Influences of Al and Si Powders on Microstructure and Hot Mechanical Properties of Al_2O_3-C Slide Plates

The basic formulation of Al2O3- C slide plates was65%（ in mass,the same hereinafter） white fused corundum particles,25% white fused corundum fines,6% active α-Al2O3 micropowder,4% carbon black and flake graphite, and additional 4% phenolic resin.Based on this formulation,3% Al powder,3% Si powder,and 3% Al ＋ 3% Si powder were used to substitute equivalent white corundum fines to improve the hot mechanical properties of Al2O3- C slide plates. The specimens with dimensions of 140 mm × 25 mm × 25 mm were pressed at 150 MPa,dried at 200 ℃ for 24 h,and hot treated at 1 400 ℃ for 3 h in carbon embedded condition. Then hot modulus of rupture and thermal shock resistance of the specimens were tested and the phase compositions and microstructure were analyzed. The results show that specimen with 3% Al powder has the higher hot modulus of rupture but lower residual modulus of rupture after thermal shock than the specimen with3% Si powder; the specimen with 3% Al ＋ 3% Si powders exhibits the highest hot modulus of rupture and the best thermal shock resistance; the change of mechanical property is closely related with the in-situ formed nonoxides： AlN in the form of bars is formed in specimens with Al powder; fibrous SiC whiskers are formed in specimens with Si powder; in the specimens with both Al and Sipowders,besides AlN and SiC whiskers,hexagonal tabular SiAlON is in-situ synthesized,which interlocks with each other.

Effect of Direct Quenching and Partitioning Treatment on Mechanical Properties of a Hot Rolled Strip Steel

Three different online heat treatment processes were designed to study the effects on the mechanical properties of a 0.19C-1.6Si-1.6Mn（wt%） hot rolled strip steel.The microstructures were characterized by means of SEM,TEM,EPMA,and XRD.The mechanical properties were estimated by tensile tests.Results showed that a satisfying combination of strength and ductility could be obtained through the ferrite relaxation and direct quenching and partitioning process.Analysis was also focused on this process.The microstructure contained proeutectoid ferrite grains,martensite packets and blocky or interlath retained austenite,and also contained carbide-free bainite in the case of relatively high quench temperatures.The retained austenite fraction was increased through proeutectoid ferrite and partial bainite transformation,while the tensile strength was also consequently decreased.The most of retained austenite transformed to ferrite under deformation and the elongation was obviously improved.

Effects of Heating and Hot Extrusion Process on Microstructure and Properties of Inconel 625 Alloy

The effects of the heating process and hot extrusion on the microstructure and properties of inconel 625 alloy were studied. The experimental results showed that the properties of Inconel 625 alloy could be improved through the heating process and hot extrusion concomitant with a reduced corrosion rate. The M23C6 carbide, generated in the heating process, was retained and distributed at the grain boundary during the process of hot extrusion, which had an important influence on both elongation and corrosion resistance. The improvement of the comprehensive properties of the material, as measured by a tensile test at room temperature, was correlated with the dissolution of segregation Nb. A typical ductile fracture changed to a cleavage fracture where secondary cracks could be clearly seen. With the increase of the extrusion ratio, the real extrusion temperature was higher, which led to more dissolution of the M23C6 carbide, decreased the number of secondary cracks, enhanced the effect of solid solution strengthening, and reduced the intergranular corrosion rate. Under the condition of a high extrusion ratio and a high extrusion speed, the less extrusion time made it possible to obtain organization with a smaller average grain size. Moreover, in this case, the M23C6 carbide and segregated Nb did not have enough time to diffuse. Thus all samples exhibited medium strengths and corrosion rates after extrusion.

Microstructure and mechanical property of MIM 418 superalloy

In this study, the influence of hot isostatic pressing（HIP） process on the 418 alloy produced by metal injection molding（MIM） technique（named as MIM 418）was investigated based on the characteristic analysis of 418 alloy powder. And comparison analysis of the microstructure and mechanical property between the MIM 418 and as-cast 418 alloys was performed by scanning electron microscopy（SEM）, energy-dispersive spectroscopy（EDS）,and X-ray diffraction（XRD）. The results show that MIM418 alloy exhibits fine grain（~30 μm） and uniform microstructure. The defects existing in MIM 418 alloy formed during sintering process can be eliminated through HIP treatment, and the relative density increases from97.0 % to 99.5 %. The mechanical property can be improved significantly because of the elimination of defects, and the tensile strength and elongation are1,271 MPa and 16.8 %, respectively, which are increased by 34.5 % and 180 % compared with K418 alloy after solution heat treatment.