**3.1 Microstructural analysis**

**Figure 9** presents the metallurgical microstructures of P410D ferritic stainless steel specimens heat-treated under different socking temperatures.

*Analysis of the Effect of Heat Treatment Conditions of a Ferritic Stainless Steel … DOI: http://dx.doi.org/10.5772/intechopen.101839*

#### **Figure 9.**

*Metallurgical microstructures of the P410D ferritic stainless steel specimens after different heat treatment conditions. (a) "Specimen 1"—822°C, (b) "Specimen 2"—854.1°C, (c) "Specimen 3"—879.5°C, (d) "Specimen 4"—895.4°C, (e) "Specimen 5"—953.3°C, and (f) "Specimen 6"—973°C.*

It was observed in *Specimen 1* (**Figure 9a**) that the socking temperature was not high enough for the recrystallization of the ferritic matrix, due to the presence of deformed grains. The presence of recrystallized grains, deformed grains, pores, and martensitic phase can be observed in the *Specimen 2* (**Figure 9b**). In *Specimen 3*— **Figure 9c**, there is a greater presence of recrystallized grains with an increase in the martensitic phase. The *Specimen 4* (**Figure 9d**) presented a higher amount of martensitic phase and grains apparently smaller than the previous samples, with the presence of some deformed grains. In *Specimen 5* (**Figure 9e**), deformed grains are hardly noticed and an increase in the amount of martensite phase was observed. Finally, in *Specimen 6* (**Figure 9f**) occurred the maximum point of martensitic structure formation, with no more deformed grains.

### **3.2 Residual stresses**

**Table 5** and **Figure 10** presents the residual stress values reported for the P410D ferritic stainless steel specimens, together with the respective hardness values. All residual stress values measured were "*tractive*" and inversely proportional to the hardness of each specimen.

#### **3.3 Tribological behavior**

**Figure 11** presents the specimens used for the analysis of results, already with all micro-abrasive wear tests by rotating ball conducted on their surface, and **Figure 12** displays images of wear craters produced.

**Table 6** shows the arithmetic-mean of the wear volumes (*V*), as well as the respective values of the standard-deviations, for each one of the specimens; it is noted that, for all specimens, the standard-deviation, in reference to the arithmetic-mean of the values of wear volumes (*V*), was below 10%.

**Figure 13** displays the behavior of the wear volume (*V*) as a function of the hardness (*H*) of the specimen—*V* = *f*(*H*).


**Table 5.**

*Values of residual stress measured in the specimens of P410D ferritic stainless steel.*

**Figure 10.** *Residual stress value acting on each specimen of P410D ferritic stainless steel, related to its hardness.*

*Analysis of the Effect of Heat Treatment Conditions of a Ferritic Stainless Steel … DOI: http://dx.doi.org/10.5772/intechopen.101839*

**Figure 11.** *Wear craters generated on P410D ferritic stainless steel specimens.*

It was observed that, with the increase in hardness of the material, the volume of worn material—the volume of the wear crater—decreased, following, in qualitative agreement, the *Archard Equation* (Eq. (3)):

$$\xi = K\_W K\_F \left[ \frac{P.v}{H\_{CP}(T)} dT \right] \tag{3}$$

By directing the quantities pertinent of the *Archard Equation* to the "*ball-cratering*" wear test, they can be defined as:


$$P = \frac{N}{A} \tag{4}$$

Where *A* the projected area of the wear crater.

• *v* is the tangential velocity of the test ball, defined by Eq. (5):

$$v = \pi.D.n \tag{5}$$

• *H* is the hardness of the specimen, as a function of the temperature (*T*)—*H* = *f*(*T*).

#### **Figure 12.**

*Wear craters obtained from "*ball-cratering*" wear tests conducted in this work: (a)* Specimen 2 *and (b)* Specimen 4*.*


#### **Table 6.**

*Arithmetic-mean of the values of wear volumes (*V*) with the respective values of standard-deviations.*

Analyzing the behavior of the physical parameters of the *Archard Equation* during the micro-abrasive wear process, it is noted that the tangential velocity value of the test ball was the same for all test conditions—*n* = 56 rpm; with this, the tangential velocity of the test ball remained constant for all specimens.

*Analysis of the Effect of Heat Treatment Conditions of a Ferritic Stainless Steel … DOI: http://dx.doi.org/10.5772/intechopen.101839*

**Figure 13.** *Behavior of the wear volume (*V*) as a function of the hardness (*H*) of the specimen—*V *=* f*(*H*).*

Additionally, the temperature of each specimen remained constant at room temperature, resulting in the hardness (*H*) of the materials analyzed remain unchanged during all ball-cratering wear tests.

However, following the *Archard Equation*, *ξ* and *H* are inversely proportional; therefore, the increase in *H* caused a decrease in *ξ*, characterizing, consequently, lower severity of wear related to a lower volume of wear (*V*) generated.

Finally, the only physical quantity that varied in a decreasing way during the ballcratering wear tests was the contact pressure (*P*)—since the normal force (*N*) remained constant, the projected area (*A*) of each wear crater increased with the progressive increase in the sliding distance.

In fact, in all wear tests, the contact pressure (*P*) followed, under the qualitative agreement, the approach detailed by Cozza [8, 9] in previous works, where *P* decreased as a function of the projected area of the wear crater for each specimen. For each hardness value, different values of *ξ* were obtained, related to the calculated values of wear volumes (*V*).

Finally, based on **Figure 13**—which exhibited practical results of the variation of wear volume (*V*) as a function of the hardness of the specimen (*H*)—and by theoretical complementation departing from *Archard Equation* (Eq. (3)), it can be said that the results generated are within the technical-scientific agreement of micro-abrasive wear.
