JPH01130860A - Manufacture of stainless steel cast billet for forging - Google Patents

Abstract

PURPOSE:To improve the yield of a cast billet by gas-cutting the continuous casting billet of a stainless steel in the specified length and forming a section fused layer on the cut face of the cast billet as well. CONSTITUTION:The powder cutting machine 12 traveling by synchronizing with the stainless steel continuous cast billet 11 prepd. by a continuous casting equipment is arranged. The cast billet 11 is fused by blowing at high speed the fluid mixture 12a adding an iron powder or flux to a cutting oxygen to the specified cutting place of the cast billet 11 from the cutting machine 12 and a cast billet 13 is moved to the following stage. In this case, all of the cut face of the cast billet 11 is fused by the reaction heat of the fluid mixture 12a and an iron and after the solidification the fused layers 11b, 13a sealing a cavity 11a are respectively formed. The air flow into the cavity 11a at the rolling time of the cast billet 13 is thus eliminated and the interior oxidation is prevented. Consequently the crack of the cast billet 13 and the end face cut-off part are reduced and the yield of the cast billet is improved.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing stainless steel slabs for forging, and in particular to a method for producing slabs for forging from continuous stainless steel slabs continuously cast in a continuous casting machine. Relating to a method of manufacturing.

(Prior art and its problems) The continuous casting method is widely applied to the production of slabs because of its higher productivity compared to the production of steel ingots using ingot cases.

In FIG. 0, which describes the process of producing slabs using a continuous casting apparatus based on the conceptual diagram shown in FIG. 2, molten steel in a ladle (not shown) is poured into a tundish 1. An immersion nozzle 2 is attached to the bottom of the tundish 1, and the molten steel stored in the tundish 1 is injected from the immersion nozzle 2 into a bottomless water-cooled mold 3. The molten steel is cooled and solidified from the part that contacts the mold 3 to form a solidified shell layer. The surface part of the molten steel solidifies and the flow of molten steel progresses toward the center, where it is pulled out by various roller groups 4 such as drawing rollers, straightening rollers, and guide rollers, and its shape is corrected to form a continuous slab 5. and then transported downstream of the device.

During this transfer process, the continuously cast piece 5 is water-cooled by a cooling water injection device (not shown), and the liquid phase 5a in the center gradually solidifies.

When the center of the continuous slab 5 is completely solidified, the continuous slab 5 is cut into slabs 7 of a predetermined length by a cutting machine 6.

The cut slab 7 is transferred to the next rolling process by transfer rolls (not shown), or the slab is cold cut into appropriate lengths, and then first heated or equalized to a predetermined temperature in a heating furnace. After being heated, it is rolled in a rolling machine. As a result, the coarse cast structure of the slab is destroyed, and the elongated holes (hereinafter referred to as cavities) and air bubbles that occur mainly in the center are compressed, resulting in a rolled material with fine workability of 11m.

This rolled material may be shipped as a finished product, but if necessary, it may be forged and put on the market.

By the way, in the process of manufacturing continuous cast pieces, shrinkage holes due to solidification shrinkage occur continuously in the center of the cross section of the continuous cast pieces, so it is extremely difficult to completely eliminate cavities at the center. Therefore, when this continuous cast slab is cut, a large number of the above-mentioned cavities are present as communicating holes in the center of the obtained cast slab.

When such a steel slab is subjected to the above-mentioned rolling treatment, air flows in through the cavity holes distributed in the cross section of the steel slab after rolling, and internal oxidation progresses along the length of the steel slab. There are many cases where this cavity is not crimped. If the steel billet is forged in this state, the steel billet will frequently crack and the forging yield will drop significantly. In order to increase the forging yield, it is necessary to cut out the parts of the rolled material obtained after rolling where internal oxidation has progressed, but such treatment also causes a decrease in the overall yield, so it is not preferable. That's not the point.

In particular, when the steel type is stainless steel, the above-mentioned disadvantages occur significantly, and in fact, it is difficult to produce slabs for forging with a good yield using continuous casting equipment. Therefore, conventionally, for stainless steel for forging, copper ingots have been manufactured using ingot cases rather than slabs using continuous casting equipment.

The present invention provides that even when stainless steel slabs are manufactured using a continuous casting device, internal oxidation does not occur during rolling due to cavities, and therefore the yield during forging can be increased. The purpose is to provide a manufacturing method for.

