JPH06297026A - Method for preventing hot crack of cu-and sn-containing steel - Google Patents

Abstract

PURPOSE:To prevent the surface crack occurring in a Cu by adding Si at need to a Cu- and Sn-contg. steel, then heating and hot rolling the steel. CONSTITUTION:The Si is added as an alloy component at need to the Cu-and Sn-contg. steel and thereafter, the steel is heated by preferentially oxidize the Si in the steel, by which the Si is taken into surface scale to form the scale the scale consisting of a low melting oxide phase of an SiO2-FeO system. The steel is rolled while the precipitation of the Cu and Sn melt formed on the surface of the steel is thereby prevented. The steel is heated at >=1350-[-200(% Cu)+500](%Si) deg.C heating temp. and is rolled in the case of <=0.5 to 1.0% Cu and <=0.1 Sn. The steel is heated at 1150 deg.C if the heating temp. is <1150 deg.C.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a hot crack preventing method for preventing surface cracks caused by Cu by adding Si to Cu and Sn-containing steel as required, and then heating and hot rolling. Regarding

[0002]

2. Description of the Related Art Recently, electric furnace steelmaking has become more active and the amount of melting has increased. The environment (waste treatment) of bad scraps such as automobiles, home appliances, and can scraps, which have a high Cu and Sn content in the Trump element contained in the scrap that is the raw material.
A problem has been raised. Well-known materials about scrap include, for example, Elliott Symposium Proceeding (P599,1
990), regarding the effect of Sn on Cu-containing steel, Sn is C-containing.
It is known to promote surface defects of u steel, but Cu,
Both Sn are difficult to remove by refining. Therefore, C
Dilution of scraps has been proposed for the recycling process of scraps containing u and Sn.

Regarding the hot workability of Cu-containing steel, for example, “Effect of public money elements on steel” (P378, Seibundo Shinkosha) states that Cu0.3-0.3
Even if it is less than%, slight surface flaws are recognized. When the Cu content is 0.3% or more, small cracks are generated, and when the Cu content is 0.8%, the cracks are significantly increased. When the Cu content is further increased, the crack flaws are further increased as the Cu content is increased. Is described.

Further, recently, by adding a predetermined amount of Ni to Cu-containing steel, C at the time of high temperature oxidation which causes a flaw is caused.
It is known that precipitation of the u melt on the steel surface can be suppressed and cracking can be prevented. However, in the above-mentioned conventional technique, the effect of Cu and Sn is reduced by recycling scrap or diluting it.
These are high in processing cost and dilution alloy cost, and have a problem as a sufficient countermeasure. It is desired to develop a more efficient use technique of Cu- and Sn-containing steel scraps with the increase of the amount of scraps used in recent steel production.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems of the prior art, the present invention aims to prevent surface cracks that occur in the production of Cu- and Sn-containing steel.
Cu is added by adding i and then heating it to form CuS.
Incorporating the n-melt into the SiO ₂ —FeO low-melting-point oxide liquid to prevent CuSn melt from precipitating on the surface of the slab, and suppressing the intergranulation of Cu and Sn in the subsequent processing steps to prevent surface cracking. A method for preventing hot cracking of steel containing Cu and Sn which does not exist.

Furthermore, even if Cu and Sn are increased,
The purpose of the present invention is to obtain a Cu- and Sn-containing steel with a good surface in a wider range by determining the conditions under which the precipitation of Sn melt does not occur from the relationship with the Cu and Sn contents.

[0007]

Means for Solving the Problems The present invention is to solve the above problems, and the gist thereof is: (1) Si is added as an alloy component to steel containing Cu and Sn, and then heated, This is incorporated into the surface scale by preferentially oxidizing the Si in the steel, and S
Cu which is produced in a scale consisting of an iO ₂ --FeO low melting point oxide phase, Cu which is produced on the surface of the steel, Cu which is taken into the melt and then rolled.
A method for preventing hot cracking of Sn-containing steel,

(2) Cu: 0.1% or more by weight%
Steel containing less than 0.5% and Sn: 0.1% or less is 1
A method for preventing hot cracking of Cu- and Sn-containing steel, which comprises heating Cu at 150 ° C. or higher and rolling, and incorporating Cu and Sn melts formed on the surface of the steel into the scale, or

(3) Cu: 0.5% or more by weight%
Steel containing 1.0% or less and Sn: 0.1% or less, S
When i is an alloy component and heating is followed by rolling, the heating temperature T is T ≧ 1350 − [− 200 (% Cu) +50.
0] (% Si) ° C., which satisfies the relational expression,
In addition, it is a method for preventing hot cracking of Cu- and Sn-containing steel, which comprises heating and rolling at a temperature of 1150 ° C. or higher.

