CN102758144A - 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, mainly is that a kind of nitrogen content is higher than 0.6wt% and the working method (the steel ingot specification is φ 660～800mm, and weight is higher than 5 tons) of the generator guard ring steel ingot that is evenly distributed.
Background technology
Retaining ring is the parts of turbo-generator most critical, also is the parts of stressed maximum.When generator turned round with rated speed, the load that retaining ring bore was 2/3 of a yield strength.When unit is big, retaining ring stressed also because multiple former thereby increase thereupon.Because its role and strained condition have determined retaining ring that the ability of the intensity of superelevation, good plasticity and toughness, nonmagnetic and outstanding stress corrosion resistant must be arranged.Therefore people have developed austenite 18Mn-18Cr-N type shelling ring material, on large-scale more than the 200MW and ultra-large type generator guard ring, are widely used at present.Find that with analyzing the strength grade of 18Mn-18Cr-N type material has determined the capacity of generator unit through practice, and nitrogen in steel content is the factor that influences a most critical of strength grade.At present; The nitrogen content of widely used 18Mn-18Cr-N shaped steel is mainly used in the power unit of 200MW less than 0.6wt%, along with the exploitation of heavy-duty generator group; The demand of 18Mn-18Cr-N shaped steel that nitrogen content is higher than 0.6wt% is also increasing; And on specification, also be tending towards the increasing trend of diameter, and the present domestic import (the external main supercharging esr device fabrication of leaning on) that also only relies on, (φ 650～800mm) and nitrogen content are higher than the high nitrogen 18 N steel guard ring of 18Mn-18Cr-N type of 0.6wt% therefore to develop big specification; For power industry, extremely urgent.
In order to obtain high nitrogen content; Both at home and abroad the method that mainly adopts of producer have (Deng Lintao, Liu Zhiying etc., " improving the research of 18Mn-18Cr-N type retaining ring nitrogen in steel content and yield ". heavy casting and forging No.3:5～9 in 2002): the FSU adopts open type induction oven process, var process, plasma arc remelting process or the like; Japan adopts pressurization induced electricity oven process, electric furnace to combine vacuum oxygen decarburization and esr process (EF-VOD-ESR); Pressurization esr process (PESR) is adopted in Europe; China producer adopts the electric furnace duplex to add electroslag remelting process (EF-EF-ESR).
The nitrogen content of seeing the 18Mn-18Cr-N type retaining ring steel that the pressurization esr process in Europe prepares from effect is the highest, can reach 1.2wt%.But, prepare with regard to the high nitrogen steel, need to drop into expensive dedicated equipment and proprietary technology with regard to increasing (adding) piezoelectricity slag remelting processing; Production cost is than higher; And adopt the supercharging smelting high-nitrogen steel, owing to its dynamic conditions also more complicated, the distribution of nitrogen in steel ingot is not easy control.China producer is introducing on the basis of day present technique in big specification; Adopt 10 tons of mixing, nitrogen protection cast of electric furnace twin furnace, and then pass through the steel ingot that esr process is produced, the steel ingot nitrogen content of production also can be more than 0.6wt%; But can not guarantee that nitrogen is evenly distributed in steel ingot; Therefore the content of sulphur, phosphorus also fail to get into big production all than higher ([S]＞0.005, [P]＞0.020).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.Nitrogen content can be controlled at more than the 0.6wt%, and ingot shape can reach Φ 900, and weight reaches 8 tons.But its electrode bar that is used for electroslag is to form (this Technology can make nitrogen content up to 0.9mass%) through Bulgarian induction furnace melting through the back-pressure casting; Also be very huge on cost; Need to drop into the back-pressure pourer; And, therefore do not carry out for the production of the large-scale steel ingot of nitrogen more than 0.6wt% at home at present owing to relate to high pressure yet.At home, the size of large steel ingot can reach Φ 900, but nitrogen content all is lower than 0.6wt%.The problem that exists is steel ingot size when bigger, pours into a mould in the electrode bar process nitrogen on the one hand and separates out easily, forms hole, makes electrode bar in follow-up electroslag operation, be easy to generate piece and causes the ingot quality of production not good; On the other hand, in the electroslag process,, cause nitrogen content also to be not easy control because the electrode sections distribution of current concerns that the temperature distribution in electroslag molten bath is also inhomogeneous.
