**3. Mechanical machining of FGSS**

Several researchers have discussed the effect of grain size and boundaries in micro/nano processing such as cutting, piercing, forming, and so on. As the removal depth becomes smaller than the grain size, which is usually more than 20 μm, it is difficult to ignore the crystalline direction, size, and distributions in such microprocessing.

Simoneau et al. discussed the grain-boundary effect in medium carbon steels, and he found the different grain deformations in cutting chips [8]. Lee et al. discussed material-induced vibration, which is caused by the changing crystallography of the material substrate [9, 10]. They also analyzed the variation in microcutting forces in diamond tool turnings of crystalline materials, based on a microplasticity model and spectrum analysis technique [11]. Furukawa and Moronuki discussed the grain-boundary effect during the cutting of large grained steel. They found that when the grain boundary is crossed by the tool, the cutting force increases [12]. Komatsu have also discussed the effects of grain size on two-dimensional microcutting [13–15]. When the grain size is less than 3 μm, the cutting tool vibration is reduced, and the quality of the groove is improved. This is because small grained materials are regarded as homogeneous materials in terms of hardness.

However, study of the effect of grain size on other processes and product functions, based on materials of various grain sizes, are limited because the size of bulk material with FGSS has been too small for the studies.

**7**

**Figure 5.**

*Integrated Manufacturing of Fine-Grained Stainless Steels for Industries and Medicals*

This chapter will present the cutting process of FGSS. Two different grain sizes were employed, as is mentioned before, to discuss the effect of the grain size on the

*Picture after microcutting by diamond tool. (A) Left: groove condition on normal grain stainless steel. The average grain size is 9.8 μm and (B) right: Groove condition on FGSS by reverse phase transformation. The average grain size* 

The effect of the grain size was discussed with measuring the cutting forces and their oscillation. The stability in the cutting process was associated with the oscilla-

When large grain material was cut, the tool was widely vibrated as shown in **Figure 5(A)**, because the deformation reached to the grain boundaries and it needed force more. On the other hand, smaller grain had narrow length of between grain boundaries, it constantly effected on the cutting force [13, 14] in **Figure 5(B)**. Komatsu discovered some more features in microcutting this FGSS. Higher shearplane angles, cutting FGSS less than 5 μm, reduce the cutting force even the tensile strength is increased [12]. This features reduced the burr. Ball end-mill cutting examined for these material and the burr size become from 1/5 to 1/3 [15]. Finally,

*Differentials of vibration results from principal and thrust cutting force. (A) Left: the average grain size is* 

**Figure 4** shows the surface finishes by diamond tool in microcutting. The groove width and depth was about 8 μm. It should be noted that the edge quality is incredibly improved as compared between **Figure 4(A)** and **(B)**. This feature had

*DOI: http://dx.doi.org/10.5772/intechopen.89754*

cutting process in the microscale.

**Figure 4.**

tion of the cutting force in **Figure 5**.

benefits for fine parts or medical equipment.

*is 1.52 μm. FGSS can get smooth edge when cutting in microscale.*

the residual strains were also reduced by using FGSS.

*9.8 μm and (B) right: the average grain size is 1.52 μm.*

*Integrated Manufacturing of Fine-Grained Stainless Steels for Industries and Medicals DOI: http://dx.doi.org/10.5772/intechopen.89754*

**Figure 4.**

*Engineering Steels and High Entropy-Alloys*

the average grain size is 1.52 μm.

the normally grained AISI304.

such microprocessing.

**3. Mechanical machining of FGSS**

microprocessing.

**Table 2.**

*Mechanical properties.*

The fine-grained stainless steel was formed with repeating plastic deformation and reverse phase transformation. **Figure 3(B)** shows the microstructure, where

Vickers Hardness [HV] 260 260 Tensile strength [MPa] RD 870 919

Elongation [%] RD 51.1 42.5

Ave. grain size [μm] 9.10 1.52

**Normal grain steel Ultra fine-grained steel**

ND 858 880

ND 57.5 46.4

Although the grain size was different among specimens, their ultimate tensile

As a summary, FGSS has refined microstructure with the average grain size of 1.5 μm and higher ultimate strength than 900 MPa. Its hardening process is governed by the reverse phase transformation in different from the work hardening in

Several researchers have discussed the effect of grain size and boundaries in micro/nano processing such as cutting, piercing, forming, and so on. As the removal depth becomes smaller than the grain size, which is usually more than 20 μm, it is difficult to ignore the crystalline direction, size, and distributions in

and he found the different grain deformations in cutting chips [8]. Lee et al. discussed material-induced vibration, which is caused by the changing crystallography of the material substrate [9, 10]. They also analyzed the variation in microcutting forces in diamond tool turnings of crystalline materials, based on a microplasticity model and spectrum analysis technique [11]. Furukawa and Moronuki discussed the grain-boundary effect during the cutting of large grained steel. They found that when the grain boundary is crossed by the tool, the cutting force increases [12]. Komatsu have also discussed the effects of grain size on two-dimensional microcutting [13–15]. When the grain size is less than 3 μm, the cutting tool vibration is reduced, and the quality of the groove is improved. This is because small grained materials are regarded as homogeneous materials in terms

Simoneau et al. discussed the grain-boundary effect in medium carbon steels,

However, study of the effect of grain size on other processes and product functions, based on materials of various grain sizes, are limited because the size of bulk

material with FGSS has been too small for the studies.

**Table 2** shows the mechanical properties of the normal stainless steel and FGSS. Here, the mechanical properties are similar to each other. The hardness and tensile strength is controlled by work handing for normal grain, and by decreasing the grain size by reverse phase transportation for FGSS. These different hardening methods for stainless steel should be distinguished in terms of

strength became around 900 MPa, irrespective of the grain size.

**6**

of hardness.

*Picture after microcutting by diamond tool. (A) Left: groove condition on normal grain stainless steel. The average grain size is 9.8 μm and (B) right: Groove condition on FGSS by reverse phase transformation. The average grain size is 1.52 μm. FGSS can get smooth edge when cutting in microscale.*

This chapter will present the cutting process of FGSS. Two different grain sizes were employed, as is mentioned before, to discuss the effect of the grain size on the cutting process in the microscale.

**Figure 4** shows the surface finishes by diamond tool in microcutting. The groove width and depth was about 8 μm. It should be noted that the edge quality is incredibly improved as compared between **Figure 4(A)** and **(B)**. This feature had benefits for fine parts or medical equipment.

The effect of the grain size was discussed with measuring the cutting forces and their oscillation. The stability in the cutting process was associated with the oscillation of the cutting force in **Figure 5**.

When large grain material was cut, the tool was widely vibrated as shown in **Figure 5(A)**, because the deformation reached to the grain boundaries and it needed force more. On the other hand, smaller grain had narrow length of between grain boundaries, it constantly effected on the cutting force [13, 14] in **Figure 5(B)**. Komatsu discovered some more features in microcutting this FGSS. Higher shearplane angles, cutting FGSS less than 5 μm, reduce the cutting force even the tensile strength is increased [12]. This features reduced the burr. Ball end-mill cutting examined for these material and the burr size become from 1/5 to 1/3 [15]. Finally, the residual strains were also reduced by using FGSS.

#### **Figure 5.**

*Differentials of vibration results from principal and thrust cutting force. (A) Left: the average grain size is 9.8 μm and (B) right: the average grain size is 1.52 μm.*

In summary, mechanical machinability of FGSS is much improved by finegrained microstructure; smooth cutting edges, reduction of in situ vibrations and burr size.
