CN101096723A - Method for AOD whole melted iron directly smelting austenitic stainless steel - Google Patents

Abstract

The invention discloses a smelting method of austenite stainless steel through AOD full-molten iron directly, which comprises the following steps: putting 15-30Kg/t steel ferrosilicon and 20-40Kg/t steel graphite or char into the furnace at the beginning of converting; heating the molten pool temperature to 1600-1700 deg. c; using top-blowing oxygen gun and side blow vent to supply oxygen; controlling the oxygen flow and inert gas flow over 10: 1; adding the nickel over 90% in the stage; finishing the course when the [C] is 1.5-2.5wt%; entering the decarburizing chromine-keeping stage and reducing desulfurizing stage.

Description

The method of AOD whole melted iron directly smelting austenitic stainless steel

Technical field

The present invention relates to the stainless steel-making process field, more particularly, relate to the method for AOD whole melted iron directly smelting austenitic stainless steel.

Background technology

At present, the processing step of common in the world AOD stove (argon oxygen decarburizing furnace) stainless steel-making process is:

In electric furnace, stainless steel refining → carry out vacuum decarburization is smelted → carried out to dephosphorization molten iron and steel scrap in the AOD stove in VOD (vacuum decarburization stove) stove and handle, or in LF/LTS (ladle furnace/ladle treatment station), handle → continuous casting.

In above-mentioned technology, existing AOD stove is mainly used in the stainless steel refining, and raw material adopts the mother liquor of stainless steel that is smelt by furnace melting steel scrap and alloy, as diluent gas, reduces Pco with argon gas, and chrome-bearing steel liquid is carried out decarburization and cr yield.

Particularly, the composition (weight percent) from the mother liquor of electric furnace is controlled to be in the AOD refinery practice: C 1.0%～3.0%, and Mn 0～0.2%, and Si 0～0.35%, and S 0～0.020%, and P 0～0.035%, and Cr 16.0%～19.0%, and Ni 0～7.5%; The mother liquor temperature: 1500～1580 ℃, 110～120 tons of mother liquor weight.

Technology by the mother liquor smelting stainless steel is divided into two main phase: decarburization and cr yield stage and reduction, desulfurization stage.The concrete operations step is as follows:

1) the electric furnace mother liquor is blended into the AOD converter, measures the mother liquor temperature, blow by oxygen supply, the air feed standard of the listed blowing pattern of table 1;

Table 1 Nm ³/ min

Stage	Si, Al oxidation	Main blowing	Dynamic 1	Dynamic 2	Dynamic 3	Reduction	Desulfurization
								Top rifle O 2Flow	0	120	0	0	0	0	0
Air port O 2Flow	110	110	60	40	30	0	0
								Air port N 2Flow	30	30	60	80	110	0	0
Air port Ar flow	0	0	0	0	110	110

2) reach 2000～3000Nm at blowing oxygen quantity ³Remaining ferrochrome of Shi Peijia and ferronickel;

3) when blowing oxygen quantity reaches whole oxygen-supplying amounts and finishes decarburization (temperature is controlled at about 1700 ℃), add reductive agent ferrosilicon 20～25kg/t and carry out restoring operation;

4) reduction is carried out desulfurization operations after finishing, and the lime of adding 10～15kg/ ton steel, the fluorite of 6～10kg/ ton steel carry out desulfurization.

5) carry out molten steel component fine setting, tap after meeting ingredient standard.

The AOD molten steel component (weight percent) of tapping: C 0.012%～0.080%, and Mn 0.60%～2.0%, and Si 0.20%～0.50%, S 0.001%～0.010%, and P 0～0.035%, and Cr 15.0%～19.0%, Ni 8.0～12.0%, and Mo 0～2%, N 0～1500ppm; Tapping liquid steel temperature: 1600～1650 ℃.

In sum, existing AOD smelting technology all adopts furnace melting steel scrap, alloy and partial molten iron, enters the AOD stove then and carries out refining, though can smelt qualified stainless steel, has following defective:

1) because quite high with the smelting mother liquor of stainless steel from electric furnace power consumption, electric power consumption per ton steel is 320～360kwh, has correspondingly increased production cost;

2) electric furnace production must blowing out be carried out the refractory materials maintenance after 7～10 days, needed to stop production 10～24 hours, and the whole piece stainless steel production line must stop production 10～24 hours like this, and the production production capacity is subjected to very big influence;

3) owing to just needing to use steel scrap in the refining process, it is higher therefore to smelt the stainless steel micro impurity element content that;

4) operational path is long, and production unit occupation of land amount is big.

