Thu, 02 Aug 2018 07:22:19 +0000

Vacuum induction furnace desulfurization

It is difficult to control the sulfur content of ultra-clean steel in vacuum induction furnace. This paper designs four different smelting schemes, and studies the influence of the composition ratio of desulphurized slag, the amount of desulphurized slag, the refining parameters, the carbon content of steel liquid, the time of desulphurized slag addition and other factors on the sulfur content of steel liquid. The results showed that the desulphurization slag containing CaO and CaF2 of 1000 g was added into the crucible with the furnace, and the proper refining parameters were selected to increase the carbon content of steel fluid within the allowable range, and the desulphurization rate of steel fluid could reach more than 80%.

Sulfur exists in steel in the form of sulfide (MnS, FeS, etc.), and its effect on mechanical properties is as follows: (2) significantly reduce the anti-hydrogen-induced crack capacity of steel, so it can be used in Marine engineering, railway Bridges, high-rise buildings and large hydrogen storage tanks [S] no more than 50 * 10-6. Sulfur also affects the corrosion resistance of steel and is used to transport pipeline steel containing acid medium such as H2S, [S] reduced to (5~10) x 10-6. In addition, sulfur has adverse effects on the hot working performance and weldability of steel. Therefore, for some kinds of steel, how to desulfurize in the smelting process is very important. The 150-kg vacuum induction furnace of the steel research institute of jiangsu province (shagang) undertakes the preliminary production task of product development. Some ultra-clean steel types are often produced. Due to the technical features of grilled slag, slag, desulfurization is a weakness, vacuum induction smelting in this paper, by improving the ratio of desulfurization slag composition, desulfurization slag quantity, refined parameters, the carbon content in liquid steel, desulfurization slag joining methods such as time, a wide range of removal of sulfur in steel liquid, provides the research for the preparation of super clean steel technology and experimental basis.

1. Experimental device and scheme design

1.1 experimental devices and methods

This experiment was carried out on a 150 kg vacuum induction furnace. The melting crucible was made of alumina. The industrial pure iron treated by surface derusting and drying was added into the furnace by cold charging. It was melted under vacuum and refined at a certain vacuum degree for 20 minutes. After the end of the refining, a certain amount of protective gas was filled in. The related materials used in the experiment are industrial pure iron, graphite and fe-s alloy.

1.2. Experimental scheme design

The desulphurization reaction of steel fluid under vacuum is mainly related to the composition ratio of desulphurized slag, the amount of desulphurized slag, the vacuum degree, the carbon content of steel fluid, the time of desulphurization slag addition and other factors. In order to find out the influence of the above factors on the desulfurization reaction of molten steel and determine the optimal desulfurization scheme of 150 kg vacuum induction furnace, four schemes A~D were designed in this experiment. The desulfurization slag selected is a mechanical mixture of CaO and CaF2. The desulfurization slag is made into powder by grinding machine with an amount of 80 kg. The initial sulfur content of each scheme is 0.015% by adding fe-s alloy. As shown in table 1, the three schemes A, B and C are refined for 20 min with A vacuum degree of 30 Pa. The difference is that in scheme A, the desulfurization slag with different proportion of 0.1% carbon and 1000 g is added after the material is melted down. In scheme B, the desulfurization slag with 0.1% carbon and fixed composition of different weight is added to the furnace. In scheme C, the desulfurization slag with different carbon content and 1000 g fixed composition is added to the furnace. In scheme D, the desulfurization residue of 0.1% carbon and 1000 g fixed composition was added after the raw material was melted and refined at different vacuum degrees for 20 min. A, B, C scheme, take ingot sample to analyze the final sulfur content; Scheme D: during the refining process, sulfur content in steel solution is sampled every 5 minutes, and carbon and sulfur analyzer is used for the determination of sulfur elements.

3, conclusion

In order to improve the desulfurization rate of ultra-low sulfur steel in vacuum induction furnace, the following measures can be taken:

(1) appropriate composition ratio of desulfurized slag was selected to improve the basicity of desulfurized slag as much as possible, so as to make the desulfurized slag have a good fluidity. The final composition ratio of desulfurized slag in this experiment was 50% for CaO and 50% for CaF2 respectively.

(2) graphite and desulfurized slag are added to the furnace with the raw materials.

(3) to increase the carbon content of steel liquid as much as possible within the permitted range of chemical composition of steelmaking.

(4) during the melting and refining period, the vacuum degree in the furnace should be improved as much as possible. Meanwhile, the optimum refining time was determined in this paper to be 10 min.

(5) the amount of desulfurization residue should be appropriate, and the amount of desulfurization residue should be increased as much as possible without affecting the production safety and product quality. In this experiment, the amount of desulfurization residue was finally determined to be 1000g. In order to obtain products with lower sulfur content, raw materials must be selected to reduce the amount of sulfur that the raw materials bring into the molten steel.