A method for direct reduction and alloying of molybdenum ore in molybdenum-containing steel production

Abstract

The application discloses a method for directly reducing and alloying molybdenum ore in molybdenum-containing steel production and belongs to the technical field of steel smelting. In the method, the molybdenum ore, lime and reducing agent are arranged in layers in a ladle, and the molybdenum element is reduced from the molybdenum ore and enters molten steel in a smelting process by using good kinetic conditions and high-temperature action of the molten steel in a converter tapping process, so that the purpose of molybdenum alloying of the molten steel is achieved, the cost of molybdenum alloying of the molten steel is reduced, and environmental pollution is reduced. Through the above molybdenum alloying operation of the molten steel, molten steel of molybdenum-containing stainless steel or molybdenum-containing plain carbon steel with required molybdenum content can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, and specifically relates to a method for direct reduction alloying of molybdenum ore in the production of molybdenum-containing steel. Background Technology

[0002] Molybdenum is one of the alloying elements that effectively improves the strength, toughness, hardenability, and corrosion resistance of steel. In steel production, especially stainless steel production, molybdenum-containing steels constitute a certain proportion of austenitic and duplex stainless steels, and the molybdenum content is usually relatively high. In the smelting and production of these steels, a significant amount of ferromolybdenum alloy needs to be added for molybdenum alloying. Current technology generally involves adding ferromolybdenum during AOD converter smelting. However, due to the high price of ferromolybdenum, the cost of molybdenum alloying is high. Similarly, in carbon-molybdenum steels containing molybdenum, the molybdenum content is also relatively high, resulting in high molybdenum alloying costs.

[0003] Molybdenum, with an average abundance of only 0.00011% in nature, is a rare metal. Although China is a major molybdenum resource country, its molybdenum ore grades are low, with the national average grade generally below 0.12%, and about 65% of the reserves even below 0.10%. Therefore, the cost and difficulty of smelting ferromolybdenum are high, resulting in a relatively expensive price. Currently, the domestic market price for Fe-Mo60 is approximately 300,000 yuan / ton, and for Fe-Mo65, it is approximately 400,000 yuan / ton. Moreover, with changes in the domestic and international situation and fluctuations in the raw material market, the price of ferromolybdenum is generally continuing to rise.

[0004] Furthermore, ferromolybdenum smelting is a highly polluting and energy-intensive process. Ferromolybdenum smelting primarily uses the Si-Al thermal reduction method, also known as the ladle smelting process. Based on the principle of redox reactions, reducing agents Si-Fe and Al powder are used to reduce roasted molybdenum concentrate (MoO3, MoO2) to Mo and Fe metals, forming a ferromolybdenum alloy, which is then used in steel production. Currently, ferromolybdenum smelting still relies on equipment and processes from the 1970s and 80s. Many small and medium-sized enterprises still operate with extensive production methods, resulting in outdated technology, low production capacity, low automation, high labor intensity, and severe pollution. The production process from mined molybdenum ore to the molybdenum concentrate used in ferromolybdenum smelting is also a highly energy-intensive, highly polluting, and high-cost process, mainly involving physical and physicochemical processes of "weight reduction" and "purification." Due to the extremely low grade of the raw ore (usually below 0.1%), the core objective of this process is to discard over 99% of the waste rock (gangue) and enrich molybdenite (MoS2). This complex process yields molybdenum concentrate containing 45% to 57% or even higher molybdenum content. The molybdenum concentrate typically needs to be roasted to become industrial molybdenum oxide before it can be used to smelt ferromolybdenum. Therefore, the process before smelting ferromolybdenum—from raw molybdenum ore to molybdenum concentrate and then to molybdenum oxide—is also a highly energy-intensive, highly polluting, and costly process.

