.45 Si2cr Structure And Behavior Of The Study

Tang Shan steel stock Ltd. Committed this task to us. 45Si2Cr reinforcing steel bar is mostly manufactured railroad concrete sleeper and in the construction of prestress concrete component. Steel 45Si2Cr has used since 80 decade. It was smelted in alkalescent electric cooker, rolled on rank rolling mill, and then disposed after sequent quenching and midst temperature tempering. Now steel 45Si2Cr is rolled on high-speed wire rolling mill after continue casting for the sake of exerting superiority of steel 45Si2Cr and washing out behindhand technique. The mostly purpose is to constitute what about heat treatment technique can make its capability achieve the best.Though steel 45Si2Cr has used in Tang Shan steel stock Ltd., it hasn't reported in other factory in home and abroad. So it attributes new steel, its technical data hasn't been perfect and technique need optimize. Therefore we firstly menstruate three groups continuous cooling transformation curve (CCT) at GLEEBLE-1500 heat simulate machine in Peking science and technology university in order to determine the best technique of heat treatment. On the one hand the curve complements basic data of steel 45Si2Cr, on the other hand it offers important basis for determine technique of heat treatment. Every critical is determined at ZRP-03 heat expend instrument. Each sample after continuous cooling transformation is taken metallographic photos and measured HV rigidity.Heat treatment technique of 45Si2Cr reinforcing steel bar is quenching and tempering. So constitute the two technical parameter is mostly content, it includes quenching (tempering) temperature, heat preservation time, and cooling fashion. On account of tempering is the last working procedure and connects with the bar's using capability and life, so confirm tempering temperature is the mostly investigate content. The good or bad of technique bases results of testing mechanics capability. Draw and extent experiment receives various heat treatment samples'tensile and yield strengths, extend and area shrink rate. Low temperature impact test finds wallop under -50℃, -40℃,-20℃,0℃,20℃. To use dynamic hanging determine E=215Gpa. Typical sample after heat treatment was taken photos under optics microscope, after impact was taken photos under electron microscope.To simulate temperature in heating stove and structure during continuous cooling makes some actions for the sake of constituting technique and realizing automatization during heat treatment.1. We have determined continuous cooling transformation curve (CCT) of steel 45Si2Cr at GLEEBLE-1500 heat simulate machine, achieved critical of this steel that Ac3 and Ac1 are separate 822℃and 790℃, Ar1 and Ar3 are separate 775℃and 805℃.2. Steel 45Si2Cr doesn't form bainite during continuous cooling transformation, gains ferrite, pearlite and martensite. Martensite transformation point Ms ascends following advance of austenite temperature and linear regression equation is TM s = 35. 3+0.3TA. Critical cooling velocity minishes along with advance of austenite temperature and regression equation is V L = ?4 .03+1.01TA?0.0006TA2.3. By many combinations of quenching temperature and tempering temperature, We finally educe best of all heat treatment technique is : quenching temperature 900±10℃, heat preservation 15 minute; tempering temperature 450±5℃, heat preservation 30 minute. After tempering the structure is tempering fine pearlite. The steel has possessed well toughness according to the hear treatment system so you say, here yield strengthsσ0.2 is 1525Mpa, tensile strengthsσb is 1669 MPa,extend rateδ5 is 11.5%,shrink rateΨis 45.1%, E is 215Gpa, yield strengths compares tensile strengths is 0.91, toughness transform brittleness temperature exceeds -50℃. It has completely achieved the request. Compared with product, which was received form former technique, tensile strengths increases 100 Mpa, yield strengths increases 200 Mpa, extend rate rises a little.4. We can get that the bar is heated up to 900℃need 230.97 second and the difference between center and surface temperature is 0.38 second by calculateΦ8mm steel 45Si2Cr in 1000℃heating stove. Therefore to this kind of thin bar the whole can be seen same temperature, doesn't consider variety of inside and outside temperature during heating or cooling.5. We can also directly receive structure content under cooling velocity and temperature randomly through simulates cooling process on CCT curve. This process is convenience and shortcut, controls the whole course use computer easily, and makes some actions for the sake of realizing automatization during heat treatment.6. Each procedure is compiled with Visual Basic, sight well and transferred by other procedure conveniently.