Presentation on Hardness Testing

ME 101: Materials Science and Technology

ME101: Materials Science and Technology

Hardness is not necessarily an indication of strength , although for some materials such as steel, a harder steel is a stronger steel.

Measure of a material’s ability to resist Measure of a material’s ability to resist surface indentation or scratchingsurface indentation or scratching

A difficult property to describe in terms of first principles Þ value depends greatly onmethod of testing.

Different testing methods Þ different scales and values


Brinell Hardness Test: 10mm diameter ball with a load of 500, 1000 or 3000kg

Rockwell Hardness Test: A cone shape indenter; the depth of penetration is measured.

Vickers Hardness Test: Pyramid shape indenter



F

Brinell’s Hardness


P from 500 - 3000 kg

D= 10 mm

2 22BHN P D D D d

d

D


1. Press a 10mm (3/8") diameter ball into material with a known amount of load.

2. Measure diameter of the indentation.3. BHN = Load = 2L

Surface Area D[D-(D2-d2)1/2]

1. L = Load placed on ball, usually 3000 kg , but 1500 kg, and 500 kg can also be used.

2. D = Diameter of steel ball ( = 10 mm)

3. d = diameter of dent, measured by looking thru a Brinell microscope.



Elastic

Plastic

H = Ae-BT

Mild steel

Copper

d / D ( % E )

H


Hardness (HB)

Ten

sile

Str

engt

h (M

Pa)

Correlations between theBrinell hardness number (BHN)and tensile strength of carbonsteels.

Tensile Strength = 3.4 BHN

Sample must be ten times thicker than the indentation depth (sample usually should be at least 3/8" thick).

Test is most accurate if the indentation depth is 2.5 - 5.0 mm. Adjust load to achieve this.

Test is no good if BHN > 650


Widely used and well accepted

Large ball gives good average reading with a single test.

Accurate Easy to learn and

use

Destructive Non-portable High initial cost

($5,000) Error due to

operator reading Brinell Microscope (10% max)




Machine measures depth of penetration and computes hardness

Select Scale - load and indentor depending on the scale

Press a point into material - Diamond Point (Brale) - 1/16" ball - 1/8" ball - ¼” ball



Symbol Minor(Pre-) Major(Total)Indenter Load, kg Load, kg C1 C2mm-1

Coefficients inR = C1 – C2 t

Normal ScalesRB, 1/16 ball*RC, cone +RA, coneRD, coneRE, 1/8 ballRF, 1/16 ballRG, 1/16 ball

Superficial SalesR15N, cone+R30N, coneR45N, coneR15T, 1/16 ballR30T, 1/16 ballR45T, 1/16 ball

10 100 130 50010 150 100 50010 60 100 50010 100 100 50010 100 130 50010 60 130 50010 150 130 500

3 15 100 1000 3 30 100 1000 3 45 100 1000 3 15 100 1000 3 30 100 1000 3 45 100 1000

Load levels and indenter sizes for Rockwell hardness tests.

Sample must be ten times thicker than the indentation depth (sample usually should be at least 1/8" thick).

Need 3 tests (minimum) to avoid inaccuracies due to impurities, hard spots.

Test is most accurate if the Rockwell Hardness is between 0 and 100. Adjust scale to achieve this.

For Steel: If HRa > 60, use HRc scale If HRa < 60, use HRb scale


Widely used and well accepted

Little operator subjectivity

Accurate Fast

Destructive Non-Portable Initial cost ($5,000)


1) If -20 < HRc < 40BHN = 1,420,000 (100 – HRc)2

2) If 40 < HRc < 100 BHN = 25,000__ (100 - HRc)

3) If 35 < HRb < 100 BHN = 7,300____

(130 - HRb)



Vickers Hardness = F/A = 3y

A

P

2

1.854PHV

L

P: applied load in kg, 5-120 kg

L: average diagonal length, mm (typically from a few µm to 1 mm)

: angle between opposite faces of indenter; 136°

Range: 5 (extremely soft metals) - 1500 (extremely hard materials)

DPH/VHN/VPH/VH = 2PSin(/2)/L2

L

Continuous hardness from soft (5 DPH) to hard materials (1500 DPH)

DPH independent on load value unlike BHN

Careful surface preparation required Slow due to careful measurement Small indentation compared to BHN Pin cushion and Barrel indentations

possible



Knoop hardness Test: Pyramid shape indenter

Scleroscope: rebound height Durometer: The resistance to

penetration (elastic deformation) Relationship between Hardness and

Strength


MPa45.3

lb/in500 2

in

inKwhereHBKTS hh

Micro Hardness Tests Major : Minor = 7 : 1

P : Applied load = 25 gf- 300 gf Ap : Unrecovered Proj. area of indentations, mm2

L : Length of long diagonal, mm C : A constant supplied by the manufacturer

(C=0.07028 for 172° 30' between long edges and 130° 0' between short edges)

ME101: Materials Science and

Technology

2

14.2PHK

L

Accurate Useful for elongated and

anisotropic constituents. Requires load to be

normal to surface plane parallel surfaces.

