管理案例困难度坐标4—4—4模型

引言案例教学需要使用大量的管理案例。每一个案例都向它的读者提出了一组特定的任务。这些任务有难有易,这一方面意味着完成案例分析任务的时间会有长有短,而学生准备分析报告、参加集体讨论的时间总是有限的。另一方面,学生的兴趣有浓有淡,能力有强有弱,层次有高有低,作为一种智力型的产品——案例也需要适应不同的要求。因此,案例的困难度成了反映不同要求的一个非常重要的概念,因而也就产生了对其困难度的估计和测量问题。我们结合企业管理的教学与科研工作,在分析比较国内外关于管理案例困难度表述的基础上,创造性地改     

RQTAl_4Si_4耐热铸铁熔铸工艺研究

ＲＱＴＡＩ＿４Ｓｉ＿４耐热铸铁的缺点是脆性较大，易产生裂纹。该缺点的克服需要从混砂、造型（制芯）、熔铸和清理等整个铸造生产过程考虑。该合金在熔炼及球化处理过程中，烧损量较大，因而在熔炼及浇注过程中对铁水不易过多搅拌。用冲天炉熔炼的ＲＱＴＡｌ＿４Ｓｉ＿４耐热铸铁件的金相组织比中频电炉熔炼要细密得多，但回炉料的回用是需进一步研究解决的新问题。     

SrxBa1-xBi4Ti4O15陶瓷及SrBi4Ti4O15／BaBi4Ti4O15复合材料的性能研究

采用固相烧结工艺制备了SrxBa1-xBi4Ti4O15铁电陶瓷和SrBi4Ti4O15／BaBi4Ti4O15铁电复合材料。在固相反应过程中，680℃时SrBi4Ti4O15或BaBi4Ti4O15开始生成：800℃时材料主晶相基本形成，但是还有微量焦绿石相存在；850℃时SrBi4Ti4O15或BaBi4Ti4O15的主要衍射峰全部出现。随着Ba含量的增加，SrxBa1-xBi4Ti4O15陶瓷的居里温度逐渐降低。Sr0.5Ba0.5Bi4Ti4O15，陶瓷的介电常数峰在高频时较宽，在100Hz时，介电常数峰被随温度升高而逐渐增大的介电常数所“屏蔽”，材料介电损耗随温度升高而增大，但在低频下增加得更快，这是高温下由氧空位引起的电子松弛极化造成的。将预烧后的SrBi4Ti4O15和BaBi4Ti4O15粉体分别造粒后冉均匀混合，压片成型，经烧结制得的SrBi4Ti4O15／BaBi4Ti4O15复合陶瓷其相变弥散特性明显优于SrxBa1-xBi4Ti4O15的相变弥散特性。     

衬套用QSn4-4-4青铜板退火试验

１　前言某有色金属加工厂提供我公司厚度为１－９ｍｍ的ＱＳｎ４４４青铜板材，质量保证书上写明供应状态为Ｙ３状态，但所列出的力学性能数据只能符合ＧＢ２０４９—８０的Ｙ状态。Ｙ和Ｙ３标准见表１所示。经公司理化测试中心复验，也确认此批板材为Ｙ状态。由于板材状态不符，强度和硬度偏高，衬套加工时感到困难。但如退货，一时难以找到订货单位，且影响生产进度。　　为了降低这批板材的强度和硬度，提高塑性，使其达到Ｙ３状态的要求，满足加工需要，我们进行了退火热处理试验。２　退火热处理试验参考ＱＳｎ４４２－５的有…     

MEK4模具钢

法国模具钢,相当于德国钢号1.8523,或表示成40CrM o V13-9。耐磨性良好,具有良好加工性能,光蚀刻花性好,高硬度、高韧性、高耐磨性和尺寸稳定性。适合于制作轻合金压铸模具,塑料模具和大型锤锻模具等。化学成份（质量分数,%）：0.40~0.60 C;3.00~5.00 Cr;1.00~1.50 Mo;0.20~0.40 V。     

