JP3025364B2 - Method for preventing surface flaws on copper and tin-containing steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing surface flaws on a hot-rolled steel material, in particular, Cu ≧ 0.3%, Sn ≧ 0.01%.
The present invention relates to a method for preventing surface flaws of a hot-rolled steel material containing.

[0002]

2. Description of the Related Art In hot working of Cu-containing steel, Cu0.
Even at less than 3%, very slight surface flaws are observed. Cu
If it exceeds 0.3%, small cracks are formed, and Cu0.8
%, The cracks become remarkably large.
It is known that as the u content is increased, cracks increase further with an increase in the Cu content (influence of alloying elements on steel, page 378, Seibundo Shinkosha).

[0003] In addition, the problem of so-called tramp elements such as automobiles and household electric appliances scraps, particularly the environment (scrap disposal) of scraps having high Cu and Sn has been raised, and the dilution of scraps has been proposed for the regeneration of scraps containing Cu and Sn. (1990 Elliott Symposium Pr
receivedings 599).

[0004] Trump elements, particularly Cu and Sn, are difficult to remove in refining, and the Cu and Sn contents are controlled to below an allowable level in raw material management, or Cu, Sn is used in hot metal, pig iron, and the like.
A method of diluting with a raw material having a small Sn content is known. In addition, a predetermined amount of Ni is added to Cu and Sn steel containing steel, and C in steel is added.
It has been proposed to fix u and Sn as an alloy of Ni-Cu-Sn to prevent generation of surface flaws. However, Ni is scarce in resources and is expensive.

The inventor of the present invention has previously disclosed Japanese Patent Application No. 3-272357.
In the specification, Cu ≧ 0.3%, Sn ≧ 0.01%
Na ₂ O / SiO ₂ ≧ 0.
5. A method for preventing surface flaws on a hot-rolled steel material in which a coating having a thickness of 2 to 30 μm is provided with a coating agent made of a low-melting oxide containing Ni and having a NiO ≦ 50% and hot-rolled is provided.

[0006]

SUMMARY OF THE INVENTION The present invention makes it possible to use a poor scrap containing Cu and Sn, which has been difficult to use in the past, and to use a hot rolled steel material which does not require the addition of Ni to a tramp element, particularly a steel containing Cu and Sn. To provide a method for preventing surface flaws.

[0007]

SUMMARY OF THE INVENTION The present invention comprises a step of heating a steel slab containing copper and tin at a temperature of 950 ° C. or lower, and a step of heating the slab to a rolling temperature in a non-oxidizing atmosphere. This is a method for preventing surface flaws of contained steel, which can be heated to a rolling temperature in a non-oxidizing atmosphere by high-frequency induction heating.

[0008] The present invention relates to a method of forming a metallic C
Preventing the u and Sn alloys from precipitating on the surface, thereby producing a steel material free of cracks and surface flaws. The target steel type is Cu ≧ 0.3% and Sn ≧ 0.01%. This is because if the content is less than 0.3% Cu and less than 0.01% Sn, there is little risk of surface flaws and cracks occurring during hot working. When Ni is included, Ni ≦ Cu / 2 is satisfied. This is because Ni in the steel can promote the formation of a Ni-Cu-Sn alloy.

According to experiments, it has been found that when a steel slab having the above-mentioned composition is heated in the atmosphere at a temperature of 950 ° C. or less, the scale formation rate is low. FIG. 1 shows the results of this experiment. Generally, the scale generation rate is 5%
%, Slab components, furnace time, and material thickness. However, as shown in FIG. 1, it is clear that the amount of scale generation rapidly increases with the slab extraction temperature of 950 ° C. as a critical point.

Therefore, in the present invention, after passing through a step of lowering the heating temperature of the slab to 950 ° C. or less, the scale formation rate is increased from 950 ° C. to the rolling temperature (typically 1100 ° C.).
The temperature range up to (° C) was heated in a non-oxidizing atmosphere to suppress scale formation. Thereby, even if it is the steel containing a trump element, a favorable steel material without a surface flaw is obtained. The non-oxidizing heating of the copper and tin-containing steel slab may be either induction heating or an existing non-oxidizing heating furnace.

FIG. 2 shows an example of a high-frequency induction heating furnace. In the drawing, 1: heat-resistant sealed wall, 2: high-frequency coil, 3: high-frequency power supply, 4: slab, 5: roll, 51: roll (non-induction heating body), 6: shield, 7: inert gas inlet Show. The high-frequency induction heating device has a curtain-shaped shield made of heat-resistant material at the front and rear openings, and has a nearly sealed structure surrounded by air-tight heat-resistant walls, and supplies an inert gas to the inside. The atmosphere is kept non-oxidizing.

Although high-frequency induction heating is effective for rapid heating and uniform heating, the present invention employs a non-oxidizing atmosphere and does not generate scale. Furthermore, since the temperature range for induction heating is small, the equipment can be small, and the amount of expensive power consumption can be small.

[0013]

EXAMPLE A continuously cast slab having the composition shown in Table 1 was heated in a normal gas heating furnace to an extraction temperature of 950 ° C., and then heated to 1100 ° C. in a nitrogen stream by a high-frequency induction heating apparatus.
mmt hot rolled hot coils were produced. There were no surface flaws. In the high-frequency induction heating device, the length of the induction coil was 2 m, the frequency was 150 Hz, the high-frequency output was 6,500 kW, and the slab moving speed was 1 m per minute.

[0014]

[Table 1]

[0015]

According to the present invention, a heating step combining a step of heating at a temperature not higher than the scale formation temperature and a step of heating to a rolling temperature in a non-oxidizing atmosphere is used. A hot rolled product without any surface flaws can be produced without the need.

[Brief description of the drawings]

FIG. 1 is a chart of a scale production amount and an extraction temperature.

FIG. 2 is an explanatory diagram of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-52-18420 (JP, A) JP-B-56-8090 (JP, B2) JP-B-55-45615 (JP, B2) JP-B-61 7448 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 3/00 B21B 1/02 B21B 45/00 C21D 8/00-8/02

Claims (2)

(57) [Claims] 1. A method comprising: heating a steel slab containing copper and tin at a temperature of 950 ° C. or lower; and heating the slab to a rolling temperature in a non-oxidizing atmosphere.
A method for preventing surface flaws on tin-containing steel. 2. The method according to claim 1, wherein the steel is heated to a rolling temperature in a non-oxidizing atmosphere by high-frequency induction heating.