CN100436603C

CN100436603C - Process of deoxygenating, desulfurizing and controlling non-metal inclusion content in steel

Info

Publication number: CN100436603C
Application number: CNB2007100648902A
Authority: CN
Inventors: 王新华; 陈斌; 姜敏; 包萨日娜; 王万军; 李宏; 张炯明; 于会香; 王灿国
Original assignee: University of Science and Technology Beijing USTB
Current assignee: University of Science and Technology Beijing USTB
Priority date: 2007-03-28
Filing date: 2007-03-28
Publication date: 2008-11-26
Anticipated expiration: 2027-03-28
Also published as: CN101020940A

Abstract

The present invention is process of deoxygenating, desulfurizing and controlling non-metal inclusion content in steel, and belongs to the field of steel making production technology. The process includes desulfurizing molten iron to S content of 0.003-0.006 wt%; smelting in a converter to reach CaO/SiO2 alkalinity of 4-7 and P content of 0.003-0.01 wt%, and tapping while blocking slag strictly and adding Al in 0.09-0.2 wt%; adding high alkalinity slag 0.4-1 wt% and Al 0.04-0.12 wt% into molten steel in a LF furnace while blowing Ar and stirring; adding Al to reach acid soluble Al content in molten steel of 0.030-0.070 wt%; vacuum treatment at 30-300 Pa for 15-30 min; and protected continuous casting. The present invention is suitable for producing high strength structural alloy steel, high strength carbon steel, low alloy steel and other special steel.

Description

The method of a kind of deoxidation, desulfurization, control nonmetallic inclusionsin steel

Technical field

The invention belongs to steelmaking technical field, the method for a kind of deoxidation, desulfurization, control nonmetallic inclusionsin steel particularly is provided, be mainly used in the high-strength alloy structure iron, also be applicable to the production of all kinds of high strength carbon steels, low alloy steel, steel and other special steel.

Background technology

The high-strength alloy structure iron is mainly used in a part, gear, connecting rod, spring, bolt etc., and the military service process stands the repeat stress, requires to possess good antifatigue destructive characteristics.The fatigure failure of steel is one of main modes of part failure.Statistics shows, the inefficacy of mechanical component, and fatigure failure accounts for more than 90%.In order to improve the fatigue lifetime of steel, just must reduce oxygen in the steel, sulphur content greatly, size, shape, type, the distribution of steel inclusion are controlled.

Great deal of experimental work was done to the relation of bearing steel oxygen level and fatigue lifetime by Sweden Aktiebolaget SKF and Japanese adret special steel company, had drawn clear conclusions: total oxygen massfraction is from 30 * 10 in steel ^-6Be reduced to 10 * 10 ^-6, the life-span can be improved 15 times; Be reduced to and be about 1 * 10 ^-6, the life-span can be improved about 30 times (Lifengzhang.Clean Steel and Inclusions.13th National SteelmaKing Conference, Kunming, Yunan, P.R.China, Dec.8,2004:138～181).

Rapids family Hao Zang thinks that sulfide is harmful in the modern hypoxemia high cleanliness steel, reduce in the steel S content and be necessary (great Tibetan, rapids family work, Chen Hongzhen translates. bearing steel, Beijing: metallurgical industry press, 2003:137).

About the influence of inclusion, known reduction, apart from the increase of distance on surface along with the inclusion size, fatigue lifetime be improve (Yin Ruiyu. following piece of the modern progress of the quality of steel, special steel, Beijing: metallurgical industry press: 99).Inclusion causes that in the inner institute of steel matrix the size of stress concentration and the shape of inclusion have confidential relation, and the radius-of-curvature of inclusion is littler, and the stress concentration that causes is healed seriously.Under the repeated stress effect, crackle is preferentially perpendicular to the germinating of the inclusion sharp corner of tensile stress direction, crack growth rate also than nodule faster (Zhang Detang writes. nonmetallic inclusionsin steel is differentiated, Beijing: Beijing National Defense Industry Press, 1991, June: 255).

In producing in present stage, two kinds of technological lines there is the fatigue lifetime of improving steel by reducing oxygen in the steel, sulphur content and inclusion being controlled.A kind of technological line adopts molten steel aluminium deoxidation and high basicity slag refining (Al in the slag ₂O ₃Massfraction be lower than 20%), the massfraction of molten steel sulphur can be dropped to (20～30) * 10 ^-6, the massfraction of total oxygen drops to (3～10) * 10 ^-6, A, category-B inclusion are few, and small D type impurity content ratio is higher.Another technological line then adopts than low basicity slag refining (Al in the slag ₂O ₃Massfraction be lower than 38%), Al does not appear basically ₂O ₃Be mingled with type impurity, but the oxygen level of steel is higher with D.

