Background technology
The high-carbon-chromium bearing steel of one-hundred-year history (is generally determined by form, size, the quantity of steel inclusion and the degree that is evenly distributed the fatigue lifetime of its degree of cleaning and bearing the fatigue lifetime of bearing.) closely bound up.(before the nineties in last century) for a long time, the metallargist always oxygen level as the key index (eighties of weighing bearing life, the leading indicator of degree of cleaning is oxygen content in steel: oxygen level is low more, bearing fatigue life is high more), and done a large amount of research and put into practice work reducing oxygen level, Japan, it (is exactly 10 * 10-6 that the oxygen level of the high-carbon-chromium bearing steel of states such as Sweden (oxygen activity+oxide inclusion) has been controlled at 0.0010%, 10ppm just) below, nowadays Japanese bearing steel oxygen level can be controlled at 3-5ppm, and domestic part special steel enterprise also can be controlled at 6-7ppm.
The beginning of the nineties, along with (fast development of automotive industry, automatic industrial, electronic industry and IT industry, the bearing that is used to make various components of machine requires microminiaturization, lightweight and low noiseization to the market requirement of the continuous research of bearing life influence factor and accurate subwoofer and quiet bearing.), it is found that: the principal element that influences bearing life also has titanium content, nitrogen content in the steel except oxygen level; The content of titanium, nitrogen is low more, and bearing life is high more.Especially oxygen content in steel 〉=0.0010% o'clock, titanium content in the steel 〉=0.0020%, the noise decibel of accurate subwoofer or quiet bearing increases greatly.The later stage nineties, some internationally recognizable precision bearing manufacturerss are to the degree of cleaning of the high-carbon-chromium bearing steel (abrasive of having higher requirement, ultrapure): to the high-carbon-chromium bearing steel of same heat, its oxygen level, titanium content and nitrogen content difference≤0.0007%, 0.0012% and 0.0055%.
Can satisfy the bearing steel manufacturer of precision bearing producer at present to the abrasive clarity basic demand of high-carbon-chromium bearing steel, mainly contain Japan abroad, developed abrasive bearing steel production method (" metal Leader, the world " as Kawasaki Steel company by the LD-RH-CC technical process, on February 25th, 2003, the 3rd edition); Datong District know many steel mills by the EAF-LF-RH-CC flow process developed oxygen level≤5ppm, Ti<≤production method of 6ppm (No. 1, Japan's " electric system steel " the 73rd volume, in January, 2002 P61), but all do not relate to the introduction of detailed technology; And domestic bibliographical information has only Baoshan Iron and Steel Group Shanghai five steel companies " a kind of smelting production method of high-purity high-carbon high-chromium bearing steel (patent No.: ZL01132236.5) ", be characterized in having developed the high-carbon-chromium bearing steel production method of oxygen level≤7ppm, titanium content≤12ppm by the DC-LF-VD-IC technical process, the weak point of ZL01132236.5 patent of invention is: though proposed the regulation that ladle must be cleaned out, but " labor cleaning fully " labour intensity of carrying out in the actual mechanical process is big, and cleaning effect is unsatisfactory; Secondly, the technological operation that adds materials after the vacuum has destroyed the slag chemical equilibrium, makes that secondary oxidation product (as Al2O3) is owing to there not being enough floating interval of floating dock to be trapped in the molten steel in the steel; Above-mentioned factor causes the smelting production process instability of high-purity high-carbon high-chromium bearing steel, and success ratio has only about 40%, has influenced manufacturing cost; In addition, 01132236.5 patent of invention has requirement to the capacity of last EBT type electric furnace, and the small-sized EBT electric furnace of furnace volume<60t can not be implemented 01132236.5 patent of invention method.
