I would like to ask about the processing process of forgings and the principles of forging

First break it, then dig it out... I’m not in manufacturing... This is my understanding of forged pipes

It is a processing method in which forging machinery is used to apply pressure to a metal blank, causing it to undergo plastic deformation in order to obtain a forged part with specific mechanical properties as well as a particular shape and size. Forging can eliminate defects such as as-cast porosity that occur during metal smelting, and optimize the microstructural structure. Meanwhile, since the complete metal flow patterns are preserved, the mechanical properties of forgings are generally superior to those of castings made from the same material. For the important components in related machinery that are subject to high loads and harsh operating conditions, forgings are often used, except for those with relatively simple shapes for which rolled sheets, profiles, or welded parts can be employed. Based on the way the blank is moved, forging can be divided into free forging, upsetting, extrusion, die forging, closed-die forging, and closed-upsetting. 　　①Free forging. Metal is deformed between two upper and lower anvil blocks using impact force or pressure to obtain the desired forged piece; the main methods are manual forging and mechanical forging. 　　②Die forging. Die forging is further divided into open die forging and closed die forging. The metal blank is deformed under pressure within a die cavity of a specific shape to produce the forged part; it can also be categorized into cold heading, roll forging, radial forging, extrusion, and so on. Materials used for forging are mainly carbon steels and alloy steels of various compositions, followed by aluminum, magnesium, copper, titanium, and their alloys. The original forms of the material include bars, ingots, metal powder, and liquid metal. The ratio of the cross-sectional area of a metal before deformation to its cross-sectional area after deformation is called the forging ratio. Choosing the forging ratio correctly, selecting appropriate heating temperatures and holding times, determining proper initial and final forging temperatures, as well as choosing suitable deformation amounts and rates are all crucial for improving product quality and reducing costs. 　　Generally, small and medium-sized forgings use circular or square bars as blanks. The billets have a uniform and good grain structure and mechanical properties, accurate shape and size, as well as good surface quality, which facilitates organized mass production. As long as the heating temperature and deformation conditions are properly controlled, high-performance forgings can be produced without excessive forging deformation. 　　Ingots are used only for large forgings. The ingot has a cast structure with large columnar grains and a porous center. Therefore, large plastic deformation is necessary to break the columnar grains into fine grains and compact the porosity, in order to achieve an excellent metal microstructure and mechanical properties. 　　The powder metallurgy preforms, which are formed through pressing and sintering, can be turned into powder forgings via flashless die forging at high temperature. The forging powder has a density close to that of conventional die forgings, exhibits good mechanical properties, and offers high precision, which reduces the need for subsequent machining. Powder forgings have a uniform internal structure without segregation, and can be used to manufacture components such as small gears. However, the price of powder is much higher than that of ordinary bars, which limits its use in production. By applying a static pressure to the liquid metal poured into the die cavity, causing it to solidify, crystallize, flow, undergo plastic deformation, and take shape under this pressure, die forgings with the desired shape and properties can be obtained. Liquid metal die forging is a forming method that lies between die casting and die forging, and is particularly suitable for complex thin-walled parts that are difficult to form using conventional die forging. 　　Different forging methods have distinct processes, among which the process for hot die forging is the longest. The general sequence is: cutting the forging billet ； Forge billet heating ； Roll forging blank ； Die forging ； trimming ； Intermediate inspection to check the dimensions and surface defects of the forgings ； Heat treatment of forgings, used to eliminate forging stresses and improve machinability ； Cleaning mainly involves removing the surface oxide scale ； Correction ； Inspection: Generally, forged parts are subject to visual and hardness checks; important forged parts also require tests such as chemical composition analysis, mechanical properties assessment, residual stress evaluation, as well as non-destructive testing. 　　In addition to the usual materials such as carbon steels and alloy steels of various compositions, forging is also used for metals like aluminum, magnesium, copper, titanium and their alloys. Deformed alloys based on iron-based superalloys, nickel-based superalloys, and cobalt-based superalloys are likewise forged or rolled; however, these alloys present greater challenges for forging due to their relatively narrow plasticity zones. There are strict requirements regarding the heating temperature, as well as the starting and finishing temperatures for forging these different materials. Forging metal can improve its microstructure and mechanical properties. After being thermally deformed by forging, the casting structure undergoes deformation and recrystallization of the metal; as a result, the original coarse dendritic and columnar grains are transformed into equiaxed recrystallized grains that are finer in size and more uniform. This process compresses and fuses any existing segregation, porosity, gas holes, or inclusions within the steel ingot, making its structure denser and improving the metal’s plasticity and mechanical properties. 　　The mechanical properties of castings are lower than those of forgings made from the same material. Furthermore, forging processes ensure the continuity of the metal fiber structure, allowing the fiber pattern in the forged part to match its shape; the metal flow lines remain intact, which ensures that the parts possess excellent mechanical properties and a long service life. Forged parts produced using techniques such as precision die forging, cold extrusion, and warm extrusion are incomparable to cast parts

1.25Gr0.5Mo, inner diameter 4200mm, thickness 180mm, length 4500 – why not consider using sheet metal?

Personally, I think a forging of such large size cannot be forged, or the cost would be too high. You might still be able to make some by piecing together a few sections. As a whole, I don’t see any!