Oxygen and nitrogen analyzer (oxygen-nitrogen-hydrogen analyzer)
Oxygen and nitrogen analyzer (oxygen-nitrogen-hydrogen analyzer)
Oxygen-nitrogen instrument testing principle
1, Determination of oxygen:
Basically, the production site uses an infrared oxygen analyzer to determine the oxygen content. The sample dropped into the spectrally pure graphite crucible by the sampler. The sample melted in the high temperature crucible. The oxygen in the sample reacted with the carbon on the hot crucible surface. Most of the carbon monoxide was generated, and a very small amount of carbon dioxide was generated. The gas is sent to the catalyst furnace by the air pump, CO is converted to CO2, and then the CO2 is detected by the infrared cell and converted to oxygen by computer processing.
2. Determination of nitrogen and hydrogen:
Both nitrogen and hydrogen are extracted in molecular form and are generally detected by thermal conductivity cells. With individual instruments, the detection of hydrogen is first converted into water vapor, and the concentration of water vapor is detected with an infrared detection cell to achieve the purpose of detecting hydrogen.
Oxygen,nitrogen and hydrogen hazards to steel products
1, the harm of oxygen:
Oxygen, like hydrogen, can have an adverse effect on the mechanical properties of steel. Not only is the concentration of oxygen, but also the number, type, and distribution of oxygen-containing inclusions are also important. Such inclusions refer to metal oxides, silicates, aluminates, oxysulfides, and similar inclusion compounds. Deoxidation is required for steelmaking because during the solidification reaction of oxygen and carbon in solution produces carbon monoxide, which can cause bubbles. In addition, oxygen can be precipitated from the solution as FeO, MnO, and other oxide inclusions during cooling, thereby impairing its hot or cold workability, as well as its ductility, toughness, fatigue strength, and machining properties of the steel. Oxygen and nitrogen and carbon can also cause aging or spontaneous increase in hardness at room temperature. For cast iron, when the ingot is solidifying, the oxides and carbon can react, thus resulting in product porosity and product embrittlement.
2, the harm or role of nitrogen:
Nitrogen can not be attributed to harmful elements in general, because some special steels are purposely added nitrogen.
All steels contain nitrogen. The amount of nitrogen present depends on the production method of the steel, the type, quantity, and mode of addition of the alloying elements, the method of casting the steel, and whether or not nitrogen is intentionally added. Some grades of stainless steel, the appropriate increase in N content, can reduce the use of Cr, Cr is relatively expensive, this method can effectively reduce costs.
Most of the nitrogen in steel is in the form of metal nitrides.
For example, after a certain period of time, when the steel is strained and aged, it cannot be deep-drawn (such as deep-drawing for automobile protection plates) because the steel will tear and cannot be uniformly stretched in all directions. This is due to the large grains and the deposition of Fe4N at the grain boundaries.
Another example: In stainless steel, the formation of chromium nitride (Cr2N) at the grain boundaries depletes the chromium contained at the interface and causes so-called intergranular corrosion. The addition of titanium, which preferentially forms titanium nitride, can prevent this harmful effect.
3, hydrogen hazards:
When the hydrogen content in the steel is greater than 2 ppm, hydrogen plays an important role in the so-called "scale flake" phenomenon. This phenomenon is generally more pronounced when internal cracking and fracture occur during cooling after rolling and forging, and this phenomenon is more often found in large sections or high carbon steels. Due to the existence of internal stress, this kind of defect will cause the large rotor to crack during the use of the engine.
When hydrogen in cast iron is more than 2 ppm, pores or general porosity tend to occur, and the porosity caused by this hydrogen will cause iron embrittlement.
"Hydrogen embrittlement" occurs mainly in martensitic steels and is not very pronounced in ferrite steels, but it is virtually unclear in austenitic steels. In addition, hydrogen embrittlement generally increases with hardness and carbon content.
Oxygen, nitrogen and hydrogen in iron and steel
1, the presence of oxygen:
Oxygen coexists in a combined state and a free state. Generally, the free state is small, and is mainly in the form of Fe2O3, Fe3O4, FeO and metal oxide inclusions, silicates, aluminates, oxysulfides, and similar inclusion compounds. The total oxygen content of the instrument is measured by T[O].
2, the presence of nitrogen forms:
A portion of the nitrogen in the steel is in the form of metal nitrides or carbonitrides; today most of the elements added to the special alloy steels can form nitrides under appropriate conditions. These elements include manganese, aluminum, boron, chromium, vanadium, molybdenum, titanium, tungsten, tantalum, niobium, zirconium, silicon, and rare earths. Considering that many nitride-forming elements have several simple or complex nitrides, up to 70 nitrides may be formed in the steel. Another part of the nitrogen is dissolved in the steel as a nitrogen atom. In rare cases, nitrogen is trapped in bubbles in the form of molecules or adsorbed on the surface of steel.
3, the existence of hydrogen form:
Hydrogen in steel is in the form of hydrogen atoms. At high temperatures, two hydrogen atoms easily form a hydrogen molecule. Hydrogen atoms are very active and naturally they form hydrogen molecules that slowly release.
Sources of oxygen, nitrogen, and hydrogen in steel
1, the source of oxygen:
Oxygen is present in molten steel in a certain amount at the end of the smelting of various steelmaking furnaces. Oxygen is supplied during the production process, because during the steelmaking process, the first is the oxidation process, which removes [P], removes [S], removes [Si]. Both [C] need to supply oxygen to hot metal. However, with the progress of the steelmaking process, despite the ever-changing process, the relationship between the [C] and [O] of the molten steel in the molten pool in the steelmaking furnace has a common regularity. That is, with the gradual reduction of [C], [O] gradually increases, and [C] and [O] have a corresponding equilibrium relationship.
2, the source of nitrogen:
The partial pressure of nitrogen in the furnace gas is very high, and the partial pressure of nitrogen in the atmosphere is generally kept at 7.8Χ104 Pa. Therefore, the nitrogen in the steel is mainly absorbed and dissolved during the bare water process. Electric furnace steelmaking, including secondary refining of arc heating, accelerates the dissociation of gas, so the [N] content is high; the open furnace smelting time increases the nitrogen content; improper control of the recombination of the converter, nitrogen and argon will not be switched in time will increase Nitrogen content; Nitrogen in ferroalloys, scrap steel, and slag is also brought into molten steel with the charge.
3, the source of hydrogen:
The partial pressure of hydrogen in the furnace gas is very low, and the partial pressure of hydrogen in the atmosphere is 0.053 Pa. Therefore, the hydrogen in steel is mainly determined by the partial pressure of water vapor in the furnace gas. The main ways for hydrogen to enter the molten steel are: through the rust of the scrap surface (xFeO•yFe3O4 • 2H2O); hydrogen in the ferroalloy; recarburizer, deoxidizer, covering agent, insulating agent, slagging agent (Ca(OH)2) Water in asphalt, asphalt, and tar; unlaunched ladle, tundish, and middle-injection pipe; spray coating of ingot molds; water in molds and moisture in the atmosphere enters steel with molten steel or slag.
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