Molybdenum oxide utilizes the latest technology

The molybdenum oxide is used as 35CrMoA, R102 like molybdenum-containing low alloy steel smelting has been successful, and has achieved significant economic benefits.

In order to further explore the application possibilities of molybdenum oxide in high alloy steel smelting, we have carried out experimental research work on molybdenum oxide for low carbon and ultra low carbon stainless steel smelting.

1. Physicochemical properties of molybdenum oxide

The molybdenum oxide we use has two grades: YMo50 and YMo54. The molybdenum oxide content of these two grades is 50% and 54%, respectively, and the weight of each of the blocks is between 1.0 and 5.0 kg, the specific gravity is not less than 2.5 g/cm ² , and the moisture is not more than 0.5%.

Second, thermodynamic analysis of molybdenum oxide

On electric - double ladle furnace process, the smelting of stainless steel material is usually returned charge composed steels, high carbon ferrochrome, low phosphorus and returns the desired alloy steel materials. Therefore, there is a certain amount of carbon, silicon, iron, chromium and manganese in the charge. For example, for the 00Cr17Ni14Mo2 steel grade. The melting composition requirements are shown in Table 1.

Table 1 00Cr17Ni14Mo2 copper part element melting content requirements

The main component of molybdenum oxide is molybdenum dioxide. The reaction and its standard when molybdenum dioxide is contacted with [Si], [Mn], Fe(1), [C], [Cr].

Free energy changes to:

_{[Si] + MoO 2 (s} ) = [Mo] + SiO 2 (1) .................................... â‘ 

â–³G ₁ ⁰ =-39814-1.02T

2[Mn]+MoO _2(s) =2(MnO)+[Mo]....................................2

â–³G ₂ ⁰ =-35814-4.06T

_{3Fe (1) + MoO 2 (} s) = [Mo] + 2FeO (1) .............................. â‘¢

â–³G ₃ ⁰ =23186-22.88T

2[C]+MoO _(s) =[Mo]+2CO................................................4

â–³G ₄ ⁰ =70386-66.24T

_{4/3 [Cr] + MoO 2 (} s) = [Mo] +2/3 (Cr 2 O 3) .............................. ⑤

â–³G ₅ ⁰ =79508-103.88T

The ΔG° of the above five reactions at 1400 ° C, 1500 ° C, 1600 ° C, 1700 ° C, and 1800 ° C were respectively calculated, and the results are shown in Table 2. As can be seen from Table 2, [Si], [Mn], Fe(1), [C], and [Cr] all reduce molybdenum oxide at the steelmaking temperature. As the temperature increases, the possibility of reaction of these five elements with molybdenum oxide is gradually increased by the following procedure: [Mn], Fe(1), [Si], [C], [Cr].

Table 2 △G° values ​​of five reactions at different temperatures

The test was carried out on a 30 t electric furnace and a 40 t ladle furnace.

Third, the test steel grade and test process

(1) The test steel grades include: 0Cr18Mo2, 0Cr18Mo2Ca, 00Cr17Ni14Mo2, 00Cr17Ni14Mo2 tubes. The finished Mo specifications for these four steel grades are shown in Table 3.

Table 3 Finished molybdenum specifications for four steel grades

(2) Test process

For the four steel grades, the original double process of electric furnace initial refining and ladle furnace refining is adopted. Moreover, according to the previous experimental experience, no amount of reducing agent is added during the reduction period of the electric furnace.

1. Method for adding molybdenum oxide Molybdenum oxide is charged into the hopper along with the charge. According to the molybdenum content of the charge, the total amount of molybdenum is about the middle limit of the specification of the finished steel product.

2, electric furnace initial refining process points During the melting period, do not blow oxygen to help dissolve or cut the material for a long time. Add 400 kg of lime in the late stage of melting. After the charge was completely dissolved, the electromagnetic stirring was turned on for 10 min, and then sampled and analyzed. The temperature is above 1600 ° C, and the double tube is oxygen decarburized. When the carbon is between 0.30% and 0.40%, the calcium carbide is added at a concentration of 3 to 4 kg/t, and an appropriate amount of C powder and Si-Fe powder are used for reduction. After the reduction slag was turned, the sample was analyzed twice. According to the analysis results, Mo and related elements were adjusted with Mo-Fe and related alloys. After the composition, temperature and slag conditions meet the requirements, the steel is tapped.

3. The main points of the refining process of the ladle furnace After the slag is removed from the ladle, 200 kg of lime is added, and the temperature is sampled and measured. When the molten steel temperature is above 1560 ° C, oxygen is refined in the vacuum position. When the oxygen concentration potential and the exhaust gas temperature drop, the oxygen consumption is determined by reference to the total oxygen consumption, and is maintained at 67 Pa for 5 min or more. Then, an alloy and a deoxidizer and an appropriate amount of lime are added. After the steel slag is well stirred, the vacuum is broken. Sampling and analysis package seat bit temperature, and add the right amount of powder or silicon aluminum - iron slag having good reducibility. Fine-tuning the ingredients according to the steel grade and analysis results. After the temperature meets the requirements, the bag is poured.