Summary of the invention

The object of the present invention is to provide the method for a kind of deoxidation, desulfurization, control nonmetallic inclusionsin steel, improved steel fatigue lifetives.Use this method and the massfraction of total oxygen and sulphur in the steel can be controlled to (3～15) * 10 respectively ^-6, (5～30) * 10 ^-6, the inclusion of generation mostly is spherical, and the equivalent diameter of inclusion is (1～10) micron, and composition is that low-melting calcium-aluminate class is mingled with, and can be out of shape slightly in the operation of rolling.

Technology of the present invention is: adopt the operational path of hot metal pretreatment+converter smelting+LF stove refining+vacuum-treat+continuous casting, [S]=0.003%～0.006% before the arrival converter behind the desulfurizing iron; Converter smelting endpoint dual alkalinity (CaO)/(SiO ₂) 4～7, [P]=0.003%～0.01%, the strict pushing off the slag of tapping, tapping process adds 0.9～2 kilogram/ton in aluminium, and thickness of slag layer is controlled at (30～60) mm; After molten steel arrived the LF stove, (weight percent was formed: CaO:60%～90%, SiO to add the high basicity slag material ₂: 2%～8%, Al ₂O ₃: 2%～38%) 4～10 kilograms/ton and aluminium are 0.4～1.2 kilogram/ton, and slag (FeO+MnO) content reaches 0%～1%, Al in the slag in the 15min ₂O ₃Massfraction is 30%～60%, and the Argon in the LF treating processes is that principle stirs with atm number as far as possible with not exposed molten steel face; Molten steel adds aluminium and adjusts that sour molten aluminium [Als] target value is 0.030%～0.070% in the molten steel before vacuum-treat, vacuum processing time (20～60) min, and wherein the treatment time of vacuum tightness (30～300) Pa is (15～30) min; Adopt the whole process protection cast during continuous casting.Can make in the steel massfraction of total oxygen and sulphur control to (3～15) * 10 respectively like this ^-6, (5～30) * 10 ^-6, the inclusion of generation mostly is spherical, and the equivalent diameter of inclusion is (1～10) micron, and composition is that low-melting calcium-aluminate class is mingled with, and can be out of shape slightly in the operation of rolling.

The invention has the advantages that: add aluminium in converter tapping, the LF refining process molten steel is carried out the scope that deoxidation can be reduced to oxygen content in steel to be needed, adopt high basicity (dual alkalinity (CaO)/(SiO in the LF stove ₂) greater than 7), high Al ₂O ₃(Al ₂O ₃Massfraction 30%～60%) slag, this slag system has lower fusing point.Operation can be with the inclusion Al that remains in the steel like this ₂O ₃Be transformed into spherical, low-melting calcium-aluminate type impurity, being in a liquid state in molten steel easy come-up is removed, remained in the steel is little nodule, does not have anisotropy in steel, does not influence the anti-fatigue performance of steel.This synthetic slag has very high basicity, and higher sweetening power is arranged, and slag system does not add or fluorite a little, and lining erosion and environment protection are all had good effect.Molten steel guarantees that in the vacuum-treat process treatment time under rough vacuum (30～300) the Pa condition is (15～30) min, can further reduce total oxygen content in the steel, promotes floating foreign.Adopt the whole process protection cast in the casting process, prevent the secondary oxidation of molten steel.

Description of drawings

The variation of total oxygen and sulphur content in Figure 142 CrMo smelting process;

Inclusion pattern and size in Figure 24 2CrMo strand;

Inclusion type in Figure 34 2CrMo strand.

Embodiment

Test steel 42CrMo (chemical component weight per-cent (%): C:0.38～0.45, Si:0.17～0.37, Mn:0.50～0.80, Mo:0.15～0.25, Cr:0.90～1.20, P＜0.035, S＜0.035).