In addition, in the high-carbon-chromium bearing steel production method of above-mentioned abrasive, no matter be domestic (patent documentation report) with concrete technical scheme, still external (only being the written report of circular formula) all do not relate to the control of nitrogen content.As everyone knows: remain in the nitrogen in the high-carbon-chromium bearing steel, titanium is angular, dystectic titanium nitride in conjunction with formation and is mingled with among the Yi Yugang, has a strong impact on the fatigue lifetime of steel; Nitrogen content≤0.0055% (55ppm just) is the bottleneck of present DC (direct current furnace) production technique.
Summary of the invention
The present invention develops a kind of smelting production method of abrasive high-carbon-chromium bearing steel; optimize by the electric furnace batching; electric furnace is just made steel the dephosphorization of liquid and is taken off titanium; the deoxidization desulfuration of ladle furnace refining molten steel process; the deoxidation degassing of vacuum oven liquid steel refining process and the coating runner brick of die casting process use and the inert atmosphere protection cast; overcome the technological deficiency of ZL01132236.5 patent of invention; not only make the high-carbon-chromium bearing steel finished product have clarity (oxygen content in steel≤0.0007% of abrasive; titanium content≤0.0012%; nitrogen content≤0.0055%); improve bearing life; also be suitable for 30 tons of electric rangette productions of EBT type; what is more important; smelting success ratio improves greatly; bring up to 80% by 40%; lay a good foundation for metallurgical production producer reduces manufacturing cost and expands the scale of production, satisfy the requirement of precision bearing manufacturer.
The smelting production method of a kind of abrasive high-carbon-chromium bearing steel provided by the invention is characterized in that: adopt five-step approach smelting technology flow process, the electric furnace batching optimizes-→ electric furnace just make steel liquid-→ the BOTTOM ARGON BLOWING ladle furnace refining-→ the vacuum oven degassing-→ die casting.
The first step, select for use low titanium, low copper and low-phosphorous cleaning steel scrap, direct-reduced iron and high duty pig iron to prepare burden as raw material metal, concrete proportioning is: cleaning steel scrap+direct-reduced iron=70-75%, (compare with cleaning steel scrap, direct-reduced iron, high duty pig iron, ordinary scrap steel, pig iron impurity are more relatively for high duty pig iron 25-30%; The carbon content of high duty pig iron is higher, should control the ratio of high duty pig iron in the raw material metal batching); To satisfy the requirement of residual element such as Cu in the steel, Sn, As, Sb, Pb.
Second step, at the EBT more than 30 tons (EBT is exactly an ECCENTRIC BOTTOM TAPPING TECHNOLOGY) type electric furnace (if the non-EBT type of furnace or furnace volume are less than 30 tons, so, during electric furnace steel tapping, oxidation sludge in the electric furnace is involved in the remaining titanium content that makes in the ladle in the molten steel easily and increases) in dephosphorization, take off titanium, phosphorus content in the steel is removed to≤0.007%, titanium is removed to≤0.0003% (if remaining titanium content>0.0005% in the steel, the titanium content in the finished product>0.0012%; If remaining titanium content=0.0004%~0.0005% in the steel, then the remaining titanium content of finished steel might be greater than 0.0012%) below:
(1) in electric furnace, the energising melting waste steel, input oxygen quickens melting waste steel;
(2) after the molten bath forms, spray into the coke powder making foamed slag of carbon containing more than 80%, suitably body of heater is tilted towards the fire door direction, make foamy slag from the fire door smooth outflow; Divide 3-4 to criticize the lime of interpolation total amount 8-12kg/ ton steel, continue making foamed slag, with shielded arc nitrogen pick-up effect (electric furnace when energising, airborne nitrogen is under arcing, the N that ionization generates infiltrates molten steel easily), fully promote the dephosphorization of slag to take off the titanium reaction (under the strong oxidizing atmosphere of height, a large amount of simple substance Ti is oxidized, be temporary in the molten steel with single-phase TiO2 or the complex chemical compound state that contains Ti, molten steel is under powerful electromagnetic field is stirred, and inclusion enters slag because the principle of density difference constantly floats.Because the Ti compound constantly increases in the slag, under certain oxygen gesture, slag is in relative balance state, and its carrying capacity to the Ti compound weakens.Therefore must make the further Ti content that reduces in the steel of new oxidation sludge ability by the slag that continues to flow, for concise operation creates favorable conditions.); When furnace charge is all molten clear, chemical analysis is carried out in sampling during temperature>1580 ℃, Ti in steel≤0.0005%, and P≤0.007% o'clock enters the temperature rise period;
