JPH0578750A - Manufacture of forged steel roll for cold rolling - Google Patents

Abstract

PURPOSE:To improve the quality properties on the surface of a roll in forged steel roll and to eliminate spheroidizing treatment after forging. CONSTITUTION:At the time of manufacturing a forged steel roll by subjecting a cast material for a forged steel roll contg. 0.7 to 1.2% C and 2.0 to 12.0% Cr to hot forging and the following heat treatment, prior to the hot forging heating and diffusing treatment in the temp. range of 1200 to 1280 deg.C is executed in such a manner that the heating and diffusing parameter P calculated by the following formula: P=log(t)-(19840/T) (where (t) denotes the heating and holding time (min) and T denotes the heating temp. K) satisfies the range of -9.8 to -9.2, next, hot forging is executed at 1050 to 1200 deg.C at the rolling reduction of >=6% rolling reduction margin as well as >=1.6S forging ratio by using upper and lower V anvils, and the subsequent cooling is executed in such a manner that it is air-cooled till the temp. range of the Ms point or above to the Ms point +150 deg.C, and after that, refining heat treatment is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forged steel roll used for whirl rolls, intermediate rolls, etc. of a cold rolling mill, and particularly advantageously improves roll surface quality characteristics (especially uniformity of shotdal roll roughness), Moreover, the present invention intends to propose a manufacturing method that can omit the spheroidizing annealing process after forging.

[0002]

2. Description of the Prior Art Work rolls for cold rolling are required to have properties such as accident resistance, wear resistance, and hardening depth. On the other hand, rough skin resistance is a very important characteristic.
When the work roll is roughened, the roughened surface is also transferred to the surface of the plate to be rolled, the quality of the product surface is deteriorated, and when the roll is significantly roughened, it is necessary to re-grind the roll. This is the reason why the work roll for cold rolling is required to have excellent resistance to surface roughening.

By the way, dendritic crystals (dendrites) are formed on the roll during solidification during casting, and a unique dendrite pattern (dendritic dendritic part and interdendritic part) is formed on this surface during the forging process. The surface has uneven hardness (waviness) along this pattern, and also has uneven texture (fine particles and coarse particles). The hardness unevenness and the texture unevenness on the roll surface are the causes of the aforementioned rough skin.

Work rolls used for temper rolling include
In order to adjust the surface roughness of the material to be rolled, a roll whose surface is roughened into a dull (fine satin) is used. The roughening of the roll is usually performed by a shot blast method, that is, a grid corresponding to the roughness is projected toward the roll. At the time of this shot blast, the grid is not the same size one by one,
Since it has a certain particle size distribution, unevenness in roughness (waviness) occurs on the roll surface due to statistical fluctuations even when projected completely randomly. The unevenness of roughness due to the non-uniformity of the projection grid overlaps with the unevenness of hardness and texture of the roll surface described above to form a large unevenness of roughness (waviness) on the roll surface, resulting in the surface quality of the cold rolled product. It has a problem in that it affects the strip shape during rolling and lowers the productivity and disturbs the operation.

In order to solve these problems, a technique for miniaturizing dendrites has been considered, for example, Japanese Patent Laid-Open No. 61-9554.
No. 61 and No. 61-9445, P added and Z respectively
r, a method of performing a composite addition of Ni is disclosed, and JP-A-56-86611 discloses that the angle formed by the outer surface of the roll cylinder of the dendrite trunk is 15 degrees or more. There is. However, neither method is a technique for essentially reducing the hardness difference between the dendrite tree branches and the inter-tree parts,
It was hard to say that a roll that is strictly required to have no unevenness of roughness, such as a shot-dal roll, is sufficiently effective.

Further, in the production of such a forged steel roll for cold rolling, the high C--Cr type forged steel roll material after the forging is usually kept in a high temperature state without being cooled to room temperature in order to prevent cracking. Charge the heat treatment furnace as it is (so-called red material),
Next, spheroidizing annealing treatment was performed to convert the coarse carbide after forging into an appropriate spherical carbide. For such processing,
Iron and Steel Institute of Japan, "3rd Edition Steel Handbook (Volume V) Casting / Forging / Powder Metallurgy" Maruzen (Published May 31, 1982) p.330, table
It is explained in detail in 11.6.