[0005] Currently, in the smelting and production of molybdenum-containing steels, especially molybdenum-containing stainless steels, molybdenum alloying is typically achieved by adding ferromolybdenum alloys. However, higher molybdenum content requires the addition of larger amounts of ferromolybdenum alloys, resulting in higher production costs. This also indirectly brings the high energy consumption and high pollution associated with ferromolybdenum smelting into the production of molybdenum-containing steels. Therefore, researching and developing a method to directly add molybdenum ore into the molten steel smelting process, utilizing the reducing atmosphere of the smelting process or adding a reducing agent to directly reduce the molybdenum ore and alloy the molten steel with molybdenum, can significantly reduce the production costs of molybdenum-containing steels, lower energy consumption, and reduce environmental pollution. This method is of great significance for the production of molybdenum-containing steels, especially high-molybdenum-content stainless steels or plain carbon steels. Summary of the Invention

[0006] To address the problems of high consumption, high energy consumption, and high pollution associated with existing technologies for smelting molybdenum-containing steel, the present invention aims to provide a method for the direct reduction alloying of molybdenum ore in the production of molybdenum-containing steel. This method enables the direct reduction alloying of molybdenum ore during the production process of molybdenum-containing steel, reduces the cost of the alloying process in the traditional smelting of molybdenum-containing steel, especially molybdenum-containing stainless steel, and solves the problems of high pollution and high energy consumption in the production of ferromolybdenum alloys.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a method for direct reduction alloying of molybdenum ore in the production of molybdenum-containing steel, comprising the following steps: molybdenum oxide ore, lime, and reducing agent are arranged in layers in a ladle, with the bottom layer being molybdenum oxide ore, the middle layer being lime, and the top layer being reducing agent; the materials are repeatedly arranged in the ladle in the same manner according to the amount of raw materials used for the steel grade being produced; a steel plate is placed on the top layer of reducing agent; the ladle is suspended at the tapping position of the converter; after tapping, argon gas is blown from the bottom of the ladle for strong stirring; the top slag of the ladle is skimmed off; and after skimming, slag is re-formed as needed.

[0009] Layering the raw materials ensures a more uniform distribution and more complete reaction between them. Placing molybdenum oxide ore at the bottom layer prevents it from being the first material to come into contact with the molten steel upon entering the ladle, thus avoiding rapid volatilization and loss of the ore due to the high temperature of the steel. More importantly, it prevents safety accidents such as explosions caused by the volatilization of molybdenum oxide ore. Lime is placed in the middle layer to facilitate easier contact and faster reaction with the molybdenum oxide ore, thus quickly inhibiting its volatilization. The reducing agent is placed in the top layer so that the molten steel comes into contact with it first, which is more conducive to the melting of the reducing agent.

[0010] Based on the above technical solution, further, the thickness of the bottom layer of oxidized molybdenum ore is ≤200 mm, the thickness of the middle layer of lime is ≤300 mm, and the thickness of the upper layer of reducing agent is ≤300 mm.

[0011] The purpose of this design is to prevent excessive thickness of each material layer from affecting the chemical reaction between the layers. The thickness requirement of the bottom molybdenum oxide ore layer is to prevent excessive volatilization of molybdenum oxide ore from causing safety accidents.

[0012] Based on the above technical solution, the total amount of molybdenum oxide ore in the molybdenum oxide layer is 1 to 15 tons, of which the molybdenum content is not less than 50%, the form is blocky, and the particle size is: the diameter of the equal-area circle r1 = 10 to 60 mm.

[0013] The purpose of specifying the molybdenum content in molybdenum ore is that too little molybdenum will lead to an increase in the amount of molybdenum ore added to the ladle, which in turn will increase the amount of slag in the ladle, which is detrimental to subsequent production operations, increases the amount of reducing agent used, and increases production costs. The purpose of specifying the morphology and particle size of the oxidized molybdenum ore is that if the molybdenum ore is too fine, it will be more prone to volatilization when exposed to high-temperature molten steel, while if the molybdenum ore is too coarse, it will be detrimental to the reduction reaction.

[0014] Based on the above technical solution, the lime is further described as active lime, in block form, with a particle size of equal volume circle diameter r2 = 5~40 mm and an activity of 350~420 ml.

[0015] The purpose of the lime requirement is to enable the lime to react quickly with molybdenum oxide in the molybdenum ore, and CaO to react with MoO3 to form the stable compound CaMoO4, thus preventing the molybdenum oxide from volatilizing when exposed to high-temperature molten steel.

[0016] Based on the above technical solution, the reducing agent is further selected from coke or ferrosilicon, and is in block form with a particle size of equal volume circle diameter r3 = 10~50 mm.