[0010]

FIG. 3 shows the mechanism of cracking caused by Cu. Fe diffuses into the oxide scale on the surface of the Cu-containing steel, and a Cu melt deposits on the interface. Thereafter, by subjecting to processing such as rolling, the precipitated Cu in the Cu melt phase penetrates into the grain boundaries of the base material, causing embrittlement and leading to cracking. According to the findings of the inventors,
The surface cracking of Cu-containing steel is C due to the selective oxidation of Fe.
It is generated by the fact that the u melt deposits on the surface of Fe and enters the grain boundaries during processing. Therefore, if the Cu and Sn melts can be removed from the Fe surface, cracking will not occur.

The present invention has been made based on the above findings. That is, as this means, Si is added to steel, and in the subsequent heating step, this Si is present in the scale to generate a SiO ₂ —FeO-based low-melting point oxide liquid scale, and Cu, Sn melts are generated. Take in it. However, since the melting point of the liquid scale is about 1150 ° C, the temperature during heating must be 1150 ° C or higher in order to transfer Si from the steel to the scale.

FIG. 2 shows a phase diagram of the FeO-SiO ₂ system. As you can see in this figure, the eutectic temperature of 2FeOSiO ₂ (fayalite) and wustite is 1177 ℃,
Since the liquid phase usually comes out at a temperature of 1150 ° C. or higher, it is understood that it is easy to take Cu and Sn melts into the liquid phase.

The present inventors have found that the upper limit of the embrittlement temperature of surface cracks caused by Cu and Sn decreases as the Si concentration in steel increases. This is because the liquid fraction of the Si oxide liquid phase that takes in the precipitated CuSn melt increases as the Si content increases. However, no matter how the Si concentration is increased, the upper limit of the crack generation temperature does not fall below 1100 ° C. This is because the melting point of the Si oxide liquid phase is 1100 ° C. or higher, and the Si oxide liquid phase is not formed at 1100 ° C. or lower.

Next, the influence of Sn will be further described below. Generally, Sn acts remarkably in the amount of about 1/10 of Cu. FIG. 4 shows an example of the result of another test Sn
This is done in order to see the temperature decrease due to
The heating temperature at which cracking occurs when the content is increased to 100% is shown. Cu at this time is 0.5%. If necessary, from this figure, for example, the cracking temperature when Sn is 0.03% is 1000 to 1200.
C., indicating a shift to the low temperature side of about 50.degree.

[0015]

Next, the effects will be described in detail based on the embodiments of the present invention. Example 1 As chemical components of carbon steel, C: 0.20%, Mn: 0.
50%, T-Al: 0.03%, and Cu: 0.4
%, Si was added as an alloy component to the steel containing no Sn, and heated in the atmosphere at 1000 to 1350 ° C. for 10 minutes to generate a scale, and then tensile deformation was applied. After this tensile test, the relationship between the presence or absence of cracking, the heating temperature, and the Si concentration was investigated. The result is shown in Figure 1.
It shows in (a). From FIG. 1 (a), in this component steel,
Cracks occurred in the range of 1050 to 1100 ° C, and 1
It can be seen that cracking does not occur at 150 ° C or higher.

Example 2 As chemical components of carbon steel, C: 0.20%, Mn: 0.
50%, T-Al: 0.03%, and Cu: 0.4
%, Sn: 0.1%, Si is added as an alloy component according to the steel, and the temperature is 1000 to 1350 ° C.
After 10 minutes of heating to generate a scale, tensile deformation was applied. After this tensile test, the relationship between the presence or absence of cracking, the heating temperature, and the Si concentration was investigated. The result is shown in Figure 1.
It shows in (b). From FIG. 1 (b), in this component steel,
Cracks occurred in the range of 1000 to 1100 ° C, and 1
It can be seen that cracking does not occur at 150 ° C or higher.