For the spheroidizing annealing treatment and temper treatment after forging of such a roll material, the work roll for cold rolling has a surface hardness of Hs: 90 or more and a deep surface of the roll body as described above. Since a hardened layer and accident resistance are required, for that purpose, in the pre-process of the surface quenching of the roll body, it has a suitable spherical carbide by adjusting the crystal grains and the structure and the adjustment of the shaft hardness and the inside of the roll. This is because it is necessary to increase the toughness. The spheroidizing annealing treatment of the roll material is an indispensable step in order to obtain a suitable spherical carbide by adjusting the crystal grains and the structure of the roll material, but this treatment occupies the heat treatment furnace for about 150 hours, There is a problem that it requires a great deal of expense and time.

Therefore, the applicant previously proposed in Japanese Patent Laid-Open No. 2-282429 a method capable of producing a forged steel roll material having the same quality as that obtained by performing the spheroidizing annealing treatment, even though the spheroidizing annealing treatment is omitted. The recent demands for strict roll surface quality cannot be adequately dealt with, and the above problems cannot be said to be sufficiently solved.

[0009]

DISCLOSURE OF THE INVENTION The present invention advantageously solves the above-mentioned problems, and in order to improve the roll surface quality characteristics (especially, the uniformity of the shotdal roll roughness), the dendritic dendritic portion is used. Even if the spheroidizing annealing treatment is omitted, the high quality C-Cr system forged steel roll material with the same quality can be manufactured by reducing the hardness unevenness between the wood and the wood to the minimum value (or saturation value). The purpose is to propose a method for manufacturing a forged steel roll that can be manufactured.

[0010]

[Means for Solving the Problems] The inventors of the present invention reduce the unevenness of hardness between dendrite dendritic parts and inter-tree parts to a minimum value (or a saturation value) by applying appropriate heat diffusion, and thereby, the surface quality of rolls is improved. By being able to produce forged steel rolls with excellent properties (especially the uniformity of shot dull roll roughness), and by combining the spheroidizing action of heat diffusion treatment, forging method, cooling method after forging, and heat treatment for tempering However, even if the spheroidizing annealing treatment is omitted, it has been found that a high C-Cr type forged steel roll material of the same quality as in the case where this treatment is performed can be manufactured, and the present invention is made based on these findings. I arrived.

That is, the present invention is C: 0.7-1.2 wt%
(For the purpose of producing a forged steel roll by hot forging and subsequent heat treatment of a cast material for forged steel roll containing (hereinafter simply indicated by%) and Cr: 2.0 to 12.0%, prior to the hot forging, 1200 Heating diffusion treatment at a temperature in the range of 1280 ° C., heating diffusion parameter P P = log (t) − (19840 / T) calculated by the following equation (where t: heating holding time (min), T: The method for producing a forged steel roll for cold rolling is characterized in that the heating temperature (K) is applied in a range of -9.8 to -9.2.

The present invention also provides C: 0.7-1.2% and C
r: For forged steel roll casting material containing 2.0 to 12.0%, in hot forging and subsequent heat treatment to produce a forged steel roll, prior to the hot forging, 1200 to 1280
In the heat diffusion treatment at a temperature in the range of ℃, the heat diffusion parameter calculated by the following equation P P = log (t)-(19840 / T) (t: heating holding time (min), T: heating temperature (K )) Is satisfied in the range of -9.8 to -9.2, and then hot forging is performed at 1050 to 1200 ° C using the upper and lower V anvils to reduce the rolling allowance by 6%.
For cold rolling, which is characterized by forging with the above reduction amount and a forging ratio of 1.6 S or more, followed by cooling by air cooling to a temperature range of Ms point or more to Ms point + 150 ° C, and then heat treatment. It is a method for manufacturing a forged steel roll.

[0013]

[Function] Hardness unevenness at the dendrites and inter-trees of the dendrites on the surface of the roll material is due to the microsegregation of Cr and Mo. Therefore, by appropriate heat diffusion treatment prior to forging,
The unevenness of hardness is greatly reduced through the unclear dendrite pattern and the uniformization of the microstructure, and the roughness of the cold-rolled forged steel roll such as a shot-dal roll can be made uniform accordingly.