[0017] The requirements for reducing agents are that they can melt rapidly, are inexpensive, and have good reducing properties. Different reducing agents are selected depending on the type of steel being smelted. Ferrosilicon is chosen as the reducing agent when smelting low-carbon or ultra-low-carbon steels; coke is chosen when smelting carbon-molybdenum steels.

[0018] Based on the above technical solution, the steel plate material is the same as the steel grade produced, and the steel plate thickness d is 5~20mm.

[0019] To prevent the initial flow of molten steel during the converter tapping process from directly impacting the molybdenum oxide ore, lime, and reducing agent arranged in the ladle, thus damaging the charging layer and preventing the molten steel from directly impacting the molybdenum oxide ore and causing its volatilization, a steel plate is placed on top of the charging layer. This ensures that the molten steel initially distributes evenly on the top steel plate of the charging layer in the ladle. After the steel plate melts, it then "slowly" comes into contact with the reducing agent, lime, and molybdenum oxide ore in sequence.

[0020] Based on the above technical solution, the argon flow rate is further specified as 300~500 NL / min.

[0021] Based on the above technical solution, the stirring time t is further 5~20 min.

[0022] After tapping, the molten steel needs to be strongly stirred with a large volume of argon gas to ensure sufficient contact between the molten steel and the raw materials such as molybdenum oxide ore added to the ladle, accelerating the reaction and maintaining a certain reaction time. After the molybdenum ore in the ladle has fully reacted with the reducing agent, the amount of top slag in the ladle increases rapidly, which is detrimental to subsequent refining processes. Therefore, after the bottom blowing argon stirring in the ladle is completed, the top slag needs to be skimmed off, and then new slag is created as needed.

[0023] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for the direct reduction and alloying of molybdenum ore in the production of molybdenum-containing steel. This method enables the direct reduction of molybdenum oxide ore to metallic molybdenum during the smelting process of molybdenum-containing steel, significantly reducing the amount of ferromolybdenum alloy used. This method solves the problem of the easy volatilization of molybdenum oxide ore upon contact with high-temperature molten steel, achieving direct alloying of molybdenum ore to molten steel. It can greatly reduce the cost of molybdenum alloying in the production of molybdenum-containing steel and significantly reduce the environmental pollution caused by smelting ferromolybdenum alloys. The method is simple to operate, low in cost, and conducive to widespread application. Attached Figure Description

[0024] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0025] Figure 1 This is a schematic diagram of the layered arrangement of molybdenum oxide ore, lime, and reducing agent in a single ladle according to an embodiment of the present invention.

[0026] Figure 2 This is a schematic diagram showing the layered arrangement of molybdenum oxide ore, lime, and reducing agent in two separate steel ladles in an embodiment of the present invention. Detailed Implementation

[0027] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0028] Example 1 The steel grade produced is 2205 duplex stainless steel. The steel ladle holds 180 tons of steel. The chemical composition of the 2205 duplex stainless steel is as follows:

[0029] In the continuous casting production of molybdenum-containing steel slabs mentioned above, the direct reduction alloying of molybdenum ore includes the following steps: Molybdenum oxide ore, lime, and reducing agent are first added to the ladle. After stainless steel is smelted in the AOD converter, the ladle is hoisted to the tapping position of the converter. During the tapping process in the AOD converter, the good kinetic conditions and heat of the molten steel are used to melt the molybdenum oxide ore, lime, and reducing agent in the ladle and reduce the molybdenum oxide ore to obtain metallic molybdenum, thus realizing the direct reduction and alloying of molybdenum ore with molten stainless steel.

[0030] 1. Layer molybdenum oxide ore, lime, and reducing agent in a ladle. The bottom layer is molybdenum oxide ore with a thickness of 150 mm; the middle layer is lime with a thickness of 200 mm; and the top layer is reducing agent with a thickness of 200 mm. Repeat this layering process once.

[0031] The total amount of molybdenum oxide ore used was 13.5 tons, with a molybdenum content of 54.3%. It was in the form of lumps with a particle size of equal-area circle diameter r1 = 40 mm. The lime used was active lime, in the form of lumps with a particle size of equal-area circle diameter r2 = 10 mm and an activity of 360 ml. The reducing agent used was ferrosilicon, in the form of lumps with a particle size of equal-area circle diameter r3 = 50 mm.

