Steel Alloys: Effects of 48 Elements

Element 1: H（Hydrogen）

Hydrogen is the most harmful element in steel, and the solution of hydrogen in steel can cause hydrogen embrittlement and white spots in the steel.

Similar to oxygen and nitrogen, the solubility of hydrogen in solid steel is very low. When hydrogen is mixed into liquid steel at high temperatures, it cannot escape in time before cooling and accumulates in the organization, forming high-pressure fine pores. This can cause the plasticity, toughness, and fatigue strength of the steel to sharply reduce or even lead to serious cracks and brittle fracture.

Hydrogen embrittlement mainly occurs in martensitic steel, but is not very prominent in ferrite steel. It generally increases along with hardness and carbon content.

On the other hand, hydrogen can improve the magnetic conductivity of steel, but it also increases coercivity and iron loss. The coercivity can be increased by 0.5 to 2 times after adding hydrogen.

Element 2:（Boron）

The main function of boron in steel is to increase the hardenability of the steel, thus saving other relatively rare metals like nickel, chromium, molybdenum, etc. For this purpose, its content is generally stipulated 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.

When boron is used to replace molybdenum, it should be noted that although molybdenum can prevent or reduce temper brittleness, boron has a slight tendency to promote it. As such, molybdenum cannot be completely replaced by boron.

Adding boron to carbon steel can improve the hardenability, which can greatly enhance the performance of steel with over 20 mm thickness. Therefore, 40B and 40MnB steel can replace 40Cr, and 20Mn2TiB steel can replace 20CrMnTi carburizing steel.

However, due to the weakened or disappeared effect of boron with increasing carbon content in steel, when choosing boron carburizing steel, it should be noted that after parts are carburized, the hardenability of the carburized layer will be lower than that of the core.

Spring steel is generally required to be fully quenched, and boron steel would be a good choice due to its small spring area. However, the effect of boron on high silicon spring steel is volatile, so it should not be used.

Boron, nitrogen, and oxygen have a strong affinity. The addition of 0.007% boron in rimming steel can eliminate the aging of the steel.

Element 3: C（Carbon）

Carbon is the main element after iron, and it directly affects the strength, plasticity, toughness, and welding properties of steel.

When the carbon content in steel is below 0.8%, the strength and hardness of the steel increase with the addition of carbon content, while the plasticity and toughness decrease.

However, when the carbon content is above 1.0%, the strength of the steel decreases as the carbon content increases.

As the carbon content increases, the welding performance of the steel reduces (when the carbon content in steel is more than 0.3%, its weldability decreases significantly). Additionally, cold brittleness and aging sensitivity increase, and atmospheric corrosion resistance decreases.

Element 4: N（Nitrogen）

The effect of nitrogen (N) on steel performance is similar to that of carbon and phosphorus. With an increase in nitrogen content, it can significantly improve the strength of steel while reducing its plasticity, especially toughness and weldability, and enhancing its cold brittleness.

Furthermore, the aging tendency, cold brittleness, and hot brittleness are increased, and the welding property and cold bending properties of the steel are damaged. Therefore, the nitrogen content in steel should be minimized and restricted.

The nitrogen content should be no higher than 0.018%. When combined with aluminum, niobium, vanadium, and other elements, nitrogen can reduce its adverse effects and improve the performance of steel. Nitrogen can also be used as an alloy element for low alloy steel.

In some stainless steel, an appropriate nitrogen content can reduce the use of Cr and effectively reduce costs.

Element 5: O（Oxygen）

Oxygen is a harmful element to steel. It is naturally present in steel during the process of steelmaking, and it is impossible to remove it completely, even with the addition of manganese, silicon, iron, and aluminum at the end of the process.

During the solidification of molten steel, the oxygen and carbon reactions in the solution produce carbon monoxide, which can cause bubbles.

In steel, oxygen mainly exists in the form of FeO, MnO, SiO2, and Al2O3, which reduces the strength and plasticity of steel. In particular, fatigue strength and toughness will be seriously affected.

