I wrote part of this in a response to a thread in the Gun Smithing section. Thought I would post it here so more would read it.
A spring is made from cast steel. A cast steel billet is first rolled into bars ( a type of forging) then it is rolled into round stock. Larger dia. springs are made directly from round stock, smaller are drawn to dia. (again a type of forging) then formed. Annealing is done after forging then normalization, harden then temper. A S&W frame starts as a cast steel billet, then is rolled and then forged to shape. Even a piece of flat steel bar was "forged" when it was rolled from a billet. The grain thing about forging is a joke. A forging requires the piece to be annealed and normalized after forging or it would have extreme grain growth because of the elevated temps required for forging and be way brittle. Annealing, normalizing, hardening and tempering resets the grain structure and type of grain anyway.
On another note castings of steel have came a long ways. Steel is no longer cast in an open hearth. Quality steel castings are first smelted in an induction oven in an inert atmosphere. Then poured. This allows for very high quality castings without the inclusions or slag from older methods and produce very high quality.
The best alloys are produced in similar furnaces but, instead of cast into billets the molten metal is sprayed in an inert atmosphere producing small particles of steel that are EXTREMELY uniform in alloy content. These are then heated to near melting temps then pressed into a solid billet. Near perfect steel billets with no stratification. You are more apt to make this type of steel worse by forging it and not better.
The big advantage that forgings USED to have over steel castings was that the older methods of producing steel billets caused some inclusions and impurities in the billet. The initial forging of those billets into bars and sheets would break down and speed those problems out in the material. The smaller the sections the more the steel was worked and refined the problems areas became. Final forgings helped reduce these. With modern smelting and casting methods these inclusion and impurity areas are minimized prior to or without forging. Modern steel castings can be superior to older forged parts.
I make custom knives I both grind from flat bar (actually preforged in the rolling processes to form the bars) and forge from bars or round stock. Forging has its own perils and requires careful controls not to destroy the steel in the process and to get its "grain" back into shape after the forging process causes it to have excessive grain growth. To forge you must raise the steels temp way above its critical temp to reshape. Temps above critical cause grain growth which is a bad thing, which must be reset by normalization before hardening and tempering.
By the way iron, wrought iron, cast iron and cast steel are all far different. Iron has no carbon and is relatively soft. Cast iron is actually very high carbon steel with way way more carbon than the iron can handle. This is usually induced in the smelting process where large amounts of carbon rich fuel are used to smelt. This extra carbon produces the large crystals you see when you break cast iron. Cast iron can be heat treated to become much more malleable though. Wrought iron is seldom produce now and was made by an old process where the metal was barely melted and the molten puddle was stirred to spread the slag in it and then poured. This produced a "stringy" steel that was tough and forged well. It is also the reason old bridges etc turned black. Cut a piece of actual wrought iron part way through and then bend it and it will break and look something like string cheese. LOL.
STEEL
All steel starts as a casting and contains carbon. Iron can "absorb" about .85% carbon. Mild steel is about .18%, tool steel start around .60% up to about 1.5% . Below .85% makes it a able to achieve a higher elastic limit and above can be used to become harder, but at the cost of elastic limit as the excess carbon tries to bond with other alloys such as vanadium, tungsten and the like to form carbides. Carbides are hard but brittle. They also setup in the structure boundaries and this cause increased "brittleness"
Hardness and toughness are not the same a spring is "tough" a metal shear blade is hard but not very "tough" it has a very low elastic limit and will break if flexed. Steel can be hardened and tempered to control its structures, hardness, elastic limits.
"Grain" is often spoken of and misunderstood by many. There is 2 types of what people commonly speak about as grain. There is the grain that occurs after a poured billet is produced. Some of the processes used to cast a billet produce amounts of small slag inclusions. These are spread and refined smaller and shaped in the rolling and forging processes used to produce basic shapes like bars and sheets. This is one type of grain and will remain in the steel as it is further shaped by machining forging or whatever. The other type of grain is actually structures. Steel exists in several grain structures that are produced and controlled by its heat treatment and alloy content. These structures are NOT molecular, but more crystalline. There are 3 basic structures and all can be controlled and modified by the heat treating processes.
Yes, I am a steel freak. I study it and learn about what REALLY happens in the processes. I know and converse occasionally with metallurgists and know and talk with some engineers on a regularly when I am working.
Want to learn about steel. I suggest the text books.
Metallurgy Fundamentals
Fundamentals of Metallurgy, 1st Edition
When did new processes become "BAD". We used to herald them. Just like MIM. 95% of the people who knock it don't actually have a real clue how it works or how good it is. I hear comment like it has plastic in it. LOL. Anything but the steel is long gone in the finished product. Ask an aerospace engineer what he thinks of MIM vs forged.
I cracks me up that guys who love S&Ws (I am one) which are forged recommend that if you want to shoot heavy loads to do it in a cast Ruger! Thompson uses castings and they are shooting high pressure rifle rounds regularly. Go figure.