Summary of the invention

The objective of the invention is to save electric furnace and just refine operation, adopt blast-melted (behind the dephosphorization) and add alloy, by the control of the temperature in the AOD smelting process, blowing pattern, decarburization and cr yield technology, top rifle oxygen supply technology, the pattern of feeding intake are improved, form a kind of in the AOD stove the direct method of smelting austenitic stainless steel.

For achieving the above object, the invention provides a kind of method of AOD whole melted iron directly smelting austenitic stainless steel, this method adopts full molten iron directly to be blended in the AOD stove to smelt, being divided into three phases carries out: in the decarburization temperature rise period, promptly in stove, drop into the ferrosilicon of 15～30Kg/ ton steel and the graphite or the coke of 20～40Kg/ ton steel after the blowing beginning, make bath temperature be climbed to 1600 ℃～1700 ℃, and by top blow oxygen lance and cross air blow confession oxygen, the ratio that this moment, oxygen rifle oxygen flow added uptake oxygen flow and the flow of air port rare gas element is controlled at more than 10: 1; The nickel of required input will drop in this stage more than 90%, and [C] finishes when content controls to 1.5～2.5wt% when the molten bath; Then enter the decarburization and cr yield stage, when bath temperature reaches 1680 ℃～1720 ℃, just drop into ferrochrome with 2～3 tons/minute speed, be controlled at more than 10: 1 at the ratio of this stage oxygen flow with inert gas flow, as molten bath [C] when reaching 0.45～0.65wt%, the ratio control of oxygen and rare gas element is equal to general AOD smelting technology, and end temp is controlled at 1680 ℃～1730 ℃; Enter the reduction and desulfurization stage then, this stage is equal to general AOD smelting technology.

Main technologic parameters control is as follows:

The operational path of the full molten iron smelting austenitic stainless steel of AOD is divided into the two step method without electric furnace, and promptly the dephosphorization molten iron is directly smelted to the finished product molten steel at AOD, handles through LF stove or LTS again; With the three-step approach without electric furnace, promptly the dephosphorization molten iron is directly smelted to C content 0.15%～0.50% at AOD, handles through VOD stove vacuum decarburization again.

1) need the composition and the temperature thereof of control to see Table 2 in the full molten iron

Table 2

C	Si	Mn	S	P	Temperature
						≥2.5％	-	-	≤0.020％	≤0.015％	≥1100℃

2) iron water amount: calculate by 60%～65% of tap.

3) AOD smelts step

With the full molten iron smelting austenitic stainless steel of AOD technology, be divided into three main phase:

The 1st stage: decarburization, temperature rise period;

The 2nd stage: decarburization and cr yield stage;

The 3rd stage: reduction, desulfurization stage (this stage is consistent with existing AOD technology).

The 1st step: the 1st stage, because molten iron temperature is lower, take off the requirement that C protects Cr in order to reach, reduce the oxidation of precious metal Cr, as early as possible with the C oxidation removal, therefore the critical point temperature according to the C-Cr selective oxidation requires (more than 1560 ℃), after AOD blowing beginning, promptly drop into the ferrosilicon of 15～30Kg/ ton steel and the graphite (also can use coke) of graphite (coke) 20～40Kg/ ton steel, make bath temperature be elevated to 1600～1700 ℃ rapidly, drop into solid-state ferrochrome so again, remove ferrochrome fusing heat absorption, bath temperature is remained on more than 1560 ℃, reach the purpose that reduces the chromium oxidation.Because there is not the problem of selective oxidation in nickel, therefore, at the metallic nickel (316 be stainless steel also will add molybdenum-iron) of this stage input more than 90%, input amount is according to the nickel composition requirement of institute's steelmaking kind.

The 2nd step: the 2nd stage, when the molten bath is warmed up to 1600～1700 ℃, C 1.00%～2.00% the time, should be with slag in the stove to clean (reduce the quantity of slag in the stove, reduce the dividing potential drop of CO, thereby improve oxygen utilization rate).In the time of 1680 ℃～1720 ℃, begin to add ferrochrome, 2～3 tons/minute, the ferrochrome add-on is calculated according to institute's steelmaking kind chromium component, keeps bath temperature to be stabilized in more than 1560;

The 3rd step: when decarburization finishes, [C]=0.012%～0.05%, the critical temperature of C-Cr is about 1680 ℃, so the molten bath optimum temps is controlled at 1680～1730 ℃, low excessively Cr excessive oxidation cost is increased, and too highly makes the lining erosion aggravation, and reduce work-ing life;

The 4th step: the 3rd stage, when blowing oxygen quantity reaches whole oxygen-supplying amounts and finishes decarburization, add reductive agent ferrosilicon 5～25kg/t and carry out restoring operation, concrete input amount can be calculated according to following formula;

W _{The oxygen amount of oxidation Cr}=W _{Total O2}-(W _{Take off C oxygen amount}+ W _{Take off Si oxygen amount})

W _{The reduction ferrosilicon}=W _{The oxygen amount of oxidation Cr}* 1.25 ÷ Si% _Ferrosilicon

The 5th step: reduction is carried out desulfurization operations after finishing, and the lime, the 6～15kg/ ton steel fluorite that add 10～20kg/ ton steel carry out desulfurization.Carry out molten steel component fine setting, tap after meeting ingredient standard.

