Foundry Alloy Cast Steels

Applications

As the leading manufacturer of mechanical power transmission equipment, we have has developed firsthand experience regarding data for tensile strength, yield strength, fatigue strength and harden ability of our alloy steels. Experience developed through years of testing and analysis.

We are our most critical casting user and, therefore, have a sincere understanding of what our customers need.

Our alloy cast steels have shown meritorious service for heavily loaded gears, coupling hubs and numerous other castings used in the construction, mining, cement, paper and automotive industries.

Material

Our family of standard low to medium carbon alloy cast steels consists of MolyTelastic (chromium-molybdenum steel) and No. I through No. 4, and No. 6 Gearalloy grades (chromium-nickel-molybdenum steels) shown in Table 1.

Our alloy cast steels can be heat treated to meet the strength requirements of ASTM A148 (High Strength Steel Castings for Structural Purposes) up to grade 165-150. Minimum tensile ductility values (elongation and reduction of area) for corresponding strength levels are shown in Table 2.

Other alloy cast steels which meet your specifications can be furnished for special pressure, low temperature and high temperature applications.

The selection of the appropriate alloy cast steel depends upon specified chemistry, hardness, strength and design considerations.

We will assist you in the proper selection of the appropriate grade to meet your design requirements.

Melting and Heat Treating

Our cast steels are manufactured in two basic electric arc furnaces with capacities of 5 & 70 tons.

Precise alloy additions are determined through computer aided melting coupled with statistical process control, and are monitored by spectrographic analysis.

The optimum balance between strength and toughness is achieved through annealing, normalizing and tempering, or quenching and tempering.

Our heat treat furnaces are equipped with programmable controllers to allow for complete control of critical times and temperatures.

The largest heat treat furnace measures 30' x 40' x 12' end allows US to do all heat treating in house. This permits close quality control over all aspects of manufacture.

Machinability and Processing

Machinability and ductility are improved through our calcium containing ladle deoxidation practice. This, in itself, can easily result in lowering machining costs by as much as 15%.

A well equipped sand laboratory monitors sand molding and core making practices. A sodium silicate sand binder is exclusively used in our core making process. This high grade material requires no oven curing, is environmentally safe, and drastically reduces potential metal solidification defects.

Pattern molding can accommodate items up to 150" in diameter or diagonal. Beyond 150'*. We utilize sweep or pit molding. The largest pits measure 24' x 50' x 7.5' and 36' x 36'x 10'.

Nondestructive Testing

As a user of castings which require a great deal of machining, we realize the need for quality control throughout all phases of manufacture, to assure the integrity of the part after rough and/or finish machining.

Prior to final heat treatment, all castings are nondestructively tested using magnetic particle inspection. Whenever possible, process welding is performed prior to final heat treatment. All welds are magnetic particle inspected to ensure their integrity. After heat treatment, castings are again given a complete magnetic particle inspection.

If specified, additional nondestructive testing, such as ultrasonic or radiographic inspection, is performed to ensure the internal integrity of the casting.

Alloy Cast Steel Designation and Chemistry

Moly-Telastic is a medium carbon, chromium-molybdenum type cast steel which is similar to an AISI 4135 specification, except with reduced chromium content. It can be heat treated by annealing or normalizing and tempering to an approximate hardness of 180 HB for all section sizes.

No. 1 Gearalloy is a medium carbon, chromium-nickel-molybdenum type cast steel used for applications requiring higher harden ability than Falk Moly-Telastic. It is similar to an AISI 8630 steel, but higher in alloy content.

No. 2 Gearalloy is a low carbon (0.20% nominal), chromium-nickel-molybdenum type cast steel containing 0.04-0.06% vanadium for grain refinement in gear castings. Chemistry is similar to an AISI 8620 steel, but higher in alloy content. This is our standard cast steel for carburized and hardened gears and has comparable harden ability to an AISI 4320 H steel.

It is also used in the through-hardened, quenched, and tempered heat treat condition to a maximum hardness range of 245-285 HB for impact applications (this condition is not intended for gearing or wear applications).

No. 3 Gearalloy has higher carbon and molybdenum content than No. I Gearalloy This results in higher harden ability for increased section size or higher hardness ranges for quench and temper heat treatment. It is similar to an "8633" steel (not a standard AISI designation) but higher in alloy content.

No. 4 Gearalloy has higher carbon content than No. 3 Gearalloy. This results in the highest harden ability alloy cast steel (maximum section size or maximum hardness) intended for hardening by quench and temper The harden ability is equivalent to an AISI 4340. Chemistry is similar to an AISI 8640 steel but higher in alloy content.

