Thermodynamics and Kinetics Study on Improving the Microstructure of High Chromium Cast Iron by Multi-Alloying

The effects of multi-alloyings(V,Ti and Nb)on carbides precipitation and as-cast microstructure of eutectic high chromium cast iron containing 2.8 wt.%carbon and 31.0wt.%chromium were investigated.The results showed that with the increase in the amount of alloy elements,the cast microstructure of 2.8C-31Cr high chromium cast iron changed gradually from refinement to coarsening and the total volume fraction of carbides decreased.When the addition of alloy was0.4V-0.40Ti-0.40Nb-0.35Mo,the solidification microstructure was largely improved,the distribution of carbides was reasonably uniform.The existence form of strong carbides forming elements(V,Ti,Nb)and the reasons of rnicrostructure change were investigated from thermodynamics and kinetics considerations.     

Influence of “Soft” Reduction on the Structure of Continuous Cast Ingot and the Properties of Rolled Products of Microalloyed Steels

Metallurgist - We study the efficiency of application of a system of soft reduction in the process of crystallization of a continuously cast slab (ССS) on the installation for...     

Construction Craft Workers’ Perceptions of the Factors Affecting Their Productivity

In efforts to quantify craft workers’ perspective of construction productivity, a nationwide survey involving 1,996 craft workers was employed. The survey quantified the relative impact of 83 productivity factors, which had been identified through a series of focus group sessions involving craft workers conducted on construction jobsites located throughout the United States. The findings show that craft workers do have a good understanding of the factors affecting their daily productivity, and most of the adversarial factors affecting productivity can be addressed by site management teams. Factors involving tools and consumables, materials, engineering drawing management and construction equipment were identified as having the greatest impact on productivity from the craft workers’ perspective. A statistical comparative analysis was employed to distinguish the significant factors encountered by craft workers on projects with relatively low perceived productivity. The research further examined the differences in the perceived relative magnitude of productivity factors’ influence on construction productivity based on respondents’ union status and trade. These findings will be beneficial for engaging craft workers in productivity improvement and improving the efficiency of construction jobsites.     

Study on Liquid Structure of Iron-Rich Fe-Si Alloy

Muchattentionhasbeendevotedtothestruc tureofliquidFe basedalloysbecauseofitsimpor tanceinironmakingandsteelmaking .Althoughvar iouspropertiesoftheliquidFe Sisystemweremea suredbyanumberofworkers ,thereexistbigdis crepanciesinthedata ,causedbyexperimentalerrorsduetothehighreactivityandtechnicaldifficultyathightemperature[1] .WasedaYetal[2 -4] studiedtheliquidFe SialloybyX raydiffraction .Accordingtotheirresults ,tothefirstapproximation ,theironandsiliconatomsactashardspheresintheliquidFe Si…     

Influence of Thermal Homogenization Treatment on the Structure and Impact Toughness of H13 ESR Steel

 High levels of isotropy and homogeneous structure are very important criterion for high quality H13 hot work steel. In this paper, the cast microstructure of H13 ESR ingot and the influence of high temperature diffusion treatment on the structure and impact toughness have been investigated. The results show that: the dendrite arm spacing gradually becomes wide from the surface to the center of ingot and the interdendritic segregation areas always exist large primary carbides particles; by means of high temperature diffusion treatment of ingot prior to hot forging, the banded segregation is nearly eliminated, the annealed structure is more uniform and the isotropy properties have been improved remarkably.     

In-Situ High Temperature X-Ray Diffraction Study of Structure and Phase Transformation of Nd-FePt Alloys

The structure and disorder-order transformation of NdxFe60.5-x Pt39.5（x = 0, 0.5, 1.0, 1.5） alloys were investigated in situ by high temperature X-ray diffraction. The results show that the lattice parameter a of disordered γ phase （FCC, Al structure type） and the lattice parameter ratio c/a of ordered γ1 phase （FCT, L10 structure type） increase linearly with increasing Nd concentration, whereas the c/a ratio decreases with increasing temperature. The transition temperature from ordered FCT to disordered FCC decreases with increasing Nd concentration, but for alloys quenched rapidly from γ phase region into ice-water it increases with increasing Nd.     

Study of the Structure and Properties of Cermets Based on the NiAl–Al2O3 System

Russian Journal of Non-Ferrous Metals - The powder metallurgy method, including the mechanical activation of powders in a planetary mill and spark plasma sintering at 1470°C in an inert...     

Study on Electronic Structure of Rare Earth Complex with Dioxygen

The electronic structure and chemical bonding of[Ce(CO_3)_3O_2]_2~(8-) have been studied by INDO(Intermediate Neglect of Differentiated Overlap)method in this paper.The results obtained show that theHOMO of[Ce(CO_3)_3O_2]_2~(8-) is mainly composed of the anti-bonding π orbitals of the pcroxide ion(O_2~(2-))and the LUMO is mainly composed of the 4f orbitals of the Ce(Ⅳ).The peroxide ion coordinates to ceric ionby means of σ and π dative bonds.After coordination the O-O bond of the peroxide ions is strengthened.Bycomparison with cerous complexes,the contribution of the 4f orbitals to bonding increases in the ceric com-plex.     

