JPH0669632B2 - Manufacturing method of hardfacing roll - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a build-up roll suitable for various rolls such as an iron-making machine and a paper-making machine.

(Prior art and problems to be solved) In various rolls of iron making machines, various rolls of paper making machines,
Conventionally, overlay welding has been frequently used to impart wear resistance, heat resistance, and oxidation resistance.

Among them, especially those requiring high hardness, a high-speed steel build-up metal having excellent crack resistance was used. For example, JP-A-61-1709, JP-A-60-162590 and JP-A-63
-307442 and others have been proposed.

However, since the overlay metal is reheated during welding, the occurrence of a reheat zone is unavoidable. Especially in the case of high-speed steel-based molten alloys based on age hardening by heat treatment, the reheat zone and non-reheat zone In some cases, hardness becomes non-uniform, which poses a practical problem. This problem is not eliminated even by the subsequent heat treatment (tempering), and uneven wear occurs during use.

For this reason, a method of performing solution treatment after overlay welding and remelting and precipitating the precipitated carbide generated in the reheat zone is considered, but this method includes high-frequency heating, flame hardening, etc. However, it has not been put to practical use because of problems such as cracking of the built-up portion during solution treatment and overaging.

On the other hand, in the case of high-speed steel, quenching and tempering are usually performed, but for example, quenching of molds is 550 to 600 ° C.
After the first stage of 850 ~ 900 ℃, the second stage of 850 ~ 900 ℃, to raise the quenching temperature, and then rapidly cool to 400 ~ 600 ℃,
Generally, a temperature lower than that is gradually cooled. However, when this method is applied to a hardfacing roll, it cannot be applied to the hardfacing roll because it exceeds the tempering temperature of the base metal, and therefore, only the hardfacing layer needs to be solution treated, and The same problem occurs with the roll roll.

The present invention solves the above-mentioned problems of the prior art, and in a build-up roll having a high-speed steel-based build-up metal, excellent crack resistance during solution treatment and uniform high hardness can be stably obtained. The purpose is to provide the technology to be used.

(Means for Solving the Problems) The inventors of the present invention have conducted extensive studies on the problems of cracking and overaging of the above-described build-up portion, and as a result, have been greatly affected by the chemical composition of the deposited metal, and have been identified. The present invention was made based on the finding that it can be put to practical use by adopting a solution treatment under the conditions.

That is, the present invention, C: 0.6 ~ 1.4%, Cr: 1.4 ~ 7.0%, M
o: 6.0-14.0%, V: 0.4-3.0%, Co: 1.4-5.0%, Mn: 0.3
~ 2.0%, Si: 0.1-2.0%, W + Nb + Ti: less than 5.0%, the remainder is iron-based weld metal consisting of iron and impurities, and after the build-up welding on the surface of the base material, the solution temperature of the roll surface 1150 ~ 1300 ℃, cooling rate up to 800 ~ 500 ℃ is 50 ℃
The solution treatment is performed under the condition of not less than 1 minute / minute, and the age hardening treatment is performed.

The present invention will be described in more detail above.

(Function) When the deposited metal is a high-speed steel system, it has been found that the cracking of the built-up portion during the solution treatment is greatly affected by the solution temperature.

That is, at a temperature of less than 1150 ° C., the liquefaction of the eutectic carbide partially reduces the strength of the grain boundary, and the matrix cannot withstand the heat shrinkage force and cracks. On the other hand, it was found that liquefaction of eutectic carbides proceeded in the temperature range higher than 1150 ° C, and cracks did not occur when the eutectic carbides were rapidly cooled from higher temperatures. Therefore, the solution temperature must be 1150 ° C or higher.

Furthermore, after solution treatment, the cooling temperature from 800 to 500 ℃ is 50 ℃.
It turns out that it is necessary to do it at a speed of at least 1 minute.

That is, regarding the problem of overaging due to improper cooling method, if the cooling rate is slow, the maximum heating temperature of the liquefaction process
It was found that during the cooling up to 500 ° C, the precipitation of carbides already started and the agglomeration of carbides proceeded, which resulted in a decrease in hardness in some cases. Therefore, as a result of investigating the optimum cooling rate, when the cooling rate up to 500 ° C is less than 50 ° C / min,
It was found that the precipitation of carbides during cooling gradually increases the hardness and enhances the effect of the subsequent age hardening treatment.