Oxygen will increase the iron loss in silicon steel, weaken the magnetic conductivity and the intensity of the magnetic induction, and enhance the magnetic aging effect.

Element 6: Mg（Magnesium）

Magnesium (Mg) can reduce the number of inclusions in steel, decrease their size, create even distribution, and improve their shape.

In bearing steel, trace amounts of magnesium can improve the size and distribution of carbides.

When the magnesium content is between 0.002% and 0.003%, the tensile strength and yield strength of the steel increase by more than 5%, while the plasticity remains essentially unchanged.

Element 7: Al（Aluminium）

Aluminum, added to steel as a deoxidizer or alloying element, is much stronger than silicon and manganese in terms of deoxidation.

The primary role of aluminum in steel is to refine grains and stabilize nitrogen, which significantly improves the impact toughness of steel and reduces cold brittle tendencies and aging tendencies.

For grade D carbon structural steel, the content of acid-soluble aluminum in steel should not be less than 0.015%. For deep stamping with cold-rolled sheet 08AL, the content of acid-soluble aluminum in steel should be 0.015%-0.065%.

Aluminum can also improve the corrosion resistance of steel, particularly when combined with molybdenum, copper, silicon, chromium, and other elements.

Aluminum is added to chromium molybdenum steel and chromium steel to increase its wear resistance.

The presence of aluminum in high carbon tool steel can make the quenching process brittle.

The disadvantage of aluminum is that it can affect the thermal processing property, welding performance, and cutting performance of steel.

Element 8: Si（Silicon）

Si is an essential reducing agent and deoxidizer in the steelmaking process.

Many materials in carbon contain less than 0.5% of Si, and this Si is typically brought in during the steelmaking process as a reducing agent and deoxidizer.

Silicon can be dissolved into ferrite and austenite to increase the hardness and strength of steel, which is second only to phosphorus and stronger than manganese, nickel, chromium, tungsten, molybdenum, and vanadium.

However, when the silicon content exceeds 3%, the plasticity and toughness of steel will significantly reduce.

Silicon can improve the elastic limit, yield strength, yield ratio of steel (Os/Ob), as well as fatigue strength and fatigue ratio (σ-1/σb), which is why silicon or silicon-manganese steel can be used as spring steel.

Silicon can reduce the density, thermal conductivity, and conductivity of steel. It can promote ferrite grain coarsening and reduce coercive force.

Silicon can also reduce the anisotropy of the crystal, making it easy to magnetize and reducing the magnetic resistance, which can be used to produce electrical steel, so the magnetic block loss of silicon steel sheet is low.

Silicon can improve the magnetic permeability of ferrite so that the steel sheet has a higher magnetic intensity under a weaker magnetic field. But in a strong magnetic field, silicon reduces the magnetic intensity of steel. Silicon has a strong deoxidizing force that reduces the magnetic aging effect of iron.

When heated in an oxidizing atmosphere, silicon steel forms a layer of SiO2 film that improves the oxidation resistance of steel at high temperature.

Silicon can promote the growth of columnar crystals in cast steel and reduce plasticity.

If the silicon steel cools rapidly when heated, due to the low thermal conductivity, the internal and external temperature difference of steel is large, which can easily cause steel to break.

Silicon can reduce the welding performance of steel because it is easier to be oxidized than iron. It is easy to generate the silicate with a low melting point during welding, which can increase the fluidity of slag and molten metal, cause splashing, and affect the welding quality.

Silicon is a good deoxidizer. When aluminum is deoxidized, a certain amount of silicon can be added to significantly improve the rate of deoxidization.

Silicon has a certain residual in the steel, which is brought into the steel as a raw material. In rimming steel, the silicon is limited to < 0.07%, and when necessary, the silicon-iron alloy is added to the steelmaking.

