Question

Which of the following abrasive materials is most appropriate for grinding hardened tool steel?
1. Aluminium oxide
2. Cubic boron nitride
3. Diamond
4. Silicon carbide

Answer 1

Correct Answer - Option 2 : Cubic boron nitride

Explanation:

Type of Abrasives / Grain type:

• It indicates materials used for the manufacturing of abrasive particles.
• Out of the abrasives B4C is giving the poor performance during machining and diamond is very costly, therefore Al2O3 or SiC is the most commonly used abrasives in the grinding wheel.
• Al2O3 soft and tougher than the SiC whereas SiC will be hard and brittle than Al2O3
• The type of abrasive is selected based on the mechanical properties of workpiece material I.e. for machining of soft and ductile workpieces, Al2O3, and machining of hard and brittle workpiece SiC will be used.   
• A- Al2O3, B – B4C, C – SiC, D - Diamond

Material	Hardness (HK)	Properties
Al2O3	2100	Used for grinding steels, high strength alloys, etc.
SiC	2400	Used for grinding cast iron, aluminium, brass, etc.
CBN	5000	2nd hardest material after Diamond. Used for grinding tool steels, hardened steels, cemented carbides tool and their alloys. Suitable for ferrous material.
Diamond	6000	Hardest material. Used for grinding of glasses, ceramics, cemented carbide tools, etc. Not suitable for ferrous material.