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I represents a type of steel: it belongs to the category of carbon steel, with a carbon content of less than 1.35% (0.1%-1.2%). Apart from iron, carbon, and impurities such as silicon, manganese, phosphorus, and sulfur in specified limits, it contains no other alloying elements. The properties of carbon steel depend mainly on its carbon content. As the carbon content increases, the strength and hardness of steel rise, while its plasticity, toughness, and weldability decrease. Compared to other types of steel, carbon steel has been used the earliest, has a low cost, a wide range of properties, and is the most widely used. Suitable for media such as water, steam, air, hydrogen, ammonia, nitrogen, and petroleum products, with a nominal pressure of PN≤32.0 MPa and temperatures ranging from -30 to 425°C. Common grades include WC1, WCB, ZG25, as well as high-quality steels such as 20, 25, and 30. The low-alloy structural steel 16Mn II represents category II steel: it is a low-alloy steel, and an alloy steel with a total content of alloying elements less than 5% is considered a low-alloy steel. Low-alloy steel is a term used in contrast to carbon steel; it is created by adding one or several alloying elements to carbon steel in order to improve one or more of its properties. When the amount of these alloying elements added exceeds the typical levels used in the normal production of carbon steel, such steel is referred to as an alloy steel. When the total alloy content is below 5%, it is called low-alloy steel. Alloy steels with an alloy content between 5-10% are called medium-alloy steels ； Those with a content of over 10% are referred to as high-alloy steels. Type III represents three categories of steel: martensitic stainless steels and ferritic stainless steels. The standard martensitic stainless steels are types 403, 410, 414, 416, 416(Se), 420, 431, 440A, 440B, and 440C, which are magnetic ； The corrosion resistance of these steels comes from \"chromium\", with levels ranging from 11.5 to 18%. The higher the chromium content, the higher the carbon content required to ensure the formation of martensite during heat treatment. These three types of 440 stainless steel are rarely considered for welding applications, and filler metals with 440 composition are not readily available. Ferritic stainless steels (400 series) have a chromium content of 15% to 30% and possess a body-centered cubic crystal structure. These types of steel generally do not contain nickel; sometimes they also contain small amounts of elements such as Mo, Ti, and Nb. They feature a high thermal conductivity, a low coefficient of expansion, good oxidation resistance, and excellent resistance to stress corrosion. They are often used to manufacture components that can withstand corrosion caused by the atmosphere, water vapor, water, and oxidizing acids. Ferritic stainless steels not only have relatively low and stable prices, but also possess many unique features and advantages. It has been proven that in many applications where austenitic stainless steels (300 series) were previously the only viable options, ferritic stainless steels serve as an excellent alternative material. Ferritic stainless steels do not contain nickel; their main elements are chromium (>10%) and iron. Chromium is the element that confers high corrosion resistance to stainless steels, and its price remains relatively stable. Class IV refers to four types of steel: austenitic stainless steels, duplex stainless steels. Austenitic stainless steels are those that maintain an austenitic structure at room temperature. When steel contains about 18% Cr, 8%~10% Ni, and about 0.1% C, it has a stable austenitic structure. Austenitic chromium-nickel stainless steels include the well-known 18Cr-8Ni steel, as well as high Cr-Ni series steels that were developed by increasing the contents of Cr and Ni and adding elements such as Mo, Cu, Si, Nb, and Ti. Austenitic stainless steels are non-magnetic and possess high toughness and plasticity, but they have low strength; they cannot be strengthened through phase transformation and can only be strengthened through cold working. The addition of elements such as S, Ca, Se, and Te gives them good machinability. Duplex Stainless Steel, abbreviated as DSS, refers to a type of stainless steel in which ferrite and austenite each make up approximately 50%; generally, the proportion of the lesser present phase must be at least 30%. At low C levels, the Cr content ranges from 18% to 28%, while the Ni content ranges from 3% to 10%. Some steels also contain alloying elements such as Mo, Cu, Nb, Ti, and N. This type of steel possesses the characteristics of both austenitic and ferritic stainless steels. Compared to ferritic steels, it has higher plasticity and toughness, no room-temperature brittleness, and significantly improved resistance to intergranular corrosion as well as weldability. At the same time, it retains the 475°C brittleness and high thermal conductivity associated with ferritic stainless steels, as well as superplasticity. Compared to austenitic stainless steels, it has higher strength, as well as significantly improved resistance to intergranular corrosion and chloride stress corrosion. Duplex stainless steel possesses excellent pitting resistance and is also a nickel-saving stainless steel.