(Means for Solving the Problems) The method for producing slabs of the present invention, which was developed to achieve the above-mentioned object, is a method for manufacturing slabs of stainless steel continuously transferred from a continuous casting device. It is characterized in that it is gas-cut to length to form a slab, and at the same time, a cross-sectional sprayed layer is formed on the cut surface of the slab.

The method of the present invention is characterized by the method of cutting continuous cast pieces, and the continuous casting method or apparatus is the same as that described in FIG. 2.

(Function) The cut surface of the continuously cast piece is gas-cut to a predetermined length, and a thin layer is formed thereon. This layer seals the cross-sectional holes of the cavity exposed during cutting. Therefore, even during rolling, this sprayed layer acts as a barrier to prevent air from penetrating into the inside of the slab and promoting internal oxidation.

FIG. 1 is a conceptual diagram for explaining cutting of a continuously cast piece.

In the figure, a large number of cavities 11a are present in the center of a continuous slab 11 that has been transferred from a continuous casting device as shown in FIG. 2 and runs in the direction of arrow P.

A powder cutting machine 12 that moves in the same direction of the arrow P in synchronization with the running of the continuous slab 11 is directed to the part of the continuous slab to be cut by adding iron powder or flux to the cutting oxygen. The mixed fluid 12a is sprayed at high speed. As a result, the continuous slab 11 is melted at this location, becomes a slab 13, and is transferred to the next process.

The cut surfaces on one side of the continuous casting are both melted by the heat of reaction between the mixed fluid 12a and the iron. When it solidifies, a sprayed layer 11b, 13b is formed on each of the cut surfaces to seal the exposed hole of the cavity 11a to the cut surface.

When cutting the powder as described above, the flow rate of cutting oxygen is 30 to 9
0 sm″/hr, the amount of iron powder added is 0 for the oxygen flow rate.
．． When conditions such as 35 to 0.5 kg/sm3 are set, a sprayed layer is formed on the cut surface of the cut stainless steel.

Continuous cast slabs were manufactured using three types of steel: 1 journey M 303304.5US316.5US304L, and the continuous cast slabs were subjected to oxygen flow 1: 60 sm3/hr, powder flow rate = 0.35
The powder was cut into steel pieces under the condition of kg/sm3.

Each obtained steel piece was heated at a temperature of 1150 to 1250°C,
Rolling was carried out under the conditions of a rolling reduction of 0 to 95%, heating energy of 111 A, and C heavy oil. Three pieces of each obtained rolled material were forged under the following conditions: heating temperature: 1200°C, rolling reduction: 20χ/blow, the number of cracks was measured, and the forging yield was calculated.

The results are shown in Table 1.

In the comparative example shown in Table 1, the steel type was 5US304, but the cutting was performed with a conventional running shearer.

As is clear from the results, all of the steel slabs produced by the method of the present invention have significantly higher forging yields than those of the comparative examples.

Note that the gas cutting method is not limited to the powder cutting method described above, and methods such as plasma arc cutting may also be applied.

(Effects of the Invention) As is clear from the above explanation, the method for manufacturing stainless steel slabs for forging of the present invention is to cut continuous cast slabs of stainless steel continuously transferred from a continuous casting machine into a predetermined length. At the same time, a cross-sectional sprayed layer is formed on the cut surface of the slab by gas cutting to form the slab, so even during rolling, the holes at both ends of the cavity existing inside the slab are removed. The cavity is sealed, and no air flows into the cavity, preventing internal oxidation of the slab. Therefore, this slab does not crack during the forging process, and the cut portions on both end faces are reduced, so that the yield during forging of this slab is increased.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a continuous casting apparatus, and FIG. 2 is a diagram showing a state in which continuous cast pieces are cut by the method of the present invention. 1... Tanditetsu, 2... Immersion nozzle, 3...
・Bottomless water-cooled mold, 4...roll, 5.11...continuous slab, 6...cutting machine, 7,13...cast slab, lla...
・Cavity, 12...Powder cutting machine, 12a...
-Mixed fluid, 11b, 13a...cross-sectional sprayed layer.

Claims (1)

[Claims] Continuously cast stainless steel slabs that are continuously transferred from continuous casting equipment are gas-cut to a predetermined length to form slabs, and at the same time, a cross-sectional sprayed layer is formed on the cut surfaces of the slabs. Features: A method for manufacturing stainless steel slabs for forging.