1 and 2, 0.90% C-4.5% Cr-0.6
The results of examining the hardness unevenness and the microsegregation of Cr and Mo when heat diffusion treatment was performed on various materials of% Mo-0.07% V under various conditions are shown. As is clear from the figure,
The roll subjected to the heat diffusion treatment (1200 to 1280 ° C) according to the present invention has a hardness of dendritic dendritic portion and inter-tree portion as compared with the heat diffusion treatment material (1180 ° C) at a temperature lower than the range of the present invention. The unevenness is reduced, and this uneven hardness is Cr,
Corresponds to reduce Mo microsegregation. The minimum value (or saturation value) of the hardness unevenness is obtained by performing the heat diffusion treatment at 1200 to 1280 ° C with the heat diffusion parameter P P = log (t)-(19840 / T) (where t is the heat retention time (mi
n), T: heating temperature (K)) in a range of -9.8 to -9.2.

The above heat diffusion treatment is also effective for omitting the spheroidizing annealing in the manufacturing process. That is, the normal forging temperature is 50 to 150 higher than the heating temperature (1050 to 1200 ° C).
Heat diffusion process (1200 ~ 1280 ℃) at high temperature ℃,
Then, at a normal forging heating temperature, it is possible to omit the spheroidizing annealing process by controlling the forging method to make the structure uniform and to refine the crystal grains, and by limiting the cooling conditions after forging. ..

When the temperature of the heat diffusion treatment is lower than 1200 ° C., the effect of reducing the microsegregation of Cr and Mo to promote the solid solution in the matrix is reduced and the effect of making the eutectic carbide into fine spheroids is small. On the other hand, when the temperature exceeds 1280 ℃, it becomes difficult to bond the voids, so the range was limited to 1200-1280 ℃. More effective diffusion can be obtained by controlling the temperature in the range of 1230 to 1280 ° C.

When the heating diffusion parameter P is larger than -9.2 (high temperature, long time heating), re-segregation of Mo occurs and the heating cost increases, which is not economical and therefore the upper limit is -9.2.
(During hot forging of the roll, the depth of the decarburized layer on the surface is not a big problem). On the other hand, when the parameter P is smaller than −9.8, ΔHv shown in FIG. 2 tends to increase, and the lower limit of −9.8 is set as the range within ΔHv: 60 which is allowable in the normal control range.

Regarding the conditions of forging and the subsequent heat treatment, in order to improve the surface properties of the roll, it may be appropriately determined under the conditions usually practiced.

Next, regarding the forging and heat treatment conditions, when the spheroidizing annealing step is to be omitted, it is essential to carry out as follows.

Forging heating temperature: 1050 to 1200 ° C. If the forging heating temperature is too low, the forging workability is poor, while if it is too high, the eutectic carbide in the segregated portion of the steel ingot is partially melted and the hot workability is lowered. Plastic processing becomes difficult. Therefore, the forging heating temperature varies depending on the Cr, Mo, and V contents, but
Limited to the range of 50-1200 ℃. More preferably 1080-11
If it is controlled within the range of 80 ℃, the workability will be more stable.

Forging method: upper and lower V anvil, reduction amount of 6% or more,
Forging ratio 1.6 S or more 50 to 150 ℃ higher than normal forging heating temperature (1050 to 1200 ℃)
When heat diffusion treatment (1200-1280 ℃) is performed at high temperature, the eutectic carbide in the ingot segregation part melts to generate voids, so it is necessary to forge the voids and separate the eutectic carbides by forging. The forging method uses the upper and lower V anvils and the rolling amount is 6%
As mentioned above, the training ratio is limited to 1.6 S or more. This is because the upper and lower V anvils can transfer a large amount of rolling force to the center of the steel ingot even if the amount of rolling is small compared to the flat anvil and apply a large amount of plastic working. If the amount of rolling is less than 6%. And the training ratio is 1.
This is because if it is smaller than 6 S, a sufficient crimping effect for void defect crimping cannot be obtained.

Cooling condition after forging: The forged product obtained under the above conditions has a martensitic transformation starting point Ms point (200 to 250 ° C. in the forged steel roll of the present invention) or more, Ms point + (50 to 15)
(0 ° C), and air-cooled to a temperature range of 300 to 400 ° C, to uniformly distribute the carbide. If the cooling rate after forging is slow, the carbide will become coarse, and this coarse carbide will remain after the heat treatment for heat treatment and surface quenching in the next step, so it is necessary to cool it by air after forging and distribute the carbide evenly. is important. However, from the standpoint of preventing cracking, the end temperature of air cooling after forging is in the temperature range from near the Ms point to the Ms point + 150 ° C, and after that, it is treated as red material and charged into the heat treatment furnace.
→ After the α phase transformation, heat treatment is performed to make the carbide spherical and toughen the matrix.

