Hardness

INTRODUCTION

(a) Vicker's Test

In this experiment, an indenter with 136° of pyramidal diamond shape is force into a square surface of a metal with certain load applied (between 5kgf to 120 kgf) up until certain amount of time. 

Figure 1 : Square shape formed on the metal surface

To find Vickers Hardness Number (VHN), the following formula can be use :

VHN = Load/Area = [2P sin (136°/2)]/ d² = 1.854 (F/d²)

Where P is the load applied (kgf) and d is the sum of d₁ and d₂ over 2.

(b) Rockwell Test

This method has two main scales which are :

(i)     Scale B, the concavity is a steel ball (1.58mmø) and load applied is 100 kgf.

(ii)    Scale C, the concavity is a diamond cone with 120° angle and load applied is 150 kgf.

In this experiment, a small load of 10kgf is applied and the dial is changed to zero. This is followed by an additional load, (90 kgf for scale B and 140 kgf for scale C) in order to get concavity, d.

The Hardness Rockwell (HR) can be define by the following :

For scale C, HRC = 100 - (d/0.002)

For scale B, HRB = 130 - (d/0.002)

Where d is the depth of indentation.

(c) Brinell Test

In this test, a harden steel ball which has a good diameter, D under a certain load and time is use to measure the effect of concavity, d. the Brinell Hardness Number (BHN) can be calculated by :

(d) Charpy Test

This test is use to determines the amount of energy absorbed by a metal during fracture. The impact specimens with small fracture or does not undergone plastic deformation is said to be in a brittle condition. Specimen that fractures with great plastic deformation is having a ductile property.

METHODOLOGY

For Vickers Test, mild steel is put onto the Vickers’ machine. A clear image of the metal is set by magnifying it. An indenter with diamond shape is force into the steel’s surface for 10 second with 10kgf load. The value of d₁, d₂ and VHN is recorded in Table 1. This procedure is repeated using carbon steel.

For Rockwell Test, ASSAB steel is put onto the Rockwell’s machine. An indenter with cone shape is force into the steel’s surface with 150kgf load. The value of HRC displayed by the machine is then recorded into Table 2. The procedure is repeated with High-quality Carbon.

For Brinell’s Test, carbon stell is put onto the Brinell’s machine. A ball shape indenter is pressed into the steel with 1000kgf for 15 seconds. The diameter of the concavity formed on the steel is measured and recorded in Table 3. The procedure is repeated using mild steel.

For Charpy Test, mild steel is fixed in place at both ends of the Charpy’s tester and the steel is impact with a striker, mounted at the end of a pendulum. This procedure is repeated for carbon steel and any observation on the impacts and the energy absorbed is recorded in Table 4.

RESULT
-for Charpy Test