No abstract

No abstract

Based on the minimum degree of disregistry mechanism in oxide metallurgy, laboratory and industrial research have been conducted on intragranular acicular ferrite (IAF) induced by microalloying elements in austenite. Based on the chemical compositions of DH36 steel and Mg, Al, Ti, V, Nb microalloyed steel, experimental results show that in ingots' organization, both V and Nb can induce IAF, but when the adding sequence was Al-Mg-Ti, smaller and dispersion inclusions were formed in austenite. When the Mg content was 0.005 wt%, the inclusion structure induced IAF in austenite is as follows: MgO and Al 2 O 3 forms the core and TixOy adheres to the Al-Mg complex inclusions to produce smaller particle size and dispersions of Al, Mg, Ti complex inclusions. Finally, upon lowering the temperature, carbonitrides of Ti, V, and Nb were precipitated on the outermost layer of the inclusions. These carbonitrides with small disregistry contribute to induce intragranular acicular ferrite.

Abstract：The distribution and characteristics of nonmetallic micro-inclusions of GCr15 bearing steel were explored through metallographic area method in virtue of tracer method and electronic microscope. The results show that the micro-inclusions, of which the average value is 0.032%, are mainly the compounds formed via the adsorption/aggregation of multielement deoxidized compounds and secondarily deoxidized products on tundish liquid level. The micro-inclusions of diameters from 0 to 5 μm are 92.5% in total, which basically determines the characteristics of inclusions distribution in casting slab. The inclusions of diameters more than 10 μm only account for less than 1% in total, which have little influence on steel quality. The relationship between equilibrium compositions of the first deoxidation products and molten steel compositions was also calculated based on thermodynamic theory. Keywords：nonmetallic micro-inclusions; GCr15; area method; tracer method; chemical equilibrium With rapid development of industry in China, the steel demand is becoming bigger and the quality requirement is getting higher. The mechanical characteristics [1] , especially the fatigue resistance performance [2][3][4] , of GCr15 bearing steel are affected mostly by the type, quantity, dimension and distribution of nonmetallic micro-inclusions [5] . In general, the nonmetallic microinclusions are analyzed using linear statistic method which needs tremendous calculations and complex conversion process of equivalent diameter [6] . Oppositely, the metallographic area method [7] to calculate the ratio of unit equivalent area to total surface area, is simple, visual and highly accurate [8] .Therefore, this paper adopts the metallographic area method to study the nonmetallic micro-inclusions in GCr15 bearing steel. At the same time, since the composition of nonmetallic micro-inclusions is directly affected by the chemical equilibrium formats [9] between molten steel and deoxidization products, the chemical equilibrium formats are also analyzed based on thermodynamic theory [10] . It provides a theoretical reference for removing inclusions to improve the quality of converter bearing steel.

No abstract