As described above, the eutectic carbide is finely spheroidized by the heat diffusion treatment at a high temperature, the microsegregation of Cr and Mo is reduced to promote the solid solution in the matrix, and the crystal grains are finely divided in the forging step. The spheroidizing process can be replaced by the spheroidizing annealing process because the spheroidizing of the carbide is carried out by the tempering heat treatment of red material after the carbide is dispersed uniformly by cooling after the forging and then the spheroidizing treatment is performed. Even if the annealing process is omitted, a roll material of the same quality can be obtained by performing this process. A block diagram of the manufacturing process is shown in FIG.

The heat treatment conditions differ depending on the specifications and material of the roll, and are appropriately determined within the above range in consideration of the hardness specifications of the roll body and the shaft.

The reason why the composition range of the forged steel roll is limited in the present invention is as follows.

C: 0.7 to 1.2% C is a component effective for improving hardenability and hardness,
In order to secure the hardenability and hardness required for a hardened forged steel roll, 0.7% or more is required, but if it exceeds 1.2%, the increase in hardness is not significant, so the range was limited to 0.7-1.2%.

Cr: 2.0 to 12.0% Cr is an effective component for obtaining the wear resistance required for cold rolling rolls, and therefore, it is necessary to contain 2.0% or more, but more than 12.0%. However, the hardenability is deteriorated, so the content is limited to the range of 2.0 to 12.0%.

Mo: 0.2 to 4.50% and V: 0.05 to 2.00% of 1 type or 2 types (in the case of 2 types, 0.50 to 5.50 wt% in total) Mo and V both form a composite carbide and the carbide itself. It is added to supplement the effect of the present invention by improving the wear resistance of. If the Mo content is less than 0.20% and the V content is less than 0.05%, the necessary wear resistance cannot be obtained, which is a disadvantage.
On the other hand, when Mo exceeds 4.50% and V exceeds 2.00%, ductility and toughness decrease, which causes the problem of easy occurrence of quench cracking. Therefore, Mo: about 0.20 to 4.50%, V: about 0.05 to 2.00%. Preferably.

Ni: 0.60 wt% or less Ni may be added in a trace amount in order to improve the hardenability and to secure the resistance to quench cracking. If Ni exceeds 0.60%, the amount of residual austenite increases and the hardness decreases, so it is preferable to set it to about 0.60% or less.

Si: 0.50 to 1.20 wt% Si is 0.50% in order to improve hardenability and to secure quench cracking resistance.
The above is added. If it exceeds 1.20%, these effects become small, so 0.50 to 1.20% is preferable.

Mn: 0.30 to 1.00 wt% Mn is an effective component for improving hardenability, and therefore 0.30% is necessary, but if it exceeds 1.00%, embrittlement becomes remarkable, so 0.30 to It is preferably about 1.00%.

[0032]

【Example】

Example 1 Steels having various compositional compositions shown in Table 1 were manufactured by ESR (electroslag remelting) method into four steel ingots each having a diameter of 850 mm and a length of 1800 mm.

[0033]

[Table 1]

Body diameter 610 mm, body length 1800 m from these steel ingots
When forging a forged steel roll material with a length of 3880 mm,
The method according to the present invention was applied to the two steel ingots in each charge, and the conventional method was applied to the other steel ingots in each charge. Here, in the method according to the present invention, the heat diffusion treatment is 1280 ° C. and 30 hours (P = −9.5), and in the conventional method, the heat diffusion treatment is 1180 ° C. and 23 hours (P = −10.5). In addition to the forging, the manufacturing process after the heat treatment was performed according to a general method for manufacturing a forged steel roll. The quality of the obtained forged steel roll is investigated by the completion inspection and the usage record, and the results are summarized in Table 2.

[0035]

[Table 2]

The hardness distribution of the roll surface of the obtained forged steel roll is shown in FIG. 4, the roll roughness distribution is shown in FIG. 5, and the comparison is made between Example ((a)) and Comparative Example ((b)). Indicate. As is clear from Table 2 and FIGS. 4 and 5, in the examples according to the present invention, the hardness unevenness between the dendritic dendritic part and the inter-tree part is significantly reduced as compared with the comparative example. The degree of uniformity was achieved.

