CN102758144B - Production method for steel ingot of large-sized high-nitrogen retaining ring steel - Google Patents
Production method for steel ingot of large-sized high-nitrogen retaining ring steel Download PDFInfo
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Abstract
The invention relates to a production method for a steel ingot of large-sized high-nitrogen retaining ring steel. The production method comprises the following steps: 1) smelting and casting: optimizing raw materials, primarily smelting molten steel EAF by using an electric arc furnace, refining AOD and LF by using a ladle furnace, performing die casting on ICM and pouring an electrode of phi 422 to 510 mm; 2) performing hot charging and annealing; 3) remelting electroslag into the steel ingot of phi 660 to 800 mm; and 4) sampling, detecting the components, performing flaw detection, peeling electroslag and steel ingot sand, detecting size and appearance and putting into a storage. In the steel ingot of the high-nitrogen retaining ring steel manufactured by the method, the phi is 660 to 800 mm, the weight is more than 5 tons, the nitrogen content is over 0.6 weight percent, the nitrogen is distributed into the steel ingot uniformly, and the |[N] head-[N]tail| of the head and the tail of the steel ingot is less than or equal to 0.05 weight percent.
Description
Technical field
The present invention relates to high nitrogen rings territory, is mainly a kind of nitrogen content higher than the production method (steel ingot specification is φ 660～800mm, and weight is higher than 5 tons) of 0.6wt% and the generator guard ring steel ingot that is evenly distributed.
Background technology
Retaining ring is the parts of turbo-generator most critical, is also the parts of stressed maximum.When generator turns round with rated speed, the load that retaining ring bears is 2/3 of yield strength.When unit is larger, the stressed of retaining ring also increases because of many reasons thereupon.Because having determined retaining ring, its role and strained condition must have the ability of the intensity of superelevation, good plasticity and toughness, nonmagnetic and outstanding stress corrosion resistant.Therefore people have developed austenite 18Mn-18Cr-N type shelling ring material, are widely used at present on large-scale more than 200MW and ultra-large type generator guard ring.By practice and analysis, find, the strength grade of 18Mn-18Cr-N shaped material has determined the capacity of generator unit, and nitrogen in steel content is the factor that affects a most critical of strength grade.At present, the nitrogen content of widely used 18Mn-18Cr-N shaped steel is less than 0.6wt%, be mainly used in the generating set of 200MW, exploitation along with heavy-duty generator group, also increasing higher than the demand of the 18Mn-18Cr-N shaped steel of 0.6wt% to nitrogen content, and in specification, be also tending towards the increasing trend of diameter, the current domestic import (external main by the device fabrication of supercharging esr) that also only relies on, therefore develop large specification (φ 650～800mm) and nitrogen content higher than the high nitrogen 18 N steel guard ring of 18Mn-18Cr-N type of 0.6wt%, for power industry, extremely urgent.
In order to obtain high nitrogen content, the method that both at home and abroad producer mainly adopts have (Deng Lintao, Liu Zhiying etc., " improving the research of nitrogen content and recovery rate in 18Mn-18Cr-N type Retaining Ring Steel ". heavy casting and forging No.3:5～9 in 2002): USSR (Union of Soviet Socialist Republics) adopts open type induction oven process, vacuum arc remelting, plasma arc remelting process etc.; Japan adopts pressurization induced electricity oven process, electric furnace in conjunction with vacuum oxygen decarburization and esr process (EF-VOD-ESR); Europe adopts pressurization esr process (PESR); China producer adopts electric furnace duplex to add esr process (EF-EF-ESR).