[0032] 2. After all the molybdenum oxide ore, lime and reducing agent have been layered and distributed, a steel plate is placed on top of the top layer of reducing agent. The steel plate is made of 2205 stainless steel and has a thickness d of 10 mm.

[0033] 3. Place the ladle at the tapping position of the AOD converter. After tapping from the AOD converter, use bottom-blown argon gas for strong stirring at a flow rate of 400 NL / min for a stirring time of 10 min. After bottom-blown argon stirring, remove the top slag from the ladle. After removing the slag, re-form slag as needed.

[0034] 4. Before entering the later refining stage, the molten steel was sampled and analyzed. The molybdenum content in the molten steel was 3.05%, and the molybdenum recovery rate in the direct reduction alloying of molybdenum ore was calculated to be 74.9%. According to the molybdenum content requirements of the steel grade, the composition of the molten steel was finely adjusted in the subsequent refining process using ferromolybdenum alloy Fe-Mo60. 220 kg of Fe-Mo60 alloy was added, and finally, qualified molten steel with a molybdenum content of 3.12% was obtained.

[0035] Example 2 The steel grade produced is 316 austenitic stainless steel. The steel ladle holds 180 tons of steel. The chemical composition of 316 austenitic stainless steel is as follows:

[0036] In the continuous casting production of molybdenum-containing steel slabs mentioned above, the direct reduction alloying of molybdenum ore includes the following steps: Molybdenum oxide ore, lime, and reducing agent are added to the ladle beforehand. After stainless steel is smelted in the AOD converter, the ladle is hoisted to the tapping position of the converter. During the tapping process in the AOD converter, the good kinetic conditions and heat of the molten steel are used to melt the molybdenum oxide ore, lime, and reducing agent in the ladle and reduce the molybdenum oxide ore to obtain metallic molybdenum, thus realizing the direct reduction alloying of molybdenum ore with molten stainless steel.

[0037] 1. Layer molybdenum oxide ore, lime, and reducing agent in a ladle. The bottom layer is molybdenum oxide ore with a thickness of 200 mm; the middle layer is lime with a thickness of 300 mm; and the top layer is reducing agent with a thickness of 300 mm. Repeat this layering process twice.

[0038] The total amount of molybdenum oxide ore used was 10.8 tons, of which the molybdenum content was 50.8%. The molybdenum ore was in the form of lumps with a particle size of equal-area circle diameter r1 = 20 mm. The lime used was active lime, in the form of lumps with a particle size of equal-area circle diameter r2 = 20 mm and an activity of 390 ml. The reducing agent used was ferrosilicon, in the form of lumps with a particle size of equal-area circle diameter r3 = 30 mm.

[0039] 2. After all the molybdenum oxide ore, lime and reducing agent are layered and laid, a steel plate is placed on top of the reducing agent layer. The steel plate is made of 316 stainless steel and has a thickness d of 18 mm.

[0040] 3. Place the ladle at the tapping position of the AOD converter. After tapping from the AOD converter, use bottom-blown argon gas for strong stirring at a flow rate of 300 NL / min for a stirring time of 20 min. After bottom-blown argon stirring, remove the top slag from the ladle. After removing the slag, re-form slag as needed.

[0041] 4. Before entering the later refining stage, the molten steel was sampled and analyzed. The molybdenum content in the molten steel was 2.49%, and the molybdenum recovery rate in the direct reduction alloying of molybdenum ore was calculated to be 81.7%. According to the molybdenum content requirements of the steel grade, the composition of the molten steel was finely adjusted in the subsequent refining process using ferromolybdenum alloy Fe-Mo60. 290 kg of Fe-Mo60 alloy was added, and finally, qualified molten steel with a molybdenum content of 2.58% was obtained.