No. 6 Gearalloy has the same carbon content as No. 4 Gearalloy but has increased alloy content. This enables hardening by normalize and temper heat treatment to higher hardness ranges (325-365 HB maximum) than can be achieved with No. 4 Gearalloy normalized and tempered. No. 6 Gearalloy is not intended to be quench hardened because of quench cracking susceptibility.

Moly-Telastic and No. I through No. 4 and No. 6 Gearalloy grades of alloy cast steel do not, by intent, conform to specific standard SAE or AISI steel designations regarding carbon and alloy content, but contain modified carbon and generally higher alloy content for improved depth of hardening (harden ability). The chemical analyses are shown in Table 1.

Mechanical Properties

Mechanical properties of steel castings are generally determined from test bars machined from standard ASTM A781 test coupons. These test coupons may be attached to the casting or cast separately.

Minimum tensile properties, obtained from standard cast test coupons, for our alloy cast steels are shown in Table 2.

Test bar results for tensile ductility (per cent elongation and reduction of area) and impact strength may not be representative of actual castings due to harden ability and section size considerations.

Strength properties such as tensile, yield, and to a lesser degree, endurance or fatigue strength, show better correlation between test bars and actual castings, provided hardnesses are equivalent.

For further information regarding the limitations of test bar data, please contact our Materials Technology Department through your local Rrexnord account executive.

Impact Properties

Typical Charpy V-Notch impact strengths for Moly-Telastic and No. I through No. 4 Gearalloys are shown in Tables 3 through 6. These values were obtained from separate cast keel blocks and 5.0 & 10.0 inch test sections. Impact strength is also a function of heat treatment, hardness and test temperature. Impact properties were evaluated at T/3 depth for test sections.

Table 3 is the typical Charpy V-Notch impact strength for Moly-Telastic cast steel in a 5.0 test section in the normalized and tempered (N&T) condition at 160-200 HB.

Impact strength in the quenched and tempered condition is higher than for the normalized and tempered condition. Specific data may be obtained upon request.

For applications requiring higher impact strength, due to shock loading and/or low ambient temperatures, No. I or No. 2 Gearalloy is recommended depending on the specified hardness.

Table 4 shows the typical Charpy V-Notch impact strength (ft-lbs.) for keel blocks of No. I Gearalloy cast steel, as a function of heat treatment and specified hardness.

Table 5 shows the typical Charpy V-Notch impact strength for No. 2 Gearalloy cast steel at 70*F in the water quenched and tempered condition at 207-223HB.

Table 6 shows the typical Charpy V-Notch impact strength for No. 4 Gearalloy cast steel (5" and 10" section thickness) according to hardness in the oil quenched and tempered condition.

Metallurgical Considerations

Harden ability -Control of melting is accomplished through computer-aided harden ability (Di) calculations, coupled with statistical process control in order to ensure uniform response to heat treatment.

The ideal critical diameter (Di) is defined as the diameter of a round that can be quenched under ideal conditions (ice brine) in order to obtain a 50% martensitic microstructure at the center of the section. The multiplication factors for calculating (Di) harden ability, which vary according to ASTM grain size, carbon, and individual alloy content, are available in literature and from the Materials Technology Department.

Cast (Di) harden ability ranges, established in our Melt Shop as acceptance criteria for our heats, are shown in Table 7.

The harden ability ranges are presented for reference purposes only and should not be considered as part of a material specification. They are intended to illustrate the degree of control used during manufacturing to assist in the production and heat treatment of castings, and may be subject to slight modification.

Jominy End Quench -Jominy end quench harden ability ranges from testing alloy cast steels per ASTM A255 are shown in Figures I through 4. For the same reason cited above for (Di), these Jominy end quench curves should not be part of a material specification. harden ability ranges in Figures I through 4 are narrower than those for wrought AISI designations, as illustrated in Figure 4 for No. 4 Gearalloy. Jominy end quench curves were not developed for No. 6 Gearalloy as the curves were expected to be nearly horizontal and No. 6 Gearalloy is not quench hardened.

Heat Treat Considerations

For the infrequent times that machining sequenes or other manufacturing considerations require that heat treating be performed at the customer's plant, our castings can be furnished in the annealed condition. The recommendations shown in Table 8 are provided as a guide.

Processing Operations The sequence of foundry processing operations is as follows:

1. Preproduction Analysis
   • Drawings, material specifications and all nondestructive testing requirements are analyzed.
   • Layouts are made to determine riser sizing and wedging. Using computer programs, foundry engineers calculate proper riser sizes, location and the necessary gating.
   • Pattern construction details are resolved and the pattern is constructed.
   • After construction, the pattern is dimensionally checked before releasing for production.
    
   
2. Moulding/Coremaking Processing
   During both operations, into ensureprocess inspections are critical to ensure the following:
   • Dimensional accuracy.
   • Proper pouring height and mold cleanliness.
   • Proper size and location of all risers and gating systems.
    
