The nickel based alloy Inconel625 N06625 has excellent performance in corrosive environments in seaw

Mondo Science Updated on 2024-01-31

Methods of fracture mechanics.

The theory of fracture mechanics is based on the fact that there are defects or cracks in the material itself, and based on degenerative mechanics, it studies the propagation, instability, and crack arrest of defects or cracks. Through the quantitative analysis of the fracture, the fatigue crack propagation rate of the component in the actual work is obtained (the most widely applicable is the PARIS fatigue crack propagation rate formula), and the fatigue life of the zero and component is reasonably estimated, the crack formation time of the component is determined, and the manufacturing quality is evaluated, which is conducive to the correct analysis of the cause of the accident. In fact, this method solves many catastrophic low-stress brittle fracture problems in engineering, makes up for the shortcomings of conventional design methods, and has now become one of the important methods for failure analysis.

Fatigue fracture is the main mode of structural failure and component failure. According to statistics, 85%-90% of major accidents due to the failure of structural components are related to fatigue fracture. According to the point of view of fracture mechanics, the fatigue failure of metal structural parts is caused by the expansion of the main crack to the critical size, and the life of the structure depends on the initiation and propagation of the crack in the dangerous part of the structure. This method divides the fatigue fracture process into three stages. First, the initial crack of the component under the action of alternating force (there is still no unified standard for the definition of initial crack, and it is customary to be 0.).5^-1mm);Second, the crack begins to expand, resulting in a large macroscopic crack;The third is the rapid expansion of cracks, which quickly leads to damage, and its life is often very short, called instantaneous fracture life, which is not examined in engineering. According to the time of crack generation, the first stage can be defined as the initial crack life, and the second stage can be defined as the crack propagation life (customarily called the remaining life). The measure of life is generally expressed in terms of the number of cyclic loads experienced. The theory holds that the fatigue limit exists objectively, that is, when the amplitude of the cyclic load borne by the component is less than the fatigue limit of the component material, the component cannot be damaged due to cracks, that is, its life is infinite from the perspective of fatigue life. In addition, the fatigue life is not only related to the amplitude of the cyclic load and the physical and chemical properties of the material, but also related to the frequency of the load, so the fatigue life is divided into high cycle fatigue and low cycle fatigue.

The above-mentioned nominal stress method and local stress-strain method are all used to study the initial crack life. The study of remaining life is more complicated. It is currently a hot issue, and the engineering community has not yet proposed a universally accepted assessment method.

In recent years, the theory of fracture mechanics has been greatly developed, but it is still very imperfect, and the mechanism of fracture failure is not very clear, so it will take time to apply this theory to obtain a simple and accurate and reliable fatigue life calculation.

Let's take a lookPerformance parameters of Inconel625 alloy

Physical and chemical properties of Inconel625

Inconel625 Thermal Properties

The melting temperature range of Inconel625 is 1290 to 1350 [1].

Inconel625 thermal conductivity

Inconel625 specific heat capacity

Inconel625 linear expansion coefficient

inconel625 density = 844g/cm3。

Inconel625 electrical properties alloy resistivity

Inconel625 Magnetic Properties The alloy is non-magnetic.

Inconel625 chemical properties

Inconel625 oxidation resistance The alloy has excellent resistance to high-temperature oxidation, and the weight change of the alloy after circulating oxidation in the air medium at high temperature.

Inconel625 Corrosion Resistance The alloy has good seawater corrosion resistance. The alloy is also resistant to corrosion by various salt solutions. In addition, it has good resistance to nitric acid and phosphoric acid corrosion, and is also quite resistant to hydrochloric acid heated below the boiling point and sulfuric acid at low concentrations [2].

Inconel625 mechanical properties

Inconel625 Physical Properties

Inconel625 mechanical properties: (20 minimum value of mechanical properties tested).

Inconel625 production execution standard

Inconel625 Organizational Structure

Inconel625 phase change temperature

Inconel625 time-temperature-tissue transition curve

Microstructure of Inconel625 alloy The structure of the alloy in the solid solution state is an austenite matrix and a small amount of Tin, NBC, and M6C phases, and the precipitated phase after long-term aging of 650 900", δ, M23C6 and M6C. Over 650 700 long

It should be precipitated after the statute of limitations", so that the alloy at room temperature, high temperature strength significantly increased, plasticity decreased, but still maintained a high level;After 780 850 aging, the δ phase should be precipitated, although the strength has been improved, but the plasticity of the alloy has decreased more. There is only a small amount of precipitated phase after 900 aging, so the mechanical properties are similar to those of the solid solution state. The δ phase is orthogonal lamellar Ni3Nb with acicular Wechslitic tissue [1,7].

Inconel625 process performance and requirements

Inconel625 formability The alloy has good cold and hot formability. The heating temperature of ingot forging is 1120, the forging temperature is not less than 1030, and the forging temperature is not less than 930;When die forging, the final deformation should not be less than 15% 20%. The rolling heating temperature is 1120 1160, the opening rolling temperature is not less than 1050, the stop rolling temperature is not less than 930, the deformation of the sheet cold-rolled semi-finished product is 25% 30%, and the deformation of the finished product is not less than 30%. The quenching temperature of the intermediate and finished products is 1100 10 [1,8].

Inconel625 welding performance The alloy has good welding performance, and can be used for argon arc welding with tungsten electrode or this alloy as an additive under a protective atmosphere, and can also be used for brazing connection and resistance seam welding.

Inconel625 parts heat treatment process Stress relief: 900 ;Annealing: 930 1040, 1h;Solution treatment: 1090 1200, air-cooled or water-cooled. When the alloy is working at 650 °C, hot-rolled, cold-rolled or annealed materials can be used on request. When the working temperature is above 650, the annealing process can be used for parts that require good fatigue properties and tensile strength, and solution treatment can be used for parts that require good creep and durability.

Inconel625 surface treatment process When removing the oxide scale on the alloy surface, alkali washing is carried out first, and then pickled in nitric acid-hydrofluoric acid-aqueous solution.

Inconel 625 Cutting and Grinding Performance Tungsten carbide or high-speed steel tools should be used. The cutting tool used should have a positive rake angle. Water-based coolant is recommended for high-speed cutting, and viscous coolant is recommended for low-speed cutting.

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