Example 3 As chemical constituents of carbon steel, C: 0.20%, Mn: 0.
50%, T-Al: 0.03%, and Cu: 0.5
%, Si is added as an alloying component depending on the steel containing no Sn, and at 10 ° C. at 1000 to 1350 ° C. in the atmosphere.
After heating for a minute to generate a scale, tensile deformation was applied. After this tensile test, the relationship between the presence or absence of cracking, the heating temperature, and the Si concentration was investigated. The results are shown in Fig. 1 (c).
Shown in. From FIG. 1 (c), in this component steel, Si <
In a region of 0.5% or less, heating temperature: T = -400 (Si
%) + 1350 ° C. or less, cracking occurs, but it is understood that cracking does not occur at temperatures higher than this. Also,
It can be seen that when Si> 0.5%, cracking does not occur at 1150 ° C. or higher.

Example 4 As chemical components of carbon steel, C: 0.20%, Mn: 0.
50%, T-Al: 0.03%, and Cu: 1.0
%, Si is added as an alloying component depending on the steel containing no Sn, and at 10 ° C. at 1000 to 1350 ° C. in the atmosphere.
After heating for a minute to generate a scale, tensile deformation was applied. After this tensile test, the relationship between the presence or absence of cracking, the heating temperature, and the Si concentration was investigated. The result is shown in Fig. 1 (d).
Shown in. From Fig. 1 (d), in this component steel, Si <
In a region of 0.5% or less, heating temperature: T = -300 (Si
%) + 1350 ° C. or less, cracking occurs, but it is understood that cracking does not occur at temperatures higher than this. Also,
It can be seen that when Si> 0.5%, cracking does not occur at 1150 ° C. or higher.

Example 5 As chemical components of carbon steel, C: 0.20%, Mn: 0.
50%, T-Al: 0.03%, and Cu: 1.0
%, Sn: 0.1, Si was added as an alloy component according to the steel, and the mixture was heated in the atmosphere at 1000 to 1350 ° C. for 10 minutes to generate a scale, and then tensile deformation was applied. After this tensile test, the relationship between the presence or absence of cracking, the heating temperature, and the Si concentration was investigated. The result is shown in Figure 1.
It shows in (e). From Fig. 1 (e), in this component steel,
In a region of Si <0.5% or less, heating temperature: T = -300
It can be seen that cracking occurs at (Si%) + 1350 ° C. or lower, but cracking does not occur at temperatures higher than this. Further, it can be seen that when Si> 0.5%, no cracks occur at 1150 ° C. or higher.

As is clear from the above examples, according to the present invention, by adding Si to steel containing Cu and Sn,
During subsequent heating, the CuSn melt, which is the cause of cracking, is converted into SiO
₂ --FeO-based liquid phase can be incorporated and C
It can be seen that the cracking of the steel containing u and Sn is prevented.

[0021]

INDUSTRIAL APPLICABILITY The present invention makes it possible to prevent surface cracks caused by CuSn melt, which is a problem in manufacturing Cu- and Sn-containing steels, and to cope with future scrap circumstances, Cu and S
Although it is expected that the n-containing steel will increase, it is possible to manufacture the Cu- and Sn-containing steel without taking a costly method such as Ni addition and hot metal dilution.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the heating temperature, Si concentration, and crack generation according to the present invention. (A) Cu 0.4%, Sn 0%,
(B) Cu 0.4%, Sn 0.1%, (c) Cu 0.5
%, Sn0%, (d) Cu1.0%, Sn0%, (e)
It is a figure in Cu1.0% and Sn1.0%.

FIG. 2 is an FeO—SiO ₂ system phase diagram according to the present invention.

FIG. 3 is a diagram showing an example of the effect of Sn of the present invention on the liquidus temperature of Fe—Cu system.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Naoki Tokumitsu 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Corporate Technology Development Division

Claims (3)

[Claims] 1. Prevention of hot cracking of Cu-Sn-containing steel, characterized in that Si is added as an alloy component to a Cu-Sn-containing steel and then heated to form a scale and then rolled. Method. 2. Cu: 0.1% or more to 0.5 by weight.
%, Sn: steel containing 0.1% or less, 1150
Cu, S characterized by being rolled at a temperature of ℃ or more
Method for preventing hot cracking of n-containing steel. 3. By weight%, Cu: 0.5% or more to 1.0
%, Sn: 0.1% or less in steel, Si is added as an alloying component, and when heating and rolling, heating temperature: T is T ≧ 1350 − [− 200 (% Cu) +50.
0] (% Si) ° C., which is a temperature equal to or higher than the temperature satisfying the relational expression, and which is determined by the relational expression: T
Is less than 1150 ° C., heating at 1150 ° C. is followed by rolling, which is a method for preventing hot cracking of Cu- and Sn-containing steel.