Iron Matrix Transformations and Mechanical Properties of Fe-25Cr-C-B Eutectic Cast Alloys

Iron matrix transformation behavior and high temperature strength of Fe-25mass%Cr-C-B cast alloys were investigated using thermal expansion method and compressive test, respectively. Five kinds of eutectic alloys were destabilized at temperatures of 1173 K, 1273 K and 1373 K for 1800 and 18000 seconds, followed with air cooling. Compressive test was made on Fe-25Cr-0C-2.2B, Fe-25Cr-2.2C-1.0B and Fe-25Cr-3.5C-0B eutectic alloys at temperatures up to 1073 K. Result of the work shows that Ms temperature rises with the decrease in destabilization temperature, but the hardness becomes larger with the increase in destabilization temperatures, for the alloys with boron content. Compressive strength of all as-cast alloys was above 2000 MPa at room temperature and above 100 MPa even at 1073 K. The true stress-true strain curves characteristics depended on the chemical composition of the alloys. The effect of destabilization heat treatment almost disappears at the temperatures above 873 K in every alloys

Residual Stress and Bonding Strength in the ElectricalSialon Ceramics Joint Made by Using the Brazing Metal Layer

Electrical Sialons which have some TiN contents were joined with Ag-Cu-Ti active brazing metal layer having a thickness from 30μm to 400μm at a temperature from 1113 K to 1213 K in a vacuum. Residual stress in the brazed joint specimens was not observed when the thickness of brazing metal layer was 30 μ m. However, the residual stress of 80 MPa was detected when the thickness of brazing metal layer increased up to 400μm. When the brazing temperature was 1113 K, four-point bending strengths of 520 MPa and 310 MPa were obtained for the brazed joint specimens with the thicknesses of brazing metal layer of 30 μm and 400 μm, respectively. While the four-point bending strength increased as the brazing temperature was raised. The maximum value of the four-point bending strength was about 700 MPa which was obtained at a condition of the brazing metal thickness of 30μm and the brazing temperature above 1163 K. However, the four-point bending strength decreased with increasing the bending test temperature. A remarkable decrease of the bending strength was observed at the test temperature of 873 K, in which the bending strength was 300 MPa

The Effectof Insert of WC Powder on the Surface Hardening of Non Magnetic Foundry Materials

Non magnetic foundry materials such as the austenitic stainless cast steel had not been used for abrasion resistant materials, because their hardnesses were very low. Usually, ceramics, cermets and cemented carbides are used for the abrasion resistant materials even though they are expensive compared with foundry materials. In this study, WC powder were inserted by using the austenitic stainless cast steel (JIS SCS13A) and the austenitic cast iron (JIS FCA-NiCr202) for producing surface hardened non magnetic materials. The melting temperature (pouring temperature) is lower in the austenitic cast iron than in the austenitic stainless cast steel while the fluidity of the melts is superior in the austenitic cast iron. For the WC powder inserted specimens, the hardness, the abrasion resistance and the magnetic property were examined. As a result, it was found that the hardness in the region of inserted WC powder was much higher than that of base metals of the cast steel and the cast iron, and that the magnetic permeability did not change by the inserting. Especially, a lot of WC powder was found to dissolve into the base metal in the cast steel than in the cast iron. In the case of the cast steel, Fe3W3C compound phase having high hardness of HV800 was formed in the region of inserted WC powder. The hardness in the region of inserted WC powder was higher in the cast steel than in the cast iron, because the cast steel contained a lot of chromium compared with the cast iron

Some Behaviors and Characteristicsof Decarburized Layer in Spheroidal Graphite Cast Iron

Spheroidal graphite cast irons are widely used for auto parts because they have large degrees of freedom in shape and are inexpensive. When they are welded, however, they show serious drawback of crack generation due to excess carbon at thehardened region of heat-affected zone. We have studied on decarburized spheroidal graphite cast iron which has a possibility of welding because of graphite free in the surface region. In the present study, some characteristics of the decarburized layer in the spheroidal graphite cast iron were investigated. The results obtained are as follows. Growth of decarburized layer is controlled by diffusion of carbon atoms toward the surface region in the iron during the heat-treatment and there is a critical temperature of 930 K for the decarburization, below which decarburization does not occur. When the area ratios of the decarburized layer to whole sectional area in the rod-shaped tensile test specimen was defined to be a ratio of decarburized layer, the tensile strength of the specimen scarcely influenced by the ratio of decarburized layer. However, when the overdecarburization was processed, the tensile strength showed a tendency to decrease. Therefore, it should be noted in practical use of the decarburized spheroidal graphite cast iron that the excessive decarburization makes the strength of thin parts of the iron to decrease

The Effectof Insert of WC Powder on the Surface Hardening of Non Magnetic Foundry Materials

Non magnetic foundry materials such as the austenitic stainless cast steel had not been used for abrasion resistant materials, because their hardnesses were very low. Usually, ceramics, cermets and cemented carbides are used for the abrasion resistant materials even though they are expensive compared with foundry materials. In this study, WC powder were inserted by using the austenitic stainless cast steel (JIS SCS13A) and the austenitic cast iron (JIS FCA-NiCr202) for producing surface hardened non magnetic materials. The melting temperature (pouring temperature) is lower in the austenitic cast iron than in the austenitic stainless cast steel while the fluidity of the melts is superior in the austenitic cast iron. For the WC powder inserted specimens, the hardness, the abrasion resistance and the magnetic property were examined. As a result, it was found that the hardness in the region of inserted WC powder was much higher than that of base metals of the cast steel and the cast iron, and that the magnetic permeability did not change by the inserting. Especially, a lot of WC powder was found to dissolve into the base metal in the cast steel than in the cast iron. In the case of the cast steel, Fe3W3C compound phase having high hardness of HV800 was formed in the region of inserted WC powder. The hardness in the region of inserted WC powder was higher in the cast steel than in the cast iron, because the cast steel contained a lot of chromium compared with the cast iron

Surface Hardening of Some Cast Irons with Inserted Hard Alloy Particles

In this paper, two experiments for locally hard facing of cast iron and cast steel will be presented. In the case of locally hard faced spheroidal graphite cast iron with hard alloy briquettes, the inserted layer as formed with penetration of the molten cast iron among tungsten carbide (henceforth, it is described as WC) particles in the hard alloy briquette. The base metal of inserted layer showed a microstructure of gray cast iron due to a hindrance to spheroidalization caused by a reaction the molten cast iron to the elements of W and Co in the hard alloy. The hardness of mother spheroidal graphite cast iron was about Vickers hardness (henceforth, it is described as HV) 200 while the hardness of the inserted layer ranged from HV600 to HV1600. In the case of locally hard faced cast steel, the inserted layer was also formed with similar process to that of the spheroidal graphite cast iron, while intermediate phases with very hard complex carbide were formed at the bonding region between the inserted layer and the base metal. The hardness of mother cast steel was about HV300, while the hardness of the inserted layer ranged from HV800 to HV1400. Especially, the intermediate layer with complex carbide showed the highest hardness of HV1800. Therefore, the inserted methods with hard alloy particles are considered to be a very effective one for locally hard facing of cast iron and cast steel