SSAB and Kemppi Advance Armour Steel Welding for Ballistic Performance

Welding armour steel for demanding defence applications

In defence manufacturing, every material choice matters. And so does every weld.

Armour steels are designed to protect against ballistic and blast threats in some of the most demanding operating environments. Their performance depends on a careful balance of hardness, toughness, processability, and structural reliability. When these steels are welded, that balance must be protected as far as possible.

Kemppi and SSAB are working together to explore how welding technology can support the fabrication of armour steel structures used in demanding protection applications.

The focus is on understanding how different welding processes and consumables affect the properties of welded armour steel structures.

Armour steel types and their welding requirements

Armour steels are developed for different protection needs. The required material properties depend on the type of threat, the structure, and the intended application.

Blast protection steels typically have lower hardness, around 400 HBW, to allow controlled deformation during an explosion. In these applications, the steel must be able to absorb energy without cracking, including in cold operating conditions.

Ballistic protection steels are generally harder. High Hardness Armour steels, around 500 HBW, are widely used because they offer a balance of protection, bendability, weldability, and fatigue resistance. Very High Hardness Armour steels, around 550 HBW, provide higher protection levels while still maintaining some bendability and weldability.

Ultra-High Hardness and Extreme High Hardness steels, around 600–650 HBW, offer higher ballistic protection levels, but with reduced processability. At the highest hardness levels, bending and welding are generally more restricted and require careful evaluation.

This creates a practical challenge for manufacturers. The material must provide protection, but it must also be suitable for fabrication. Welding process selection, filler material choice, heat input control, and production repeatability all become important factors in achieving reliable results.

Why heat input is critical in armour steel welding

Armour steels are based on a tempered martensitic microstructure. This microstructure is central to their hardness and protection capability. During welding, the surrounding base material is exposed to a thermal cycle, which can reduce hardness in the heat-affected zone.

Some softening in the heat-affected zone is unavoidable. However, the extent of softening depends strongly on heat input, welding parameters, joint design, plate thickness, and the selected process.

In defence vessels and vehicles, the welded joint is part of the structure that, in most cases, is exposed to ballistic impact, blast loading, vibration, fatigue, and harsh environmental conditions. A wider softened zone may affect how the structure behaves under load or impact.

Heat input can be reduced through several methods, including multipass welding with smaller beads, low heat-input welding processes, modified short-arc MIG/MAG, and laser welding. The correct approach depends on the material grade, thickness, joint configuration, production environment, and performance requirements.

Welding process comparison

We have done some comparison between arc welding and laser welding and found: Early comparisons show clear differences between handheld laser welding and pulse MAG welding.

• Handheld laser welding uses a laser beam with wobbling. It provides deep penetration and produces a narrow weld profile with a narrow heat-affected zone. In the initial comparison, handheld laser welding showed lower heat input. It depends the case how much it is lower but some cases it 50% less and especially with thinner materials it is even less, about 10-20% of arc welding heat input

• Pulse MAG welding uses pulsed current. It offers lower penetration compared with laser welding, but a much higher filler material deposition rate. In the initial comparison, pulse MAG welding showed higher heat input and produced a wider weld and heat-affected zone.

These differences are relevant for defence manufacturing because process selection is rarely based on one parameter alone. A lower heat input and narrower heat-affected zone can be beneficial when preserving base material properties is a priority. Higher deposition rate, established production use, and process robustness remain important where productivity, joint fill, and industrial scalability are required.

Handheld laser welding may be particularly interesting for thinner armour steel components, precision joints, and applications where a narrow heat-affected zone is beneficial. Pulse MAG welding remains highly relevant for larger assemblies, thicker sections, longer welds, and production environments where high deposition rates and familiar welding procedures are needed.

Filler material selection and weld performance

Armor steel can be welded both ferritic and austenitic filler materials, including ER70S-6 and ER307. Austenitic consumables such as AWS 307 and AWS 309 are also commonly considered in armour steel welding. Filler material selection can influence weld metal properties, cracking resistance, toughness, dilution behaviour, and overall joint performance.

In armour steel welding, a suitable filler material is selected to support a reliable and crack-resistant joint while maintaining the required structural performance. This is particularly imperative when welding high-hardness steels, where hydrogen cracking, residual stresses, and local hardness changes must be controlled. The most suitable filler material depends on the base material grade, plate thickness, joint design, restraint level, welding process, and application requirements.

Production control in defence manufacturing

In defence manufacturing, a successful test weld is valuable only if the same result can be reproduced consistently in manufacturing. This makes welding procedure qualification, parameter control, welder competence, inspection and traceability important parts of armour steel fabrication.

Manufacturers need to understand which process was used, which filler material was selected, what heat input was achieved, and whether the welding procedure remained within the required limits. Preheat and interpass temperature control may also be important, depending on the material, plate thickness, joint restraint, hydrogen level, and workshop conditions. These factors can influence cracking risk, distortion, residual stresses, and the final performance of the welded structure.

Supporting future armour steel fabrication

The cooperation between Kemppi and SSAB is focused on building practical knowledge around armour steel welding. The early results highlight the importance of heat input control and show that different welding processes offer different advantages. Handheld laser welding appears promising where a narrow heat-affected zone is required. Pulse MAG welding continues to offer established benefits in deposition rate, productivity, and industrial use.

Further mechanical and ballistic testing will provide deeper understanding of how the welded structures perform after fabrication.

For defence manufacturers, the key point is clear. Armour steel performance depends not only on the material grade, but also on how the material is processed, welded, controlled, and verified. In conclusion, there is no doubt that welding technology plays a central role in ensuring that protective structures can be manufactured with the required quality, consistency, and reliability.