Research On Microstructure Characteristics And Its Effects On Performance Of Hot-rolled Ferritic Stainless Steels

Corrossion,as one of the three invalidation main forms of the mechanical parts,is related to all the departments of the national economy.With the rapid development of modern industry,stainless steel production and processing in modern machinery is widely applied,ferritic stainless steel is becoming more and more attention so as to save the cost of production.In this paper,the effects on the microstructure and performance of three types of ferritic stainless steel of hot-rolled state which are 410S (0Cr13),430(1Cr17) and 409L(00Cr12Ti) are studied.The composition and source of Non-metallic inclusions,microstructure composed,causes of side-face layered crack and mechanism of denudation are studied by means of special corrosive, SEM,EDS,EPAM,TEM,microhardness,the specific heat curve,immersion corrosion in different media of corrosion.Tensile properties,corrosion properties and microstructure characteristics of study combined with the quantitative method.The results are as follow:the lognitudinal and transverse inclusions in three types of ferritic stainless steel is basically the same,mainly oxide-based,≤1.5 level,the overall inclusion is to be fine line,in line with the requirements of steel-making.The inclusions in 410S and 430 stainless steel are mainly from materials,slag,refractories and the reaction between oxides and silica in the deoxidation process.409L stainless steel contains the elements such as Al and Ti which have a strong affinity with the N, these elements can combine with the atmosphere of nitrogen(blowing N₂) and dissolved nitrogen in the steel to form nitride inclusions.Microstructure composed of state of 410S,430 and 409L three hot-rolled ferritic stainless are as follows:the matrix of ferrite±～30%martensite+a small number of (Cr,Fe)₂₃C₆ carbide particles,the matrix of ferrite+(Cr,Fe)₂₃C₆ carbide particles and the matrix of ferrite+a small number of(Cr,Fe)₂₃C₆ carbide particles.Banded structure in 410S and 430 Stainless steel is more obviously,which is the changes in product,and is the metallurgical combination,as the distribution of the second phase in the matrix of ferrite,or a certain amount of strength phase,or mainly clusters distribution of fine carbides.Therefore,the banded structures in 410S and 430 stainless steel have little effect to their mechanical properties.With the tensile test conditions in the rate of 5mm/min,longitudinal and transverse tensile properties of three types of hot-rolled ferritic stainless steel or less the same, which is the results of the specificity of its banded structures and the full-proliferation of the alloying elements along the rolling process.Side fracture phenomenon is obviously in the tensile process of 410S and 430 stainless steel,which is mainly due to ultra-low carbon martensite,hard and brittle carbides along the grain boundaries so as to constitute of the weak links of the 410S,430 stainless steel.In the tensile deformation,dislocations can bypass them only,increase the deformation resistance, and also undermines the continuity in the thickness direction of the plate.But there is no layered crack in the tensile fracture of 409L stainless steel,which is consist with uniformity of its microstructure.The tendency of inter-crystal corrosion in the corrosive medium of 0.5 mol/LH₂SO₄+0.01 mol/L KSCN solution is 410S＞430＞409L of this three types of ferritic stainless steel.There is an obviously erosion of layered phenomenon in the media of different acid corrosions of 410S and 430 stainless steel,and the corrosion layer spacing is consistent with its rolling-direction banded structure spacing.Full corrosion and many corrosion pits on the surface are showned for 409L stainless steel, and the corrosion pits'size are basically consistent with its ferrite grains' size.By comprehensive analyzing of the fracture characters,corrosion features and microstructure characteristics,show that both the fracture morphology and corrosion features are induced by their banded structure along the rolling-direction and the distribution of second phase which are carbon particles in the grain boundaries of the test of steel.