A spring is made from cast steel. A cast steel billet is first rolled into bars ( a type of forging) then it is rolled into round stock. Larger dia. springs are made directly from round stock, smaller are drawn to dia. (again a type of forging) then formed. Annealing is done after forging then normalization, harden then temper. A S&W frame starts as a cast steel billet, then is rolled and then forged to shape. Even a piece of flat steel bar was "forged" when it was rolled from a billet. The grain thing about forging is a joke. A forging requires the piece to be annealed and normalized after forging or it would have extreme grain growth because of the elevated temps required for forging and be way brittle. Annealing, normalizing, hardening and tempering resets the grain structure and type of grain anyway.
On another note castings of steel have came a long ways. Steel is no longer cast in an open hearth. Quality steel castings are first smelted in an induction oven in an inert atmosphere. Then poured. This allows for very high quality castings without the inclusions or slag from older methods and produce very high quality.
The best alloys are produced in similar furnaces but, instead of cast into billets the molten metal is sprayed in an inert atmosphere producing small particles of steel that are EXTREMELY uniform in alloy content. These are then heated to near melting temps then pressed into a solid billet. Near perfect steel billets with no stratification. You are more apt to make this type of steel worse by forging it and not better.
The big advantage that forgings USED to have over steel castings was that the older methods of producing steel billets caused some inclusions and impurities in the billet. The initial forging of those billets into bars and sheets would break down and speed those problems out in the material. The smaller the sections the more the steel was worked and refined the problems areas became. Final forgings helped reduce these. With modern smelting and casting methods these inclusion and impurity areas are minimized prior to or without forging. Modern steel castings can be superior to older forged parts.
I make custom knives I both grind from flat bar (actually preforged in the rolling processes to form the bars) and forge from bars or round stock. Forging has its own perils and requires careful controls not to destroy the steel in the process and to get its "grain" back into shape after the forging process causes it to have excessive grain growth. To forge you must raise the steels temp way above its critical temp to reshape. Temps above critical cause grain growth which is a bad thing, which must be reset by normalization before hardening and tempering.
By the way iron, wrought iron, cast iron and cast steel are all far different. Iron has no carbon and is relatively soft. Cast iron is actually very high carbon steel with way way more carbon than the iron can handle. This is usually induced in the smelting process where large amounts of carbon rich fuel are used to smelt. This extra carbon produces the large crystals you see when you break cast iron. Cast iron can be heat treated to become much more malleable though. Wrought iron is seldom produce now and was made by an old process where the metal was barely melted and the molten puddle was stirred to spread the slag in it and then poured. This produced a "stringy" steel that was tough and forged well. It is also the reason old bridges etc turned black. Cut a piece of actual wrought iron part way through and then bend it and it will break and look something like string cheese. LOL.
STEEL
All steel starts as a casting and contains carbon. Iron can "absorb" about .85% carbon. Mild steel is about .18%, tool steel start around .60% up to about 1.5% . Below .85% makes it a able to achieve a higher elastic limit and above can be used to become harder, but at the cost of elastic limit as the excess carbon tries to bond with other alloys such as vanadium, tungsten and the like to form carbides. Carbides are hard but brittle. They also setup in the structure boundaries and this cause increased "brittleness"
Hardness and toughness are not the same a spring is "tough" a metal shear blade is hard but not very "tough" it has a very low elastic limit and will break if flexed. Steel can be hardened and tempered to control its structures, hardness, elastic limits.
"Grain" is often spoken of and misunderstood by many. There is 2 types of what people commonly speak about as grain. There is the grain that occurs after a poured billet is produced. Some of the processes used to cast a billet produce amounts of small slag inclusions. These are spread and refined smaller and shaped in the rolling and forging processes used to produce basic shapes like bars and sheets. This is one type of grain and will remain in the steel as it is further shaped by machining forging or whatever. The other type of grain is actually structures. Steel exists in several grain structures that are produced and controlled by its heat treatment and alloy content. These structures are NOT molecular, but more crystalline. There are 3 basic structures and all can be controlled and modified by the heat treating processes.
Yes, I am a steel freak. I study it and learn about what REALLY happens in the processes. I know and converse occasionally with metallurgists and know and talk with some engineers on a regularly when I am working.
Want to learn about steel. I suggest the text books.
Metallurgy Fundamentals
Fundamentals of Metallurgy, 1st Edition
When did new processes become "BAD". We used to herald them. Just like MIM. 95% of the people who knock it don't actually have a real clue how it works or how good it is. I hear comment like it has plastic in it. LOL. Anything but the steel is long gone in the finished product. Ask an aerospace engineer what he thinks of MIM vs forged.
I cracks me up that guys who love S&Ws (I am one) which are forged recommend that if you want to shoot heavy loads to do it in a cast Ruger! Thompson uses castings and they are shooting high pressure rifle rounds regularly. Go figure.
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