Method for improving purity of 14Cr17Ni2 martensitic stainless steel

Abstract

The invention relates to the technical field of ferrous metallurgy, and provides a method for improving the purity of 14Cr17Ni2 martensitic stainless steel, which sequentially comprises the following steps: charging, smelting, deoxidizing and alloying, refining and casting. The refining slag for refining is a CaO-SiO2-Al2O3-MgO-CaF2 five-membered slag system, and the five-membered slag system is prepared from the following components in percentage by weight: 20 percent to 30 percent of Al2O3, 8 percent to 12 percent of SiO2, 3 percent to 8 percent of MgO, 2 percent to 8 percent of CaF2 and the balance of CaO. Through the technical scheme, the problem of low purity of the 14Cr17Ni2 martensitic stainless steel in related technologies is solved.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a method for improving the purity of 14Cr17Ni2 martensitic stainless steel. Background Art

[0002] 14Cr17Ni2 is a kind of martensitic stainless steel with good corrosion resistance. It can be used for high-end shafts, piston rods, valves, oil pumps and other parts that require both toughness and corrosion resistance. It is currently mainly imported. It was found in domestic conventional production that the non-metallic inclusions in the 14Cr17Ni2 martensitic stainless steel ingot smelted by Al deoxidation through the electric furnace-AOD-LF-die casting process did not meet the detection standards, and the "hairline" phenomenon was found on the finished parts, which seriously affected the product qualification rate. Therefore, it is necessary to propose a method to improve the purity of 14Cr17Ni2 martensitic stainless steel. Summary of the invention

[0003] The invention provides a method for improving the purity of 14Cr17Ni2 martensitic stainless steel, which solves the problem of low purity of 14Cr17Ni2 martensitic stainless steel in the related art.

[0004] The technical scheme of the present invention is as follows: The present invention proposes a method for improving the purity of 14Cr17Ni2 martensitic stainless steel, which comprises the following steps in sequence: charging, smelting, deoxidation alloying, refining, and casting; the refined slag is a CaO-SiO2-Al2O3-MgO-CaF2 five-element slag system, which is composed of the following components by weight percentage: Al2O3 20%~30%, SiO2 8%~12%, MgO 3%~8%, CaF2 2%~8%, and the balance is CaO.

[0005] As a further technical solution, the 14Cr17Ni2 martensitic stainless steel is composed of the following components by weight percentage: C 0.15%~0.17%, Si 0.40%~0.50%, Mn 0.70%~0.80%, P<0.025%, S<0.004%, Cr16.05%~16.25%, Ni 2.28%~2.34%, N<0.06%, and the balance is Fe and unavoidable impurities.

[0006] As a further technical solution, the mass ratio of the Al2O3 to the MgO is 25:4~5.

[0007] In the present invention, by limiting the mass ratio of Al2O3 to MgO, the desulfurization and dephosphorization capabilities of the refined slag are enhanced, the performance of the refined slag is optimized, the stability of the refining process is maintained, and the purity of the 14Cr17Ni2 martensitic stainless steel is further improved.

[0008] As a further technical solution, the refining is carried out in two steps. The mass ratio of SiO2 to CaF2 in the refining slag system of the first refining step is 7~8:1, and the mass ratio of SiO2 to CaF2 in the refining slag system of the second refining step is 2~3:4.

[0009] In the present invention, refining is carried out in two steps and the amount of CaF2 is increased in the second step of refining. The increase in the amount of CaF2 further reduces the melting point and viscosity of the refined slag, so that the fluidity of the refined slag in the molten steel is better, and the slag can penetrate deeper into the molten steel to fully react with the residual tiny inclusions and harmful impurity elements, thereby further improving the purity of the 14Cr17Ni2 martensitic stainless steel.

[0010] As a further technical solution, the mass ratio of the refined slag system in the first refining step to the refined slag system in the second refining step is 1:1, the refined slag in the first refining step is added at the start of refining, and the refined slag in the second refining step is added 20 to 30 minutes after the start of refining.

[0011] As a further technical solution, the total mass of the refined slag is 3% to 5% of the mass of the 14Cr17Ni2 martensitic stainless steel.

[0012] As a further technical solution, the refining time is 55 to 65 minutes.

[0013] As a further technical solution, the charging includes the following steps: Cr, Ni and Fe are mixed and added into a crucible according to target composition, and then placed into the center of the MoSi2 furnace.

[0014] As a further technical solution, the crucible is a MgO crucible, and a graphite crucible is sheathed on the outer side of the MgO crucible.

