The influence of 49 elements on the properties of steel

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Effect of elements on steel properties: H (Hydrogen). H is the most harmful element in ordinary steel; the presence of hydrogen in steel can cause defects such as hydrogen embrittlement and white spots. Like oxygen and nitrogen, hydrogen has an extremely low solubility in solid steel. At high temperatures, it dissolves into the molten steel; when cooling, it does not have time to escape and accumulates within the structure, forming high-pressure microvoids. This reduces the plasticity, toughness, and fatigue strength of the steel significantly, and in severe cases, it can cause cracks and brittle fracture. “\"Hydrogen embrittlement\" occurs mainly in martensitic steels; it is not very prominent in ferritic steels, and generally increases along with hardness and carbon content. On the other hand, H can increase the magnetic permeability of steel, but it also increases the coercivity and hysteresis loss (the coercivity can increase by 0.5 to 2 times after the application of H). B (Boron): The main role of B in steel is to increase its hardenability, thereby saving other more expensive metals such as nickel, chromium, and molybdenum. For this purpose, its content is generally specified to be within the range of 0.001% to 0.005%. It can replace 1.6% nickel, 0.3% chromium, or 0.2% molybdenum. When using boron to replace molybdenum, it should be noted that while molybdenum helps prevent or reduce temper brittleness, boron has a slight tendency to promote it; therefore, boron cannot completely replace molybdenum. By adding boron to medium-carbon carbon steel, its hardenability is improved, which allows the properties of steel sheets with a thickness of over 20 mm to be greatly enhanced after quenching and tempering. Therefore, 40B and 40MnB steels can be used in place of 40Cr, and 20Mn2TiB steel can be used in place of 20CrMnTi carburized steel. However, since the effect of boron weakens or even disappears as the carbon content in the steel increases, when selecting boron-containing carburizing steels, it is necessary to take into account the fact that after carburizing the part, the hardenability of the carburized layer will be lower than that of the core. Spring steel generally requires complete hardening; since the area of springs is usually small, it is advantageous to use boron-containing steel. The effect of boron on high-silicon spring steel varies greatly, making it unsuitable for use. Boron has a strong affinity for nitrogen and oxygen; adding 0.007% boron to boiling steel can eliminate the aging phenomenon in the steel. C (Carbon) C is the second most important element after iron; it directly affects the strength, plasticity, toughness, and weldability of steel. When the carbon content in steel is below 0.8%, as the carbon content increases, the strength and hardness of the steel increase, while its plasticity and toughness decrease ； However, when the carbon content is above 1.0%, as the carbon content increases, the strength of the steel actually decreases. As the carbon content increases, the weldability of steel deteriorates (for steels with a carbon content above 0.3%, weldability declines significantly), cold brittleness and sensitivity to aging increase, and resistance to atmospheric corrosion decreases. N (Nitrogen): The effect of nitrogen on the properties of steel is similar to that of carbon and phosphorus. As the nitrogen content increases, the strength of the steel rises significantly, while its plasticity – and particularly its toughness – decreases markedly. The weldability also gets worse, and cold brittleness increases ； It also increases the tendency to ageing, as well as cold and hot brittleness, thereby compromising the welding properties and cold bending properties of the steel. Therefore, the nitrogen content in steel should be minimized and restricted as much as possible. Generally, the nitrogen content should not exceed 0.018%. Nitrogen, in combination with elements such as aluminum, niobium, and vanadium, can reduce their adverse effects and improve the properties of steel; it can be used as an alloying element in low-alloy steels. For certain grades of stainless steel, increasing the N content appropriately can reduce the amount of Cr needed, thereby effectively lowering costs. O (oxygen) O is a harmful element in steel. It enters the steel naturally during the steelmaking process; although manganese, silicon, iron, and aluminum are added toward the end of steelmaking for deoxidation, it is impossible to remove it completely. During the solidification of molten steel, the reaction between oxygen and carbon