Effect Law Of Cooling Rate On Inclusion Size Distribution In Different Deoxidized Steel

The number and size distribution of inclusions in steel have a significant impact on the mechanical properties of steel.Practice shows that the cooling and solidification rate of steel can change the number and size distribution of inclusions in steel.Therefore,how to obtain fine and dispersed inclusions by controlling the cooling rate of steel solidification,thereby improving the quality of steel,is a method of inclusion control worth exploring.This paper takes low carbon steel as the research object,and uses Al-Ti deoxidation and Si-Mn deoxidation to study the effect of cooling rate on the size distribution and number of inclusions in steel,and obtains the quantitative relationship between the cooling rate and the size and number of inclusions.At the same time,the formation and evolution of inclusions were discussed.Use a high-temperature tubular resistance furnace and a high-temperature confocal microscope to control the cooling rate.Use field emission scanning electron microscope and energy spectrometer to observe the inclusions in Al-Ti and Si-Mn deoxidized steels;Use automatic analysis software for inclusions to calculate the size and distribution of inclusions;The Fact Sage thermodynamic software was used to calculate the stable phases existing in the steel in the Al-Ti-S-O system and the Si-Mn-O-S system at different temperatures,and the formation order of inclusions was discussed.Six different cooling rate experiments were performed on Al-Ti deoxidized steel.The inclusions in the steel mainly include Al₂O₃-Ti₂O₃,Al₂O₃-Ti S,Al₂O₃-Ti₂O₃-Ti S,etc.;With the increase of the cooling rate,the average dimensions under the conditions of furnace cooling(3.86 K/min),20 K/min,50 K/min,100 K/min,1000 K/min and 6000K/min are 5?m,4.05?m,4.96?m,3.55?m,2.57?m,2.53?m,respectively.The overall average sizes of all types of inclusions are 4.1?m,3.68?m,2.88?m,2.38?m,2.35?m,2.46?m;the number of inclusion sizes of 0-3?m at different cooling speeds accounts for 51.84%,65.04%,75.56%,78.52%,77.43%.Three kinds of cooling rate experiments were carried out on Si-Mn deoxidized steel.The main inclusions in the steel are Mn O-Ti S,Mn O-Si O₂-Ti S,etc.;With the increase of cooling rate,the average size of Mn O inclusions in steel under water cooling(2940 K/min),air cooling(804K/min)and furnace cooling(3.86 K/min)are 3.71?m and 3.46?m,10.77?m,respectively;The overall average sizes of all types of inclusions are 4.86?m,2.93?m and 5.59?m,respectively;The number of inclusions with sizes of 0-5?m accounts for98.21%,97.53%and 93.55%of the total number of inclusions,respectively.The influence law of cooling rate on the size distribution of inclusions is calculated theoretically,and compared with the statistical results of automatic analysis software for inclusions.The results of the two are basically consistent.The overall law is that the size of inclusions decreases as the cooling rate increases.