[0015] As a further technical solution, the smelting includes the following steps: after heating, argon and oxygen are introduced in sequence to carry out smelting.

[0016] As a further technical solution, the temperature of the argon gas is 1300°C, the flow rate is 3-5NL / min, and the temperature of the oxygen gas is 1600°C, the time is 10s, and the flow rate is 2NL / min.

[0017] As a further technical solution, the deoxidation alloying comprises the following steps: adding pure Al for deoxidation after the smelting is completed, and then adding C, Mn and Si of the target component batches for alloying.

[0018] As a further technical solution, the amount of pure Al added is 1‰~2‰ of the mass of the 14Cr17Ni2 martensitic stainless steel.

[0019] The working principle and beneficial effects of the present invention are: In the present invention, a CaO-SiO2-Al2O3-MgO-CaF2 quinary slag system is used as the refining slag. By deeply exploring the proportion of the refining slag and the role of inclusions, the refining slag is promoted to better absorb and dissolve inclusions in the steel, thereby achieving high-quality and stable production of 14Cr17Ni2, improving the product qualification rate, and improving the purity of 14Cr17Ni2 martensitic stainless steel. DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] In the following examples and comparative examples: Ferrochrome alloy: chromium content 69wt%, carbon content 0.03wt%; Iron-nickel alloy: nickel content 80wt%; Scrap steel: iron content 98wt%; Ferromanganese alloy: manganese content 68wt%; Ferrosilicon alloy: silicon content 25wt%; Carbon: coke, fixed carbon 85wt%.

[0022] Example 1 14Cr17Ni2 martensitic stainless steel, composed of the following components by weight percentage: C 0.15%, Si 0.40%, Mn 0.70%, P 0.0079%, S 0.0023%, Cr 16.05%, Ni 2.28%, N 0.010%, the balance being Fe and unavoidable impurities; A method for improving the purity of 14Cr17Ni2 martensitic stainless steel comprises the following steps: mixing chromium-iron alloy, iron-nickel alloy and scrap steel according to target composition and adding them into a MgO crucible, wherein a graphite crucible is sleeved on the outer side of the MgO crucible, and putting them into the center of a MoSi2 furnace together, heating them to 1300°C by power, introducing argon gas with a flow rate of 3NL / min, blowing oxygen for 10s at a flow rate of 2NL / min when the temperature reaches 1600°C, adding pure Al for deoxidation after the oxygen blowing is completed, wherein the amount of pure Al added is 1‰ of the mass of the 14Cr17Ni2 martensitic stainless steel, and then adding coke, ferromanganese alloy and ferrosilicon alloy with target composition for alloying, adding refining slag to start refining, and casting after refining for 55 minutes to obtain 14Cr17Ni2 martensitic stainless steel, wherein the refining slag is composed of the following components by weight percentage: Al2O3 20%, SiO2 8%, MgO 3%, CaF2 2%, and the balance CaO. The total mass of the refined slag is 3% of the mass of 14Cr17Ni2 martensitic stainless steel.

[0023] Example 2 14Cr17Ni2 martensitic stainless steel, composed of the following components by weight percentage: C 0.16%, Si 0.45%, Mn 0.75%, P 0.0080%, S 0.0024%, Cr 16.15%, Ni 2.31%, N 0.012%, the balance being Fe and unavoidable impurities; A method for improving the purity of 14Cr17Ni2 martensitic stainless steel comprises the following steps: mixing chromium-iron alloy, iron-nickel alloy and scrap steel according to target composition and adding them into a MgO crucible, wherein a graphite crucible is sleeved on the outer side of the MgO crucible, and putting them into the center of a MoSi2 furnace together, heating them to 1300°C by power, introducing argon gas with a flow rate of 4NL / min, blowing oxygen for 10s at a flow rate of 2NL / min when the temperature reaches 1600°C, adding pure Al for deoxidation after the oxygen blowing is completed, wherein the amount of pure Al added is 1.5‰ of the mass of the 14Cr17Ni2 martensitic stainless steel, and then adding coke, ferromanganese alloy and ferrosilicon alloy with target composition for alloying, adding refined slag to start refining, and casting after refining for 60 minutes to obtain 14Cr17Ni2 martensitic stainless steel, wherein the refined slag consists of the following components by weight percentage: Al2O3 25%, SiO2 10%, MgO 5%, CaF25%, and the balance is CaO. The total mass of the refined slag is 4% of the mass of 14Cr17Ni2 martensitic stainless steel.

