JPH0481215A - Ehrhardt tube making method - Google Patents

Abstract

PURPOSE:To manufacture a hollow tube stock excellent in surface property from an ingot as cast by giving working strain to its surface area before the ingot is heated. CONSTITUTION:The ingot 1 as cast is a macro columnar structure and when working strain is given to its surface layer before this ingot 1 is heated, the columnar structure of the surface layer is broken and the columnar structure broken in a heating stage is recrystallized and extinguished, deformability of the surface layer is improved and therefore, crack defects become hard to occur.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an Erhardt pipe manufacturing method for obtaining a hollow shell pipe with excellent surface properties from an as-cast steel ingot.

(Prior art) As shown in Fig.
The steel ingot 1 is charged into a container 2 whose inner surface has a circular horizontal cross-sectional shape (Figure (a)), and the mandrel 3 is press-fitted into the container 2 to form a hole (Figure (b)). Form into a tube 4 (Figure (C)). During the drilling process, the steel ingot into which the mandrel was press-fitted fills the container 1, and then rises to the top to form a cup-shaped hollow tube with a bottom.

Most of the steel ingots have a square or rectangular cross section, but some have a round or patterned cross section. These steel ingots are generally subjected to drilling in the as-cast state, but the as-cast steel ingots have a huge columnar crystal structure and have extremely low hot deformability, making them difficult to drill during drilling. It may not be able to withstand processing, and as shown in FIG. 2, a crack-like defect 5 (hereinafter referred to as a crack defect) may occur on the outer surface of the hollow tube 4. This tendency is particularly noticeable in high alloy steels such as stainless steel.

(Problem to be Solved by the Invention) In the drilling process, a mandrel is press-fitted into a steel ingot, the press-fitted part of the steel ingot fills the container, and then as it rises to the top, a tensile force is applied to the sides and bottom of the steel ingot. It takes. This tensile force causes cracks to form on the sides and bottom of the steel ingot. Furthermore, when the mandrel is press-fitted into the steel ingot, tensile force also acts on the top surface of the steel ingot, so cracks also occur on the top surface. If such crack defects appear in the hollow tube, the product value will be significantly reduced.

The object of the present invention is to solve the problem of such crack defects,
An object of the present invention is to provide an Erhardt pipe manufacturing method that allows obtaining a hollow pipe with excellent surface properties from an as-cast steel ingot.

(Means for solving the problem) As mentioned above, the as-cast steel ingot has a huge columnar crystal structure, has low hot deformability, and the outer surface of the steel ingot is difficult to form during drilling. The hot deformability further decreases as the temperature decreases. This reduction in the hot deformability of the outer surface and the shear force generated by the friction between the steel ingot surface and the tool combine to generate crack defects on the outer surface of the hollow tube. Therefore, even if the deformability decreases during processing, as long as the surface layer of the steel ingot has enough deformability to withstand the shearing force, crack defects will not appear on the outer surface of the hollow tube. It will be done.

Therefore, the present inventors investigated a method to increase the deformability of the as-cast steel ingot surface layer, and found that the process strain was applied to the steel ingot surface layer before heating to destroy the columnar crystal structure, and the heating process It has been found that recrystallization improves the deformability of the outer surface and makes crack-like defects less likely to occur.

The present invention is based on ``the Erhardt pipe making method in which a cast steel ingot is used as a raw material, and the steel ingot is heated and then drilled. This article summarizes the characteristic features of Erhardt pipe manufacturing method J.

(effect) The method of the present invention will be explained in detail below.

The as-cast steel ingot has a huge columnar crystal structure,
Before heating this steel ingot, a processing strain is applied to its surface layer (
The deformability of the surface layer can be improved by destroying the columnar crystal structure of the surface layer, recrystallizing the columnar crystal structure destroyed in the heating process, and eliminating it by recrystallizing it. , crack defects are less likely to occur.

As shown in the examples described later, this effect appears simply by applying processing strain to the surface of the steel ingot, but the effect is small if the processed layer is thin.
More preferably, processing strain is applied to a surface layer having a thickness of 10 mm or more from the surface of the steel ingot.

Processing strain may be applied to the entire surface of the steel ingot, or
It may be applied only to the surface of the product obtained by punching after the perforation process.

