The principal application of high-speed steel is (a) - cutting tools (b) - internal combustion engine block (c) rails for high-speed trains (d) turbine blades

(a) - cutting tools

Explanation:

High speed steel is the cutting tool material. It is widely used in the production process. it also represent as HSS. High speed steel is made from heat treatment process of steel.

The high speed steel have following compositions

1. Tungsten - 18 %

2. Chromium - 4%

3. Vanadium - 1 %

4. Carbon - 0.7 %

5. Iron - 76.3 %

So the option a is correct.

(a) - cutting tools