[0024] Example 3 14Cr17Ni2 martensitic stainless steel, composed of the following components by weight percentage: C 0.17%, Si 0.50%, Mn 0.80%, P 0.0084%, S 0.0025%, Cr 16.25%, Ni 2.34%, N 0.014%, the balance being Fe and unavoidable impurities; A method for improving the purity of 14Cr17Ni2 martensitic stainless steel comprises the following steps: mixing chromium-iron alloy, iron-nickel alloy and scrap steel according to target composition and adding them into a MgO crucible, wherein a graphite crucible is sleeved on the outer side of the MgO crucible, and putting them into the center of a MoSi2 furnace together, heating them to 1300°C by power, introducing argon gas with a flow rate of 5NL / min, blowing oxygen for 10s at a flow rate of 2NL / min when the temperature reaches 1600°C, adding pure Al for deoxidation after the oxygen blowing is completed, wherein the amount of pure Al added is 2‰ of the mass of the 14Cr17Ni2 martensitic stainless steel, and then adding coke, ferromanganese alloy and ferrosilicon alloy with target composition for alloying, adding refining slag to start refining, and casting after refining for 65 minutes to obtain 14Cr17Ni2 martensitic stainless steel, wherein the refining slag is composed of the following components by weight percentage: Al2O3 30%, SiO2 12%, MgO 8%, CaF28%, and the balance is CaO. The total mass of the refined slag is 5% of the mass of 14Cr17Ni2 martensitic stainless steel.

[0025] Example 4 Compared with Example 2, the difference in Example 4 is that the added amount of MgO is 3%.

[0026] Example 5 Compared with Example 2, the difference in Example 5 is that the added amount of MgO is 4%.

[0027] Example 6 Compared with Example 2, the difference in Example 6 is that the added amount of MgO is 6%.

[0028] Example 7 Compared with Example 2, the difference of Example 7 is that the refining of the refined slag is carried out in two steps. The amount of SiO2 added to the refined slag system in the first step is 8%, and the amount of CaF2 added to the refined slag system is 2%. The amount of SiO2 added to the refined slag system in the second step is 12%, and the amount of CaF2 added to the refined slag system is 8%.

[0029] Example 8 Compared with Example 7, the difference of Example 8 is that the amount of SiO2 added to the refined slag system in the first refining step is 9%, and the amount of CaF2 added is 2%, and the amount of SiO2 added to the refined slag system in the second refining step is 11%, and the amount of CaF2 added is 8%.

[0030] Example 9 Compared with Example 7, the difference of Example 9 is that the amount of SiO2 added to the refined slag system in the first refining step is 11%, and the amount of CaF2 added is 2%, and the amount of SiO2 added to the refined slag system in the second refining step is 9%, and the amount of CaF2 added is 8%.

[0031] Example 10 Compared with Example 7, the difference of Example 10 is that the amount of SiO2 added to the refined slag system in the first refining step is 12%, and the amount of CaF2 added is 2%, and the amount of SiO2 added to the refined slag system in the second refining step is 8%, and the amount of CaF2 added is 8%.

[0032] Comparative Example 1 Compared with Example 2, the difference of Comparative Example 1 is that the refined slag consists of the following components by weight percentage: Al2O3 15%, SiO2 7%, MgO 2%, CaF2 1%, and the balance is CaO.

[0033] Comparative Example 2 Compared with Example 2, the difference of Comparative Example 2 is that the refined slag consists of the following components by weight percentage: Al2O3 35%, SiO2 13%, MgO 9%, CaF2 9%, and the balance is CaO.

[0034] Using a quartz tube with an inner diameter of 6 mm, the molten steel refined with the addition of refined slag in Examples 1 to 10 and Comparative Examples 1 to 2 was taken as samples, and the test was carried out according to the following method: TO mass fraction: Use a nitrogen and oxygen detector to test the TO mass fraction of the sample. The 14Cr17Ni2 martensitic stainless steel prepared in Examples 1 to 10 and Comparative Examples 1 to 2 was tested according to the following method: 2. Average diameter of inclusions: Observed under 500 times magnification using an Olympus metallographic optical microscope, divided into 16 fields of view and selected 3.4 mm 2 The observation area is determined, and the inclusions in all viewing fields are processed to obtain the average diameter of the inclusions in the sample steel.

[0035] The test results are shown in the following table: Table 1 Performance test results of Examples 1 to 10 and Comparative Examples 1 to 2

[0036] Compared with Comparative Examples 1 and 2, the refined slag of Example 2 consists of the following components in weight percentage: Al2O3 20%~30%, SiO2 9%~11%, MgO 3%~8%, CaF2 3%~8%, and the balance is CaO. As a result, the TO mass fraction and the average diameter of inclusions in Example 2 are smaller than those in Comparative Examples 1 and 2, indicating that when the refined slag consists of the following components in weight percentage: Al2O3 20%~30%, SiO2 9%~11%, MgO 5%, CaF25%, and the balance is CaO, the purity of 14Cr17Ni2 martensitic stainless steel can be improved.

