*1.2. Thermophysical Properties of Selected Barrel Steels*

The thermophysical properties, i.e., thermal conductivity, specific heat and density as a function of temperature in the RT range up to 1000 ◦C, were adopted as a contribution to the initial boundary value problem of heat transfer in the barrel wall of a 35 mm caliber cannon, as shown in Figures 3–5 and in Tables 2–4.

For the selected steels, the experimental data on thermal conductivity was introduced in the form of Table 2. Data between measurement points were approximated in COMSOL software using cubic splines.

**Figure 3.** Thermal conductivity of selected barrel steels: 30HN2MFA, 38HMJ, DUPLEX [12].


**Table 2.** Data on thermal conductivity of selected barrel steels [12].

The experimental specific heat data are presented in Table 3 and illustrated in Figure 4. Data between points were approximated in COMSOL using cubic splines.

**Figure 4.** Apparent specific heat of chosen barrel steels: 30HN2MFA, 38HMJ, DUPLEX [12].


**Table 3.** Data on apparent specific heat of selected barrel steels [12].

The experimental density data are presented in Table 4 and illustrated in Figure 3. Data between points were approximated in COMSOL using cubic splines.

**Figure 5.** Density of chosen barrel steels: 30HN2MFA, 38HMJ, DUPLEX [12].


**Table 4.** Data on density of selected barrel steels [12].

Our tests described in [12] showed that for the 38HMJ steel at about and 30HN2MFA at about 740 ◦C there was a ferrite–austenite phase transition, which was responsible for the material shrinkage. In numerical simulations of heat transfer in the cannon barrels, the energy related to the phase transition was included only in the material density and thermal conductivity, while in the specific heat this energy was ignored. Phase transition energy should not be taken into account multiple times, e.g., both in thermal conductivity and specific heat [12].