The temperature was measured using a radiation thermometer, and the measurement position was on the roll surface.

It was also found that the composition of the deposited metal is an important point in improving the crack resistance during solution treatment.

That is, it was found that when the deposited metal contained a large amount of Mo, the interfacial bond strength between the eutectic carbide and the matrix primary crystal austenite grains was significantly improved, and liquefaction cracking of the eutectic carbide was prevented. It has been found that, especially in the composition of the deposited metal, when the Mo content is less than 6.0%, cracking is likely to occur during the solution heat treatment, and it is difficult to prevent the crack only by optimizing the solution heat treatment conditions.

The present invention is based on the above findings, by a combination of a weld metal having a component composition excellent in crack resistance during solution heat treatment, and an optimum solution heat treatment condition, and particularly, a reheat region of a cladding metal and a non-heat region. The non-uniformity of hardness in the reheat zone can be eliminated, and uneven wear that occurs during use of the overlay roll can be prevented, which has led to practical application.

Next, the reasons for limiting the chemical components in the present invention will be described.

C: 0.6 to 1.4% C is an essential element for enhancing the hardenability of steel, and has an action of forming a secondary hardening phenomenon by tempering in combination with other carbide forming elements. However, if it is less than 0.6%, secondary hardening is hardly obtained, and if it exceeds 1.4%, hot cracking at the time of welding increases, which is not preferable.

Cr: 1.4-7.0% Cr has the effect of increasing the hardness as it is welded and stabilizing it. Although it has a low contribution to secondary curing, it is added because it imparts oxidation resistance. However, if it is less than 1.4%, it has no effect, and if it exceeds 7.0%, it promotes hot cracking during welding, so it is made 7.0% or less.

Mo: 6.0 to 14.0% Mo is a main element that causes the secondary tempering. But 6.
If it is less than 0%, the hardening is small, and hot cracking occurs during welding and solution treatment. Further, when it exceeds 14.0%, its curing is saturated and it is uneconomical, so it is set to 14.0% or less.

V: 0.4-3.0% V is effective in preventing hot cracking during welding. The effect is obtained at 0.4% or more, but if it exceeds 3.0%, the peelability of the slag at the time of welding deteriorates, which is not preferable because it poses a practical problem.

Co: 1.4 to 5.0% Co has the function of preventing shrinkage cracking during welding and promoting secondary hardening. However, less than 1.4% has no effect, and 5.0%
If it exceeds, it will be uneconomical, so 1.4 to 5.0% range.

Mn: 0.3-2.0%, Si: 0.1-2.0% Both of Mn and Si are components that exert a deoxidizing action and clean the steel. However, Mn is less than 0.3%, Si is 0.1
If it is less than 1.0%, the effect is small, and if it exceeds 2.0%, the crack resistance deteriorates, which is not preferable.

W + Nb + Ti: Less than 5.0% W, Nb, and Ti are secondary hardening elements, and appropriate amounts of them are added. Addition of less than 5.0% has the effect of increasing hardness, but addition of more than 5.0% is not preferred because shrinkage cracking during welding tends to occur. The amount added is W, N
It is the total amount of one or more of b and Ti.

Next, manufacturing conditions will be described.

The weld metal having the above component composition is obtained by overlay welding on a roll base material made of an appropriate material by a conventional method, but it is necessary to perform solution treatment under the following conditions.

Solution heat treatment temperature: 1150 to 1300 ° C Various solution heat treatment methods can be considered, but high frequency heating or flame hardening is generally used. At that time, if the solution temperature is less than 1150 ° C, cracking during solution treatment is unavoidable, and the solution carbide is not sufficiently solidified and the precipitated carbide is not sufficiently solid-soluted. Will be insufficient. On the other hand, when the temperature exceeds 1300 ° C, the melting point of the weld metal is exceeded, which is not practical.

Cooling rate: 50 ° C / min or more If the cooling rate from the solution temperature to 800-500 ° C is 50 ° C / min or more, cooling can be performed without impairing the solutionizing effect, but if it is less than 50 ° C / min, cooling is in progress. Precipitation of carbides begins at and is gradually aged, which is not preferable. It should be noted that the faster the cooling rate is, the better, but when the applied member is large, the excessive cooling rate causes shrinkage cracking, so it goes without saying that the cooling is performed within a cooling rate range in which no cracking occurs.

