3.6.3 Developing and Maintaining Product Performance

When the required structural performance has been achieved in pre-production samples, the next concern is the potential variation in product performance over the production life of the product. Any such variation can be maintained within acceptable limits by:

  • Evaluating the selected forging alloy for its response to the anticipated processes
  • Maintaining close control over manufacturing processes, such as preheat temperature and atmosphere and cooling rates (where hot or warm forging are employed); preforming, forging and trimming operations; and heat treating (where it is employed)
  • Establishing test procedures for periodically evaluating the properties or performance of the forgings

The first two factors underscore the need for careful selection of the material, and working with a forger who has the capability of producing the forgings with the required repeatability. It is axiomatic, if the materials and processes are maintained within the proper limits, the properties of the forging will be consistent.

When it is desirable or necessary to verify mechanical properties, standard inspection methods are available. Some of the most commonly employed test methods are briefly described below. A more detailed discussion, including references to relevant ASTM specifications, is available in FIA publications.

1. Chemical Analysis Control of the chemical composition of the forging stock is essential to attaining consistent properties in the forging. The supplier of forging stock routinely furnishes certified reports of the chemical analysis of the melt from which the material was produced. The analysis is verified by the forge plant either by comparative methods or analysis.
2. Hardness Testing is widely used for steel forgings for several reasons.

  • The procedure, including sample preparation, is simple
  • Hardness correlates closely with tensile strength
  • It is nondestructive
  • Portable equipment is available for forgings that are too large to test with stationary equipment

3. Tensile Tests are used to establish:

  • ultimate strength
  • yield strength
  • ductility

They are performed on specimens taken from the forging according to guidelines, mutually agreed between the forger and purchaser, for location and orientation, and usually constitute destructive testing. In some cases, particularly for open die forging and ring rolling, specimens may be taken from a prolongation, which is an area of the forging at an agreed location that is used for test, and is not part of the finished part. When prolongations are used, the tensile test is nondestructive.

4. Notched-Bar Impact Tests are also performed on specimens taken from the forging. The tests are dynamic, and are used to define:

  • impact strength
  • notch toughness
  • fracture mode (brittle, ductile or combination)

5. Fracture Toughness Testing measures the resistance of a given material in a given condition to catastrophic failure in the presence of a pre-existing crack.
6. Bend Tests are performed on samples taken from the forging to test for ductility by bending the specimen through a specified angle to a specified inside radius of curvature. The criterion for failure is whether cracks form on the tension surface after bending.
7. Ultrasonic Testing is one of the most reliable and widely used methods of nondestructive testing for steel forgings. It provides a means for evaluating the internal quality of forgings using a portable instrument. The process yields information on the size, location and orientation of discontinuities.
8. Eddy Current Testing is a non-destructive test method for detecting surface imperfections in bar and rod stock, cold forgings and fully cooled warm and hot forgings. It can be used for 100% automatic production testing.
9. Magnetic Particle Testing is one of the easiest nondestructive methods for detecting surface and near-surface discontinuities in ferro-magnetic materials.
10. Liquid Penetrant Testing is used to detect discontinuities that are open to the surface. For ferrous parts a permeable red dye is used with a white developer. For non-ferrous parts, a fluorescent die penetrant is most commonly used, viewed under black light. Any discontinuities are outlined and are readily detected.
11. Metallography is the technique of microscopic examination of polished or etched sections of metal specimens. It is employed to evaluate:

  • micro cleanliness
  • grain size
  • microstructure

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When the required structural performance has been achieved in pre-production samples, the next concern is the potential variation in product performance over the production life of the product. Any such variation can be maintained within acceptable limits by:

  • Evaluating the selected forging alloy for its response to the anticipated processes
  • Maintaining close control over manufacturing processes, such as preheat temperature and atmosphere and cooling rates (where hot or warm forging are employed); preforming, forging and trimming operations; and heat treating (where it is employed)
  • Establishing test procedures for periodically evaluating the properties or performance of the forgings

The first two factors underscore the need for careful selection of the material, and working with a forger who has the capability of producing the forgings with the required repeatability. It is axiomatic, if the materials and processes are maintained within the proper limits, the properties of the forging will be consistent.

When it is desirable or necessary to verify mechanical properties, standard inspection methods are available. Some of the most commonly employed test methods are briefly described below. A more detailed discussion, including references to relevant ASTM specifications, is available in FIA publications.

1. Chemical Analysis Control of the chemical composition of the forging stock is essential to attaining consistent properties in the forging. The supplier of forging stock routinely furnishes certified reports of the chemical analysis of the melt from which the material was produced. The analysis is verified by the forge plant either by comparative methods or analysis.
2. Hardness Testing is widely used for steel forgings for several reasons.

  • The procedure, including sample preparation, is simple
  • Hardness correlates closely with tensile strength
  • It is nondestructive
  • Portable equipment is available for forgings that are too large to test with stationary equipment

3. Tensile Tests are used to establish:

  • ultimate strength
  • yield strength
  • ductility

They are performed on specimens taken from the forging according to guidelines, mutually agreed between the forger and purchaser, for location and orientation, and usually constitute destructive testing. In some cases, particularly for open die forging and ring rolling, specimens may be taken from a prolongation, which is an area of the forging at an agreed location that is used for test, and is not part of the finished part. When prolongations are used, the tensile test is nondestructive.