The nitrogen content of seeing 18Mn-18Cr-N type Retaining Ring Steel prepared by European pressurization esr process from effect is the highest, can reach 1.2wt%.But, with regard to increasing (adding) pressure electroslag remelting process is prepared high nitrogen steel, need to drop into expensive specific equipment and proprietary technology, production cost is higher, and adopt supercharging smelting high-nitrogen steel, due to its dynamic conditions also more complicated, the distribution of nitrogen in steel ingot is not easy to control.China producer in large specification on the basis of Introduced from Japan technology; adopt that 10 tons of electric furnace twin furnaces are mixing, nitrogen protection cast; and then the steel ingot of producing by esr process; the steel ingot nitrogen content of producing also can be more than 0.6wt%; but can not guarantee that nitrogen is evenly distributed in steel ingot; the content of sulphur, phosphorus is higher ([S] > 0.005, [P] > 0.020) all, therefore also fails to enter large production.Shanghai Heavy Machinery Plant once utilized esr to carry out the research of the high nitrogen 18 N steel guard ring of 18Mn-18Cr-N type.More than nitrogen content can be controlled at 0.6wt%, ingot shape can reach Φ 900, and weight reaches 8 tons.But its electrode bar that is used for electroslag is by Bulgarian induction furnace melting, by back-pressure, to cast to form (this Technology can make nitrogen content up to 0.9mass%), on cost, be also very huge, need to drop into back-pressure casting equipment, therefore at present and owing to relating to high pressure, for nitrogen, the production of the large-scale steel ingot more than 0.6wt% is not carried out yet at home.At home, the size of large steel ingot can reach Φ 900, but nitrogen content is all lower than 0.6wt%.The problem existing is steel ingot size when larger, pours into a mould nitrogen in electrode bar process on the one hand and easily separates out, and forms hole, makes electrode bar in follow-up electroslag operation, easily produce piece and causes the ingot quality of production not good; On the other hand, in Electroslag Process, due to electrode sections distribution of current relation, the temperature distribution in electroslag molten bath is also inhomogeneous, causes nitrogen content to be also not easy to control.
In sum, the production method of conventional high nitrogen (nitrogen content is lower than 0.6wt%) Retaining Ring Steel still can not meet nitrogen content between nitrogen Retaining Ring Steel tissue large with a high standard and the performance requriements of 0.6～0.7wt% scope at present, and some special equipment are still in laboratory applications stage or the expensive facility investment of needs, therefore in the urgent need to seeking the smelting process that a kind of production cost is low, operation is uncomplicated and do not need expensive device to invest, make nitrogen content between the nitrogen Retaining Ring Steel large with a high standard of 0.6～0.7wt% scope.
Summary of the invention
The object of the invention is to propose the method for the high nitrogen Retaining Ring Steel steel ingot of the large specification of a kind of production (Φ 660～800mm, weight is higher than 5 tons), meet its nitrogen content be evenly distributed higher than 0.6wt% and in steel ingot (ingot head and afterbody) | [N]
head-[N]
tail|≤0.05wt%.
For achieving the above object, technical scheme of the present invention is:
The present invention produces the high nitrogen Retaining Ring Steel steel ingot of large specification (Φ 660～800mm), in steel ingot nitrogen content higher than 0.6wt% and in steel ingot, be evenly distributed (ingot head and afterbody | [N]
head-[N]
tail|≤0.05wt%).
Processing step of the present invention is: starting material batchings optimization → electric arc furnace is just made steel liquid EAF+ ladle furnace refining AOD, LF → die casting ICM, cast Φ 422～510mm electrode → hot charging annealing slow cooling → peeling (car) → esr becomes Φ 660～800mm steel ingot → cover cold → sampling → composition detection → flaw detection → electroslag ingot sand stripping → size, visual inspection → warehouse-in.
Particularly, the step of the inventive method is as follows:
6) smelt, cast
The present invention is applicable to large specification and requires ingot head and afterbody nitrogen content is evenly distributed that high nitrogen steel is produced.Mainly for be that nitrogen content is higher than the production of the 18Mn-18Cr-N shaped steel of 0.6wt%.The chemical component weight per-cent of steel is: C≤0.12%, and Si≤0.80%, Mn 18.50～20.00%, and Cr 18.50～20.00%, N >=0.60%.
