Effect of various elements on properties of steel

Time:2023-05-17 08:37:47 / Popularity: / Source:

Element 1: H (hydrogen)

Effects on steel properties:
H is the most harmful element in general steel. Dissolving hydrogen in steel will cause defects such as hydrogen embrittlement and white spot of steel. Like oxygen and nitrogen, hydrogen has a very small solubility in solid steel. It dissolves into molten steel at high temperature, and when it is cooled, it is too late to escape and accumulates in structure to form high-pressure fine pores, which drastically reduces plasticity, toughness and fatigue strength of steel, may cause cracks and brittle fractures in severe cases. "Hydrogen embrittlement" mainly occurs in martensitic steels, not very prominent in ferrite steels, generally increases with hardness and carbon content.
On the other hand, H can improve magnetic permeability of steel, but it also increases coercivity and iron loss (coercivity can be increased by 0.5 to 2 times after adding H).
carbon structural steel 

Element 2: B (boron)

Effects on steel properties:
Main function of B in steel is to increase hardenability of steel, thereby saving other rarer metals, such as 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% nickel, 0.3% chromium or 0.2% molybdenum. It should be noted that molybdenum can be replaced by boron, because molybdenum can prevent or reduce temper brittleness, while boron has a slight tendency to promote temper brittleness, boron cannot be used to completely replace molybdenum.
Adding boron to medium carbon carbon steel can greatly improve properties of steel with a thickness of more than 20mm after quenching and tempering due to improvement of hardenability. Therefore, 40B and 40MnB steel can be used instead of 40Cr, and 20Mn2TiB steel can be used instead of 20CrMnTi carburized steel. However, since effect of boron weakens or even disappears with increase of carbon content in steel, when selecting boron-containing carburized steel, it must be considered that hardenability of carburized layer will be lower than hardenability of core after parts are carburized.
Spring steel generally requires complete hardening, and usually spring area is not large, so it is advantageous to use boron-containing steel. Effect of boron on high silicon spring steel fluctuates greatly, which is inconvenient to use.
Boron has strong affinity with nitrogen and oxygen. Adding 0.007% boron to boiling steel can eliminate aging phenomenon of steel.

Element 3: C (Carbon)

Effects on steel properties:
C is main element next to iron, which directly affects strength, plasticity, toughness and weldability of steel.
When carbon content in steel is below 0.8%, strength and hardness of steel increase as carbon content increases, while ductility and toughness decrease; but when carbon content is above 1.0%, as carbon content increases, strength of steel decreases.
With increase of carbon content, weldability of steel deteriorates (for steel with carbon content greater than 0.3%, weldability decreases significantly), cold brittleness and aging sensitivity increase, and atmospheric corrosion resistance decreases.

Element 4: N (nitrogen)

Effects on steel properties:
Effect of N on properties of steel is similar to that of carbon and phosphorus. With increase of nitrogen content, strength of steel can be significantly improved, plasticity, especially toughness, can also be significantly reduced, weldability is deteriorated, and cold brittleness is increased; at the same time, it increases aging tendency, cold brittleness and hot brittleness, damages welding performance and cold bending performance of steel. Therefore, nitrogen content in steel should be minimized and limited. It is generally stipulated that nitrogen content should not be higher than 0.018%.
Nitrogen can reduce its adverse effects with combination of aluminum, niobium, vanadium and other elements, improve properties of steel, can be used as an alloying element for low-alloy steel. For some grades of stainless steel, appropriately increasing N content can reduce amount of Cr used, which can effectively reduce cost.

Element 5: O (oxygen)

Effects on steel properties:
O is a harmful element in steel. It enters steel naturally during steelmaking process. Although manganese, silicon, iron and aluminum are added for deoxidation at the end of steelmaking process, it is impossible to remove it completely. During solidification of molten steel, carbon monoxide is formed by reaction of oxygen and carbon in solution, which can cause bubbles. Oxygen mainly exists in the form of FeO, MnO, SiO2, Al2O3 and other inclusions in steel, which reduces strength and plasticity of steel. In particular, it has a serious impact on fatigue strength and impact toughness.
Oxygen will increase iron loss in silicon steel, weaken magnetic permeability and magnetic induction, and increase magnetic aging effect.

