DEVELOPMENT AND MICROSTRUCTURE OF 6mm LOW-TEMPERATURE PRESSURE VESSEL STEEL
6 mm low-temperature pressure vessel steel was manufactured through flat rolling combined with roll milling employing a low-C content along with Nb-Ti microalloying design.Optical electron microscopy,tensile testing methods as well as experiments on low temperature impact toughness were utilized to investigate its microstructure variations under diverse processing conditions.Results indicate that under controlled rolled processing conditions,resulting in a polygonal ferrite plus limited pearlite composition for one type,while another type achieved via controlled cooling exhibited a combination comprising polygonal ferrite alongside granular bainite plus some pearlite-without any evidence of band or anisotropic deformation structures induced from longitudinal milling processes.In comparison to air-cooled procedures,post-milling strength for plates subjected to controlled cooling experienced an increase ranging between 40～60 MPa owing to reinforced phase bainitic structures.Furthermore,grain sizes for plates processed via control rolled techniques were notably smaller compared to those lacking such controls;additionally,impact toughness at-40 ℃ significantly surpassed non-controlled counterparts-exceeding values greater than 60 J.Employing rough-rolling followed by fine milling then roll milling coupled with three-stage water-cooled control during production resulted in final temperatures reaching 870 ℃ during roller operations and 630 ℃during subsequent cooling stages.The resultant product-a composite structured material consisting primarily of polygonal ferrites complemented by granular bainites alongside minor amounts of pearlite-exhibited superior overall mechanical properties.
temperature pressure vesselcontrolled rolling and coolingdislocation strengtheningprecipitation strengtheningcomposite structure
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