# Hot Forging of DIN 8555 E6-UM-60 Alloy Produced by Directed Energy Deposition: Understanding the Metallurgical Effects

## TL;DR

This study explores combining additive manufacturing and hot forging to produce complex metal parts, focusing on material behavior and structural reliability.

## Contribution

The paper reveals atypical metallurgical behavior of DIN 8555 E6-UM-60 alloy during hybrid processing and identifies critical factors for structural reliability.

## Key findings

- Hybrid processing reduced porosity and improved microstructural homogeneity in the alloy.
- Hot tensile tests showed limited hot workability and premature fracture due to microcracks formed during forging.
- Chromium carbides formed consistently under specific thermomechanical conditions, affecting phase stabilization.

## Abstract

This study investigates a hybrid processing route that integrates localized fusion-based additive manufacturing and hot forging for the production of complex-shaped components, with emphasis on metallurgical integrity and mechanical performance. The DIN 8555 E6-UM-60 alloy, traditionally classified as martensitic and applied under severe wear conditions, exhibited atypical metallurgical behavior during hybrid processing, notably the consistent formation of chromium carbides under specific thermomechanical conditions. Metallographic analyses, microhardness measurements, thermographic monitoring, hot tensile tests, and room-temperature tensile tests were performed to establish correlations between microstructure, thermal history, and mechanical response. Specimens produced by additive manufacturing and subsequently hot forged showed a significant reduction in porosity, improved microstructural homogeneity, and partial retention of hardening phases, enabling discussion of recrystallization mechanisms, phase stabilization, and precipitation phenomena in martensitic alloys processed by additive manufacturing. Hot tensile tests revealed limited hot workability of the alloy, while room-temperature tensile tests led to premature fracture, with failure consistently initiating at pre-existing microcracks formed during the forging stage. Although detrimental, these microcracks provide valuable insight into critical processing conditions and ductility limits of the material. Overall, the hybrid route demonstrates strong potential for industrial applications, highlighting the importance of precise thermomechanical cycle control to mitigate defects and enhance structural reliability.