Abstract
In this paper, water quenching of large ingots was simulated using FORGE NxT 1.1® Finite Element code. Simulations were carried out for as-forged medium-carbon low-alloy steel. A novel method is proposed to simulate the different parts of a large size forged block with different chemical compositions and grain sizes using the multiple materials method. The effects of macrosegregation, grain size variation and cooling rate on phase distribution through the volume of the forged block were investigated. The delay in transformation kinetics, which is due to the effect of grain size variation and carbon content, was analyzed. Results show that macrosegregation and grain size variations significantly influence transformation start points and the volume fraction of phases that are present in each location of the forged ingot. The proposed prediction method was validated using high-resolution dilatometry experiments and X-ray diffraction measurements to evaluate accurately the volume fraction of martensite, bainite and the percentage of retained austenite for each condition.
Highlights
Large-size forged ingots, made from medium carbon high-strength steel, are extensively used as dies in the automotive industry [1]
The influence of variable grain size on distribution and volume fraction of phases was considered in condition (C) and the results are reported in Figure 7 where a comparison with condition (A) is presented
The following conclusions can be drawn from the present study: 1. The fastest variation in martensite volume fraction was observed for uniform grain size and carbon concentration while an increase in the carbon concentration in austenite led to a decrease in the bainite start temperature Bs
Summary
Large-size forged ingots, made from medium carbon high-strength steel, are extensively used as dies in the automotive industry [1]. The above variabilities affect the phase transformation kinetics from austenite to martensite, bainite or pearlite during the quench operation and result in non-uniform microstructures and properties. Little information is available on the influence of chemical heterogeneity and grain size variation on the volume fraction of the phases during the cooling process of large-size forged blocks [10,13]. Experimental determination of the volume fraction of phases during water-quenching of large blocks is not always possible due to the difficulty of obtaining samples from different sections of the forged slab. To this end, a simulation approach using the multiple-materials numerical method was employed in the present investigation. Dilatometry experiments simulating actual cooling rates inside the large-size forged block were carried out and in order to validate simulation results of electron microscopy (FE-SEM), as well as X-ray diffraction to determine grain size and the nature and proportions of the different phases
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