Wherein, oxygen supply control in the described smelting process, the ratio control of oxygen and rare gas element sees Table 3 (AOD blow pattern):

Table 3

Pattern	The 1st stage	The 2nd stage
						Main blowing the stage	Dynamic 1	Dynamic 2	Dynamic 3
		Oxygen rifle oxygen Nm 3/min	100～160	100～160
Air port oxygen Nm 3/min	110～120					110～120	60	40	30
		Air port rare gas element Nm 3/min	20	20～30	60					80	110
The ratio of oxygen and rare gas element	More than 10: 1					More than 10: 1	1∶1	1∶2	1∶3.5

Parameter designing is set according to AOD " decarburization and cr yield " principle in the table.Oxygen and rare gas element ratio control purpose are that the oxidation of control chromium drops to minimum level, improve the recovery rate of chromium metal.In the 1st stage, do not add ferrochrome, be to avoid the selective oxidation of Cr-C, improve oxygen supply intensity to greatest extent, accelerate decarbonization rate.When bath temperature during greater than 1600 ℃, add ferrochrome again, at this moment, reduce the oxidation of chromium, the raising oxygen utilization rate because the temperature height can guarantee that oxygen combines with carbon.

AOD " decarburization and cr yield " principle is set forth: well-known, under certain temperature and CO partial pressure conditions, Cr is to O ₂Avidity be better than C, make the Cr in the stainless steel molten bath that preferential C is oxidized, C to be dropped to very difficult that stainless steel target C content (0.02%～0.08%) just becomes like this.In order to realize the purpose of decarburization and cr yield, at AOD stove carbon period initial stage, O ₂And Ar (N ₂) mixed gas, by the nozzle of stove lower sides, part oxygen then is blown into from the top rifle.Because the present invention adopts the full molten iron smelting of AOD, is molten iron fully, therefore also there is not the problem of decarburization and cr yield in the molten bath.According to this point, we Chrome metal powder is a large amount of drop into before, consider to strengthen to the oxygen supply ratio, particularly AOD top oxygen rifle of iron bath oxygen-supplying amount, accelerate decarbonization rate.But when beginning to drop into ferrochrome, because the content of chromium heightens in the molten bath, will consider how to guarantee to reduce the oxidation of chromium, decarburization to greatest extent mainly reduces the oxidation (more than 1580 ℃) of chromium by controlled temperature.The concrete oxygen-supplying amount in each stage can calculate according to prior art.

The present invention compared with prior art, have following advantage: 1) impurity element is controlled.Adopt overall height stove molten iron smelting, avoided stainless molten steel to be subjected to the quality influence of impure steel scrap, the trace element that Cu, Ni, Sn, Pb, As etc. have a significant effect to the stainless steel quality can be controlled in the extremely low scope, even can ignore, greatly reduce the difficulty of smelting the high cleanliness austenitic stainless steel.2) [P] is effectively controlled.Because do not have the pollution of steel scrap, finished product [P] can reach below 0.025% more like a cork, contain that [P] is low to help improving stainless corrosion resistance nature, improve stainless quality product.3) cost advantage.Because the technology that adopts AOD directly to smelt, mother liquor of stainless steel that need not electrosmelting (slightly make steel water) is like this in common process, to be saved by the cost that electric furnace produces, such as electric energy saving, power shortages now, its generation be not only the direct economic benefit of enterprise just; The saving of the electric furnace liner cost of anti-the material, avoiding of consumption such as goods, materials and equipments, equipment, electrode also is a very considerable income.

Embodiment

Below be specifying of embodiment of the invention 1-3.

Embodiment 1

The molten iron condition:

Hot metal composition: C 2.98%, Mn 0.03%, and Si 0.00%, and S 0.028%, and P 0.010%;

Molten iron temperature: 1224 ℃, weight of molten iron: 91 tons;

Converting process:

Add Si-Fe 15kg/t during the blowing beginning, graphite (coke) 40kg/t heats up;

Drop into 90% of total nickel amount in the 1st stage, the metallic nickel of about 70kg/t.

