CN1670224A - Stainless steel dephosphorization agent under reducing atmosphere - Google Patents

Abstract

Disclosed is a stainless steel dephosphorization agent under reducing atmosphere comprising (by weight ratio) calcium Ca 25-55, balancing magnesium Mg, carbon C <0.1, manganese Mn <0.05, ferrum Fe <0.2, copper Cu <0.01, sulfur S <0.003, phosphor P <0.001. A chemical purity reagent CaF2 is employed as the fluxing agent. The invention can be applied for vacuum induction furnace for not only deep dephosphorization to stainless steel, but also for further deoxidization and desulfuration.

Description

Stainless steel reduction dephosphorization agent

The technical field;

the invention relates to a preparation technology of stainless steel, and particularly provides a stainless steel reduction dephosphorization agent.

Background art:

the proportion of the return material of the stainless steel in the furnace charge is increased continuously, so that the phosphorus content in the molten steel is increased continuously. The dephosphorization effect of the traditional oxidation dephosphorization method on molten steel with the carbon content lower than 2 percent is very poor, and the oxidation loss of alloy elements Cr, Mn and Si in the stainless steel is inevitably caused; the adoption of the oxidation dephosphorization inevitably brings impurity element carbon into the added CaO or BaO, so that the carbon in the steel is easy to exceed the standard; even if the reduction dephosphorization method commonly used at present is adopted, namely CaC is used₂And the impurities such as carbon, silicon or aluminum are easily brought in by CaSi or AlCa dephosphorization, and the later process of removing the newly introduced impurities is added.

The invention content is as follows:

the invention aims to provide a stainless steel reduction dephosphorization agent, which can conveniently remove oxygen and sulfur while reducing dephosphorization, and does not increase the content of carbon, thereby greatly reducing non-metallic inclusions in steel.

The invention provides a stainless steel reduction dephosphorization agent which is characterized by comprising the following chemical components in percentage by weight: ca: 25-55, and the balance of Mg.

In the stainless steel reduction dephosphorization agent, the impurities of C is less than 0.1, Mn is less than 0.05, Fe is less than 0.2, Cu is less than 0.01, S is less than 0.003 and P is less than 0.001.

When the stainless steel reduction dephosphorization agent is used for dephosphorization, a chemical pure reagent CaF can be adopted₂As a flux.

It is known that magnesium has a higher solubility in steel than calcium, with 1873K the solubility of calcium in steel being about 0.016% and magnesium in steel being about 0.04%, so magnesium has a greater dephosphorising potential than calcium. The thermodynamic equation of the dephosphorization of the Mg-Ca alloy is as follows:

$\begin{array}{c}\mathrm{Ca}+\frac{2}{3}\left[P\right]=\frac{1}{3}\left({\mathrm{Ca}}_3{P}_2\right)\\ \mathrm{\&Delta;}{G}_1^o=-440280+167.4T----\left(1\right)\\ \mathrm{Mg}+\frac{2}{3}\left[P\right]=\frac{1}{3}\left({\mathrm{Mg}}_3{P}_2\right)\\ \mathrm{\&Delta;}{G}_2^o=-413067+161.64T----\left(2\right)\end{array}$

dephosphorizing product Ca₃P₂、Mg₃P₂The reactions (3) and (4) can occur under a certain oxygen potential, and Ca can be calculated and obtained₃P₂、Mg₃P₂The Gibbs free energy of the reactions (3) and (4) was determined from the standard Gibbs free energy of (g).

${\mathrm{\&Delta;G}}_3^o=-3056219.88+348.85\mathrm{\&Tgr;}----\left(3\right)$

$\mathrm{\&Delta;}{G}_4^o=-2985152.94+398.83T----\left(4\right)$

When reactions (3) and (4) reach equilibrium under standard conditions, the equilibrium constant K can be obtained₃、K₄The expression of (a) is:

$\begin{array}{c}{K}_3=\frac{1}{{(P_{O_2}^{{\mathrm{Ca}}_3{P}_2}/P^{\mathrm{\&theta;}})}^4}----\left(5\right)\\ K_4=\frac{1}{{(P_{O_2}^{{\mathrm{Mg}}_3{P}_2}/P^{\mathrm{\&theta;}})}^4}----\left(6\right)\end{array}$

and using formulas $\ln K=\frac{-{\mathrm{\&Delta;G}}^o}{\mathrm{RT}},$ The critical oxygen partial pressures of reactions (3) and (4) can be calculated as follows:

$\begin{array}{c}{P}_{O_2}^{{\mathrm{Ca}}_3{P}_2}=4\sqrt{\exp (\mathrm{\&Delta;}{G}_3^o/\mathrm{RT})}\&CenterDot;P^{\mathrm{\&theta;}}----\left(7\right)\\ P_{O_2}^{{\mathrm{Mg}}_3{P}_2}=4\sqrt{\exp (\mathrm{\&Delta;}{G}_4^o/\mathrm{RT})}\&CenterDot;P^{\mathrm{\&theta;}}----\left(8\right)\end{array}$

under the standard state, the critical oxygen potential P of the mutual conversion of the oxidative dephosphorization and the reductive dephosphorization at a certain temperature of the reactions (3) and (4) can be obtained according to the calculation_O2 ^Ca3P2And P_O2 ^Mg3P2As shown in table 1:

TABLE 1 oxygen at certain temperaturesCritical oxygen potential for interconversion of dephosphorization by reduction and dephosphorization

T(℃)	1450	1500	1550	1600	1650	1700
							PO2 Ca3P2(10-12Pa) PO2 Mg3P2(10-11Pa)	0.024 0.0375	0.107 0.164	0.447 0.648	1.73 2.34	6.17 8.51	21.0 21.0

From the above calculation, the oxygen partial pressure of the system reaches 10 respectively in the standard state and the steel-making temperature range^-12Pa、10^-11When Pa is used, the molten steel can be subjected to reduction dephosphorization by using calcium or magnesium, and the trends are the same. Therefore, we can consider that when the total oxygen partial pressure of the system is less than 10^-13And when Pa is adopted, Mg-Ca alloy can be adopted for reduction dephosphorization.

The invention considers that the magnesium as the main element of the reduction dephosphorization has wide sources: magnesium is abundant in the crust, with a storage of 2.7%, second to Al and Fe, accounting for position 3. Magnesium ores are found in most countries. The seawater also contains abundant magnesium with a content of about 0.13%, and can provide inexhaustible magnesium resources for human beings. Particularly, China is one of the most abundant countries of magnesium resources in the world, dolomite is abundant in mineral production, the storage amount of magnesite brought by Liaoning large stone bridges accounts for more than 60% of the world, and the ore grade is as high as 40%. This provides an extremely advantageous guarantee for the development of magnesium alloys and ferrous metallurgy.

The invention can be applied to a vacuum induction furnace, and can further deoxidize and desulfurize while deeply dephosphorizing the stainless steel. The dephosphorization rate can reach 50 percent, and the deoxidation and desulfurization rates are more than 95 percent.

Description of the drawings:

FIG. 1 is a morphology diagram of inclusions of 00Cr18Ni10 after dephosphorization.

The specific implementation mode is as follows:

using a common vacuum induction furnace (without positive pressure) or an electric furnace, firstly, returning stainless steelPutting into a knotted and baked MgO crucible, and adding Mg-Ca alloy as dephosphorizing agent with particle diameter less than 2 and CaF as fluxing agent₂Putting the mixture into a hopper according to the mass percentage of 4: 1, and then vacuumizing the hopper to 10%^-4～10^-3And Pa, supplying power to heat until the raw materials in the crucible are completely melted. After the refining period is finished, a certain amount of argon is filled into the furnace, the heating power is adjusted to ensure that the temperature of the molten steel is 1450-1500 ℃, and a dephosphorizing agent Mg-Ca alloy and a fluxing agent CaF are added in three batches at intervals of 2 minutes in the middle₂And vacuumizing again after the dephosphorization operation is finished for 2 minutes. And controlling the casting temperature before casting, and casting the steel ingot at a constant speed.

