JPH03126844A - Steel for hot roll having excellent wear resistance - Google Patents

Abstract

PURPOSE:To manufacture the steel for a roll for hot rolling having excellent wear resistance by mixing the atomizing powder of a high alloy steel having a specified compsn. with the powder of hard metallic carbides and compacting the mixed powder into the shape of a roll by a powder metallurgy method. CONSTITUTION:The powder of a high alloy subjected to particle size regulation so that the particle size of the atomizing powder having a compsn. constituted of, by weight, 1.5 to 4.8% C, 0.2 to 2.0% Si, <1.0% Mn, 3.0 to 8.0% Cr, <10% Mo, <10% W, 5 to 15% V and the balance Fe as well as satisfying W%+2Mo%>=4.0% and C% >=0.4%+0.2V%+0.033(W%+2Mo%) or furthermore contg. <10% Co is regulated to 4 to 10mum is mixed with 5 to 20vol.% of at least one kind from among hard carbides such as WC, MoC and TaC having 4 to 10mum average particle size. The mixed powder is regulated as a raw material, which is subjected to compacting into the shape of a roll by hot isostatic pressing (HIP), is thereafter sintered and is subjected to high temp. quenching and tempering treatment, by which a work roll for hot finish rolling having excellent wear resistance can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention provides a hot rolling mill with excellent wear resistance suitable for use under harsh conditions, such as finishing work rolls for hot rolling of steel materials. The present invention relates to steel materials for rolls, and particularly to steel materials for hot rolls manufactured by a powder metallurgy method in which wear resistance is improved by dispersing hard carbides in a matrix of high alloy steel.

(Prior art) Hot rolls for steel used under harsh conditions, such as finishing rolls used for hot rolling of hot rolled steel sheets, thick steel plates, steel bars, sections, etc. As a material, the carbide in steel is Fe, C or Cr7C2 (carbon).
．． Wear-resistant tough cast irons such as adamite cast iron containing 5 to 1.6%, high alloy grain cast iron, or high chromium cast iron have been mainly used.

However, in recent years, the usage conditions for rolls have become more severe due to the spread of high-pressure rolling, etc., and conventional roll materials containing carbides in the form of Fe1Cf'$2, Cr, and Cs do not have sufficient wear resistance. However, many man-hours are required for changing rolls, resulting in a decrease in manufacturing efficiency.

Therefore, MC type added with ■ which is harder than Fe, C or CrvCi, M type added with Mo or W, C type or M,
There is a trend toward using high-C high-speed tool steel containing carbides such as C-type for roll materials.

This high C high speed tool steel roll material is manufactured by either a melting method or a powder metallurgy method. That is, high-speed tool steel of a predetermined composition is melted to make an ingot, and this is made into a hot rolled material, or an atomized powder of high-speed tool steel is formed by hot isostatic pressing (IIIP) treatment, etc. This method is used to make hot rolled material.

The roll material obtained by these methods uses high-C high-speed tool steel, so it can be MC type, M, C type, or L type.
A hard carbide such as C-type is formed. However, in the case of roll materials manufactured by the melting method, the size of the carbide is coarse, and the wear resistance is not greatly improved due to uneven distribution of the carbide, such as flaking. In the case of roll materials manufactured by powder metallurgy, uniform fine dispersion of carbides, which is a characteristic of powder materials, can be obtained, but on the contrary, this uniform fine dispersion hinders the abrasion resistance in hot conditions. In order to have good wear resistance, the carbide must be made large to a certain extent.There is a method of heat treating the powder compact to coarsen the fine carbide, but it is not possible to make the fine carbide coarser. In order to ensure sufficient wear resistance even under severe conditions, the size of the carbide must be adjusted to between 4 and 4 as described below.
It is necessary to coarsen it to 10 μm. However, it is difficult to coarsen it to such a size by heat treatment.

