27 150 0,15 0,05 0,8 56,7 76,3 86,3 128,39

28 210 0,15 0,05 0,8 59,8 70,1 93,9 131,56

29 150 0,05 0,2 0,8 44,2 62,9 104,4 129,65

30 210 0,05 0,2 0,8 49,2 62,9 111,3 136,98

31 150 0,15 0,2 0,8 102,9 160,4 243,9 309,52

32 210 0,15 0,2 0,8 92,9 143,2 176,8 245,75

The Table 1 indicates the obtained values for the cutting forces measurements。

It was adopted, for the experiment analysis, a complete factorial planning of four factors and two levels without replication, in a total of 32 measurements for the penetration cutting force and for the resulting cutting force, for the fact of being the first, the portion that more contributes to the development of the residual stresses in the piece during the machining, and for the second as a form to involve the three cutting force measurements, since it could have some influence from the other cutting forces in the residual stresses generation。

It can be observed at the Fig。 2 and 3 (the effects on the penetration cutting forces and resultant cutting forces), that the significant effects are the same ones, that is, the feed rate and the cutting  depth,  what  allowed  continuing  with  the  research only

using the cutting penetration force。 Fig。 2。 Main effects plot for the penetration cutting force

Fig。 3。 Main effects plot for the resultant cutting force

The Table 2 shows residual stresses values at  a circumferential direction on the machined parts, tested according to the methodology early described [25]。 It is observed that in all of the measurements, the residual stresses are compressive。 The measurements before machining has resulted in tensile residual stresses levels of: +76, +95 and +50 MPa。

Table 2。Residual stresses measurements

Fig。 4。 Main effects plot for the residual stresses

The metallographic analysis made on the 32 work pieces, with objective of detecting the presence of the white layer at machine surface, showed that for these machined conditions the superheat and consequent re-quenched didn't happen here under these conditions。 The microstructure of the metal practically didn't lose hardness, staying as tempered martensite with primary carbides dispersed into the whole metal。 The Fig。 5 shows an example。