Starting material batching is optimized
In the present invention, furnace charge is selected the returns such as clean steel scrap, crop of low-phosphorous, low-sulfur, low titanium and low copper, direct-reduced iron and high duty pig iron are prepared burden as raw material metal, concrete proportioning is clean steel scrap+direct-reduced iron=70-75%, high duty pig iron 25-30%, to meet the requirement of the residual element such as Cu in steel, Sn, As, Sb, Pb; Alloy: high carbon ferro-chrome, electrolytic manganese, nitrided ferro-chromium and nitrogenize ferromanganese; Reductive agent: aluminum shot, ferrosilicon, silicon ball, silicon carbide; Slag former: unslaked lime, fluorite, MgO.
Electric arc furnace is just made steel liquid EAF+ ladle furnace refining AOD+ ladle furnace refining LF+ die casting ICM
At 20-40 ton electric arc furnace, just make steel in liquid EAF process, by general stainless steel Returning blowing keto technique operation, adopt nitrogen to carry out end stirring.Between oxidation period, flow slag dephosphorization, reductive agent is used silicon carbide, silicon ball and ferrosilicon, draws reducing slag clearly, to reduce the quantity of slag of follow-up AOD before tapping.Draw slag temperature to control >=1660 ℃, tapping temperature is controlled >=1630 ℃.Composition before entering AOD in steel meets: C≤2.0%, Si≤0.3%, Mn≤5.0%, P≤0.02%, Cr18.50～19.00%.
In the ladle furnace AOD of corresponding tonnage refining process, be blended into thermometric sampling after molten steel, oxygen decarburization, and add a certain amount of lime and MgO.During in temperature T >=1680 ℃, add alloy, control Cr at 17.00～17.50wt%.Oxygen decarburization, makes C content reach 0.03～0.04wt%.In oxidation, draw high the rear oxygen blast flow that reduces of molten steel temperature (T >=1700 ℃) latter stage, add electrolytic manganese, control Mn at 17.00～20.50wt%.Carbon control≤0.03wt% when prereduction starts, basicity of slag (CaO/SiO
2) control=1.2-1.3, steel per ton adds 7.5～12.5 kilograms, lime; After prereduction, draw slag; After reduction, except Cr, N, according to one-tenth, be dispensed into alloy to target value, carry out desulfurization and deoxidation simultaneously; During tapping, adding by steel per ton adds 25～50 kilograms of nitrided ferro-chromiums to ladle.
In the ladle furnace LF of corresponding tonnage refining process, after energising heats up, adjust bits, make slag turn white.According to sampling analysis result, finely tune composition, make S≤0.005wt%.Add again nitrided ferro-chromium and nitrogenize ferromanganese, strictly control nitrogen content in target value, guarantee other alloying element rear bull ladle in span of control simultaneously.1465～1475 ℃ of bull ladle temperature, upper control limit bull ladle.
In die casting ICM process, cast Φ 422-510mm circle electrode ingot, argon for protecting pouring, cap mouth is supplied fully, waters to finish to add heat-generating agent and carbonated paddy insulation.Pouring speed be controlled at 3～4 Kilograms Per Seconds/, be poured rear calcining temperature and be controlled at 550～600 ℃, and hot charging annealing.
Utilizing electric arc furnace just to make steel the benefit of liquid EAF+ ladle furnace refining AOD+ ladle furnace refining LF+ die casting ICM cast electroslag electrode casting is to control well the phosphorus content in steel in stage of smelting at the beginning, because phosphorus content is more insoluble problem to stainless steel.Then utilize AOD ladle refining to carry out desulfurization and deoxidation, control well inclusion content of steel.Utilize LF ladle refining to adjust steel interalloy composition, and carry out molten steel nitriding treatment, remove remaining inclusion in steel.In casting process, control pouring speed and argon shield, avoid occurring in electroslag electrode gas hole and secondary oxidation.
