H (Hydrogen)
The main role of B in steel is to increase the hardenability of the steel, thus saving other more rare metals, with nickel, chromium, molybdenum, etc.. For this purpose, its content is generally specified in the range of 0.001% to 0.005%. It can replace 1.6% of nickel, 0.3% of chromium or 0.2% of molybdenum, to boron instead of molybdenum should be noted, because molybdenum can prevent or reduce temper brittleness, while boron slightly promote the tendency of temper brittleness, so you can not use boron will be completely replaced by molybdenum.
Medium carbon carbon steel with boron, due to improve the hardenability, can make more than 20mm thick steel after tempering performance greatly improved, therefore, available 40B and 40MnB steel instead of 40Cr, available 20Mn2TiB steel instead of 20CrMnTi carburized steel. But because the role of boron with the increase in carbon content in steel and weaken, or even disappear, in the selection of boron-carburizing steel, must take into account the parts after carburizing, the hardenability of the carburizing layer will be lower than the hardenability of the core of this feature.
Boron and Nitrogen and Oxygen have a strong affinity for boiling steel with 0.007% of boron, can eliminate the aging phenomenon of steel.
C (Carbon)
C is the main element second only to iron, it directly affects the strength, plasticity, toughness and welding properties of steel.
When the carbon content in steel is below 0.8%, with the increase of carbon content, the strength and hardness of steel increases, while plasticity and toughness decreases; but when the carbon content is above 1.0%, with the increase of carbon content, the strength of steel decreases instead.
With the increase of carbon content, the welding performance of steel becomes worse (steel with carbon content greater than 0.3%, weldability decreases significantly), cold brittleness and aging sensitivity increases, and atmospheric rust resistance decreases.
N (Nitrogen)
N on steel properties and carbon, phosphorus similar, with the increase in nitrogen content, can make the steel strength significantly increased, plasticity, especially toughness is also significantly reduced, weldability becomes poor, cold brittleness intensified; while increasing the tendency to aging and cold brittleness and hot brittleness, damage to the steel welding properties and cold bending properties. Therefore, should minimize and limit the amount of nitrogen in steel. General provisions of nitrogen content should not be higher than 0.018%.
Nitrogen in Aluminum, Niobium, Vanadium and other elements can be reduced in conjunction with its adverse effects, improve the performance of steel, can be used as an alloying element of low-alloy steel. Some grades of stainless steel, the appropriate increase in the content of N, can reduce the use of Cr, can effectively reduce costs.
O (Oxygen)
O is a harmful element in steel. It enters the steel naturally during the steelmaking process, and although manganese, silicon, iron and aluminum are added at the end of the steelmaking process for deoxidation, it is not possible to get rid of it. During the solidification of the steel, the reaction between oxygen and carbon in solution produces carbon monoxide, which can cause bubbles. Oxygen in steel mainly in the form of FeO, MnO, SiO2, Al2O3 and other inclusions, so that the strength and plasticity of steel is reduced. In particular, it has a serious impact on fatigue strength, impact toughness, etc.
Oxygen will increase the iron loss in silicon steel, the magnetic permeability and magnetic susceptibility strength is weakened, and the magnetic aging effect is intensified.
Mg (Magnesium)
Magnesium can make the number of inclusions in steel reduced, size reduction, uniform distribution, morphology improvement, etc. Trace magnesium can improve the carbide size and distribution of bearing steel, magnesium bearing steel carbide particles fine and uniform. When the magnesium content of 0.002% to 0.003%, its tensile strength and yield strength increased by more than 5%, plasticity remains basically the same.
Al (Aluminum)
Aluminum is added to steel as a deoxidizer or alloying element, aluminum deoxidation ability is much stronger than silicon and manganese. The main role of aluminum in steel is to refine the grain, fix the nitrogen in the steel, thus significantly improve the impact toughness of steel, reduce the tendency of cold brittleness and aging tendency. Such as D carbon structural steel requirements in steel acid soluble aluminum content of not less than 0.015%, deep stamping with cold rolled thin steel plate 08AL requirements in steel acid soluble aluminum content of 0.015% -0.065%.
Aluminum can also improve the corrosion resistance of steel, especially with molybdenum, copper, silicon, chromium and other elements used with better results.
Si (Silicon)
Si is an important reducing and deoxidizing agent in the steelmaking process: for many materials in carbon steel, it contains less than 0.5% Si, which is generally brought in as a reducing and deoxidizing agent as a result of the steelmaking process.