(3) when temperature>1650 ℃, sampling checking chemical ingredients is guaranteed Ti in the steel≤0.0003%, P≤0.007%.Tapping temperature 1650-1680 ℃;
(4) electric furnace steel tapping requires: (tap is many, and EBT may descend slag at the 90-95% of conventional tap should to control the electric furnace steel tapping amount; Tap has been lacked, and causes that cost increases.); In the electric furnace steel tapping process, carry out alloying operation synchronously, (alloying level is low can weightening finish ladle furnace alloying task, causes the ladle furnace treatment time long, is unfavorable for deoxidation and controls titanium content greater than 90% for alloying level.), guarantee the lower limit of the first analytical value of [C], [Cr] of ladle furnace, difference 0.05%-0.10% near finished product C, Cr composition range;
In the 3rd step, on the ladle refining furnace that capacity and electric furnace are complementary, by single slag process deoxidation, desulfurization, remove inclusion, make oxygen activity≤0.0005%, Ti≤0.0011%, N≤0.0075% of refining liquid steel:
(1) ladle is prepared: the ladle that collects molten steel uses conventional Al2O3-MgO-C matter and MgO-C fire resistant materials; Before using, should remove ladle the cold steel residue of inwall, and the residue on the cleaning vacuum oven screening cover is (if the internal surface of ladle and vacuum oven screening cover has cold steel residue, then in intensification and whipping process, remaining titanium and titanium dioxide in the cold steel residue can dissolve in molten steel, even have only the cold steel residue of minute quantity to enter, can cause also that titanium content increases in the molten steel.); In the production plan layout, before smelting the abrasive bearing steel, smelt the above plain bearing steel of 1~2 stove (to clean ladle, cleaning ladle furnace bell and vacuum oven screening cover, it is unclean to remedy the labor cleaning, and the titaniferous or the cold steel residue of titanium dioxide that prevent to stick on ladle inner wall and the bell enter molten steel);
(2) in the ladle furnace refining process, carrying out the BOTTOM ARGON BLOWING molten steel in ladle furnace station whole process stirs, overall treatment time control 50-70min (low refining time deficiency, deoxidization desulfuration is insufficient, the top layer of high ladle lining is washed away for a long time by molten steel and is peeled off and enter molten steel, enter the titanium dioxide in the fire-resistant top layer of molten steel, and the titanium dioxide in the slag may be by the aluminium reducing in the steel, make titanium content in the steel greater than 11ppm), early stage with the Argon intensity BOTTOM ARGON BLOWING of 0.35-0.40Mpa 25-35 minute (to make molten steel component and equalizing temperature and further carburetting fast, be alloyed into target component.), Argon intensity was crossed conference and was caused molten steel to suck nitrogen, hydrogen or oxygen gas, the too small inclusion removal that is unfavorable for of Argon intensity with Argon intensity BOTTOM ARGON BLOWING 25-35 minute (promote the deoxidization desulfuration reaction and be convenient to inclusion floating to stir molten steel) of 0.25-0.30Mpa the later stage.
(3) in the ladle furnace refining process, the total add-on 4-8 kilogram/ton steel of material (alloy, slag charge) (mainly be the control alloy addition, add-on is too high, can increase the ladle furnace refining time);
(4) the ladle furnace deoxidation process adopts the complex deoxidization technology of " precipitation+diffusion ": bulk deoxidation is two conventional step feeding aluminium methods; Diffusive deoxidation is to add the crystallization silica flour to the top of the slag, adds the high purity fluorite of fluorinated calcium more than 98% simultaneously and adjusts slag fluidity.
