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. When it is cooled, it is too late to escape and accumulates in the structure to form high-pressure fine pores, which drastically reduces the plasticity, toughness and fatigue strength of the steel. , which will cause cracks and brittle fractures in severe cases. "Hydrogen embrittlement" mainly occurs in martensitic steels, not very prominent in ferrite steels, and generally increases with hardness and carbon content.
On the other hand, H can improve the magnetic permeability of steel, but it also increases the coercivity and iron loss (the coercivity can be increased by 0.5 to 2 times after adding H).
Element 2: B (boron)
Effects on steel properties:
The main function of B in steel is to increase the 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 percent to 0.005 percent . It can replace 1.6 percent nickel, 0.3 percent chromium or 0.2 percent 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, so it cannot be used. Boron completely replaces molybdenum.
Adding boron to medium carbon carbon steel can greatly improve the properties of steel with a thickness of more than 20mm after quenching and tempering due to the 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 the effect of boron weakens or even disappears with the increase of carbon content in the steel, when selecting boron-containing carburized steel, it must be considered that after the parts are carburized, the hardenability of the carburized layer will be lower than that of the core. This feature of permeability.
Spring steel generally requires complete hardening, and usually the spring area is not large, so it is advantageous to use boron-containing steel. The 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 percent boron to boiling steel can eliminate the aging phenomenon of steel.
Element 3: C (Carbon)
Effects on steel properties:
C is the main element next to iron, which directly affects the strength, plasticity, toughness and weldability of steel.
When the carbon content in the steel is below {{0}}.8 percent , the strength and hardness of the steel increase as the carbon content increases, while the ductility and toughness decrease; but when the carbon content is above 1.0 percent , as the carbon content increases increase, the strength of the steel decreases.
With the increase of carbon content, the weldability of steel deteriorates (for steel with carbon content greater than 0.3 percent , the weldability decreases significantly), cold brittleness and aging sensitivity increase, and atmospheric corrosion resistance decreases.
Element 4: N (nitrogen)
Effects on steel properties:
The effect of N on the properties of steel is similar to that of carbon and phosphorus. With the increase of nitrogen content, the strength of the steel can be significantly improved, the plasticity, especially the toughness, can also be significantly reduced, the weldability is deteriorated, and the cold brittleness is increased; at the same time, the aging tendency and Cold brittleness and hot brittleness, damage the welding performance and cold bending performance of steel. Therefore, the nitrogen content in the steel should be minimized and limited. It is generally stipulated that the nitrogen content should not be higher than 0.018 percent .
Nitrogen can reduce its adverse effects with the combination of aluminum, niobium, vanadium and other elements, improve the properties of steel, and can be used as an alloying element for low-alloy steel. For some grades of stainless steel, appropriately increasing the N content can reduce the amount of Cr used, which can effectively reduce the cost.
Element 5: O (oxygen)
Effects on steel properties:
O is a harmful element in steel. It enters the steel naturally during the steelmaking process. Although manganese, silicon, iron and aluminum are added for deoxidation at the end of the steelmaking process, it is impossible to remove it completely. During the solidification of molten steel, carbon monoxide is formed by the reaction of oxygen and carbon in the solution, which can cause bubbles. Oxygen mainly exists in the form of FeO, MnO, SiO2, Al2O3 and other inclusions in the steel, which reduces the strength and plasticity of the steel. In particular, it has a serious impact on fatigue strength and impact toughness.
Oxygen will increase the iron loss in silicon steel, weaken the magnetic permeability and magnetic induction, and increase the magnetic aging effect.
Element 6: Mg (magnesium)
Effects on steel properties:
It can reduce the number, size, uniform distribution and shape improvement of inclusions in steel. A small amount of magnesium can improve the carbide size and distribution of bearing steel, and the carbide particles of magnesium{{0}}containing bearing steel are fine and uniform. When the magnesium content is 0.002 percent to 0.003 percent , the tensile strength and yield strength increase by more than 5 percent , and the plasticity remains basically unchanged.