Si can dissolve in ferrite and austenite to improve the hardness and strength of steel, its role is second only to phosphorus, stronger than manganese, nickel, chromium, tungsten, molybdenum, vanadium and other elements. However, when the silicon content exceeds 3%, it will significantly reduce the plasticity and toughness of steel. Silicon can improve the elastic limit of steel, yield strength and yield ratio (σs/σb), as well as fatigue strength and fatigue ratio (σ-1/σb). This is the reason why silicon or silicon-manganese steel can be used as a spring steel grade.
Silicon can reduce the density, thermal conductivity and electrical conductivity of steel. It can contribute to the coarsening of ferrite grains and reduce the coercivity. There is a tendency to reduce the anisotropy of the crystal, so that the magnetization is easy and the magnetoresistance is reduced, which can be used to produce electrical steel, so the hysteresis loss of silicon steel sheet is low. Silicon increases the permeability of ferrite, so that the steel has a high magnetic susceptibility strength in a weak magnetic field. However, silicon reduces the magnetic susceptibility strength of steel in strong magnetic fields. Silicon reduces the magnetic aging effect of iron because of its strong deoxidizing power.
When steel containing silicon is heated in an oxidizing atmosphere, a thin film of SiO2 will form on the surface, thus improving the oxidation resistance of the steel at high temperatures. Silicon can promote the growth of columnar crystals in cast steel, reducing plasticity. If silicon steel is heated and cooled faster, it will fracture due to the low thermal conductivity and the large temperature difference between the interior and exterior of the steel.
Silicon can reduce the welding properties of steel. Because the ability to combine with oxygen silicon is stronger than iron, it is easy to generate low melting point silicate when welding, increasing the mobility of slag and molten metal, causing spattering phenomenon, affecting the quality of welding. Silicon is a good deoxidizer. Deoxidation with aluminum with a certain amount of silicon, as appropriate, can significantly improve the rate of deoxidation. Silicon in the steel would have been a certain amount of residual, which is brought in as a raw material due to ironmaking steelmaking. In boiling steel, silicon is limited to <0.07%, and when added intentionally, a silicon-iron alloy is added to the steelmaking.
P (Phosphorus)
P is brought into the steel by the ore, it is generally said that phosphorus is also a harmful element. Although Phosphorus can make the steel strength, hardness, but caused by plasticity, impact toughness significantly reduced. Especially at low temperatures, it makes the steel significantly brittle, a phenomenon known as "cold brittle". Cold brittle steel cold processing and weldability, the higher the Phosphorus content, the greater the cold brittleness, so the control of Phosphorus content in steel is more stringent. Senior quality steel: P < 0.025%; quality steel: P < 0.04%; ordinary steel: P < 0.085%.
P solution strengthening and cold hardening effect is very good, and the joint use of copper, improve the atmospheric corrosion resistance of low-alloy high-strength steel, but reduce its cold stamping performance, and sulfur, manganese joint use, improve the machinability, increased tempering brittleness and cold brittleness sensitivity. Phosphorus is the element that has the strongest effect on strengthening ferrite.
S (Sulfur)
Sulfur comes from the ore and fuel coke used to make steel. It is a harmful element in steel. Sulfur exists in steel in the form of iron sulfide (FeS), and FeS and Fe form a low melting point (985°C) compound. And steel hot working temperature is generally 1150 ~ 1200 ℃ or more, so when the steel hot working, due to premature melting of FeS compound and lead to workpiece cracking, this phenomenon is called "hot brittle". Reduces the ductility and toughness of steel, causing cracks in forging and rolling. Sulfur is also detrimental to welding performance and reduces corrosion resistance. High quality steel: S <0.02% ~ 0.03%; high quality steel: S <0.03% ~ 0.045%; ordinary steel: S <0.055% ~ 0.7% or less.
K/Na (Potassium/Sodium)
Potassium/sodium can be used as a densifier to spheroidize the carbide group in white iron, so that the toughness of white iron (and lainitic steel) can be increased by more than two times while maintaining the original hardness. It can refine the organization of ductile iron and stabilize the treatment process of creeping iron. It is a strong element to promote austenitization, for example, it can reduce the manganese/carbon ratio of austenitic manganese steel from 10:1~13:1 to 4:1~5:1.
Ca (Calcium)
The addition of calcium to steel refines the grain, partially desulfurizes it, and changes the composition, quantity and form of non-metallic inclusions. The effect is essentially similar to that of adding rare earths to steel.
