## 3 Results  
Laser treatment of austenitic steel X18H10T by pulsed CO\({}_{2}\) laser in an air atmosphere is modeled. The parameters of the target and the ambient gas are listed in Tables 1 and 2, respectively. Binding energy \(U\) from Equation (11) is approximated by latent heat of evaporation \(q_{v}\). The temporal profile of the laser pulse is specified by a triangle with the increasing front of \(\tau_{f}=50\) ns and the decreasing back of \(\tau_{b}=250\) ns (see Figure 2). The maximum of intensity \(I_{\text{max}}\) is a variable parameter. It is attained at 50 ns after the pulse beginning. To exclude the uncertainty due to the absorptance of the target, the absorbed part of laser energy \(K_{a}\) is specified as the model parameter. In the energy balance, Equation (11), it is explicitly defined as the following function of time:  
\[K_{a}=\left\{ \begin{array}{ccc}I_{\text{max}}\frac{t}{\tau_{f}}&,&0<t<\tau_ {f}\\ I_{\text{max}}\frac{\tau_{f}+\tau_{b}-t}{\tau_{b}}&,&\tau_{f}<t<\tau_{f}+\tau_ {b}\end{array} \right., \tag{17}\]  
The pulse parameters are listed in Table 3.  
Figures 2-4 show the effect of a single pulse with the maximum absorbed intensity \(I_{\text{max}}=15\) MW/cm\({}^{2}\). Figure 2 shows the temporal profile of the laser pulse spe \begin{table}
\begin{tabular}{l l} \hline Melting point, \(T_{m}\), (K) & 1750 \\ \hline Boiling point, \(T_{b}\) (K) & 3200 \\ \hline Latent heat of melting, \(q_{m}\) (G/m\({}^{3}\)) & 2.18 \\ \hline Latent heat of evaporation, \(q_{v}\) (G/m\({}^{3}\)) & 49.7 \\ \hline Specific heat in solid phase, \(c_{s}\) (MJ/(m\({}^{3}\) K)) & 4.25 \\ \hline Specific heat in liquid phase, \(c_{t}\) (MJ/(m\({}^{3}\) K)) & 5.95 \\ \hline Thermal conductivity, \(\lambda\) (W/(m K)) & 20 \\ \hline Density, \(\rho\) (kg/m\({}^{3}\)) & 7890 \\ \hline Atomic mass, \(m_{v}\), (a.m.u.)\(\mu\) & 55.85 \\ \hline Adiabatic exponent of vapor, \(\mu_{v}\) & 5/3 \\ \hline \end{tabular}
\end{table} 
Table 1: Properties of steel X18H10 Taccepted for modeling [30]. \begin{table}
\begin{tabular}{l l} \hline Ambient pressure, \(p_{a}\) (atm.) & 1 \\ \hline Ambient temperature, \(T_{a}\) (K) & 298 \\ \hline Density at the ambient conditions, \(\rho_{0}\) (kg/m\({}^{3}\)) & 1.185 [30] \\ \hline Atomic mass, \(m_{g}\), (a.m.u.) & 29 [30] \\ \hline Adiabatic exponent, \(\mu_{g}\) & 7/5 [30] \\ \hline \end{tabular}
\end{table} 
Table 2: Properties of air accepted for modeling. of absorbed laser power \(K_{a}\) versus time \(t\). Figure 3 shows temperature fields in the target calculated for this pulse. Surface temperature attains the boiling point \(T_{b}\) and becomes greater than \(T_{b}\). Therefore, an intensive vapor flow is formed along with a compressible flow of ambient air. Figure 4 shows gas-dynamic fields. Notice a shock front separating undisturbed and disturbed domains of air and a contact jump between air and vapor. The shock front is very close to the boundary of the computation domain for \(t\) = 0.2, 0.3, and 1 us. Those are the instances just before the enlargement of the domain and the rearrangement of the computation grid. The shock front never touch the right boundary. At \(t\) = 0.1 and 0.2 us (see Figure 4), gas-dynamic velocity \(u\) is positive at the interface \(z\) = 0 indicating net evaporation but at the end of the laser pulse at \(t\) = 0.3 us, \(u(0)\) becomes negative indicating net condensation. Figure 2 shows the dynamics of the surface temperature \(T_{s}\) and the heat loss to evaporation calculated from the right hand side of Equation (11). One can see that the evaporation loss is much smaller than the absorbed laser energy for this pulse and the surface temperature can be considerably greater than the boiling point \(T_{b}\) = 3200 K.  
A single pulse with smaller intensity \(I_{\text{max}}\) = 10 MW/cm\({}^{2}\) cannot heat the target up to the boiling point (see the dotted line in Figure 5). However, the heat of the pulse is accumulated in the surface layer of the target.