Element 9: （Phosphorus）

P is brought into steel by ore, which is generally considered a harmful element. Although phosphorus can increase the strength and hardness of steel, it significantly decreases plasticity and impact toughness.

Especially at low temperatures, it makes the steel significantly brittle, which is called “cold brittleness”.

Cold brittleness weakens the steel’s cold processing and weldability.

The higher the phosphorus content, the bigger the cold brittleness, so the phosphorus content in the steel is strictly controlled.

High-quality steel: P < 0.025%; Quality steel: P < 0.04%; Common steel: P < 0.085%.

P is strong in solid solution strengthening and cooling hardening.

When combined with copper, it can improve the atmospheric corrosion resistance of high-strength low-alloy steel while reducing its cold stamping performance;

When combined with sulfur and manganese, P can improve steel’s machinability, temper brittleness, and cold brittleness sensitivity.

Phosphorus can improve ratio resistance and can reduce coercive force and eddy current loss due to coarse grain.

For magnetic induction, the magnetic induction of steel with higher P content will be improved in the weak magnetic field.

The hot working of P-containing silicon steel is not difficult, but because P can make the silicon steel brittle, its content should be ≯ 0.15% (such as in cold-rolled electrical silicon steel, the P content is 0.07 ~ 0.10%).

Phosphorus is the most powerful element of ferrite. (the effect of P on the silicon steel recrystallization temperature and grain growth is 4 ~ 5 times that of silicon with the same content.)

Element 10: S（Sulfur）

Sulfur is derived from the ore and fuel coke used in steelmaking. It is a harmful element for steel.

Sulfur exists in steel in the form of FeS. FeS and Fe form a compound at a low melting point of 985 ℃. The hot working temperature of steel is commonly above 1150 ℃. Therefore, during hot working, FeS compounds can melt prematurely, causing the workpiece to break. This phenomenon is called “hot brittleness”. It reduces the ductility and toughness of steel, causing cracks in forging and rolling.

Sulfur is also harmful to the welding performance and reduces corrosion resistance of steel. The sulfur content in high-quality steel should be less than 0.02% to 0.03%, in quality steel less than 0.03% to 0.045%, and in common steel less than 0.055% to 0.7%.

Sulfur can be used to produce steel parts that require low capacity and higher surface shine, known as fast cutting steel, such as Cr14 with a small amount of sulfur intentionally added (0.2% to 0.4%). Some high-speed steel and tool steel use S to process the surface.

Element 11 and 12: K/Na（Kalium / Natrium）

K/Na can be used as modifiers to spheroidize the carbides in white iron, improving its toughness by up to twofold while maintaining its hardness.

They can also refine the structure of ductile iron and stabilize the production process of vermicular iron.

In addition, K/Na are effective elements for promoting austenitization. For example, they can lower the manganese/carbon ratio of austenitic manganese steel from 10:1-13:1 to 4:1-5:1.

Element 13: Ca（Calcium）

Adding calcium to steel can refine its grain, partially desulfurize it, and change the composition, quantity, and form of non-metallic inclusions, similar to adding rare earth to steel.

This can improve the corrosion resistance, wear resistance, high-temperature and low-temperature performance of steel, as well as its impact toughness, fatigue strength, plasticity, and welding properties.

Additionally, adding calcium can enhance the cold heading, shock resistance, hardness, and contact strength of steel. In cast steel, adding calcium increases the mobility of molten steel, improves the surface of the casting, and eliminates the anisotropy of organizations in the casting. Its casting performance, thermal cracking resistance, mechanical properties, and machining performance all increase.

Furthermore, adding calcium to steel can improve its performance against hydrogen crack and lamellar tear, and prolong the service life of equipment and tools. Calcium is added to the mother alloy as a deoxidizer, inoculant, and microalloying agent.

Element 14: Ti（Titanium）

Titanium has a strong affinity with nitrogen, oxygen, and carbon and a stronger affinity with S than iron, making it an effective element for deoxidization and fixing nitrogen and carbon.

