摘要
通过高温短时加热,模拟产生球化级别不同的珠光体。利用脉冲回波法测定超声波在球化样品中传播速度。依据弹性模量与声速和密度之间的相关性推算时效样品的弹性指标。结果表明:随时效时间的增加,弹性指标单调递减,杨氏模量E从213 GPa下降到199.6 GPa,剪切模量G从82.5 GPa下降到77.5 GPa,体弹模量K从159.1 GPa下降到147.1 GPa,泊松比σ变化较小,从0.291变化到0.286。分析认为:球化过程中,片状渗碳体分解以及球状碳化物在晶界的析出与聚集成网状严重削弱了晶界强度;时效时间延长到2300 h,材料组织局部发生石墨化,石墨是低弹性"软"介质,与铁素体基体之间的结合能力差,这严重降低材料的弹性性能指标。
Pearlite with various spheroidizing levels in 20 steel was obtained by short-time heating at elevated temperature. Velocity of ultrasonic wave propagating in spheroidized samples was measured by pulse echo method. Based on the correlation of velocity, density with elastic modulus, indexes of elastic property were deduced. The results show that the indexes of elastic property decrease monotonously with increasing aging time. Young＇ s modulus decreases from 213 GPa to 199.6 GPa, shear modulus declines from 82.5 GPa to 77.5 GPa, bulk modulus reduces from 159. 1 GPa to 147. 1 GPa, while Poisson ratio changes slightly from 0. 291 to 0. 286 for the steel aged at 600 ~C for 75 h to 2300 h. It is argued that during the spheroidization of pearlite, cementite lamellae decomposes, spherical carbide precipitates and gathers into reticulation on the grain boundary, which severely weakens the grain boundary when the aging time prolongs to 2300 h, since graphite is the ＂ soft＂ media with low elasticity, graphitization occurs in local material and the binding force between graphite and ferrite is weak, which induces the obvious reduction of elastic modulus.
出处
《材料热处理学报》
EI
CAS
CSCD
北大核心
2010年第5期102-106,共5页
Transactions of Materials and Heat Treatment
关键词
超声无损评价
球化
声速
弹性性能
nondestructive evaluation
spheroidization
velocity
elastic properties
