45Si2Cr钢组织与性能的研究

【作者】 王婧；

【导师】 任吉堂；

【作者基本信息】 河北理工学院 ， 钢铁冶金， 2002， 硕士

【摘要】 本课题是由唐山钢铁股份有限公司委托研究的,45Si2Cr钢筋主要用于制造铁路混凝土轨枕和建筑用预应力混凝土构件。45Si2Cr钢自80年代投入使用,用碱性电炉冶炼,在横列式轧机上轧制,后经连续淬火和中温回火处理。为了充分发挥45Si2Cr钢的优势,淘汰落后的生产工艺,现在45Si2Cr钢连铸后在高速线材轧机上轧制成材,提高了钢筋的质量,对高线轧出的产品制定怎样的热处理工艺,才能使其性能达到最优是研究的主要目的。45Si2Cr钢虽然在唐钢已经投入使用,但在国内外其它厂家均未见报导,仍然属于新钢种,其各方面的技术资料还很不完善,生产工艺还有待优化。所以为了制定其最优的热处理工艺,首先在北京科技大学GLEEBLE-1500热模拟机上测定了三组此钢的连续冷却转变曲线(CCT曲线),一方面补充了45Si2Cr钢的基础资料,找出不同奥氏体化温度下曲线有何变化;另一方面为制定热处理工艺提供了重要依据。用ZRP-03热膨胀仪测定了钢的各个临界点。对每个连续转变后的试样在光学显微镜下拍了金相显微照片并测了维氏硬度。45Si2Cr钢筋采用淬火加回火的热处理工艺,所以制定这两项工艺参数是主要内容,具体内容包括淬(回)火温度、保温时间及冷却方式。又由于回火是热处理的最后工序,直接关系到钢筋的使用性能和寿命,因此回火温度的确定又是主要的研究内容。热处理工艺的优劣是通过对钢筋的力学性能测试后的结果得出的,拉伸试验得到了各种热处理后试样的抗拉强度、屈服强度等强度指标和延伸率、面缩率等塑性指标。低温冲击试验得出了试样在-50℃、-40℃、-20℃、0℃、20℃这5个温度下的冲击值,用动态悬挂法测定出45Si2Cr钢的弹性模量E=215Gpa。把热处理后的典型试样拍金相照片,冲击试样断口的组织在电镜下观察。对钢筋在加热炉内温度场和连续冷却时组织场的模拟,为钢的热处理工艺制定和实现热处理自动化起到一定作用。1.用GLEEBLE-1500热模拟机测定了45Si2Cr钢的连续冷却曲线(CCT),测出了该钢的临界点Ac3和Ac1分别是822℃和790℃, Ar1和Ar3分别是775℃和805℃。2. 45Si2Cr钢在连续冷却条件下不形成贝氏体。可以得到铁素体、屈氏体和马氏体的混合组织。钢的马氏体转变点Ms随奥氏体化温度的提高而上升,线性回归后得到TM s = 35. 3+0.3TA。临界冷却速度随奥氏体化温度的提高减小,关系式为V L = -4. 03+1.01TA-0.0006TA2。3.经过多种淬火温度和回火温度的组合,最终得出钢的最佳热处理工艺为:淬火温度900±10℃,保温15分钟;回火温度450±5℃,保温30分钟。回火后的组织为回火屈氏体。钢按上述热处理制度处理后具有良好的韧性,此时钢筋的屈服强度σ0.2为1525MPa,抗拉强度σb为1669 MPa,延伸率δ5为11.5%,断面收缩率Ψ为45.1%,弹性模量E为215GPa,屈强比为0.91,韧脆转化温度大于-50℃,已经完全达到性能要求。与原唐钢生产工艺下得到的产品相比较,抗拉强度增加100 Mpa,屈服强度增加200 Mpa,延伸率略有增长。4.通过对Φ8mm 45Si2Cr钢筋在1000℃加热炉内温度场的计算,得出钢筋加热到900℃需要230.97s,钢筋中心温度和表面温度相差0.38s,所以对于此类细钢筋在加热或冷却时可以不考虑其内外温度变化,整体视为同一温度。5.对CCT曲线的冷却过程模拟可以直接得到任意冷却速度下任何温度下的组织含量,方便快捷,便于实现整个过程的计算机控制,为热处理实现自动化起到一些作用。6.程序均用Visual Basic语言编写,可视性强,可被其它程序方便调用。更多还原

【Abstract】 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.更多还原