Example 2 Steels having various compositional compositions shown in Table 3 were prepared by ESR (electroslag remelting) method into steel ingots having a diameter of 610 mm and a length of 1800 mm shown in FIG. 6 (a). I made four each.

[0038]

[Table 3]

From these steel ingots, the body diameter 420 shown in FIG.
In forging a forged steel roll having a length of mm, a body length of 1640 mm, and a total length of 4490 mm, the method according to the present invention was applied to one steel ingot (two pieces) of each steel type, and the conventional method was applied to the other steel ingots. The method according to the present invention is as follows: First, as heat diffusion treatment, 1280 ° C. for 30 hours for steels A and B and 12 hours for steels CG.
30 ℃, 30 hours, 1280 ℃, 30 hours for steel H to J, then normal forging heating temperature (A and B steel: 1180 ℃, D steel: 1150
℃, C, G steel: 1100 ℃, E, F steel: 1080 ℃, H steel: 1180
℃, I steel: 1180 ℃, J steel: 1180 ℃,) After forging to a forging ratio of 2S within a rolling reduction range of 6 to 10% using a top and bottom V anvil, the surface temperature of the forged product becomes 300 ℃. After air cooling, the material was treated as a red material and placed in a heat treatment furnace for temper treatment. Further, the conventional method is that after performing a predetermined forging (using an upper and lower V anvil, forging to a forging ratio of 2S within a range of a rolling allowance of 6 to 10%),
After normalizing and spheroidizing annealing in the heat cycle shown in, heat treatment was performed. The manufacturing process after the heat treatment was performed according to a general method for manufacturing a forged steel roll. The quality of the thus-obtained forged steel roll was investigated by completion inspection and actual use, and the results are summarized in Table 4.

[0040]

[Table 4]

As is clear from the table, the examples according to the present invention have the same quality as the comparative examples obtained by the conventional method even if the spheroidizing annealing is omitted.

[0042]

As described above, according to the present invention, the roll surface quality characteristics can be improved, and therefore, the productivity is improved and the operation is stabilized in the rolling line of the cold rolled steel sheet. Further, the spheroidizing annealing can be omitted, so that the manufacturing cost can be reduced and the efficiency can be significantly improved.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of heat diffusion treatment on reducing hardness unevenness.

FIG. 2 is a graph showing the effect of heat diffusion treatment on reduction of microsegregation.

FIG. 3 is a block diagram of a manufacturing process according to the present invention.

FIG. 4 is a graph showing a hardness distribution on a roll surface of a forged steel roll.

FIG. 5 is a graph showing a roughness distribution on a roll surface of a forged steel roll.

FIG. 6 is an explanatory diagram showing sizes of a steel ingot and a forged product in the example.

FIG. 7 is an explanatory diagram showing a heat treatment cycle in a comparative example.

Claims (2)

[Claims] 1. A forged steel roll casting material containing C: 0.7 to 1.2 wt% and Cr: 2.0 to 12.0 wt% is subjected to hot forging and subsequent heat treatment to produce a forged steel roll. Prior to forging, the heat diffusion treatment at a temperature in the range of 1200 to 1280 ° C. is performed by the heat diffusion parameter P P = log (t) − (19840 / T) calculated by the following formula (where t: heat retention time). (min), T: heating temperature (K)) satisfying the range of -9.8 to -9.2, and applying it, The manufacturing method of the forged steel roll for cold rolling characterized by the above-mentioned. 2. Hot forging and subsequent heat treatment are applied to a cast material for forged steel roll containing C: 0.7 to 1.2 wt% and Cr: 2.0 to 12.0 wt% to produce a forged steel roll. Prior to forging, a heat diffusion treatment at a temperature in the range of 1200 to 1280 ° C. is performed by a heat diffusion parameter P P = log (t) − (19840 / T) (t: heat retention time (min ), T: heating temperature (K)) satisfying the range of −9.8 to −9.2, and then hot forging is performed at 1050 to 1200 ° C. using an upper and lower V anvil with a reduction amount of 6% or more. And a forging ratio of 1.6 S or more, and subsequent cooling is air-cooled to a temperature range of Ms point or higher to Ms point + 150 ° C, and then heat-treated for tempering. ..