Element 7: Al (aluminum)
Effects on steel properties:
Aluminum is added to steel as a deoxidizer or alloying element, and the deoxidation ability of aluminum is much stronger than that of silicon and manganese. The main function of aluminum in steel is to refine grains and fix nitrogen in steel, thereby significantly improving the impact toughness of steel and reducing the tendency of cold brittleness and aging. For example, the D grade carbon structural steel requires that the acid{{0}}soluble aluminum content in the steel is not less than 0.015 percent , and the cold-rolled steel sheet 08AL for deep drawing requires the acid-soluble aluminum content in the steel to be 0.015 percent -0.065 percent .
Aluminum can also improve the 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. The presence of Al in high carbon tool steel can cause quench brittleness. The disadvantage of aluminum is that it affects the hot workability, weldability and machinability of steel.
Element 8: Si (Silicon)
Effects on steel properties:
Si is an important reducing agent and deoxidizer in the steelmaking process: for many materials in carbon steel, Si contains less than 0.5 percent Si, which is generally brought into the steelmaking process as a reducing agent and deoxidizer. of.
Silicon can dissolve in ferrite and austenite to improve the 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 the silicon content exceeds 3 percent , the plasticity and toughness of the steel will be significantly reduced. Silicon can improve the elastic limit, yield strength and yield ratio (σs/σb), and 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 the density, thermal conductivity and electrical conductivity of steel. It can promote the coarsening of ferrite grains and reduce the coercivity. There is a tendency to reduce the anisotropy of the crystal, making the magnetization easy and reducing the magnetoresistance, which can be used to produce electrical steel, so the magnetoresistance loss of the silicon steel sheet is low. Silicon can improve the magnetic permeability of ferrite, so that the steel sheet has a higher magnetic induction in a weaker magnetic field. But silicon reduces the magnetic induction of steel under strong magnetic fields. Silicon has a strong deoxidizing power, thereby reducing the magnetic aging effect of iron.
When the silicon-containing steel is heated in an oxidizing atmosphere, a layer of SiO2 film will be formed on the surface, thereby improving the oxidation resistance of the steel at high temperature.
Silicon can promote the growth of columnar crystals in cast steel and reduce plasticity. If the silicon steel cools quickly when heated, due to the low thermal conductivity, the temperature difference between the inside and outside of the steel is large, so it will break.
Silicon can reduce the 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 the 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 the 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="">
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 the strength and hardness of steel, it causes a significant decrease in plasticity and impact toughness. Especially at low temperatures, it makes the steel significantly brittle, a phenomenon called "cold brittleness". Cold brittleness deteriorates the cold working and weldability of steel. The higher the phosphorus content, the greater the cold brittleness, so the 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=""><>
P has good solid solution strengthening and cold work hardening effects. It is used in combination with copper to improve the 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 and increase recovery. Fire brittleness and cold brittleness sensitivity.
Phosphorus can improve the specific resistance, and because it is easy to coarsely crystallize, it can reduce the coercive force and eddy current loss. In terms of magnetic induction, the magnetic induction of steel with high phosphorus content will increase under weak and medium magnetic fields. Hot working of P{{0}}containing silicon steel It is not difficult, but because it will make the silicon steel cold brittle, the content is ≯ 0.15 percent (for example, the silicon steel for cold-rolled motors contains P=0.07-0.10 percent ).
Phosphorus is the element with the strongest effect of strengthening ferrite. (The effect of P on the recrystallization temperature and grain growth of silicon steel will exceed the effect of the 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), and FeS and Fe form low melting point (985 degree ) compounds. The hot working temperature of steel is generally above 1150 1200 degree , so when the steel is hot worked, the workpiece is cracked due to the premature melting of the FeS compound, which is called "hot embrittlement". Decreases the ductility and toughness of the 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="">
Because its chips are brittle and can get a very shiny surface, it can be used to make steel parts (named free{{0}}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 percent ). Certain HSS tool steels carry a vulcanized surface.
