Effect of austempering temperature on machinability of Cu–Ni–Mo alloyed austempered ductile iron for heavy section parts

Abstract

The machinability of an austempered ductile iron with a suitable chemical composition for heavy sections has been assessed. Austempering heat treatment was carried out at three temperatures, 300, 340 and 375°C, after austenitising at 870°C for 100?min. Drilling tests, tool wear and surface roughness measurements were used to evaluate the machinability. Drilling operation failure, severe tool wear and the poorer surface roughness of the specimens austempered at lower temperatures indicated that austempering at higher temperatures clearly resulted in better machinability. The machinability of testpieces austempered at 375°C, which contained higher fractions of retained austenite, was superior to that of testpieces autenitised at lower temperatures, indicating that hardness is an important factor in assessing machinability in addition to high carbon austenite content.     

ISO 17804:2020《铸造等温淬火球墨铸铁分类》标准解读

介绍了ISO 17804:2020《铸造等温淬火球墨铸铁分类》标准的概况、标准修订的主要内容、标准的主要内容和等温淬火球墨铸铁的性能特点和典型应用。详细说明了该标准包括的范围、材料牌号、制造、铸造试样拉伸性能及冲击性能、硬度、铸件本体试样、石墨形态、基体组织和试样制备的方法。     

Study of Cheese Associated Lactic Acid Bacteria Under Carbohydrate-Limited Conditions Using D-Stat Cultivation

The metabolic pathways alternative to glycolytic energy (ATP) during growth of starter and nonstarter lactic acid bacteria were studied simulating the depletion of carbohydrates during cheese ripening. D-stat cultivation strategy with the gradual decrease of galactose concentration in tryptone-arginine feeding medium was used. With the decrease of galactose feeding, the biomass yield calculated on carbohydrate consumption (Y_X/HEX) and acetate/lactate production ratio of all strains increased. We assume that ATP and biomass yields improved by directing the pyruvate flow from lactate to acetate and that metabolic energy could be obtained either by producing acetate from carbohydrates or from arginine metabolism in ADI-positive strains. Four LAB strains out of eight produced ornithine from arginine indicating active arginine-deiminase (ADI) pathway. These ADI-positive strains achieved 3–10 times higher Y_X/HEX than ADI-negative strains in tryptone-arginine medium. Lactobacillus plantarum also used serine as an energy source. Starters and NSLAB strains using the amino acids arginine and serine or limited amounts of carbohydrates therefore have the potential to influence flavor production in cheese more efficiently.     

ADI拨叉的壳型铸造和等温淬火工艺

介绍了拨叉铸件的结构和技术要求。铸件采用无冒口铸造工艺生产,原铁液化学成分控制范围为:w(C)3.75%~3.98%、w(Si)1.2%~1.7%、w(S)≤0.08%、w(Mn)≤0.3、w(P)≤0.04,w(Si终)为2.5%~2.8%;出铁温度控制在1 520℃,采用喂丝法进行球化、孕育处理;采用盐浴等温淬火,奥氏体化温度为900℃,保温时间75 min,等淬温度为300~350℃,等淬时间为60 min。最终生产的铸件经过X光检测后可以达到2级甚至1级,铸态金相组织为:球径大小16~60μm,基体组织为铁素体+珠光体;淬火后的金相组织为致密的下贝氏体和20%的残余奥氏体组织,淬火后硬度为302~375 HB。     

High Order Difference Schemes for a Time Fractional Differential Equation with Neumann Boundary Conditions

A compact finite difference scheme is derived for a time fractional differential equation subject to Neumann boundary conditions. The proposed scheme is second-order accurate in time and fourth-order accurate in space. In addition, a high order alternating direction implicit (ADI) scheme is also constructed for the two-dimensional case. The stability and convergence of the schemes are analysed using their matrix forms.     