The 4th step, on the vacuum oven that capacity and electric furnace mate, molten steel is carried out vacuum-treat, make oxygen activity≤2ppm in titanium content≤11ppm in the steel and the steel:
(1) (, is unfavorable for separating out of hydrogen in the molten steel, nitrogen and oxygen at 1570-1580 ℃, S≤0.006% when molten steel temperature if sulphur content greater than 0.006%, because sulphur is surfactant, can cause that the molten steel interfacial tension is big.), when all chemical ingredientss all satisfy standard, enter vacuum oven and carry out vacuum-treat;
(2) vacuum time is 20~25 minutes, vacuum tightness≤140Pa; Ladle bottom is blown into argon gas, and (molten steel and slag fully react Argon intensity 0.2~0.3Mpa, and the deoxidation products in the steel fully floats, and make oxygen, hydrogen and nitrogen content in the steel reduce to 2ppm, 1ppm respectively and below the 55ppm, and make titanium content≤11ppm in the steel.);
(3) vacuum-treat finishes, and (destroy the slag chemical equilibrium because add materials after the vacuum, the secondary pollution molten steel helps oxygen in the atmosphere, nitrogen to the molten steel mass transfer not allow to add any material.); And carry out weak BOTTOM ARGON BLOWING operation of stirring, time 10-15 minute, stirring intensity 0.05-0.1Mpa so that the further gathering of steel inclusion is grown up and on float in the slag;
In the 5th step, high-temperature molten steel enters the casting that the die casting station carries out the totally-enclosed protection of inert atmosphere, is molded into qualified steel ingot:
(1) conventional molten steel pouring temperature is 1500-1510 ℃ as the pouring temperature of RSAE52100SF abrasive high-carbon-chromium bearing steel; Ingot mold inwall cleaning does not have cold steel residue; 60-80 ℃ of ingot mold use temperature;
(2) runner brick of die casting use is the coating runner brick, inwall at common runner brick refractory materials bakings such as (adopt make) silicon oxide scribbles one deck high temperature resistant (〉=1600 ℃), erosion resistant zirconium white protective layer (if do not use the coating runner brick exactly, then the runner brick internal surface is caused producing in the steel macroscopical inclusion by the high-temperature molten steel erosion); The die casting process all have the material that contacts all should guarantee moisture content less than 0.5% with molten steel, prevents that molten steel from increasing hydrogen;
(3) molten steel is opened the ladle bottom slide plate after the die casting station is in place, and with the useless mould of molten steel injection of 0.3-0.5 ton, extremely normal then flat board is cast; The casting whole process is used the totally-enclosed protection cast of argon gas: protector is a refractory materials cavity; top communicates with the ladle nozzle bottom; the bottom communicates with die casting feed trumpet top; connecting argon gas makes steel stream inject ingot mold (if do not protect cast from ladle nozzle, feed trumpet under the argon gas sealing; can cause molten steel oxidation and air-breathing; wherein oxygen increases 0.5-1.0ppm, and nitrogen increases 5-10ppm.); Ingot body casting rate be controlled at 4.5-5.5 ton steel/minute, cap mouth casting rate be controlled at 0.8-1.0 ton steel/minute.
Be [C] that guarantee ladle furnace, [Cr] first analytical value requirement near finished product C, Cr composition range lower limit, the alloying of electric furnace steel tapping process (alloying level is greater than 90%) concrete grammar is as follows: in collecting the ladle of molten steel, when the electric furnace steel tapping amount arrives 25-35%, the fine aluminium that adds 2.0-2.5 kilogram/ton steel is used for deoxidation, add all kinds of iron alloys simultaneously, comprise that the titaniferous amount that contains pure chromium 13-14 kilogram/ton steel is lower than 0.01% medium carbon ferrochrome or high carbon ferro-chrome, the electrolytic manganese of 25-30 kilogram/ton steel, the silicon metal of 20-25 kilogram/ton steel; When tap arrives 40-45%, add the 9-10 kilogram/low nitrogen carburelant of ton Carbon Content Of Steel more than 95%; When tap arrived 70-80%, interpolation contained the lime 7-8 kilogram/ton steel of calcium oxide more than 90%, simultaneously with addition of the high purity fluorite 0.5-0.6 kilogram/ton steel of fluorinated calcium more than 98%.
