Fusion-based additive manufacturingAdditive manufacturing (AM) technologies, such as wire arc, laser powder bed, selective laser melting, and electron beam, enable intricate designs but face challenges when applied to steel fabrications. These challenges include residual stressResidual stress buildup, microstructureMicrostructure anisotropy, porosity, chemical composition segregationSegregation, and vaporization of alloying elements. Solid-phase AM technologies, operating below melting pointsMelting point, significantly mitigate these issues. Notable methods include ultrasonic, cold spray, and friction-based AM, with additive friction surfacingAdditive friction surfacing (AFS) standing out by eliminating the need for costly tooling and feedstock. This study demonstrates the use of AFS to produce high-strength low-alloy steelHigh-strength low-alloy steel depositions. The microstructuralMicrostructural evolution is explored as the tempered martensite condition of the feedstock results in a freshly deposited martensitic layer after AFS. As AFS progresses, the previously deposited martensitic layer undergoes post-deposition tempering and phase transformationPhase transformation into tempered martensite, ferrite, or a combination of these phases. These transformations are influenced by multiple thermal cycles during each layer deposition process, demonstrating that AFS can potentially achieve local microstructureMicrostructure control by tuning its parameters. Moreover, AFS shows promise for other high-strength, high-temperatureTemperature metallic materials that are traditionally considered “unprintable” through melt-based processes.