[0042] Example 3 The steel grade produced is 4023 carbon molybdenum steel. The steel ladle holds 200 tons of steel. The chemical composition of the 4023 carbon molybdenum steel is as follows:

[0043] In the continuous casting production of molybdenum-containing steel slabs mentioned above, the direct reduction alloying of molybdenum ore includes the following steps: Molybdenum oxide ore, lime, and reducing agent are first added to the ladle. After the carbon-molybdenum steel is smelted in the converter, the ladle is hoisted to the tapping position of the converter. During the tapping process, the good kinetic conditions and heat of the molten steel are used to melt the molybdenum oxide ore, lime, and reducing agent in the ladle and reduce the molybdenum oxide ore to obtain metallic molybdenum, thus realizing the direct reduction and alloying of molybdenum ore with molten steel.

[0044] 1. Layer molybdenum oxide ore, lime, and reducing agent in a ladle. The bottom layer is molybdenum oxide ore with a thickness of 120 mm; the middle layer is lime with a thickness of 150 mm; and the top layer is reducing agent with a thickness of 180 mm. Repeat this layering process once.

[0045] The total amount of molybdenum oxide ore used was 1.37 tons, of which the molybdenum content was 51.5%. The molybdenum ore was in the form of lumps with a particle size of equal-area circle diameter r1 = 60 mm. The lime used was active lime, in the form of lumps with a particle size of equal-area circle diameter r2 = 40 mm and an activity of 420 ml. The reducing agent used was coke, in the form of lumps with a particle size of equal-area circle diameter r3 = 10 mm.

[0046] 2. After all the molybdenum oxide ore, lime and reducing agent are layered and laid, a steel plate is placed on top of the reducing agent layer. The steel plate is made of 4023 carbon molybdenum steel plate and the thickness d is 15 mm.

[0047] 3. The ladle is hoisted to the tapping position of the converter. After the converter tapping is completed, the ladle needs to be strongly stirred by bottom blowing argon gas. The argon gas flow rate is 450 NL / min and the stirring time t is 15 min. After the bottom blowing argon gas stirring of the ladle is completed, the top slag of the ladle is removed. After the slag removal is completed, slag is re-formed as needed.

[0048] 4. Before entering the later refining stage, the molten steel was sampled and analyzed. The molybdenum content in the molten steel was 0.25%, and the molybdenum recovery rate in the direct reduction alloying of molybdenum ore was calculated to be 70.9%. According to the molybdenum content requirements of the steel grade, the composition of the molten steel was finely adjusted in the subsequent refining process using ferromolybdenum alloy Fe-Mo60. 70 kg of Fe-Mo60 alloy was added, and finally, qualified molten steel with a molybdenum content of 0.27% was obtained.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for direct reduction alloying of molybdenum ore in the production of molybdenum-containing steel, characterized in that, Includes the following steps: Molybdenum oxide ore, lime, and reducing agent are layered in the ladle. The bottom layer is molybdenum oxide ore, the middle layer is lime, and the top layer is reducing agent. The same method of material distribution is repeated in the ladle according to the amount of raw materials used for the steel grade. A steel plate is placed on top of the reducing agent layer, and the ladle is hoisted to the tapping position of the converter. After tapping, argon gas is blown from the bottom of the ladle for strong stirring, and the top slag of the ladle is removed. After the slag removal is completed, slag is re-formed as needed.

2. The method according to claim 1, characterized in that, The thickness of the bottom layer of oxidized molybdenum ore is ≤200 mm, the thickness of the middle layer of lime is ≤300 mm, and the thickness of the top layer of reducing agent is ≤300 mm.

3. The method according to claim 1, characterized in that, The total amount of molybdenum oxide ore in the molybdenum oxide layer is 1 to 15 tons, of which the molybdenum content is not less than 50%, and the morphology is blocky with a particle size of equal-area circle diameter r1 = 10 to 60 mm.

4. The method according to claim 1, characterized in that, The lime is active lime, in the form of lumps, with a particle size of equal volume circle diameter r2 = 5~40 mm and an activity of 350~420 ml.

5. The method according to claim 1, characterized in that, The reducing agent is selected from coke or ferrosilicon, and is in block form with a particle size of equal-area circle diameter r3 = 10~50 mm.

6. The method according to claim 1, characterized in that, The steel plate is made of the same material as the steel grade produced, and the thickness d of the steel plate is 5~20 mm.

7. The method according to claim 1, characterized in that, The argon flow rate is 300~500 NL / min.

8. The method according to claim 1, characterized in that, The stirring time t is 5~20 min.

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