2) hot charging annealing
After the steel ingot demoulding, carry out hot charging annealing to eliminate structural stress, Crack prevention produces, and also plays dehydrogenation diffusion annealing effect simultaneously.Annealing furnace starting temperature 550-600 ℃, with the rate of heating of 30-50 ℃/h, be slowly warming up to 650-690 ℃, heating and thermal insulation time 15-20 hour, eliminates surface of steel ingot and heart portion inside and outside temperature difference, with the cooling rate stove of 10-20 ℃/h, be chilled to 150 ℃ subsequently and come out of the stove, reduce thermal stresses.
3) esr
Adopt the two transverse arm alternative expression electroslag furnaces of twin columns, under atmospheric pressure, carry out esr.By a plurality of electrode bar esrs, become an ESR ingot Φ 660～800mm, weight is higher than 5 tons.The slag system that esr is selected is CaF
2, Al
2o
3, CaO and a certain amount of MgO, prevent slag bath oxygen uptake and the oxide compound that prevents from appraising at the current rate in slag transmits oxygen supply to metal pool, reduce thermosteresis.Slag system proportioning is: CaF
2: Al
2o
3: CaO: Mg=(55-65): (21-17): (14～20): (3～14).According to the weight of electroslag ingot, determine the quantity of slag used, follow G
slag=G
ingot/ (22～25) kilogram.Starting the arc mode is: the melt cinder starting the arc.Change in slag process and adjust voltage (45～55 volts) and electric current (2500～4500 amperes), assuranceization slag time >=40 minute, change the complete transfer electron rod of slag time≤5 minute (adopting Graphite Electrodes while changing slag).Before electroslag, electrode bar is preheating to 500～600 ℃.The crystallizer diameter adopting is Φ 660～800mm, and uses same steel grade Dummy plate to carry out esr.In esr process, according to the diameter of crystallizer, select the molten fast V of electrode bar
molten=(0.7～0.8) D
knotkg/hr, and adjust voltage (85～95 volts) and electric current (10000～15000 amperes), the molten speed of control electrode rod.Molten fast selection is mainly that metal pool can not be too dark, prevents nitrogen in steel loss, ensures good macrostructure simultaneously, avoids low power segregation; Molten bath can not be too shallow, otherwise also can cause serious macro defect.Time≤5 minute of transfer electron rod.The feeding of esr later stage is bound the stage, adjusts voltage and current, and pool depth is reduced.The feeding time is controlled >=90 minutes.
4) after feeding is bound, the demoulding behind ESR ingot cooling time >=100 minute, and annealing.Annealing temperature is 650～700 ℃, and after soaking time 40～60h, stove is cold.
5) electroslag ingot is sampled end to end, and carry out surperficial sand stripping and process, eliminate surface imperfection and rod iron size, shape, surface quality are met design requirement, make finished product electroslag ingot.
Beneficial effect of the present invention
Feedstock optimization batching of the present invention, effectively controls the phosphorus content in steel, and the residual element contents such as Cu in steel, Sn, As, Sb, Pb is met the requirements.Adopt electric arc furnace just to make steel liquid EAF+ ladle furnace refining AOD+ ladle furnace refining LF+ die casting ICM, the content that can not only guarantee the principal elements such as C in steel, Cr, Mn obtains, and by progressively adding nitrided ferro-chromium and nitrogenized manganese iron alloy, make in poured into a mould round electrode bar nitrogen content higher than >=0.65mass% and do not form nitrogen hole.By esr operation, select the electroslag system of rational slag system and optimization and the feeding system that binds, the effective molten speed of control electrode rod, has guaranteed in electroslag ingot | [N]
head-[N]
tail|≤0.05wt% and pure property.
Embodiment
Below in conjunction with embodiment, the present invention will be further described.
