A Comparative Study On The Mechanical Properties And Continuous Cooling Structure Transformation Of High Carbon Steel 82B And 87Si

High carbon steel wire rod 82 B is the main raw materials to produce large size,high strength,prestressed stranded wire and wire rope.High carbon steel wire rod 82 B is processed by heat treatment,drawing,galvanizing and other processes to produce high strength and higher strength steel wire rope.Strand products are indispensable important raw materials to the construction industry in China.The products are widely used in construction,railways,highways,terminals and other fields.A large number of domestic and foreign experts and scholars are committed to improving the strength of 82 B wire rod and the development of the new wire rod products with higher strength.Replacing vanadium,nickel and other precious alloy elements by carbon and silicon elements to strengthen the 82 B wire rod,is currently a hot research at home and abroad.With high carbon and high silicon,which both to protect the strength of the wire rod,but also can effectively save production costs.In this paper,82 B steel wire rod is the object of the study,by improving the heat treatment process,we can enhance the comprehensive performance of 82 B high carbon steel wire rod,and we developed a new product 87 Si steel wire rod by increasing the carbon and silicon content to enhance the strength of wire rod.In this paper,we describe the application effect of high carbon and high silicon by comparing the mechanical properties,microstructure,continuous cooling structure and hardness after the thermal simulation experiment of the 82 B and 87 Si steel wire rods.Mechanical testing of 82 B and 87 Si steel wire rods is carried out,compared with 82 B steel wire rod,the tensile strength of the 87 Si steel wire rod is increased by 50 MPa,the elongation decreased by 0.1% and the section shrinkage decreased by 1.8%.The carbon element can be dissolved in the ferrite,and it influence the strength and hardness of the wire rod greatest,but the existence of carbon elements also will reduce the plasticity and toughness of the wire rod;when the silicon content is less than 0.5%,the silicon content increase 0.1%,the tensile strength of the wire rod will increase 8MPa,when the silicon content is more than 0.5%,the wire rod tensile strength decreases;In the 82 B and 87 Si steel wire rod manganese content range,the manganese content increase 0.1%,the tensile strength of the wire rod will increase 8MPa.Compared to 82 B steel wire rod,the strength of 87 Si steel rod increased significantly,but the plastic decline slightly,the results is the combined effect by the carbon,silicon,manganese and other elements.The microscopic structure of 82 B and 87 Si steel wire rods was observed under 500 times of metallographic microscope,the white tissue was pearlite,and the gray structure was sorbite.The statistical results of sorbite content by metallographic analysis software Image tools are shown the sorbite content of 82 B steel is about 89%,the sorbite content of 87 Si steel is about 89%.With the increasing of the carbon and silicon elements,more ferrite and cementite were produced,and there were more sorbite generate in the pearlite transformation process.The sorbite sheets of 82 B and 87 Si steel wire rods were observed under scanning electron microscope,the sorbite sheets of 82 B was 162.6 nm,and the sorbite sheets of 87 Si was 138 nm.Compared with the 82 B steel wire rod,87 Si steel wire rod sintered layer spacing reduced by 24.6nm.87 Si steel wire rod sintered layer spacing is small,indicating 87 Si steel wire rods with high strength and hardness.Thermal simulation testing of the 82 B and 87 Si steel wire rods,the experimental results show that the content of sorbite is highest when the cooling rate is 5?/s,and the comprehensive mechanical properties are the best.When the cooling rate does not exceed 7?/s,87 Si steel wire rod possess more sorbite;when the cooling rate between 7?/s ~ 20?/s,82 B steel wire rod possess more sorbite;when the cooling rate is 5?/s,Martensite appears;when the cooling rate is 5?/s ~ 7?/s,82 B steel wire rod possess more martensite;when the cooling rate between 7?/s ~ 20?/s,87 Si steel wire rod possess more martensite.At low cooling rates,87 Si steel wire rods generate more sorbite,and at high cooling rates,87 Si steel wire rods generate more martensite.Compared with the 82 B steel wire rod,the starting temperature of the pearlite phase change about 87 Si steel is lower at each cooling rate,and the CCT curve of the 87 Si steel wire rod is lower left offset.The hardness test of 82 B and 87 Si steel wire rods after the thermal simulation experiment was carried out under the Vickers hardness tester.With the increase of the cooling rate,the hardness of the 82 B and 87 Si steel wire rods increased.When the cooling rate is 5?/s,82 B steel wire rod hardness value of 409.4HV,87 Si steel wire rod hardness value of 418 HV.According to Vickers hardness and tensile strength of the corresponding relationship conversion,the tensile strength of the 82 B steel wire rod is 1318.8MPa,which is 44.8MPa higher than that of the original sample,the tensile strength of the 87 Si steel wire rod is 1344 MPa,which is higher than the original sample Strength increased by 20 MPa.