Improves corrosion resistance, wear resistance, high and low temperature resistance of steel; improves impact toughness, fatigue strength, plasticity and welding properties; increases cold heading, shock resistance, hardness and contact endurance strength of steel. Adding calcium to steel can improve the resistance to hydrogen-induced cracking and laminar tearing, and prolong the service life of equipment and tools.
Ti (Titanium)
In high Chromium stainless steel usually need to add about 5 times the carbon content of titanium, not only can improve the corrosion resistance of steel (mainly against intergranular corrosion) and toughness. Can also organize the steel at high temperatures when the grain growth tendency and improve the welding properties of steel.
V (Vanadium)
Vanadium has an extremely strong affinity for carbon, ammonia and oxygen, with which it forms the corresponding stable compounds. Vanadium is present in steel mainly in the form of carbides. Its main effect is to refine the organization and grain size of the steel and to reduce the strength and toughness of the steel. When dissolved in solid solution at high temperatures, it increases hardenability; conversely, when present in the form of carbides, it decreases hardenability. Vanadium increases the tempering stability of hardened steels and produces a secondary hardening effect. The amount of vanadium in steel, except for high-speed tool steel, is generally not more than 0.5%. Vanadium in ordinary low carbon alloy steel can refine the grain, improve the strength and yield ratio and low temperature characteristics after normalization, improve the welding properties of steel.
Cr (Chromium)
Chromium can increase the hardenability of steel and has the effect of secondary hardening, can improve the hardness and wear resistance of carbon steel without making the steel brittle. Content of more than 12%, so that the steel has good high temperature oxidation resistance and oxidative corrosion resistance, but also to increase the thermal strength of steel. Chromium for stainless steel acid-resistant steel and heat-resistant steel, the main alloying elements.
Mn (Manganese)
Mn can improve the strength of steel: Because Mn is relatively inexpensive and can be infinitely solid-soluble with Fe, it has relatively little effect on plasticity while improving the strength of steel. Therefore, Manganese is widely used as a strengthening element in steel. It can be said that basically all carbon steels contain Mn. Our common pressed soft steels, duplex steels, phase change induced plasticity steels (TR steels), and martensitic steels, all contain the element Mn. Generally, the Mn content in soft steels does not exceed 0.5%; the Mn content in high-strength steels rises with the strength level, for example, in martensitic steels, the Mn content can be as high as 3%.
Co (Cobalt)
Cobalt is mostly used in special steels and alloys. High-speed steels containing cobalt have high high-temperature hardness and can be added to maraging steels at the same time with molybdenum to obtain ultra-hardness and good comprehensive mechanical properties. In addition, cobalt is also an important alloying element in hot-strength steels and magnetic materials.
Ni (Nickel)
The beneficial effects of nickel are: high strength, high toughness and good hardenability, high resistance and high corrosion resistance.
On the one hand it strongly increases the strength of the steel, while on the other hand it always keeps the toughness of iron at an extremely high level. Its temperature of becoming brittle is then extremely low. (When nickel <0.3%, the brittleness temperature is below -100 ℃, when the amount of Ni increases, about 4-5%, the brittleness temperature can be reduced to -180 ℃. So it can simultaneously improve the strength and plasticity of quenched structural steel. Containing Ni = 3.5%, no Cr steel can be air quenched, containing Ni = 8% of the Cr steel in a very small cold rate can also be transformed into M body.
Cu (Copper)
The prominent role of copper in steel is to improve the ordinary low-alloy steel resistance to atmospheric corrosion, especially when used in conjunction with phosphorus, adding copper can also improve the strength and yield ratio of steel, while there is no adverse effect on the welding performance. Containing 0.20% to 0.50% copper rail steel (U-Cu), in addition to wear resistance its corrosion resistance life for the general carbon steel rail 2-5 times.
Ga (Gallium)
Gallium in steel is the element that closes the γ region. Trace amounts of gallium are easily solid soluble in ferrite, forming a surrogate solid solution. It is not a carbide forming element, and also does not form oxides, nitrides, sulfides. In the γ+a two-phase region, trace gallium is easy to diffuse from austenite to ferrite, and it has high concentration in ferrite. The effect of trace gallium on the mechanical properties of steel is mainly solid solution strengthening. Gallium has a small improvement on the corrosion resistance of steel.
As (Arsenic)
Arsenic in the ore in the sintering process can only remove part of the sintering process, can also be removed by chlorination roasting method, arsenic in the blast furnace smelting process all the reduction into the pig iron, steel containing arsenic greater than 0.1% or more, so that the steel increases brittleness and make the welding properties deteriorate. Arsenic content in the ore should be controlled, requiring that the arsenic content in the ore should not exceed 0.07%.