Although titanium is a strong carbide-forming element, it does not combine with other elements to form compounds.

Titanium carbide has a strong binding force, is stable, and is difficult to decompose. It can only slowly dissolve into steel at temperatures above 1000℃.

Before isolation, titanium carbide particles can prevent grain growth.

Due to titanium’s greater affinity with carbon than chromium, it is commonly used in stainless steel to fix carbon, remove chromium dilution in the grain boundary, and eliminate or reduce intergranular corrosion in steel.

Titanium is also a strong ferrite-forming element that greatly enhances the A1 and A3 temperatures of steel.

In ordinary low-alloy steel, titanium can improve plasticity and toughness while increasing steel strength by fixing nitrogen and sulfur and forming titanium carbide.

Grain refinement formed by normalizing, precipitation carbides can greatly improve the plasticity and impact toughness of steel.

Alloy structural steel containing titanium has good mechanical properties and process performance, but its main drawback is low hardenability.

In high-chromium stainless steel, titanium content is usually five times that of carbon, which can improve the corrosion resistance (mainly anti-intergranular corrosion) and toughness of steel, promote grain growth at high temperatures, and improve the welding performance of steel.

Element 15: V（Vanadium）

Vanadium has a strong affinity with carbon, nitrogen, and oxygen, forming stable compounds with them. In steel, vanadium is mainly present as carbides.

Vanadium functions to refine the structure and grain of steel and can increase the hardenability when dissolved in the solid solution at high temperatures. However, when present in the form of carbides, it can reduce hardenability. Vanadium also increases the tempering stability of hardened steel and produces a secondary hardening effect.

The amount of vanadium in steel is generally limited to 0.5% except in high-speed tool steel. In ordinary low carbon alloy steel, vanadium can refine grain and improve the strength, yield ratio, low-temperature properties, and welding properties of steel. In alloy structural steel, it can reduce hardenability under normal heat treatment when used in combination with manganese, chromium, molybdenum, and tungsten.

Vanadium can improve the strength and yield ratio in spring steel and bearing steel, especially the ratio limit and elastic limit, and reduce carbon sensitivity during heat treatment, thus improving surface quality. When added to tool steels, it refines the grain, reduces overheating sensitivity, and increases tempering stability and wear resistance, extending the service life of tools.

In carburizing steel, vanadium allows the steel to be directly quenched after carburizing, without the need for secondary quenching. Bearing steel containing vanadium and chromium has high dispersion and good performance.

Element 16：Cr（Chromium）

Chromium can increase the hardenability of steel and has the effect of secondary hardening, and can improve the hardness and wear resistance of carbon steel without making it brittle.

When the Cr content is more than 12%, it makes the steel have good high-temperature oxidation resistance and corrosion resistance, and also increases its hot strength.

Chromium is the main alloying element in stainless steel, acid-resistant steel, and heat-resistant steel.

Chromium can improve the strength and hardness of carbon steel under rolling, reduce the elongation and shrinkage of cross-section.

When the chromium content exceeds 15%, the strength and hardness will decrease, and the elongation and the shrinkage of the cross-section will be increased correspondingly. By grinding, parts made of chromium steel are easy to obtain high surface quality.

The main function of Chromium in the tempering structure is to improve the hardenability, make the steel have good comprehensive mechanical performance after quenching and tempering, produce chromium carbide in carburizing steel to improve the wear resistance of the material surface.

Chromium-bearing spring steel is not easy to decarburize during heat treatment.

Chromium can improve the wear resistance, hardness, and red hardness of tool steel, and make it have good tempering stability.

In electrothermal alloys, chromium can improve the oxidation resistance, resistance, and strength of the alloy.

Element 17：Mn（Manganese）

Mn can improve the strength of steel. Since Mn is relatively cheap and can be alloyed with Fe, it has little effect on plasticity while improving the strength of steel. Therefore, Mn is widely used to reinforce steel.

