KR100340554B1 - High-temperature oxidation inhibitor using metal chrome powder and alumina - Google Patents

Abstract

PURPOSE: A high temperature antioxidant using chrome metal powders and alumina is provided to have the same antioxidizing ability even though the low cost alumina is substituted for 20% of chrome metal powders and the good antioxidizing effect even in the steel materials such as the high manganese steel. CONSTITUTION: The high temperature antioxidant using the chrome metal powders and the alumina comprises 20 to 70 wt.% of the chrome metal powders, not more than 20 wt.% of the alumina powders, 2.5 to 25 wt.% of a binder selected from the group consisting of polyvinyl alcohol, methyl cellulose and carboxymethyl cellulose, 10 to 50 wt.% of solvent selected from the group consisting of water and alcohol, and 0.5 to 1.5 wt.% of normal octyl alcohol antifoaming agent based on the weight of the total composition.

Description

High-temperature oxidation inhibitor using metal chrome powder and alumina}

The present invention relates to a high temperature antioxidant for preventing oxidation scale formation on the surface of steel in a high temperature oxidizing atmosphere, and more particularly to an excellent high temperature antioxidant for preventing scale formation on steel using metal chromium powder and alumina.

In general, since steel is heated at a high temperature for a long time in a steel manufacturing process, a large amount of scale is generated during heating, thereby reducing production yield. In addition, in order to satisfy the mechanical properties of the steel, when a large amount of Mn, Ni, Al, Si, etc., which have a large difference in oxidizing power, are added, these elements cause selective oxidation so that the grain boundaries are preferentially oxidized, such as secondary processing such as hot rolling. At the time of the plate surface on the surface of the sliver (sliver) defects and scalp (scab) defects of the scalp (like scalp) is caused to reduce the quality of the product, there is a problem that the production cost rises when the removal is polished.

Atmosphere control can be used as a way to prevent the formation of oxidative scale when heating steel, but in this case, not only coke oven gas and furnace gases used as by-products of the process can be used, but also the existing equipment must be completely replaced. Facility investment is required.

Therefore, the has been a widely used method for applying an anti-oxidation coating agent, in particular _{Al 2 O 3, SiO 2,} MnO 2, sintered in a number of metal oxides MgO-based accelerator, various metal powders, or metal carbide such as a film reinforcement, etc. Although a mixed antioxidant coating agent has been developed and used, in the case of containing a large amount of elements with a selective oxidation power, depending on the alloy component system, it may promote the selective oxidation rather.

In particular, when an antioxidant coating agent containing Si is used for steel containing a large amount of Mn, the coating agent may react with the steel to form a low melting point compound to promote grain boundary oxidation by capillary action.

In view of the fact that chromium forms a dense Cr ₂ O ₃ layer, the present inventors have found that the grain boundary of 25Mn-1.5Al-0.5C steel, which was formed deeper by several millimeters during heating to 1250 ° C. in a reheating furnace using chromium metal powder. Patent results have been obtained with the result that the oxidation can be inhibited (Patent Application Nos. 95-46805).

However, depending on the material, even if a less dense oxide layer is formed, it exhibits sufficient antioxidant activity.

Therefore, the present inventors replaced some of the high-temperature antioxidants made of expensive chromium metal powder with alumina to provide excellent oxidation resistance not only for ordinary steel but also for steels containing a large amount of Mn, Ni, Al, and Si, which cause selective oxidation. It is to provide an economical and high temperature antioxidant.

Metal chromium powder consisting of 20-70% by weight of metal chromium powder, 20% by weight or less of alumina powder, 2.5-25% by weight of binder, 10-50% by weight of solvent and 0.5-1.5% by weight of antifoaming agent, based on the total weight of the composition. A high temperature antioxidant using alumina is provided.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

High temperature antioxidants are made of metal chromium powder, alumina powder, binders, solvents and antifoaming agents.

The metal chromium powder and the alumina powder are selected as a basic powder material to form an oxidation resistant layer, ie, an oxidation resistant layer that inhibits the diffusion of external oxygen into the steel by sintering while heating the steel in a high temperature heating furnace. The metal chromium powder required to form the dense Cr ₂ O ₃ layer is 20-70% by weight based on the weight of the total composition and the alumina is capable of forming an Al ₂ O ₃ layer without damaging the formed Cr ₂ O ₃ layer. Use up to 20% by weight.

If the amount of alumina exceeds 20% by weight, it inhibits the formation of a dense Cr ₂ O ₃ layer, causing local oxidation.

Since the antioxidant should be applied to the surface of the steel to have a strength that does not peel off at room temperature, it is necessary to contain an appropriate amount of binder. Such a binder is preferably 2.5-25% by weight.

When the caking additive is added at 2.5% by weight or less, the coating film strength at room temperature is not sufficient, and the coating film is peeled off when the coating film is impacted.

In addition, when a large amount of the binder is added in an amount of 25% by weight or more, it is impossible to form a dense coating film during high-temperature sintering, and thus, it does not suppress the selective oxidation of these elements in the case of containing a large amount of alloying elements with strong oxidizing power.

It is preferable to select and use 1 type of polyvinyl alcohol, methyl cellulose, and carboxyl methyl cellulose as said caking additive.

