Three high basicity slags (A, B and C) were used in laboratory to refine Al killed steel to target high oxide cleanliness and low melting temperature inclusions. Inclusions were of CaO-MgO-Al 2 O 3 -SiO 2 system after 90 min reaction, parts of which were MgO based. Total oxygen were in the range of 0?0007-0?0010 and 0?0005-0?0010% respectively when slag A (CaO/SiO 2 , 6-8; Al 2 O 3 , ,40%) and slag B (CaO/SiO 2 , 6-8; Al 2 O 3 , ,30%) were applied, with inclusions all in spherical shape and mainly ,5 mm. Inclusion composition concentrated in or around the lower melting point region (,1500uC) under slag A, while it became more scattered under slag B. Total oxygen varied between 0?0008 and 0?0011% under slag C (CaO/SiO 2 , 3-4; Al 2 O 3 , about 20-25%). Many of the inclusions were in larger size, irregular morphology and located far away from the lower melting point region. Formation of MgO based inclusions closely related to solubility behaviour of MgO in the slag.
To improve the interfacial bonding of dissimilar composites,
the
interaction mechanism between the surface state and severe plastic
deformation to strengthen the interfacial bonding strength was revealed.
In this study, the different surface states of the steel strip were
designed by louver blade grinding (LBG) and diamond bowl grinding
(DBG), and the cold-rolled composite method was developed to prepare
the brass/carbon steel composite strips. The results show that the
steel surface after DBG has a large roughness of 9.79 μm, a
hard hardening layer of 6.2 GPa, and high cleanliness of 1.34 atomic
% oxygen content, while that after LBG has a roughness of 1.31 μm,
a hardening layer of 4.2 GPa, and an oxygen content of 2.37 atomic
%. The large roughness promotes the breaking of the hardening layer;
the hardening layer is beneficial to obtain sufficient interfacial
stress to expose the fresh metal; and the high cleanliness reduces
the barrier to the fresh metal and contributes to the bonding of the
fresh metal. The interface of the cold-rolled brass/carbon steel composite
strip after LBG and DBG is mechanical bonding and metallurgical bonding,
respectively. In the process of the cold-rolling composite, large
shear deformation occurs at the interface of brass and steel, resulting
in a high concentration of vacancy and dislocation defects, which
provides a channel for interdiffusion of atoms at the interface. Under
the diffusion driving force provided by the cold-rolling shear deformation
heat, a nanodiffusion layer with a thickness of 60 nm and high interfacial
bond strength was formed.
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