Example 1

The dephosphorizing agent comprises the following components of magnesium Mg: 73.1, calcium Ca: 26.6, carbon C: 0.042, manganese Mn: 0.012, iron Fe: 0.14, copper Cu<0.01, sulfur S: 0.0028, phosphorus P:0.001.

according to the reduction dephosphorization process, the martensitic stainless steel 2Cr13 is dephosphorized in a25 Kg vacuum induction furnace. C, O, S, P, Mg and Ca content by mass percent before and after dephosphorization are compared as shown in Table 2:

example 2

The dephosphorizing agent comprises the following components of magnesium Mg: 68.9, calcium Ca: 30.8, carbon C: 0.042, manganese Mn: 0.012, iron Fe: 0.14, copper Cu<0.01, sulfur S: 0.0028, phosphorus P: 0.001.

according to the reduction dephosphorization process, the martensitic stainless steel 2Cr13 is dephosphorized in a25 Kg vacuum induction furnace. C, O, S, P, Mg and Ca content by mass percent before and after dephosphorization are compared as shown in Table 2:

TABLE 22 Cr13 before and after dephosphorization by reduction of C, O, S, P, Mg, Ca

Ordinal number	C(％)	S(％)	P(％)	O(％)	Mg(％)	Ca(％)
							Before dephosphorization	0.16	0.008	0.034	0.0049	-	-
Example 1 Example 2	0.016 0.018	0.0008 0.0011	0.011 0.014	0.0010 0.0011	0.003 0.003	0.005 0.003

Example 3

The dephosphorizing agent comprises the following components of magnesium Mg: 64.2, calcium Ca: 35.6, carbon C: 0.071, manganese Mn: 0.0113, Fe: 0.11, copper Cu<0.01, sulfur S: 0.0019, phosphorus P: 0.001.

according to the reduction dephosphorization process, austenitic stainless steel 00Cr18Ni10 is dephosphorized in a25 Kg vacuum induction furnace. C, O, S, P, Mg and Ca content by mass percent before and after dephosphorization are compared as shown in Table 3:

example 4

The dephosphorizing agent comprises the following components of magnesium Mg: 61.6, calcium Ca: 38.2, carbon C: 0.059, manganese Mn: 0.011, iron Fe: 0.14, copper Cu<0.01, sulfur S: 0.0022, phosphorus P: 0.001.

according to the reduction dephosphorization process, austenitic stainless steel 00Cr18Ni10 is dephosphorized in a25 Kg vacuum induction furnace. C, O, S, P, Mg and Ca content by mass percent before and after dephosphorization are compared as shown in Table 3:

TABLE 300 quality percentage contents of C, O, S, P, Mg, Ca before and after reduction dephosphorization of Cr18Ni10

Ordinal number	C(％)	S(％)	P(％)	O(％)	Mg(％)	Ca(％)
							Before dephosphorization	0.014	0.030	0.0099	0.017	-	-
Example 3 Example 4	0.015 0.014	0.0010 0.0011	0.0063 0.0051	0.0004 0.0006	0.004 0.003	0.005 0.004

As can be seen from tables 2 and 3, the dephosphorization rate is 30-50%, the deoxidation rate and the desulphurization rate are both more than 95%, the non-metallic inclusions in the steel are greatly reduced, the change of carbon elements before and after the reduction dephosphorization is slight, and the residual amount of magnesium and calcium is in a trace range.

FIG. 1 is a morphology diagram of inclusions of 00Cr18Ni10 after dephosphorization, and it can be seen that the average volume fraction fv value of the inclusions after refining is reduced from 1.15-1.9% to 0.3-0.6%, and the average radius of the inclusions is reduced from 5-10 um to 3-5 um. Therefore, the size of the ingot inclusions after Mg-Ca treatment is obviously reduced, the percentage of the ingot inclusions is obviously reduced at the same time, and the shapes and the inclusion components are basically the same.

Claims (2)

1. The stainless steel reduction dephosphorization agent is characterized by comprising the following chemical components in percentage by weight: 25-55 parts of Ca, and the balance of Mg.

2. The reductive dephosphorization agent for stainless steel according to claim 1, wherein: less than 0.1C, less than 0.05 Mn, less than 0.2 Fe, less than 0.01 Cu, less than 0.003S, and less than 0.001P.