**Correlation between Microstructural Alteration, Mechanical Properties and Manufacturability after Cryogenic Treatment: A Review**

### **Abbas Razavykia, Cristiana Delprete and Paolo Baldissera \***

Department of Mechanical and Aerospace Engineering, Politecnico di Torino, 10138 Torino, Italy; abbas.razavykia@polito.it (A.R.); cristiana.delprete@polito.it (C.D.) **\***Correspondence:paolo.baldissera@polito.it

Received: 25 August 2019; Accepted: 9 October 2019; Published: 11 October 2019

**Abstract:** Cryogenic treatment is a supplemental structural and mechanical properties refinement process to conventional heat treatment processes, quenching, and tempering. Cryogenic treatment encourages the improvement of material properties and durability by means of microstructural alteration comprising phase transfer, particle size, and distribution. These e ffects are almost permanent and irreversible; furthermore, cryogenic treatment is recognized as an eco-friendly, nontoxic, and nonexplosive process. In addition, to encourage the application of sustainable techniques in mechanical and manufacturing engineering and to improve productivity in current competitive markets, cryo-treatment can be considered as a promising process. However, while improvements in the properties of materials after cryogenic treatment are discussed by the majority of reported studies, the correlation between microstructural alteration and mechanical properties are unclear, and sometimes the conducted investigations are contradictory with each other. These contradictions provide di fferent approaches to perform and combine cryogenic treatment with pre-and post-processing. The present literature survey, mainly focused on the last decade, is aimed to address the e ffects of cryogenic treatment on microstructural alteration and to correlate these changes with mechanical property variations as a consequence of cryo-processing. The conclusion of the current review discusses the development and outlines the trends for the future research in this field.

**Keywords:** cryogenic treatment; cryo-treatment; mechanical properties; microstructure; cryo-processing
