JPS594953A - Casting and working method of hardly workable metal - Google Patents

Abstract

PURPOSE:To prevent the generation of any defect on a product surface in the stage of casting a hardly workable metal, by applying forced flow on molten metal during solidifying of the surface layer part of an ingot to produce the ingot, and subjecting the ingot to hot extrusion working thereby obtaining the product. CONSTITUTION:Molten metal 1 is electromagnetically stirred by an electromagnetic stirring coil 4 and is thereby flowed forcibly when the metal 1 starts solidification in a casting mold 3, that is, when a surface skin is formed, in the stage of casting continuously a hardly workable metal to the size of a blank material to be worked to the product. The solidifying state near the surface of the ingot is thus changed, whereby the texture of the columnar crystal is fined and the grain size of the crystal is made extremely small.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a casting method for a difficult-to-work metal that causes surface defects in the product during processing due to coarse crystal grains formed during casting. The purpose is to prevent the occurrence of surface defects on products.

In general, some alloy steels such as stainless steel or metals such as FiNi-based alloys do not undergo transformation during the cooling process after solidification due to the composition of alloying elements, or even if they are transformed, crystal grains grow significantly. There are so-called difficult-to-process metals that cannot withstand severe processing (hereinafter referred to as die processing) such as hot extrusion molding because their crystal grains are coarse tt even in the subsequent processing process (metals that transform during the cooling process). In this case, it is often not a problem because the crystal grains during subsequent processing have become finer).

By the way, the method of casting and processing metals that has been generally adopted in the past is to first cast an ingot larger than the size of the material for processing, then to intermediate hot roll the ingot to the size of the material for processing. , the method of reheating and processing into finished products is adopted. According to this method, coarse crystal grains formed during solidification are deformed and crushed during the subsequent intermediate hot rolling, and recrystallized into fine crystal grains before being processed into finished products. No problems such as surface defects occurred during processing.

However, this method requires heating twice after forming the ingot, which increases the heating cost, and when removing material from the intermediate rolling ridge, the part that has been deformed into an undesirable shape must be cut and discarded, resulting in a loss of quality in the finished product. There were problems such as a decrease in yield.

For this reason, except when molding the above-mentioned difficult-to-process metals, it is recommended to use continuous casting, for example, to cast to the dimensions of the finished product and omit the intermediate steps of heating, rolling, and material removal. Exclusively employed.

However, when molding the above-mentioned difficult-to-process metals, cracking and surface defects frequently occur during heavy processing of the material, so it is necessary to cast the material to the dimensions for finished product processing and then perform intermediate rolling, as in the method described above. It was impossible to omit it.

In addition, even if mold processing is not required, the degree of processing per slot on the intermediate rolling rolls must be limited in many cases to prevent cracking for the above-mentioned difficult-to-process metals, and heating-
Measures such as repeated rolling are required, and there is also the problem that heating energy is consumed.

On the other hand, as a method of refining the crystal grains of the above-mentioned difficult-to-process metal without performing intermediate rolling, it is used in the secondary cooling zone during continuous casting to the dimensions of the material for finished product processing.

A method has been attempted in which the molten metal is stirred by applying electromagnetic force to equiaxed crystallize the center of the slab, but this method only refines the crystal grains in the center of the slab. Coarse crystal grains remained in the one surface layer, and defects were still unavoidable on the surface of the product due to mold processing during product processing. The cause of this defect is that when a cast slab of a difficult-to-process metal with coarse grain size is molded, in addition to cracking defects at grain boundaries, each grain has a different crystal orientation. This is thought to be due to the fact that when processing is performed to deform in a certain direction, the amount of deformation differs for each crystal, resulting in the occurrence of streaks in the processing direction.

The present invention was made in order to prevent the above-mentioned defects, and when casting difficult-to-process metals, forced flow is applied to the molten metal during solidification of the surface layer of the slab to produce a slab, and this slab is directly cast. This is a method for casting and processing difficult-to-process metals, which is characterized by obtaining a finished product through hot extrusion processing.