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 the toughness of white iron (and ledeburite steel) can be increased by more than two times while maintaining the original hardness; Refining, vermicular iron treatment process stabilization; is a strong austenitizing element, for example, it can reduce the manganese/carbon ratio of austenitic manganese steel from 10:113:1 to 4:1 5:1.
Element 13: Ca (Calcium)
Effects on steel properties:
Adding calcium to steel can refine grains, partially desulfurize, and change the composition, quantity and morphology of non-metallic inclusions. It is basically similar to the effect of adding rare earth to steel.
Improve the corrosion resistance, wear resistance, high temperature and low temperature performance of the steel; improve the impact toughness, fatigue strength, plasticity and welding performance of the steel; increase the cold heading, shock resistance, hardness and contact durability of the steel.
The addition of calcium to the cast steel greatly improves the fluidity of the molten steel; the surface finish of the casting is improved, and the anisotropy of the structure in the 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 the resistance to hydrogen-induced cracking and lamellar tearing, and prolong the use of equipment and tools
life. Calcium can be used as a deoxidizer and inoculant when added to the 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 degree in steel can it slowly dissolve into solid solution.
Before being dissolved, the titanium carbide particles have the effect of preventing grain growth. Since the 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 the depletion of chromium at the grain boundary, thereby eliminating or reducing intergranular corrosion of steel.
Titanium is also one of the strong ferrite forming elements, which strongly increases the A1 and A3 temperatures of the steel. Titanium can improve plasticity and toughness in ordinary low alloy steel. The strength of the steel is increased as titanium fixes nitrogen and sulfur and forms titanium carbide. After normalizing, the grains are refined, and the precipitation to form carbides can significantly improve the plasticity and impact toughness of the steel. Titanium-containing alloy structural steels have good mechanical properties and process properties. The main disadvantage is that the 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 the corrosion resistance (mainly anti-intergranular corrosion) and toughness of the steel, but also organize the grain growth tendency of the steel at high temperature and improve Weldability 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 the structure and grain of the steel and reduce the strength and toughness of the steel. When it is dissolved into a solid solution at high temperature, it increases the hardenability; on the contrary, when it exists in the form of carbide, it reduces the hardenability. Vanadium increases the tempering stability of hardened steel and produces a secondary hardening effect. The vanadium content in steel, except for high{{0}}speed tool steel, is generally not more than 0.5 percent .
Vanadium can refine grains in ordinary low carbon alloy steel, improve the strength and yield ratio after normalizing and low temperature characteristics, and improve the 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 the hardenability under general heat treatment conditions. Vanadium is mainly used in quenched and tempered steel to improve the strength and yield ratio of steel, refine grains, and pick up overheating sensitivity. In the case of carburizing steel, the grain can be refined, so that the steel can be directly quenched after carburizing without secondary quenching.
Vanadium in spring steel and bearing steel can improve the strength and yield ratio, especially the proportional limit and elastic limit, reduce the sensitivity of decarburization during heat treatment, thereby improving the surface quality. The 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.
Element 16: Cr (Chromium)
Effects on steel properties:
Chromium can increase the hardenability of steel and has the effect of secondary hardening, which can improve the hardness and wear resistance of carbon steel without making the steel brittle. When the content exceeds 12 percent , the steel has good high temperature oxidation resistance and oxidation corrosion resistance, and also increases the thermal strength of the steel. Chromium is the main alloying element of stainless acid-resistant steel and heat-resistant steel.
Chromium can improve the strength and hardness of carbon steel in the rolled state, and reduce the elongation and reduction of area. When the chromium content exceeds 15 percent , the strength and hardness will decrease, and the elongation and reduction of area will increase accordingly. Chromium-containing steel parts are easy to obtain high surface finish quality by grinding.
The main function of chromium in the quenched and tempered structure is to improve the hardenability, so that the steel has better comprehensive mechanical properties after quenching and tempering. In the carburized steel, chromium-containing carbides can also be formed, thereby improving the surface resistance of the material. Abrasiveness.
