JPH01111818A - Production of forged steel roll for cold rolling - Google Patents

Abstract

PURPOSE:To produce a forged roll for cold rolling having excellent accident resistance by heating a stock consisting of specifically composed C, Si, Mn, Cr, Mo, Ni, Al, and Fe to a specific temp., and subjecting the heated steel to force cooling then to tempering at a specific temp. immediately after the cooling. CONSTITUTION:The stock contg. 1.0-2.0wt.% C, 0.3-2.0% Si, 0.3-2.0% Mn, 7-12% Cr, 0.2-1.5% Mo, 0.3-1.5% Ni, and <=0.02% Al, contg. 0.02-0.30% Nb or V in total at need and consisting of the balance Fe and inevitable impurities is heated to 900-1,100 deg.C and is then forcibly cooled to form the structure in which >=50% residual austenite is assured. The steel is thereafter immediately tempered to 400-600 deg.C without subjecting the steel to a sub-zero treatment. The above-mentioned residual austenite is thereby changed to martensite. Carbonitrides of Cr, Mo, V, Nb, etc., are deposited simultaneously therewith. The roll for low-temp. rolling which is highly resistant to wear, is dulled in susceptibility to heat and is improved in the accident resistance is thereby obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing rolls for cold rolling of metal;
The present invention relates to a method for manufacturing a quenched and tempered rolling roll made of forged steel, which has excellent wear resistance and is less susceptible to rolling accidents such as slipping and squeezing (thermal shock).

[Prior art] Conventionally, metal cold rolling rolls such as steel strips have a weight ratio of C
a75~0.95%, Cr2~5%, Moo, 15~0
．． Based on 55% ingredients, NIl, 0% or less, vo,
Hardened rolls made of forged steel with an appropriate addition of 5% or less have been used.

However, with recent cold rolling rolls, there are increasing demands for improved roll consumption, high reduction rolling, schedule-free rolling, etc., and the usage conditions for the rolls are becoming increasingly severe. The damage caused by thermal shock due to accidents is also increasing.

Cracks that occur on the surface of the rolls due to thermal shock during these rolling accidents are thought to occur because plastic strain caused by restraint of thermal expansion due to temperature rise is converted into large tensile stress during cooling. It is believed that this crack not only causes a decrease in the roll consumption rate, but also
This is the starting point for spalling.

However, it is difficult to completely eliminate these rolling accidents, and rolls are difficult to crack due to thermal shock.
Furthermore, there is a demand for something with excellent accident resistance so that even if an accident occurs, it will be small.

In addition, slipping is likely to occur when the initial roughness decreases due to wear, and a roll material with excellent wear resistance is required from the standpoint of the unit consumption of the roll.

[Problem to be solved by the invention] The structure of conventional rolls is mainly composed of low-temperature tempered martensite, and also consists of less than 10% carbon/nitride and less than 10% retained austenite. . Therefore, wear resistance depends on the amount of residual carbon/nitride and the hardness of the matrix, and a carbon/nitride amount of 10% or less is not sufficient.

In addition, if you try to increase the quenching depth and obtain sufficient quenching hardness to the target depth position, there will be a lot of retained austenite after quenching on the surface side where the cooling rate is high, making it difficult to achieve sufficient quenching. Since hardness cannot be obtained, it is necessary to perform sub-zero treatment (low temperature treatment) within a certain period of time after quenching and cooling.

In addition, after sub-zero treatment, tempering is further performed for the purpose of hardness adjustment, etc., but in that case, if low temperature tempering is not performed at a temperature of 200°C or less, the wear resistance will decrease due to the decrease in hardness due to tempering, and low temperature tempering is also necessary. Therefore, it is highly sensitive to heat, and there are also problems in terms of the effects of rolling accidents, that is, its accident (thermal shock) resistance.

The present invention solves these problems and provides a method for manufacturing a cold rolling roll with excellent wear resistance and accident resistance.

[Means for Solving the Problems] The present invention increases Cm to increase residual carbon and nitrides, and at the same time increases the amount of Cr to prevent an increase in Cff1 in the matrix and ensure ductility. Also, by increasing the heating temperature, Cr, Mo, Nb, V
The necessary amount of carbon/nitride is dissolved in austenite to improve hardenability, and by forced cooling after heating, an appropriate amount of residual austenite is secured, and the temperature is 400 to 600℃ without sub-zero treatment. The remaining austenite is changed into martensite by tempering, and at the same time, a part of the matrix transformed into martensite after quenching is changed into tempered martensite, and Cr, which was partially dissolved in solid solution by tempering, is By re-precipitating the carbon/nitrides of Mo and the carbon/nitrides of V and Nb, the final result is a mixture of martensite obtained by tempering, tempered martensite, carbon/nitrides, and a small amount of retained austenite. The objective is to obtain a hardened structure with high elasticity and toughness.

