JPS60221121A - Method of hot extrusion of continuous cast material - Google Patents

Abstract

PURPOSE:To obtain a hot extruded product of good property without requiring special additional processes or equipment by performing die insertion cold reducing, heating a billet obtained by cutting off the surface layer and hot extruding said billet. CONSTITUTION:Die insertion cold reducing of working ratio sufficient to make crystal grains to fine grains to the inside by heating is made on a continuous cast material, and the surface layer of black skin part is removed by cutting and a billet for extrusion is obtained. This billet is heated to make the structure of whole section minute, and then hot extruded. Thus, a hot extruded product of high quality can be manufactured at high out cut yield without requiring special means to prevent occurrence of seams at the tip of extruded product.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a hot extrusion processing method for producing pipes, shapes, round bars, etc. from continuous casting materials such as stainless steel and other alloy steels. It is related to.

Continuously cast materials generally have a cast structure with strong directionality, and hot extrusion of continuously cast materials can result in frequent streak-like defects on the surface of the product, significantly reducing its commercial value. Are known.

This tendency is particularly noticeable in the case of stainless steel and other alloy steels, and in fact it has been impossible to directly manufacture extruded products from continuous casting materials.

<Prior art> For these reasons, recently, ○ Long continuous cast materials are subjected to light reduction rolling with an area reduction ratio of 1 inch or less after external milling, ○ Long continuous cast materials with a circular cross section are subjected to centerless rolling. When externally machining with a peeling machine, cold rolling is performed using the pressing force of a presser roll, and particle spraying is performed before or after external machining of O continuous casting material. After destroying the casting structure of
A method for manufacturing hot extruded alloy materials was proposed in which a microcrystalline structure is formed through recrystallization through a heating process that precedes hot extrusion processing, and then hot extrusion processing is performed (Japanese Patent Application Laid-Open No. 1983-1999).
19429).

According to this method, it is possible to eliminate streak-like defects in extruded products and to obtain extruded products made from continuous casting materials and having the same surface quality as conventional extruded products made from hot-rolled materials. surface.

There were problems as shown below.

<Problems to be solved by the invention> ■ In hot extrusion processing, it is essential to remove black scale from the billet in order to ensure the surface quality of the extruded product, and external machining is usually performed. The outer diameter of continuous casting material has a curved side diameter due to uneven thermal contraction during solidification (for example.

Average outer diameter: 3.4 on average for continuous casting materials of about 200 m
In the previously proposed method, the outer surface with the side diameter must be cut, resulting in a significantly poor cutting yield.

■ Since the end face of the extruded billet becomes the surface of the end of the extruded product, in order to prevent streak-like defects from occurring on the front end surface of the extruded product, the end face of the billet end after cutting must also be cold-worked. Alternatively, it is necessary to extrude using a reverse taper die, but cold working the end face of the billet after cutting requires an extra step, whereas extrusion using a reverse taper die is a normal method. Since a larger pressing force is required compared to the above, special equipment is required in any case, leading to an increase in cost.

<Purpose of the Invention> The purpose of this invention is to solve the various problems mentioned above, to eliminate the need for extra processes and equipment, and to minimize the need for external machining.

The object of the present invention is to provide a method for producing hot extruded products with good properties from continuous casting materials with a high yield.

This invention was made as a result of research conducted by the inventors through repeated trial and error in order to achieve the above-mentioned object. A billet for extrusion is obtained by inserting a die and performing cold diameter reduction processing with a processing degree sufficient to reduce the crystal grains to the inner grain, and then cutting and removing the surface layer, and heating this billet. By hot extruding after refining the structure over the entire cross section, there is no need for special means to prevent streaks at the tip of the extruded product.

It is characterized by the improvement in the roundness of thick materials, the production of high-quality hot extruded products with a good external cutting yield.

That is, this invention destroys the casting structure down to its inner substance by subjecting the continuous casting material to diameter reduction cold working once through die insertion, and refines the casting structure by a heating process that precedes hot extrusion processing, and continuously The main idea is to correct the side diameter of the cast material through the cold working to reduce the need for external cutting, thereby producing hot extruded products with good properties at low cost.

Note that the term "continuous casting material" used here refers to a long material obtained by a normal continuous casting method using, for example, a round mold, and the quality of the material is not particularly important. do not have.

In addition, "cold diameter reduction processing through die insertion" is carried out by descaling the continuous casting material as necessary, then lubricating it, and then reducing the diameter in the cold using a die with a predetermined inner diameter. The processing method may be any of drawing, punching, or a combination of drawing and punching. just.

The inner diameter of the die used must be determined so that the continuous casting material is subjected to a working degree sufficient to destroy the cast structure of the continuous casting material down to its inner substance.

