| As special and important types of steel, pipeline steel and plastic die steel aremajor project of the domestic iron and steel industry efforts to develop and product.At the same time the performance of these two kinds of steel are closely affected byinclusion levels. In order to transport oil and gas more safely, efficiently andeconomically，pipeline steel is developed towards high-grade and large deformation.Inclusions in different location of continuous casting will influence the property ofthe steel pipe. The inclusions level of HAZ in steel tube seriously affects the servicelife of steel. Arbitrary cross section in die steel is likely to be used as working face. Inorder to guarantee the uniformity of the performance property, it is necessary to studythe inclusion in different location of steel. Firstly, the inclusions distribution along thethickness direction in the X80HD pipeline steel continuous casting billet were rated,the statistical distribution of inclusions in different particle size range were analyzed,the Morphology and composition of The main inclusions were studied. Then, thecontrol level of inclusions and organization and impact toughness of both the place90°to the welding line and HAZ in X90steel pipe were comparative studied, theinfluence of inclusions and organization to toughness were analyzed. Finally, themorphology and chemical composition of inclusions and the microstructure in P20plastic die steel were investigated by using of SEM and EDS analysis. The quantitystatistics and size distribution of inclusions were observed by metallographicmicroscope. Hardness test and electrochemical test were employed to analyze thechange rule of hardness and corrosion resistant along the thickness direction. Theresults of the study are as follows:In X80HD casting blank, D type inclusions in the2/4to the inner arc are theclass of2.5fine, The other types of inclusion levels are no more than2levels.Inclusions smaller than8μm accounts for95.36%of the total. The total number ofinclusion decreases from the inner arc to the outer arc, so does the value of I; and themaximum appears in the1/4to the inner arc because of the Inclusions Easily Capture Zone. Small inclusion such as MnS is well combined with the matrix, middleinclusion as CaO MgO is easy to broken, big globular complex phase inclusionCaO MgO Al2O3SiO2will have bad influence on steel. Both CaO Al2O3CaS andAl2O3CaO MgO will not have bad influence on steel.In X90steel pipe, inclusions are controlled well that no more than2level. Supersize D type inclusions appeared local near the HAZ will be a very adverse impact onthe toughness of steel. CaO Al2O3SiO2is hard and the junction with the matrix iseasy to crack. CaO SiO2is crisp and easy to crack itself. CaO Al2O3is big and easyto crack when rolled. No super size D type inclusion is here the place90°to the weldposition. Al2O3SiO2, FeO Al2O3, calcium aluminates phase inclusions. Stressaffected zones in the junction of ferrite and inclusion are small, the zone bainitecombined with inclusion has large deformation. Structure near HAZ is coarse withhigh composition of bainite, and the inclusion there is serious. The interaction effectof inclusion and microstructure makes the toughness here is lower than that of90°from HAZ.In P20plastic die steel, inclusions are mainly spherical. Inclusions smaller than8μm accounts for92.99%of the total. Inclusions are concentrated in the1/4to3/4ofthe whole thickness direction with relatively large particle size. The microstructure ofhot rolled P20steel is ferrite plus pearlite which changed to tempered sorbite afterquenching and tempering and the microstructure is more uniform and fine. There isno change of the type, size and distribution of inclusions after quenching andtempering, but the inclusion combines closely to the matrix and the stress affectedzone turns to be small. For the combined action of inclusion and matrix, the hardnessincreases obviously and become more uniform. The distribution of Inclusion do nothave much impact on the corrosion resistance along the thickness direction. |
