JPS619558A - Forged steel roll for cold rolling - Google Patents

Abstract

PURPOSE:To obtain a forged steel roll for cold rolling having superior resistance to surface ruggedness by combinedly adding Ni and Zr so as to form an excellent fine dendritic structure. CONSTITUTION:The composition of a forged Cr-Mo steel as the material of a forged steel roll for cold rolling is composed of, by weight, 0.7-1.2% C, 0.5- 1.2% Si, 0.3-1% Mn, 2.5-5.5% Cr, 0.2-1% Mo, 0.2-1.2% Ni, 0.1-0.6% Zr and the balance Fe with inevitable impurities. The excellent fine dendritic structure is formed by combinedly adding Ni and Zr.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a forged steel roll used as a work roll of a cold rolling mill, and more particularly to a forged steel roll for cold rolling that has excellent surface roughening resistance.

If the work roll of a cold rolling mill becomes rough, the surface of the product plate rolled by the work roll will also become rough, degrading the surface quality of the product.If the roughness of the roll becomes significant, the roll will need to be re-ground. The need arises. Therefore, work rolls for cold rolling are required to have excellent surface roughness resistance in terms of maintaining the surface quality of the product and reducing roll consumption.Especially rolls used for rolling ultra-thin sheets such as tin plate steel sheets are required to have excellent roughening resistance. It is strongly desired that the material has good roughness resistance. Conventional work rolls for cold rolling mills include Cr-M as disclosed in Japanese Patent Application Laid-Open No. 57-47849 from the viewpoint of wear resistance.

Although forged steel rolls having a high hardness having a composition of Cr--No.

By the way, the phenomenon of rough surface of the roll is mainly caused by micro-segregation, especially dendrite segregation, which occurs during agglomeration, based on observations of the occurrence and dimensional correspondence. In other words, dendrite segregation is micro-segregation that occurs when alloying elements are concentrated between the branches of dendrites (dendrites) that occur during agglomeration, but this micro-segregation causes local wear on the roll surface. It is said that unevenness occurs, which causes rough skin. Therefore, in order to improve the roughness resistance of the roll, it is necessary to refine the dendrite structure generated during agglomeration and to suppress microscopic non-uniformity of alloying elements as much as possible. In order to refine the dendrite structure formed during agglomeration, it is generally effective to increase the cooling rate during molten metal solidification, but it is difficult to significantly increase the cooling rate in actual manufacturing equipment. Therefore, there has been a strong desire to develop a technology that improves the roughening resistance of rolls at low cost by refining the dendrite structure from a point other than the cooling rate.

This invention was made against the background of the above circumstances, and
r-Mo-based forged steel rolls can be made to have a structure with a fine dendrite structure from a composition point of view, without adopting methods that are difficult to apply in actual manufacturing sites, such as significantly increasing the cooling rate. The object of the present invention is to provide a forged steel roll for cold rolling with improved properties.

In order to achieve the above-mentioned object, the present inventors have developed a high-hardness Cr
- Regarding the effects of various elements on the dendrite structure during agglomeration in Mo-based forged steel rolls, the species are Ni and Zr.
It was discovered that the combined addition of (a) is extremely effective in refining the dendrite structure, and in turn can significantly improve the roughening resistance of the roll, leading to the creation of this invention. It should be noted that the addition of Zr to Cr-Mo steel for forged steel rolls has already been shown to be effective in refining the dendrite structure in the Japanese Patent Publication No. 5.
Although disclosed in Japanese Patent No. 7-14750, the present inventors have discovered that by adding z'' and Ni in combination, rather than simply adding Zr, a finer dendrite structure can be created compared to the case of adding zr alone. They found that it could be obtained and completed this invention.

Specifically, the forged steel roll for cold rolling of this invention has a C0
,70-1,20%, Si0.50-1.20%, Mn
0.30~1.00'A, Cr 2.50~5.5
0%, Mo 0.20-1.00%, Ni 0.2
0-1.20%, Zr0. It is a fine forged steel roll with a dendrite structure containing 1O to 0.60S, with the remainder being Fe and inevitable impurities.

The reasons for limiting the components of the cold rolling roll of this invention are as follows.

C: C is an element effective in improving hardenability and hardness, and 0.70 To or more is necessary to ensure the hardenability and hardness necessary for a hardened forged steel roll, but 1 .2
Since the increase in hardness is not significant above 0%, 0.70
-1.20 inches.

Si: St is an element added as a deoxidizing agent in the normal steelmaking process, and it is added at 0.501 or more to improve hardenability and ensure cracking resistance, but if it is 1,201 or more, these effects are reduced. Therefore, 0.50 to 1.20
% range.

Mn: Mn is an effective element for improving hardenability, and for this purpose it needs to be 0.301 or more, but if it exceeds 1.00, embrittlement becomes noticeable, so it must be 0.30 to 1. It was limited to the range of 00.

Cr: Cr is an effective element for obtaining the wear resistance necessary for cold rolling rolls, and therefore 2,501
However, since excessive addition lowers hardenability, the amount is set in the range of 2.50 to 5.50%.

