JPS601392B2 - Pilger rolling material - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a roll material for a Pilger rolling mill, which is used in the manufacturing process of pipes such as copper and stainless steel.
It is a roll material that has high wear resistance and good grindability, the effective surface layer part can obtain the required hardness by appropriate heat treatment conditions, and the internal part has excellent plowability.

Pilger rolling mills are used in some parts as a method for manufacturing copper, copper alloy, and stainless steel pipes, but the material for the rolls for this pilger rolling mill is SUJ-2, which is high C-Cr-MO steel, or tools. The steel SKD-11 or improved materials thereof have been used, and have achieved acceptable results.

However, there is a desire in the rolling industry to increase the amount of rolling reduction from the standpoint of improving efficiency, etc., but if the above-mentioned materials are used in high rolling operations, the life will be shortened due to roughening of the surface, etc., making them unsuitable for practical use. SKD-11 is a material with excellent wear resistance, but it has good hardenability and lacks internal whipping properties, so when used as a material for pilger rolls, it is necessary to increase the tempering temperature to reduce internal hardness.

As a result, the surface hardness inevitably decreases, and the original sufficient wear resistance cannot be obtained. Although SUJ-2 has high hardness, it is not a particularly wear-resistant material, so problems such as surface roughness occur under severe rolling conditions.

The purpose of the present invention is to develop a roll material for Pilger rolling that can withstand high pressure rolling, and basically aims to increase wear resistance and extend life by precipitating a large amount of V carbide.

If the hardenability is too good during heat treatment, the inside will harden, resulting in poor plowability and poor accident resistance. A material used for this purpose is required, which hardens only the surface layer but does not harden the inside and has excellent ballability. Furthermore, if the grindability is significantly deteriorated, it is not desirable for roll manufacturing, so a material that is not significantly inferior in grindability compared to conventional materials is required. The present invention was made with the aim of developing a roll material having the above characteristics. V carbide has higher hardness than other carbides (e.g. iron carbide 115
Materials in which a large amount of V carbide is precipitated are expected to have excellent wear resistance.

Therefore, the solution to the above problem is based on steel that contains a large amount of V and C contains the sum of the V, the stoichiometric amount, and the amount that strengthens the base.
This was achieved by developing a material with preferable hardenability by containing an appropriate amount of r, and specifically, CI. 5-2.5, Sio. 2-1.0, Mno. 2～
1.2, Cro. A roll material for Pilger rolling, which is characterized by containing elements of 5 to 2.0 and V4 to 8, with the remainder consisting of Fe and impurity elements, has excellent wear resistance and grindability, and has appropriate hardenability. It is something. The conventional material for pilger rolls is SUJ-, which is a high C-Cr-Mo steel.
2. SKD-11, which is a tool steel, or improved steel grades thereof have been used and have achieved somewhat satisfactory results; however, when operated under high pressure, surface roughness tends to occur and the situation is not completely satisfactory.

Various high-speed steels are known as materials with excellent wear resistance, but these contain C, Cr, V, W, Mo, Co, etc., and hard carbides precipitate out, giving them excellent wear resistance. have.

Carbide of each element has different hardness depending on its crystal structure,
Generally, MC type carbides have high hardness. Like the carbides of W and Ti, V carbide forms an MC type carbide and has high hardness, but the present invention provides a roll material for Pilger rolling that has excellent wear resistance by precipitating a large amount of medium V carbide for the following reasons. It was successfully obtained. Since W has a large atomic weight and the specific gravity of W carbide is large, a large amount must be added to obtain the same effect as V carbide.

Furthermore, Ti is an active element and poses great difficulties in steel manufacturing. On the other hand, V is easily added during steel manufacturing, has the highest hardness among these carbides, and has almost no effect on hardenability. For the above reasons, it was decided to precipitate a large amount of V carbide to improve wear resistance. Figure 1 shows the relationship between the V content and precipitated carbides in high-speed steel.As V increases, the amount of hard MC type carbides increases instead of M6C type carbides, and the wear resistance also increases. It is expected.

This can also be understood from the relationship between the hardness of each type of high-speed steel and the degree of wear shown in FIG. 2. In the figure, the C and V contents of each steel type are as follows.