The coating runner brick that die casting is used, high temperature resistant, erosion resistant zirconium white inside coating need toast to be made, and storing temperature 250-400 ℃, coat-thickness 1-5mm.
Compare with prior art, the present invention has following advantage:
1, molten steel degree of cleaning height: oxygen content in steel≤6ppm, titanium content≤12ppm, nitrogen content≤55ppm.
2, the ladle furnace process adopts the single slag process operation, and technology is simple and convenient.
3, the oxygen of Finished Steel, nitrogen, titanium content first-time qualification rate height, it is low to smelt production cost, the production efficiency height.
4, equipment and technology highly versatile: must not add specific equipment in addition, all EBT type electric furnaces capacity more than 30 tons with addition of basic equipments such as the ladle furnace of respective volume and vacuum ovens, all can satisfy the production needs.
Specific embodiments
Certain Iron And Steel Company implements patented method of the present invention, adopt five-step approach smelting technology flow process: the electric arc furnace that the electric furnace batching is optimized-→ 30 tons and 100 tons just make steel liquid-→ the BOTTOM ARGON BLOWING ladle furnace refining of respective volume-→ vacuum oven of respective volume outgases-→ the die casting production line, successfully produced RSAE52100SF abrasive high-carbon-chromium bearing steel (oxygen level≤0.0007%, titanium content≤0.0011%, nitrogen content≤0.0055%, sulphur content≤0.005%).
The first step, batching are selected low titanium, low copper and low-phosphorous steel scrap and direct-reduced iron for use: cleaning steel scrap 55-60%, direct-reduced iron 10-15%, high duty pig iron 25-30%.Second step, in 30 tons/100 tons EBT type electric furnaces dephosphorization, take off titanium, the phosphorus content in the steel is removed to≤0.007%, titanium is removed to≤below 0.0003%: in electric furnace, energising, oxygen therapy melting waste steel; After the molten bath forms, spray into the coke powder making foamed slag of carbon containing more than 80%, make foamy slag from the fire door smooth outflow; Divide 4 batches of lime that add total amount 8-12kg/ ton steel, continue making foamed slag,, fully promote the dephosphorization of slag to take off the titanium reaction with shielded arc nitrogen pick-up effect; When furnace charge is all molten clear, chemical analysis is carried out in sampling during temperature>1580 ℃, Ti in steel≤0.0005%, and P≤0.007% o'clock enters the temperature rise period; When temperature>1650 ℃, sampling checking chemical ingredients is guaranteed Ti=0.0003% in the steel (≤0.0003%), P=0.0006% (≤0.007%); Tapping temperature 1650-1680 ℃; (4) electric furnace steel tapping requires: should control the 90-95% of electric furnace steel tapping amount in conventional tap; In the electric furnace steel tapping process, carry out the alloying operation synchronously, alloying level is greater than 90%, when tap to 30%, the fine aluminium that adds 2-2.5 kilogram/ton steel is used for deoxidation, adds all kinds of iron alloys simultaneously, comprises that the titaniferous amount that contains 13.5 kilograms of/ton steel of pure chromium is lower than 0.01% medium carbon ferrochrome, the electrolytic manganese of 28 kilograms of/ton steel, the silicon metal of 25 kilograms of/ton steel; When tap to 40% the time, add the low nitrogen carburelant of 9.5 kilograms of/ton Carbon Content Of Steel more than 95%; When tap to 75% the time, add and contain 8 kilograms of/ton steel of the lime of calcium oxide 90% or more, the while is with addition of 0.6 kilogram of/ton steel of the high purity fluorite of fluorinated calcium more than 98%; The first analytical value of [C], [Cr] of guaranteeing ladle furnace is near finished product C, the Cr composition range (lower limit of [C]>0.95-1.05%, [Cr]>1.45-1.60%): [C]>0.90%, [Cr]>1.35%.
