# Research on the Solidification Structure and Thermoplasticity of CJ5L Recycled Stainless Steel

## TL;DR

This study examines how the solidification structure of CJ5L recycled stainless steel affects its thermoplasticity, revealing changes in microstructure and residual ferrite with casting thickness.

## Contribution

The paper identifies a transition in solidification mode and its impact on thermoplasticity in CJ5L recycled stainless steel.

## Key findings

- The solidification structure changes from dendritic to worm-like with increasing thickness.
- Residual ferrite transforms from skeletal to granular and forms a network at the center.
- Thermoplasticity is optimal between 800°C and 900°C, reducing crack formation during processing.

## Abstract

The objective of this study is to investigate the effect of the solidification microstructure of CJ5L Recycled Stainless Steel in the cast state on its thermoplasticity. Therefore, the residual ferrite, solidification structure, and high-temperature thermoplasticity in both Recycled and Non-Recycled steel ingots are examined. The principal experimental techniques employed include SEM, OM, EPMA, and EDS. It was observed that the solidification microstructure underwent a gradual transformation from a dendritic structure with a skeletal shape to a worm-like dendrite as the thickness increased. This resulted in the formation of large equiaxed grains at the center of the steel ingots. The cooling rate decreased from 3~16 °C/s at the surface to below 0.8 °C/s at the center. The residual ferrite gradually transformed from a skeletal to granular and rod-like form with increasing depth, eventually forming a ferrite network at the center of the casting. In the Recycled steel, the composition segregation resulted in the formation of a network ferrite aggregation at the center of the steel ingots. The analysis of microstructure changes in conjunction with thermodynamic calculations revealed that the solidification mode of CJ5L stainless steel underwent a transition from the ferritic–austenitic (FA) mode to the austenitic–ferritic (AF) mode with increasing casting thickness. This resulted in an increase in the amount of residual ferrite from the surface to the center. The high-temperature thermoplasticity analysis of CJ5L stainless steel showed that at temperatures between 800 °C and 900 °C, the casting displayed optimal properties, minimizing crack formation during subsequent processing.