Drill bit for mining industry

Cross-section reduction ratio of rolled bar

≥ 8:1  

Steel bar heat treatment

Annealed

Austenite grain size ASTM E112

ASTM#  ≥6 (finer grain size than 5, i.e. 6,7...)

Phosphorous content

≤ 0.015 wt%

Sulphur content

≤ 0.025 wt%

Hydrogen content

< 2ppm

Macrostructure ASTM E381

≤ S2, R2, C2

No visible defects: pipe, bursts, pinhole, cracks, intergranular cracks, thermal flakes

Non-metallic inclusions ASTM E45 Method A

Type A (sulfides):       thin ≤2.5, heavy ≤1.5

Type B (aluminates): thin ≤2.0, heavy ≤1.0

Type C (silicates):      thin ≤1.0, heavy ≤0.5

Type D (oxides):         thin ≤1.5, heavy ≤1.0

Charpy impact test ASTM E23  

Charpy: ≥ 45J

Tensile test ASTM E8-E8M, A370

Tensile elongation: ≥ 15%

Forging specifications

Forging process

closed die

Press size

Heating temperature

1000-1100°C

Forging temperature

Dimensions

According to agreed drawing  

Heat treatment post-forging C

Full annealing at 870-890°C  

Normalising at 860-890°C & tempering at 670-690°C

Hardness

Decarburisation or oxidation depth from surface

< 1.5mm  

Austenite grain size ASTM E112

ASTM# ≥7 (finer grain size, i.e. 7,8...)

Ultrasonic testingASTM A388

≤ 3mm FBH

Surface finish condition ASTM A29

Clean without oxide scale, shot peened

Surface defect < 1mm

Asymmetry < 7 mm for big size

Asymmetry < 5 mm for smaller size

Continuous flow lines, no knots or S-shaped flow

Part numbering

Stamp serial number on each forging in sequence of part production

Forging inspection frequency

Ultrasonic testing

First piece, after that 5% of batch at regular intervals
）

MPI testing

Surface finish condition

100% of batch

Dimension check

Every shift checks the first 3 pieces, 10% of batch at regular intervals

%

Document requirements with each order

Steel mill

Include: tensile, impact toughness, hardness (annealed), chemical composition, inclusions, macrostructure, austenite grain size, steelmaking process, reduction ratio, heat treatment, hardenability

Forging examination results document

Include: austenite grain size, ultrasonic, MPI, flow lines image, dimension inspection, visual inspection