Comprehensive Performance of Ductile Iron Pipe Pricing

After the workpiece is heated and austenitized, it is first immersed in a salt bath or alkali bath near the M point temperature (150℃~260℃), with a holding time until the entire workpiece reaches the medium temperature. Then, it is removed and air-cooled. The quenching process for ductile iron pipe fittings to obtain martensitic structure is called martensitic 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 rapid cooling the workpiece to the bainite transformation temperature range (260℃~240℃) and holding 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 complexly shaped workpieces with high dimensional accuracy requirements and both 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 achieve a certain depth of hardening layer under specified conditions (workpiece size, quenching medium), i.e., 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 with 0.77% carbon content in ductile iron pipe fittings has good hardenability in carbon steel. Most alloy elements (except Co) can significantly improve the hardenability of steel. In addition,What are the types of coatings for ductile iron pipes?The quenching heating temperature and the original microstructure of the steel also affect the steel's hardenability. The hardenability of steel is a basic property, which is an important basis for rational material selection and the correct formulation of heat treatment processes.

For structural components subjected to high loads (especially tensile, compressive, and shear forces), it is advisable to choose steel with good hardenability; for shaft components subjected to bending and torsional stresses, due to the high stress on the surface and low stress on the core, 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 opt for steel with low hardenability. Weldments generally do not use high hardenability steel, as it may 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 components and realizing the potential of steel. The hardenability of steel refers to its ability to achieve the highest hardness during quench hardening under ideal conditions, primarily dependent on the carbon content in the steel. The higher the carbon content, 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, although carbon tool steel has a high hardness after quenching (good hardenability), its hardenability is low. Certain low-alloy steels may not have high hardness after quenching but exhibit good hardenability. Tempering is performed at temperatures above 500°C to achieve a balance of strength, ductility, and toughness. The resulting structure is the tempered sorbite with a hardness of 200~350 HBW. It is mainly suitable for critical load-bearing structural components such as connecting rods, bolts, gears, and shaft components. The composite heat treatment process of quenching and high-temperature tempering after quenching is known as normalization. The heat treatment of spheroidal cast iron pipes not only serves as the final heat treatment for certain critical components like shafts, gears, connecting rods, and bolts but also as preliminary heat treatment for precision components such as lead screws, measuring tools, and molds, ensuring uniform and fine structures to reduce deformation during final heat treatment. In cases where tensile strength and hardness are roughly similar, the plasticity and toughness of normalized steel are significantly higher than those of normalized steel, as the structure of the steel after normalization is the tempered sorbite, with carbides in granular form, whereas the structure obtained by normalizing is lamellar sorbite.

Quenching brittleness refers to the phenomenon where the toughness of a workpiece significantly decreases during tempering within certain temperature ranges after quenching. There are two types of tempering brittleness: tempering brittleness that occurs within the temperature range of 250℃ to 350℃ is known as the first type of tempering brittleness, also referred to as "low-temperature tempering brittleness" or "irreversible tempering brittleness." This type of brittleness should be avoided in both carbon steel and alloy steel. For alloy steels containing elements like chromium, nickel, and manganese, tempering within the range of 450℃ to 650℃ followed by slow cooling is prone to the second type of tempering brittleness, also known as "high-temperature tempering brittleness" or "reversible tempering brittleness." To prevent the occurrence of the second type of tempering brittleness, small parts can be rapidly cooled during tempering, while larger parts can be made from alloy steels containing tungsten or molybdenum. Many mechanical components, 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 possess sufficient strength and toughness. In such cases, the use of whole-body heat treatment methods is insufficient to meet the requirements, and surface heat treatment or carbonitriding, nitriding, and other chemical heat treatment methods are widely employed in production.