Kinematic　immersion　tests　were　conducted　in　order　to　substantiate　quantitatively　a　mechanism　for　the　Locat　corrosion　of　immersion　nozzles　at　the　slag-metal　interface．Based　on　the　mechanism，then，experiments　were　designed　to　find　out　effective　countermeasures　for　preventing　the　local　corrosion． 　The　results　obtained　are　summarized　as　follows： 　For　steels　containing　low　carbon　levels（e．g．，steel　for　continuous　casting），the　dissolution　of　oxides　from　the　nozzle　into　the　slag　film　is　the　rate　controlling　step　of　the　local　corrosion　process．For　metals　containing　high　carbon　content（e．g．，in　the　vicinity　of　carbon　saturation），dlssolution　of　graphite　from　the　nozzle　into　the　metal　is　rate　controlling． 　If　the　nozzle： 　1）　has　a　high　resistance　to　corrosion　by　liquid　slags，and 　2）　is　easily　wetted　by　the　slag． 　then　it　will　exhibit　a　good　resistance　to　local　corrosion　at　the　slag-metal　interface． 　Zirconia-graphite　nozzle　containing　ZrO2　which　has　a　high　resistance　to　corrosion　by　the　slag　much　reduces　its　dissolution　rate　into　the　slag　film．This　mainly　results　in　a　remarkable　lowering　of　the　local　corrosion　rate． 　Alumina-graphite　nozzle　containing　BN　and　zlrconia－graphite　nozzle　containing　SIC　show　good　resistances　to　the　local　corrosion，which　can　be　attributed　to　the　fact　that　BN　and　SiC　have　good　resistences　to　corrosion　by　the　slag　and　are　easily　wetted　by　the　slag． 　The　apparatus　used　for　present　lmmersion　test　is　feasible　for　evaluating　the　local　corrosion　rate　of　zirconia-graphite　nozzles　for　the　condition　of　practical　use．

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　B2O3－MgO　and　B2O3－CaO　compound　oxides　were　added　in　MgO-C　bricks　and　changes　in　wejght，mineral，strength　and　resistance　to　oxidation　were　investigated　after　heating　at　various　temperatures　ranging　from　600℃　to　1400℃． 　Adding　only　B2O3　compound，B2O3　reacted　with　C　at　temperature　over　1200℃　and　accordingly　CO　gas　and　boric　vapors　dlffused　to　outside．However，the　addition　of　Al　powder　in　MgO-C　brick　containing　B2O3　compound　controlled　the　diffusion　and　then　the　contribution　to　oxidation　resistance　and　strength　were　developed． 　Boric　compounds　function　as　both　accelerator　and　inhibitor　for　oxidation　depending　on　temperature　and　atmosphere．Therefore，when　MgO-C　brlck　containing　boric　compound　is　practically　used，it　is　necessary　to　use　it　in　combination　with　metallc　powder　and　to　carefully　study　the　proper　amounts　of　additives．

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