CN1302914A - Technology for smelting Mo-contained alloy steel with molybdenum oxide - Google Patents

Abstract

The invention belongs to the field of metallurgical steelmaking methods. It is especially suitable for the method of directly alloying molybdenum oxide to smelt molybdenum-containing alloy steel. In the method, molybdenum oxide and reducing agent are crushed and mixed, and then added in proportion to an electric arc furnace with a furnace temperature greater than 600°C, and scrap steel raw materials are added to smelt molybdenum-containing alloy steel. Compared with the prior art, the method has the characteristics of short smelting time, high molybdenum yield, safe and economical operation, and the like.

Description

Method for Smelting Molybdenum-Containing Alloy Steel Using Molybdenum Oxide

The invention belongs to the field of metallurgical steelmaking methods. It is especially suitable for the method of directly alloying molybdenum oxide to smelt molybdenum-containing alloy steel.

Using molybdenum oxide instead of ferromolybdenum to smelt molybdenum-containing alloy steel can reduce smelting costs and has achieved certain results. However, in the current use process, it is felt that in the production process of using molybdenum oxide instead of ferromolybdenum to smelt molybdenum-containing alloy steel, the reduction reaction speed of molybdenum oxide is relatively slow, and there is still a certain amount of molybdenum that has not been reduced when the scrap steel is melted, which increases the smelting time. . Another disadvantage is that during smelting, due to the intense reaction of carbon and oxygen, it is easy to cause large boiling phenomenon in the slag. If ferrosilicon is used as the reducing agent, when the amount of molybdenum oxide added is large, the amount of slag will increase a lot during the smelting process, which will affect the operation. Therefore, it has been obtained through practice that using the existing technology to directly alloy smelt molybdenum-containing alloy steel with molybdenum oxide, generally only low-molybdenum steel can be smelted. The recovery rate is only about 90%.

The object of the present invention is to propose a method for smelting molybdenum alloy steel with molybdenum oxide with fast reduction, high yield, low cost and good comprehensive performance.

According to the purpose of the present invention, the method for smelting molybdenum-containing alloy steel by direct alloying of molybdenum oxide proposed by us is characterized in that molybdenum oxide and reducing agent are all broken into particles with a particle size of ≤5mm before mixing and charging. The mixed material is mixed evenly with the reducing agent and molybdenum oxide in a weight ratio of 0.15-0.40:1, and then the prepared mixed material and scrap steel raw materials are put into an electric arc furnace with a furnace temperature ≥ 600°C for smelting. Other features in the smelting method of the present invention are that the above-mentioned reducing agent refers to any one or the sum of both of carbon and silicon carbide. Furnace loading is to fill the mixture of molybdenum oxide and reducing agent in the bottom of the electric arc furnace and then load the scrap steel raw material.

The working principle of the smelting method of the present invention is related to the temperature in the furnace when the raw materials are loaded into the furnace, the proportioning and particle size of the mixture and the chemical reaction between them. In the method of the present invention, the main component of molybdenum oxide is MoO ₃ . During the smelting process, molybdenum oxide can chemically react with carbon, silicon carbide and other substances to generate molybdenum and then enter molten steel. The reactions include:

    

    

According to thermodynamic calculations, it is possible for carbon, silicon carbide, etc. to react chemically with _MoO3 above 500 °C. But chemical reactions are not only determined by thermodynamics, but more importantly, by reaction kinetics. The reduction rate of _MoO3 is firstly related to the type of reducing agent, and secondly depends on the reaction area. The larger the reaction area, the faster the reaction rate. The reduction process of molybdenum oxide can be divided into the reduction reaction between solid MoO ₃ and solid reducing agent at low temperature, and the reduction between MoO ₃ in slag and molten steel at high temperature. When the blockiness of molybdenum oxide is large, the chemical reaction at low temperature cannot be reflected because the contact area is too small, so the reaction will be dominated by high temperature reduction, that is, the reaction proceeds late. If the particle size of molybdenum oxide is small, mixing it with a reducing agent will greatly increase the reaction area, so that _MoO3 can react at a lower temperature, and the reduction reaction can be completed in the early stage of smelting. The reduction of molybdenum oxide at the early stage of smelting can reduce the boiling intensity of slag, shorten the smelting time and increase the yield of molybdenum compared with the reduction at the later stage of smelting.