That is, during quenching heating, Cr dissolved in austenite
400-600 after quenching carbides such as Mo, Nb, and V.
Secondary hardening by precipitation at ℃ and 79% Cr
By adding 6 or more and 1296 or less, it is effective to dissolve C into solid solution in the carbon and nitrides precipitated during tempering and retard the agglomeration of carbon and nitrides. Amount of C, Cr, Mo or Nb dissolved in solid solution,
Austenite in which elements such as V and 0.3 to 1.5% Ni added as a solid solution remains as austenite at room temperature after forced cooling, and then transforms into martensite by tempering at 400 to 600 ° C. They discovered that it is possible to manufacture rolls with the target hardness even if the tempering temperature is increased.

In addition, an increase in carbon/nitride increases the modulus of longitudinal elasticity and prevents flattening under roll load, contributing to improvement in wear resistance and accident resistance.

The roll manufacturing method of the present invention will be explained in detail below.

The roll manufacturing method of the present invention basically involves adding an appropriate amount of special ingredients to the steel material for rolls, and then applying effective heat treatment to bring out the characteristic effects, and the tempering temperature is significantly higher than that of conventional rolls. The aim is to desensitize heat sensitivity by increasing it.

That is, in order to increase the amount of Cr added and fix it as Cr carbon/nitride, add a corresponding amount of Cr, disperse fine Cr carbon/nitride throughout the structure, and further improve the roll surface during quenching. to the desired depth, ensuring the residual austenite m necessary to obtain sufficient hardness after tempering, the amount of residual carbon and nitrides, and secondary hardening by precipitating as carbon and nitrides during tempering. Cr, Mo, and Nb to make it sufficient.

Due to the dissolution of carbon and nitrides such as V into austenite, 9
Heat to a temperature of 00-1100°C.

After heating, it is forced to cool down. The carbon/nitride forming element Cr is then tempered at a temperature of 400 to 600° C. without subzero treatment.

Secondary hardening is achieved through the precipitation of carbon and nitrides such as Mo+Nb and v, and softening is delayed by increasing the amount of carbon and nitrides added to the carbon and nitrides.
Furthermore, by transforming residual austenite into martensite after forced cooling, the desired hardness can be obtained, and by increasing the tempering temperature to 400 to 600°C, which is higher than the conventional method, cooling with excellent accident resistance can be achieved. The purpose is to obtain a roll for inter-rolling.

Next, the reasons for limiting the chemical components in the manufacturing method defined by the present invention will be explained.

First, C forms carbides with additive elements such as Cr, Mo, Nb, and V, and contributes to improving wear resistance;
If C is less than %, in the case of the present invention, there is a large amount of Cr, and C is used to form carbides with Cr, and precipitation hardening of Mo, Nb, and V as carbon/nitrides cannot be expected. On the other hand, if it exceeds 2.0%, the amount of carbon/nitride is sufficient, but the toughness and elongation of the matrix are significantly reduced, making it unsuitable for cold rolling rolls.

SI has a deoxidizing effect during the melting process, and at the same time is dissolved in solid solution in the matrix, increasing the hardness after quenching. In order to maintain high hardness and high wear resistance, which is the objective of the present invention,
At least 0.3% of Sl is required, and if it is less than this, it is difficult to obtain the rolling roll targeted by the present invention.

Moreover, if it exceeds 2%, embrittlement becomes significant, which is not preferable. Therefore, it was set at 0.3 to 2.0%.

Mn is effective in improving the strength and toughness of the matrix as well as improving the hardenability, but these effects cannot be observed if it is less than 0.3%. Moreover, if it exceeds 2.0%, retained austenite increases more than necessary, which adversely affects elongation and toughness after tempering, which is not preferable. Therefore, the limited range was set to 0.3 to 2.0%.

Cr is one of the important elements of the present invention, and it forms a solid solution in the matrix and significantly improves hardenability, and also combines with C to form high hardness carbon/nitride, which significantly improves wear resistance. . The reason why the lower limit is set to 7% in the present invention is to ensure that the required amount of carbon and nitride is obtained by heating during quenching, and to dissolve all the carbon and nitride necessary to leave sufficient residual austenite in the austenite after quenching. This is to retard the decomposition of martensite and the softening due to the agglomeration of generated carbon and nitrides during tempering.
It is difficult to ensure hardness and wear resistance after tempering at 00 to 500°C. The upper limit was set at 12% in order to prevent embrittlement due to excessive amounts of carbon and nitrides.