In sum; The working method of conventional high nitrogen (nitrogen content is lower than 0.6wt%) retaining ring steel still can not satisfy big with a high standard nitrogen retaining ring structure of steel and the performance requriements of nitrogen content between 0.6～0.7wt% scope at present; And some special equipment still are in the laboratory applications stage or need expensive facility investment; Therefore press for the smelting process of seeking that a kind of production cost is low, operation is uncomplicated and not needing the expensive device investment, make the nitrogen retaining ring steel big with a high standard of nitrogen content between 0.6～0.7wt% scope.
Summary of the invention
The objective of the invention is to propose the method for the high nitrogen retaining ring steel ingot of the big specification of a kind of production (Φ 660～800mm, weight is higher than 5 tons), satisfy its nitrogen content and be higher than 0.6wt% and in steel ingot, be evenly distributed (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 produce big specification (Φ 660～800mm) high nitrogen retaining ring steel ingots, in the steel ingot nitrogen content be higher than 0.6wt% and in steel ingot, be evenly distributed (ingot head and afterbody | [N]
Head-[N]
Tail|≤0.05wt%).
Process 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 become 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 following:
6) smelt, cast
The present invention is applicable to big specification and requires ingot head and the afterbody nitrogen content is evenly distributed that high nitrogen steel is produced.What be primarily aimed at is the production that nitrogen content is higher than 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%.
The starting material batching is optimized
Furnace charge is selected the returns such as cleaning steel scrap, crop of low-phosphorous, low-sulfur, low titanium and low copper for use among the present invention; Dri and high duty pig iron are prepared burden as raw material metal; Concrete proportioning is cleaning steel scrap+dri=70-75%; High duty pig iron 25-30% is to satisfy the requirement of residual element such as Cu in the 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, silit; 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
In 20-40 ton electric arc furnace is just made steel liquid EAF process,, adopt nitrogen to carry out the end and stir by general stainless steel Returning blowing keto technique operation.Between oxidation period, flow the slag dephosphorization, reductive agent uses silit, silicon ball and ferrosilicon, draws reducing slag clearly before the tapping, to reduce the quantity of slag of follow-up AOD.Draw >=1660 ℃ of slag temperature controls, >=1630 ℃ of tapping temperature controls.Composition before getting into AOD in the steel satisfies: 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 behind the molten steel, oxygen decarburization, and add a certain amount of lime and MgO.Add alloy during in temperature T >=1680 ℃, Cr is at 17.00～17.50wt% in control.Oxygen decarburization makes C content reach 0.03～0.04wt%.Draw high molten steel temperature (T >=1700 ℃) back latter stage in oxidation and reduce the oxygen blast flow, add electrolytic manganese, Mn is at 17.00～20.50wt% in control.Carbon control≤0.03wt% when prereduction begins, basicity of slag (CaO/SiO
2) control=1.2-1.3, steel per ton adds 7.5～12.5 kilograms in lime; Draw slag after the prereduction; The reduction back is dispensed into alloy to target value according to one-tenth except that Cr, N, carry out desulfurization and deoxidation simultaneously; Add during tapping by steel per ton and add 25～50 kilograms of nitrided ferro-chromiums to ladle.
In the ladle furnace LF of corresponding tonnage refining process, after energising heated up, the adjustment bits made slag change white.The result finely tunes composition according to sampling analysis, makes S≤0.005wt%.Add nitrided ferro-chromium and nitrogenize ferromanganese again, strict control nitrogen content is guaranteed other alloying element back bull ladle in span of control simultaneously in target value.1465～1475 ℃ of bull ladle temperature, the upper control limit bull ladle.
In die casting ICM process, cast Φ 422-510mm circle electrode ingot, argon for protecting pouring, the cap mouth is supplied fully, waters to finish to add heat-generating agent and the insulation of carbonization paddy.Pouring speed be controlled at 3～4 Kilograms Per Seconds/, the cast back calcining temperature that finishes is 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 the phosphorus content in the steel well in stage of smelting at the beginning, because phosphorus content is difficult problem to solve to stainless steel.Then utilize the AOD ladle refining to carry out desulfurization and deoxidation, control inclusion content of steel well.Utilize LF ladle refining adjustment steel interalloy composition, and carry out the molten steel nitriding treatment, remove remaining inclusion in the steel.Control pouring speed and argon shield avoid occurring in the electroslag electrode gas hole and secondary oxidation in casting process.
