【正文】 contact of “toolchip” in case of increased loading and a heavily deformed zone are formed following the applied load.When the potential loading achieves a threshold value, a crack initiation appears easily in the zone where a considerable amount of chromium carbide is found in the matrix by forming an angle 0 with the direction of the cutting speed. This crack appears at the point of the tool leading a short relaxation. The crack initiation will produce the slip of the matter where the formation of a segment (slice). This phenomenon is repeated again by giving a new segment. And accordingly, the chip is formed in sawtooth type since the process is cyclic.In macroscale however, the chips obtained by hard turning, are relatively in different forms and they can change according to the cutting speed (Figure 4). These forms are developed helicoidally, tangled up either in detached form or in the form of continuous arc in the colour of blue and gray.Here typical chip morphology was identified to realize theeffect of cutting speed, feed rate, and depth of cut, etc. during the orthogonal cutting. However, more detailed research on the chip morphology in hard machining should be carried out to help reveal the segmentation chip formation mechanisms as well as encourage hard machining to be a practical expertise.Secondary carbidePrimary carbide Fig. 1. Microstructure as hardened state of AISI D2 amp。 f = 。C/s and machined surface encounters an extremely short cyclethermomechanical process with very high heating rate 106 176。 Vc = 50 and 250 m/min and f = and mm/rev.By keeping constant the depth of cut as ap=2mm, all of the tests have been carried out and each test has been repeated 3 times for using as the mean value (Table 3).The calculation of the average and total effects, the construction of the matrix and calculation of the squares totals, squares errors (SStotal, SSerror) can give us to build ANOVA table with A= f and B = Vc as indicated in Table 4. Considering the experimental results given in the present work, an interesting work was presented in the literature that their results are agree with those of the present study [1720]. The specific cutting forces are determined in order to understand the interference of chips that occur during the threading. With the increase in the cumulative radial feed, the corresponding specific cutting forces bee higher. They indicated that the difference in the specific cutting forces results from the alteration of the interference of the flowing chips. The specific cutting forces decrease in the beginning of the threading and then increases with the cumulative radial feed. The results show that the interference of the chip flow influences the threading force ponents to a very large extent Table ANOVA and the test of Fisher show that on a significant level of 5%, the calculated value, Ftcalculated, for A, B are higher than the theoretical value, Fttheoretical.However, for AB, the calculated value, FtABcalculated, is lower than the theoretical, FtABtheoretical. It can be concluded that the cutting speed and the feed rate influence considerably the cutting force, but their interaction does not have so much effect on the cutting force. For the parameter A, Ftest is higher than that of B, and is very high regarding to AB, from where A is more important than B. The effects and the interaction of the cutting conditions on the cutting force have been presented graphically in the Figure 10. One can be seen that cutting force is pulsory to deform the material plastically though there is a dependency on certain factors. As we mentioned in the former section, the cutting forces are very sensitive to chemical position, hardness, and microstructure, type o