Novel inclusion control method for ultra-pure steel

Abstract

The invention discloses a novel inclusion control method for ultra-pure steel, and relates to the technical field of steel production. The tapping oxygen content is controlled, and the tapping temperature is controlled; diffusion deoxidation is carried out in the refining slag melting process; a ferrotitanium core-spun yarn is fed before refining is finished; and the continuous casting tundish adopts an integral water gap, and full-protection pouring is carried out. According to the method, the number of oxide inclusions in steel is reduced, and the problems of large-size oxide inclusions and external inclusions caused by erosion of refractory materials easily occurring in a traditional process are solved.

Description

Technical Field

[0001] The invention relates to the technical field of steel production, and in particular to a novel inclusion control method for ultra-pure steel. Background Art

[0002] In the context of high-strengthening steel to achieve weight reduction and carbon reduction, occasional large-diameter inclusions in steel often seriously reduce the service stress of steel and are an important obstacle to the development of high-strengthening materials.

[0003] Traditional pure steel has two processes: aluminum deoxidation ultra-low oxygen process and silicon-manganese deoxidation inclusion plasticization process. Among them, the silicon-manganese deoxidation inclusion plasticization process controls the composition of inclusions to achieve low melting point of inclusions, and finally enables inclusions to be plastically deformed during the billet rolling process, so that the product has a higher fatigue life. However, due to the high equilibrium oxygen content in the steel during smelting, the number of oxide inclusions in the silicon-manganese deoxidation inclusion plasticization process is often difficult to reduce to an extremely low level. Once the oxide inclusions accumulate, they will form larger inclusions with a diameter of 50μm, and easily induce the formation of a small amount of large-sized MgO-SiO2 inclusions with a diameter of more than 80μm. Moreover, since the CaO-SiO2 inclusions produced by silicon-manganese deoxidation have obvious erosion on the refractory, the plug rod curve of the middle package decreases, and foreign inclusions are introduced. The above ultimately results in the product's fatigue life being unstable. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a new inclusion control method for ultra-pure steel.

[0005] In order to solve the above technical problems, the technical solution of the present invention is as follows: A novel inclusion control method for ultra-clean steel, comprising: Hot metal desulfurization: Add desulfurizer to hot metal for desulfurization; BOF or EAF tapping: Control the oxygen content of tapping steel below 300ppm and the tapping temperature between 1570℃ and 1650℃; LF refining: During the refining and slagging process, ferrosilicon powder is added in batches for diffusion deoxidation, and ferrotitanium cored wire is fed before the end of refining; Continuous casting: The continuous casting tundish adopts an integral nozzle and performs full protection casting.

[0006] As a preferred solution of the inclusion control method of the novel ultra-clean steel of the present invention, the sulfur content in the molten iron after desulfurization is less than or equal to 0.03%.

[0007] As a preferred solution of the inclusion control method of the novel ultra-clean steel of the present invention, after controlling the oxygen content of the steel to be below 300 ppm and the steel tapping temperature to be between 1570° C. and 1650° C., the method further comprises: After 20% of the steel is tapped, ferrosilicon, ferromanganese and carburizer are added in sequence, and slightly acidic slag with a basicity of 0.8-1.0 is added before the end of steel tapping.

[0008] As a preferred solution of the inclusion control method of the novel ultra-clean steel of the present invention, it also includes: maintaining argon blowing and stirring during the steel tapping process.

[0009] As a preferred solution of the inclusion control method of the novel ultra-clean steel of the present invention, the total addition amount of the ferrosilicon powder is 80-120 kg.

[0010] As a preferred solution of the inclusion control method of the novel ultra-clean steel of the present invention, after feeding the titanium-iron cored wire before the end of the refining, the method further comprises: The titanium content in the molten steel is controlled at 0.015-0.035%, and soft stirring is performed.

[0011] As a preferred solution of the inclusion control method of the novel ultra-clean steel of the present invention, the soft stirring time is greater than or equal to 30 minutes.

[0012] As a preferred solution of the inclusion control method of the novel ultra-clean steel of the present invention, the full protection casting process adopts a CaO-SiO2 covering agent with a TFe content of less than 1%.