2) hot charging annealing
After the steel ingot demoulding, carry out hot charging annealing, avoid crackle to produce, also play simultaneously dehydrogenation diffusion annealing effect to eliminate structural stress.550-600 ℃ of lehre starting temperature; Slowly be warming up to 650-690 ℃ with 30-50 ℃/hour rate of heating, 15-20 hour heat tracing time, eliminate surface of steel ingot and heart portion inside and outside temperature difference; Be chilled to 150 ℃ with 10-20 ℃/hour cooling rate stove subsequently and come out of the stove, reduce thermal stresses.
3) esr
Adopt the two transverse arm alternative expression electroslag furnaces of twin columns, carry out esr under the atmospheric pressure.Become ESR ingot Φ a 660～800mm by a plurality of electrode bar esrs, weight is higher than 5 tons.The slag system that esr is selected for use is CaF
2, Al
2O
3, CaO and a certain amount of MgO, prevent the slag bath oxygen uptake and the oxide compound that prevents to appraise at the current rate in the slag transmits oxygen supply to metal pool, reduce thermosteresis.The slag system proportioning is: CaF
2: Al
2O
3: CaO: Mg=(55-65): (21-17): (14～20): (3～14).Weight according to electroslag ingot determines the used quantity of slag, follows G
Slag=G
Ingot/ (22～25) kilogram.Starting the arc mode is: the melt cinder starting the arc.Change in the slag process and adjust voltage (45～55 volts) and electric current (2500～4500 amperes), slag excellent time≤5 of transfer electron minute (employing Graphite Electrodes during the change slag) that finish are changed in assuranceizations slag time>=40 minute.Electrode bar is preheating to 500～600 ℃ before the electroslag.The mold diameter that adopts is Φ 660～800mm, and uses with the steel grade Dummy plate and carry out esr.Select the molten fast V of electrode bar in the esr process according to the diameter of mold
Molten=(0.7～0.8) D
KnotKilogram/hour, and adjustment voltage (85～95 volts) and electric current (10000～15000 amperes), the molten speed of control electrode rod.The selection of molten speed mainly is that metal pool can not be too dark, prevents the nitrogen in steel loss, and guaranteeing simultaneously has good macrostructure, avoids the low power segregation; The molten bath can not be too shallow, otherwise also can cause serious macro defect.Time≤5 of transfer electron rod minute.The feeding of esr later stage is bound the stage, and the adjustment voltage and current makes pool depth reduce.Feeding time control >=90 minutes.
4) after feeding is bound, the demoulding behind ESR ingot cooling time >=100 minute, and annealing.Annealing temperature is 650～700 ℃, and stove is cold behind soaking time 40～60h.
5) electroslag ingot is taken a sample end to end, and carry out surperficial sand stripping and handle, eliminate surface imperfection and rod iron size, shape, surface quality are met design requirement, make the finished product electroslag ingot.
Beneficial effect of the present invention
Feedstock optimization batching of the present invention is effectively controlled the phosphorus content in the steel, and residual element contents such as Cu in the 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 principal elements such as C in the steel, Cr, Mn obtains; And through progressively adding nitrided ferro-chromium and nitrogenized manganese iron alloy, make that nitrogen content is higher than in the round electrode bar of being poured into a mould >=0.65mass% and do not form the nitrogen hole.Through the esr operation, select electroslag system and the feeding of rational slag system and the optimization system that binds, the effective molten speed of control electrode rod has guaranteed in the electroslag ingot | [N]
Head-[N]
Tail|≤0.05wt% and pure property.
Embodiment
Below in conjunction with embodiment the present invention is further specified.
