**4.2 X-ray analysis results**

**Table 2** presents the quantitative phase analysis results for abrasive contamination in both CS and DSS substrates. 36.20% of the SDS and 20.21% of the carbon steel blasted area were contaminated by SB particles. When analyzing the DA abrasive, 15.77% of the SDS area was contaminated, while 10.45% of the CS substrate depicted particle contamination. The higher percentage of contamination on the SDS substrate can be related with its high values of hardness. The consequences of such higher particle contamination, for the performance of anticorrosive organic

coatings, can be found in a subsequent work [46].

*Inelastic X-Ray Scattering and X-Ray Powder Diffraction Applications*

**4. Case 2: ferrite/austenite (α/γ) ratio in duplex steels and the occurrence of sigma phase: quantification of unbalanced phase formation and precipitation due to thermal treatments on the steel**

Super duplex stainless steel (SDSS) is a class of steels that retain two equal balanced main phases within their microstructure, BCC α-Fe (ferrite) and FCC γ-Fe (austenite). In that manner, this material can combine good mechanical properties with high corrosion resistance. However, when subjected to welding or to hightemperature applications, thermal-activated diffusion mechanisms promote the precipitation of some deleterious phases in the SDSS matrix in addition to creating

an unbalanced volume of ferrite and austenite. The unequal proportions of

temperature values that lead to this kind of phase unbalance.

**4.1 Heat treatments for different amounts of phase formation**

The solution heat treatment was conducted as follows:

evaluation techniques [48].

**90**

schematic of the heat treatment steps.

ferrite/austenite and the occurrence of phases such as sigma phase (also known as σ phase) can highly compromise the ability of these steels to support loads and to avoid corrosion, leading to higher rates of degradation. Therefore, it is mandatory that investigations on thermal cycles are carried on determining the critical time/

Previous studies in different classes of duplex steels [47] have identified the temperature range of 300–1000°C as a critical range for phase transformations. Therefore, a series of heat treatments, involving different temperature ranges and time intervals, were performed in a UNS S32750 to study the phase formation in this specific class of duplex steel and to determine the amounts of ferrite, austenite, and sigma phase formed after each treatment. For this specific calculation, X-ray diffraction was displayed as a crucial tool for precise phase quantification in a specific volume of material. After all the samples were scanned, phase amounts were calculated using quantitative phase analysis by Rietveld refinement. These calculations lead to further experimental investigations using nondestructive

Samples were cut as 70 mm 40 mm 6 mm steel plates. All samples were submitted to a preliminary solution heat treatment in order to obtain a balance of approximately 50% of α and γ phases. Then, aging treatments were performed to create the α/γ unbalance and the precipitation of sigma phase. **Figure 5** shows a

1.Three samples remained in the as-received condition, i.e., without any heat

2.The remaining samples were subjected to a solubilization treatment, which consists of heating up to 1220°C for 1 h, followed by water quenching.

treatment for further comparison with the heat-treated samples.

Phase volumetric fractions were measured in nine different regions of each sample, as depicted in **Figure 6**. Diffraction parameters used were the same presented in item 3.2 from this chapter.

*Schematics of heat treatments performed in the SDSS samples.*

**Figure 6.** *Schematics of a sample with its nine analyzed points.*

*4.2.1 Fitting parameters*

**Table 3.**

*4.2.2 Fitting criteria*

*4.2.3 Phase calculations*

calculated values.

**5. Conclusions**

**93**

preferred orientation March-Dollase model [39–41].

*DOI: http://dx.doi.org/10.5772/intechopen.91823*

*Phase volume contents according to heat treatment temperatures and time intervals.*

assure a GOF between 1.0 and 1.5, i.e., the best fit possible.

during service and processing is ultimate.

The structure refinement used the fifth-degree Chebyshev polynomial [38] to fit the background intensities, *yib*, (according to Eq. 2), as well as the 1/x background function, from Topas 4.2. α-Fe and γ-Fe and sigma phases were fitted to the

**Samples Temperature (°C) Time (min) γ phase (%) α phase (%) σ phase (%)** 1320 60 38.8 3.3 61.1 2.9 0.0 1320 60 28.3 5.1 71.6 5.0 0.0 1320 120 44.8 3.0 55.1 3.0 0.0 1320 60 36.2 7.4 63.7 7.4 0.0 1320 240 41.7 6.9 58.2 6.9 0.0 1350 60 34.4 6.4 65.7 6.3 0.0 1350 60 40.5 8.7 59.4 8.6 0.0

*Identification and Quantification of Phases in Steels by X Ray Diffraction Using Rietveld…*

The fitting criteria followed the same methodology applied in Case 1, using

**Figure 7** depicts two diffractograms—one from a sample containing only ferrite and austenite and another containing both phases and sigma. QPA (using Rietveld refinement) was carried on each one of the nine described points for each sample, generating similar scans to the ones presented in **Figure 7**. Each scan was then carefully analyzed and adjusted accordingly to the chosen fitting parameters to

