1、Harm of Hydrogen
When the hydrogen content in steel is greater than 2 ppm, hydrogen plays an important role in the so-called "flaking off" phenomenon. When internal cracks and fractures occur during the cooling process after rolling and forging, this spalling phenomenon is generally more obvious, and it is more often found in large cross-sections or high-carbon steels. Due to the existence of internal stress, this defect will cause the large rotor to crack during engine use. When the hydrogen in cast iron is greater than 2ppm, pores or general porosity are prone to appear, and the porosity caused by hydrogen will cause the embrittlement of iron. "Hydrogen embrittlement" mainly occurs in martensitic steel, not very prominent in ferrite steel, and it is actually not clear in austenitic steel. In addition, hydrogen embrittlement generally increases with hardness and carbon content.
2、Harm of Oxygen
Oxygen, like hydrogen, has an adverse effect on the mechanical properties of steel. Not only the concentration of oxygen, but also the number, type and distribution of oxygen-containing inclusions also have a very important influence. Such inclusions refer to metal oxides, silicates, aluminates, oxygen-containing sulfides and similar inclusion compounds. Steelmaking requires deoxidation, because during solidification, oxygen and carbon in the solution react to produce carbon monoxide, which can cause bubbles. In addition, oxygen can precipitate out of the solution as FeO, MnO, and other oxidized inclusions during cooling, thereby weakening its hot work or cold workability, as well as ductility, toughness, fatigue strength, and steel machining performance. Oxygen, nitrogen and carbon can also cause aging or a spontaneous increase in hardness at room temperature. For cast iron, when the ingot is solidifying, oxides and carbon can react, thus causing product porosity and product embrittlement.
3、Harm of Nitrogen
Nitrogen cannot be attributed to harmful gas elements in general, because some special steels are purposely added with nitrogen. All steel contains nitrogen, the amount of which depends on the production method of the steel, the type and quantity of alloying elements and the way of adding them, the method of casting the steel, and whether nitrogen is added on purpose. For some grades of stainless steel, appropriately increasing the content of N can reduce the amount of Cr used. Cr is relatively expensive. This method can effectively reduce the cost. Most of the nitrogen in steel is in the form of metal nitrides. For example, after storage for some time, the steel is strain-aged and cannot be deep-drawn (for example, deep-drawn for car protection panels), because the steel will tear and cannot be stretched uniformly in all directions. This is due to the large grain size and the deposition of Fe4N on the grain interface. Another example: in stainless steel, the formation of chromium nitride (Cr2N) on the grain interface will deplete the chromium contained on the interface and cause the so-called intergranular corrosion phenomenon. Adding titanium to give priority to the formation of titanium nitride can prevent such harmful effects.
1、Harm of Hydrogen
Post time: Oct-11-2021