42Mn2气瓶钢中存在有内部白点(即不露头白点)和露头白点,经正常冲压和拔伸制成气瓶后,进行解剖,用低倍、断口、超声波、金相以及扫描电子显微镜观条,证实内部白点可以焊合。而露头白点因表面在高温热成形过程中被氧化需要较大的变形才能焊合完全。 强度考核证明,这类气瓶的静压爆破强度(在550—630kg/cm~2)符合正常要求,在10?150 kg/cm~2循环应力下,整体疲劳次数达到30,000—60,000次,声发射仪跟踪监听,未发现有疲劳裂纹产生和扩展的信号。
42Mn2 steel cylinders processed by hot extrusion and drawing of flake-con-taining billets have been examined by SEM and by other methods to ascertain theimmunization of flakes in the final products. All internal flakes in the billets werecompletely healed after processing into cylinders, with the exception of those origi-nally exposed to the surface of the billet owing to oxidation. From practical appli-cation point of view, however, little difference in properties has been found betweencylinders completely or incompletely immunized from flakes. Thus, in the fatiguetest of the cylinders within cyclic stress ranges of 10?150 kg/cm~2, no signalsinduced by the formation and propagation of cracks were detected by acoustic emis-sion till 30,000-60,000 cycles. Likewise, the static bursting test of all cylindersalso met the standard set up by the users.
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