[0013] The beneficial effects of the present invention are: Compared with the common silicon-manganese deoxidation inclusion plasticization process, the present invention significantly improves the common continuous casting stopper rod curve downward erosion refractory material situation, and the stopper rod curve changes from downward to horizontal. The number of oxide inclusions in the rolled wire with a diameter of more than 2μm can be reduced from the normal 60 to 100 / 100mm2 to 20 to 40 / 100mm2. ASPEX scanning shows that the maximum oxide inclusion diameter is generally less than 10μm. Although a certain amount of TiN inclusions are formed in the steel, their diameter is generally less than 10μm, and has no adverse effect on fatigue. The purity of the steel is greatly improved. DETAILED DESCRIPTION

[0014] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific implementation methods.

[0015] The present application provides a novel method for controlling inclusions in ultra-clean steel, which specifically comprises the following steps: Step S101: desulfurization of molten iron: adding a desulfurizing agent to the molten iron for desulfurization.

[0016] Specifically, a desulfurizing agent is added to the molten iron for desulfurization. The amount of the desulfurizing agent added is controlled with the sulfur content in the molten iron after desulfurization being less than or equal to 0.03%.

[0017] Step S102: BOF or EAF steelmaking: Use oxygen top-blown converter steelmaking method or electric arc furnace smelting to tap steel, control the oxygen content of the steel to be below 300ppm, and control the tapping temperature to be between 1570℃ and 1650℃. After 20% of the steel is tapped, add ferrosilicon, ferromanganese and carburizer in sequence, and add slightly acidic slag with a basicity of 0.8-1.0 before the end of tapping.

[0018] It should be noted that during the steel-making process, a large amount of bottom blowing of argon gas is maintained for stirring to promote alloy melting and deoxidation reaction.

[0019] Step S103: LF refining: During the refining and slag-refining process, ferrosilicon powder is added in batches for diffusion deoxidation. The total amount of ferrosilicon powder added is 80-120 kg. After slag-refining, alloying is performed to adjust the composition to the target. Before the end of refining, titanium iron cored wire is fed to control the titanium content of the molten steel to 0.015-0.035%. Finally, soft stirring is performed for more than 30 minutes to promote further floating of inclusions.

[0020] Step S104: Continuous casting: The continuous casting tundish adopts an integral nozzle and performs full protection pouring. The full protection pouring process uses a CaO-SiO2 covering agent with a TFe content of less than 1%.

[0021] Compared with the common silicon-manganese deoxidation inclusion plasticization process, the common continuous casting stopper rod curve downward erosion refractory situation has been significantly improved, and the stopper rod curve has changed from downward to horizontal. The number of oxide inclusions in the rolled wire with a diameter of more than 2μm can be reduced from the normal 60-100 / 100mm2 to 20-40 / 100mm2. After ASPEX scanning, the maximum oxide inclusion diameter is generally less than 10μm. Although a certain amount of TiN inclusions are formed in the steel, their diameter is generally less than 10μm, which has no adverse effect on fatigue. The purity of the steel is greatly improved.

[0022] The following is further described by means of specific examples.

[0023] Example 1: Controlling inclusions in 55SiCr spring steel, the specific steps are as follows: Desulfurizer is added to the molten iron, and the sulfur content of the molten iron after desulfurization is 0.002%.

[0024] 100 tons of BOF steel tapping oxygen 220ppm, tapping temperature 1630 ℃. During the tapping process, large argon stirring, 2000kg ferrosilicon, 300kg carbon powder added at 20% of the tapping, 1000kg acidic refined slag added at the end of the tapping, and continued large argon stirring for 6 minutes.

[0025] LF refining slag is added with 100kg of ferrosilicon powder in batches, heated for 20 minutes, and then 1000kg of ferromanganese and 1000kg of ferrochrome are added. Continue heating for 5 minutes, take samples for analysis. Then continue to add alloy to the target value. Before the end of refining, feed 130 meters of ferrotitanium cored wire, and the titanium content of the molten steel is 0.021%. Then stir softly for 40 minutes.

