**3. Investigation of corrosion resistance of different melts of one brand of austenitic Fe-Cr-Ni alloys that do not contain δ-ferrite**

Considerable attention has been paid to the study of the influence of various factors on the corrosion process of austenitic chromium-nickel steels. In the previous section, the dependence of the corrosion rate *K* of AISI 304, 08Cr18Ni10, AISI 321, 08Cr18Ni10Ti steels containing δ-ferrite on the atomic-magnetic state of austenite, i.e. on the specific paramagnetic susceptibility χ<sup>0</sup> of austenite, which is an integral value and many factors on corrosion behavior. In this regard, it is necessary to investigate the corrosion of austenitic Fe-Cr-Ni alloys that do not contain α-phase. Five melts of 08Cr28N27 alloy, which does not contain δ-ferrite, were selected. The chemical composition of the melts of this alloy are given in **Table 3**.

Samples were selected from sheet (thickness 1 mm) industrial supplies of alloy 08Cr28N27. Since the numerical values of the specific magnetic susceptibility across the width of the cold-rolled sheet were locally unevenly distributed, in order to average from different places in a checkerboard pattern from each melting cut 10 samples in the form of parallelepipeds (<sup>6</sup> <sup>4</sup> 1 mm<sup>3</sup> ). The obtained values of the specific paramagnetic susceptibility to corrosion tests are given in **Table 4**. For melts 1...5 of alloy 08Cr28Ni27 the average values of specific paramagnetic susceptibility <sup>χ</sup><sup>0</sup> of austenite are received: 2.95 <sup>10</sup><sup>8</sup> ; 2.86 <sup>10</sup><sup>8</sup> ; 3.58 <sup>10</sup><sup>8</sup> ; 3.09 <sup>10</sup><sup>8</sup> ; 2.96 <sup>10</sup><sup>8</sup> <sup>m</sup><sup>3</sup> /kg, respectively [12].

In order to accelerate chemical corrosion, a model aggressive medium was used: a mixture of concentrated acids—hydrochloric and nitric (HCl:HNO3 3:1) and the samples were kept continuously for 0.5 h at t = 30°C. The corrosion rate *K* was determined by the formula *K* = Δ*m*/(*S* τ), where Δ*m* is the loss of mass before and after corrosion, *S* is the surface area of the sample, τ is the exposure time in an aggressive environment. **Table 5** shows the obtained average values of corrosion rate: 1381, 1397, 1519, 1540, 1470 g/(m<sup>2</sup> h), respectively, for melts 1...5.

Analysis of the experimental dependences of the corrosion rate *K* on the paramagnetic susceptibility χ<sup>0</sup> of austenite (to corrosion tests) of different melts, but one grade of alloy 08Cr28N27, which does not contain δ-ferrite (**Figure 5**) shows: the greater χ0, the greater the corrosion rate *K* [12], i.e. there is an opposite dependence compared to austenitic chromium-nickel steels that contain δ-ferrite (see **Figure 1**).

Therefore, the selected sensitive parameter χ0, able to distinguish the corrosion rate of similar chemical composition of different melts of the same brand of alloy 08Cr28Ni27. For the existence of a paramagnetic effect, it is necessary that the electronic shells of matter have uncompensated orbital and spin magnetic moments, which are oriented in the magnetic field *H*. Hence, by studying the magnetic


### **Table 3.**

*Chemical composition of melts of 08Cr28Ni27 alloy.*


### **Table 4.**

*The value of the specific magnetic susceptibility χ<sup>0</sup> of austenite cut samples from the melts № 1...5 alloy 08Cr28Ni27.*


### **Table 5.**

*The value of corrosion rate* K *cut samples of the alloy 08Cr28Ni27.*

properties of austenite, it is possible to obtain information about the behavior of austenite under the influence of external factors, such as its corrosion resistance.

The obtained results do not contradict the value of the corrosion rate K (attracted from [9]) for these 1...5 melts of alloy 08Cr28Ni27 (respectively: 0.095; *Dependence of Corrosion Resistance of Austenitic Chromium-Nickel Steels on the Magnetic… DOI: http://dx.doi.org/10.5772/intechopen.102388*

### **Figure 5.**

*Tendencies of change of corrosion rate* K *in a mixture of concentrated acids-hydrochloric and nitric (HCl:HNO3 3:1) and specific magnetic susceptibility χ<sup>0</sup> austenite of different melts of alloy 08Cr28Ni27, which do not contain δ-ferrite.*

0.095; 0.143; 0.190 and 0.143 g/(m<sup>2</sup> h)). In the environment that contains chlorine (**Figure 6**).

Compare the graphs of **Figures 5** and **6**. From **Figure 6** it follows that the corrosion rates for two pairs of swimming trunks 1, 2 and 3, 5 are the same (0.095 and 0.143 g/(m2 h)), and according to our studies, the corrosion rates of all these

### **Figure 6.**

*The relationship of borrowed values of the corrosion rate* K *[9] in a chloride-containing medium and found the specific magnetic susceptibility χ<sup>0</sup> [12] of austenite of the same melts of the alloy 08Cr28Ni27, which do not contain δ-ferrite.*

five swimming trunks are different (which corresponds to different χ0), i.e. the resolution is slightly better, but coincides qualitatively with the general nature of the curves (**Figures 5** and **6**).

It is experimentally established that the corrosion resistance of the austenitic alloy 08Cr28Ni27 (analog AISI 904L) correlates with the atomic-magnetic state of austenite, which is determined by the susceptibility χ0: the less χ0, the higher the corrosion resistance (lower corrosion rate), in contrast to austenitic chromiumnickel steels, which contain δ-ferrite. The obtained results can be used to predict the local corrosion resistance of austenitic alloys that do not contain δ-ferrite.