Embodiment 1
For the high nitrogen retaining ring steel ingot of producing Φ 760mm specification, embodiment is as follows:
1) smelt, cast
Starting material batching is optimized, the present invention is directed to 40 tons of electric arc furnace, select the returns such as clean steel scrap, crop of low-phosphorous, low-sulfur, low titanium and low copper, direct-reduced iron and high duty pig iron are prepared burden as raw material metal, concrete proportioning is clean steel scrap+direct-reduced iron=75%, high duty pig iron 25%, to meet the requirement of the residual element such as Cu in steel, Sn, As, Sb, Pb; Alloy: high carbon ferro-chrome, electrolytic manganese, nitrided ferro-chromium and nitrogenize ferromanganese; Reductive agent: aluminum shot, ferrosilicon, silicon ball, silicon carbide; Slag former: unslaked lime, fluorite, MgO.
Electric arc furnace is just made steel liquid EAF+ ladle furnace refining AOD+ ladle furnace refining LF+ die casting ICM
At 40 tons of electric arc furnace, just make steel in liquid EAF process, by general stainless steel Returning blowing keto technique operation, adopt nitrogen to carry out end stirring.Between oxidation period, flow slag dephosphorization, reductive agent is used silicon carbide, silicon ball and ferrosilicon, draws reducing slag clearly, to reduce the quantity of slag of follow-up AOD before tapping.Draw slag temperature to be controlled at 1660～1700 ℃ of scopes, tapping temperature is controlled at 1630～1650 ℃.
In the ladle furnace AOD of corresponding tonnage refining process, be blended into thermometric sampling after molten steel, oxygen decarburization, and add a certain amount of lime and MgO.When temperature T is 1690 ℃, add alloy, control Cr at 17.30wt%.Oxygen decarburization, makes C content reach 0.03wt%.In oxidation, draw high the rear oxygen blast flow that reduces of molten steel temperature (1710 ℃) latter stage, add electrolytic manganese in batches, control Mn at 20wt%.When prereduction starts, carbon is 0.03wt%, and basicity controls 1.2, lime 400kg; After prereduction, draw slag; After reduction, except Cr, N, according to one-tenth, be dispensed into alloy to target value; During tapping, add 2 tons of chromium nitrides to ladle.
In the ladle furnace LF of corresponding tonnage refining process, after energising heats up, adjust bits, guarantee that slag turns white.According to sampling analysis result fine setting composition, make S≤0.002wt%.Add nitrided ferro-chromium and nitrogenize ferromanganese, strictly control nitrogen content in target value, guarantee other alloying element rear bull ladle in span of control simultaneously.Bull ladle temperature 1465-1475 ℃, upper control limit bull ladle.
In die casting (ICM) process, cast Φ 422mm circle electrode ingot, argon for protecting pouring, cap mouth is supplied fully, waters to finish to add heat-generating agent and carbonated paddy insulation.Pouring speed be controlled at 3.2 Kilograms Per Seconds/, be poured rear calcining temperature and be controlled at 550 ℃, and hot charging annealing.
Electric arc furnace is just made steel constituent content in liquid EAF+ ladle furnace refining AOD+ ladle furnace refining LF+ die casting ICM process and is changed as shown in table 1.
2) hot charging annealing
After the steel ingot demoulding, carry out hot charging annealing to eliminate structural stress, Crack prevention produces.550 ℃ of annealing furnace starting temperatures, are slowly warming up to 680 ℃ with the rate of heating of 30 ℃/h, 20 hours heating and thermal insulation time, eliminate surface of steel ingot and heart portion inside and outside temperature difference, and with the cooling rate stove of 10 ℃/h, be chilled to 150 ℃ subsequently and come out of the stove, reduce thermal stresses.
3) esr
Adopt the two transverse arm alternative expression electroslag furnaces of twin columns, under atmospheric pressure, carry out esr.By 2.5 electrode bar esrs, become an ESR ingot Φ 760mm, weight is 6.5 tons.
