Ding Peidao

A scanning electron microscopy study of carbides in high-speed steels

Abstract Investigations were made using scanning electron microscopy to examine deeply etched specimens and electrolytically extracted carbides of as-cast high-speed steels. It is shown that eutectic carbides appear in three types of eutectic morphologies. A carbide “wall” exists around type I skeleton eutectic, and growth steps are evident on the top of carbide platelets of the lamellar type II eutectic. Type III generally develops a thick plate or bar form. The delta-eutectoid carbide attains a “bunched fiber” shape. Increasing molybdenum and decreasing tungsten leads to a change of eutectic carbide from skeleton to platelike and fiberlike morphologies. Vanadium not only promotes the formation of MC carbide, but also the formation of M2C carbide. It was noted to be unfavorable to the formation of M6C carbide, and increasing the vanadium content results in an increase in the size of eutectic and eutectoid carbides.

Laser surface alloying of a low alloy steel with cobalt

Abstract Features of laser surface alloying on a 0.21C1.46Cr3.52Ni0.80W steel with cobalt powder are studied. Experimental results show that laser surface cobaltizing is possible and that the cobalt content of the surface alloy may achieve 3.10 wt.%–5.63 wt.%. The maximum cobalt content attained is 9.96 wt.%. After alloying with cobalt, the performance of the surface at elevated temperature is clearly improved. The hardness at 700 °C is 880 MPa, while the fatigue performance in the presence of thermal cycles is improved by 160%, when compared with the surface of the untreated steel.

A scanning electron microscopy study of laser coating microstructures

Abstract Investigations were made, using scanning electron microscopy, to examine microstructural features of laser coatings. The scanning electron microscope makes it possible to observe clearly the detail of the structure in the laser-irradiated zone. It is shown that the microstructures in the laser-coated zone have various features, including a dendritic eutectic, dendritic solid solution, and residual graphite, and that the microstructures in the transitional zone are more complex, including cellular dendritic-cellular, dendritic eutectic, planar, and residual graphite. The laser coating process changes the nature of solidification of the coating melt, compared with common solidification.

THE STUDY OF IRON BASED METAL AND CERAMIC COMPOSITE MATERIAL

ABATRACT The surface infiltrating method was used to produce a metal-ceramic layer on the surface of cast iron. The microstructure of surface composited layer was studied by Optical Microscope and SEM. It was shown that with this method a composited layer with thickness of 2~ 3 mm can be obtained. Ceramic particles distributes uniformly in cast iron matrix. The composited layer has higher hardness compared with cast iron matrix.