Which of the following powders should be fed for effective oxy-fuel cutting of stainless steel

Which pair among the following solid state welding processes uses heat from an external source
$$P$$- Diffusion welding
$$Q$$- Friction welding
$$R$$- Ultrasonic welding
$$S$$- Forge welding

Diamond cutting tools are not recommended for machining of ferrous metals to

In an orthogonal cutting experiment, an $$HSS$$ tool having the following tool signature in the orthogonal reference system $$(ORS)$$ has been used: $$0-10-7-7-10-75-1$$
Given : Width of cut $$=3.6mm;$$
Shear strength of work piece material $$460N/m{m^2};$$
Depth of cut $$=0.25mm;$$
Coefficient of friction at chip tool interface $$=0.7.$$

Shear plane angle (in degrees) for minimum cutting force is