Element 6: Mg (magnesium)

Effects on steel properties:
It can reduce number, size, uniform distribution and shape improvement of inclusions in steel. A small amount of magnesium can improve carbide size and distribution of bearing steel, carbide particles of magnesium-containing bearing steel are fine and uniform. When magnesium content is 0.002% to 0.003%, tensile strength and yield strength increase by more than 5%, and plasticity remains basically unchanged.

Element 7: Al (aluminum)

Effects on steel properties:
Aluminum is added to steel as a deoxidizer or alloying element, and deoxidation ability of aluminum is much stronger than that of silicon and manganese. Main function of aluminum in steel is to refine grains and fix nitrogen in steel, thereby significantly improving impact toughness of steel, reducing tendency of cold brittleness and aging. For example, D grade carbon structural steel requires that acid-soluble aluminum content in steel is not less than 0.015%, and cold-rolled steel sheet 08AL for deep drawing requires acid-soluble aluminum content in steel to be 0.015%-0.065%.
Aluminum can also improve corrosion resistance of steel, especially when used in combination with elements such as molybdenum, copper, silicon, and chromium.
Chromium molybdenum steel and chromium steel containing Al can increase its wear resistance. Presence of Al in high carbon tool steel can cause quench brittleness. Disadvantage of aluminum is that it affects hot workability, weldability and machinability of steel.
carbon structural steel 

Element 8: Si (Silicon)

Effects on steel properties:
Si is an important reducing agent and deoxidizer in steelmaking process: for many materials in carbon steel, Si contains less than 0.5%, these Si are generally brought in as a reducing agent and deoxidizer during steelmaking process.
Silicon can dissolve in ferrite and austenite to improve hardness and strength of steel, its role is second only to phosphorus, and stronger than manganese, nickel, chromium, tungsten, molybdenum, vanadium and other elements. However, when silicon content exceeds 3%, plasticity and toughness of steel will be significantly reduced. Silicon can improve elastic limit, yield strength and yield ratio (σs/σb), fatigue strength and fatigue ratio (σ-1/σb) of steel. This is because silicon or silicon-manganese steel can be used as spring steel.
Silicon can reduce density, thermal conductivity and electrical conductivity of steel. It can promote coarsening of ferrite grains and reduce coercivity. There is a tendency to reduce anisotropy of crystal, making magnetization easy and reducing magnetoresistance, which can be used to produce electrical steel, so magnetoresistance loss of silicon steel sheet is low. Silicon can improve magnetic permeability of ferrite, so that steel sheet has a higher magnetic induction in a weaker magnetic field. But silicon reduces magnetic induction of steel under strong magnetic fields. Silicon has a strong deoxidizing power, thereby reducing magnetic aging effect of iron.
When silicon-containing steel is heated in an oxidizing atmosphere, a layer of SiO2 film will be formed on the surface, thereby improving oxidation resistance of steel at high temperature.
Silicon can promote growth of columnar crystals in cast steel and reduce plasticity. If silicon steel cools quickly when heated, due to low thermal conductivity, temperature difference between inside and outside of steel is large, so it will break.
Silicon can reduce weldability of steel. Because silicon has a stronger binding ability with oxygen than iron, it is easy to generate low-melting silicate during welding, which increases fluidity of slag and molten metal, causes splashing, and affects welding quality. Silicon is a good deoxidizer. When deoxidizing with aluminum, adding a certain amount of silicon as appropriate can significantly improve rate of deoxidation. There is a certain amount of residual silicon in steel, which is brought in as a raw material during iron and steel making. In boiling steel, silicon is limited to <0.07%, and when intentionally added, ferrosilicon is added during steelmaking.