   
3. Melting Analysis
   • Computer-aided melting is used, coupled with statistical process control, to melt to a harden ability range that will ensure uniform response to heat treating.
   • The melt shop personnel have a "go"/ no go criteria established by a computer program.
   • Actual chemical analysis is determined through spectrographic analysis and is recorded.
    
   
4. Pouring the Casting
   • Precise pouring instructions are established and monitored. Results are recorded.
    
   
5. Cooling
   • Thermocouples monitor temperatures to determine the proper time for shakeout.
    
   
6. Shakeout
   • Removes a high percentage of the adhering sand from the casting.
    
   
7. Inspection
   • Prior to gas cutting. the casting is visually inspected to ensure that it was poured to the proper pouring height.
   • The proper cut-off height for riser removal is established.
   • Riser removal temperatures, of at least 350*F are monitored.
    
   
8. Gas Cutting
   • A semi-automatic gas cutting machine is used for riser removal.
    
   
9. Annealing
   • Full annealing is required to alleviate stresses that developed during the solidification of the casting and also to remove any stresses that may have developed during gas cutting.
    
   
10. Shot Blasting
    • Removes heat treat scale.
     
    
11. Rough Clean
    • Includes arc air of pads and fins, stress relieving and blasting.
     
    
12. Inspection
    • Rough casting layout.
    • Dimensions are recorded to ensure proper as-cast tolerances.
    • Critical areas, such as rim l.D., pocket radii and bolting flanges are ground for dry magnetic particle inspection.
    • Entire casting is also given a 100% wet magnetic particle inspection if specified.
    • All results are recorded.
     
    
13. Preheat Casting
    • Furnace preheat for defect removal.
     
    
14. Defect Removal
    • Defects are removed by arc air.
     
    
15. Inspection
    • Magnetic particle inspection is performed to ensure complete defect removal.
    • Defect size and location are recorded.
     
    
16. Upgrade
    • Whenever possible, all process welding is performed prior to final heat treatment using heat treatable electrodes.
    • Welding is done by qualified welders, and when required, according to qualified procedures.
    • Furnace preheating and furnace stress relieving are utilized.
     
    
17. Final Heat Treatment in Car-bottom Furnaces
    • Furnaces are run with programmable controllers.
    • Furnace charts are available upon request.
     
    
18. Inspection
    • Upgraded areas and all critical areas are again magnetic particle inspected.
    • Brinell readings are taken to ensure casting is within specified hardness range.
    • Layout and rough dimensions are recorded after heat treatment to ensure sufficient stock for machining.
    • Defect sketches are recorded both before and after final heat treatment.
    • Any defects that become apparent after anal heat treatment are subjected to the procedures as noted in points # 12 through #16.
    • If required, the casting will receive a complete reheat treatment.
    • If required, test bars are pulled to verify mechanical properties.
     
    
19. Rough and/or Finish Machining and Additional NDT Requirements
    • Ultrasonic and/or radiographic inspection per the appropriate specification.
    • Magnetic particle inspection.
    • Brinell readings in designated areas.
    • All results are recorded.

Weldability

Moly-Telastic and Gearalloy grades can be welded satisfactorily, providing that necessary preheating and post-heating precautions are followed. Minimum preheating temperatures are shown in Table 9.

The maximum preheat temperature should not be greater than 200 F above the minimum required. Minimum preheat temperature should be maintained during welding by torch heating and monitored by temperature indicating pencils or a surface pyrometer.

The stress relieving temperature should be 1000-1250°F for annealed castings and 50-1 00°F below the final tempering temperature for normalized and tempered or quenched and tempered castings of all grades.

Whenever possible, furnace preheating and post-heating are preferred to local heating with large torches. The choice of electrodes and welding techniques is normally governed by the nature and position of the weld and the mechanical properties required. Low hydrogen type manual arc weld rods, or CO2 shielded flux core process wire, selected on the basis of the required strength, are recommended. When the deposited weld metal is designed to meet the tensile properties of the casting, welding before heat treating, using heat treatable electrodes, e.g., 4340, is recommended.

Machinability

Alloy grades of cast steels (Moly-Telastic and Gearalloy grades) are readily machinable, due to our ladle deoxidation practice which uses primarily calcium and not aluminum. The use of aluminum is limited to castings less than 8T finish weight, as it develops aluminum oxides and decreases machinability. Aluminum content used is less than 0.020%. The index of machinability, shown in Table 10, is based on hardness and is related to machinability of B1112 steel (100%).

Although microstructure considerations, as well as hardness, determine machinability, our machinability rating system is based on tool life as a function of cutting speed (surface feet per minute).