It can be said that almost all carbon steel contains Mn. Stamping soft steel, dual-phase steel (DP steel), transformation-induced plasticity steel (TR steel), and martensitic steel (MS steel) contain manganese.

Generally, Mn content in soft steel will not exceed 0.5%. Mn content in high-strength steel increases with the increase of strength level, such as in martensitic steel, Mn content can reach up to 3%.

Mn improves the hardenability of steel and improves the thermal processing performance of steel. A typical example is 40Mn and No. 40 steel.

Mn can eliminate the influence of S (sulfur). Mn can form MnS with a high melting point in steel smelting, thereby weakening and eliminating the adverse effects of S.

However, the content of Mn is also a double-edged sword. The increase of Mn content will reduce the plasticity and welding properties of steel.

Element 18：Co（Cobalt）

Cobalt (Co) is used in special steel and alloys. High-speed steel containing Co exhibits strong high-temperature hardness.

When added to martensitic aging steel along with molybdenum, Co can increase the steel’s hardness and overall mechanical properties.

Additionally, Co is an important alloy element in hot steel and magnetic materials.

However, Co can reduce the hardenability of steel and thereby decrease its comprehensive mechanical properties, especially in carbon steel.

Moreover, Co can strengthen ferrite, and when added to carbon steel during annealing or normalizing, it can improve the steel’s hardness, yield point, and tensile strength but have a negative effect on its elongation and cross-sectional shrinkage.

Furthermore, increasing the Co content in steel reduces its impact toughness.

Lastly, due to its antioxidant properties, Co is used in heat-resistant steel and alloys, particularly in Co-based alloy gas turbines.

Element 19：Ni（Nickel）

The beneficial effects of nickel include high strength, high toughness, good hardenability, high resistance, and high corrosion resistance.

Nickel can significantly enhance the strength of steel while maintaining high toughness. Moreover, its brittle temperature is exceptionally low (below -100℃ when nickel < 0.3%, and it can drop to -180℃ when Co content is increased to about 4-5%), which can improve the strength and plasticity of hardened steel.

A steel with Ni=3.5% cannot be quenched, but adding Ni=8% to Cr steel can transform it into M-type at a very low cooling rate.

Nickel has a lattice constant similar to γ‐Fe, which makes it conducive to enhancing steel hardening by forming a continuous solid solution.

Nickel can reduce the critical point and increase the stability of austenite, which leads to reduced quenching temperature and good quenching.

Ni steel is generally used for heavy parts of large sections. When combined with Cr, W, or Cr and Mo, the hardenability can be increased. Nickel-molybdenum steel has a high fatigue limit, and Ni steel has good thermal fatigue resistance, capable of working in hot and cold conditions.

In stainless steel, Ni is used to create a uniform A-body to improve corrosion resistance.

Ni steel is not easily overheated, which can prevent the growth of grain in high temperature and maintain a fine grain structure.

Element 20：Cu（cuprum）

The prominent role of copper (Cu) in steel is to improve the atmospheric corrosion resistance of ordinary low-alloy steel. When mixed with phosphorus, Cu can also improve the strength and yield ratio of steel without any adverse effect on its welding performance.

Steel rail (U-Cu) containing 0.20% to 0.50% of Cu has a corrosion resistance period 2-5 times longer than that of normal carbon steel.

When the Cu content exceeds 0.75%, an aging effect can occur after solid solution treatment and aging.

At low Cu content, its effect is similar to that of nickel but weaker. At high Cu content, it is not suitable for thermal deformation processing, which can lead to copper brittleness.

Adding 2-3% copper to austenitic stainless steel can enhance the corrosion resistance of sulfuric acid, phosphoric acid, and hydrochloric acid as well as the stability of stress corrosion.

Element 21：Ga（Gallium）

Gallium (Ga) is an element located in the enclosed γ section. Microgallium is soluble in ferrite and forms a substitutive solid solution. It is not a carbide-forming element, but it also does not form oxides, nitrides, and sulphides.