Element 9: P (phosphorus)

Effects on steel properties:
P is brought into steel by ore, and phosphorus is generally a harmful element. Although phosphorus can increase strength and hardness of steel, it causes a significant decrease in plasticity and impact toughness. Especially at low temperatures, it makes steel significantly brittle, a phenomenon called "cold brittleness". Cold brittleness deteriorates cold working and weldability of steel. The higher phosphorus content, the greater cold brittleness, so control of phosphorus content in steel is stricter. High-quality high-quality steel: P < 0.025%; high-quality steel: P < 0.04%; ordinary steel: P < 0.085%.
Solid solution strengthening and cold work hardening effects of P are very good. It is used in combination with copper to improve atmospheric corrosion resistance of low-alloy high-strength steel, but reduces its cold stamping performance. It is used in combination with sulfur and manganese to improve machinability, increase temper brittleness and cold brittleness sensitivity.
Phosphorus can improve specific resistance, and because it is easy to coarsely crystallize, it can reduce coercive force and eddy current loss. In terms of magnetic induction, magnetic induction of steel with high phosphorus content will increase under weak and medium magnetic fields. Hot processing of P-containing silicon steel is not difficult, but because it will make silicon steel cold brittle, content is ≯ 0.15% (for example, silicon steel for cold-rolled motors contains P=0.07-0.10%).
Phosphorus is element with the strongest effect of strengthening ferrite. (Effect of P on recrystallization temperature and grain growth of silicon steel will exceed effect of same silicon content by 4 to 5 times.)

Element 10: S (Sulfur)

Effects on steel properties:
Sulfur comes from ore and fuel coke for steelmaking. It is a harmful element in steel. Sulfur exists in steel in the form of iron sulfide (FeS), FeS and Fe form low melting point (985℃) compounds. Hot working temperature of steel is generally above 1150 ~ 1200 ℃, so when steel is hot worked, workpiece is cracked due to premature melting of FeS compound, which is called "hot embrittlement". Decreases ductility and toughness of steel, causing cracks during forging and rolling. Sulfur is also detrimental to weldability, reducing corrosion resistance. High-grade 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.
Because its chips are brittle and can get a very shiny surface, it can be used to make steel parts (named free-cutting steel) that require low load and high surface finish, (such as Cr14) intentionally added a small amount of sulfur (= 0.2 to 0.4%). Certain HSS tool steels carry a vulcanized surface.
carbon structural steel 

Elements 11, 12: K/Na (potassium/sodium)

Effects on steel properties:
Potassium/sodium can be used as a modifier to spheroidize carbides in white iron, so that toughness of white iron (and ledeburite steel) can be increased by more than two times while maintaining original hardness; Refining, vermicular iron treatment process stabilization; it is a strong austenitizing element, for example, it can reduce manganese/carbon ratio of austenitic manganese steel from 10:1~13:1 to 4:1 ~5:1.

Element 13: Ca (Calcium)

Effects on steel properties:
Adding calcium to steel can refine grains, partially desulfurize, change composition, quantity and morphology of non-metallic inclusions. It is basically similar to effect of adding rare earth to steel.
Improve corrosion resistance, wear resistance, high temperature and low temperature performance of steel; improve impact toughness, fatigue strength, plasticity and welding performance of steel; increase cold heading, shock resistance, hardness and contact durability of steel.
Addition of calcium to cast steel greatly improves fluidity of molten steel; surface finish of casting is improved, and anisotropy of structure in casting is eliminated; its casting performance, thermal crack resistance, mechanical performance and machining performance are increased to varying degrees.
Adding calcium to steel can improve resistance to hydrogen-induced cracking and laminar tearing, prolong service life of equipment and tools. Calcium can be used as a deoxidizer and inoculant when added to master alloy, and plays a role in microalloying.

