Powder-pack Method Research Articles

SURFACE IMPROVEMENT OF DUCTILE CAST-IRON

Diffusion impregnation with chromium is widley used as a surface treatment for steel and gray cast-iron, but very limited in ductile cast-iron. Two types of ductile cast-iron, ferretic and 60 % pearlitic, are surface chromised under different conditions using powder pack method. The maximum attaind chromised layer thickness of 22 um with surface micro-hardness of 1950 HV. is achived after treatment at 1000.0 for 30 hours. The rate controlling of the carbide layer growth process during chromising is being the diffusion of the chroium element and the direction of layer growth is determined to be inward chromium diffusion. The evaluation of the newly formed layers by corrosion, oxidation and wear resistance are carried out and discussed in the light of the obtained results.

鉄鋼表面へのクロムならびにチタン炭化物の二層被覆

Carbon steel (S45C) for machine construction and alloy tool steel (SKS3) were coated with chromium or chromium carbide by using electroplating or powder pack-method (Chromizing) and then titanium carbide. It is possible thermodynamically that titanium carbide (TiC) forms on the chromium carbide (Cr7C3) layer. The total thickness of this dual layer was approximatelly constant, i.e. 10-12μm. The hardness distribution profile of the dual layer changed gradually from the surface. When the chemical potential of carbon in the substrate became higher or the chromium carbide- or electroplated chromium layer became thinner, a thicker double carbide layer consisting of chromium- and titanium carbide was achieved.

TiC-Coating on the High Carbon Steels SK3 and SKS93 Using the Powder-pack Method

TiC coatings on high carbon steels are suggested to improve wear resistance as well as resistance to corrosive atmospheres. However, coating high carbon steels with pure TiC is technically difficult due to the rather strong affinity of Ti to N 2 , O 2 or H 2 . A coating reagent including mainly ferro-Ti, A1 2 O 3 and small amount of NH 4 C1 was applied to two high carbon steels of SK3 and SKS93 at various temperatures and time periods in a closed crucible . The layers were inspected under the microscope and their hardness profiles determined. The TiC coatings were also identified by X-ray diffraction and EPMA

On Some Features of Chromium Carbide Diffusion Layer Formation

The formation of chromium carbide diffusion layers on iron-carbon alloys was studied in this investigation. The investigation was carried out on graphite, plain carbon steels, gray cast iron, and white cast iron. The carbide layers were obtained by the powder pack method. To distinguish the effect of iron from the chromizing medium on the layer morphology, high purity iron and chromium powders were used as the components of the powder mixture. The samples were chromized in the temperature range of 870 to 1373 K for five to 1500 minutes. Phase composition of the layers was examined by X-ray diffraction method. To assess chromium and iron distribution in the layers, an electron micro-probe was employed. Microstructure of the layers was examined with the aid of light and electron microscopes. Both replica and thin foil methods were used in this work. The original method of thin foil preparation was used to show the M7C3 layer substructure and to define its crystallographic orientation. It was found that formation of the carbide layer began at temperatures below A1 transformation, when the samples were heated to a normal chromizing temperature. It was proved that M3C appearance in the layer depends on both chromizing temperature and amount of carbon in the alloy. The Fe : Cr ratio in the chromized medium was found to affect the microstructure and thickness of the layers strongly. The needle-shaped grains of the M7C3 layer showed particular crystallographic orientation,i.e., [0001] M7C3 crystallographic direction was perpendicular to the diffusion front. The new data on microstructure of the carbide layers were obtained by thin foil method. The growth direction of the carbide layer was defined, which allowed the suggestion of the diffusion model for the carbide layer formation.