In the γ+a two-phase regions, microgallium is easily diffused from austenite to ferrite, where its concentration is high. The effect of microgallium on the mechanical properties of steel is mainly solid solution strengthening.

Ga has a minor effect on the corrosion resistance of steel.

Element 22：As（arsenic）

Arsenic (As) in ore can only be partially removed in the sintering process, but it can be removed with chloridizing roasting. As will be mixed into pig iron during the blast furnace smelting process.

When the As content in steel exceeds 0.1%, it can increase steel brittleness while weakening its welding performance. Thus, the As content in ore should be controlled, and the amount of As in ore should not exceed 0.07%.

Arsenic has a tendency to increase the yield point σs and tensile strength σb of low-carbon round steel while reducing its elongation. Additionally, its effect on reducing the impact toughness Akv of carbon round steel at normal temperature is significant.

Element 23：Se（selenium）

Selenium (Se) can improve the machining properties of carbon steel, stainless steel, and copper, and make the surface of parts bright and clean.

High magnetic induction oriented silicon steel often uses MnSe2 as an inhibitor. Its good inclusion, compared with that of MnS, is stronger in curbing the growth of initial recrystallization grain and is more conducive to promoting the selected secondary recrystallization grain growth. This can obtain a high orientation (110) [001] texture.

Element 24：Zr（zirconium）

Zirconium (Zr) 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 Zr has the effects of degassing, purifying, and refining the grain, which is advantageous for improving the low-temperature performance and stamping performance of steel.

Zr is often used in the manufacture of gas engines and ultra-high-strength steel and Ni-based high-temperature alloys that are necessary for missile structures.

Element 25：Nb（niobium）

Niobium (Nb) is often associated with tantalum, and their roles in steel are similar. Nb and tantalum can partially dissolve in solid solution, and strengthen it.

The quenching of steel is significantly improved when the austenitic body is dissolved. However, in the form of carbides and oxide particles, Nb can refine the grain and reduce the hardenability of steel. It can increase the tempering stability of steel and has a secondary hardening effect.

Microniobium can improve the strength of steel without affecting its plasticity or toughness. Moreover, it can refine the grain, improve the impact toughness, and reduce the brittle transition temperature of steel. When the Nb content is more than 8 times that of carbon, almost all of the carbon in the steel can be fixed, making the steel have good resistance to hydrogen.

In austenitic steels, Nb can prevent oxidizing media from causing intergranular corrosion of steel. It can also improve the high-temperature performance of hot steel, such as creep strength, due to its fixed carbon and precipitation hardening effect.

Nb can improve the yield strength and impact toughness of ordinary low-alloy steel, and reduce its brittle transition temperature, which is beneficial for welding. In carburizing and tempering alloy structural steel, it can increase hardenability while improving toughness and low-temperature performance. Additionally, Nb can reduce the air hardening of low-carbon martensitic stainless steel, avoid the hardening temper brittleness, and increase the creep strength.

Element 26：Mo（molybdenum）

Molybdenum (Mo) can improve the hardenability and heat intensity of steel, prevent temper brittleness, increase residual magnetism, coercivity, and resistance to corrosion in some media.

In quenched and tempered steel, Mo can strengthen the quenching depth, hardening of large cross-section parts, and improve the drawability resistance or tempering stability of steel. This can make the parts more effectively eliminate (or reduce) residual stresses and improve their plasticity under high temperature.

In carburizing steel, Mo can reduce the tendency of carbide formation in a continuous mesh at the grain boundary during the carburized layer, reduce the residual austenite in the carburized layer, and relatively increase the surface wear resistance.

In forging die steel, Mo can maintain a stable hardness of steel and increase its resistance to deformation, cracking, and abrasion.