Chromium-containing spring steel is not easily decarburized during heat treatment. Chromium can improve the wear resistance, hardness and red hardness of tool steel, and has good tempering stability. In electrothermal alloys, chromium can improve the oxidation resistance, resistance and strength of the alloy.
Element 17: Mn (manganese)
Effects on steel properties:
Mn can improve the strength of steel: Since Mn is relatively cheap and can be infinitely dissolved 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 stamping mild steel, dual{{0}}phase steel (DP steel), transformation-induced plasticity steel (TR steel), martensitic steel (MS steel), all contain manganese. Generally, the Mn content in mild steel does not exceed 0.5 percent ; the Mn content in high-strength steels increases with the strength level, such as martensitic steels, which can be as high as 3 percent .
Mn improves the hardenability of steel and improves the 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 the adverse effects of S.
However, the content of Mn is also a double-edged sword. The Mn content is not as high as possible. The increase of manganese content will reduce the 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 the hardenability of steel, so adding it to carbon steel alone will reduce the comprehensive mechanical properties after quenching and tempering. Cobalt can strengthen ferrite, and when added to carbon steel, it can improve the hardness, yield point and tensile strength of steel in the 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:
The beneficial effects of nickel are: high strength, high toughness and good hardenability, high electrical resistance, high corrosion resistance.
On the one hand, the strength of the steel is strongly increased, and on the other hand, the toughness of the 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="" the="" amount="" of="" ni="" increases,="" about="" 4~5%,="" its="" embrittlement="" temperature="" can="" be="" reduced="" to="" -180℃.="" therefore,="" it="" can="" improve="" the="" quenching="" structural="" steel="" at="" the="" same="" time.="" the="" strength="" and="" ductility="" of="" the="" steel="" containing="" ni="3.5%," without="" cr="" can="" be="" air="" quenched,="" and="" the="" cr="" steel="" containing="" ni="8%" can="" also="" be="" transformed="" into="" m="" body="" at="" a="" very="" small="" cooling="">
The lattice constant of Ni is similar to that of -iron, so it can form a continuous solid solution. This is beneficial to improve the hardenability of steel. Ni can reduce the critical point and increase the stability of austenite, so the quenching temperature can be reduced and the 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, the hardenability can be increased especially. Nickel-molybdenum steel also has a high fatigue limit. (Ni steel has good thermal fatigue resistance, and works in repeated hot and cold conditions. σ, k are high)
Ni is used in stainless steel to make the steel have a uniform A body structure to improve corrosion resistance. Steel with Ni is generally not easy to overheat, so it can prevent the growth of grains at high temperatures and still maintain a fine-grained structure.
Element 20: Cu (copper)
Effects on steel properties:
The prominent role of copper in steel is to improve the atmospheric corrosion resistance of ordinary low{{0}}alloy steel, especially when used in combination with phosphorus, adding copper can also improve the strength and yield ratio of steel without adversely affecting the welding performance. Rail steel (U-Cu) containing 0.20 percent to 0.50 percent copper, in addition to wear resistance, its corrosion resistance life is 2-5 times that of ordinary carbon steel rails.
When the copper content exceeds 0.75 percent , the aging strengthening effect can be produced after solution treatment and aging. When the content is low, its effect is similar to that of nickel, but it is weaker. When the content is high, it is unfavorable for hot deformation processing, which leads to copper embrittlement during hot deformation processing. 2 percent to 3 percent copper in austenitic stainless steel can have corrosion resistance to sulfuric acid, phosphoric acid and hydrochloric acid and stability to stress corrosion.
Element 21: Ga (gallium)
Effects on steel properties:
Gallium is an element that closes the 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 the plus a two-phase region, a small amount of gallium is easy to diffuse from austenite to ferrite, and its concentration in ferrite is high. The effect of trace gallium on the mechanical properties of steel is mainly solid solution strengthening. Gallium has little effect on improving the corrosion resistance of steel.