The slag system that esr is selected is CaF
2, Al
2o
3, CaO and MgO, proportioning is: CaF
2: Al
2o
3: CaO: MgO=62: 20: 12: 6, the quantity of slag was 270kg.Starting the arc mode is: the melt cinder starting the arc.In change slag process, adjust 3000 amperes, 50 volts of voltages and electric current, change 41 minutes slag time, changing the complete transfer electron rod time of slag is 2 minutes (during change slag, adopting Graphite Electrodes).Before electroslag, electrode bar is preheating to 600 ℃.The crystallizer diameter adopting is Φ 760mm, and uses same steel grade Dummy plate to carry out esr.Adjust 13500 amperes, 90 volts of voltages and electric current, the molten fast 460kg/ hour of control electrode rod.The 3 minutes time of transfer electron rod.The feeding of esr later stage is bound the stage, adjusts voltage and current, and pool depth is reduced; The control of feeding time is 90 minutes.
After feeding is bound, ESR ingot demoulding after 120 minutes cooling times, and annealing.Annealing temperature is 680 ℃, and after soaking time 50h, stove is cold.
Electroslag ingot is sampled end to end, and carry out surperficial sand stripping and process, eliminate surface imperfection and rod iron size, shape, surface quality are met design requirement, make finished product electroslag ingot.
Electroslag ingot is sampled end to end, and carry out surperficial sand stripping and process, eliminate surface imperfection and rod iron size, shape, surface quality are met design requirement, make finished product electroslag ingot.Electroslag ingot alloying element content is end to end as shown in table 2.Can see that the resulting ingot composition of the inventive method is more even, high purity and | [N]
head-[N]
tail|≤0.05wt%.
Embodiment 2
For the high nitrogen retaining ring steel ingot of producing Φ 660mm specification, embodiment is as follows:
1) smelt, cast
Starting material batching is optimized, the present invention is directed to 40 tons of electric arc furnace, select the returns such as clean steel scrap, crop of low-phosphorous, low-sulfur, low titanium and low copper, direct-reduced iron and high duty pig iron are prepared burden as raw material metal, concrete proportioning is clean steel scrap+direct-reduced iron=75%, high duty pig iron 25%, to meet the requirement of the residual element such as Cu in steel, Sn, As, Sb, Pb; Alloy: high carbon ferro-chrome, electrolytic manganese, nitrided ferro-chromium and nitrogenize ferromanganese; Reductive agent: aluminum shot, ferrosilicon, silicon ball, silicon carbide; Slag former: unslaked lime, fluorite, MgO.
Electric arc furnace is just made steel liquid EAF+ ladle furnace refining AOD+ ladle furnace refining LF+ die casting ICM.
At 40 tons of electric arc furnace, just make steel in liquid EAF process, by general stainless steel Returning blowing keto technique operation, adopt nitrogen to carry out end stirring.Between oxidation period, flow slag dephosphorization, reductive agent is used silicon carbide, silicon ball and ferrosilicon, draws reducing slag clearly, to reduce the quantity of slag of follow-up AOD before tapping.Draw slag temperature to be controlled at 1660～1700 ℃ of scopes, tapping temperature is controlled at 1630～1650 ℃.
In the ladle furnace AOD of corresponding tonnage refining process, be blended into thermometric sampling after molten steel, oxygen decarburization, and add a certain amount of unslaked lime and MgO.When temperature T is 1690 ℃, add alloy, control Cr at 17.30wt%.Oxygen decarburization, makes C content reach 0.03wt%.In oxidation, reduce oxygen blast flow after drawing high molten steel temperature latter stage, add electrolytic manganese in batches.When prereduction starts, C is 0.03wt%, and basicity controls 1.2, lime 400kg; After prereduction, draw slag; After reduction, except Cr, N, according to one-tenth, be dispensed into alloy to target value; During tapping, add 2 tons of chromium nitrides to ladle.
In the ladle furnace LF of corresponding tonnage refining process, after energising heats up, adjust bits, guarantee that slag turns white.Thermometric sampling comprises the full elemental analysis of nitrogen element, according to analytical results fine setting composition, guarantees S≤0.002%.Add nitrided ferro-chromium and nitrogenize ferromanganese, strictly control nitrogen content in target value, guarantee other alloying element rear bull ladle in span of control simultaneously.1465～1475 ℃ of bull ladle temperature, upper control limit bull ladle.
