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1、1. Appearance of plate defects I - hot shortness II - separation of material during rolling III - internal grain structure3. Recommendations I - chemical analysis II - reduce temperature drop by rolling strategy II - reducing thermal losses through heat cover III - rolling force reduction by roll ga
2、p lubrication2. Reasons I hot shortness liquid layers of Cu As Zn Sn II - separation of material during rolling AlxNyNbxNy III - internal grain structure rolling forceSuggestions Visit 20.07.2006Cu 0.16%Rolling DirectionPlate defect appearance I - hot shortness (Cu Sn Zn As)Plate defect appearance I
3、I - separation of material during rollingPlate defect appearance III - internal grain structureDifferent grain structureBanding1. Appearance of plate defects I - hot shortness II - separation of material during rolling III - internal grain structure3. Recommendations I - chemical analysis II - reduc
4、e temperature drop by rolling strategy II - reducing thermal losses through heat cover III - rolling force reduction by roll gap lubrication2. Reasons I hot shortness liquid layers of Cu As Zn Sn II - separation of material during rolling AlxNyNbxNy III - internal grain structure rolling forceI - ho
5、t shortness reasons Precipitation of Cu As Sn ZnKajitani : Tetsu to Hagane Vol.81(1995) No.3 185Melting points of different elementsCu - Copper 1084 CAs -Arsenic 817C (28bar)Sn Tin232CZn Zink419CExample : precipitation mechanism copper These elements are liquid during rolling Too high concentration
6、at grain boundaries leadsto separation of grains during rollingI - hot shortness reasons Liquid layer on grain boundariesPrecipitations of Cu / As / Zn / Snalong grain boundaries of slabII - material separation during rolling reasons Precipitations on grain boundariesPrecipitations of AlxNyNbxNyetc.
7、along grain boundaries of slab0.01.02.03.04.05.06.07.08.0 5.06.07.08.09.010.011.0Reciprocal Temperature in 104 * 1/K- log(M%N%)Titaniumnitride log TiN = 5.0-14400/T Aluminiumnitride log AlN = 1.553-7261/T Boronnitride log BN = 5.24-13970/T Niobiumnitride log NbN = 2.8-8500/T1150C 950C1000Csolubility
8、 limitsIII internal grain structure defect reason Deformation not into core of slabDeformation forces - do not reach the center of the slab - do not destroy the as-cast structure1. Appearance of plate defects I - hot shortness II - separation of material during rolling III - internal grain structure
9、3. Recommendations I - chemical analysis II - reduce temperature drop by rolling strategy II - reducing thermal losses through heat cover III - rolling force reduction by roll gap lubrication2. Reasons I hot shortness liquid layers of Cu As Zn Sn II - separation of material during rolling AlxNyNbxNy
10、 III - internal grain structure rolling forceI - hot shortness chemical analysisfrom each ladle take full chemical analysis of all elements at- ladle furnace - tundish (2-3 times each ladle) - finished platewith these results the limits for Cu, As, Sn, Sb, N and the counteraction with Ni and Si can
11、be determinedII separation of material during hot rolling reduce temperature drop- for sensitive steel grades use short distance furnace millstand evaluate: furnace heating time final temperature holding time- turn slab more often during rolling to avoid frequent contact of same slab side with cold
12、roll- reduce work roll cooling to keep rolls more hot- check heat conductivity of roll material- use heat shields to cover roller tablesIII separation of material during hot rolling reduce rolling force through lubrication- roll gap lubrication can reduce required rolling forces up to approx. 40%- for this purpose lubricant is sprayed on the work roll- less force will allow higher reduction ratios which will lead to - less passes - less temperature losses - full breaking of slab internal structure
