Sanbar 64 is an air-hardening, high nickel alloy steel with good response to carburizing. It has excellent fatigue strength and wear resistance in the case hardened condition.
Chemical composition (nominal) %
Sanbar 64 is used for extension rods, shank rods and tapered rods.
Forms of supply
Hollow drill steel is supplied as hollow, hot-rolled, round or hexagon bar. The ends are trimmed square to within 0.15 mm (0.006 in.) maximum.
Surface condition and protection
Both the outer and inner surfaces are free from harmful slag marks, cracks and scratches. The maximum depth of defects is 0.20 mm (0.008 in.) on the outer surface and 0.15 mm (0.006 in.) on the inner surface.
The outer surface can be supplied dry or oiled for protection against corrosion during transportation. The flushing holes are normally sealed with plastic caps.
Maximum deviation is 1 mm per 1000 mm (0.04 in. per 39.4 in.).
Fixed lengths can be supplied upon request. The length tolerance for fixed lengths are:
|Lengths, mm (in.)||Tolerance, mm (in.)|
|≤ 3375 (132.87)||+/- 2 (0.0787)|
|3376-5750 (132.91-226.38)||+/- 3 (0.1181)|
|> 5750 (226.38)||+/- 4 (0.1575)|
Bars are supplied in standard bundles containing max 1500 kg (3300 lbs).
|Proof strength||Tensile strength||Hardness|
|MPa (ksi)||MPa (ksi)|
|900 (131)||1250 (181)||37-44|
The maximum permissible decarburization depth is 0.30 mm (0.012 in.) on the outer surface and 0.20 mm (0.008 in.) on the inner surface.
Sanbar 64 can be machined in the hot rolled condition.
Induction heating to 1000–1100°C (1830–2010°F), 10–60 seconds, depending on dimension. Forging range 1100–850°C (2010–1560°F).
Read more about forging of Sanbar 64 under Fabrication.
Annealing (induction heating) 680–720°C (1260–1330°F). Cooling in air.
Read more about heat treatment of Sanbar 64 under Fabrication.
Gas carburizing and direct quenching
920–930°C (1690–1705°F). Time depends on the required carbon content and the case depth. Cooling in forced air.
Recommended surface hardness 57–62 HRC and core hardness 36–44 HRC temperature appr. 180–230°C (355–450°F) for one hour.
Surface induction hardening
Hardening: Induction heating to 900– 1000°C (1650–1830°F), 3-6 seconds. Quenching in water or in oil.
Recommended surface hardness 50–55 HRC, temperature 150 to 250°C (300– 480°F). Tempering may not be needed.
Sanbar 64 requires rapid heating to the forging temperature and, above all, the soaking time at full temperature should be as short as possible. This will minimize grain growth and decarburization, both of which drastically impair the fatigue strength. Heat the rod end locally to the correct forging temperature. Forge within the temperature range specified for Sanbar 64.
Overall gas carburizing gives Sanbar 64 excellent fatigue strength and wear resistant properties. It is very important to control the atmosphere in the furnace by having a stable gas flow and an even temperature. The recommended surface carbon content is 0.5 to 0.7%. To increase the toughness, tempering needs to be carried out immediately after carburizing, according to the recommendations above.
The required case depth must be a function of the thread dimension but is in the area of 0.6 to 1.2 mm (0.020 to 0.057 in.). It is essential to ensure that rods are carburized internally in order to obtain maximum service life. The absence of internal carburizing can be extremely detrimental, especially in corrosive environments. In some applications, e.g. surface drilling in poor conditions, surface induction hardening, carried out according to the recommendations above, can be an alternative to overall carburizing.
The required case depth must be a function of the thread dimension but is in the area of 1.5 to 3 mm (0.06 to 0.12 in.).
Shot peening of an adequate intensity and coverage is recommended. It improves fatigue strength due to:
- Introduced compressive stresses
- Increased hardness
- Smoother surface defects
Corrosion of a material subjected to fluctuating loads accelerates the fatigue process. In underground applications particularly, products should be protected to avoid premature fatigue breakages starting from the hole surface.