Next, the method of the present invention will be explained in detail using a specific example.1. When the molten metal begins to solidify in the mold, that is, when the skin is formed, the molten metal is stirred by electromagnetic or other means to create a forced flow, and the slab is produced and subjected to the next process of rolling into finished products. In this way, the solidification form near the surface of the obtained slab can be changed, the structure of the columnar crystals becomes finer, and the crystal grain size is also significantly finer.

On the other hand, the above-mentioned conventionally known electromagnetic stirring method has a disadvantage.

It changes the solidification form from columnar crystals to equiaxed crystals at the final solidification part of the slab during continuous casting, that is, at a distance from the surface of the slab, and it is impossible to change the solidification form near the surface. Ta.

Fig. 1 shows an example in which the method of the present invention is applied to continuous casting, in which molten metal is molten metal, (2) is a molten metal container, (3) is a mold, and (4) is an electromagnetic stirring coil. The electro-magnetic stirring coil (4) is attached to the mold (as shown in this figure).
After the step 3), that is, when the surface layer of the slab is solidified, forced flow is applied to the molten metal by electromagnetic stirring. Of course, an electromagnetic stirring device may be provided at the outer circumference of the mold (3), but since the material of the mold (3) is copper, the electromagnetic force will be reduced, so it is preferable to ) is recommended. In the example in this figure, the simple diameter is 170~
At the time of test casting of 400-φ stainless alloy steel and Ni-based alloy steel, an electromagnetic stirring coil (4) installed at the outlet of the mold (3) was used to create a high resistance 1. The molten metal was stirred at a flow rate of up to 5 m/sec.

In this case, the stirring flow rate in the mold (3) (as shown in the figure, the electromagnetic stirring at the coil position spreads into the mold and also stirs the molten metal at that position) is approximately the acceleration of the coil position. The experimental conditions are shown in Table 1 below.

Table 1 *: Peripheral speed in the mold **: Solidification start temperature + ΔT = casting temperature An example of the results obtained in this experiment is shown in FIG. 2.

As is clear from this figure, the crystal grain size becomes significantly finer due to the influence of stirring.

Next, Fig. 3 shows the occurrence of defects on the surface of the product when a seamless pipe is manufactured from this slab using a hot extruder. The horizontal axis of this figure shows the amount of surface grinding of the slab before charging into the hot extruder as the amount of reduction in diameter, and the vertical axis shows the percentage of the sum of the lengths of product surface defects in the pipe length direction relative to the pipe length. 5
0% is the upper limit of the amount of defects allowed in the process. As is clear from this figure, if the agitation is weak or no agitation, and there are few surface cracks, many surface defects will occur due to defects such as irregularities and cracks on the surface of the slab, but the amount of grinding However, as shown in Fig. 2, the crystal grain size on the surface of the slab after grinding increases, causing vertical streaks, and the flow rate of 0.07 m/
Stirring below we causes problems in the process. However, the flow rate is 0
．． If it is 0 - or more, even though the amount of surface grinding increases, the amount of surface defects on the manufactured product will be small, and the value will be sufficiently satisfactory.

It was found that this tendency was hardly affected by the casting speed (2) and the superheating temperature ΔT.

Moreover, this effect could be confirmed for all K steel types shown in Table 1.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing an example of the method of the present invention, Figure 2 is a graph showing the influence of stirring on crystal grain size, and Figure 6 is a graph showing the surface of the product after hot extrusion. It is a graph showing the influence of stirring, which does not affect the amount of defects. (1) Molten metal, (2) Molten metal container, (3) Mold, (4) Electromagnetic stirring coil b Agent: Patent attorney: Ryoji Kimura, same: Muneharu Sasaki Figure 1 Figure 2 QS table 717px50 * Distance (mm) 3rd V! I
I 2468 & 1 horse mackerel lftmm]

Claims (1)

[Claims] A method for casting and processing difficult-to-process metals, which is characterized by producing a slab by applying forced flow to the molten metal during solidification of the surface layer of the slab, and directly hot extruding the slab to obtain a finished product.