Application

Alloy 6B wrought base-cobalt alloys No. 6B and 6K have been used successfully for many years in applications involving severe conditions of wear or wear combined with corrosion and/or high temperature. They are used particularly for shaft sleeves, bushings, valve parts, pump plungers, doctor blades, feed screws, knives, wear plates, and bearings.

Tough and Abrasion Resistant

Alloys No. 6B and 6K are cobalt-based alloys with outstanding resistance to most types of wear. Their wear resistance is inherent. It is a "built-in" characteristic and not the result of heat-treatment, plating, nitriding, or other methods used to produce a superficial hardness on metal parts.
Half bushings and haft sleeves made of alloy No. 6B can be used in locations where abrasive particles like fly ash, coke, metal powder, shale, or cement dust tend to collect in bearing surfaces. The ability of these parts to withstand the wearing effects of hard, sharp particles makes them especially useful in screw conveyors, rock crushing rollers, tile-making machines, and cement and steel-mill equipment.

Resist Seizing and Galling

Alloy No. 6B is resistant to the effects of seizing or galling. In many cases, its low coefficient of friction allows sliding contact with other metals without damage by metal pick-up.
Alloy No. 6B has been used in equipment where no lubricants were used because of the nature of the product being handled. Sleeves made of alloy No. 6B move smoothly, with a minimum of resistance, even when operating in contact with other metal parts. They have been useful in inaccessible areas where efficient lubrication is impossible. Sleeves and bushings have resisted seizing even when lubricants were diluted by gasoline, cleaning fluids, and other liquids that wash out an oil film. They have operated at peak efficiency even when lubricants decomposed under heat, or were destroyed by abrasive particles.

Resist Erosive Wear

Parts made of alloy No. 6B have had long service life - even under constant erosive conditions. It has outstanding resistance to cavitation-erosion. Alloy No. 6B used for steam turbine erosion shields has protected the blades of one turbine for over 19 years of continuous service.

Good Impact and Thermal Shock Resistance

Alloy No. 6B combines wear and corrosion resistance with good impact strength and resistance to thermal stock.

Resist Heat and Oxidation

High temperatures have little effect on the hardness, toughness, and dimensional stability of these alloys. They are highly resistant to atmospheric oxidation at ordinary temperatures, and have good resistance to oxidation at elevated temperatures.

Excellent Hot Hardness

Alloy 6B wrought, cobalt-based alloy No. 6B retains high hardness even at red heat. Once cooled back to room temperature, it recovers it's full original hardness.

Corrosion Resistance

In addition to its wear-resistance, alloy No. 6B has good resistance to a variety of corrosive media. This combination of properties makes alloy No. 6B particularly useful in such applications as food handling machinery, chemical equipment, and others where both wear - and corrosion-resistance are necessary.
Where extraordinary resistance to corrosion is required, one of the Hastelloy nickel-based alloys may prove more suitable.

Available Forms

Alloy No. 6B and No. 6K are available in the form of sheet, plate, and fabricated shapes. Alloy No. 6B is also available as bar.

Heat Treatment

Wrought forms of alloy No. 6B and No. 6K are supplied in the solution heat-treated condition unless otherwise specified. The standard heat-treatment is at 2250°F (1232°C) followed by air cooling.

Properties Data

The properties listed in this page are typical or average values based on laboratory tests conducted by the manufacturer. They are indicative only of the results obtained in such tests and should not be considered as guaranteed maximums or minimums. Materials must be tested under actual service conditions to determine their suitability for a particular purpose. All data represent the average of four or less tests unless otherwise noted. The secondary units (metric) used in this page are those of the SI system.

Chemical Composition, Percent

Average Physical Properties

Average Hot Hardness

Average Compressive Strength

Average Modulus of Rupture

Average Modulus of Elasticity

Average Izod Impact Strength (un-notched)

Average Charpy Impact Strength

*Solution heat-treated at 2250°F (1232°C), air cooled.

Average Room Temperature Data - Alloy No. 6B

a - Average of 27-31 tests
b - Average of 23 tests
c - Average fo 22-24 tests
d - Average of 9 tests
*Solution heat-treated at 2250°F (1232°C), air cooled.

Average Tensile Data*

* Solution heat-treated at 2250°F (1232°C), air cooled.
**Elongation, percent in 1 in. (25.4 mm)
***Test bars cut transverse to rolling direction.

Average Stress Rupture and Creep Data

* Test discontinued before rupture.
**Specimens were solution heat-treated at 2250°F (1232°C) and air cooled prior to testing.

