The present investigation was carried out in order to obtain some fundamental information concerning the influence of non-metallic inclusions on the mechanical properties of steels.
In most of the investigations performed by many research workers on the subject, the steel specimens were prepared by usual melting procedures. In consequence, such specimens contained many uncertain factors, affecting the mechanical properties of steels, and making it considerably difficult to investigate the influence of inclusions independently.
In the present investigations, in order to exclude such difficulties as mentioned above as possible, steel specimens containing uniformly a certain amount of particular oxide inclusions were prepared by powder metallurgy technique.
These steel specimens were hot-rolled under the following conditions: the rolling temperature ranges were 1250-1000°C and 1000-800°C, the rolling ratio was 1/5.
Then, the change of inclusion in shape, composition and crystallographic structure during hot-rolling were observed. In the present experiment the behaviors of Al2O3, SiO2, TiO2, FeO·Al2O3, 2FeO·SiO2 and 2FeO·TiO2 were examined.
The main results were as follows:
(1) Al2O3 and SiO2 inclusions having the particle size of 105-74μ, showed fragile fracture, and the degree of fracture was increased in the case of lower rolling temperature.
(2) Those complex oxide inclusions whose melting points were nearly the same as the rolling temperature were deformed plastically, while some others, whose melting points were higher, showed fragile fracture.They were possibly more fragile than simple oxide inclusions.
(3) The crystalization of amorphous SiO2 was accelerated by surrounding solid iron, and most of SiO2 inclusions were transformed to α-cristobalite.