The Study On The Microstructure And Properties Of Ferrite Nodular Cast Iron With High Toughness

The article regards the solid solution strengthened ferritic ductile iron of high silicon as the object of research.The content of silicon is added on EN-GJS-400-18U-LT,and get the ferritic nodular cast iron which has excellent properties.The test has studied out two kinds of ferrite nodular cast iron with high strength and high tenacity by designing test cubes with different modulus,carbon equivalent(silicon,carbon),nodulizer,inoculant,trace elements,etc.the two kinds ferrite nodular cast iron are EN-GJS-420-18U-LT and EN-GJS-500-14,both them are suitable for heavy section ductile iron.The test researches on EN-GJS-420-18U-LT by increasing the silicon content to 2.6%,and pours the test cube of modulus 5cm and the Y attached block of 70 mm thickness.The strength and toughness of the attached casting block are very excellent,it’s tensile strength reaches to 420 MPa.The impact of V-notch is more than 12 J under-20 ℃ the low-temperature.Through observing the internal microscopic of 5cm module cube,The test finds that EN-GJS-420-18U-LT meets the requirements of heavy section ductile iron.The micro structures in different positions differ slightly,and the mechanical properties change slightly as well.However,we found two defects in the test cube of 5cm module.One is the combination of blowholes and the nodularizer slag.The other defect,which is mainly due to the unreasonable gating system design,is internal sweating.Because of that,the filling process produces the turbulence and air entrapment.By the study on carbon equivalent of EN-GJS-500-14,the test pours the test cube of modulus 4cm and the Y attached block of 70 mm thickness.The test finds that with increasing silicion content from 3.2% to 3.5%,the graphite count has increased.But the graphite morphology has changed,and the eveness and roundness of it are depressed.This article define the location of big graphite ball and fragmental graphite as "weak area”,which mainly is the location of the modulus 4cm test cube near the edge of 10 mm to 50 mm.At the same time,we find with increasing silicon content,the bulky graphite and chunky graphite are growing,and the “weak area” has a tendency to expand.By the study on carbon equivalent of EN-GJS-500-14,the test finds that the intensity and hardness of four attached casting block has increased and elongation has slightly reduced with the increase of silicon content.Impact value is low,the impact energy in 20 ℃ was 3~4 J,and the impact energy in room temperature was 5~8J.At the same of silicon content,with the increase of carbon content,impact value is lower.As well when they have silicon content as much,the test of noumenal mechanics performance shows that the tensile strength and elongation is decreasing from the middle to the edge.“weak area” is obvious.Whats more,the hardness of different test cube will increase with the increasing silicon content,but the hardness of different locations of the same test cube is stable.When nodularizer 1# and 80 ppm stibium are used in EN-GJS-500-14,the test pours the four test cube of modulus 2cm and modulus 3cm and modulus 4cm and modulus 5cm.Chunky graphite is disappearing,but a small number of large spherical graphite occurs in “weak area”.With the increase of the modulus,the graphite amount gradually reduces.From the center to the edge,the graphite count in the same of the test cube is greatly reduces.The nonmetallic inclusion which has metallic luster in metallograph occurs at the edge area of test cubes.Pearlite is found around the inclusion after corrosion.EDS test results show that the majority of nonmetallic inclusion is MgO slag.The segregation of stibium and phosphide eutectic are also founded in inclusion.When nodularizer 2# and 50 ppm stibium are used in EN-GJS-500-14,the test pours a set of test cubes.But Chunky graphite,inclusion,pearlite haven’t been found.During the study of EN-GJS-500-14,the tests found two miniature shrinkage defects.The appearance of the defects are polygon,sunk to inside.They were taken shape in the late of solidification by pumping molten iron from the gap of austenite branch crystals.Therefore graphite expansion of the solid solution strengthened ferritic ductile iron can’t make up for solidification shrinkage of the molten iron.