Element 14: Ti (titanium)

Effects on steel properties:
Titanium has strong affinity with nitrogen, oxygen and carbon, and has a stronger affinity with sulfur than iron. It is a good deoxidizer and degasser and an effective element for fixing nitrogen and carbon. Although titanium is a strong carbide-forming element, it does not combine with other elements to form complex compounds. Titanium carbide has strong binding force, stability, and is not easy to decompose. Only when it is heated to above 1000 ℃ in steel can it slowly dissolve into solid solution.
Before being dissolved, titanium carbide particles have effect of preventing grain growth. Since affinity between titanium and carbon is much greater than that between chromium and carbon, titanium is often used to fix carbon in stainless steel to eliminate depletion of chromium at grain boundary, thereby eliminating or reducing intergranular corrosion of steel.
Titanium is also one of strong ferrite forming elements, which strongly increases A1 and A3 temperatures of steel. Titanium improves ductility and toughness in common low alloy steels. Strength of steel is increased as titanium fixes nitrogen and sulfur and forms titanium carbide. After normalizing, grains are refined, precipitation to form carbides can significantly improve plasticity and impact toughness of steel. Titanium-containing alloy structural steels have good mechanical properties and process properties. Main disadvantage is that hardenability is slightly poor.
Titanium with a content of about 5 times carbon is usually added to high chromium stainless steel, which can not only improve corrosion resistance (mainly anti-intergranular corrosion) and toughness of steel, but also organize grain growth tendency of steel at high temperature and improve welding performance of steel.

Element 15: V (Vanadium)

Effects on steel properties:
Vanadium has a strong affinity with carbon, ammonia and oxygen, and forms corresponding stable compounds with it. Vanadium exists mainly in the form of carbides in steel. Its main function is to refine structure and grain of steel, reduce strength and toughness of steel. When it is dissolved into a solid solution at high temperature, it increases hardenability; on the contrary, when it exists in the of carbide, it reduces hardenability. Vanadium increases tempering stability of hardened steel, produces a secondary hardening effect. Vanadium content in steel, except for high-speed tool steel, is generally not more than 0.5%.
Vanadium can refine grains in ordinary low carbon alloy steel, improve strength and yield ratio after normalizing and low temperature characteristics, improve welding performance of steel.
Vanadium in alloy structural steel is often used in combination with elements such as manganese, chromium, molybdenum and tungsten in structural steel because it will reduce hardenability under general heat treatment conditions. Vanadium is mainly used in quenched and tempered steel to improve strength and yield ratio of steel, refine grains, and pick up overheating sensitivity. In the case of carburizing steel, grain can be refined, so that steel can be directly quenched after carburizing without secondary quenching.
Vanadium in spring steel and bearing steel can improve strength and yield ratio, especially proportional limit and elastic limit, reduce sensitivity of decarburization during heat treatment, thereby improving surface quality. Bearing steel containing pentachrome and vanadium has high carbonization dispersion and good performance.
Vanadium refines grains in tool steels, reduces overheating sensitivity, increases tempering stability and wear resistance, thereby extending tool life.
carbon structural steel 

Element 16: Cr (Chromium)

Effects on steel properties:
Chromium can increase hardenability of steel and has effect of secondary hardening, which can improve hardness and wear resistance of carbon steel without making steel brittle. When content exceeds 12%, steel has good high temperature oxidation resistance and oxidation corrosion resistance, and also increases thermal strength of steel. Chromium is main alloying element of stainless acid-resistant steel and heat-resistant steel.
Chromium can improve strength and hardness of carbon steel in rolled state, reduce elongation and reduction of area. When chromium content exceeds 15%, strength and hardness will decrease, elongation and reduction of area will increase accordingly. Chromium-containing steel parts are easy to obtain high surface finish quality by grinding.
Main function of chromium in quenched and tempered structure is to improve hardenability, so that steel has better comprehensive mechanical properties after quenching and tempering. In carburized steel, chromium-containing carbides can also be formed, thereby improving wear resistance of material surface.
Chromium-containing spring steel is not easily decarburized during heat treatment. Chromium can improve wear resistance, hardness and red hardness of tool steel, and has good tempering stability. In electrothermal alloys, chromium can improve oxidation resistance, resistance and strength of alloy.

