, respectively. Moreover, the effect of rare earth oxide on the growth dynamics of primary aus- tenite grain was analyzed, and then discussed with the misfit theory. The experimental results showed that, by adding rare earth oxide, the av- erage dimension of primary austenite grains in hardfacing layer of medium-high carbon steel decreased, and it was the smallest when the ad- dition of rare earth oxide was 5.17 wt.%. Meanwhile, at this rare earth oxide addition, the primary austenite grain growth activating energy in hardfacing layer was the largest, while its index was the smallest. The calculated results indicated that the primary austenite grain could be refined because LaAlO3 as heterogeneous nuclei of γ-Fe was the most effective.

Measurement of Residual Stress Field of Hardfacing Metal with RE Oxide and Its Numerical Simulation

The temperature and residual stress fields of a medium-high carbon steel, welded by a cracking resistance electrode with rare earth (RE) oxide, were measured by thermo-vision analyzer and X-ray stress analyzer respectively. Meanwhile, the martensitic transformation temperatures of matrix, hard-face welding (hardfacing) metal welded by conventional hardfacing electrode and that welded by cracking resistance electrode with RE oxide were determined. According to the experimental data and the thermo-physical, mechanical parameters of materials, finite element method (FEM) of temperature and stress fields was established. In this FEM, the effect of martensitic transformation on residual stress of hardfacing metal of medium-high carbon steel was taken into account. The results show that, by adding RE oxide in the coat of hardfacing electrode, the martensitic transformation temperature can be decreased, so that the residual tensile stress on the dangerous position can be decreased. Therefore, the cracking resistance of hardfacing metal can be improved.

Hot Deformation Behavior of Vanadium-microalloyed Medium-carbon Steel for Fracture Splitting Connecting Rod

Single compression tests were carried out with a Gleeble-3800 thermal simulator to investigate hot deform- ation behavior of two vanadium-microalloyed medium-carbon steels for fracture splitting connecting rod. The tests were performed to a total true strain of 0.92 at true strain rates ranging from 10-2 to 10 s-1 and deformation temper- ature of 900--1 150 ℃, The results show that hot deformation behavior of the tested steels is similar to that of con- ventional medium-carbon microalloyed steels and dynamic recrystallization is easier to occur at higher deformation temperature and lower strain rate. The austenite deformation resistance and activation energy of deformation increase with increasing vanadium content from 0.15% to 0. 28% and thus the starting time of dynamic recrystallization was delayed. Finer recrystallized austenite grain could he obtained at higher strain rate, lower deformation temperature and higher vanadium content. TEM observation of the specimens quenched just before and after deformation reveals that vanadium is mainly in dissolved solute condition in austenite and thus affects the dynamic recrystallization behavior of the tested steels mainly through solute-drag effect.

中碳结构钢表面翘皮原因分析与改进

为了研究中高碳钢表面翘皮缺陷的形成原因,采用体视显微镜、金相检测、扫描电镜和能谱分析等检测手段对缺陷形成机制进行了分析,结果表明,磷、硫等元素偏析以及二冷水冷却不均引起的铸坯中间裂纹在热轧轧制过程中延伸至钢板表面,导致了翘皮缺陷的产生。通过控制钢水纯净度、优化二冷配水、板坯下线保温等措施的实施,板坯质量良好,板坯低倍组织改善明显,翘皮缺陷得到有效改善。

一种中碳高强韧合金钢的组织与力学性能

中碳高强度钢可以用作高强度钢材分切刀片,其力学性能对于刀片的使用寿命等有重要的影响。设计了一种高强韧性中碳合金钢,测得了其特性参数,利用Thermal-Calc软件计算了其相图。采用光学显微镜、扫描电镜、洛氏硬度计和拉伸及冲击试验等研究了不同热处理工艺对试验钢的组织、力学性能和断口形貌的影响。结果表明:在H13钢的基础上添加3.5~4.0 mass%Ni和2.0 mass%Mo元素可以进一步提高其强韧性。试验钢淬火后的组织为板条马氏体及少量未溶MC型碳化物和残留奥氏体;试验钢存在回火二次硬化现象,520℃回火时硬度达到峰值,产生二次硬化的主要原因是回火时析出弥散细小与基体共格的MC、M2C型碳化物,以及棒状M_(7)C_(3)型碳化物;500℃以下回火,试验钢的拉伸和冲击断口形貌主要是解理+准解理,随着回火温度进一步升高,准解理断裂比例增加,解理断裂比例减少,600℃回火开始出现韧窝,韧性随之改善。试验钢的最佳热处理工艺为900℃×2 h+730℃×4 h球化退火+1025℃油淬+520℃两次回火,经最佳工艺热处理后其硬度为58.8 HRC、抗拉强度为1955.4 MPa、夏氏冲击韧性为3.2 J/cm^(2)。