(Problems to be Solved by the Invention) The purpose of the present invention is to solve the above-mentioned problems that have been pointed out to conventional hot rolled materials, and to solve the problems under increasingly severe usage conditions such as high-load rolling and low-temperature rolling. However, it is an object of the present invention to provide a steel material for hot rolls having sufficiently satisfactory wear resistance.

<Means for Solving am> As a result of repeated research in accordance with the above objectives, the present inventors obtained the findings shown in (a) to (C) below and completed the present invention. That is, (a) To improve wear resistance, Fe x C% Cr
1 Cs carbide (micro Vickers hardness? 100
MC type, M&C type carbide (micropinkers hardness j 1500~2500)
It is advantageous to change the degree of

For this purpose, it is preferable to use a high alloy steel such as a high C high speed tool steel containing Mo, W, V.

Middle) To improve wear resistance, it is preferable to control the size of the MC type and MiC type carbides to 4 to 10 μm and to uniformly disperse these carbides.

However, if high alloy steel is manufactured by the melting method, the carbides become coarse and non-uniform, so the improvement in wear resistance is small.
Further, when manufacturing by powder metallurgy, uniform dispersion of carbides can be obtained, but it is difficult to control the size of the carbides.

(C) However, even in the powder metallurgy method, high alloy steel powder with a specified particle size is used, and in addition to the MC type, M, and C type carbides that are formed when this is formed, there is also a hard material with a specified particle size. If the product is manufactured from a mixture in which a specific amount of carbide is added to the base material powder, the wear resistance will be significantly improved.

The gist of the present invention lies in (i) and (ii) below.

(i) A steel material for hot rolls manufactured from a mixture of atomized powder of high alloy steel with a maximum particle size of 44 μm or less and hard carbide with an average particle size of 4 to 1 Ot1 ml,
The high alloy steel contains, in weight percent, C: 1.5 to 4.8%, Si: 0.2 to 2.0%,
Mn: 1.0% or less, Cr: 3.0 to 8.0%,
Mo: 10% or less, W: 10% or less, V: 5-1
5%, the remainder: Fe and inevitable impurities, and the following [
It is a high alloy steel with a composition that satisfies formulas 1] and 2),
A steel material for hot rolls having excellent wear resistance, wherein the hard carbide is WC or MoC5↑aC, and the total content of one or more types is 5 to 20% by volume.

W+2Mo≧4.0(%) ・・・・・・[1]C20
,4+0.2V+0.033(W+2Mo)...
・[2] [However, the element symbol is the content (weight%) of each element.
] (ii) The steel material for hot rolls having excellent wear resistance according to claim 1, wherein the high alloy steel further contains 10% by weight or less of CO.

The hot roll steel material of the present invention is manufactured by a powder metallurgy method, and the matrix is made of high alloy steel having the above chemical composition. In this matrix, 'dC, Mac, which is different from the MC type, M, and C type carbides generated from high alloy steel,
, one or more hard carbides of TaC are uniformly dispersed.

(Function) Hereinafter, the steel material for hot rolls of the present invention will be explained in detail.

First, the reason why the composition of the matrix high alloy steel is limited as described above will be explained.

Note that "1%" of the component content is all "wt% J."

C= A part of C is dissolved in the matrix to form a mardensite m weave, increasing the hardness and strength of the matrix, and most of the rest are carbide-forming elements described later, such as Cr, Mo,
It combines with W and Fe to form M, C, and MC type carbides, which has the effect of improving wear resistance.

In the present invention, C is within the range of 1.5 to 4.8%, and C
20,4+0.2V +0.033(W+2Mo)
If the formula is not satisfied, it is considered as the content.

This means that the rate of carbide formation requires 0.2% C for every 1% V and 0.033% C for every 1% C1 (W + 2 Mo), and at least Since 0.4% is required, the C content is defined according to the contents of V, W and Mo.

The C content that satisfies the above formula is 1.53% or more when the contents of ■, W, and Mo are the lowest, so C
The lower limit of the content was set at 1.5%. When the C content is less than 1.5%, carbide formation is small and the wear resistance of the base material is not improved.