Mo, like Cr, is one of the important elements of the present invention, and part of it dissolves in the matrix and improves hardenability, but the rest combines with C and precipitates as carbon/nitride during tempering. do.

This precipitation is noticeable at temperatures above 400°C.

In this case, Mofi depends on the amount of other carbon/nitride forming elements of the present invention, but within the specified range of the amounts of Cr, V, and Nb of the present invention, the most appropriate amount is 0.2 to 1.5%. If the content is less than 0.2%, the target wear resistance cannot be obtained during high-temperature tempering, and if it exceeds 1.5%, the effect is saturated. Therefore, the limited amount of Mo was set to 0.2 to 1.596.

Ni is necessary for the purpose of increasing the hardened layer from the surface of the roll in order to lower the transformation temperature and improve the hardenability, especially the hardening depth. In the roll of the present invention, at least 0.3% is required within the limited range of other elements, but if too large a amount is added, more retained austenite than necessary and stable austenite will be produced, resulting in the The desired hardness cannot be obtained. This upper limit is 1.5%.

Al is necessary as a deoxidizing agent during dissolution, but in the present invention, since the amount of C is large, only a small amount of A, 17 as a deoxidizing agent is required.
Further, in order to avoid inclusion of inclusions such as A II 20 a and AfiN, only the upper limit was set to 0.020%.

In the present invention, even if one or both of V and Nb are added in addition to these elements, carbon/nitrides are similarly formed by bonding with C, and secondary hardening during tempering can be expected. This facilitates the production of a highly wear-resistant mill roll with high accident resistance, which is the object of the present invention.

In order to achieve this effect, the total amount of one or both of Nb and V is 0.02% or more. On the other hand, if the amount increases, the amount of eutectic carbide increases, and if it becomes excessive, it will precipitate in a network shape and will not be crushed even if forged, resulting in a significant decrease in toughness, which is undesirable. This limit amount is N
The total amount of one or both of b and (i) is 0.30%.

Elements other than those described above are not particularly limited, but impurity elements, especially P, S, and oxides, become inclusions and become the starting point of cracks in the rolling roll, which is the object of the present invention.
It goes without saying that it is preferable to reduce as much as possible 0, which causes spalling, and to reduce these trace elements and nonmetallic inclusions, ESR method, VOD method, LF method, etc. It is preferable to adopt the refining method.

Next, the reason for limiting the manufacturing conditions of the present invention will be explained.

In the present invention, after forging steel having the above-mentioned chemical composition into a roll material of a predetermined shape and size, the desired characteristics of the rolling roll are secured by heat treatment.However, regarding the forging method and conditions, In order to maintain the inclination angle of the columnar crystals in the surface layer of the steel ingot, it is preferable to perform relatively light reduction forging at a forging ratio of 2.0 or less.

Heat treatment is performed after forging, and after annealing, heat treatment is performed to spheroidize the nitride, followed by forced heating, cooling, and tempering to ensure the desired properties of the rolling roll.

In the case of the roll manufacturing method of the present invention, in the tempering process after forced cooling, as described above, <Cr, Mo, Nb.

By adding V, etc., the decrease in hardness during tempering is minimized due to the secondary hardening due to the composite precipitation of carbon and nitride of these elements and the agglomeration retardation effect due to the solid solution of Cr into carbon and nitride. .

Furthermore, by adding appropriate amounts of Cr, Nl, Mo, etc. and adjusting the concentration of alloying elements in austenite at the start of forced cooling, residual austenite is left after forced cooling, and this is further reduced to 400 to 60%.
This method utilizes transformation into martensite during tempering at a high temperature of 0°C, and in order to maximize these effects, the heating temperature before forced cooling is set to a temperature at which various carbons and nitrides dissolve, that is, 900°C. ℃ or higher is required.

However, if the temperature is too high, rapid grain growth of austenite will occur due to heating, the toughness will not recover even after the specified heat treatment, and large network carbon/nitrides will precipitate again during tempering.
This causes toughness deterioration.

Furthermore, if the temperature at the start of forced cooling is too high, excessive thermal stress will be generated during forced cooling, which will induce cracking, which is undesirable, and this limit temperature is 1100°C. Therefore, the heating temperature before forced cooling was limited to 900 to 1100°C.

In the case of heating before forced cooling, even if the entire roll is heated to a predetermined temperature, it is not possible to obtain a sufficient cooling rate for the roll surface layer and the hardness guaranteed depth range, so heating to the target temperature is not possible. The range is 50~too m from the surface of the roll material.
The depth is preferably up to m, and the heating means for this purpose is preferably a heating method using low frequency to medium frequency induction or a combination thereof, such as a continuous partial heating and cooling method.

