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    Presentation on Hardness Testing Presentation on Hardness Testing Presentation Transcript

    • 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 surface indentation or scratching A difficult property to describe in terms of first principles Þ value depends greatly on method of testing. Different testing methods Þ different scales and values ME101: Materials Science and Technology
    •    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 ME101: Materials Science and Technology
    • F Brinell’s Hardness ME101: Materials Science and Technology
    • P from 500 - 3000 kg D= 10 mm D d BHN =( 2 P ) { πD D −   ME101: Materials Science and Technology ( ) } D 2 −d 2   
    • ME101: Materials Science and Technology
    • 1. 2. 3. Press a 10mm (3/8") diameter ball into material with a known amount of load. Measure diameter of the indentation. BHN = Load = 2L Surface Area πD[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. ME101: Materials Science and Technology
    • Plastic Mild steel Elastic H Copper H = Ae-BT d/D(%E) ME101: Materials Science and Technology
    • Tensile Strength (MPa) Tensile Strength = 3.4 BHN Correlations between the Brinell hardness number (BHN) and tensile strength of carbon steels. ME101: Materials Science and Technology Hardness (HB)
    •  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 ME101: Materials Science and Technology
    •     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) ME101: Materials Science and Technology
    • ME101: Materials Science and Technology
    • Machine measures depth of penetration and computes hardness ME101: Materials Science and Technology
    •   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 ME101: Materials Science and Technology
    • Load levels and indenter sizes for Rockwell hardness tests. Symbol Indenter Normal Scales RB, 1/16 ball* RC, cone + RA, cone RD, cone RE, 1/8 ball RF, 1/16 ball RG, 1/16 ball Superficial Sales R15N, cone+ R30N, cone R45N, cone R15T, 1/16 ball R30T, 1/16 ball R45T, 1/16 ball Minor(Pre-) Load, kg Coefficients in R = C1 – C2 t Major(Total) Load, kg C1 C2mm-1 10 10 10 10 10 10 10 100 150 60 100 100 60 150 130 100 100 100 130 130 130 500 500 500 500 500 500 500 3 3 3 3 3 3 15 30 45 15 30 45 100 100 100 100 100 100 1000 1000 1000 1000 1000 1000 ME101: Materials Science and Technology
    •    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 ME101: Materials Science and Technology
    •     Widely used and well accepted Little operator subjectivity Accurate Fast    Destructive Non-Portable Initial cost ($5,000) ME101: Materials Science and Technology
    • 1) If -20 < HRc < 40 BHN = 1,420,000 (100 – HRc)2 2) 3) If 40 < HRc < 100 If 35 < HRb < 100 BHN = 25,000__ (100 - HRc) BHN = 7,300____ (130 - HRb) ME101: Materials Science and Technology
    • DPH/VHN/VPH/VH = 2PSin(θ/2)/L2 P P: applied load in kg, 5-120 kg L: average diagonal length, mm (typically from a few µm to 1 mm) θ θ: angle between opposite faces of indenter; ≡ 136° L Range: 5 (extremely soft metals) 1500 (extremely hard materials) 1.854P HV = 2 L A Vickers Hardness = F/A = 3σ ME101: Materials Science and Technology
    •       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 ME101: Materials Science and Technology
    • ME101: Materials Science and Technology
    •     Knoop hardness Test: Pyramid shape indenter Scleroscope: rebound height Durometer: The resistance to penetration (elastic deformation) Relationship between Hardness and Strength TS = K h ( HB ) where K h = 500 in lb/in ME101: Materials Science and Technology = 3.45 in MPa 2
    •  Micro Hardness Tests  Major : Minor = 7 : 1  P : Ap : L : C :    14.2P HK = 2 L Applied load = 25 gf- 300 gf Unrecovered Proj. area of indentations, mm 2 Length of long diagonal, mm 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
    •     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 ME101: Materials Science and Technology
    • 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 the fusion line is traversed. ME101: Materials Science and Technology
    • ME101: Materials Science and Technology
    •    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 scale is used for 'softer' rubbers while the Shore D scale is used for 'harder' ones. Because of the resilience of rubbers and plastics, the hardness reading may change over time - so the indentation time is sometimes reported along with the hardness number. The ASTM test number is ASTM D2240 number while the analogous ISO test method is ISO 868. ME101: Materials Science and Technology
    • ME101: Materials Science and Technology
    • ME101: Materials Science and Technology
    • ME101: Materials Science and Technology
    • 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 ME101: Materials Science and Technology
    • 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 Solution corresponding tensile strength of the material. BHN = ( 2 P ) { π D D −   ( ) D2 − d 2    } Substituting the values from the problem statement yields : 355 = ( 2 ) ( 2000 ) { 10π 10 −   ( ) 10 2 − d 2    } which after some algebra gives d = 2.65mm ME101: Materials Science and Technology
    • 5mm ME101: Materials Science and Technology
    •  Indentation Hardness used for steel   It is indicative of ultimate tensile strength   as opposed to scratch or rebound hardness 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.
    • B N= H ( 2 P ) π − ( −d ) DD D 2 2
    •    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 Softwood (e.g., pine) Hardwood Aluminum Copper Mild steel 18-8 (304) stainless steel annealed Glass Hardened tool steel Rhenium diboride Hardness 1.6 HBS 10/100 2.6–7.0 HBS 1.6 10/100 15 HB 35 HB 120 HB 200 HB 1550 HB 1500–1900 HB 4600 HB
    • Scale Code Load Indenter Use 120° diamond cone Tungsten carbide A HRA 60 kgf B Al, brass, and HRB 100 kgf 1/16 in diameter steel sphere soft steels C D HRC 150 kgf 120° diamond cone HRD 100 kgf 120° diamond cone E HRE 100 kgf 1/8 in diameter steel sphere F HRF 60 kgf G HRG 150 kgf 1/16 in diameter steel sphere 1/16 in diameter steel sphere Harder steels
    • 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