On the other hand, when the content of ■, W and No is the highest, the C content calculated from the above formula is 4.39% or more, but
Even if the content exceeds 4.8%, the improvement in wear resistance is saturated and the toughness decreases.

Si: In the conventional cast iron roll mentioned above, Si is contained in a large amount (0.3 to 2
．． 5%) and was used for cementite precipitation and graphite precipitation, but in the present invention, Si is used only to improve temper softening resistance, so a large amount is not required.

If the Si content is less than 0.2%, no improvement in tempering softening resistance can be obtained.On the other hand, it is not necessary to measure the precipitation of cementite or graphite by adding a large amount of Si, but if the Si content exceeds 2.0%, Crystalline graphite precipitates and becomes white cast iron, which deteriorates toughness, so the content should be reduced to 0.2~
It shall be 2.0%.

An: Mn has the effect of forming MnS and making S harmless, but when added excessively, it lowers the Ac+ transformation point, stabilizes austenite, and reduces quenching hardness, so its inclusion is The amount should be 1.0% or less.

Cr: Cr is a preferred element that improves hardenability, wear resistance, and oxidation resistance. However, if the content is less than 3.0%, these improvement effects will be small, and if the content exceeds 8.0%, ferrite will be generated and the hardness will decrease, so the content should be reduced to 0.
．． 3 to 8.0%.

A0 and W: These elements combine with C to form LC type and MtC type carbides, which have the effect of improving not only wear resistance but also heat resistance.

In the present invention, the content of each of these elements is 10% or less, and the content satisfies the formula (W +2 Mo)≧4(%).

(W + 2 Mo) is the W equivalent, and if the total content of W and Mo is less than 1 (W + 2 Mo> 4%, the above effect cannot be sufficiently obtained. On the other hand, if the content of each is 10%) Abrasion resistance does not improve significantly even if the

■ = V forms MC-type high-hardness carbides and has the effect of improving surface wear resistance.In order to ensure the wear resistance of the matrix, V is required to be at least 5%, but 15 Since the improvement in wear resistance is small even if the content exceeds 5% to 15%.

In addition to the above-mentioned components, 10% or less of Co can also be contained.

CO: Co tends to increase the amount of carbon dissolved in Fe without forming carbides, thereby increasing or reducing high-temperature hardness.

However, even if the content exceeds 10%, the effect is saturated and the hardenability deteriorates, so when CO is included, the content is preferably 10% or less.

A desirable range is 4% or more and 10% or less. The above effect increases from 4% or more.

The high alloy steel that forms the matrix of the steel material for hot rolls of the present invention has the above-mentioned chemical components, and the remainder is essentially Fe.
It consists of:

In the hot roll steel material of the present invention, the powder has a maximum particle size of 44. - WC, MoC with an average particle size of 4 to 10 μm,
Hard carbide of TaC 111! Alternatively, it is manufactured by a powder metallurgy method from a mixture containing two or more types in a volume ratio of 5 to 20%.

The reason for using carbides of WC, MoC, and TaC as hard carbides is that these carbides are different from conventional Fe, C, and Cr.
This is because it has higher hardness than tC and is stable even at high temperatures. In other words, Fe5C and CrtC become F at high temperatures.
It decomposes into e and C, Cr and C, but -(:, MoC5T
This does not happen with aC carbide.

Further, the reason why the particle size of the high alloy steel powder and the particle size and content of the hard carbide powder are limited as described above is as follows.

Table 1 shows 2.9%C-0.3%Si as base material powder.
-0,5%Mn-4,2%Cr-5,0%Mo-5,8
Using high alloy steel powder of various particle sizes consisting of %W-8.5%V-balance Fe, hard carbide particles with an average particle size of 2 to 20
Using a micrometer of 10 μm, a base material powder with hard carbide added at a volume ratio of 25% or less was mixed in a ball mill for 1 hour, then filled into a mild steel capsule, deaerated and sealed, and then from 70 mm diameter by heating to a temperature of 30 °C.
- extruded into one diameter, then annealed at 860°C,
After quenching at a temperature of 1150℃ and tempering at a temperature of 570℃, it is 10mm thick x 10mm wide x 20mm + m
This figure shows the results of examining the amount of wear at a temperature of 600° C. by taking length wear test pieces.