(1) 143 tons of molten iron is poured in the converter into molten iron [S]=0.014%, [P]=0.08%, [C]=3.75%, T=1345 ℃, add active lime 7862Kg, high Mg lime 3654Kg begins blowing, the time of bessemerizing is 29min, blow end point [C]=0.12%, [P]=0.008%, [S]=0.008%, T=1696 ℃, finishing slag basicity 5.The strict pushing off the slag of converter tapping, with big jar of clean splendid attire molten steel of the bucket end, the tapping initial stage adds the 80Kg aluminum shot, tap and added the 80Kg aluminum shot at 1/3 o'clock again, and add the 170Kg carbon dust in the lump, low ferro-silicon-aluminium 55Kg, silicomanganese 875Kg, ferrochrome 1950Kg, molybdenum-iron 300Kg, tapping added the 90Kg aluminum shot at 2/3 o'clock again, and the tapping time is 5min, tapping finishes the thick 60mm of slag, overhead clearance 350mm.

(2) at the LF station, molten steel weighs 136.4 tons, [C]=0.321% in the molten steel, [Si]=0.142%, [Mn]=0.666%, [P]=0.012%, [S]=0.005%, [O]=0.00306%, [Cr]=1.012%, [Mo]=0.187%, [Als]=0.055%, before the refining of LF stove begins, disposable adding high basicity slag material (chemical weight percentage composition: CaO:75%, SiO ₂: 6%, Al ₂O ₃: 15%, CaF ₂: 900Kg 5%), begin refining after adding the aluminum shot of 90Kg simultaneously, add the aluminum shot of 90Kg behind the 13min again, record dual alkalinity (CaO)/(SiO of slag during 20min ₂) be 11.8, Al ₂O ₃Content is 46%, and (FeO+MnO) content is 0.4%, and the LF stove purified time is 45min, when going out the LF station, molten steel composition is [C]=0.312%, [Si]=0.200%, [Mn]=0.636%, [P]=0.012%, [S]=0.0014%, [Cr]=1.025%, [Mo]=0.185%, [O]=0.00149%, [Als]=0.053%, T=1642 ℃.

(3) after reaching RH, molten steel adds aluminum shot 20Kg, molten steel weighs 136.4 tons, the RH vacuum-treat begins to add ferromanganese 185Kg behind the 13min, ferrosilicon 50Kg, carbon dust 170Kg, the RH vacuum processing time always is 44min, wherein the treatment time of 220pa is 21min, liquid steel temperature was 1601 ℃ when RH finished, and molten steel composition is [C]=0.40%, [Si=0.23%, [Mn]=0.71%, [P]=0.013%, [S]=0.0012%, [Cr]=1.025%, [Mo]=0.185%, [O]=0.00113%, [H]=0.00017%, [Als]=0.036%.

(4) continuous casting adopts the whole process protection cast, and the cast section is 280mm * 380mm, pulling rate 0.55m/min, [O]=0.00085% in the strand, [S]=0.0013% (see figure 1).Inclusion size in the strand all less than 3 μ m, is shaped as spherical (see figure 2), and the composition overwhelming majority is that low-melting calcium-aluminate class is mingled with (see figure 3).

Claims

The method of 1, a kind of deoxidation, desulfurization, control nonmetallic inclusionsin steel, it is characterized in that, technology is: adopt hot metal pretreatment to add converter smelting and add the refining of LF stove and add the operational path that vacuum-treat adds continuous casting, arrive [S]=0.003%～0.006% before the converter behind the desulfurizing iron; Converter smelting endpoint dual alkalinity (CaO)/(SiO ₂) 4～7, [P]=0.003%～0.01%, tapping process adds 0.9～2 kilogram/ton in aluminium, and thickness of slag layer is controlled at 30～60mm; After molten steel arrives the LF stove, add high basicity slag material and aluminium, slag FeO+MnO content reaches 0%～1%, Al in the slag in the 15min ₂O ₃Massfraction is 30%～60%, and the Argon in the LF treating processes is that principle stirs with not exposed molten steel face; Molten steel adds aluminium and adjusts that sour molten aluminium [Als] target value is 0.030%～0.070% in the molten steel before vacuum-treat, vacuum tightness is that the treatment time of 30～300Pa is 15～30min; Can make in the steel massfraction of total oxygen and sulphur control to (3～15) * 10 respectively like this ^-6, (5～30) * 10 ^-6, the inclusion of generation mostly is spherical, and the equivalent diameter of inclusion is 1～10 micron, and composition is that low-melting calcium-aluminate class is mingled with, and can be out of shape slightly in the operation of rolling; Described steel is 42CrMo.
2, the method for claim 1 is characterized in that, after molten steel arrived the LF stove, described high basicity slag material weight percent consisted of: CaO:60%～90%, SiO ₂: 2%～8%, Al ₂O ₃: 2%～38%, slag charge: 4～10 kilograms/ton; Aluminium is 0.4～1.2 kilogram/ton.