Abstract Thermo-mechanical processing is performed to engineer the microstructure comprising of nano-spheroidized cementites in ultrafine-grained ferrite in high carbon steel to enhance strength-ductility relationship. Spheroidization is achieved through heavy warm rolling (4-passes of 30% reduction at 823 K and 873 K) followed by extended annealing (1 h and 2 h) at the respective deformation temperatures. The influence of annealing temperature and time on the evolution of carbide precipitates, the extent of spheroidization and ferrite softening is investigated employing scanning electron microscopy, electron back scatter diffraction and transmission electron microscopy techniques. A near-complete spheroidization is achieved following heavy warm rolling and subsequent annealing for 2 h at 873 K (WR873K-2H). Although ferrite grain size increases with time and temperature of annealing, it ceases to cross the ultrafine regime (470–750 nm) due to the pinning effect of the carbides that restricts the migration of ferrite grain boundaries. A simultaneous increase in strength and ductility is achieved following heavy warm rolling and subsequent annealing for 1 to 2 h at 873 K. Maximum elongation (~ 30%) is achieved in the WR873-2H specimen in contrast to ~ 20% elongation in as-received specimen. Such an increase in ductility is due to the near-complete spheroidization as revealed by the ductile mode of fracture in fractrographic analysis.

中文翻译：

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纳米球状渗碳体分散在超细晶铁素体中的微观结构工程及其对高碳钢强度-延展性关系的影响

摘要 进行热机械加工以设计由纳米球化渗碳体在高碳钢中的超细晶粒铁素体中组成的微观结构，以增强强度-延展性关系。球化是通过重温轧制（4 道次，在 823 K 和 873 K 下压下 30%）然后在各自的变形温度下延长退火（1 小时和 2 小时）实现的。采用扫描电子显微镜、电子背散射衍射和透射电子显微镜技术研究了退火温度和时间对碳化物析出物的演变、球化程度和铁素体软化的影响。在重温轧制和随后在 873 K (WR873K-2H) 下退火 2 小时后，实现了近乎完全的球化。尽管铁素体晶粒尺寸随着退火时间和温度而增加，但由于限制铁素体晶界迁移的碳化物的钉扎效应，它不再跨越超细区域（470-750 nm）。在重温轧制和随后在 873 K 下退火 1 到 2 小时后，强度和延展性同时增加。 WR873-2H 试样实现了最大伸长率（~ 30%），而 WR873-2H 试样的伸长率为~20% -收到标本。韧性的这种增加是由于断裂分析中断裂的韧性模式所揭示的近乎完全的球化。在重温轧制和随后在 873 K 下退火 1 到 2 小时后，强度和延展性同时增加。 WR873-2H 试样实现了最大伸长率（~ 30%），而 WR873-2H 试样的伸长率为~20% -收到标本。韧性的这种增加是由于断裂分析中断裂的韧性模式所揭示的近乎完全的球化。在重温轧制和随后在 873 K 下退火 1 到 2 小时后，强度和延展性同时增加。 WR873-2H 试样实现了最大伸长率（~ 30%），而 WR873-2H 试样的伸长率为~20% -收到标本。韧性的这种增加是由于断裂分析中断裂的韧性模式所揭示的近乎完全的球化。