By adopting the smelting method of the invention, the molybdenum oxide can be rapidly reduced in the early stage of electric arc furnace smelting, and the reduction process of the molybdenum oxide can be completed before the scrap steel is melted. It has been proved by experiments that when the temperature is higher than 600°C, molybdenum oxide can undergo a reduction reaction with the reducing agent, and when the temperature rises to 1400°C, the reduction process of molybdenum oxide can be completed, and the reduction time is about 17 minutes. The test results are shown in the accompanying drawing, which is a diagram showing the relationship between the reduction rate of molybdenum oxide and time and temperature. In the accompanying drawings, 1 is the temperature curve, and 2 is the reduction rate curve.

Compared with the prior art, the method for directly alloying and smelting molybdenum-containing alloy steel by using the molybdenum oxide mixture of the present invention has the following characteristics:

(1) The low-temperature rapid reduction technology accelerates the reduction process of molybdenum oxide, does not increase the smelting time, and can adapt to the ultra-high-power electric arc furnace steelmaking process.

(2) Since a large amount of gas produced by the reduction reaction can be released in the early stage of smelting, the possibility of large boiling phenomenon during the smelting process is greatly reduced, thereby improving the safety of the smelting process.

(3) This process uses carbon powder or silicon carbide as a reducing agent, so the amount of slag in the smelting process is less, and the labor intensity of workers in the smelting process is reduced.

(4) Use the residual heat of the previous electric furnace and the heat loss in the early stage of the electric arc furnace as the energy source for the molybdenum oxide reduction process, so the power consumption in the smelting process does not increase significantly.

(5) The present invention is not only applicable to high-molybdenum alloy steel (such as high-speed steel), but also applicable to smelting low-molybdenum alloy steel.

Example 1

The comparative experiment of different technology, comparative experiment is to adopt carbon powder to reduce molybdenum oxide experiment carried out in carbon tube furnace, set molybdenum content in the steel as 5%, scheme 1 is to adopt low-temperature fast reduction technology smelting of the present invention (carbon powder Mix with molybdenum oxide and add). Scheme 2 is to adopt the smelting method of the prior art instead of the low-temperature reduction technology (add molybdenum oxide and carbon powder separately). The experiment is the measured molybdenum oxide reduction rate under the same conditions, and draws by experiment, adopt scheme 1 low-temperature reduction technology of the present invention in carbon tube furnace, although change the molybdenum oxide add-on of setting to use respectively the molybdenum content in the steel is 2% and 5%, but the yield of each molybdenum is more than 98%, and there is no boiling phenomenon in the smelting process. And the method of the present invention is also applicable to the experiment of silicon carbide as reducing agent, and its result is the same. Compared with Experimental Scheme 2, when the low-temperature rapid reduction technology is not used in the smelting process, a large boiling phenomenon occurs, the density of the foamy slag is 0.157g/cm ³ , and the yield of molybdenum oxide is also low.