In stainless acid-resistant steel, Mo can further improve its corrosion resistance to organic acids such as formic acid, acetic acid, oxalic acid, hydrogen peroxide, sulfuric acid, sulfurous acid, sulfate, acid dyes, bleaching powder, or fluid. In particular, the addition of Mo can prevent the corrosion tendency of chlorine ion.

The W12Cr4V4Mo high-speed steel with about 1% Mo has excellent wear resistance, tempering hardness, and red hardness.

Element 27：Sn（Stannum）

Tin (Sn) has been considered a harmful impurity element in steel. It can affect the quality of steel, especially the continuous casting billet quality. Sn can cause steel to produce hot brittleness, temper brittleness, crack and fracture, affecting the welding performance of the steel, and is one of the ‘five evils’ to steel.

However, Sn plays an important role in electrical steel, cast iron, and easy cutting steel. The size of silicon steel grains is related to the segregation of Sn, and the segregation of Sn can prevent the growth of the grain. The higher the content of Sn, the larger the grain precipitation, and the more effective it is in hindering the growth of the grain. The smaller the grain size, the less the iron loss.

Sn can change the magnetic properties of silicon steel and improve the strength of the favorable texture {100} in the finished product of oriented silicon steel. This can lead to an obvious increase in magnetic induction intensity. When a small amount of Sn is contained in cast iron, it can improve the wear resistance of steel and affect the fluidity of molten iron. Pearlitic malleable cast iron has high strength and high wear resistance. To obtain the cast pearlite, Sn is added to the alloy solution during melting. Since Sn is an element that blocks the spherification of graphite, it is necessary to control the amount of Sn addition, which is generally less than 0.1%.

Easy cutting steel can be divided into sulfur, calcium, lead, and composite easy cutting steel. Sn has an obvious tendency to gather around inclusions and defects. Sn does not change the shape of sulfide inclusions in steel, but it can improve the brittleness and cutting performance of steel by the segregation of grain boundary and phase boundary. When the Sn content is >0.05%, steel has good cutting ability.

Element 28：Sb（Stibium）

After adding antimony (Sb) to high magnetic orientation silicon steel, the grain size of the first and secondary recrystallization can be refined, leading to more perfect second recrystallization and improved magnetism.

After cold rolling and decarbonizing Sb steel, the texture composition components {110} < 115 > or {110} < 001 > favorable for the development of secondary recrystallization will be enhanced, and the number of secondary crystal nuclei will increase.

In building welding steel containing Sb, under austenitic temperature, Sb precipitates around MnS inclusions and along the original austenite grain boundary. Precipitation enriched around MnS inclusions can refine the organization of the steel and improve its toughness.

Element 29：W（tungsten）

In steel, tungsten (W) is partially dissolved in iron forming a solid solution, in addition to producing carbide.

Its effect is similar to that of Mo, and the general effect is not as significant as Mo if calculated by quantity.

The main role of W in steel is to increase tempering stability, red hardness, heat intensity, and wear resistance due to the formation of carbide.

Therefore, it is mainly used for tool steel, such as high-speed steel and hot forging steel.

W is a refractory carbide in high-quality spring steel, which can reduce the concentration process of carbides and maintain high-temperature strength at higher temperatures.

W can also reduce the overheating sensitivity of steel, increase its hardenability and hardness.

Air cooling makes 65SiMnWA spring steel have high hardness after hot rolling.

A spring steel with a cross-section of 50mm2 can be hardened in oil and can bear a heavy load, be heat-resistant (not greater than 350 ℃).

30W4Cr2VA high-strength heat-resistant high-quality spring steel has large hardenability, and its tensile strength can be 1470 ~ 1666 pa after 1050 ~ 1100 ℃ quenching and 550 ~ 650 ℃ tempering.

It is mainly used for manufacturing springs that are used under high temperature (500 ℃).

Because of the addition of W, it can significantly improve the abrasion and cutting properties of steel, so W is the main element of alloy tool steel.

