Grain refining in metals is a general pathway for alloy strengthening. It happens in countless metallic systems and alloys. It is based on the principle of reducing the dislocation mean free path and increasing the activation stress of dislocation sources. Therefore, it is applicable to all metals (as well as nonmetallic crystalline materials) without distinction. What is unique to steels is the martensification process, which results in a high strength due to a combination of several factors, including grain refinement and solute hardening.

Dear Kamalashwaran Sivasubaramanian and Jaime Marian,

I give some preliminary remarks.

*The Hall-Petch relation can be considered as a practical rule of thumb. The question above hints at possible limits of application (think of the grain size approaching zero or infinitely large).

*So within the common range of application of the Hall-Petch relation Jaime Marian's answer is valid.

*Grain refining is commonly the result of appropriate combinations of deformation and recrystallization. 

*Besides, the Fe-C phase diagram offers the possibility of grain refining of common Fe-C steels by phase transformations by passing through the phase diagram lines. This is unique for Fe-C alloys.

*Martensitic transformations are of utmost importance for hardening and tempering of a large range of steels, but martensitic transformations also play a part in the heattreatment of e.g. certain titanium alloys. 

Thanks @Hamed Mirzadeh  and @P.Van Mourik  @Jaime Marian

I agree with previous answers and I also want to add there is a complex combination between the range of application of the Hall-Petch relation and its inverse. There is a new work that tries to combine both the Hall-Petch and its inverse in one model through presenting a multiscale model that enables description of both the Hall-Petch relation and its inverse in one equation without the need of prior knowledge of the grain size distribution, for more details, please see the following link:

https://www.researchgate.net/publication/324507369_A_new_multiscale_model_to_describe_a_modified_Hall-Petch_relation_at_different_scales_for_Nano_and_micro_materials