The article presents a method of developing a mathematical model of the arc surfacing process performed using the self-shielded flux-cored filler metal wire with the chromium cast iron (Fe15) weld deposit. A three-level design (static, determined, and complete) was used to determine the function of the test object, thus enabling the simulation of deposition rate in relation to wire feed speed and electrode extension. The deposition rate for the specified set of surfacing parameters amounted to between 4.31 kg/h and 11.25 kg/h. The study was also concerned with identifying the effect of the significance level of test factors and interactions between them on the resultant factor, as well as an assessment of the adequacy of the test object function. In relation to significance level α = 0.01, regression coefficients b0, b1, b2, and b11 significantly affected the deposition rate of the surfacing process. Coefficient b22 was significant at a level of 0.40, whereas coefficient b12 was significant at a level of 0.15. The mathematical model presenting the effect of wire feed speed and electrode extension, as well as interactions between them on the deposition rate of the surfacing process, was adequate for the adopted level of significance α = 0.05.