In the 3rd step, on 30 tons/100 tons ladle refining furnaces, refining liquid steel: ladle is prepared, and smelts 1 stove plain bearing steel earlier, then this ladle is removed the cold steel residue of inwall, and the residue on the cleaning vacuum oven screening cover; (2) in the ladle furnace refining process, carrying out the BOTTOM ARGON BLOWING molten steel in ladle furnace station whole process stirs, by single slag process deoxidation, desulfurization, remove inclusion: overall treatment time control 50-70min, early stage is with the Argon intensity BOTTOM ARGON BLOWING of 0.35-0.40Mpa 25-30 minute, and the later stage was with the Argon intensity BOTTOM ARGON BLOWING of 0.25-0.30Mpa 25-35 minute; In the ladle furnace refining process, the total add-on 4-8 kilogram/ton steel of material (alloy, slag charge); (3) deoxidation process adopts the complex deoxidization technology of " precipitation+diffusion ": bulk deoxidation is that two of routine goes on foot feeding aluminium methods, when molten steel temperature is got first sample for 1540 ℃, and [C]>0.90%, [Cr]>1.35% is adjusted to 0.045% with aluminium; When molten steel temperature during, aluminium is adjusted to 0.040% at 1565-1575 ℃; Diffusive deoxidation is to add the crystallization silica flour to the top of the slag, adds the high purity fluorite of fluorinated calcium more than 98% simultaneously and adjusts slag fluidity; (4), enter the vacuum oven degassing when oxygen activity≤0.0005%, Ti≤0.0010%, N≤0.0075% of molten steel.The 4th step, on 30 tons/100 tons vacuum ovens, molten steel is carried out vacuum-treat, make oxygen activity in titanium content≤11ppm in the steel and the steel≤2ppm:(1) with the condition of high vacuum degree of 67Pa (≤140Pa) kept 25 minutes, vacuum BOTTOM ARGON BLOWING intensity: 0.2~0.3MPa makes oxygen, hydrogen and nitrogen content in the steel reduce to 2ppm, 1ppm respectively and below the 55ppm.(2) vacuum-treat finishes, and does not allow to add any material, and the control stirring intensity carried out weak churning time 10-15 minute at 0.05-0.1Mpa.In the 5th step, high-temperature molten steel enters the casting that the die casting station carries out the totally-enclosed protection of inert atmosphere, is molded into qualified steel ingot: 1500-1510 ℃ of (1) molten steel pouring temperature (the conventional pouring temperature of DSAE52100SF abrasive high-carbon-chromium bearing steel); (2) ingot mold temperature 60-80 ℃; The runner brick that uses is that inwall scribbles that one deck is high temperature resistant, the coating runner brick of erosion resistant protective oxide film, and the equal moisture of all materials that contact with molten steel is less than 0.5%; (3) open the ladle bottom slide plate, 0.5 ton molten steel is injected useless mould, extremely normal then flat board is cast; (4) the casting whole process is used the totally-enclosed protection cast of argon gas, 5 tons of steel of ingot body casting rate/minute, 0.8 ton of steel of cap mouth casting rate/minute.
Implement the abrasive high-carbon-chromium bearing steel of the 25 stove RSAE52100SF trades mark of patented method production of the present invention, metallurgical first-time qualification rate 84% (21 stove), the oxygen level 5-6ppm of Finished Steel, titanium content 9-11ppm, sulphur content 0.002-0.0054%, nitrogen content 45-55ppm.The reflection of bearing manufacturers: the high-carbon-chromium bearing steel that patent of the present invention is produced, the clarity height, leading domestic; Miniature bearings lasso and the ball made are lower than 10/1000000ths through the magnetic-particle inspection disqualification rate, reach external advanced level.