Of course, the required value of the degree of processing (a) expressed by (A) changes depending on the material of the material, and it can be determined using the value obtained from preliminary tests as a guide, but for example, SU
In the case of S304 stainless steel, about 3% is appropriate.

The reason why cold working using a die was specifically selected as the cold working method was to improve the dimensional accuracy (for example, roundness) of the material and ensure uniform external machining conditions.

By the way, the above-mentioned "up to the internal matter" means "the entire cross section" when the billet at the time of extrusion is solid, but when the billet at the time of extrusion is hollow, the holes are directly,
In the case of processing by turning, it also refers to the range from the outer surface to the inner diameter after turning, and it also refers to the range from the outer surface to the inner diameter after turning.It also refers to the range from the outer surface to the inner diameter after turning.It also means that the billet at the time of extrusion is hollow, and this hole has a predetermined inner diameter by press drilling or expanding the diameter by pressing. In this case, it also means the area excluding the area near the inner surface where the casting structure is destroyed by the press working from the outer surface. In short, it is sufficient that processing strain is applied to the entire cross section of the billet during extrusion processing, and thereby sufficient grain refinement of both end faces of the billet can be achieved in the subsequent heating step.

The "surface layer" to be removed refers to the black scale part of the continuous casting material, and this black scale removal process is an indispensable process for obtaining extruded products with good surface properties.

The continuous casting material processed in this manner is cut into a predetermined length or perforated as necessary to form a billet for extrusion processing.

In order to obtain good hot workability, the optimum temperature for heating during hot extrusion should be selected according to the grain size and extrusion ratio, but since all of these temperatures are above the recrystallization temperature of the material,
The billet is recrystallized by this heating and becomes fine grained, thereby eliminating streak-like defects in the extruded product.

Next, the present invention will be explained by comparing examples and comparative examples.

<Example> First, a material equivalent to 5US304 was cast by the usual continuous casting method using a round mold (213φ setup).
A long continuous casting material with a circular cross section was manufactured.

Next, the obtained continuous casting material was subjected to die insertion diameter reduction cold working, external machining, cutting, and perforation under the conditions shown in Table 1, and then heated to 120 (IC) and subjected to normal hot extrusion processing. and each dimension is 66.5TRJnφX 8
．． A stainless steel tube of 25+u+t x 9000yl was manufactured.

Table 1 also shows the results of investigating the occurrence of vertical streak-like flaws on the surface of the stainless steel pipe thus obtained.

As is clear from the results shown in Table 1, when a billet whose entire cross section has been refined by the method of the present invention is used, even when hot extrusion using a continuous casting material is used, the tip It can be seen that steel pipes with streak-like defects suppressed within the permissible limits, including the parts, can be stably obtained.

1. Regarding the continuous νj fabrication fabrication (average outer diameter: 212.7mφ) manufactured as described above, the side diameter of the material as it is continuously cast and after the die insertion and diameter reduction cold working described above. When comparing the side diameter of the material as it was continuously cast, the maximum side diameter was 5.5 mm.

Minimum side diameter amount...1.0M.

Average side diameter amount...3.4 mice.

Material after die insertion and diameter reduction cold working: Diameter on the most heated side...0.5 mm.

Minimum side diameter amount...O, Omm.

Average side diameter amount...0.2 u.

The minimum required machining allowance for removing black scale was 6 mm in the case where die insertion and diameter reduction was not performed, whereas the minimum required cutting allowance for black scale removal was 6 pieces when die insertion and diameter reduction was performed according to the method of the present invention. It was confirmed that the machining yield was improved by more than 2%, to 1 h in the case of the cold-worked material.

Overall Effects> As described above, according to the present invention, hot extruded products of good quality can be produced at low yields and without the need for extra processes or equipment, using continuous casting materials as starting materials. It can be manufactured at a low cost and has extremely excellent industrial effects.

Applicant Sumitomo Metal Industries Co., Ltd. Agent Tomi 1) Kazuo and 1 other personContinued from page 10 Inventor Tadashi Toshiro Nio ■Inventor Furuken Munekatsu 1-3 Nishi-Nagasu Hondori, Amaosaki City Sumitomo Metals Inside Nakasugi Kogyo Technical Research Institute, Kogyo Co., Ltd.

Claims (1)

[Claims] A billet for extrusion is obtained by subjecting the continuous casting material to cold diameter reduction processing through insertion of a die to a degree of processing sufficient to refine the crystal grains down to the internal quality by heating, and then cutting and removing the surface layer. A hot extrusion processing method for continuous casting materials, characterized by heating the billet and then hot extruding it.