Embodiment 1
To the high nitrogen retaining ring steel ingot of producing Φ 760mm specification, embodiment is following:
1) smelts, casts
The starting material batching is optimized; The present invention is directed to 40 tons of electric arc furnace; Select the returns such as cleaning steel scrap, crop of low-phosphorous, low-sulfur, low titanium and low copper for use, dri and high duty pig iron are prepared burden as raw material metal, and concrete proportioning is cleaning steel scrap+dri=75%; High duty pig iron 25% is to satisfy the requirement of residual element such as Cu in the 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, silit; 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
In 40 tons of electric arc furnace are just made steel liquid EAF process,, adopt nitrogen to carry out the end and stir by general stainless steel Returning blowing keto technique operation.Between oxidation period, flow the slag dephosphorization, reductive agent uses silit, silicon ball and ferrosilicon, draws reducing slag clearly before the tapping, to reduce the quantity of slag of follow-up AOD.Draw the 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 behind the molten steel, oxygen decarburization, and add a certain amount of lime and MgO.When temperature T is 1690 ℃, add alloy, Cr is at 17.30wt% in control.Oxygen decarburization makes C content reach 0.03wt%.Draw high molten steel temperature (1710 ℃) back reduction oxygen blast flow latter stage in oxidation, add electrolytic manganese in batches, Mn is at 20wt% in control.Carbon is 0.03wt% when prereduction begins, basicity control 1.2, lime 400kg; Draw slag after the prereduction; The reduction back is dispensed into alloy to target value according to one-tenth except that Cr, N; Add 2 tons of chromium nitrides during tapping to ladle.
In the ladle furnace LF of corresponding tonnage refining process, after energising heated up, the adjustment bits guaranteed that slag changes white.The result finely tunes composition according to sampling analysis, makes S≤0.002wt%.Add nitrided ferro-chromium and nitrogenize ferromanganese, strict control nitrogen content is guaranteed other alloying element back bull ladle in span of control simultaneously in target value.1465-1475 ℃ of bull ladle temperature, the upper control limit bull ladle.
In die casting (ICM) process, cast Φ 422mm circle electrode ingot, argon for protecting pouring, the cap mouth is supplied fully, waters to finish to add heat-generating agent and the insulation of carbonization paddy.Pouring speed be controlled at 3.2 Kilograms Per Seconds/, the cast back calcining temperature that finishes is controlled at 550 ℃, and hot charging annealing.
Electric arc furnace makes steel just that constituent content changes as shown in table 1 in the liquid EAF+ ladle furnace refining AOD+ ladle furnace refining LF+ die casting ICM process.
2) hot charging annealing
After the steel ingot demoulding, carry out hot charging annealing, avoid crackle to produce to eliminate structural stress.550 ℃ of lehre starting temperatures slowly are warming up to 680 ℃ with 30 ℃/hour rate of heating, 20 hours heat tracing time, eliminate surface of steel ingot and heart portion inside and outside temperature difference, and be chilled to 150 ℃ with 10 ℃/hour cooling rate stove subsequently and come out of the stove the minimizing thermal stresses.
3) esr
Adopt the two transverse arm alternative expression electroslag furnaces of twin columns, carry out esr under the atmospheric pressure.Become an ESR ingot Φ 760mm by 2.5 electrode bar esrs, weight is 6.5 tons.
The slag system that esr is selected for use 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.Change in the slag process 50 volts of adjustment voltages and 3000 amperes in electric current, change 41 minutes slag time, changing slag transfer electron rod time that finishes is 2 minutes (adopting Graphite Electrodes when changing slag).Electrode bar is preheating to 600 ℃ before the electroslag.The mold diameter that adopts is Φ 760mm, and uses with the steel grade Dummy plate and carry out esr.90 volts of voltages of adjustment and 13500 amperes in electric current, 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, and the adjustment voltage and current makes pool depth reduce; The feeding time is controlled to be 90 minutes.
After feeding is bound, ESR ingot demoulding after 120 minutes cooling times, and annealing.Annealing temperature is 680 ℃, and stove is cold behind the soaking time 50h.
Electroslag ingot is taken a sample end to end, and carry out surperficial sand stripping and handle, eliminate surface imperfection and rod iron size, shape, surface quality are met design requirement, make the finished product electroslag ingot.
Electroslag ingot is taken a sample end to end, and carry out surperficial sand stripping and handle, eliminate surface imperfection and rod iron size, shape, surface quality are met design requirement, make the finished product electroslag ingot.Electroslag ingot alloying element content end to end is as shown in table 2.Can see that the resulting steel ingot composition of the inventive method is more even, high purity and | [N]
Head-[N]
Tail|≤0.05wt%.
Embodiment 2
To the high nitrogen retaining ring steel ingot of producing Φ 660mm specification, embodiment is following:
1) smelts, casts
The starting material batching is optimized; The present invention is directed to 40 tons of electric arc furnace; Select the returns such as cleaning steel scrap, crop of low-phosphorous, low-sulfur, low titanium and low copper for use, dri and high duty pig iron are prepared burden as raw material metal, and concrete proportioning is cleaning steel scrap+dri=75%; High duty pig iron 25% is to satisfy the requirement of residual element such as Cu in the 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, silit; 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.
