Effect of second phase precipitation behavior on mechanical properties of casting Al-Cu alloys

The effect of the second phase precipitation behavior on the mechanical properties and fracture behavior of the modified casting Al-Cu alloys was investigated. The tensile strength of the alloys increases firstly and then decreases due to the appearance of θ＇ precipitation phases, which increases firstly and then become coarser with the aging time increasing from 10 h to 20 h at 155 ℃. The strength of the alloys reaches the peak, resulting from ,Ω and θ＇ precipitation phases, and decreases due to ,Ω phases becoming coarser and θ＇ precipitation decreasing with the aging time increasing from 10 h to 20 h at 165 ℃. ,θ phase becoming coarser and θ＇ precipitation decreasing result in the strength of the alloys drastically decreasing after aging at 175 ℃ for 20 h. The ductility remains high level with increasing aging time at 155 ℃. The ductility irregularly changes as aging time prolongs at 165 ℃. The ductility is very low and at the same time gradually decreases with increasing aging time at 175 ℃. The Al-Cu alloy with a promising combination of tensile strength and ductility of about 474 MPa and 12.0% after aging at 165℃ for 10 h is due to a dense, uniform distribution of,Ω precipitation phases together with a heterogeneous distribution of θ＇ precipitations.     

红外线测温系统在矿用高强度圆环链连续中频热处理中的应用

阐述了在矿用高强度圆环链连续中频热处理中红外线测温的一些关键问题,建立了红外线在线测温系统,实现了对热处理工艺的精确控制.结果表明,采用红外线在线测温后,矿用高强度圆环链热处理后的合格率明显提高.     

5CrMnMo钢制热锻模热处理工艺改进

5CrMnMo钢制热锻模的失效形式为早期开裂,模腔变形塌陷.在生产现场反复考察、分析和用金相显微镜分析模具热处理前后的显微组织特征后,通过改进锻后淬火强韧化热处理工艺,显著提高了模具的使用寿命,平均寿命达到20000件.     

MICROSTRUCTURE TRANSFORMATION IN THE WELDING HEAT AFFECTED ZONE OF 800MPa GRADE ULTRA FINE STRUCTURED STEEL

The transformation behavior and microstructure development in the heat affected zone (HAZ) of 800MPa grade ultra fine structured steel was investigated. It was found that the HAZ has intermediate temperature transformation characteristics in a wide range of cooling rates, with the bainite sheaves consisting of bainite ferrite plates without carbide precipitation and retained austenite in the .fast cooling regime. At relatively high cooling rates, which corresponded to low heat inputs, the hardness o.f the simulated HAZ was above that of the base metal. When the cooling rate was below 9℃/s, the welding HAZ would have an obvious softening. The analysis of transformation rates in continuous cooling processes was completed by numerical differential method. The result indicated that the microstructure transformation rate o.f the HAZ in 800MPa grade ultra fine structured steel changed sharply to slow speeds when the cooling time t8/5 is longer than 7s.     

RTCr2低铬耐热铸铁的熔炼工艺

介绍了低铬耐热铸铁（RTcr2）的生产过程，用1.5t／h冲天炉和选择化学成分为：ω（cr）1.5％-1.8％，ω（C）3.0％～3.3％，ω（Si）2.0％～2.5％，ω（Mn）≤0.8％，ω（P）、ω（S）≤0.10％的铁液，生产现场严格控制底焦高度、铬铁块度，石灰石加入量等，生产的耐热铸铁完全满足了产品的各项性能要求。     

Effect of Heat Treatment on Microstructures and Properties of Near-Isothermally Forged TiAl Alloy Containing Minor Ni

The heat treatment, including two steps, was proposed to obtain Fine Fully Lamellar (FFL) microstructure on TiAl containing minor Ni. The first step was in t (α γ) phn~se region to get Duplex (DP) microstructure, and the second step was in α phase region transforming DP microstructure into FFL microstructure. The effect of heat treatment on microstructures and properties was sludied. The results showed that the static recrystallization kinetics in i (α γ) phase region took the form of Avrami equitation, and the remnant lamellae in DP microstructure were detrimental to room temperature tensile properties. The FL microstructures were obtained after heat treatment in α phase region using DP microstructure, the uniform FFL microstructure wns beneficial to comprehensive properties.     

IMPROVEMENT OF TYPE IV CRACKING RESISTANCE OF 9Cr HEAT RESISTING STEEL WELDMENT BY BORON ADDITION

Creep lives of high Cr ferritic heat resisting steel weldments decrease due to Type Ⅳ fracture, which occurs as a result of formation and growth of creep voids and cracks on grain boundaries in fine-grained heat affected zone (HAZ). Because boron is considered to suppress the coarsening of grain boundary precipitates and growth of creep voids, we have investigated the effect of boron addition on the creep properties of 9Cr steel weldments. Four kinds of 9Cr3WSCoVNb steels with boron content varying from 4.7×10-5 to 1.8×10-4 and with nitrogen as low as 2.0×10-5 were prepared. The steel plates were welded by gas tungsten arc welding and crept at 923K. It was found that the microstructures of HAZ were quite different from those of conventional high Cr steels such as P91 and P92, namely the fine-grained HAZ did not exist in the present steel weldments. Boron addition also has the effect to suppress coarsening of grain boundary carbides in HAZ during creep. As a result of these phenomena, the welded join     

Finite element prediction of material removal rate due to electro-chemical spark machining

Electro-chemical spark machining (ECSM) is an innovative hybrid machining process, which combines the features of the electro-chemical machining (ECM) and electrodischarge machining (EDM). Unlike ECM and EDM, ECSM is capable of machining electrically non-conducting materials. This paper attempts to develop a thermal model for the calculation of material removal rate (MRR) during ECSM. First, temperature distribution within zone of influence of single spark is obtained with the application of finite element method (FEM). The nodal temperatures are further post processed for estimating MRR. The developed FEM based thermal model is found to be in the range of accuracy with the experimental results. Further the parametric studies are carried out for different parameters like electrolyte concentration, duty factor and energy partition. The increase in MRR is found to increase with increase in electrolyte concentration due to ECSM of soda lime glass workpiece material. Also, the change in the value of MRR for soda lime glass with concentration is found to be more than that of alumina. MRR is found to increase with increase in duty factor and energy partition for both soda lime glass and alumina workpiece material.     

Fe3Si基合金不同热处理工艺的软化机制

Fe3 Si基合金具有优异的软磁性能 ,但由于有序相的出现导致其很强的环境脆性和本征脆性。文中采用不同的热处理工艺来研究软化机理 ,指出在再结晶温度以上采用水冷工艺能使Fe3 Si基合金得到很大程度的软化