In die casting (ICM) process, cast Φ 510mm circle electrode ingot, argon for protecting pouring, cap mouth is supplied fully, waters to finish to add heat-generating agent and carbonated paddy insulation.Pouring speed is controlled at 3.0kg/s/ and props up, and be poured rear calcining temperature and be controlled at 550 ℃, and hot charging annealing.
Electric arc furnace is just made steel constituent content in liquid EAF+ ladle furnace refining AOD+ ladle furnace refining LF+ die casting ICM process and is changed as shown in table 3.
2) hot charging annealing
After the steel ingot demoulding, carry out hot charging annealing to eliminate structural stress, Crack prevention produces.550 ℃ of annealing furnace starting temperatures, are slowly warming up to 680 ℃ with the rate of heating of 30 ℃/h, 20 hours heating and thermal insulation time, eliminate surface of steel ingot and heart portion inside and outside temperature difference, and with the cooling rate stove of 10 ℃/h, be chilled to 150 ℃ subsequently and come out of the stove, reduce thermal stresses.
3) esr
Adopt the two transverse arm alternative expression electroslag furnaces of twin columns, under atmospheric pressure, carry out esr.By 2 electrode bar esrs, become an ESR ingot Φ 660mm, weight is 5.5 tons.
The slag system that esr is selected is CaF
2, Al
2o
3, CaO and MgO, proportioning is: CaF
2: Al
2o
3: CaO: MgO=62: 20: 12: 6, the quantity of slag was 220kg.Starting the arc mode is: the melt cinder starting the arc.In change slag process, adjust 4500 amperes, 45 volts of voltages and electric current, change 40 minutes slag time, changing the complete transfer electron rod time of slag is 3 minutes (during change slag, adopting Graphite Electrodes).Before electroslag, electrode bar is preheating to 600 ℃.The crystallizer diameter adopting is Φ 660mm, and uses same steel grade Dummy plate to carry out esr.Adjust voltage and current, the molten fast 420kg/ hour of control electrode rod.The 3 minutes time of transfer electron rod.The feeding of esr later stage is bound the stage, adjusts voltage and current, and pool depth is reduced.The control of feeding time is 90 minutes.
4) after feeding is bound, ESR ingot demoulding after 120 minutes cooling times, and annealing.Annealing temperature is 680 ℃, and after soaking time 52h, stove is cold.
5) electroslag ingot is sampled end to end, and carry out surperficial sand stripping and process, eliminate surface imperfection and rod iron size, shape, surface quality are met design requirement, make finished product electroslag ingot.Electroslag ingot alloying element content is end to end as shown in table 4.Can see that the resulting ingot composition of the inventive method is more even, high purity and | [N]
head-[N]
tail|≤0.05wt%.