In 40 tons of electric arc furnace are just made steel liquid EAF process,, adopt nitrogen to carry out the end and stir by general stainless steel Returning blowing keto technique operation.Between oxidation period, flow the slag dephosphorization, reductive agent uses silit, silicon ball and ferrosilicon, draws reducing slag clearly before the tapping, to reduce the quantity of slag of follow-up AOD.Draw the 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 behind the molten steel, oxygen decarburization, and add a certain amount of unslaked lime and MgO.When temperature T is 1690 ℃, add alloy, Cr is at 17.30wt% in control.Oxygen decarburization makes C content reach 0.03wt%.After latter stage is drawn high molten steel temperature in oxidation, reduce the oxygen blast flow, add electrolytic manganese in batches.C is 0.03wt% when prereduction begins, basicity control 1.2, lime 400kg; Draw slag after the prereduction; The reduction back is dispensed into alloy to target value according to one-tenth except that Cr, N; Add 2 tons of chromium nitrides during tapping to ladle.
In the ladle furnace LF of corresponding tonnage refining process, after energising heated up, the adjustment bits guaranteed that slag changes white.The 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, strict control nitrogen content is guaranteed other alloying element back bull ladle in span of control simultaneously in target value.1465～1475 ℃ of bull ladle temperature, the upper control limit bull ladle.
In die casting (ICM) process, cast Φ 510mm circle electrode ingot, argon for protecting pouring, the cap mouth is supplied fully, waters to finish to add heat-generating agent and the insulation of carbonization paddy.Pouring speed is controlled at 3.0kg/s/ and props up, and calcining temperature was controlled at 550 ℃ after cast finished, and hot charging annealing.
Electric arc furnace makes steel just that constituent content changes as shown in table 3 in the liquid EAF+ ladle furnace refining AOD+ ladle furnace refining LF+ die casting ICM process.
2) hot charging annealing
After the steel ingot demoulding, carry out hot charging annealing, avoid crackle to produce to eliminate structural stress.550 ℃ of lehre starting temperatures slowly are warming up to 680 ℃ with 30 ℃/hour rate of heating, 20 hours heat tracing time, eliminate surface of steel ingot and heart portion inside and outside temperature difference, and be chilled to 150 ℃ with 10 ℃/hour cooling rate stove subsequently and come out of the stove the minimizing thermal stresses.
3) esr
Adopt the two transverse arm alternative expression electroslag furnaces of twin columns, carry out esr under the atmospheric pressure.Become an ESR ingot Φ 660mm by 2 electrode bar esrs, weight is 5.5 tons.
The slag system that esr is selected for use 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.Change in the slag process 45 volts of adjustment voltages and 4500 amperes in electric current, change 40 minutes slag time, changing slag transfer electron rod time that finishes is 3 minutes (adopting Graphite Electrodes when changing slag).Electrode bar is preheating to 600 ℃ before the electroslag.The mold diameter that adopts is Φ 660mm, and uses with the steel grade Dummy plate and carry out esr.The adjustment voltage and current, 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, and the adjustment voltage and current makes pool depth reduce.The feeding time is controlled to be 90 minutes.
4) after feeding is bound, ESR ingot demoulding after 120 minutes cooling times, and annealing.Annealing temperature is 680 ℃, and stove is cold behind the soaking time 52h.
5) electroslag ingot is taken a sample end to end, and carry out surperficial sand stripping and handle, eliminate surface imperfection and rod iron size, shape, surface quality are met design requirement, make the finished product electroslag ingot.Electroslag ingot alloying element content end to end is as shown in table 4.Can see that the resulting steel ingot composition of the inventive method is more even, high purity and | [N]
Head-[N]
Tail|≤0.05wt%.
