What are the aspects involved in steel processing?

(1) Mechanical properties of steel: The mechanical properties of structural steel include yield strength, tensile strength, elongation, and low-temperature impact toughness. These criteria should meet the requirements of the Code for Design of Steel Structures, except that low-temperature impact toughness is only required to be tested when the structure may operate in low-temperature environments. The determination of the mechanical properties of steel must comply with the \"Regulations on Sampling for Testing the Mechanical and Process Properties of Steel\" (GB2975-82). (2) Chemical composition of steel: It is related to factors such as the workability, toughness, and durability of steel. The main factors include the carbon content, the content of alloying elements, and the allowable limits for impurity elements such as sulfur and phosphorus, all of which must meet the requirements of the standard (GB222-84). (3) Processability: Processability mainly includes weldability and machinability. Weldability is related to carbon content or carbon equivalent (in low-alloy steel), and can be determined through weldability tests. The formability is determined through a cold bending test. Compliant with (GB232-88) standards. (4) Geometric dimension deviation: The deviation of the external dimensions of steel materials (steel plates, section steels, round bars, steel pipes) from their theoretical dimensions must be within the allowable range. The allowable deviation values can be referred to in the standards **GB709-88, GB706-88, GB787-88, GB978-88, GB707-88, GB816-87, etc. (5) Surface defects of steel: The surface of the steel shall be free from bubbles, scabs, pulls, cracks, folds, inclusions, and embedded scale. These defects must be removed, and after removal, the depth of the depression in that area shall not exceed the negative deviation value of the steel thickness. Furthermore, when the surface of the steel material has defects such as rust, pitting, or scratches, the depth of these defects shall not exceed 1/2 of the negative deviation value of the steel’s thickness. (6) Mechanical cutting: Cutting is carried out using mechanical forces such as shearing, sawing, or grinding; the corresponding tools include plate shears, sawing machines, and grinders. This method is suitable for making straight cuts in steel plates or profiles with a thickness of 12–16 mm or less. (7) Gas cutting: Metal is heated and melted using flames such as oxygen-acetylene, propane, or liquefied petroleum gas, and the molten metal is blown away with compressed air to separate the metal; this method is suitable for cutting curves and multiple sections at once. ） (8) Plasma cutting: Cutting is achieved using a plasma arc; it is suitable for cutting materials with high melting points such as stainless steel. (9) Hot forming: It refers to the processing of steel by heating it to a certain temperature first. This method is suitable for shaping, bending, and correcting workpieces that cannot be done at room temperature. The termination temperature for heat processing shall not be lower than 700°C. When the heating temperature is between 200 and 300°C, the steel becomes brittle at low temperatures; hammering and bending are strictly prohibited. Steel with a carbon content outside the range of low-carbon steel generally cannot be hot-worked. (10) Cold forming: It is carried out at room temperature. The material undergoes the desired permanent deformation due to external forces exceeding its yield strength, or certain parts of the material separate from it as required when the external forces exceed its ultimate strength. Cold working always tends to make materials harder and more brittle; therefore, heat treatment can be used to restore the steel to its normal state or to remove the parts at the edges that have become severely hardened. Carbon steel shall not be cold-worked when the ambient temperature is below -16°C. Low-alloy steel shall not be processed when the temperature is below -12°C. (11) Bending processing: A manufacturing method that, in accordance with design requirements, uses processing equipment and appropriate tooling to bend sheets or steel profiles into a specific shape. Cold bending is suitable for thin sheets and small steel pieces ； Hot bending is suitable for thicker sheets as well as more complex components and sections, with a hot bending temperature of 950–1100°C. (12) Sheet bending: A method in which, under external force, the outer fibers of a flat steel sheet are stretched while the inner fibers are shortened, resulting in bending deformation. Coiling is done by a coiler. Depending on the temperature of the material, it is further divided into cold-rolled and hot-rolled sheets. Coiled plates are mainly used for welding circular tube columns, pipes, air tanks, etc. (13) Folding: The process of bending the edges of steel structural components at a certain angle or into a specific shape is called folding. Bending is generally used for thin plate components. Folding is usually done using a folding machine, with appropriate molds. (14) Molding: Molding is a method of shaping steel using molds in pressure equipment. Specific methods include blank forming, stamping forming, bending, rolling, drawing, rolling, etc.