[0037] Compared with Example 2, Examples 4 to 6 added Al2O3 and MgO in different proportions. As a result, the TO mass fraction and the average diameter of inclusions in Examples 2 and 5 were smaller than those in Examples 4 and 6, indicating that when the mass ratio of Al2O3 to MgO was 25:4 to 5, the purity of the obtained 14Cr17Ni2 martensitic stainless steel was higher.

[0038] Compared with Example 2, the refining of Examples 7 to 10 was carried out in two steps. As a result, the TO mass fraction and the average diameter of inclusions in Examples 7 to 10 were smaller than those in Example 2, indicating that when the refining was carried out in two steps, the purity of 14Cr17Ni2 martensitic stainless steel could be further improved.

[0039] In Examples 7 to 10, SiO2 and CaF2 in different mass ratios were added to the refined slag system refined in steps. As a result, the TO mass fraction and the average diameter of inclusions in Examples 8 and 9 were smaller than those in Examples 7 and 10, indicating that when the mass ratio of SiO2 to CaF2 in the refined slag system in the first step of refining was 9 to 11:2 and the mass ratio of SiO2 to CaF2 in the refined slag system in the second step of refining was 9 to 11:8, the purity of the obtained 14Cr17Ni2 martensitic stainless steel was higher.

[0040] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the purity of 14Cr17Ni2 martensitic stainless steel, characterized in that: The following steps are included in sequence: Charging, smelting, deoxidation alloying, refining and casting; the refined slag is a CaO-SiO2-Al2O3-MgO-CaF2 five-element slag system, which is composed of the following components by weight percentage: Al2O3 20%~30%, SiO2 8%~12%, MgO 3%~8%, CaF2 2%~8%, and the balance is CaO.

2. The method for improving the purity of 14Cr17Ni2 martensitic stainless steel according to claim 1, characterized in that: The 14Cr17Ni2 martensitic stainless steel consists of the following components by weight percentage: C 0.15%-0.17%, Si 0.40%-0.50%, Mn 0.70%-0.80%, P < 0.025%, S < 0.004%, Cr 16.05%-16.25%, Ni 2.28%-2.34%, N < 0.06%, and the balance is Fe and inevitable impurities.

3. A method for improving the purity of 14Cr17Ni2 martensitic stainless steel according to claim 1, characterized in that: The mass ratio of the Al2O3 to the MgO is 25:4-5.

4. A method for improving the purity of 14Cr17Ni2 martensitic stainless steel according to claim 1, characterized in that: The refining is carried out in two steps. The mass ratio of SiO2 to CaF2 in the refining slag system of the first refining step is 9-11:2, and the mass ratio of SiO2 to CaF2 in the refining slag system of the second refining step is 9-11:

8.

5. A method for improving the purity of 14Cr17Ni2 martensitic stainless steel according to claim 1, characterized in that: The mass ratio of the refined slag system in the first refining step to the refined slag system in the second refining step is 1:

1. The refined slag in the first refining step is added at the start of refining, and the refined slag in the second refining step is added 20 to 30 minutes after the start of refining.

6. A method for improving the purity of 14Cr17Ni2 martensitic stainless steel according to claim 5, characterized in that: The total mass of the refined slag is 3% to 5% of the mass of the 14Cr17Ni2 martensitic stainless steel.

7. A method for improving the purity of 14Cr17Ni2 martensitic stainless steel according to claim 5, characterized in that: The refining time is 55 to 65 minutes.

8. The method for improving the purity of 14Cr17Ni2 martensitic stainless steel according to claim 1, characterized in that: The smelting comprises the following steps: after heating, argon and oxygen are introduced in sequence to carry out smelting.

9. A method for improving the purity of 14Cr17Ni2 martensitic stainless steel according to claim 8, characterized in that: The temperature of the argon gas when introduced is 1300° C., the flow rate is 3-5 NL / min, the temperature of the oxygen gas when introduced is 1600° C., the time is 10 s, and the flow rate is 2 NL / min.

10. The method for improving the purity of 14Cr17Ni2 martensitic stainless steel according to claim 1, characterized in that: The deoxidation alloying comprises the following steps: adding pure Al for deoxidation after the smelting is completed, and then adding C, Mn and Si of the target component batches for alloying.

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