Element 30：Pb（Plumbum）

Pb can improve the machinability of steel. Steel containing Pb has good mechanical properties and can be heat-treated. However, due to its environmental pollution and harmful effects in the recycling process of waste steel, Pb has gradually been replaced.

Pb is difficult to form a solid solution or compounds with Fe. Instead, it tends to gather in the grain boundary in a globular form, which can cause brittleness in steel at temperatures between 200-480°C and result in cracks during welding.

Element 31：Bi（Bismuth）

The cutting performance of steel can be improved by adding 0.1-0.4% Bi in free-cutting steel.

When Bi is evenly distributed in steel, particles of Bi will melt after contacting the cutting tool, acting as a lubricant, making the cutting tool break to avoid overheating and increase cutting speed.

Recently, Bi has been added to many stainless steels to improve their cutting performance.

Bi exists in three types of free-cutting steels: independently in steel matrix, wrapped by sulfide, and between steel matrix and sulfide.

The deformation rate of MnS inclusions decreases with the increase of Bi content in S-Bi free-cutting steel ingots.

The Bi-metal in steel can restrain the deformation of sulfide in the forging process of steel ingot.

Adding 0.002-0.005% of Bi to cast iron can improve the casting performance of malleable cast iron, increase the whitening tendency, shorten annealing time, and optimize the extension performance of the parts.

Adding 0.005% of Bi to nodular cast iron can improve its anti-seismicity and tensile strength.

It is difficult to add Bi to steel because Bi largely volatilizes at 1500 ℃ and is thus difficult to be evenly infiltrated into steel.

Currently, abroad, Bi is replaced by Bi-Mn alloy plate with a melting point of 1050 ℃ as the additive, but the utilization rate of Bi is still about 20%.

Nippon Steel & Sumitomo Metal, Posco, TYO, and other enterprises have proposed that adding Bi can significantly improve the B8 value of oriented silicon steel.

According to statistics, Nippon Steel & Sumitomo Metal and JFE have over one hundred high-magnetic oriented silicon steel inventions having added Bi.

After adding Bi, the magnetic induction reaches 1.90T, and the maximum is 1.99T.

Other Element 32-48：Re (Rare Earths)

Rare earth elements commonly refer to the lanthanides with atomic numbers ranging from 57 to 71 (lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium), plus scandium (No. 21) and yttrium (No. 39), for a total of 17 elements. Their properties are similar, making them difficult to separate. Mixed rare earths, which are cheaper, refer to those that have not been separated.

Rare earths can be used for deoxidizing, desulfurizing, and microalloying, and can also alter the deformability of rare earth inclusions. They can affect the brittleness of Al2O3 to a certain extent and improve the fatigue performance of most steel types.

Rare earth elements, along with Ca, Ti, Zr, Mg, and Be, are the most effective deforming agents for sulfide. By adding the appropriate amount of rare earth to steel, oxide and sulfide inclusions can be transformed into small, dispersed globular inclusions, which eliminate the harmful effects of MnS and other inclusions.

In steel production practice, sulfur is typically present as FeS and MnS. When the Mn content is high in steel, MnS is more likely to form. Although MnS has a high melting point and can avoid heat brittleness, during machining deformation, it can extend in the direction of processing and form into strips. This can significantly reduce the plasticity, toughness, and fatigue strength of the steel, making it necessary to add RE to steel for deformation processing.

Rare earth elements can also enhance the oxidation and corrosion resistance of steel. Their effect on oxidation resistance is greater than that of silicon, aluminum, and titanium. They can improve the flow of steel, reduce non-metallic inclusion, and make the steel structure dense and pure. The role of rare earth in steel is mainly purification, metamorphism, and alloying.

With the gradual control of oxygen sulfur content, traditional purification of molten steel and metamorphism are gradually weakening, while new purification technology and alloying effects are being improved. Rare earth elements increase the antioxidant capacity of ferrochrome aluminum alloy and maintain the fine grain of steel at high temperatures, increasing its high-temperature strength and the service life of electrothermal alloy significantly.