UDC圆满结束ADI市场战略升级

目前,半导体公司的竞争触角早已深入到大学资源,所谓未雨绸缪,各种大学计划的背后正是企业产品在广大的未来工程师们的经验领域的软着陆。ADI公司的中国大     

Lubich Second-Order Methods for Distributed-Order Time-Fractional Differential Equations with Smooth Solutions

This article is devoted to the study of some high-order difference schemes for the distributed-order time-fractional equations in both one and two space dimensions. Based on the composite Simpson formula and Lubich second-order operator, a difference scheme is constructed with $\mathscr{O}(τ^2+h^4+σ^4)$ convergence in the $L_1$($L_∞$)-norm for the one-dimensional case, where $τ$, $h$ and $σ$ are the respective step sizes in time, space and distributed-order. Unconditional stability and convergence are proven. An ADI difference scheme is also derived for the two-dimensional case, and proven to be unconditionally stable and $\mathscr{O}(τ^2|lnτ|+h^4_1+h^4_2+σ^4)$ convergent in the $L_1$($L_∞$)-norm, where $h_1$ and $h_2$ are the spatial step sizes. Some numerical examples are also given to demonstrate our theoretical results.     

我国铸铁生产技术回顾与展望

我国是铸铁生产大国,铸铁件产量约占世界的40％; 2010年我国铸铁件产量达到2 950万t(其中,灰铸铁1 900万t,球墨铸铁990万t),铸铁件占全部铸件产量的74.5％.本文回顾了60年来我国球墨铸铁、等温淬火球墨铸铁(ADI)、蠕墨铸铁和灰铸铁在生产技术、性能水平、技术标准、应用领域、质量检测和控制等方面的进展;对比分析了与国外先进工业国家在铸铁材质结构、生产规模、成分和性能波动、熔炼造型和质量控制等方面的差距;展望了铸铁生产技术发展趋势,供同行探讨和参考.     

Environmental pH determines citrulline and ornithine release through the arginine deiminase pathway in Lactobacillus fermentum IMDO 130101

Sourdough lactic acid bacteria (LAB) need to be adapted to a highly acidic and, therefore, challenging environment. Different mechanisms are employed to enhance competitiveness, among which conversion of arginine into ornithine through the arginine deiminase (ADI) pathway is an important one. A combined molecular and kinetic approach of the ADI pathway in Lactobacillus fermentum IMDO 130101, a highly competitive sourdough LAB strain, identified mechanisms with advantageous technological effects and quantified the impact of these effects. First, molecular analysis of the arcBCAD operon of 4.8 kb revealed the genes encoding the enzymes ornithine transcarbamoylase, carbamate kinase, arginine deiminase, and an arginine/ornithine (A/O) antiporter, respectively, with an additional A/O antiporter 702.5 kb downstream of the ADI operon. The latter could play a role in citrulline transport. Second, pH-controlled batch fermentations were carried out, generating data for the development of a mathematical model to describe the temporal evolution of the three amino acids involved in the ADI pathway (arginine, citrulline, and ornithine) as a result of the activity of these enzymes and transporter(s). Free arginine in the medium was converted completely into a mixture of citrulline and ornithine under all conditions tested. However, the ratio between these end-products and the pattern of their formation showed variation as a function of environmental pH. Under optimal pH conditions for growth, citrulline release and some further conversion into ornithine was observed. When growing under sub-optimal pH conditions, ornithine was the main product of the ADI pathway. These kinetic data suggest a role in adaptation of L. fermentum IMDO 130101 to growth under sub-optimal conditions.     

The arginine deiminase pathway of Lactobacillus fermentum IMDO 130101 responds to growth under stress conditions of both temperature and salt

The arginine deiminase (ADI) pathway is a means by which certain sourdough lactic acid bacteria (LAB) convert arginine into ornithine via citrulline while producing ammonia and ATP, thereby coping with acid stress and gaining an energetic advantage. Lactobacillus fermentum IMDO 130101, an isolate from a spontaneous laboratory rye sourdough, possesses an ADI pathway which is modulated by environmental pH. In the present study, a broader view of the activity of the ADI pathway in response to growth under two other commonly encountered stress factors, temperature and added salt, was obtained. In both cases, an increase in ornithine production was observed as a response to growth under both temperature and salt stress conditions. Biokinetic parameters were obtained to describe the kinetics of the ADI pathway as a function of temperature and added salt. The arginine conversion rate increased as a function of added NaCl concentrations but was hardly affected by temperature. In addition, arginine-into-citrulline conversion rate was not affected by temperature but increased with increasing NaCl concentrations. Citrulline-into-ornithine conversion rate increased with increasing temperature, while it dropped to zero with added salt. These findings suggest a more pronounced adaptation of the strain through the ADI pathway to added salt, as compared with different constant temperatures. Furthermore, these results suggest that the ADI pathway in L. fermentum IMDO 130101 is active in adapting to non-optimal growth conditions.