Steel is among the most widely used materials on Earth. Modern metallurgy offers a range of approaches to manufacturing and processing steels, each suitable for its own types of materials and purposes. The following paper presents an overview of steel as a highly versatile material and discusses metal strengthening practices, typical welding tools, and causes of corrosion in stainless welds.
Steel possesses a number of characteristics that contribute to its versatility. First, steel is a cost-efficient material, offering a range of properties that are superior in comparison to other popular materials. For instance, structural steel constructions are lighter than their wooden analogs. Second, it is highly durable and naturally resistant to many environmental effects such as decay and pests, eliminating the need for maintenance and repairs. By extension, steel offers substantial cost savings in the long term. Finally, it is possible to manufacture a wide array of steels with desirable mechanical and chemical properties, increasing its area of application. Finally, it allows for the production of relatively complex and aesthetically pleasing products on a mass scale, making it suitable for utilization in many industries.
Modern metallurgy utilizes several methods of material strengthening. One of the most widely recognized methods is solution strengthening, also referred to as alloying. For solution strengthening, one of the metals is combined with one or more additional ones. On a molecular level, the atoms of additional metals take the unoccupied spaces in a crystalline structure, creating an interstitial defect (Pelleg, 2013). The introduction of new atoms changes the mechanical properties of a lattice by introducing distortions that limit dislocation movement of host atoms. Specifically, atoms that are smaller those of the host metal improves tensile strength whereas the larger ones contribute to compressive strength.
The second widely used method is strain hardening, also referred to as work hardening. In this method, strengthening is achieved through plastic deformation of metal. During the process, dislocations are formed or multiplied in the crystal structure of a metal, which increases its yield strength, hardness, and tensile strength. In addition, the distance between dislocations is decreased, further enhancing the effect.
The third method is strengthening through grain size reduction. This method is used for polycrystalline metal, in which mechanical properties are determined primarily by grain size. Typically, grains have a common boundary but are oriented differently. As a result, the dislocations that pass through such grains need to change direction, which serves as an impediment to dislocation motion. The effect is enhanced by the misalignment of slip planes in the structure. Thus, the reduction of grain size results in higher total grain boundary and, by extension, yield strength.
Less common ways of strengthening metals include precipitation hardening and transformation hardening. The former is a heat treatment procedure aimed at introducing impurities at a particle level, impeding movement of dislocations and, by extension, reducing plasticity of the material. The latter incorporates complex heat treatment procedures intended for the formation of ferrite and martensite and is reserved primarily for certain types of high-strength steels.
Welding Instruments
Welding is the process of joining metals or other materials through fusion. Since fusion requires melting of the base materials, the process usually requires tools capable of heating metal to melting temperature. Currently, a number of solutions with different principles of operation are used for the purpose. The first is oxy-fuel welding, in which the heat is supplied by a fuel that burns at high temperatures. Common fuel choices include propane, butane, and acetylene, with the addition of pure oxygen for increased flamer temperature. An apparatus for oxy-fuel welding essentially consists of two gas containers connected to a torch via flexible hoses (TWI, n.d.).
The second type is shielded metal arc welding (SMAW), in which the base metal is molten by an electric arc formed between an apparatus and a metal piece. Most commonly, disposable electrodes covered with flux are used to create an arc. In the process, an electrode is molten whereas the flux is vaporized to form an inert gas that protects the junction point from atmospheric effects and oxidization. A typical SMAW apparatus consists of an electrode (fixed in an electrode holder) connected to a power source via flexible cables, and a ground clamp. A variation of SMAW exists in which shielding gas is supplied separately through welding gun.
The third type of equipment, known as gas tungsten arc welding (GTAW), utilizes a non-consumable tungsten electrode. Unlike SMAW, GTAW requires an additional filler in the form of a consumable rod. A typical GTAW apparatus is largely similar in construction to a SMAW one with an important addition of a source of shielding gas necessary for protecting the welding spot (Miller Welds, 2017).
Corrosion in stainless welds, more commonly referred to as weld decay, is a type of corrosion observed in stainless steels and certain alloys. The corrosion usually occurs in the immediate proximity to the joint, known as a heat-affected zone (Mwiks, 2017). The cause of the corrosion is the precipitation of chromium carbides that occurs near the grain boundary. As a result, a zone depleted of chromium becomes prone to structural damage such as cracks and, after application of tensile strength, decay.
As can be seen, steel is a highly versatile material, in part due to its variety. Modern metallurgy offers a wide number of approaches to strengthening and welding metals used for specific purposes and tasks. This variety provides a range of options for creating cost-efficient, reliable, and aesthetically pleasing products.
References
Miller Welds. (2017). Guidelines for gas tungsten arc welding (GTAW). Web.
Mwiks, K. (2017).Causes and prevention of corrosion on welded joints. Web.
Pelleg, J. (2013). Mechanical properties of materials. Chicago, IL: Springer.
TWI. (n.d.). Equipment for oxyacetylene welding. Web.