Fourth, test results and discussion

(1) Test results

The results of the test 8 furnace steels are shown in Table 4.

Table 4 Test results of eight furnace steel

(2) Discussion of test results

1. Molybdenum recovery rate of molybdenum oxide As can be seen from Table 4, the molybdenum recovery rate of molybdenum oxide charged into the hopper with the charge is between 80.8% and 100%, with an average of 92.3%. Slightly higher than the molybdenum recovery rate using ferromolybdenum. Table 5 is the statistics of molybdenum recovery rates of the same process, the same type of steel, and molybdenum-iron combined with molybdenum. As can be seen from Table 5, the recovery of molybdenum is between 80.16% and 100%, with an average of 91.32%.

Table 5 Molybdenum recovery rate using ferromolybdenum (10 furnaces)

It can also be seen from Table 4 that the molybdenum molybdenum molybdenum recovery rate of the furnace without adding ferromolybium during the smelting process is above 94%. This shows that the molybdenum recovery of molybdenum oxide is relatively stable.

2. Reduction of molybdenum oxide The presence of chromium, silicon, carbon and other elements in the stainless steel charge causes the molybdenum oxide to be substantially reduced in the continuous melting of the charge and the continuous increase in the temperature of the oxidation period, which is the full melting of the test furnace. The results of the analysis and molybdenum oxide analysis were confirmed, as shown in Table 6.

Table 6 Reduction of Molybdenum Oxide in Melting and Oxidation Periods of Electric Furnace

In the reduction period, since the specific gravity of the molybdenum oxide is not less than 2.5 g/cm ² , it is further reduced in the reduction slag or on the surface of the slag.

3. Effect of molybdenum oxide on the recovery of chromium The chromium content of molten steel is about 17% and the higher temperature of molten steel creates a good thermodynamic and kinetic condition for the reaction to the right. This has affected the recovery of chromium, as shown in Table 7.

Table 7 Comparison of chromium recovery rates of stainless steel using molybdenum oxide and ferromolybdenum

As can be seen from Table 7, the use of molybdenum oxide reduced the chromium recovery of the electric furnace by 1.97% compared with ferromolybdenum. Therefore, it is necessary to strengthen the reduction period, especially the reduction of slag before tapping.

4. Stability of molybdenum in molybdenum oxide in the refining process of ladle furnace After the molybdenum oxide is reduced, the molybdenum entering the molten steel is quite stable. This has been confirmed by the refining process of the ladle furnace. Table 8 shows the changes of the molybdenum of the steel of the test furnace before and after vacuum oxygen decarburization.

Table 8 Changes in the molybdenum of the test furnace No. in the vacuum refining process

As can be seen from Table 8, the change in the molybdenum content before and after vacuum refining is mainly caused by the addition of the alloy.

5. About smelting time, power consumption and steel content

(1) The time and power consumption of the test steel grade

It is known from the test process that the use of molybdenum oxide does not affect the time and power consumption of the electric furnace. The data in Table 9 also illustrates this.

Table 9 Comparison of time and power consumption of electric furnace stainless steel using molybdenum oxide and ferromolybdenum

(2) Quality of test steel grades

The chemical composition of the finished steel of the test steel is in addition to the failure of the furnace due to equipment failure, and the finished carbon exceeds the specifications (851-1812), all of which comply with the relevant regulations.

The high-strength, low-fold test and mechanical properties of the test steels all meet the relevant technical requirements.

6. Economic benefits

According to the data provided by the branch, the unit price of molybdenum oxide is 18,706 yuan / t, and the unit price of molybdenum iron is 37,400 yuan / t (1989).

The total tonnage of molten steel in this test was: 231.54t, the test shared 6.53t of molybdenum oxide, and the pure molybdenum of molybdenum oxide was 3.412t. 3.421 tons of pure molybdenum can replace molybdenum iron with molybdenum content of 62% as 5.577t. Therefore, this test can reduce the cost of steelmaking charging of ton steel by 373.28 yuan / t.

Seven, the conclusion

(1) Molybdenum oxide can be used for the smelting of low carbon and ultra low carbon stainless steel under the double furnace process of electric furnace-ladle furnace.

(2) Under the test conditions, the molybdenum recovery rate of molybdenum oxide is up to 92.30%, which is slightly higher than the recovery rate of ferromolybdenum, but the recovery rate of chromium is decreased. It is necessary to strengthen the reduction of the reduction slag.

(3) Molybdenum oxide is used for the smelting of low-carbon and ultra-low-carbon stainless steel, and the cost of ton steel charging is reduced by 373 yuan, which does not affect the smelting time and power consumption of the electric furnace.

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