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<p>The interface bonding behavior of 40Cr/Q345B bimetallic blank prepared by centrifugal casting process was studied using hot forging at the temperatures of 900-1200&#xa0;°C and the strains of 20-60%. The effects of temperature and strain on the grain size, recrystallization and element diffusion across the bonding interface were clarified by optical microscope (OM), electron backscatter diffraction (EBSD) and electron probe micro-analyzer (EPMA) technique. The centrifugal casted and hot-forged 40Cr/Q345B bimetallic blanks exhibit a heterogeneous microstructure consisting of coarse grains in the Q345B layer and fine grains in the 40Cr layer. Hot forging leads to discontinuous dynamic recrystallization (DDRX) nucleation of the bonding layer in a bowing-out mode to heal the bonding interface. The fine and equiaxed recrystallized grains are uniformly distributed in the bonding layer after hot forging. Enhancing the accumulative strain causes the bending and migration of the flat grain boundaries. Recrystallization is not significant at a low strain distribution. As the temperature increases, the mechanism of continuous dynamic recrystallization (CDRX) transforms into DDRX. Accumulation of high-density dislocations introduced by higher strain causes the main softening mechanism dominated by the DDRX which includes the nucleation along the original grain boundaries and subsequent growth with the migration of high-angle grain boundaries (HAGBs). The apparent interface in the centrifugal casted blank disappears after hot forging, implying a metallurgical bonding mechanism. The imposed accumulative strain and temperature in the hot forging promote the element diffusion across the bonding interface. Especially for Cr element, the most significant diffusion is closely related to the width of bonding interface with 1.8 to 4.52&#xa0;mm. The external diffusion in the bonding interface causes the heterogeneous microstructure.</p>

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Effect of Hot Forging on the Interfacial Grain Refinement and Bonding Behavior of a 40Cr/Q345B Bimetallic Blank Prepared by Centrifugal Casting

  • 期刊论文

  • 发表日期：

    2025年3月5日

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  • Yuxin Cui,
  • Fangcheng Qin,
  • Yachen He,
  • Jixun Jiang,
  • Yuehua Kang

摘要

The interface bonding behavior of 40Cr/Q345B bimetallic blank prepared by centrifugal casting process was studied using hot forging at the temperatures of 900-1200 °C and the strains of 20-60%. The effects of temperature and strain on the grain size, recrystallization and element diffusion across the bonding interface were clarified by optical microscope (OM), electron backscatter diffraction (EBSD) and electron probe micro-analyzer (EPMA) technique. The centrifugal casted and hot-forged 40Cr/Q345B bimetallic blanks exhibit a heterogeneous microstructure consisting of coarse grains in the Q345B layer and fine grains in the 40Cr layer. Hot forging leads to discontinuous dynamic recrystallization (DDRX) nucleation of the bonding layer in a bowing-out mode to heal the bonding interface. The fine and equiaxed recrystallized grains are uniformly distributed in the bonding layer after hot forging. Enhancing the accumulative strain causes the bending and migration of the flat grain boundaries. Recrystallization is not significant at a low strain distribution. As the temperature increases, the mechanism of continuous dynamic recrystallization (CDRX) transforms into DDRX. Accumulation of high-density dislocations introduced by higher strain causes the main softening mechanism dominated by the DDRX which includes the nucleation along the original grain boundaries and subsequent growth with the migration of high-angle grain boundaries (HAGBs). The apparent interface in the centrifugal casted blank disappears after hot forging, implying a metallurgical bonding mechanism. The imposed accumulative strain and temperature in the hot forging promote the element diffusion across the bonding interface. Especially for Cr element, the most significant diffusion is closely related to the width of bonding interface with 1.8 to 4.52 mm. The external diffusion in the bonding interface causes the heterogeneous microstructure.