Comprehensive Performance of Ductile Iron Pipe Pricing

The process involves heating the workpiece to austenitize it, then immersing it in a salt bath or alkali bath near the M point (150℃~260℃), holding the temperature, and allowing the workpiece to reach the medium temperature uniformly before removing it to air cool. This is a quenching process for ductile iron pipe fittings to obtain martensitic structure, known as martensite grading quenching. This method is easier to operate than double medium quenching, significantly reducing internal stress in the workpiece, minimizing deformation and cracking, and resulting in more uniform hardness. It is mainly suitable for smaller, complexly shaped, or unevenly cross-sectioned carbon steel and alloy steel workpieces. The quenching process called bainite isothermal quenching involves heating the workpiece to austenitize it, then rapidly cooling it to the bainite transformation temperature range (260℃~240℃) and holding it isothermally to transform austenite into lower bainite. This method significantly reduces quenching stress and deformation, resulting in better strength, toughness, and wear resistance after bainite isothermal quenching, although the production cycle is longer and efficiency is lower. It is suitable for workpieces with complex shapes, high dimensional accuracy requirements, and both high hardness and toughness, such as various small cold and hot stamping dies, forming tools, and springs. The hardenability of steel refers to its ability to obtain a hardening layer depth during quenching under specified conditions (workpiece size, quenching medium), which is the depth of martensitic structure obtained during quenching under specified conditions. Hardenability is a primary thermal treatment property of steel. The depth of the hardening layer is the vertical distance from the quenched surface of the workpiece to the specified hardness value (usually 550HV). The deeper the hardening layer, the better the hardenability. The main factors affecting the hardenability of steel are its chemical composition; the eutectoid steel in ductile iron pipe fittings with a carbon content of 0.77% has good hardenability in carbon steel, and most alloy elements (except Co) can significantly improve the hardenability of steel. Additionally, the type of ductile iron pipe coating, quenching heating temperature, and the original microstructure of the steel also affect the hardenability. The hardenability of steel is a fundamental property and an important basis for rational material selection and correct heat treatment process planning.

For structural parts subjected to high loads (especially tension, compression, and shear forces), steels with good hardenability should be chosen; for shaft parts subjected to bending and torsional stresses, since the surface bears high stress while the core bears low stress, spheroidal cast iron pipes - GB spheroidal cast iron pipes - K9 spheroidal cast iron pipes - spheroidal cast iron pipe prices - spheroidal cast iron pipe manufacturers - XinTongDa Pipe Material Co., Ltd. can use steels with low hardenability. Weldments generally do not use high-hardness steels, as this can lead to quenching structures in the weld and heat-affected zones, causing workpiece deformation and cracking. The hardenability of steel is crucial for enhancing the mechanical properties of parts and realizing the potential of the steel. The hardenability of steel refers to its ability to achieve the highest hardness during quench hardening under ideal conditions. The hardenability of steel primarily depends on the carbon content. The higher the carbon content in the steel, the better the hardenability. Hardenability and hardenability are two distinct concepts. A steel with good hardenability may not have good hardenability, and vice versa. For instance, while carbon tool steel has a high hardness after quenching (good hardenability), its hardenability is low; certain low-alloy steels may have low hardness after quenching but good hardenability. Tempering is performed at temperatures above 500°C. The purpose is to achieve a comprehensive mechanical property of good strength, ductility, and toughness. The resulting structure is tempered sorbite, with a hardness of 200~350HBW. It is mainly suitable for various important load-bearing structural components, such as connecting rods, bolts, gears, and shaft parts. The composite heat treatment process of quenching and high-temperature tempering after the workpiece is quenched is called tempering treatment. The tempering treatment of spheroidal cast iron pipes not only serves as the final heat treatment for certain important parts, such as shafts, gears, connecting rods, and bolts, but also as a preliminary heat treatment for some precision parts, such as lead screws, measuring tools, and molds, to achieve a uniform and fine structure, reducing deformation during the final heat treatment process. In cases where tensile strength and hardness are roughly the same, the tempering treatment significantly improves plasticity and toughness compared to normalizing. This is because the structure of steel after tempering treatment is tempered sorbite, with carbides in granular form, whereas the structure obtained through normalizing is lamellar sorbite.

Quenching brittleness refers to the phenomenon of a significant decrease in toughness when a workpiece is tempered within certain temperature ranges after quenching. There are two types of quenching brittleness: quenching brittleness that occurs within the range of 250℃ to 350℃ is known as "Type I quenching brittleness," also referred to as "low-temperature quenching brittleness" or "irreversible quenching brittleness." It should be avoided in both carbon and alloy steels. After quenching, alloy steels containing elements like chromium, nickel, and manganese, when tempered within the range of 450℃ to 650℃ and then cooled slowly, are prone to "Type II quenching brittleness," also known as "high-temperature quenching brittleness" or "reversible quenching brittleness." To prevent the occurrence of Type II quenching brittleness, small parts can be rapidly cooled during tempering, while larger parts can be made from alloy steels containing tungsten or molybdenum. Many mechanical parts, such as gears, shafts, and cams, operate under conditions of friction, impact loads, and alternating loads, requiring the surface of spheroidal cast iron pipes to have high hardness and wear resistance, while the core needs to have sufficient strength and toughness. In such cases, the use of overall heat treatment methods is insufficient to meet the requirements, and surface heat treatment or carbonitriding, nitriding, and other chemical heat treatment methods are widely used in production.