Se (Selenium)
Selenium improves the machinability of carbon steel, stainless steel and copper, and the surface finish of parts.
Zr (Zirconium)
Zirconium is a strong carbide-forming element, and its role in steel is similar to that of niobium, tantalum and vanadium. Adding a small amount of zirconium has degassing, purification and grain refinement, which is beneficial to the low-temperature properties of steel and improve stamping performance, it is commonly used in the manufacture of gas engines and ballistic missile structures used in ultra-high strength steel and nickel-based high-temperature alloys.
Nb (Niobium)
Niobium is often symbiotic with Tantalum, and their role in steel is similar. Niobium and tantalum are partially dissolved in solid solution and play a solid solution strengthening role. When dissolved in austenite, it significantly increases the hardenability of the steel. However, when present in the form of carbide and oxide particles, it refines the grain and reduces the hardenability of the steel. It increases the tempering stability of the steel and has a secondary hardening effect. Trace amounts of niobium can increase the strength of steel without affecting its plasticity or toughness. It improves the impact toughness of steel and reduces its brittle transition temperature due to its grain refining effect. When the content is greater than 8 times that of carbon, it fixes almost all the carbon in the steel, giving it good hydrogen resistance. In austenitic steel can prevent intergranular corrosion of steel by oxidizing medium. Due to the fixed carbon and precipitation hardening effect, it can improve the high-temperature properties of hot-strength steels, such as creep strength.
Mo (Molybdenum)
Molybdenum in steel improves hardenability and thermal strength, prevents temper brittleness, increases remanence and coercivity as well as corrosion resistance in certain media. In stainless acid-resistant steels, molybdenum further improves corrosion resistance to organic acids (such as anthranilic acid, acetic acid, oxalic acid, etc.) as well as hydrogen peroxide, sulfuric acid, sulfite, sulfates, acid dyes, bleaching powder solutions, etc. In particular, the addition of molybdenum prevents the tendency to pitting corrosion caused by the presence of chloride ions. W12Cr4V4Mo high-speed steel containing about 1% molybdenum has wear resistance, tempering hardness and red-hardness, etc.
Sn (Tin)
Tin has been as a harmful impurity element in steel, it affects the quality of steel, especially the quality of continuous casting billets, so that steel thermal embrittlement, tempering brittleness, cracking and fracture, affecting the welding properties of steel, is one of the "five hazards" of steel. However, tin has a very important role in electrical steel, cast iron, free cutting steel.
Sb (Antimony)
Sb-containing construction welding steel, austenite temperature, steel Sb in Mn S inclusions and along the original austenite grain boundary precipitation, increase in Mn S inclusions on the enrichment of precipitation, can make the steel organization is refined and improve toughness.
W (Tungsten)
As the addition of Tungsten can significantly improve the wear resistance and machinability of steel, so tungsten is the main element of alloy tool steel.
Pb (Lead)
Lead is difficult to form solid solution or compound with iron, and it is easy to bias in the grain boundaries in spherical form, which is one of the root causes of brittleness of steel at 200~480℃ and cracks in the weld.
Bi (Bismuth)
Adding 0.1~0.4 of bismuth in free-cutting steel can improve the cutting performance of steel. When Bismuth is evenly dispersed in the steel, particulate bismuth melts in contact with the cutting tool and acts as a lubricant, and makes cutting fracture to avoid overheating, which can increase the cutting speed. Recently a large amount of bismuth has been added to stainless steel to improve the cutting properties of stainless steel.
Re (Rare earth elements)
Rare earth elements, as they are generally referred to, are the lanthanides (Lanthanum, Cerium, Praseodymium, Neodymium, Promethium, Samarium, Europium, Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium, Lutetium) with atomic numbers from 57 to 71 in the periodic table plus Scandium 21 and Yttrium 39, a total of 17 elements. They are close in nature and cannot be easily separated.
Rare earth elements can also improve the oxidation resistance and corrosion resistance of steel. The effect of anti-oxidation exceeds that of elements such as silicon, aluminum and titanium. It improves the fluidity of steel, reduces non-metallic inclusions, and makes the steel dense and pure in organization. Rare earth elements in FeCr-Al alloy increase the oxygen resistance of the alloy, maintain the fine grain of steel at high temperature, improve the high temperature strength, and thus make the life of electric heating alloy improve significantly.
