The effect of oxygen
The solubility of oxygen in steel is very small, and the oxide in steel appears in the form of inclusions. Generally speaking, the oxygen content is increased, the inclusions are more, the toughness of steel plate is reduced, and other mechanical properties
such as fatigue strength and wear resistance are also reduced in varying degrees. In steel making, oxygen is used to remove the impurity elements in the steel liquid, so oxygen has played a positive role. But it is harmful to solid steel. Therefore, deoxidization
Effect of nitrogen
The nitrogen in the steel comes from the furnace charge. During smelting, the molten steel also absorbs nitrogen from the furnace gas. Nitrogen causes quenching aging and Deformation Aging of carbon steel,
which has a significant impact on the performance of carbon steel. As a result of aging, the hardness and strength of steel are increased, but the toughness should be reduced. Especially in the case of Deformation Aging, the reduction of toughness is
relatively significant. For ordinary low alloy steel, aging phenomenon is harmful, so nitrogen is a harmful element.
Adding enough aluminum to steel can form aluminum nitride, which can eliminate or weaken aging phenomenon. Because aluminum nitride
is highly dispersed and has stable texture, it can refine grains. In this respect, nitrogen is a beneficial element.
The effect of hydrogen
In the smlting process, the molten steel can not only bring hydrogen from the rusty and watery charge,
but also directly absorb hydrogen from the furnace gas. When the steel is heated in the reducing protective gas containing hydrogen, it can absorb hydrogen in the pickling process, electroplating or electrolysis process. Hydrogen dissolves into liquid
or solid steel in the form of ions or atoms, and then melts into solid steel to form intermittent solid melt. Hydrogen is a harmful element in steel, which reduces the toughness of steel and causes so-called hydrogen embrittlement. On the other hand,
the higher the strength of steel, the greater the sensitivity of hydrogen embrittlement.
The influence of aluminum
Aluminum is added to steel as a deoxidizing element, and the aluminum part in the molten steel combines with oxygen to form
Al2O3 or various inclusions containing Al2O3. In addition to the deoxidizing effect of aluminum, the dispersed AlN particles formed by the combination of aluminum and nitrogen can prevent austenite grain growth. Therefore, a certain amount of acid soluble
aluminum must be ensured in the steel.
Influence of other residual elements
There are als some elements brought into carbon steel by scrap steel or ore, such as copper, nickel, chromium, etc. in order to keep the performance fluctuation range
of all kinds of carbon steel from too large, their contents are limited to a certain extent. But the existence of these elements will improve the strength of hot rolling to a certain extent.