# Microstructural Evolution and Mechanical Performance of A500 Bulletproof Steel Joints Welded with Austenitic and Ferritic Filler Materials

## TL;DR

This study compares the performance of two welding materials on bulletproof steel, finding that a new ferritic filler improves hardness and resistance.

## Contribution

A newly developed ferritic filler material is proposed as an alternative to traditional austenitic fillers for improved mechanical performance in bulletproof steel joints.

## Key findings

- Ferritic filler material achieved significantly higher weld metal hardness (470 HV1) compared to austenitic filler (185 HV1).
- FGHAZ showed the highest hardness in A500-T91 joints (518 HV1) and A500-ER371 joints (480 HV1).
- Ballistic testing showed enhanced penetration resistance with the ferritic filler material.

## Abstract

This study examines the microstructural evolution and mechanical properties of A500 bulletproof steel joints welded with austenitic stainless steel (ER371) and ferritic (T91) filler materials. While austenitic fillers are traditionally used in bulletproof steel welding to prevent cracking and hydrogen embrittlement, their lower hardness creates a potential weakness in welded joints. This research explores an alternative approach using a newly developed ferritic filler material to achieve strength matching with the base material. Detailed microstructural characterization was conducted using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM), while mechanical properties were evaluated through tensile testing, impact testing, and hardness measurements. The results revealed significantly different mechanical behaviors between the two filler materials, with the ferritic filler achieving superior weld metal hardness (470 HV1) compared to the austenitic filler (185 HV1) in WZ. The fine-grained heat-affected zone (FGHAZ) exhibited the highest hardness (518 HV1) in A500-T91 joints and (480 HV1) in A500-ER371 joints, while ballistic testing demonstrated enhanced penetration resistance with the ferritic filler material.