The antioxidant must have an appropriate viscosity in order to have good applicability, and therefore an appropriate amount of solvent is required. Preferred solvents are water and alcohols, with water being more preferred. It is preferable to use 10-50% by weight of the solvent, when using 10% by weight or less, the viscosity is so high that it is difficult to uniformly apply the coating, when it exceeds 50% by weight the viscosity is too low As it flows down, it is difficult to apply.

In addition, when manufacturing a high temperature antioxidant having such a composition, since a large amount of bubbles are formed, many pores remain in the coating layer. Thus an antifoaming agent is added.

The antifoaming agent is added at 0.5-1.5% by weight using normal octyl alcohol. This is because when added at 1.5% by weight or more, the defoaming ability is saturated, and even if it is added there is no effect, the viscosity is lowered and the flow rate during application is disadvantageous to increase the number of applications.

Furthermore, when the composition of the high temperature antioxidant is applied to the steel, when the coating amount is 0.5kg / mm 2, the general steel shows a good anti-oxidation ability, but it contains a large amount of alloying elements causing selective oxidation along the grain boundaries. In this case, it is preferable to apply 0.9 kg / mm 2 or more.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example

In order to examine the antioxidant performance of the anti-oxidant coating agent using the metal chromium powder and alumina powder, the metal chromium powder, alumina powder, polyvinyl alcohol as a binder, water and an antifoaming agent as a solvent as shown in Table 1 by mixing 10 Eggplant antioxidants were prepared.

Experimental Example Metal chrome powder Alumina powder Polyvinyl alcohol water Antifoam One 55 wt% 5 wt% 8% by weight 31% by weight 1 wt% 2 50 wt% 10% by weight 8% by weight 31% by weight 1% increase 3 45 wt% 15 wt% 8% by weight 31% by weight 1 wt% 4 40 wt% 20 wt% 8% by weight 31% by weight 1 wt% 5 35 wt% 25% by weight 8% by weight 30.5 wt% 1.5 wt% 6 30 wt% 30 wt% 8% by weight 30.5 wt% 1.5 wt% 7 45 wt% 15 wt% 8% by weight 31% by weight 0% by weight 8 45 wt% 15 wt% 8% by weight 31% by weight 0.5 wt% 9 45 wt% 15 wt% 8% by weight 31% by weight 1 wt% 10 45 wt% 15 wt% 8% by weight 31% by weight 1.5 wt%

The antioxidants thus prepared were respectively applied to Fe-25Mn-2Al-0.5C steel at a thickness of 0.9 kg / mm 2, and then heated up to 1250 ° C. at a rate of 5 ° C. per minute and maintained for 2 hours. Was observed.

In addition, the weight before and after the oxidation test from the oxide layer and the weight change and the degree of grain boundary oxidation was measured and the results are shown in Table 2 below.

At this time, the oxidation to 1250 ℃ is because the slab reheating temperature for hot rolling is about 1250 ℃.

Experimental Example Weight before oxidation test Weight after oxidation test Grain boundary oxidation One 6.78 6.64 radish 2 6.89 6.75 radish 3 6.57 6.44 radish 4 6.65 6.52 radish 5 6.86 6.41 Local occurrence 6 6.67 6.01 Local occurrence 47 6.58 6.13 Local occurrence 8 6.72 6.56 radish 9 6.84 6.70 radish 10 6.79 6.57 radish

As can be seen in Table 2, in the alumina mixing ratio of 20% by weight or less (Experimental Examples 1-4, 8-10), the weight loss ratio change was very small, and grain boundary oxidation causing defects on the surface of the plate during hot rolling. Gave very good results with little occurrence. On the other hand, when 25 wt% (Experimental Example 5) was added, the weight reduction ratio was increased along with local oxidation. When 30 wt% (Experimental Example 6) was added, grain boundary oxidation generally occurred in more regions, and the weight reduction ratio was also increased.

Meanwhile, in Experimental Example 7, alumina was added in an appropriate amount of 15% by weight, but the grain boundary oxidation occurred locally at the site where pores were formed due to the addition of the antifoaming agent.

However, as shown in the experimental example in which the antifoaming agent was added, such local grain boundary erosion was suppressed. On the other hand, when the addition amount thereof is 2% by weight or more, the viscosity decreases, so that the number of coatings must be increased for the application of the same thickness, and even if added, the defoaming ability was saturated.

As described above, good results could be obtained even if the inexpensive alumina was mixed with the existing expensive metal chromium powder in a weight ratio of up to 20% by weight.

According to the above, even when the metal chromium powder using alumina, which is cheaper than the conventional metal chromium powder, replaces up to 20% by weight, the oxidation resistance is almost the same. It has an antioxidant effect.

Claims (1)

(Correction) 20-70% by weight of metal chromium powder, 20% by weight or less of alumina powder, 2.5-25% by weight of one binder selected from polyvinyl alcohol, methyl cellulose and carboxyl methyl cellulose, based on the total composition weight, High temperature antioxidant using alumina and metal chromium powder consisting of 10-50 wt% solvent selected from water and alcohol and 0.5-1.5 wt% normal octyl alcohol defoamer