Al4SiC4陶瓷的高温氧化行为

从高温氧化动力学、组织的微观进化及高温氧化机理3部分对Al4SiC4陶瓷在1200℃-1700℃的高温氧化行为进行了系统的研究。研究结果表明，Al4SiC4陶瓷具有优异的高温抗氧化性能。氧化动力学符合抛物线规律，其氧化活化能经计算为220kJ／mol。XRD及SEM研究结果表明：Al4SiC4陶瓷在1200～1500℃的氧化表面物相为Al2O3和铝硅酸盐玻璃；而高温氧化表面（1600℃～1700℃）的物相由Al2O3，莫来石和铝硅酸盐玻璃构成。由氧化试样横截面观察得知氧化层按其特征的不同分为3个部分：具有较多细小尺寸孔洞的反应层；具有较大尺寸孔洞的中间层和致密的外氧化层。在高温抗氧化机理部分中首先从热力学上计算了氧化过程中各反应的生成焓和吉布斯自由能；然后对高温氧化过程进行了推理和分析；最后根据上述试验及推理结果建立了Al4SiC4陶瓷的高温抗氧化模型。     

以NH4FePO4·H2O制备LiFePO4及其性能研究

用FeSO4,H3PO4,NH3·H2O为原料合成NH4FePO4·H2O前驱体,再与Li2CO3和蔗糖均匀混合,通过高温固相反应法合成了LiFePO4正极材料.用X射线衍射和扫描电镜分析对NH4FePO4·H2O和LiFePO4的结构进行了表征.研究了不同含碳量对LiFePO4晶体结构和电化学性能的影响.结果表明,NH4FePO4·H2O前驱体和LiFePO4具有结构相似性,在高温固相反应时NH4FePO4·H2O与Li2CO3发生置换反应.材料具有较好的电化学性能.     

G13Cr4Mo4Ni4V轴承套圈酸洗白斑分析

对滚道酸洗白斑处和正常处进行化学成分、显微组织、表面硬度及渗碳层深度进行分析对比。结果表明,白斑处滚道表面硬度、含碳量及渗碳层深度均低于正常处,表面含碳量低是引起白斑的主要原因。     

QAl10—4—4热处理工艺试验研究

分析了ＱＡｌ１０－４－４制铜阀性能波动的原因,采用正交试验优选了ＱＡｌ１０－４－４材料的热处理工艺,研究和讨论了其不同热处理条件下组织与性能的变化规律及实际热处理条件对铜阀性能的影响。     

快速凝固Al—4Cr—4Zr—2Ti合金的时效特性

利用透射电镜观察了Al-4Cr-4Zr-2Ti（原子百分比）合金的显微组织,并测定了相应的显微硬度。结果表明：快凝合金在400℃,4h时效达到峰值硬度,Hv达2420MPa,此时的析出相为Al13Cr2和与基体共格的亚稳相Ll2-Al3Zr。合金经400℃,96h时效后的显微硬度与急冷态硬度和峰值硬度相比仅分别下降10％和14％。而500℃,4h时效后,由于Ll2-Al3Zr转变为DO23－Al3Zr并且析出相粗化,导致合金硬度急剧下降。     

Inhibierung von wässerigen und alkoholisch wässerigen Wärmeträgern

Inhibition of aqueous and alcoholic-aqueous heat-carriers To examine the effect of corrosion inhibitors mainly ®Preventol CI-2 in aqueous and aqueous alcoholic heat transfer media gravimetric and electrochemical corrosion tests were carried out with the materials grey cast iron, unalloyed steel, copper, brass, lead-tin-solder, aluminium and aluminium alloys up to a temperature of 90°C. In the presence of the inhibitor Preventol CI-2 uniform layers from 10 to ? 50 nm thickness are found on the metal surfaces and the measured massloss (ASTM, EMPA) decreased decidedly. Local corrosion as occurs e.g. by insufficient concentration of inhibitors forming surface layers, was found in none of the cases. The electrochemical examinations confirm the results of the chemical tests and provide indications with regard to the effective mechanisms. The influence of temperature and flow rate on the protective efficiency of the inhibitor can be showed. It is possible to eliminate the risk of galvanic corrosion by contacting copper and aluminium. The cavitation corrosion of grey cast iron is also appreciably reduced. Preventol CI-2 is a broad spectrum inhibitor for aqueous and aqueous alcoholic heat transfer media.     