○ V T 1 o. 75% ・% MIO. 80 1 M 2 0.85 2 M 4 1.30 4 T15 1.55 5 MIO O. 90 2 M 3 1.05 2.5 Based on this knowledge, in the present invention, the amount of V added was adjusted in relation to C in order to precipitate MC type carbides, and the composition as described above was obtained.

Next, the reasons for limiting each element will be shown. C and V are V as mentioned above.
It is a carbide-forming element, and CO.
It is necessary to add VI% to 24% (by weight), and approximately 0.5% of C is added to strengthen the matrix.
Contain ~0.6% more. The higher V and C are, the more VC can be generated and the wear resistance can be improved.
If C and C are too high, macroscopic deflection of C and V will occur during ingot formation, and forging will become difficult.In the example of 3% C-10% V, the ratio of C and V at the top and bottom of the steel ingot is 1. 38, 1.4
3, which exceeds the practically acceptable range, and furthermore, when this steel ingot is forged, cracks occur, which is extremely problematic in terms of manufacturing.

Therefore, the upper limit of C was set to 2.5% and V was set to 8% stoichiometrically. On the other hand, Cr has a large effect on hardenability.

For example, a Jomini test was conducted on 2% C-6% V steel containing 0.5 to 5% Cr. When Cr was added in excess of 2%, the quenching depth was greater than necessary no matter what the quenching temperature was. I don't like it. Therefore, the upper limit of Cr is limited to 2%. Next, test results for the following materials, which are the main composition of the component, are shown.

C: 2.0%, Si: 0.5%, Mn: 0.5%, Cr
: 1.0%, V: 6.0% [1] Regarding the hardenability test, JIS Jomini test was conducted.

FIG. 3 shows the results of a test conducted using 84,000. It is inferred that the hardenability is appropriate and the interior is rich in sardine characteristics.
[2] Regarding the quenching hardness, Fig. 4 shows a tempering curve when quenching and tempering was performed at 840 oo, and a hardness of approximately HRc 60 was obtained at a tempering temperature of 300 qo.

[3] Figure 5 (photo) shows the quenched structure (3000x magnification), and it is observed that a large amount of V carbide is precipitated. [4
] Figure 6 shows the results of the abrasion resistance test of various materials by Belder.

Abrasion resistance comparable to that of high speed steel has been obtained. The test conditions and curve numbers in the figure are as follows.

Test conditions [5] Grindability test results and mechanical properties are shown in Tables 1 and 2.

Curve 1: Invention 2: M15 3: 10-30r-IV steel 4: High alloy Ni-grain cast iron 5: SKD-11 6: Equivalent to SUJ-2 .

Table 1 Grindability test results 2 'Mechanical properties [6] When a 1 ton steel ingot was produced with the above ingredients and forged with a hammer, it was forged very easily without any cracks, and the top and bottom of the steel ingot were When we investigated the component segregation, the top to bottom ratio was found to be CI. 001VI. 02, almost no macroscopic polarization was observed.

[7] Forgeability and wear resistance were investigated by changing C and V.

That is, C/1.5%, V/4.0% and C/2.
When steel ingots of 5% and V/8.0% were manufactured and forged, both were easily forged and stretched. The wear test results are shown in Figure 7.C
, Slightly better results were obtained with higher V, but no difference was observed in practice.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between V content and MC type carbide and pigeon C type carbide in high speed steel, Figure 2 is a graph showing the relationship between hardness and wear degree of each steel type, and Figure 3 is a graph showing the relationship between the content of V and MC type carbide and pigeon C type carbide. A graph showing the aging test results of the invented product, Figure 4 shows the results of the aging test of the invented product.
A graph showing the tempering curve when phosphoroused at 40 qo, Fig. 5 is a micrograph showing the hardened structure of the product of the present invention, Fig. 6 is a graph comparing the wear resistance of various materials by Belder type abrasion test, Fig. 7 The figure is a graph showing the relationship between C and V contents and wear resistance. Figure 'Figure 2 Figure 4 Figure 5 Figure 7

Claims (1)

[Claims] 1 C1.5-2.5%, Si0.2-1.2%, Mn
0.2-1.2%, Cr0.5-2.0%, V4-8%
, the balance being Fe and unavoidable impurity elements, the roll material for Pilger rolling has excellent wear resistance and grindability, is hardened on the surface layer, and has high toughness on the inside.