Element 22: As (arsenic)
Effects on steel properties:
The arsenic in the ore can only be partially removed during the sintering process, and it can also be removed by chlorination roasting. All the arsenic is reduced into the pig iron during the blast furnace smelting process. Welding performance deteriorates. The arsenic content in the ore should be controlled, and the arsenic content in the ore should not exceed 0.07 percent .
Arsenic has a tendency to increase the yield point σs, tensile strength σb and elongation δ5 of low carbon round steel, and has obvious effect on reducing the impact toughness Akv of ordinary carbon round steel at room temperature.
Element 23: Se (selenium)
Effects on steel properties:
Selenium can improve the machining performance of carbon steel, stainless steel and copper, and the surface of the parts is smooth.
In high magnetic induction oriented silicon steel, MnSe2 is often used as an inhibitor. The beneficial inclusions of MnSe2 have a stronger inhibitory effect on the growth of the primary recrystallized grains than the beneficial inclusions of MnS, and are more conducive to promoting the preferential growth of the 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 the effect of degassing, purifying and refining grains, which is beneficial to the low temperature performance of steel and improves the 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 dissolved in austenite, the hardenability of steel is significantly improved. However, in the form of carbides and oxide particles, it refines the grains and reduces the hardenability of the steel. It can increase the tempering stability of steel and has a secondary hardening effect. Trace amounts of niobium can increase the strength of steel without affecting its ductility or toughness. Due to the effect of grain refinement, it can improve the impact toughness of steel and reduce its brittle transition temperature. When the content is more than 8 times that of carbon, almost all the carbon in the steel can be fixed, so that the 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 the high temperature properties of thermal strength steel, such as creep strength.
Niobium can improve the yield strength and impact toughness of ordinary low alloy steel for construction, and reduce the brittle transition temperature, which is beneficial to welding performance. In carburizing and quenched and tempered alloy structural steel while increasing the hardenability. Improve toughness and low temperature properties of steel. It can reduce the 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 and coercivity and corrosion resistance in certain media.
In quenched and tempered steel, molybdenum can harden and harden parts with larger sections, improve the tempering resistance or tempering stability of the steel, and enable the parts to be tempered at a higher temperature, thereby more effectively eliminating ( or reduce) residual stress and increase plasticity.
In addition to the above functions, molybdenum in carburized steel can also reduce the tendency of carbides to form a continuous network on the grain boundary in the carburized layer, reduce the residual austenite in the carburized layer, and relatively increase the surface layer. wear resistance.
In forging die steel, molybdenum can also maintain a relatively stable hardness of the steel and increase the resistance to deformation. Resistance to cracking and abrasion, etc.
In stainless acid-resistant steel, molybdenum can further improve the 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 the addition of molybdenum, the tendency to pitting corrosion caused by the presence of chloride ions is prevented. W12Cr4V4Mo high-speed steel containing about 1 percent 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 the quality of steel, especially the quality of continuous casting billets, making steel hot brittleness, temper brittleness, cracks and fractures, and affecting the welding performance of steel. It is one of the "five evils" of steel. one. However, tin plays an important role in electrical steel, cast iron, and free-cutting steel.
The size of silicon steel grains is related to the segregation of tin, which hinders the growth of grains. The higher the tin content, the greater the grain precipitation, which effectively hinders the growth of grains. The higher the tin content, the greater the grain precipitation, the stronger the ability to hinder the grain growth, the smaller the grain size, and the less iron loss. Tin can change the magnetic properties of silicon steel, improve the favorable texture {100} intensity in the finished oriented silicon steel, and the magnetic induction intensity increases significantly.
When the cast iron contains a small amount of tin, it can improve its wear resistance and affect the fluidity of molten iron. Pearlitic ductile iron has high strength and high wear resistance. In order to obtain as{{0}}cast pearlite, tin is added to the alloy liquid during smelting. Since tin is an element that hinders the spheroidization of graphite, the amount added should be controlled. Generally controlled at Less than or equal to 0.1 percent .
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 the shape of sulfide inclusions in steel, but improves brittleness through the segregation of grain boundaries and phase boundaries, and improves the free machinability of steel. When the tin content is greater than 0.05 percent , the steel has good machinability.