Element 17: Mn (manganese)

Effects on steel properties:
Mn can improve strength of steel: Since Mn is relatively cheap and can be infinitely dissolved with Fe, it has relatively little effect on plasticity while improving 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 stamping mild steel, dual-phase steel (DP steel), transformation-induced plasticity steel (TR steel), martensitic steel (MS steel), all contain manganese. Generally, Mn content in mild steel does not exceed 0.5%; Mn content in high-strength steels increases with strength level, such as martensitic steels, which can be as high as 3%.
Mn improves hardenability of steel and improves hot workability of steel: typical examples are 40Mn and 40 steel.
Mn can eliminate the influence of S (sulfur): Mn can form high melting point MnS with S in iron and steel smelting, thereby weakening and eliminating adverse effects of S.
However, content of Mn is also a double-edged sword. Mn content is not as high as possible. Increase of manganese content will reduce plasticity and weldability of steel.

Element 18: Co (Cobalt)

Effects on steel properties:
Cobalt is mostly used in special steels and alloys. Cobalt-containing high-speed steel has high high-temperature hardness. Adding molybdenum to maraging steel at the same time can obtain ultra-high hardness and good comprehensive mechanical properties. In addition, cobalt is also an important alloying element in thermally strong steels and magnetic materials.
Cobalt reduces hardenability of steel, so adding it to carbon steel alone will reduce comprehensive mechanical properties after quenching and tempering. Cobalt can strengthen ferrite, and when added to carbon steel, it can improve hardness, yield point and tensile strength of steel in annealed or normalized state. decreased with increasing cobalt content. Due to its anti-oxidation properties, cobalt is used in heat-resistant steels and heat-resistant alloys. Cobalt-based alloy gas turbines show its unique role.

Element 19: Ni (nickel)

Effects on steel properties:
Beneficial effects of nickel are: high strength, high toughness and good hardenability, high electrical resistance, high corrosion resistance.
On the one hand, strength of steel is strongly increased, and on the other hand, toughness of iron is always maintained at a very high level. Its brittle temperature is extremely low. (When Ni <0.3%, its brittle temperature is below -100℃. When amount of Ni increases, about 4~5%, its embrittlement temperature can be reduced to -180℃. Therefore, it can improve quenching structural steel at the same time. Strength and ductility of steel containing Ni=3.5%, without Cr can be air quenched, and Cr steel containing Ni=8% can also be transformed into M body at a very small cooling rate.
Lattice constant of Ni is similar to that of γ-iron, so it can form a continuous solid solution. This is beneficial to improve hardenability of steel. Ni can reduce critical point and increase stability of austenite, so quenching temperature can be reduced and hardenability is good. Generally, thick and heavy parts with large sections are made of Ni-added steel. When it is combined with Cr, W or Cr, Mo, hardenability can be increased especially. Nickel-molybdenum steel also has a high fatigue limit. (Ni steel has good thermal fatigue resistance, works in repeated hot and cold conditions. σ and αk are high)
Ni is used in stainless steel to make steel have a uniform A-body structure to improve corrosion resistance. Steel with Ni is generally not easy to overheat, so it can prevent growth of grains at high temperatures and still maintain a fine-grained structure.
carbon structural steel 

Element 20: Cu (copper)

Effects on steel properties:
Prominent role of copper in steel is to improve atmospheric corrosion resistance of ordinary low-alloy steel, especially when used in combination with phosphorus, adding copper can also improve strength and yield ratio of steel without adversely affecting welding performance. Rail steel (U-Cu) containing 0.20% to 0.50% copper, in addition to wear resistance, its corrosion resistance life is 2-5 times that of ordinary carbon steel rails.
When copper content exceeds 0.75%, aging strengthening effect can be produced after solution treatment and aging. When content is low, its effect is similar to that of nickel, but it is weaker. When content is high, it is unfavorable for hot deformation processing, which leads to copper embrittlement during hot deformation processing. 2% to 3% copper in austenitic stainless steel can have corrosion resistance to sulfuric acid, phosphoric acid, hydrochloric acid and stability to stress corrosion.