Homogenität und Korrosionsbeständigkeit hochlegierter Stähle

Homogeneity and corrosion resistance of high alloy steels A major number of case histories in the chemical industry are due to local corrosion the origin of which can be attributed to the inhomogeneity of the steels produced according to conventional melting process. Special processes such as electro slag remelting may give rise to a considerable increase in structural homogeneity of corrosion resistant alloys. Typical examples are increased resistance to nitric acid, Streicher's solution, seawater or reaction mixtures of urea synthesis. These results clearly demonstrate the superiority of the material which is largely free from inhomogeneities such as segregations which give rise to local corrosion phenomena.     

Order-disorder phase transition in NH4AlF4

In this study we calculate the specific heat C_VI for NH₄AlF₄ due to the nearest-neighbor interactions between the NH⁺ ₄ tetrahedra using an Ising model superimposed on an Einstein and/or Debye model. The specific heat C_VI calculated using a power-law formula is in good agreement with the observed C_P for the NH₄AlF₄ system. This is an indication that NH₄AlF₄ undergoes a weak first-order or a nearly second-order phase transition as predicted by our model.     

Widerstandsfähigkeit hitzebeständiger Stähle gegen Aufkohlung

Cementation resistance of heat-resistant steels The cementation process in atmosphere used for the cementation of unalloyed and low-alloyed steels has been examined in 79 melts of Cr and CrNi steels. A characteristic feature was the simultaneous cementation and oxidation of the steels, with characteristic differences depending on the steel composition. These differences can be explained by the different composition and structure of the oxide layers which appear at the outset and may, in certain circumstances, inhibit the carbon diffusion into the interior of the metal. Sometimes, however, an inner oxidation may also occur below a cemented zone. In principle, elements capable of improving the heat resistance — e.g. Ni, Si, Cr, Al — have a favourable effect whilst Mn has a markedly unfavourable effect. The favourable effect of Ti, recently observed, is probably connected with the grain-refining effect.     

SKT4

正SKT4钢具有良好的韧性、强度和高耐磨性;在室温和500~600℃时力学性能几乎相同,加热到500℃时,仍能保持住300 HB左右的硬度;由于钢中含有钼,因而对回火脆性并不敏感;从600℃缓慢冷却下来后,冲击韧性仅稍有降低;具有良好的淬透性,300 mm×400 mm×300 mm的大块钢料,自820℃油淬和560℃回     

YXM4

正YXM4为钨钢高速度钢,适宜于制造强力切割用耐磨,耐冲击各种工具,高级冲模,螺丝模,较需韧性及形状繁杂工具,铣刀,钻头等。化学成份(%):0. 87～0. 95 C;0. 45 Si;0. 40 Mn; 3. 80～4. 50 Cr; 5. 90～6. 70 W; 1. 70～2. 10 Mo;4. 80 V。热处理:锻造温度1100～900℃;退火温度800～850℃,保温2～4 h后随炉冷却;淬火温度,先预热至550～600℃,二次预热至950℃,再加热至奥氏体温度1220～1250℃或1200～1230℃,油淬,油温必须40～60℃;回火温度550～570℃,在静止空气中冷却,重复二次;硬度63 HRC以上;退火硬度265 HBS,淬火回火硬度 63 HRS。     

Phase diagrams of Li2MoO4-Na2MoO4 and Na2MoO4-K2MoO4 systems

The phase diagrams of the Li2MoO4-Na2MoO4 and Na2MoO4-K2MoO4 systems have been reassessed using differential thermal analysis together with high-temperature and room-temperature X-ray diffraction analysis. The results showed that the compound Li2MoO4.6Na2MoO4 did not exist; however, it confirmed the existence of the compound Li2MoO4.3Na2MoO4 in the Li2MoO4-Na2MoO4 systen＇ls. With regard to the system of Na2MoO4-K2MoO4, we could not confirm the results reported by Bukhanova who claimed that the system was eutectic type with 1：1 and 1：2 intermediate compounds, refuting the statement of Amadori who thought there was an apparent phase boundary at high temperature in α-solid solution region of the Na2MoO4-K2MoO4 binary system. The revised phase diagrams of these systems are illustrated in this article. These experimental results are in agreement with the computerized prediction using the support vector machine-atomic parameter method for the assessment of phase diagrams.