Preheating before solution heat treatment Preheating before the main heating of the solution heat treatment has the effect of preventing cracks during the solution heat treatment, so it may be preheated if necessary. In that case, if the preheating temperature is less than 200 ° C., that effect is not obtained, and if it exceeds 500 ° C., the cooling rate at the time of cooling becomes slow, which causes overaging, which is not preferable. If the overlay roll component is small, preheating can be omitted.

Age hardening treatment after solution heat treatment After solution treatment, fine carbide is dispersed in matrix,
Precipitation and age hardening treatment are performed to increase hardness. However, if the heating temperature is lower than 500 ° C, the temperature will be below the carbide precipitation temperature, and if the heating temperature exceeds 650 ° C, the precipitation and agglomeration of the carbide will proceed rapidly and the hardness will decrease, so the heating temperature will be 50%.
The temperature is preferably 0 to 650 ° C.

At that time, the holding time is also one of the factors, and it is most preferable to perform the heat treatment at the holding time t such that the value of the so-called Larson-Miller parameter P shown below falls within the range of 15.5 to 18.5.

P = T (logt + 20) × 10 ^-3 where T: heating temperature (absolute temperature) t: holding time (hr) In this case, if the value of P is less than 15.5, carbide precipitation is insufficient and the hardness is low. , P values of more than 18.5 are not preferable, because carbide precipitation proceeds, and they agglomerate and coarsen, resulting in a decrease in hardness. The optimum heating conditions may be selected according to the aging state after the solution treatment.

Next, examples of the present invention will be described.

(Example) Overlay welding was performed on a base material under the following welding conditions to prepare a test roll having a weld metal having the chemical composition shown in Table 1.

Then, solution treatment and age hardening treatment were performed under the conditions shown in the table.

[Welding conditions]

Base material: S25C 〃 Dimensions (mm): 300φ × 500 to 1000l Wire diameter: 3.2mmφ Current: 300 to 400A (DCRP) Arc voltage: 23 to 25V Speed: 40cpm Preheating pass temperature: RT to 400 ℃ Formation Method: 3-layer build-up Table 1 shows the results of examining whether cracking occurred during solution treatment and hardness after age hardening treatment.

As is clear from Table 1, in all the examples of the present invention, no cracks were generated during the solution treatment, and the hardness after the age hardening treatment was high, and the variations in hardness were small.

On the other hand, in the comparative example, even if cracking occurs during solution treatment, or even if cracking does not occur, high hardness cannot be obtained without variation. Some have already cracked during overlay welding.

(Effects of the Invention) As described in detail above, according to the present invention, in a build-up roll having a high-speed steel-based weld metal having a specific component composition, cracking does not occur, and high hardness does not vary. It is obtained stably, and in particular, it is excellent in crack resistance during solution treatment and can prevent uneven wear during use of the roll. Therefore, the effect of enabling practical use is remarkable.

Claims (4)

[Claims] 1. By weight% (hereinafter the same), C: 0.6 to 1.4%,
Cr: 1.4-7.0%, Mo: 6.0-14.0%, V: 0.4-3.0%, Co: 1.
4-5.0%, Mn: 0.3-2.0%, Si: 0.1-2.0%, W + Nb + T
i: less than 5.0% is contained, the remainder is iron-based weld metal consisting of iron and impurities, which is overlay welded on the surface of the base metal, and the roll surface has a solution temperature of 1150 to 1300 ° C and 800 to 500 ° C. A method for manufacturing a hardfacing roll, which comprises subjecting the solution treatment to a cooling rate of 50 ° C / min or more and then subjecting it to an age hardening treatment. 2. The method according to claim 1, wherein preheating at 200 to 500 ° C. is performed before the solution heat treatment. 3. The heating temperature of the age hardening treatment is 500 to 650 ° C.
The method according to claim 1 or 2, wherein 4. A heating temperature of 500 to 6 as the age hardening treatment.
The heat treatment is performed at 50 ° C. for a holding time t such that the value of the following parameter P is within the range of 15.5 to 18.5.
The method described in. P = T (logt + 20) × 10 ^-3 where T: heating temperature (absolute temperature) t: holding time (hr)