Example 2

The industrial experiment of using molybdenum oxide to smelt high-speed steel was carried out on an electric arc furnace (transformer rated power 5,500kV.A) with a charging capacity of 20 tons, using the method of the present invention (Scheme 1) and not using the low-temperature rapid reduction technology (Scheme 2) Two schemes of smelting W6Mo5Cr4V high-speed steel experiments. And a comparative experiment of smelting W6Mo5Cr4V steel with ferromolybdenum was carried out (Scheme 3). A total of 4 heat tests were carried out for scheme 1, 1 heat test was carried out for scheme 2, and the smelting of high-speed steel with ferromolybdenum for scheme 3 belongs to the traditional process test. In scheme 1, the molybdenum oxide block and carbon are crushed into molybdenum oxide fine particles with a particle size of less than 5mm, and the weight ratio of molybdenum oxide to molybdenum oxide is shown in the table. Scheme 2 uses molybdenum oxide blocks (the block size is greater than 100mm). The weight ratio of carbon powder to molybdenum oxide is also shown in the table. Both scheme 1 and scheme 2 are added to the bottom of the electric arc furnace after the tapping of the previous furnace is completed and the furnace is repaired. The furnace chamber temperature is between 630°C and 870°C. In Scheme 1, molybdenum oxide and reducing agent are mixed and added to the bottom of the furnace, while in Scheme 2, molybdenum oxide is added to the bottom of the furnace, and carbon powder is placed on top of it. Experimental result is as shown in the table, and this table is to adopt the comparative table of the inventive method and prior art method embodiment, and the test furnace number 1,2,3,4 listed in this table is the implementation of scheme 1 inventive method For example, test furnace No. 5 is an embodiment of the prior art of scheme 2, and test furnace No. 6 is an embodiment of the prior art of scheme 3. The reducing agents listed in the table are all carbon powder except that test furnace No. 2 is silicon carbide, and test furnace No. 4 is 50% silicon carbide+carbon powder. The latter indicators in the table are based on Scheme 3. It can be seen from the table that good smelting effect can be obtained by adopting the method of the present invention, not only the yield of molybdenum is high, but also the fluctuation is minimum and the operation is stable. Scheme 2 not only has the lowest yield rate of molybdenum, but also has the largest fluctuation in yield rate, unstable operation, and prone to large slag boiling. In addition, option 1 can also achieve considerable economic benefits: for example, the price of ferromolybdenum (containing 56% molybdenum) is 41,000 yuan/ton, and molybdenum oxide (containing 52% molybdenum) is calculated at 28,600 yuan/ton, considering power consumption and reducing agent cost, plan 1 smelts 1 ton of W6Mo5Cr4V high-speed steel, which can reduce the cost by about 1,000 yuan/ton compared with plan 3.

Table 1 Industrial experiment results of smelting W6Mo5cr4V high speed steel Iron smelting plan Test furnace number Molybdenum oxide average particle size (mm) Weight ratio of reducing agent to molybdenum oxide Electric arc furnace furnace temperature before charging (℃) Molybdenum yield (%) melting period phenomenon Power consumption per ton of steel (kW.h) Smelting time (min) Production cost per furnace (yuan) plan 1 1 0.5mm 0.20:1 630°C 93.7% normal 553kW.h 228min 188,720 yuan 2 1.5mm 0.25:1 720°C 96.6% normal 550kW.h 226min 187,420 yuan 3 2.5mm 0.30:1 830°C 99.3% normal 543kW.h 223min 186,520 yuan 4 4.0mm 0.35:1 870°C 98.7% normal 548kW.h 224min 186,720 yuan average 2.1mm 0.275:1 763°C 97.1% normal 549kW.h 225min 187,345 yuan Scenario 2 5 >100mm 0.30:1 830°C 90.0% The flame is strong, and there is a large boiling phenomenon 570kW.h 235min 192,500 yuan Option 3 6 - - 850°C 95.0% normal 535kW.h 220min 206,220 yuan

Claims (4)

1. A method for smelting molybdenum-containing alloy steel by direct alloying of molybdenum oxide, which is characterized in that molybdenum oxide and reducing agent are crushed into particles with a particle size of ≤5mm, and then mixed and charged. The mixed material is the reduced Molybdenum oxide and molybdenum oxide are mixed according to the ratio of 0.15-0.40:1 by weight, and then the prepared mixture and scrap steel raw materials are put into an electric arc furnace whose temperature in the furnace should be ≥600°C for smelting. 2. The method according to claim 1, wherein the reducing agent is any one of carbon and silicon carbide. 3. The method according to claim 1, characterized in that the reducing agent is the sum of carbon and silicon carbide. 4. The method according to claim 1, characterized in that the charging of the furnace is to fill the mixture of molybdenum oxide and reducing agent in the bottom of the electric arc furnace and then load the scrap steel raw material.

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