TiAlN coatings were deposited on the YT15 tungsten carbide inserts by magnetron sputtering technique. The TiAlN coated tools were deep cryogenic treatment (DCT) at $-196^{circ}C$ for 30 h. The dry turning tests of 40Cr steel were carried out to evaluate performances of uncoated, no cryogenically treated (NCT) and DCT coated tools on the CA6140A lathe. The effect of the three kinds of tools on cutting forces, cutting temperature, surface qualities and tool wear had been investigated to assess the performance of DCT coated tools. Results of the investigation showed that the cutting forces and cutting temperature obtained by DCT coated tools were significantly decreased in comparison with the uncoated and NCT coated tools, especially at higher cutting speeds. Flank wear of the DCT coated inserts was less than that of the NCT coated inserts under the same cutting conditions. The DCT coated inserts produced a good surface finish and yield a tool life of about 65 min. The wear mechanisms of the DCT coated carbide tools are mainly abrasive and adhesive wear, accompanied with diffusion and oxidation wear.