TP439 Stainless steel in 800 ℃ Initial Oxidation Behavior in High-Temperature Water Vapor

Research Background

TP439 It is a ferritic stainless steel (high Cr , containing stabilizing elements You ), owing to its excellent comprehensive mechanical properties, intergranular corrosion resistance, low coefficient of thermal expansion, and high thermal conductivity, it is widely used as tubing material for high-pressure heaters in nuclear power plants. The typical service conditions involve high-temperature, high-pressure steam environments, in which oxidation is one of the primary causes of failure, such as leakage.

Research Methods

1. Experimental Materials

TP439 Ferritic stainless steel, after wire-cutting, is processed into dimensions of 16 times 15 times 1.5mm of rectangular specimens.

2. Water Oxygen Experiment

800 ℃, the atmosphere is 90%H₂ O+10%Ar ( Volume fraction %) , maintain the gas flow rate at 0.15mm³/min . Oxidize separately 15、30、45、60、90、120、240、480、720、1440 and 2880min The oxidized samples were weighed using a high-precision balance to obtain the oxidation kinetics curve.

3. Oxidation Kinetics

1. Initial stage 0-2h : Rapid oxidation-induced weight gain, following a linear trend.
2. Phase Two 2-48h : The oxidation rate slows down, following a parabolic law.

4. Thermodynamically, Cr than Fe More prone to oxidation. Over time, Cr Diffuses from the matrix to the surface, gradually forming a more protective, enriched Cr Oxide layer

Figure . TP439 Stainless steel in 800 ℃ In high-temperature steam 48 and 2 h Oxidation kinetic curve

Research Results

(1) TP439 In the initial stage, stainless steel exhibits a relatively high oxidation rate, and its oxidation kinetics conform to linear oxidation kinetics, with a linear rate constant. k _l For 5.21×10 ^-2 mg·cm ^-2 ·h ^-1 ; The oxidation kinetics in the second stage follow a parabolic growth law, with a parabolic rate constant k _p For 1.54×10 ^-3 mg·cm ^-2 ·h ^-1 。

(2) TP439 Stainless steel oxidation 2 h After, X-ray diffraction A weak signal has been detected. (Cr ， Fe) ₂ O ₃、 Cr ₂ O ₃ and Fe ₂ O ₃ Diffraction peak; oxidation 48 h Subsequently, the main components of the oxidation products are (Cr ， Fe) ₂ O ₃ and a small amount of Cr ₂ O ₃、 Fe ₂ O ₃、 FeCr ₂ O ₄ Spinel oxide.

(3) In 800 ℃ In a high-temperature steam environment, TP439 In the initial stage of oxidation, the oxidation process in stainless steel is governed by interfacial reactions. As the oxide film continues to thicken, ion diffusion within the film is increasingly impeded, and the rate-controlling step shifts from interfacial reaction to diffusion. Since grain boundaries serve as rapid diffusion pathways for atomic species, network-like oxide formations tend to develop along grain boundaries during oxidation; however, with prolonged oxidation, these network structures become less pronounced.

Tianjin Zhonghuan launches High-temperature static / High-Speed Water-Oxygen Corrosion Testing Equipment Series , using laboratory testing methods , Accurately simulating the high-temperature, high water-vapor partial-pressure, and high water-vapor-velocity conditions of a turboengine operating environment, this equipment conducts cyclic tests on material thermal corrosion and steam oxidation corrosion to properly evaluate the material’s thermochemical stability. The system comprises an intake-control unit, a liquid-precision-dosing unit for precise control of liquid feed, a heated evaporator that ensures uniform vaporization of water and thorough gas mixing, trace-heated piping, and a heating reactor, among other components. It is primarily used for : Various functional ceramics, structural ceramics and ceramic matrix composites, ultra-high-temperature alloy materials, and high-temperature thermal barrier coatings, among others.

Static water oxygen:

·Precise and controllable vaporization of liquid water

·Multiple flow ranges available for the carrier gas: 300ml/1000ml/3000ml

· Maximum temperature options: 1200℃/1600℃/1800℃

· Multiple process sets can be preconfigured, with each set 50 Program segment Control

High-speed water oxygen:

·Achieving steam impingement: 160m/s ( Calculated value)

·Precise control of liquid inflow

·Uniform vaporization of liquid water and gas mixing