$F = μN$ will fail because of the excessive heat generated if the normal force or the speed of motion gets too big. Why is that?
"$F = μN$, where μ is called the coefficient of friction (Fig. 12-1). Although this coefficient is not exactly constant, the formula is a good empirical rule for judging approximately the amount of force that will be needed in certain practical or engineering circumstances. If the normal force or the speed of motion gets too big, the law fails because of the excessive heat generated. It is important to realize that each of these empirical laws has its limitations, beyond which it does not really work."