Element 21: Ga (gallium)

Effects on steel properties:
Gallium is an element that closes gamma region in steel. A small amount of gallium is easily dissolved in ferrite to form a substitutional solid solution. It is not a carbide former, nor does it form oxides, nitrides, or sulfides. In γ+a two-phase region, a small amount of gallium is easy to diffuse from austenite to ferrite, and its concentration in ferrite is high. Effect of trace gallium on mechanical properties of steel is mainly solid solution strengthening. Gallium has little effect on improving corrosion resistance of steel.

Element 22: As (arsenic)

Effects on steel properties:
Arsenic in ore can only be partially removed during sintering process, and it can also be removed by chlorination roasting. Arsenic is completely reduced into pig iron in blast furnace smelting process. When arsenic content in steel is more than 0.1%, it will increase brittleness of steel and deteriorate welding performance. Arsenic content in ore should be controlled, and arsenic content in ore should not exceed 0.07%.
Arsenic has a tendency to increase yield point σs, tensile strength σb and elongation δ5 of low carbon round steel, and has obvious effect on reducing impact toughness Akv of ordinary carbon round steel at room temperature.

Element 23: Se (selenium)

Effects on steel properties:
Selenium can improve machining performance of carbon steel, stainless steel and copper, and surface of parts is smooth.
In high magnetic induction oriented silicon steel, MnSe2 is often used as an inhibitor. Beneficial inclusions of MnSe2 have a stronger inhibitory effect on growth of primary recrystallized grains than beneficial inclusions of MnS, and are more conducive to promoting preferential growth of secondary recrystallized grains. A highly oriented (110)[001] texture is obtained.

Element 24: Zr (zirconium)

Effects on steel properties:
Zirconium is a strong carbide former, and its role in steel is similar to that of niobium, tantalum, and vanadium. Adding a small amount of zirconium has effect of degassing, purifying and refining grains, which is beneficial to low temperature performance of steel and improves stamping performance.

Element 25: Nb (niobium)

Effects on steel properties:
Niobium often coexists with tantalum, and their roles in steel are similar. Niobium and tantalum partially dissolve into solid solution and play a role in solid solution strengthening. When austenite is dissolved, hardenability of steel is significantly improved. However, in the form of carbides and oxide particles, it refines grains and reduces hardenability of steel. It can increase tempering stability of steel and has a secondary hardening effect. Trace amounts of niobium can increase strength of steel without affecting its ductility or toughness. Due to effect of grain refinement, it can improve impact toughness of steel and reduce its brittle transition temperature. When content is more than 8 times that of carbon, almost all carbon in steel can be fixed, so that steel has good hydrogen resistance. In austenitic steels, it can prevent intergranular corrosion of steel by oxidizing media. Due to fixed carbon and precipitation hardening, it can improve high temperature properties of thermal strength steel, such as creep strength.
Niobium can improve yield strength and impact toughness of ordinary low alloy steel for construction, and reduce brittle transition temperature, which is beneficial to welding performance. In carburizing and quenched and tempered alloy structural steel, while increasing hardenability, toughness and low temperature performance of steel can be improved, air hardenability of low-carbon martensitic heat-resistant stainless steel can be reduced, it can reduce air hardenability of low carbon martensitic heat-resistant stainless steel, avoid hardening and tempering brittleness, and improve creep strength.

Element 26: Mo (Molybdenum)

Effects on steel properties:
Molybdenum can improve hardenability and thermal strength in steel, prevent temper brittleness, increase remanence, coercivity and corrosion resistance in certain media.
In quenched and tempered steel, molybdenum can harden and harden parts with larger sections, improve tempering resistance or tempering stability of steel, and enable parts to be tempered at a higher temperature, thereby more effectively eliminating ( or reduce) residual stress and increase plasticity.
In addition to above functions, molybdenum in carburized steel can also reduce tendency of carbides to form a continuous network on grain boundary in carburized layer, reduce residual austenite in carburized layer, relatively increase wear resistance of surface layer.
In forging die steel, molybdenum can also maintain a relatively stable hardness of steel and increase resistance to deformation, cracking and wear.
In stainless acid-resistant steel, molybdenum can further improve corrosion resistance to organic acids (such as formic acid, acetic acid, oxalic acid, etc.) and hydrogen peroxide, sulfuric acid, sulfurous acid, sulfate, acid dyes, bleaching powder liquid, etc. Especially due to addition of molybdenum, tendency to pitting corrosion caused by presence of chloride ions is prevented. W12Cr4V4Mo high-speed steel containing about 1% molybdenum has wear resistance, tempering hardness and red hardness.

