Study On Precipitation Phase And Mechanical Properties Of Hot Forming Marine Duplex Stainless Steel

High-strength duplex stainless steel has high strength,good toughness,superior welding performance and other properties.Especially the design of ultra-low-C and high-Cr,Mo and N components of duplex stainless steel make them widely used in ship-engineering,marine-engineering and other special harsh corrosive environments.However,the dual-phase structure of the high-strength duplex stainless steel results in the strength that is more than twice that of the austenitic stainless steel whose pitting corrosion resistance is equivalent to the high-strength duplex stainless steel,making the high-strength duplex stainless steel become the material which is difficult to shape.This article takes the SAF2507 Duplex Stainless Steel(SAF2507 DSS)plate as the research object,hot stamping forming test at different hot stamping temperatures and different holding times;Studying the kinds,precipitation patterns,and chemical element changes of the SAF2507 DSS at different hot stamping temperatures and different holding times by SEM,XRD,EDS,and use JMatPro software for simulation calculations and compare with the sample results;Testing the main mechanical properties such as tensile strength,microhardness and shocking resistance of SAF2507 DSS which had been hot-stamped by universal testing machine,microhardness tester,shock tester,in oder to study the relationship between the precipitation phase of SAF2507 DSS and the change of mechanical properties under different hot stamping temperature and different holding time and to study the influence of the change of relative mechanical properties;Simultaneously studying the relationship between the morphology and the changes of the precipitates of the SAF2507 DSS under different hot stamping temperatures and different holding times.The main findings of this article are as follows:(1)The precipitation phase of SAF2507 DSS hot stamping is mainly composed of ? phase and ? phase.The ? phase is a metastable phase.When the hot stamping temperature between650°C and 800°C,the ? phase content increases first and then drops rapidly as the temperature rises.The ? phase is mainly distributed in the ?/? grain boundary,and the stable existence temperature range is 750°C-800°C.At 800°C? phase is transformed into? phase by lattice recombination and temperatureaction.The ? phase is mainly distributed in the ?/? phase boundary.When the hot stamping temperature between 650°C and 900°C,the ? phase content graduallyincreases with the increase of temperature.When the hot stamping temperature is 950°C,the ?phase content sharply rises to the peak,then drops rapidly and completely dissolves at1050°C.The basical results of the hot stamping SAF2507 DSS test are consistent with those of the JMatPro software.(2)The ? and ? phase are hard and brittle phase.The content changes of ? and ? phases precipitated during hot stamping SAF 2507 DSS directly affect the mechanical properties of the material.The hot stamping temperature ranged from 650°C to 1100°C,and the tensile strength of SAF2507 DSS under hot stamping increases first,then decreases sharply and then slightly increased;hardness increases first,then drops sharply and then slightly increases;extensibility shows a trend of decreasing first then rising sharply and then decreasing again;shocking resistance first drops sharply then falls again.When the hot stamping temperature is 950°C,the ?phase is completely transformed into ? phase.The ? phase precipitated reaches its peak,and the tensile strength and hardness of the material reach a maximum.(3)The hot stamping forming temperature is 650°C,950°C,and 1050°C.After 5 minutes of heat preservation,the fracture morphology of the material is dimple fracture-cleavage fracture-dimple fracture respectively.Only a very small amount of ?phase precipitates at 650 °C,with almost no effect on the fracture morphology;The precipitation of ? phase reaches a peak at950°C,and the fracture morphology consists of a large number of cleavage planes;The ? phase dissolves at 1050°C and the material recovers its toughness,and it's still a dimple fracture.When the hot stamping temperature is 950°C,the content of ? phase increases with the increase of holding time,and the number of cleaved faces of the fracture morphology decreases,the area of cleaved surface also gradually increases.When the hot stamping temperature is 1050°C,the ?phase gradually increases with the increase of holding time,and the fracture morphology gradually changes from a dimple fracture to a quasi-cleavage fracture.