[0026] The tundish adopts an integral nozzle and full protection casting, and uses a CaO-SiO2 covering agent with a TFe content of 0.3%.

[0027] The rolled Φ8 specification wire was tested by ASPEX scanning. The density of oxide inclusions with a diameter of more than 2μm was 33 / 100mm2, the maximum oxide inclusion diameter was 4.19μm, and the maximum TiN inclusion diameter was 9.48μm.

[0028] Example 2: Controlling inclusions in 54SiCr6 spring steel, the specific steps are as follows: Desulfurizer is added to the molten iron, and the sulfur content of the molten iron after desulfurization is 0.001%.

[0029] 100 tons of BOF steel tapping oxygen 190ppm, tapping temperature 1590 ℃. During the tapping process, large argon stirring, 2000kg ferrosilicon, 280kg carbon powder added at 20% of the tapping, 1000kg of acidic refined slag added at the end of the tapping, and continued large argon stirring for 8 minutes.

[0030] LF refining slag is added with 120kg of ferrosilicon powder in batches, heated for 15 minutes, and then 1000kg of ferromanganese and 1000kg of ferrochrome are added. Continue heating for 5 minutes, take samples for analysis. Then continue to add alloy to the target value. Before the end of refining, feed 114 meters of ferrotitanium cored wire, and the titanium content of the molten steel is 0.018%. Then soft stirring is carried out for 50 minutes.

[0031] The tundish adopts an integral nozzle and full protection casting, and uses a CaO-SiO2 covering agent with a TFe content of 0.2%.

[0032] The rolled Φ11 specification wire was tested by ASPEX scanning. The density of oxide inclusions with a diameter of more than 2μm was 36 / 100mm2, the maximum oxide inclusion diameter was 7.14μm, and the maximum TiN inclusion diameter was 7.74μm.

[0033] Therefore, the technical solution of the present application reduces the number of oxide inclusions in steel, and eliminates the problem of large-sized oxide inclusions and foreign inclusions caused by corrosion of refractory materials that are prone to occur in traditional processes.

[0034] In addition to the above embodiments, the present invention may also have other implementation modes; any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

Claims

1. A novel method for controlling inclusions in ultra-pure steel, characterized in that: include: Hot metal desulfurization: Add desulfurizer to hot metal for desulfurization; BOF or EAF tapping: Control the oxygen content of tapping steel below 300ppm and the tapping temperature between 1570℃ and 1650℃; LF refining: During the refining and slagging process, ferrosilicon powder is added in batches for diffusion deoxidation, and ferrotitanium cored wire is fed before the end of refining; Continuous casting: The continuous casting tundish adopts an integral nozzle and performs full protection casting.

2. The new method for controlling inclusions in ultra-clean steel according to claim 1, characterized in that: The sulfur content in molten iron after desulfurization is less than or equal to 0.03%.

3. The new method for controlling inclusions in ultra-clean steel according to claim 1, characterized in that: After controlling the oxygen content of the steel to be below 300 ppm and the steel tapping temperature to be between 1570° C. and 1650° C., the method further comprises: After 20% of the steel is tapped, ferrosilicon, ferromanganese and carburizer are added in sequence, and slightly acidic slag with a basicity of 0.8-1.0 is added before the end of steel tapping.

4. The new method for controlling inclusions in ultra-clean steel according to claim 2, characterized in that: Also includes: During the steel tapping process, argon blowing and stirring are maintained.

5. The novel inclusion control method for ultra-clean steel according to claim 1, characterized in that: The total amount of the ferrosilicon powder added is 80-120 kg.

6. The novel inclusion control method for ultra-clean steel according to claim 1, characterized in that: After the ferro-titanium cored wire is fed before the refining is finished, the method further comprises: The titanium content in the molten steel is controlled at 0.015-0.035%, and soft stirring is performed.

7. The novel inclusion control method for ultra-clean steel according to claim 6, characterized in that: The soft stirring time is greater than or equal to 30 minutes.

8. The new method for controlling inclusions in ultra-clean steel according to claim 1, characterized in that: The full protection casting process uses a CaO-SiO2 covering agent with a TFe content of less than 1%.