一种中碳高强度合金钢的组织与性能研究

中碳高强度合金钢可用作分切高强度钢材的刀片。试制了一种含0.44%C、5.04%Cr、3.01%Mo、1.01%Ni、0.69%V和0.18%Nb(质量分数)的中碳合金钢,对其进行了球化退火、分别从975℃、1000℃、1025℃、1050℃和1075℃油淬及淬火后于200~600℃回火。检测了试验钢的热处理特性参数、不同工艺热处理后钢的显微组织和力学性能及拉伸与冲击试样的断口形貌。结果表明:适当增加Mo、Ni含量能进一步提高可用于制作高强度钢材分切刀片的中碳高强度合金钢的强韧性;试验钢淬火态组织为板条马氏体、少量未溶MC型碳化物和残留奥氏体,回火过程中会产生二次硬化效应,520℃回火的钢硬度最高;试验钢的最佳热处理工艺为900℃保温2 h随后730℃保温4 h球化退火,1025℃油淬随后520℃两次回火。

中高碳钢在UCM连轧机组稳定轧制攻关

通过对中高碳钢(45、65Mn)在酸轧UCM五机架连轧机组轧制过程中频繁发生1#机架出口失稳断带原因分析,明确了断带发生的具体原因,并开展了UCM轧机二级模型控制参数优化试验。通过不断的模拟试验和现场实际生产试验,优化了中高碳钢轧制过程参数控制,实现了中高碳钢在UCM五机架连轧机组连续稳定轧制,并为后期更高强度钢带在UCM轧机的稳定轧制积累了经验,为冷轧新产品研发创造了有利条件。

钒对中碳非调质钢疲劳性能的影响

采用旋转弯曲疲劳实验研究了含钒的38MnVS钢与不含钒的38MnS钢在热锻态和退火态下的疲劳行为．结果表明, V元素主要通过析出强化和组织细化改善铁素体+珠光体型非调质钢的疲劳性能．在热锻态,V(C,N)呈细小弥做分布,与铁素体间具有特定位向关系,具有明显的析出强化和细化组织作用．铁素体的强化使得疲劳裂纹萌生和扩展的抗力提高,因而38MnVS钢的疲劳性能明显优于38MnS钢;在退火态,V(C,N)质点长大,与铁素体间失去共格关系,不再具有明显的析出强化作用．因而退火态38MnVS钢的疲劳性能明显低于热锻态,而与38MnS钢的疲劳性能相当．

高速钢/结构钢双金属复合材料界面研究

采用镶铸法 ,以液固结合的方式制备了高碳钒系高速钢 /结构钢双金属复合材料。研究了不同结合条件下 ,双金属复合材料界面结构及形态。试验结果表明 ,镶铸是靠外层合金带入的过热热量来获得界面结合的 ,当外材与芯材在体积比大于 8.0的条件下 ,才有可能获得界面结合 ,其界面结合为扩散结合。复合材料界面结构由芯材扩散层、激冷凝固层、方向性生长层和胞状晶粒层组成。外层材料凝固时有明显的方向性生长 ,其液固相线推移速度对在液固结合条件下外层材料的凝固组织具有明显影响。当外材与芯材体积比为 1.2 5时 ,外层材料的凝固速度最快 ,出现了棒状伪共晶组织 ,随体积比的增长 。

高碳高钒系高速钢的耐磨性研究

制备了不同成分的新型高碳高钒系高速钢 ,并与高铬铸铁对比考察了其耐磨性和磨损机理 .结果表明 :高碳高钒系高速钢的耐磨性明显优于高铬铸铁 ;其组织中的碳化物形态对耐磨性具有显著影响 ,其中具有细小及弥散分布的颗粒状 MC型碳化物组织的试样的耐磨性最佳 ;

奥氏体化保温时间对高速钢工作辊组织和耐磨性的影响

制备了高碳高钒系高速钢辊环,通过SEM、EDS、XRD分析以及硬度测量研究了奥氏体化保温时间对高碳高钒系高速钢轧辊材料的组织和耐磨性的影响。结果表明,随着奥氏体化保温时间的增加,在铸造过程中形成的M3C型碳化物逐渐溶解或向M2C型碳化物转变;MC型碳化物在晶内逐渐析出,且随着奥氏体化保温时间的延长逐渐圆整为粒状或棒状。在奥氏体化保温过程中,M2C型碳化物按如下公式发生分解:M2C+γ-Fe→MC+M6C;未溶的大块M3C型共晶碳化物是高速钢试样耐磨性差的原因,随着奥氏体化保温时间的增加晶内不断析出的MC型碳化物是高速钢试样耐磨性提高的主要因素;长度<100μm、宽度<20μm的条状碳化物在磨损过程中不易脱落。

碳、钒含量对高钒高速钢组织和力学性能的影响

在ωV/ωC≈3与ωV≈10%的条件下,研究了钒、碳含量对高钒高速钢组织和力学性能的影响.结果表明:高钒高速钢的耐磨性决定于硬度与组织.硬度低于HRC 57时,耐磨性主要决定于硬度;硬度超过HRC 57之后,耐磨性主要决定于碳化钒的数量、形态、分布与基体组织.ωV=8.15%～10.20%、ωC=2.70%～3.15%时,经适当变质处理和热处理,可使团球状或团块状的碳化钒均匀分布在经1 050 ℃淬火,550 ℃回火的坚硬基体上,从而获得优良的耐磨性能.