The amount of wear was tested by the same method as in Examples described later, and the specific amount of wear was measured.

The attached figures are graphs of the results shown in Table 1. Figure 1 summarizes the relationship between the maximum particle size of the base material powder and the specific wear amount, and Figure 2 shows the relationship between the maximum particle size of the base material powder and the specific wear amount. Figure 3 summarizes the relationship between the average diameter of carbide and specific wear amount, and FIG. 3 shows the relationship between the amount of added carbide and specific wear amount.

(Hereafter, in the margins) Table 1 (hereinafter, in the margins) From Figure 1, the larger the particle size of the base material $51 powder, the worse the wear resistance, but if the particle size of the base material powder is 44 μm or less, wear is reduced. It can be seen that the wear resistance is excellent. In addition, as shown in Figure 2, carbides with grain sizes in the range of 4 to 10 μm have excellent wear resistance, but those with grain sizes of less than 4 μm and 10 μm
It can be seen that the abrasion resistance decreases when it exceeds the field.

Furthermore, from Figure 3, the amount of carbide added is 5.0 to 5.0% by volume.
If it is within the range of 20%, there will be less wear, but if it is less than 5.0%, it will not contribute to improving the wear resistance, and if it exceeds 20%, the carbides will stick together and become easy to peel off, so the wear resistance will be reduced. It can be seen that the performance has not improved.

From this result, in the present invention, the maximum particle size of the high alloy @ powder was set to 4.
The average particle size of the hard carbide added thereto should be 4 to 10 microns, and the amount added should be 5 to 20% by volume.
That's what I did.

As described above, when the particle size of the high alloy steel powder is 44 μm or less, the carbides are uniformly dispersed, and the wear resistance is greatly improved. In addition, by appropriately selecting the grain size of the carbide, when the grain size is small, there is less chipping due to matrix wear compared to when the grain size is large, and the force applied to each carbide is moderate compared to when the grain size is large, resulting in chipping. Since the amount of carbide is small, the toughness of the entire material does not deteriorate.Furthermore, if the carbide content is appropriate, wear resistance is improved without degrading the toughness of the matrix.

Note that the average particle size of the hard carbide to be added is defined as follows.

That is, a powder having an average particle size of X μm is a powder in which 40% by weight or more of the powder is X+-3 μm.

For example, if the powder has an average particle size of 6 μm, the particle size is 3 to 9 μm.
This means that powder between m is contained at 40% by weight or more.

The above-mentioned powder particle size can be measured by a sieve method in the case of a high alloy powder, and can be measured by a light transmission method in a flow down method in the case of a hard carbide.

The steel material for hot rolls of the present invention described above is obtained by heating high-alloy steel powder having a predetermined particle size produced by an atomization method with various metal powders in a graphite crucible or graphite N powder to form carbides. A predetermined hard carbide with a predetermined particle size! After adding i and mixing this uniformly with a ball mill etc., this mixed powder is extruded or HI
It can be manufactured by molding using a P forging method or the like.

Thereafter, a predetermined heat treatment is performed to form a hot roll into a predetermined size and shape.

The reason why high-alloy steel powder is atomized powder is that atomized powder is more spherical in shape than crushed powder;
This is because uniform dispersion can be obtained when mixed with hard carbide.

Note that atomized powder can be classified into water atomized powder, oil atomized powder, and gas atomized powder depending on the manufacturing method, but gas atomized powder has a surface oxygen level of 1100 pp or less and has excellent toughness, so in the present invention, high alloy steel is used. It is recommended to use gas atomized powder.

