4.1.2 Microalloy (MA) Steels

The new microalloy steels are becoming increasingly recognized as offering both cost savings and high performance for use in hot forged products. They find wide application in automotive, off-highway and similar original equipment industries. The yield strengths exhibited with these materials range from 415 to 825 Mpa (60,000 to 120,000 psi) without heat treatment. These strength capabilities make MA steels an economical alternative to quenched-and-tempered alloy steels.

MA steels provide for uniform hardness across cross sections up to 100 mm (4 in.) thick. Cost savings with MA steel forgings are realized through the elimination of heat treatments such as quench and temper (Q&T), when a straightening heat treatment is required. However, some processes require the use of special equipment such as cooling fans, water spray cabinets and conveyors, which can add to manufacturing costs. Therefore, theoretical cost reductions based purely on eliminated processes can be misleading.

The elimination of heat treating and often straightening operations facilitates just-in-time delivery schedules. One company reports shipping components in the afternoon that were forged in the morning.

The rapidly growing use of microalloy forging has been encouraged by recently developed microalloy grades and by the introduction of a comprehensive, new ASTM specification A-909 Standard Specification for Steel Forgings, Microalloy, for General Industrial Use. This specification includes compositions for achieving at least four (4) strength and hardness levels. It is intended to make it easier for designers to select the proper combination of steel composition, processing and properties for MA forgings.

MA steels and forgings have been in widespread use internationally. Nationally accepted specifications for microalloy steels and forgings, such as the new ASTM specification and other ASTM specifications for MA forging steels, will encourage the selection of microalloy forgings for safety critical parts as well as for more generic forgings.

Microalloy steels usually have carbon contents in the range of 0.15 to 0.55%, manganese in the range of 0.60 to 1.65%, silicon in the range of 0.15 to 0.65% and either small amounts of vanadium, columbium (niobium), titanium or nickel and molybdenum in various combinations. Vanadium, columbium and titanium form carbides and/or nitrides that remain in solid solution at most forging temperatures, but precipitate during the subsequent cooling at controlled rates. The precipitation phenomenon assists in enhancing the strength of these steels after forging and controlled cooling.

MA steels can be categorized into two types based on their microstructural characteristics. The first are of ferritic-pearlitic microstructure and the second are of a bainitic structure. Both the ferritic-pearlitic and bainitic MA steels exhibit good yield strengths while the bainitic MA steels generally show higher impact toughness.

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The new microalloy steels are becoming increasingly recognized as offering both cost savings and high performance for use in hot forged products. They find wide application in automotive, off-highway and similar original equipment industries. The yield strengths exhibited with these materials range from 415 to 825 Mpa (60,000 to 120,000 psi) without heat treatment. These strength capabilities make MA steels an economical alternative to quenched-and-tempered alloy steels.

MA steels provide for uniform hardness across cross sections up to 100 mm (4 in.) thick. Cost savings with MA steel forgings are realized through the elimination of heat treatments such as quench and temper (Q&T), when a straightening heat treatment is required. However, some processes require the use of special equipment such as cooling fans, water spray cabinets and conveyors, which can add to manufacturing costs. Therefore, theoretical cost reductions based purely on eliminated processes can be misleading.

The elimination of heat treating and often straightening operations facilitates just-in-time delivery schedules. One company reports shipping components in the afternoon that were forged in the morning.

The rapidly growing use of microalloy forging has been encouraged by recently developed microalloy grades and by the introduction of a comprehensive, new ASTM specification A-909 Standard Specification for Steel Forgings, Microalloy, for General Industrial Use. This specification includes compositions for achieving at least four (4) strength and hardness levels. It is intended to make it easier for designers to select the proper combination of steel composition, processing and properties for MA forgings.

MA steels and forgings have been in widespread use internationally. Nationally accepted specifications for microalloy steels and forgings, such as the new ASTM specification and other ASTM specifications for MA forging steels, will encourage the selection of microalloy forgings for safety critical parts as well as for more generic forgings.

Microalloy steels usually have carbon contents in the range of 0.15 to 0.55%, manganese in the range of 0.60 to 1.65%, silicon in the range of 0.15 to 0.65% and either small amounts of vanadium, columbium (niobium), titanium or nickel and molybdenum in various combinations. Vanadium, columbium and titanium form carbides and/or nitrides that remain in solid solution at most forging temperatures, but precipitate during the subsequent cooling at controlled rates. The precipitation phenomenon assists in enhancing the strength of these steels after forging and controlled cooling.

MA steels can be categorized into two types based on their microstructural characteristics. The first are of ferritic-pearlitic microstructure and the second are of a bainitic structure. Both the ferritic-pearlitic and bainitic MA steels exhibit good yield strengths while the bainitic MA steels generally show higher impact toughness.

Return to Table of Contents

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The new microalloy steels are becoming increasingly recognized as offering both cost savings and high performance for use in hot forged products. They find wide application in automotive, off-highway and similar original equipment industries. The yield strengths exhibited with these materials range from 415 to 825 Mpa (60,000 to 120,000 psi) without heat treatment. These strength capabilities make MA steels an economical alternative to quenched-and-tempered alloy steels.

MA steels provide for uniform hardness across cross sections up to 100 mm (4 in.) thick. Cost savings with MA steel forgings are realized through the elimination of heat treatments such as quench and temper (Q&T), when a straightening heat treatment is required. However, some processes require the use of special equipment such as cooling fans, water spray cabinets and conveyors, which can add to manufacturing costs. Therefore, theoretical cost reductions based purely on eliminated processes can be misleading.

The elimination of heat treating and often straightening operations facilitates just-in-time delivery schedules. One company reports shipping components in the afternoon that were forged in the morning.

The rapidly growing use of microalloy forging has been encouraged by recently developed microalloy grades and by the introduction of a comprehensive, new ASTM specification A-909 Standard Specification for Steel Forgings, Microalloy, for General Industrial Use. This specification includes compositions for achieving at least four (4) strength and hardness levels. It is intended to make it easier for designers to select the proper combination of steel composition, processing and properties for MA forgings.

MA steels and forgings have been in widespread use internationally. Nationally accepted specifications for microalloy steels and forgings, such as the new ASTM specification and other ASTM specifications for MA forging steels, will encourage the selection of microalloy forgings for safety critical parts as well as for more generic forgings.

Microalloy steels usually have carbon contents in the range of 0.15 to 0.55%, manganese in the range of 0.60 to 1.65%, silicon in the range of 0.15 to 0.65% and either small amounts of vanadium, columbium (niobium), titanium or nickel and molybdenum in various combinations. Vanadium, columbium and titanium form carbides and/or nitrides that remain in solid solution at most forging temperatures, but precipitate during the subsequent cooling at controlled rates. The precipitation phenomenon assists in enhancing the strength of these steels after forging and controlled cooling.

MA steels can be categorized into two types based on their microstructural characteristics. The first are of ferritic-pearlitic microstructure and the second are of a bainitic structure. Both the ferritic-pearlitic and bainitic MA steels exhibit good yield strengths while the bainitic MA steels generally show higher impact toughness.

Return to Table of Contents

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