Cooling after heating is performed at a depth of about 50 mm from the surface of the roll body.
It is necessary that the structure is uniform up to 100 mm and that it is possible to obtain sufficient hardness during tempering.

The method is not particularly limited, but a well-controlled forced cooling method such as a high-pressure jet stream from a water-cooled nozzle is desirable.

After cooling, conventional cold rolling rolls undergo a so-called sub-zero treatment to increase quench hardness by cooling some residual austenite to a predetermined temperature below 0°C in order to turn it into martensite, and then heat it to 200°C. Tempering was performed at a low temperature of
The next step, tempering at 400 to 600°C, transforms it into martensite.

In this case, the reason why the amount of retained austenite is limited to 50% or more in the present invention is that if it is less than this, the amount of austenite that will be transformed into martensite during the subsequent tempering at 400 to 600°C will be small, resulting in the desired hardness. This is because it becomes impossible to obtain a roll with wear resistance.

Tempering is performed by reheating to 400 to 600°C. The purpose of this is to convert the austenite that exists even after forced cooling into martensite, to increase the toughness of the martensite partially formed after forced cooling, and to finely precipitate carbons and nitrides such as Cr, Mo, Nb, and V that are dissolved in solid solution. The objective is to obtain a predetermined material for the roll through secondary curing.

The reason why the temperature was set at 400 to 600°C was because the most effective roll with the least heat sensitivity during rolling accidents could not be obtained at a lower temperature, and the reason why the upper limit was set at 600°C was because the temperature was lower than this. This is because martensite decomposes violently at high temperatures, making it impossible to obtain the desired hardness and, as a result, making it impossible to manufacture rolling rolls with excellent wear resistance.

[Example] Table 1 shows the chemical components (kA-1 to A-6) of the test materials of the present invention melted in a 50 kg vacuum melting furnace, and the melted components (No., B-1 to B) for comparison. -2) is shown.

Forging and spheroidizing annealing were performed under the conditions shown in the margin.

Furthermore, after heating and forced cooling under the conditions shown in Table 2, tempering was immediately performed.

Accident resistance was investigated by measuring hardness, which directly indicates wear resistance, and by conducting a heat shock test, which is known as a test method for evaluating accident resistance (thermal shock).

The results are also shown in Table 2.

According to these results, in manufacturing tests of rolls manufactured using the chemical composition and heat treatment conditions according to the present invention, the hardness that directly indicates wear resistance was good as shown in Nα1 to Nα6, and the accident resistance was excellent. Accident resistance as the object of the invention;
Rolls with excellent wear resistance can be manufactured.

For these, N[L7. No. 8 has a component outside the chemical component range of the present invention, and No. 9. No,
Although the chemical components of IO are within the chemical composition range of the present invention, the heat treatment conditions are outside the limited range, and it is impossible to manufacture the roll intended for the present invention in either case.

Heat forging ratio 2.0 at 1100℃ from a 114φ round steel ingot
Forging was performed at 800°C, and carbide spheroidizing annealing was performed at 800°C.

[Effects of the invention] As described above, by adding a large amount of Cr to the cold rolling roll material, martensite decomposition is delayed during tempering, and by adding appropriate amounts of Mo, Nb, V, etc., these carbon/nitrides are suppressed during heating. A suitable amount of material is dissolved in austenite, and after forced cooling, it becomes a mixed structure of residual austenite, martensite, carbon and nitride, and without further sub-zero treatment.
By tempering at a temperature of 00 to 600°C, residual austenite becomes martensitic Cr, Mo, or Nb,
By utilizing the secondary precipitation hardening effect of V or the like, it is possible to produce a low-temperature rolling roll that reduces the heat sensitivity caused by tempering at high temperatures and improves accident resistance, which is highly effective.

Agent Patent Attorney Tatsuo Chanoki Procedural Amendment (
(Voluntary) April 8, 1986

Claims (1)

[Claims] 1. C1.0-2.0% by weight, Si0.3-2.0%, Mn0.3-2.0%, Cr7-12%, Mo0.2-1.5 %, Ni 0.3 to 1.5%, Al 0.02% or less, and the balance is Fe and unavoidable impurities.
After heating to a temperature of 1100°C and forced cooling to create a structure with retained austenite of 50% or more, immediately
A method for manufacturing a forged steel cold rolling roll, characterized by tempering at a temperature of 0 to 600°C. 2. Weight ratio: C1.0~2.0%, Si0.3~2.0%, Mn0.3~2.0%, Cr7~12%, Mo0.2~1.5%, Ni0.3~ 1.5%, Al 0.02% or less, and the total of one or both of Nb and V is 0.02 to 0.3
2. The method for producing a cold rolling roll made of forged steel according to claim 1, wherein a material is used in which the remaining part is Fe and unavoidable impurities.