The values obtained for each point were then summed and averaged and the standard deviation calculated for each sample average. **Table 3** presents those

X-ray diffraction has demonstrated to be an effective tool for phase analysis in metallic materials, especially in steels. Because this type of material is the most used material on earth nowadays, due to its versatility in terms of physical, mechanical, and chemical properties, knowledge of the phase transformations that might occur

Steel surfaces subjected to abrasive surface cleaning, which suffered contamination from the blasting operation, and duplex steels subjected to aggressive environments and high temperatures of service, which experienced phase transformation, were analyzed by X-ray diffraction using peak refinement, by the Rietveld method. The refinement method demonstrated that phase identification and quantification enabled the diagnosis of forthcoming problems related to the presence of such

Eqs. (4)–(6). For every sample, the GOF was within the range of 1.0–1.5.

#### **Figure 7.**

*XRD spectrum for two different conditions. Sample number 18 without σ phase and sample number 01 with 3.4% of σ phase.*


*Identification and Quantification of Phases in Steels by X Ray Diffraction Using Rietveld… DOI: http://dx.doi.org/10.5772/intechopen.91823*


**Table 3.**

*Phase volume contents according to heat treatment temperatures and time intervals.*

#### *4.2.1 Fitting parameters*

The structure refinement used the fifth-degree Chebyshev polynomial [38] to fit the background intensities, *yib*, (according to Eq. 2), as well as the 1/x background function, from Topas 4.2. α-Fe and γ-Fe and sigma phases were fitted to the preferred orientation March-Dollase model [39–41].

#### *4.2.2 Fitting criteria*

The fitting criteria followed the same methodology applied in Case 1, using Eqs. (4)–(6). For every sample, the GOF was within the range of 1.0–1.5.

#### *4.2.3 Phase calculations*

**Samples Temperature (°C) Time (min) γ phase (%) α phase (%) σ phase (%)** 1000 60 64.0 2.3 32.5 2.7 3.4 1.0 1000 45 49.3 3.0 47.5 3.5 3.1 0.9 1000 22 64.3 3.9 32.6 4.0 3.0 0.6 1000 45 62.4 4.3 34.8 4.1 2.7 0.7 1000 25 52.2 12.1 45.1 11.5 2.6 1.2 1000 25 65.1 9.8 31.7 7.8 2.4 1.1 1000 5 68.1 7.9 29.6 8.2 2.2 0.7 1000 60 61.1 5.0 36.6 4.9 2.1 1.9 1000 20 64.4 4.5 33.4 4.5 2.1 0.2 1000 20 56.7 6.5 41.2 6.9 2.0 0.7 1000 1 57.9 5.5 40.4 5.3 1.6 0.6 1000 1 59.3 7.1 39.0 7.1 1.6 0.2 1000 6 68.5 3.6 29.9 3.6 1.5 0.4 1000 10 61.6 5.4 37.0 5.3 1.2 0.4 As received 47.7 2.0 52.2 2.0 0.0 As received 44.2 4.9 55.7 4.9 0.0 As received 47.1 1.6 52.8 1.6 0.0 1220 60 50.2 7.8 49.7 7.7 0.0 1220 60 56.8 5.1 43.1 5.1 0.0 1220 60 54.3 5.7 45.7 5.7 0.0

*XRD spectrum for two different conditions. Sample number 18 without σ phase and sample number 01 with*

*Inelastic X-Ray Scattering and X-Ray Powder Diffraction Applications*

**Figure 7.**

**92**

*3.4% of σ phase.*

**Figure 7** depicts two diffractograms—one from a sample containing only ferrite and austenite and another containing both phases and sigma. QPA (using Rietveld refinement) was carried on each one of the nine described points for each sample, generating similar scans to the ones presented in **Figure 7**. Each scan was then carefully analyzed and adjusted accordingly to the chosen fitting parameters to assure a GOF between 1.0 and 1.5, i.e., the best fit possible.

The values obtained for each point were then summed and averaged and the standard deviation calculated for each sample average. **Table 3** presents those calculated values.

#### **5. Conclusions**

X-ray diffraction has demonstrated to be an effective tool for phase analysis in metallic materials, especially in steels. Because this type of material is the most used material on earth nowadays, due to its versatility in terms of physical, mechanical, and chemical properties, knowledge of the phase transformations that might occur during service and processing is ultimate.

Steel surfaces subjected to abrasive surface cleaning, which suffered contamination from the blasting operation, and duplex steels subjected to aggressive environments and high temperatures of service, which experienced phase transformation, were analyzed by X-ray diffraction using peak refinement, by the Rietveld method.

The refinement method demonstrated that phase identification and quantification enabled the diagnosis of forthcoming problems related to the presence of such phases in the investigated steels, allowing the optimization of techniques and the choice of correct process parameters.

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*DOI: http://dx.doi.org/10.5772/intechopen.91823*

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