Claims (1)
1. a production method for large nitrogen Retaining Ring Steel steel ingot with a high standard, it comprises the steps:
1) smelt, cast
The chemical component weight per-cent of large nitrogen Retaining Ring Steel with a high standard: C≤0.12%, Si≤0.80%, Mn18.50～20.00%, Cr18.50～20.00%, N >=0.60%, surplus Fe and inevitable impurity;
Adopt electric arc furnace just to make steel liquid EAF+ ladle furnace AOD refining+ladle furnace LF refining+die casting ICM;
At electric arc furnace, just make steel in liquid EAF process, adopt nitrogen to carry out end stirring; Before tapping, draw reducing slag clearly, draw slag temperature to control >=1660 ℃, tapping temperature is controlled >=1630 ℃; Composition before entering AOD in steel meets: C≤2.0wt%, Si≤0.3wt%, Mn≤5.0wt%, P≤0.02wt%, Cr18.50～19.00wt%;
In ladle furnace AOD refining process, during in temperature T>=1680 ℃, add alloy, control Cr at 17.00～17.50wt%; Oxygen decarburization, makes C content reach 0.03～0.04wt%; After latter stage is drawn high molten steel temperature T>=1700 ℃ in oxidation, reduce oxygen blast flow, add electrolytic manganese, control Mn at 17.00～20.50wt%; When prereduction starts, control C≤0.03wt%, basicity of slag is CaO/SiO
2be controlled at 1.2～1.3, steel per ton adds 7.5～12.5 kilograms, lime; After prereduction, draw slag; After reduction, except Cr, N, according to one-tenth, be dispensed into alloy to target value, carry out desulfurization and deoxidation simultaneously; During tapping, adding by steel per ton adds 25～50 kilograms of nitrided ferro-chromiums to ladle;
In ladle furnace LF refining process, after energising heats up, adjust bits, make slag turn white; According to sampling analysis result, finely tune composition, make S≤0.005wt%; Add again nitrided ferro-chromium and nitrogenize ferromanganese, strictly control nitrogen content in target value, guarantee other alloying element rear bull ladle in span of control, 1465～1475 ℃ of bull ladle temperature, upper control limit bull ladle simultaneously;
In die casting ICM process, cast Φ 422-510mm circle electrode ingot, argon for protecting pouring, cap mouth is supplied fully, waters to finish to add heat-generating agent and carbonated paddy insulation; Pouring speed be controlled at 3～4 Kilograms Per Seconds/, be poured rear calcining temperature and be controlled at 550～600 ℃, and hot charging annealing;
2) hot charging annealing
After the steel ingot demoulding, carry out hot charging annealing, 550～600 ℃ of annealing furnace starting temperatures, with the rate of heating of 30～50 ℃/h, be slowly warming up to 650～690 ℃, 15～20 hours heating and thermal insulation time, eliminate surface of steel ingot and heart portion inside and outside temperature difference, with the cooling rate stove of 10～20 ℃/h, be chilled to 100～150 ℃ subsequently and come out of the stove, reduce thermal stresses;
3) esr
Adopt the two transverse arm alternative expression electroslag furnaces of twin columns, under atmospheric pressure, carry out esr; By a plurality of electrode bar esrs, become an ESR ingot Φ 660～800mm, weight is higher than 5 tons; The slag system that esr is selected is CaF
2, Al
2o
3, CaO and MgO; Slag system proportioning: CaF
2: Al
2o
3: CaO:MgO=(55-65): (21-17): (14～20): (3～14); According to the weight of electroslag ingot, determine the quantity of slag used, follow G
slag=G
ingot/ (22～25) kg; Starting the arc mode is: the melt cinder starting the arc; In change slag process, adjust 2500～4500 amperes, 45～55 volts of voltages and electric current, assuranceization slag time>=40 minute, change the complete transfer electron rod of slag time≤5 minute, adopt Graphite Electrodes while changing slag; Before electroslag, electrode bar is preheating to 500～600 ℃; The crystallizer diameter adopting is Φ 660～800mm, and uses same steel grade Dummy plate to carry out esr; In esr process, according to the diameter of crystallizer, select the molten fast V of electrode bar
molten=(0.7～0.8) D
knotkg/ hour, and adjust 10000～15000 amperes, 85～95 volts of voltages and electric current, the molten speed of control electrode rod; Time≤5 minute of transfer electron rod; The feeding of esr later stage is bound the stage, and the feeding time is controlled>=90 minutes;
4) after feeding is bound, the demoulding after ESR ingot is greater than 100 minutes cooling time, and annealing; 650～700 ℃ of annealing temperatures, after soaking time 40～60h, stove is cold;
5) electroslag ingot is sampled end to end, and carry out surperficial sand stripping and process, eliminate surface imperfection and rod iron size, shape, surface quality are met design requirement, make finished product electroslag ingot, in electroslag ingot, nitrogen is evenly distributed, and | [N]
head-[N]
tail|≤0.05wt%.
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