For example, in a steel ingot with a rectangular cross section, the inner periphery of the bottom of the steel ingot does not become the surface of the product after punching and is removed by cutting. By applying processing strain to the outer edge, a product with excellent surface quality and no crack defects can be obtained.

For processing distortion, select an appropriate method according to the shape of the steel ingot,
It may be applied to the surface. For example, a rolling method, a die punching method, a forging method, a processing method using a chain as shown in FIG. 3, etc. can be employed. The method shown in FIG.
A rotatable drum 8 with a chain 7 attached to its outer periphery as shown in Fig. 4 is arranged on the side and lower sides of the steel ingot 1, and the drum 8 is rotated to hit the surface of the steel ingot 1 with the chain 7. It is.

In the rolling method and the die punching method, four peripheral surfaces of a steel ingot can be processed simultaneously. Since it is difficult to process the upper and lower surfaces using the rolling method and the die punching method, it is preferable to use another method such as the chain hammering method described above. The forging process allows opposing parts to be processed at the same time, so by rotating the steel ingot, the entire surface can be processed. The chain tapping method is effective for tapered steel ingots. The surface of the steel ingot has some undulations and is not necessarily in good condition. According to the chain beating method, even such a steel ingot can be uniformly subjected to processing strain on its surface. Alternatively, by using the apparatus disclosed in Japanese Patent Publication No. 61-11690, processing strain can be reliably applied to the concave surface of the corrugated steel ingot.

In the present invention, the material of the raw steel ingot is not particularly limited as long as it is as cast, but the present invention has great advantages when applied to difficult-to-process materials such as stainless steel and other high alloy steels. be effective.

Further, the shape of the steel ingot does not matter. For example, the present invention can be applied to steel ingots having any shape such as a square cross section, a rectangular cross section, a flat cross section, a round cross section, a lobe cross section, etc.

The present invention will be further explained below with reference to Examples.

(Example) A steel ingot of 20Cr-3ONi alloy (Alloy 800 I+) and 22Cr 26Ni -5 were made by the bottom pouring ingot method.
A Mo-based alloy steel ingot was cast. All of the steel ingots had a rectangular cross-sectional shape, and the dimensions were an upper surface of 491 mm square, a lower surface of 449 mm square, an average of 470 mm square, and a length of 1200 mm. Next, some of the steel ingots were left as they were, while others were subjected to processing distortion by chain hammering using a drum-rotating device shown in FIG. The thickness of the processed layer was adjusted by changing the thickness of the chain and the rotation speed of the rotating drum. Table 1 shows the detailed conditions. The chain is made up of oval rings connected together as shown in Figure 4.

Thereafter, these steel ingots were heated and perforated to form a cup-shaped hollow tube with a bottom. Ten hollow tubes were manufactured under the same conditions.

Visually inspect the surface of the hollow tube obtained in this way,
The results of investigating the incidence of crack defects are shown in Table 2 along with the thickness of the processed layer and the drilling conditions.

Table 2 shows that according to the method of the present invention, the incidence of crack defects is reduced compared to the conventional method. In particular, there are no crack defects in the case where processing strain is applied to the surface layer 10 mm from the surface, heated, and punched.

(Hereinafter, blanks) (Effects of the Invention) According to the method of the present invention, a product with a high yield and excellent surface properties can be manufactured from an as-cast steel ingot.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional explanatory diagram showing the Elhar 1 pipe manufacturing method, Figure 2 is a diagram showing a hollow tube with crack defects, and Figure 3 is a diagram showing the process of applying processing distortion by the chain beating method. FIG. 4 is a schematic diagram showing the embodiment. FIG. 4 is a diagram showing the shape of the chain used in the example. 1: Steel ingot, 2: Container, 3: Mandrel, 4: Hollow tube, 5: Crack defect, 6: Gripping claw, 7: Chain, 8 Ni drums.

Claims (1)

[Claims] An Erhardt pipe making method in which a cast steel ingot is used as a raw material, and the steel ingot is heated and then drilled, characterized in that a processing strain is imparted to the surface layer of the steel ingot before heating it. Erhardt pipe manufacturing method.