Mo: Mo is an element necessary to improve hardenability, and for that purpose, 0.20 or more is required.
If added in excess of i, oo*, the hardenability will not improve any further, so from a cost perspective, it is 0.20 to 1.
．． It was set within the range of 00.

Ni: Addition of Ni in combination with NlZr is effective in refining the dendrite structure, and the effect is 0.
It becomes noticeable at 201 or more, but if it exceeds 1.20%, the defdryed structure refinement effect is saturated, and addition of Ni increases the amount of retained austenite and reduces hardness, etc., so the upper limit is set at 1.20%. In the end, it is 0.20~1.20%
was within the range of

Zr: Zr is effective in refining the dendrite structure, and its effect becomes remarkable when added in combination with &C1, especially Ni. This effect can be obtained when the thrust is 0 when the Zr content is 0.10% or more, but the effect is almost saturated at 0.60%, so it was set within the range of 0.10 to 0.60%.

Steel with the above-mentioned composition is melted in a converter furnace or an arc furnace according to conventional methods, and the composition is usually adjusted through a steel refining furnace, and then poured into a mold to form a steel ingot. Then, normal forging and heat treatment are performed to obtain a cold rolling roll.

As mentioned above, by adding Ni and Zr in combination, it is possible to obtain fine Punto 2 which is even better than the case of adding Zr alone.
It is possible to obtain light tissue. FIG. 1 shows the experimental results of the present inventors regarding the effect of finer Punto 2ite due to the combined addition of Zr+Ni. This experiment was conducted using steels with the components shown in sample numbers 1 to 5 in Table 1, namely Zr,
Steel 1 containing no Ni and Steels 2 to 5 with various changes in Zr + Ni li, and Zr added alone with component elements other than Ni and Zr at approximately the same level as Steels 1 to 5 shown in Table 1. A unidirectional solidification test was conducted on the comparative steel and the comparative steel with Ni added alone under the same cooling conditions.
The number of primary dendrite arms per unit cross-sectional area of the obtained ingot was investigated. As shown in FIG. 1, Zr.

It is clear that the number of dendrite arms increases with the combined addition of Ni, that is, the dendrite structure is refined, and the degree of refinement is even more remarkable than when Ni or Zr is added alone. I know that there is. Also, among the ingots from this experiment, Ni, Z
Steel 1 without r addition and N10.51% + Zr 0.4
Figures 2 (A) and (B) show the casting structure of Steel 4 with 9% addition.
It is clear from both FIG. 2 and FIG. 2 that the effect of the combined addition of Ni and Zr on the refinement of the dendrite structure is apparent.

Examples of the present invention based on the above experimental results will be described below along with comparative examples.

The inventive steel and the comparative steel having the components shown in sample symbols A to D in Table 2 were melted according to the conventional method, poured into a 13 ton mold by the bottom pouring method, and the average diameter was 10,301 mm under the same cooling conditions.
1111 steel ingot. Each steel ingot was heated to 1180° C. and forged using upper and lower V anvils (anvil width so wide). The forging punch diameter is 650 mm, and therefore the forging ratio (forging elongation ratio) is 2.5. Then, by cutting, the outer diameter of the body is 61.
Finished into a 011110 cold rolling roll. When the primary dendrite arm spacing on the body surface of each of the obtained cold rolling rolls was examined, the results shown in Table 3 were obtained.

As is clear from Table 3, forged steel rolls within the composition range of the present invention containing composite addition of Zr and Ni (Samples C and D)
It is clear that the -order dendrite arm spacing is small and the dendrite structure is refined. In the forged steel rolls of this invention of samples C and D,
In fact, it was confirmed that the skin roughness resistance was extremely excellent.

As is clear from the above explanation, the forged steel roll for cold rolling of the present invention is a Cr-Mo based forged steel roll in which the dendrite structure can be significantly refined by adding Ni and Zr in combination. Since it has less dendrite segregation, its roughness resistance is better than that of conventional Cr.
-It is significantly superior to Mo-based forged steel rolls, and there is no need to significantly increase the cooling rate during solidification of the ingot due to dendrite refinement, providing rolls with excellent surface roughness resistance at low cost. can.

[Brief explanation of the drawing]

Figure 1 is a correlation diagram showing the effect of combined addition of Ni and Zr on the number of primary dendrite arms in an ingot in Cr-Mo steel, and Figure 2 is a metal diagram showing the casting structure of a cross-section of a directionally solidified ingot. In the structure photograph, Fig. 2 (A) shows Ni,
In the case of no Zr addition, No. 211q (B) is Ni 0.51%
, the case of adding 0.49% Zr is shown, respectively.

Claims (1)

[Claims] C0.70-1.20% (weight%, same below), Si0
．． 50-1.20%, Mn0.30-1.00%, Cr
2.50-5.50%, Mo0.20-1.00%, N
A forged steel roll for cold rolling with a fine dendrite structure, containing 0.20 to 1.20% i, 0.10 to 0.60% Zr, and the remainder consisting of Fe and inevitable impurities.