Numerical Study on Solidification Behavior and Structure of Continuously Cast U71Mn Steel

Bao Wang,Qing Fang,Chengsong Liu,Hua Zhang,Hongwei Ni

doi:10.3390/met7110483

Abstract

The solidification behavior and structure of continuous casting high rail U71Mn bloom, under different secondary cooling conditions and superheat, were numerically investigated using the Cellular Automaton-Finite Element (CAFE) model implemented with ProCAST software. Nail shooting and macro etch experiments of the bloom samples under different cooling conditions were conducted to verify the model of macroscopic solidification and structure. The results showed that the simulated results of the solidified shell and solidification structure are basically consistent with experimental results. The secondary cooling condition has little effect on the grain size and distribution of the bloom, while both the bloom surface and corner temperatures are higher and the temperature rise at the beginning of the air-cooling zone is smaller under the super-slow cooling condition. The percentage of center-equiaxed grains decreases from 44.6% to 20.1% and the grain average radius increases from 1.025 to 1.128 mm when the superheat increases from 15 to 40 K, with little change in the grain size occurring between 15 and 20 K. Moreover, for a step increase in the superheat of 5 K, the solidification end is lengthened by about 0.19 m and the surface temperature is enhanced by 3 K. The super-slow secondary cooling condition with the superheat controlled within 20 K is suitable for big-bloom casting.

Highlights

The solidification structure of continuous casting bloom has significant effects on the quality of the final products [1]
After comprehensively considering the results of the temperature field and solidification structure under SCC and SC, in order to reduce the chance of bloom surface defects, center porosity and segregation, the super-slow cooling condition is more acceptable for continuous casting blooms
The solidification behavior and structure of the continuous casting process under different secondary cooling conditions and superheat were discussed and compared in this paper, and both nail-shooting and macro etch experiments were conducted to validate the numerical results of solidification behavior and structure, respectively

Summary

Introduction

The solidification structure of continuous casting bloom (especially the center shrinkage and segregation of the bloom) has significant effects on the quality of the final products [1]. Numerical simulation has become an effective way to analyze the solidification behavior and structure during the continuous casting process. This CAFE model has been successfully applied in simulating the solidification behavior and structure [8,9,10]. Several published works have used the CAFE model to investigate the solidification structure during the continuous casting process [11,12,13,14,15]. The effects of both the secondary cooling types and superheat on the macroscopic solidification and structure are discussed and compared to find ideal casting conditions for the bloom

Basic Assumptions

Thermal Transport

Heterogeneous Nucleation

Kinetics of Dendritic Tip Growth

Casting Conditions and Parameters

10 I: spray cooling

Initial and Boundary Conditions

Validation of Heat Transfer

Photographs

Validation of Solidification Structure

Effect of Secondary Cooling Types

Effect of Superheat