When accumulative total reaches oxygen-supplying amount 4500Nm ³The time, the 1st stage finished; Recording temperature is 1600 ℃.

Molten steel composition saw Table 1-1 when the 1st stage finished:

Table 1-1

C	Mn	Si	S	P	Cr	Ni
							2.50％	0.03％	0.01％	0.012％	0.015％	0.070％	10.51％

The 2nd stage began the speed with 2 tons/minute, added ferrochrome 34000kg continuously, and dropping into the beginning temperature is 1680 ℃.

At the main blowing bundle in the 2nd stage, recording C is 0.45wt%.

Molten steel composition saw Table 1-2 when the 2nd stage dynamic 3 finished:

Table 1-2

C	Mn	Si	S	P	Cr	Ni
							0.030％	0.05％	0.05％	0.023％	0.019％	16.08％	8.29％

Liquid steel temperature when decarburization finishes: 1725 ℃;

The blowing pattern sees Table 1-3

Table 1-3 Nm ³/ min

Stage	The 1st stage	The 2nd stage				Reduction	Desulfurization
								Main blowing	Dynamic 1	Dynamic 2	Dynamic 3
		Oxygen-supplying amount Nm 3	4500	10760	11100							11390	11620
Top rifle O 2Flow	100					120		0	0	0	0
		Air port O 2Flow	120	120	60							40	30	0	0
Air port N 2Flow	20					20	60	80	0	0	0
		Air port Ar flow	0	0	0							0	110	110	110

Reduction and desulfurization:

Adding reductive agent ferrosilicon 2548kg reduces;

Reduction is carried out desulfurization operations after finishing, and the lime, the 1200kg fluorite that add 1700kg carry out desulfurization.

Go out composition of steel and see Table 1-4:

Table 1-4

C	Mn	Si	S	P	Cr	Ni	N
								0.042％	0.71％	0.44％	0.009％	0.021％	17.88％	8.13％	430ppm

Tapping liquid steel temperature: 1632 ℃ of tapping molten steel weight: 132 tons

Embodiment 2

The molten iron condition:

Hot metal composition: C 2.91%, Mn 0.03%, and Si 0.00%, and S 0.0321%, and P 0.006%;

Molten iron temperature: 1243 ℃, weight of molten iron: 86.6 tons;

Converting process:

Add Si-Fe 30kg/t during the blowing beginning, graphite (coke) 20kg/t heats up;

Drop into 95% of total nickel amount in the 1st stage, the metallic nickel of about 76kg/t.

Accumulative total reaches oxygen-supplying amount 5000Nm ³The 1st stage finished; Temperature is 1700 ℃.

At the main blowing bundle in the 2nd stage, recording C is 0.56wt%.

Molten steel composition saw Table 2-1 when the 2nd stage dynamic 3 finished:

Table 2-1

C	Mn	Si	S	P	Cr	Ni
							1.88％	0.05％	0.08％	0.024％	0.016％	0.54％	10.40％

The 2nd stage began the speed with 2.3 tons/minute, added ferrochrome 31000kg continuously, and dropping into the beginning temperature is 1700 ℃.

Molten steel composition saw Table 2-2 when the decarburization of the 2nd stage finished:

Table 2-2

C	Mn	Si	S	P	Cr	Ni
							0.032％	0.04％	0.01％	0.05％	0.021％	16.03％	8.27％

Liquid steel temperature when decarburization finishes: 1730 ℃;

The blowing pattern sees Table 2-3:

Table 2-3 Nm ³/ min

Stage	The 1st stage	The 2nd stage				Reduction	Desulfurization
								Main blowing	Dynamic 1	Dynamic 2	Dynamic 3

Oxygen-supplying amount Nm 3	5000	9700	10960	11150	11350
								Top rifle O 2Flow	160	120		0	0	0	0
Air port O 2Flow	110	110	60	40	30	0	0
								Air port N 2Flow	27	20	60	80	0	0	0
Air port Ar flow	0	0	0	0	110	110	110

Reduction and desulfurization:

Adding reductive agent ferrosilicon 3000kg reduces;

Reduction is carried out desulfurization operations after finishing, and the lime, the 2000kg fluorite that add 2000kg carry out desulfurization.

