IR
新型低碳马氏体高强钢在不同低温下解理断裂物理模型的研究
Project Number50671047
陈剑虹
Abstract通过拉伸、COD及四点弯曲试验,结合相应的组织观察、断面观察以及必要的有限元计算,对高强钢不同温度下的断裂机理以及低合金钢韧脆转变的断裂机理进行了详细研究,结果表明:这种钢具有很好的强韧综合力学性能。-196℃下拉伸出现特殊的"Z"字形断口,不同温度下断裂机理不同。室温到-80℃为韧性断裂。随着试验温度降低出现解理面。当温度降低到-130℃以下时断口主要是准解理形态,出现典型的POP-IN现象。POP-IN现象是由于解理裂纹起裂前弹性能积累不足以及裂纹扩展需要克服较大的阻力。裂纹扩展的高阻力取决于原奥氏体晶粒边界、贝氏体团边界以及贝氏体片之间的韧性撕裂脊。下平台可分为三个区:-150℃~-130℃断裂由起裂控制,-130℃~-80℃由第二相裂纹扩展至母材晶粒控制,此时由塑性应变的增加导致位错堆积引起的应力值大大增加,这不仅补偿了正应力的损失而且使得断裂应力增加到一临界值,因此足以诱发解理断裂的发生,-80℃~-60℃仍由第二相裂纹扩展进入母材晶粒控制,但此时预裂纹尖端产生塑变,进一步提高正应力来补偿屈服强度的下降,从而导致解理断裂。这些机理就是韧脆转变韧性陡然上升的机理。
【英文摘要】Basedontensile,COD,4PBtests,correspondingobservationsofmicrostructureandfracturesurfacesandfiniteelementmethodcalculation,fracturemechanismsunderdifferenttemperaturesforhigh-strengthsteelandfracturephysicalmodeloflowershelfofductile-brittletransitionforlow-alloysteel(16MnR)werestudiedindetail.Theresultsshowthat:Thissteelhasgoodcomprehensivemechanicalpropertiesbothstrengthandtoughness.Intensiletest,at-196℃thespecial"Z"-shapedfracturesurfaceappears.fracturemechanismaredifferentatvarioustemperature.Atroomtemperatureto-80℃,thecrackisinitiatedandpropagatedfromthefatiguecracktipwiththefibrousrupturemode.Withtesttemperaturedecreasing,anincreasingnumberofcleavagefacetspresents,andthefracturesurfacesshowthequasi-cleavagemode.Thepropagationofthecleavagecrackwithpop-inmodeisobservedattemperaturesbelow-130℃.Thispop-inphenomenonisattributedtoinsufficientaccumulationofelasticenergybeforecleavagecrackinitiationandthesteel'sinherentlyhighresistancetocrackextension.Highresistancetocrackpropagationismanifestedbythetearridgeoftheoriginalaustenitegrainboundaries,thebainitecolonyboundariesandtheinter-layersbetweenbainitelaths.Lowershelfregionofductile-brittletransitionzonecanbedividedintothreezones:at-150℃--130℃,cleavagefractureisnucleation-controlledandthecrackcanbeinitiateddirectlyattheprecracktipintheferrite.At-130℃--80℃,thecleavagefractureiscontrolledbythepropagationofacarbidecrackintocontiguousgrains.Beforecleavagefractureoccurs,thetipoftheprecrackisonlybluntedwithoutfibrouscrackextension.TheσLincreaseswiththenumberofpile-updislocationsi.e.withincreasingtheplasticstrain.WithincreasingofappliedloadrepresentedbyCODvalues,thestressσLnotonlycompensatesforthelossofyieldstress,butalsoincreasingworkhardeningmakesfracturestresstoacriticalvalue,sufficienttoinducethecleavagefracture.At-80℃-60℃,thecleavagefractureiscontrolledbythepropagationofacarbidecrackintocontiguousgrains.Butfibrouscrackareproducedattheprecracktip,thenormalstressσLinducedbythedislocationpile-upfurtherincreasesandcompensatesfor?thelossofnormalstress?σyyduetothedecliningintheyieldstrength,untilcleavagefractureisinduced.Thisisthereasonwhytoughnessissharpincreasedattheductile-brittletransitionzone.
【结题摘要】通过拉伸、COD及四点弯曲试验,结合相应的组织观察、断面观察以及必要的有限元计算,对高强钢不同温度下的断裂机理以及低合金钢韧脆转变的断裂机理进行了详细研究,结果表明:这种钢具有很好的强韧综合力学性能。-196℃下拉伸出现特殊的"Z"字形断口,不同温度下断裂机理不同。室温到-80℃为韧性断裂。随着试验温度降低出现解理面。当温度降低到-130℃以下时断口主要是准解理形态,出现典型的POP-IN现象。POP-IN现象是由于解理裂纹起裂前弹性能积累不足以及裂纹扩展需要克服较大的阻力。裂纹扩展的高阻力取决于原奥氏体晶粒边界、贝氏体团边界以及贝氏体片之间的韧性撕裂脊。下平台可分为三个区:-150℃~-130℃断裂由起裂控制,-130℃~-80℃由第二相裂纹扩展至母材晶粒控制,此时由塑性应变的增加导致位错堆积引起的应力值大大增加,这不仅补偿了正应力的损失而且使得断裂应力增加到一临界值,因此足以诱发解理断裂的发生,-80℃~-60℃仍由第二相裂纹扩展进入母材晶粒控制,但此时预裂纹尖端产生塑变,进一步提高正应力来补偿屈服强度的下降,从而导致解理断裂。这些机理就是韧脆转变韧性陡然上升的机理。
Subtype面上项目
Project Source国家自然科学基金
2007
End Date2009-12-31
MOST Discipline Catalogue1001 - 金属材料 ; 10 - 材料科学
Host Institution兰州理工大学
Project Funding300000.0
CountryCN
Language中文
Document Type项目
Identifierhttp://ir.lut.edu.cn/handle/2XXMBERH/64984
Collection兰州理工大学
Recommended Citation
GB/T 7714
陈剑虹.新型低碳马氏体高强钢在不同低温下解理断裂物理模型的研究.2007.
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