Average Cavitation-Erosion Data

Average Abrasive Wear Data

Average Abrasive Wear Data **

Average Coefficients of Static Friction For Some Common Materials

Coefficient represents tangent of angle of repose. Tests made on dry surfaces having better than 120 grit finishes. All Values based on averages and are to be used comparatively and not as absolute values.
**Average of two or more tests against a case-hardened SAE 4620 steel ring (Rockwell C-63)
*The wear coefficient (K) was calculated using the equation: V= KPL/3h
where V= Wear Volume (mm(3))
P = Load (kg)
L = Sliding distance (mm)
h = Diamond pyramid hardness
A combination of a low wear coefficient and a high hardness is desirable for good wear resistance.

Fusion Welding

Alloys No. 6B and 6K can be welded by gas tungsten-arc (TIG) with an argon flow of 25 CFH, gas metal-arc (MIG), shielded metal-arc (coated electrode), and oxy-acetylene in this order of preference. The oxy-acetylene method should be used with discretion and care in that alloys No. 6B and 6K will "boil" during welding which may cause porosity. Use a 3X reducting flame to minimize oxidation, penetration and inter-alloying.
Alloy 6B and 6K should be preheated and maintained at 1000°F (538°C) minimum to prevent cracking during welding and then still air-cooled. Fixturing which would chill the weld rapidly should not be used. Standard weld joints are recommended. Haynes alloy No. 25 or Hastelloy alloy W filler metals are recommended for joining alloy No. 6B to softer materials such as carbon steel or stainless steel, while the harder cobalt-based filler metals such as Alloy 6, No. 6B, and No. 21 are recommended for joining alloy No. 6B to itself, especially if wear resistance is required in the weld areas. In the latter case, Haynes No. 25 or Hastelloy alloy W may be used for the root passes and then be overlayed with the harder materials. Gas shielding of the root side of the gas tungsten-arc weldments is not mandatory, but it is recommended in order to improve weld penetration.

Brazing

Alloys No. 6B and 6K are readily joined to other materials by brazing. All forms of surface dirt such as paint, ink, oil, chemical residues, etc., must be removed from the mating parts by etching, solvent scrubbing, degreasing, or other means. In addition, fluxing will be required during torch brazing operations when using silver brazing filler metal, to help clean the joint and allow the filler metal to flow more freely over the mating surfaces. Brush joining areas generously with brazing filler metal melts, the source of heat should be removed and the parts positioned. The assembly should then be pressed together to squeeze out the excess flux and still air-cooled. The part should not be quenched.
Other brazing filler metals (i.e., gold, palladium, or nickel-based alloys) are satisfactory for joining alloys No. 6B and 6K. Brazing filler metal selection depends on the service conditions expected.
A close fit of the mating surfaces is recommended. The finished joints will have greater strength if the filler metal is very thin, generally 0.001-0.005" (0.03-0.14 mm) thick.
Brazing, with high-temperature filler materials, is generally performed in a furnace. Induction and resistance heating with salt-bath and metal-bath dip brazing have limited application. Vacuum furnaces held at less than one micron pressure or controlled atmosphere furnaces, having adequate moisture control at brazing temperatures (less than -60°F (-51°C) dew point), produce the most satisfatory results. Controlled atmospheres such as hydrogen or cracked ammonia are suitable for brazing alloys No. 6B and 6K base materials.

Machining

Alloys No. 6B and 6K are machined with tungsten-carbide tools. Carbide inserts are used with a 5-degree (0.09 rad.) negative tool holder and a 30-degree (0.52 rad.) or 45-degree (0.79 rad.) lead angle. Tools for facing or boring are essentially the same except for greater clearances where needed. For best results in drilling, the drill web should be kept thin. Screw machine length, carbide tipped drills should be used. In reaming, a 45-degree (0.79 rad.) cutting lead angle should be used. High speed tabs are not recommended for alloys No. 6B and 6K, but threads can be produced by EDM techniques. For better surface finish, these alloys should be ground.
The table which follows gives some general information which may be used as a guide in machining alloys No. 6B and No. 6K.

Guide for Machining Alloys No. 6B and No. 6K

*Use C-3 tungsten carbide tools. Coolant-water base fluid diluted 15 parts water to one part fluid. Tools for facing and boring are basically the same as turning tools except for greater clearance where needed.
**C-2 tungsten carbide twist drills with drill web kept as thin as possible. Coolant - same as item * above
***C-2 tungsten carbide tools. Reamers should have a 45-degree (0.79 rad.) side cutting edge angle. Coolant - same as item * above.

Grinding

Whenever close tolerances are required, grinding is recommended for finishing Alloys No. 6B and 6K. Honing can be used to finish inside diameters. Recommended wheels and coolants are listed in the table below. For convenience, the manufacturers of grinding wheels are also listed; however, similar wheels of other brands can also be used if desired.
Grinding speeds should be kept between 2800 and 6000 s.f.p.m (14-31 m/s). Alloys being ground dry should not be quenched, because this may cause surface checking.

*Or any good grade of water soluble oil
**Or any good grade of sulfur-base cutting oil