Element 28: Sb (antimony)
Effects on steel properties:
After adding Sb to the high magnetic induction oriented silicon steel, the grain size of the primary recrystallization and the secondary recrystallization is refined, the secondary recrystallization structure is more perfect, and the magnetic properties are improved. After cold rolling and decarburization annealing of Sb-containing steel, among its texture components, the components {110}<115> or {110}<001> that are conducive to the development of secondary recrystallization are strengthened, and the secondary crystal correction increase in number.
In Sb-containing construction welding steel, at the austenite temperature, Sb in the steel precipitates at the Mn S inclusions and along the prior austenite grain boundaries. Refinement and increased 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, the general effect is not as significant as that of molybdenum. The main pattern of tungsten in steel is to increase tempering stability, red hardness, thermal strength and increased wear resistance due to the 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 the aggregation process of carbides and maintain high high temperature strength. Tungsten can also reduce the 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 degree ) and shock. 30W4Cr2VA high-strength, heat-resistant and high-quality spring steel has great hardenability, quenched at 1050-1100 degree , and has a tensile strength of 1470-1666Pa after tempering at 550-650 degree . It is mainly used to manufacture springs used under high temperature (not more than 500 degree ).
Due to the addition of tungsten, the wear resistance and machinability of steel can be significantly improved, so tungsten is the 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 the 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 the causes of brittleness of steel and cracks in welds at 200-480 degree .
Element 31: Bi (bismuth)
Effects on steel properties:
Adding 0.10.4 bismuth to free cutting steel can improve the cutting performance of steel. When the bismuth is evenly dispersed in the steel, the particulate bismuth melts after contact with the cutting tool, acts as a lubricant, and breaks the cutting, avoiding overheating, thereby increasing the cutting speed. Recently, a large amount of bismuth has been added to stainless steel to improve the cutting performance of stainless steel.
Bi exists in three forms in free-cutting steel: it exists alone in the steel matrix, it is surrounded by sulfides, and it is between the steel matrix and the sulfides. In S-Bi free-cutting steel ingots, the deformation rate of MnS inclusions decreases with the increase of Bi content. Bi metal in steel can play a role in inhibiting sulfide deformation during ingot forging.
Adding {{0}}.002-0.005 percent bismuth to cast iron can improve the casting properties of malleable cast iron, increase the tendency of white mouth and shorten the annealing time, and the elongation properties of the parts become better. Adding 0.005 percent bismuth to ductile iron improves its shock and tensile properties. It is difficult to add bismuth to steel, because bismuth has volatilized in large quantities at 1500 degree C, and it is difficult to infiltrate bismuth into steel evenly. At present, the Bi-Mn composite plate with a melting point of 1050 degree is used abroad as an additive instead of bismuth, but the utilization rate of bismuth is still only about 20 percent .
Nippon Steel, Posco, Kawasaki Steel and other companies have successively proposed that adding Bi can significantly improve the 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, the 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 the lanthanide elements with atomic numbers from 57 to 71 in the 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. The 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 the deformability of rare earth inclusions. In particular, it can denature the brittle Al2O3 to a certain extent, which can improve the 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 the harmfulness of MnS and other inclusions. In production practice, sulfur exists in the form of FeS and MnS in the steel. When the Mn in the steel is high, the formation tendency of MnS is high. Although its high melting point can avoid the occurrence of hot brittleness, MnS can extend into a strip along the processing direction during processing and deformation, and the plasticity, toughness, and fatigue strength of the steel are significantly reduced. Therefore, it is necessary to add RE to the steel for deformation treatment. .
Rare earth elements can also improve the oxidation and corrosion resistance of steel. The effect of oxidation resistance exceeds that of elements such as silicon, aluminum, and titanium. It can improve the fluidity of steel, reduce non-metallic inclusions, and make the steel structure dense and pure.
The role of rare earth in steel mainly includes purification, modification and alloying. As the oxygen and sulfur content gradually controlled