In the case of water atomized powder, there is oxidation on the powder surface, so when a steel material is manufactured using an extrusion method using this powder, the bonding at the powder interface is weak. In addition, in the case of oil atomized powder, although the oxygen level on the surface is low, it still has a
It has about p+, and its toughness is inferior to that of gas atomized powder. However, if the surface oxygen level is 10 ppm or less, there is no problem in using water atomized powder and oil atomized powder, although the shape may be more irregular than that of gas atomized powder.

The present invention will be further explained below with reference to Examples.

(Example) Table 2 shows the chemical composition of the base steel used.

This steel is made into powder by gas atomization method, t5) powder of various MC type hard carbide or nitride shown in the table is added, this is mixed in a ball mill, and after being filled into a capsule, it is degassed and the cap is closed. After that, HIP treatment was performed at 2000 atm for 1 hour at a temperature of 1100°C.

After that, annealing is performed at a temperature of 860°C, quenching is performed from a temperature of 1150°C, and tempering is performed at a temperature of 570°C.
A wear test piece of n thickness x 10 mm width x 20 cm length was taken,
The amount of wear was investigated at a temperature of 600°C. The results are shown in Table 3.

The amount of wear was determined by using a 545C lohm diameter rod as the mating material, heating this rod to a temperature of 600''C with high frequency, and contacting the abrasion test piece with a load of 50 kgf. Conduct a test of moving for 60 hours at a speed of sec)
The specific wear amount of the wear test piece at that time was investigated. Note that no lubricant was used in this test.

(Hereinafter, blank spaces) Table 3 (Continued) Ko1 to FkL13 are the steel materials of the present invention.0 The steel materials of the present invention are:
The wear resistance is far superior to that of the comparative steel materials manufactured by the melting methods of No. 14 and No. 15.

N1116 to No.40 are comparative steel materials manufactured from a mixture of high alloy steel powder with carbide or nitride added, and the conditions are outside the range specified by the present invention.

That is, k16 and k17 are the grain size of the high alloy side powder, N
a18 to 20 are the amount of added carbide, N1121 and Hiro 22 are the particle size of added carbide, Hiro 23 to 36 are high alloy steel powder chemistry & II precepts are outside the scope of the present invention, Na37 to 40
In this case, a material other than the carbide defined in the present invention is used.

In this case, the wear resistance is N1114 and ? Although it is superior to J1115 ingot material, it is inferior to the steel material of the present invention.

(Effects of the Invention) As explained above, the steel material for hot rolls of the present invention has excellent wear resistance. Therefore, rolls made of this steel material exhibit excellent durability especially when used in recent severe hot rolling.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the maximum grain size of the base paddy powder and the specific wear amount. Figure 2 is a graph showing the relationship between the average grain size of the added carbide and the specific wear amount. , a graph showing the relationship between the amount of carbide added and the specific wear amount. No. ■ 444 4444 1%0 "ls6 2250 Mother's powder loss tree No. dog grain sink (μm)

Claims (2)

[Claims] (1) A hot roll steel material manufactured from a mixture of atomized powder of high alloy steel with a maximum particle size of 44 μm or less and hard carbide with an average particle size of 4 to 10 μm, wherein the high alloy steel is , in weight%, C: 1.5-4.8%, Si: 0.2-2.0%, Mn
1.0% or less, Cr: 3.0-8.0%, Mo: 10%
Below, W: 10% or less, V: 5-15%, balance: Fe and inevitable impurities, and the following [
It is a high alloy steel with a composition that satisfies formulas 1] and 2),
A steel material for hot rolls having excellent wear resistance, wherein the hard carbide is WC, MoC, or TaC, and the total content of one or more types is 5 to 20% by volume. W+2Mo≧4.0(%)...[1]C≧0.4
+0.2V+0.033 (W+2Mo)...[2]
[However, the element symbol represents the content (weight %) of each element. ] (2) The steel material for hot rolls having excellent wear resistance according to claim 1, wherein the high alloy steel further contains 10% by weight or less of Co.