4. Notched-Bar Impact Tests are also performed on specimens taken from the forging. The tests are dynamic, and are used to define:

  • impact strength
  • notch toughness
  • fracture mode (brittle, ductile or combination)

5. Fracture Toughness Testing measures the resistance of a given material in a given condition to catastrophic failure in the presence of a pre-existing crack.
6. Bend Tests are performed on samples taken from the forging to test for ductility by bending the specimen through a specified angle to a specified inside radius of curvature. The criterion for failure is whether cracks form on the tension surface after bending.
7. Ultrasonic Testing is one of the most reliable and widely used methods of nondestructive testing for steel forgings. It provides a means for evaluating the internal quality of forgings using a portable instrument. The process yields information on the size, location and orientation of discontinuities.
8. Eddy Current Testing is a non-destructive test method for detecting surface imperfections in bar and rod stock, cold forgings and fully cooled warm and hot forgings. It can be used for 100% automatic production testing.
9. Magnetic Particle Testing is one of the easiest nondestructive methods for detecting surface and near-surface discontinuities in ferro-magnetic materials.
10. Liquid Penetrant Testing is used to detect discontinuities that are open to the surface. For ferrous parts a permeable red dye is used with a white developer. For non-ferrous parts, a fluorescent die penetrant is most commonly used, viewed under black light. Any discontinuities are outlined and are readily detected.
11. Metallography is the technique of microscopic examination of polished or etched sections of metal specimens. It is employed to evaluate:

  • micro cleanliness
  • grain size
  • microstructure

Return to Table of Contents

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When the required structural performance has been achieved in pre-production samples, the next concern is the potential variation in product performance over the production life of the product. Any such variation can be maintained within acceptable limits by:

  • Evaluating the selected forging alloy for its response to the anticipated processes
  • Maintaining close control over manufacturing processes, such as preheat temperature and atmosphere and cooling rates (where hot or warm forging are employed); preforming, forging and trimming operations; and heat treating (where it is employed)
  • Establishing test procedures for periodically evaluating the properties or performance of the forgings

The first two factors underscore the need for careful selection of the material, and working with a forger who has the capability of producing the forgings with the required repeatability. It is axiomatic, if the materials and processes are maintained within the proper limits, the properties of the forging will be consistent.

When it is desirable or necessary to verify mechanical properties, standard inspection methods are available. Some of the most commonly employed test methods are briefly described below. A more detailed discussion, including references to relevant ASTM specifications, is available in FIA publications.

1. Chemical Analysis Control of the chemical composition of the forging stock is essential to attaining consistent properties in the forging. The supplier of forging stock routinely furnishes certified reports of the chemical analysis of the melt from which the material was produced. The analysis is verified by the forge plant either by comparative methods or analysis.
2. Hardness Testing is widely used for steel forgings for several reasons.

  • The procedure, including sample preparation, is simple
  • Hardness correlates closely with tensile strength
  • It is nondestructive
  • Portable equipment is available for forgings that are too large to test with stationary equipment

3. Tensile Tests are used to establish:

  • ultimate strength
  • yield strength
  • ductility

They are performed on specimens taken from the forging according to guidelines, mutually agreed between the forger and purchaser, for location and orientation, and usually constitute destructive testing. In some cases, particularly for open die forging and ring rolling, specimens may be taken from a prolongation, which is an area of the forging at an agreed location that is used for test, and is not part of the finished part. When prolongations are used, the tensile test is nondestructive.

4. Notched-Bar Impact Tests are also performed on specimens taken from the forging. The tests are dynamic, and are used to define:

  • impact strength
  • notch toughness
  • fracture mode (brittle, ductile or combination)

5. Fracture Toughness Testing measures the resistance of a given material in a given condition to catastrophic failure in the presence of a pre-existing crack.
6. Bend Tests are performed on samples taken from the forging to test for ductility by bending the specimen through a specified angle to a specified inside radius of curvature. The criterion for failure is whether cracks form on the tension surface after bending.
7. Ultrasonic Testing is one of the most reliable and widely used methods of nondestructive testing for steel forgings. It provides a means for evaluating the internal quality of forgings using a portable instrument. The process yields information on the size, location and orientation of discontinuities.
8. Eddy Current Testing is a non-destructive test method for detecting surface imperfections in bar and rod stock, cold forgings and fully cooled warm and hot forgings. It can be used for 100% automatic production testing.
9. Magnetic Particle Testing is one of the easiest nondestructive methods for detecting surface and near-surface discontinuities in ferro-magnetic materials.
10. Liquid Penetrant Testing is used to detect discontinuities that are open to the surface. For ferrous parts a permeable red dye is used with a white developer. For non-ferrous parts, a fluorescent die penetrant is most commonly used, viewed under black light. Any discontinuities are outlined and are readily detected.
11. Metallography is the technique of microscopic examination of polished or etched sections of metal specimens. It is employed to evaluate:

  • micro cleanliness
  • grain size
  • microstructure

Return to Table of Contents

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