(15) Edge trimming: Edge trimming involves removing the excess metal from the edge by striking the cutting tool, thereby creating a bevel. Edge shoveling can be done manually or with air power, with air-powered tools being used for the latter. The precision of edge shaving is low; it is generally used for processing grooves with low requirements and in small quantities. (16) Edge profiling: During edge profiling, the workpiece is pressed firmly, and the profiling tool moves back and forth along the edge to be processed, thereby creating a bevel. Edge shaving can be done on straight or beveled edges. (17) Edge milling: Edge milling is similar to planing, except that the tool holder and planing tool in the feed box of the planer are replaced by disc milling cutters; thus, while moving linearly along the edge, the milling cutter also rotates, resulting in higher processing efficiency. (18) Carbon arc gas gouging: A carbon rod is used as an electrode, and an arc is generated between it and the metal to be gouged, heating the metal to a molten state; the molten metal is then blown away using compressed air. It has high work efficiency. (19) Site sample method: Scale models of the components are placed on the assembly platform at a 1:1 ratio, and then the components are assembled based on their positions on these scale models. (20) Molding replication method: First, a single-sided structure is assembled using the sample method and spot welding is applied; then it is turned over to serve as a replication mold, on which another single-sided structure is assembled. Applicable to truss structures with symmetric cross-sections. (21) Vertical installation: Depending on the characteristics of the components and the stable positions of their parts, assembly from top to bottom or from bottom to top is chosen; this method is suitable for structures that can be placed stably and are not very tall. (22) Horizontal installation: Components are assembled in a horizontal position. Used for slender members with a small cross-section but large length. (23) Membrane assembly method: Position the parts of the component using a membrane and assemble them in their intended positions. Used to manufacture products in large batches with high precision. (24) Arc welding: The process of fusing metals using the heat generated by the arc between the electrode and the workpiece is called arc welding. Arc welding is divided into manual welding, automatic welding, semi-automatic welding, and gas shielded welding. (25) Resistance welding: Current is passed through two weld pieces in contact; the resistance is highest at the point of contact, and the flow of current generates high temperatures that cause the material to become semi-molten, allowing it to be fused together under applied pressure. It is generally used for welding round steel or spot-welding steel plates. (26) Electroslag welding: Welding is carried out by melting metal using the resistive heat generated by an electric current passing through the slag. Such as the penetration welding of stiffening plates at the upper and lower flanges of the connecting beam inside the column when used for a rigid connection between box columns and beams. (27) Manual welding: Arc welding that is carried out entirely by hand; it has low productivity, the quality depends on the welder’s skills, and stability is poor. However, it is flexible and suitable for shorter, more complex welds or welding in field conditions. (28) Submerged arc automatic welding: During welding, the arc is buried beneath a powdered flux; the flux is automatically applied mechanically while the welding wire is fed forward. Suitable for longer welds. Good weld quality and high efficiency. (29) Gas shielded welding: It uses CO2 or argon to protect the metal that is being welded by the arc; both the wire and the gas are fed automatically, with only the welding torch needing to be moved manually. It belongs to the semi-automatic welding category, offering good welding quality and high efficiency. (30) Shot blasting: In shot blasting, steel shots with a particle size of 0.8–2.0 mm are drawn in through the center of the impeller of the blasting machine and then ejected at high speed from the tip of the impeller toward the surface of the steel structures that need rust prevention treatment, thereby achieving mechanical rust removal. This method features high rust removal efficiency, low cost, and minimal pollution.