Forging is a manufacturing process for shaping metal. Forging involves a series of compression under locally applied pressure, often delivered by a power hammer or a die. This manufacturing process typically delivers a variety of benefits, including increased ductility, high tensile and fatigue strength, low porosity along the surface, and fine grain structure.
The materials of steel forging include stainless steel (SS303, SS304, SS316, ect.), carbon steel (1020, 1035, 1045, A105, Q235, 20CrMnTi, ect.) and alloy steel (20Cr, 20CrMo, 30CrMo, 35CrMo, 42CrMo, ect.). Forged steel is an alloy mixture of carbon and iron. During the forging process of steel, the steel is heated until it reaches a specific malleability and is molded into a specific shape, using locally applied force. This process allows for shaping without cracking and strengthens the resulting steel product.
CATEGORIES OF FORGED STEEL
Steel forgings are classified by their forming temperatures. The three classifications of steel forgings are:
The narrowness of the tolerances achievable changes with the forming temperature, with the narrowest tolerances achievable being cold forging.
Drop forging is a process in which a hammer is raised and dropped onto a metal piece to deform it into the shape of the die. Forged LR90 and SR90* elbows are examples of products made by drop forging. Drop forged steel can also be further categorized into two basic types. These basic types are open die forging and closed die forging.
Open Die Forging
Open die forging is also known as free forging. It is typically used on large parts, like forged rollers and forged cylinders. Railway and aircraft industries rely on open die forging.
Open die forging is a process in which a metal piece is hammered or stamped by multiple dies that do not enclose the piece completely. The series of movements made by the dies create the desired shape of the metal piece. Additional machining is often required to achieve accuracies. Open die forging benefits include less material waste, a finer grain structure, higher strength, longer life, lower cost and reduced chances of voids.
Closed Die Forging
In closed die forging, a metal piece, which is pre-cut to the desired shape, is enclosed between two dies that move toward each other. The heated metal piece is placed in the bottom die.
Another name for closed die forging is impression forging. Closed die forging is often used on small parts, such as forged flanges and forged fittings. Closed die forging is a popular method used in the petroleum, mining and automotive industries.
Closed die forging is not economical for short runs because setup costs and die production costs tend to be high. Additionally, closed die forging can present a dangerous work environment. However, with closed die forging, the finished product is stronger, tighter and displays a better surface finish. Plus, the need for additional machining is either minimal or nonexistent.
FORGED STEEL PROPERTIES
The properties of forged steel are quite significant and stand out among those of other treatments, like casting and machining. The strength of a steel forging is anisotropic. During the forging process, the internal grain structure of the steel is shaped along with the part, giving it a continuous texture variation throughout the part. As a result, forged steel offers greater toughness, strength, and durability, and can accommodate high loads and extreme stresses. It is less likely to be shattered upon contact with other objects.
The size and thickness of the steel that can be forged is limited, but the compositional and structural uniformity of steel forgings is a notable benefit. The process of forging calls for controlled, deliberate steps with each forging. This allows for consistent mechanical properties.
THE APPLICATION OF FORGED STEEL
The high degree of reliability, strength, tolerance, and resilience makes forged steel appealing across every industry. For instance, forged steel is used to make pulleys in the automotive industry, pipe fittings in the petroleum and natural gas industry, and fasteners in the aircraft industry. Forged steel is also suitable for mechanical and industrial parts. Forged steel fittings come in unions, reducers, outlets, caps, inserts, couplings, bushings, plugs, elbows, street elbows, crosses and tees (i.e., tee, red tee, conc red., etc.).
THE DIFFERENCE BETWEEN CASTING AND FORGING
Casting requires heating a metal piece until it reaches a molten state, before shaping it with a mold or a vessel. Forging, on the other hand, uses thermal or mechanical force to change the shape of a material, while it remains in a solid state. Forging, by nature, has lower occurrences of shrinkage, porosity, cavities and cold pour defects.
Casting is ideal for parts that are too large in size or too intricate to forge. The tooling used in casting is often less expensive than forge dies. Forging, however, usually produces more strength and reliability than casting. Forged steel will also better handle impact than steel castings.
*LR90 stands for long radius, 90º elbow and SR90 stands short radius, 90º elbow.