发展我国高速钢的战略分析

多年来我国以出口钨铁、钼铁、钒铁为主,造成资源廉价出口。因此,有必要综合应用熔融还原、电渣重熔、微合金化等高新技术生产优质高速钢,以提高冶金质量节约能源,降低能耗,缩短生产流程,减轻环境负担。同时,建立生产基地,并按国际生产标准深加工成刀具、模具、冷轧轧辊等产品,满足国内制造业不断增长的需求,在国际市场上变资源出口为制品出口,提高出口效益。     

发展我国高速钢的战略

为合理利用我国丰富的钨、钼、钒矿物资源,综合应用熔融还原、电渣重熔、微合金化等高新技术,生产优质高速钢。达到提高冶金质量节约能源,降低能耗,缩短生产流程,减轻环境负担。同时,建立生产基地,并按国际生产标准深加工成刀具、模具、冷轧轧辊等产品,满足国内制造业不断增长的需求,在国际市场上变资源出口为制品出口。     

影响高速钢韧性的因素

 分析了化学成分、冶炼方法、钢中碳化物和热处理工艺等因素对高速钢韧性的影响。结果表明：纯净度高、杂质元素含量低和夹杂物少的钢韧性较高;同一钢种随碳含量升高其韧性降低;在同一类型钢种中,通常W Mo系钢的韧性优于W系钢;碳化物分布均匀、颗粒尺寸细小的钢韧性高,而碳化物分布不均匀、粗大角状碳化物多的钢韧性差;粉末高速钢的韧性显著优于常规方法生产的高速钢。热处理是影响高速钢韧性的另一个重要因素：随淬火温度升高,钢的韧性下降;回火温度较低和回火程度不充分时,也会显著降低钢的韧性。     

高速钢轧辊材料的研究进展

 概述了近期高速钢轧辊材料方面的研究结果，总结了高速钢轧辊材料的成分设计及其元素的作用，各类型碳化物的特点以及高速钢轧辊的主要性能研究。建议加强碳化物控制研究和优化制造工艺，以进一步提高高速钢轧辊的性能。     

喷射成形高速钢显微结构和性能

采用光学显微镜、扫描电镜研究了沉积高速钢孔隙的大小、形状、分布及显微结构.测定了试样的力学性能,并与相同成分的铸态、锻造态高速钢进行了对比.结果表明,沉积高速钢显微结构和性能都优于铸态和锻造态高速钢.     

高速钢中的碳化物缺陷

 大量碳化物的存在是高速钢组织的重要特征,也是影响高速钢质量和性能的关键因素。碳化物颗粒细小、形状规则和分布均匀的钢其质量和性能都好。但是,钢中的碳化物并不都这样理想,往往存在缺陷。根据对W18Cr4V、W6Mo5Cr4V2、W9Mo3Cr4V和W2Mo9Cr4VCo8等钢中碳化物的研究结果,分析了高速钢中常见的几种缺陷：①碳化物分布不均匀;②颗粒尺寸粗大,形状不规则,多为角状等;③碳化物微裂纹;④碳化物粘连等;⑤二次碳化物稀少。另外,还分析了以上碳化物缺陷产生的原因和危害性,并指出了减少缺陷应采取的措施。     

W9Mo3Cr4VRE稀土高速工具钢的研制

在高速钢中加入稀土元素有助于净化钢质,改善钢的组织和性能。介绍了通过电渣重熔生产Ｗ９Ｍｏ３Ｃｒ４ＶＲＥ稀土高速工具钢的工艺。     

电渣重熔板锭的温度场计算

建立了电渣重熔板锭过程的非稳态模型,计算了板锭重熔过程中的温度场,得到不同熔速、不同重熔时刻的熔池深度;分析了影响熔池深度的主要因素及板锭的凝固规律,计算表明:熔速是影响熔池深度的最大因素,当铸锭到达一定高度时,系统处于准稳定状态,熔池深度不再变化.同时铸锭底部的冷却条件对熔池深度影响不大.     

W9高速钢的电磁连续铸造研究

 研究了W9高速钢的电磁连续铸造工艺和铸坯的凝固组织特征,并与普通的模铸高速钢中共晶碳化物的类型和分布情况进行了比较,测定了在不同制备条件下高速钢莱氏体网的厚度和凝固冷却速度。结果表明：电磁连续铸造得到的高速钢铸坯表面光滑、振痕轻微、外观形状规整、内部组织致密无缺陷,莱氏体网明显变薄,晶粒明显细化;M2C和MC型碳化物的析出量增多,M6C型碳化物的析出量减少,合金碳化物变得细小、均匀和弥散;铸坯边部的凝固冷却速度为3.4×104 K/s,r/2处为6.5×103 K/s,心部为3.9×102 K/s,冶金质量明显优于普通模铸。     

T型结晶器抽锭电渣重熔高速钢90 mm方锭新工艺

 晶界处碳化物严重影响高速工模具钢的红硬性和耐磨性能,电渣重熔工艺能够有效地改善钢锭中碳化物尺寸及分布。传统电渣重熔生产较小钢锭的截面尺寸约为[?]200 mm,减小钢锭截面尺寸和增大冷却速率将会进一步减轻碳化物的偏析程度,但将降低生产效率、提高生产成本。采用双极串联、T型结晶器、抽锭电渣重熔新工艺生产90 mm方锭,并与相同熔化速度传统电渣重熔生产[?]200 mm钢锭进行对比试验。对钢锭成分、低倍、夹杂物、显微组织进行检验分析结果表明,90 mm方钢锭中碳化物尺寸和分布明显优于[?]200 mm钢锭,碳化物在后序锻造或轧制过程中更容易被破碎。新工艺电耗也低于传统电渣重熔工艺。