Element 27: Sn (tin)

Effects on steel properties:
Tin has always been a harmful impurity element in steel. It affects quality of steel, especially quality of continuous casting billets, making steel hot brittleness, temper brittleness, cracks and fractures, and affecting welding performance of steel, which is one of "five evils" of steel. However, tin plays an important role in electrical steel, cast iron, and free-cutting steel.
Size of silicon steel grains is related to segregation of tin, which hinders growth of grains. The higher tin content, the greater grain precipitation, which effectively hinders growth of grains. The higher tin content, the greater grain precipitation, the stronger ability to hinder grain growth, the smaller grain size, and the less iron loss. Tin can change magnetic properties of silicon steel, improve favorable texture {100} intensity in finished oriented silicon steel, and magnetic induction intensity increases significantly.
When cast iron contains a small amount of tin, it can improve its wear resistance and affect fluidity of molten iron. Pearlitic ductile cast iron has high strength and high wear resistance. In order to obtain as-cast pearlite, tin is added to alloy liquid during smelting. Since tin is an element that hinders spheroidization of graphite, amount added should be controlled. Generally controlled at ≤0.1%.
Free cutting steel can be divided into sulfur series, calcium series, lead series and composite free cutting steel. Tin has a clear tendency to segregate near inclusions and defects. Tin does not change shape of sulfide inclusions in steel, but improves brittleness through segregation of grain boundaries and phase boundaries, and improves free machinability of steel. When tin content is greater than 0.05%, steel has good machinability.
carbon structural steel 

Element 28: Sb (antimony)

Effects on steel properties:
After adding Sb to high magnetic induction oriented silicon steel, grain size of primary recrystallization and secondary recrystallization is refined, secondary recrystallization structure is more perfect, and magnetic properties are improved. After cold rolling and decarburization annealing of Sb-containing steel, among its texture components, components {110}<115> or {110}<001> that are conducive to development of secondary recrystallization are strengthened, and secondary crystal correction increase in number.
In Sb-containing construction welding steel, at austenite temperature, Sb in steel precipitates at Mn S inclusions and along prior austenite grain boundaries. Increasing enrichment and precipitation on Mn S inclusions can refine microstructure of steel and improve toughness.

Element 29: W (Tungsten)

Effects on steel properties:
In addition to forming carbides in steel, tungsten partially dissolves into iron to form a solid solution. Its effect is similar to that of molybdenum. Calculated by mass fraction, general effect is not as significant as that of molybdenum. Main pattern of tungsten in steel is to increase tempering stability, red hardness, thermal strength and increased wear resistance due to formation of carbides. Therefore, it is mainly used for tool steel, such as high-speed steel, steel for hot forging dies, etc.
Tungsten forms refractory carbides in high-quality spring steel. When tempering at higher temperatures, it can ease aggregation process of carbides and maintain high high temperature strength. Tungsten can also reduce thermal sensitivity of steel, increase hardenability and increase hardness. 65SiMnWA spring steel has high hardness after air cooling after hot rolling. Spring steel with a cross-section of 50mm2 can be hardened in oil, and can be used as an important spring that can withstand large loads, heat resistance (not more than 350 ℃) and shock. 30W4Cr2VA high-strength, heat-resistant and high-quality spring steel has great hardenability, quenched at 1050-1100℃, and has a tensile strength of 1470-1666Pa after tempering at 550-650℃. It is mainly used to manufacture springs used under high temperature (not more than 500℃).
Due to addition of tungsten, wear resistance and machinability of steel can be significantly improved, so tungsten is main element of alloy tool steel.