Claims (1)
1. the working method of one kind big nitrogen retaining ring steel ingot with a high standard, it comprises the steps:
1) smelts, casts
The chemical component weight per-cent of retaining ring steel: 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 refining AOD+ ladle furnace refining LF+ die casting ICM;
In electric arc furnace is just made steel liquid EAF process, adopt nitrogen to carry out the end and stir; Draw reducing slag clearly before the tapping, draw>=1660 ℃ of slag temperature controls,>=1630 ℃ of tapping temperature controls; Composition before getting into AOD in the steel satisfies: C≤2.0wt%, Si≤0.3wt%, Mn≤5.0wt%, P≤0.02wt%, Cr 18.50～19.00wt%;
In ladle furnace AOD refining process, add alloy during in temperature T>=1680 ℃, Cr is at 17.00～17.50wt% in control; Oxygen decarburization makes C content reach 0.03～0.04wt%; After molten steel temperature T>=1700 ℃ are drawn high in oxidation latter stage, reduce the oxygen blast flow, add electrolytic manganese, Mn is at 17.00～20.50wt% in control; Control C≤0.03wt% when prereduction begins, basicity of slag is CaO/SiO
2Be controlled at 1.2～1.3, steel per ton adds 7.5～12.5 kilograms in lime; Draw slag after the prereduction; The reduction back is dispensed into alloy to target value according to one-tenth except that Cr, N, carry out desulfurization and deoxidation simultaneously; Add during tapping by steel per ton and add 25～50 kilograms of nitrided ferro-chromiums to ladle;
In ladle furnace LF refining process, after energising heated up, the adjustment bits made slag change white.The result finely tunes composition according to sampling analysis, makes S≤0.005wt%; Add nitrided ferro-chromium and nitrogenize ferromanganese again, strict control nitrogen content is guaranteed other alloying element back bull ladle in span of control, 1465～1475 ℃ of bull ladle temperature, upper control limit bull ladle simultaneously in target value; In die casting ICM process, cast Φ 422-510mm circle electrode ingot, argon shield
Cast, the cap mouth is supplied fully, waters to finish to add heat-generating agent and the insulation of carbonization paddy.Pouring speed be controlled at 3～4 Kilograms Per Seconds/, the cast back calcining temperature that finishes is controlled at 550～600 ℃, and hot charging annealing;
2) hot charging annealing
Carry out hot charging annealing after the steel ingot demoulding; 550～600 ℃ of lehre starting temperatures; Slowly be warming up to 650～690 ℃ with 30～50 ℃/hour rate of heating, 15～20 hours heat tracing time, eliminate surface of steel ingot and heart portion inside and outside temperature difference; Be chilled to 100～150 ℃ with 10～20 ℃/hour cooling rate stove subsequently and come out of the stove, reduce thermal stresses;
3) esr
Adopt the two transverse arm alternative expression electroslag furnaces of twin columns, carry out esr under the atmospheric pressure.Become ESR ingot Φ a 660～800mm by a plurality of electrode bar esrs, weight is higher than 5 tons.The slag system that esr is selected for use is CaF
2, Al
2O
3, CaO and MgO; Slag system proportioning: CaF
2: Al
2O
3: CaO: Mg=(55-65): (21-17): (14～20): (3～14); Weight according to electroslag ingot determines the used quantity of slag, follows G
Slag=G
Ingot/ (22～25) kg; Starting the arc mode is: the melt cinder starting the arc; Change in the slag process 45～55 volts of adjustment voltages and 2500～4500 amperes in electric current, finish transfer electron rod time≤5 minute of slag are changed, employing Graphite Electrodes during the change slag in assuranceizations slag time>=40 minute; Electrode bar is preheating to 500～600 ℃ before the electroslag; The mold diameter that adopts is Φ 660～800mm, and uses with the steel grade Dummy plate and carry out esr; Select the molten fast V of electrode bar in the esr process according to the diameter of mold
Molten=(0.7～0.8) D
KnotKg/ hour, and 85～95 volts of voltages of adjustment and 10000～15000 amperes in electric current, the molten speed of control electrode rod; Time≤5 of transfer electron rod minute; The feeding of esr later stage is bound the stage, feeding time control>=90 minutes;
4) after feeding is bound, ESR ingot cooling time is greater than the demoulding after 100 minutes, and annealing; 650～700 ℃ of annealing temperatures, stove is cold behind soaking time 40～60h;
5) electroslag ingot is taken a sample end to end, and carry out surperficial sand stripping and handle, eliminate surface imperfection and rod iron size, shape, surface quality are met design requirement, make the finished product electroslag ingot, nitrogen is evenly distributed in the electroslag ingot, and | [N]
Head-[N]
Tail|≤0.05wt%.
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