Go out composition of steel and see Table 2-4:

Table 2-4

C	Mn	Si	S	P	Cr	Ni	N
								0.042％	0.74％	0.44％	0.003％	0.021％	17.93％	8.14％	370ppm

Tapping liquid steel temperature: 1650 ℃ of tapping molten steel weight: 125 tons

Embodiment 3

The molten iron condition:

Hot metal composition: hot metal composition: C 2.83%, Mn 0.03%, and Si 0.00%, and S 0.010%, P0.007%;

Molten iron temperature: 1154 ℃, weight of molten iron: 85 tons

Embodiment 3 converting processes:

Add Si-Fe 20kg/t during the blowing beginning, graphite (coke) 30kg/t heats up;

Drop into 10% of total nickel amount in the 1st stage, the metallic nickel of about 85kg/t.

Accumulative total reaches oxygen-supplying amount 5500Nm ³The 1st stage finished; Temperature is 1668 ℃.

At the main blowing bundle in the 2nd stage, recording C is 0.65wt%.

Molten steel composition saw Table 3-1 when the 2nd stage dynamic 3 finished:

Table 3-1

C	Mn	Si	S	P	Cr	Ni
							1.50％	0.03％	0.07％	0.014％	0.021％	0.10％	10.98％

The 2nd stage began the speed with 3 tons/minute, added ferrochrome 32400kg continuously, and dropping into the beginning temperature is 1720 ℃.

Molten steel composition saw Table 3-2 when the decarburization of the 2nd stage finished:

Table 3-2

C	Mn	Si	S	P	Cr	Ni
							0.03％	0.04％	0.04％	0.011％	0.022％	16.49％	8.12％

Liquid steel temperature when decarburization finishes: 1680 ℃

The blowing pattern sees Table 3-3:

Table 3-3 Nm ³/ min

Stage	The 1st stage	The 2nd stage				Reduction	Desulfurization
								Main blowing	Dynamic 1	Dynamic 2	Dynamic 3
		Oxygen-supplying amount Nm 3	5500	9800	10250							10630	11000
Top rifle O 2Flow	140					120		0	0	0	0
		Air port O 2Flow	110	110	60							40	30	0	0
Air port N 2Flow	25					20	60	80	0	0	0
		Air port Ar flow	0	0	0							0	110	110	110

Reduction and desulfurization:

Adding reductive agent ferrosilicon 3000kg reduces;

Reduction is carried out desulfurization operations after finishing, and the lime, the 1210kg fluorite that add 1528kg carry out desulfurization.

Go out composition of steel and see Table 3-4:

Table 3-4

C	Mn	Si	S	P	Cr	Ni	N
								0.032％	0.64％	0.20％	0.012％	0.022％	18.21％	8.45％	0.033％

The tapping liquid steel temperature: 1626 ℃, tapping molten steel weight: 129 tons.

As everyone knows, adopt full molten iron smelting austenitic stainless steel, its thermal equilibrium control is very difficult and since this point worldwide smelting stainless steel all adopt mother liquor of stainless steel (slightly make steel water) that steel scrap becomes certain ingredients and temperature by furnace melting to carry out the technology of Decarburising and refining to AOD again.Even adopt blast-melted (behind the dephosphorization), also must and steel scrap collocation use and in electric furnace, be fused into mother liquor of stainless steel (slightly make steel water), carry out Decarburising and refining through AOD again.

The present invention has made full use of the blast-melted C of containing height, the characteristics that chemical heat is high, and the flexible Application compensated technology, stable control bath temperature and reasonable blowing pattern in converting process is controlled at the oxidation of Cr in the small range.

Claims (1)

1. the method for an AOD whole melted iron directly smelting austenitic stainless steel, this method adopt full molten iron directly to be blended in the AOD stove to smelt, be divided into three phases and carry out:

In the decarburization temperature rise period, promptly in stove, drop into the ferrosilicon of 15～30Kg/ ton steel and the graphite or the coke of 20～40Kg/ ton steel after the blowing beginning, make bath temperature rise to 1600 ℃～1700 ℃, and by top blow oxygen lance and cross air blow confession oxygen, oxygen flow is controlled at more than 10: 1 with the ratio of inert gas flow; Will dropping in this stage more than 90% of the nickel amount of required input, [C] finishes when content controls to 1.5～2.5wt% when the molten bath;

Then enter the decarburization and cr yield stage, when bath temperature reaches 1680 ℃～1720 ℃, just drop into ferrochrome with 2～3 tons/minute speed, be controlled at more than 10: 1 at the ratio of this stage oxygen flow with inert gas flow, as molten bath [C] when reaching 0.45～0.65wt%, the ratio control of oxygen and rare gas element is equal to general AOD smelting technology, and end temp is controlled at 1680 ℃～1730 ℃;

Enter the reduction and desulfurization stage then, this stage is equal to general AOD smelting technology.