Surface cleanliness evaluation in Ti stabilised ultralow carbon (Ti-IF) steel

Abstract

The surface cleanness of Ti-IF steel, including head, transition, end and normal slabs, was studied by original position analyser. The content, number, size and porosity of inclusions on the surface were obtained. The results showed that: the contents of inclusions in head and end slabs were significantly higher than in normal or transition slabs and fluctuated significantly in nonsteady state slabs within 3.5 mm of the surface; the porosity in 3.5 mm of slab surface was lower than other positions; the surface cleanliness order was normal slab.transition slab.end slab.head slab; a reasonable surface peeling thickness for non-steady state slabs was 3.5 mm. The energy dispersive spectroscopy showed that more lump Al 2 O 3 existed in the head slabs, and slag entrapment inclusions also appeared frequently in the end slabs. The main effect factors for cleanness of the head and end slabs were reoxidation and slag entrapment.

Hook evolution and inclusion entrapment during initial solidification process of continuous casting slab

“…Figure 11 also shows that with increasing casting speed, the inclusion particle entrapment probability decreased. The aforementioned conclusions were consistent with the statistical conclusions concerning slab cleanliness presented in References [27][28][29]. When the shell moved downwards, the molten steel at the meniscus overflowed out of the shell, leading to particles gathering near the meniscus being deposited above the nascent hook.…”

“…Shorter and thinner hooks were formed after the continuous casting process was optimized by using a higher casting speed or pouring temperature or higher crystalline tendency of the mold flux (mech-I of OM formation) to suppress the solidification of the meniscus or by using a mold flux with low viscosity and solidification temperature (mech-II and mech-III) to enhance the lubrication for infiltration of the mold flux and reduce the slag rim size [26]. Previous studies have confirmed that the entrapment of inclusions by hooks results in more macro-inclusions being present at the subsurface than in the slab interior [27][28][29]. To the best of our knowledge, however, a study on the specific process of hook inclusion entrapment has not yet been published.…”

Distribution of macro-inclusions in low carbon aluminium-killed steel slabs

“…They found that inclusions larger than 200μm were usually entrapped by hooks and fewer inclusions were detected with higher flow velocity at the S/L interface. Other researchers also reported the distribution of large-sized inclusions by different methods, including X-ray analysis [12], ultrasonic examination [13], original position analyzer (OPA) [14,15], direct observation [16] and ASPEX [17,18]. Their findings are summarised in Table 1.…”

Source of Inclusion in IF Steel End Slabs

“…IF steel is widely used in the production of automobile panel [1][2][3], cleanliness control is becoming ever more important as steel surface quality demands increase [4][5][6][7]. In order to avoid increasing slab inclusions from slag entrainment in tundish, there must be a certain amount of molten steel in tundish in the end of a cast, making the height of molten steel more than critical height of slag entrainment [8], but it will reduce the metal yield and increase costs.…”