in the solution produces carbon monoxide, which can cause bubbles. Oxygen in steel exists mainly in the form of impurities such as FeO, MnO, SiO2, and Al2O3, which reduces the strength and ductility of the steel. It has a particularly severe impact on fatigue strength, impact toughness, etc. Oxygen increases the iron loss in silicon steel, reduces its permeability and magnetic flux density, and exacerbates magnetic aging. Mg (magnesium) can reduce the number of inclusions in steel, decrease their size, improve their distribution, and enhance their morphology. Trace amounts of magnesium can improve the size and distribution of carbides in bearing steel, resulting in fine and uniform carbide particles in magnesium-containing bearing steel. When the magnesium content is 0.002%–0.003%, its tensile strength and yield strength increase by more than 5%, while the plasticity remains essentially unchanged. Al (aluminum): Aluminum is added to steel as a deoxidizer or alloying element, and its deoxidizing capacity is much greater than that of silicon and manganese. The main role of aluminum in steel is to refine the grain structure and retain nitrogen within the steel, thereby significantly improving the steel’s impact toughness and reducing its tendency to become brittle at low temperatures as well as its susceptibility to aging. For Grade D carbon structural steel, the acid-soluble aluminum content in the steel is required to be no less than 0.015%; for cold-rolled thin steel sheets used in deep drawing, such as 08AL, the acid-soluble aluminum content is required to be between 0.015% and 0.065%. Aluminum can also improve the corrosion resistance of steel, especially when used in combination with elements such as molybdenum, copper, silicon, and chromium. The presence of Al in chromium-molybdenum steel and chromium steel can increase their wear resistance. The presence of Al in high-carbon tool steels can lead to quenching brittleness. The disadvantage of aluminum is that it affects the hot working properties, welding properties, and machining properties of steel. Si (silicon) is an important reducing agent and deoxidizer in the steelmaking process. Many grades of carbon steel contain less than 0.5% Si, which is generally introduced during steelmaking as a reducing agent and deoxidizer. Silicon can dissolve in ferrite and austenite to increase the hardness and strength of steel; its effect is second only to that of phosphorus, and it is stronger than elements such as manganese, nickel, chromium, tungsten, molybdenum, and vanadium. However, when the silicon content exceeds 3%, it significantly reduces the plasticity and toughness of the steel. Silicon can increase the elastic limit, yield strength, and yield ratio (σs/σb) of steel, as well as its fatigue strength and fatigue ratio (σ-1/σb). This is why silicon or silicomanganese steel can be used as spring steel. Silicon can reduce the density, thermal conductivity, and electrical conductivity of steel. It can promote the coarsening of ferrite grains and reduce coercivity. It has a tendency to reduce the anisotropy of the crystal, facilitating magnetization and reducing magnetic resistance; it can be used in the production of electrical steel, which is why silicon steel sheets have low hysteresis losses. Silicon can increase the magnetic permeability of ferrite, enabling the steel sheet to achieve a higher magnetic flux density in weaker magnetic fields. However, under a strong magnetic field, silicon reduces the magnetic susceptibility of steel. Silicon reduces the magnetic aging effect of iron due to its strong deoxidizing ability. When silicon-containing steel is heated in an oxidizing atmosphere, a SiO2 film forms on its surface, thereby improving the steel’s oxidation resistance at high temperatures. Silicon can promote the growth of columnar crystals in cast steel, reducing its plasticity. If silicon steel is cooled rapidly after heating, due to its low thermal conductivity, a large temperature difference arises between the interior and exterior of the steel, resulting in fracture. Silicon can reduce the weldability of steel. Because silicon has a stronger ability to bind with oxygen than iron, low-melting-point silicates are easily formed during welding, increasing the fluidity of the slag and the molten metal and causing spattering, which affects the quality of the weld. Silicon is a good deoxidizer. Adding an appropriate amount of silicon when using aluminum for deoxidation can significantly improve the deoxidizing efficiency. Silicon is already present in steel to a certain extent, as it is introduced as a raw material during iron and steel production. In boiling steel, silicon is limited to