Can be done on mounted specimens

Slow Sensitive to surface

condition Subject to error in

diagonal measurement



Microhardness variation in a 9Cr-1 Mo steel weldment as a function of position.Note the structural changes and the corresponding changes in hardness as thefusion line is traversed.


The Shore (Durometer) test provides an empirical hardness value that doesn't correlate to other properties or fundamental characteristics.

Shore Hardness, using either the Shore A or Shore D scale, is the preferred method for rubbers/elastomers and is also commonly used for 'softer' plastics such as polyolefins, fluoropolymers, and vinyls. The Shore A The Shore A scale is used for 'softer' rubbers while the Shore D scale is used for 'softer' rubbers while the Shore D scale is used for 'harder' ones.scale is used for 'harder' ones.

Because of the resilience of rubbers and plastics, the Because of the resilience of rubbers and plastics, the hardness reading may change over time - so the hardness reading may change over time - so the indentation time is sometimes reported along with the indentation time is sometimes reported along with the hardness numberhardness number. The ASTM test number is ASTM D2240 while the analogous ISO test method is ISO 868.






The Brinell’s Hardness Test of an alloy steel was measured to be 355. What is the diameter of the indentation if a load of 2000 kg was used. Also compute the tensile strength of the material.

D= 10 mm

d = 2.65 mm

Tensile Strength = 1207 MPa


Solution

Substituting the values from the problem statement yields :

2 2355 2 2000 10 10 10 d

2 22BHN P D D D d

which after some alge db ra = giv 2.es 65mm

The Brinell hardness of an alloy steel is 355. Compute the diameter of the indentation if a load of 200 kg was used and estimate the corresponding tensile strength of the material.


which after some alge db ra = giv 2.es 65mm

Indentation Hardness used for steel as opposed to scratch or rebound hardness

It is indicative of ultimate tensile strength Atoms move out of the way to create

indentation Two main types: Brinell and Rockwell

A spherical indenter (1 cm diameter) is shot with 29 kN force at the target

Frequently the indenter is steel, but for harder materials it is replaced with a tungsten carbide sphere

The diameter of the indentation is recorded

The indentation diameter can be correlated with the volume of the indentation.

BHN 2P

D D D2 d2

ASTM and ISO use the HB value. It can be HBS (Hardness, Brinell, Steel) or the HBW (Hardness, Brinell, Tungsten)

HBW = 0.102 BHN Sometimes written as HBW 10/3000

(Tungsten, 10 mm diameter, 3,000 kg force)

Material Hardness

Softwood (e.g., pine) 1.6 HBS 10/100

Hardwood 2.6–7.0 HBS 1.6 10/100Aluminum 15 HBCopper 35 HBMild steel 120 HB

18-8 (304) stainless steel annealed 200 HBGlass 1550 HB

Hardened tool steel 1500–1900 HB

Rhenium diboride 4600 HB

Scale Code Load Indenter Use

A HRA 60 kgf 120° diamond coneTungsten carbide

B HRB 100 kgf 1/16 in diameter steel sphere Al, brass, and soft steels

C HRC 150 kgf 120° diamond cone Harder steelsD HRD 100 kgf 120° diamond cone

E HRE 100 kgf 1/8 in diameter steel sphere

F HRF 60 kgf 1/16 in diameter steel sphere

G HRG 150 kgf 1/16 in diameter steel sphere

HBW 10/3000 HRA 60KG HRB 100KG HRC 150KG

Tensile Strength (Approx)

638 80.8 - 59.2 329,000

578 79.1 - 56 297,000

461 74.9 - 48.5 235,000

375 70.6 - 40.4 188,000

311 66.9 - 33.1 155,000

241 61.8 100 22.8 118,000

207 - 94.6 16 100,000

179 - 89 - 87,000

149 - 80.8 - 73,000

111 - 65.7 - 56,000

Education

Presentation on Hardness Testing