Element 30: Pb (lead)

Effects on steel properties:
Lead can improve machinability. Lead free cutting steel has good mechanical properties and heat treatment. Lead has a tendency to be gradually replaced due to environmental pollution and harmful effects in recycling and smelting process of scrap steel.
Lead and iron are difficult to form solid solutions or compounds, and are easy to segregate at grain boundaries in spherical form, which is one of causes of brittleness of steel and cracks in welds at 200-480℃.

Element 31: Bi (bismuth)

Effects on steel properties:
Adding 0.1~0.4 bismuth to free cutting steel can improve cutting performance of steel. When bismuth is evenly dispersed in steel, particulate bismuth melts after contact with cutting tool, acts as a lubricant, and breaks cutting, avoiding overheating, thereby increasing cutting speed. Recently, a large amount of bismuth has been added to stainless steel to improve cutting performance of stainless steel.
Bi exists in three forms in free-cutting steel: it exists alone in steel matrix, it is surrounded by sulfides, it is between steel matrix and sulfides. In S-Bi free-cutting steel ingots, deformation rate of MnS inclusions decreases with increase of Bi content. Bi metal in steel can play a role in inhibiting sulfide deformation during ingot forging.
Adding 0.002-0.005% bismuth to cast iron can improve casting properties of malleable cast iron, increase tendency of white mouth and shorten annealing time, and elongation properties of parts become better. Adding 0.005% bismuth to ductile iron improves its shock and tensile properties. It is difficult to add bismuth to steel, because bismuth has volatilized in a large amount at 1500℃, and it is difficult to infiltrate bismuth into steel evenly. At present, Bi-Mn composite disk with a melting point of 1050℃ is used abroad as an additive instead of bismuth, but utilization rate of bismuth is still only about 20%.
Nippon Steel, Posco, Kawasaki Steel and other companies have successively proposed that adding Bi can significantly improve B8 value of oriented silicon steel. According to statistics, the total number of inventions of Nippon Steel and JFE adding Bi to produce high magnetic induction oriented silicon steel has exceeded 100. After adding Bi, magnetic induction reaches more than 1.90T, and the highest reaches 1.99T.

Other elements: Re rare earth

Effects on steel properties:
Generally speaking, rare earth elements refer to lanthanide elements with atomic numbers from 57 to 71 in periodic table (lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, Thulium, ytterbium, lutetium) plus scandium 21 and yttrium 39, a total of 17 elements. They are close in nature and cannot be easily separated. Unseparated rare earth is called mixed rare earth, which is relatively cheap. In steel, rare earth can be deoxidized, desulfurized, and microalloyed can also change deformability of rare earth inclusions. In particular, it can denature brittle Al2O3 to a certain extent, which can improve fatigue properties of most steel grades.
Rare earth elements like Ca, Ti, Zr, Mg, Be are the most effective deformers for sulfides. Adding an appropriate amount of RE in steel can make oxide and sulfide inclusions into finely dispersed spherical inclusions to eliminate harmfulness of MnS and other inclusions. In production practice, sulfur exists in the form of FeS and MnS in steel. When Mn in steel is high, formation tendency of MnS is high. Although its high melting point can avoid hot brittleness, MnS can extend into strips along processing direction during processing and deformation, plasticity, toughness, and fatigue strength of steel are significantly reduced, so it is necessary to add RE to steel for deformation treatment.
Rare earth elements can also improve oxidation and corrosion resistance of steel. Effect of oxidation resistance exceeds that of elements such as silicon, aluminum, and titanium. It can improve fluidity of steel, reduce non-metallic inclusions, make steel structure dense and pure.
Role of rare earth in steel mainly includes purification, modification and alloying. With gradual control of oxygen and sulfur content, traditional purification and metamorphism of molten steel is gradually weakening, more perfect cleaning technology and alloying functions are replaced.
Rare earth elements in Fe-Cr-Al alloys increase oxidation resistance of alloy, maintain fine grains of steel at high temperatures, and improve high-temperature strength, thus significantly improving life of electrothermal alloy.

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