JPH04182012A - Wear resistant composite roll with excellent crack resistance and its manufacture - Google Patents

Abstract

PURPOSE:To improve the performance of the wear resistant composite roll by mechanically jointing the outer layer of iron based alloy of specific chemical composition on the cast steel shaft with continuous tinkering build-up part. CONSTITUTION:On the outer layer of cast steel shaft, the iron based alloy composed of by weight 0.5% C, <=2.0% Si, <=1.5% Mn, 2.0-7.0% Cr, >=0.5% <3.0% V, <=9.0% Mo, <=20% W, (2Mo+W=4-20%) and consisting of balance Fe essentially and an inevitable impurities is jointed metallically with continuous tinkering casting method. Therefore, the wear resistant composite roll having a good mechanical strength, together with an excellent wear resistance and a crack resistance can be manufactured, and especially it can be utilized effectively as the roll for hot rolling.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wear-resistant composite roll with excellent crack resistance for hot or cold rolling, and a method for manufacturing the same.

[Prior Art and Problems to be Solved by the Invention] Cast iron composite rolls manufactured by centrifugal casting are widely used as rolling rolls. This has a structure in which the outer layer is made of a cast iron material containing a large amount of highly wear-resistant carbide, and the inner layer is made of tough gray cast iron or ductile cast iron. The range of materials that can be applied is limited.

Carbides formed by elements such as W, V, and Nb are hard with a Vickers hardness Hv of 2000 or more, and if these carbides are included in the outer layer material, is it effective for improving the wear resistance of the roll? In reality, it is impossible to manufacture a composite roll in which an outer layer and an inner layer, in which the crystallization occurs, are properly welded by centrifugal casting.

The reason for this is that the carbides formed by these elements have a different specific gravity from the molten metal, so segregation is likely to occur during casting due to the action of so-called centrifugation.

Additionally, some of these elements have a strong tendency to oxidize, making it difficult to weld them to the inner layer. Furthermore, in the centrifugal casting method, toughness is obtained by using gray cast iron or ductile cast iron with crystallized graphite for the inner layer material, or if the outer layer material contains large amounts of elements that have a strong tendency to become white as described above. Since the outer layer components slightly dissolve into the inner layer, the graphitization of the inner layer deteriorates and becomes brittle. Particularly near the boundary with the inner layer, carbides are concentrated and formed, making it brittle and causing peeling of the outer layer starting from the boundary.

Furthermore, the tensile strength of the inner layer of gray cast iron or ductile cast iron is limited to about 55 kg/mm2, and the elongation is less than 1%. In order to obtain a value higher than this, it is necessary to use steel thread material for the inner layer, which is also difficult with the centrifugal casting method. The reason for this is that the inner layer has a higher melting point than the outer layer, so when the inner layer is cast, the boundary area where the outer layer melts and becomes a mixed state has a lower melting point than the inner layer and becomes the final solidified layer. This is because defects are more likely to occur.

In addition, in order to streamline rolling by rolling a large amount at once, and to improve the dimensional accuracy of rolled materials,
It has become necessary to significantly improve the wear resistance of rolling rolls. At the same time, in order to improve the dimensional accuracy of the rolled material, we are adding bends to the shafts of the rolls in the opposite direction to the deflection caused by rolling, and we are also adding bending to the roll shafts in the opposite direction to the deflection caused by rolling, and using a single rolling stand to complete rolling with fewer stands. Due to the application of large rolling blades, the bending stress applied to the roll shaft is increasing, and it has become necessary to improve the strength of the roll shaft. However, rolls with a structure in which the outer layer material and the shaft material are fired or assembled have the problem that the outer layer and shaft may slip during rolling or the outer layer may easily break, so the outer layer and shaft must be completely joined metallically. Is it necessary?

In order to satisfy these requirements at the same time, it is necessary to use the outer layer W, V
It is necessary that the material is made of a material that crystallizes a large amount of carbides of elements such as Nb, the shaft is made of strong steel, and the outer layer and shaft are completely joined metallically. For this reason, it cannot be manufactured using a casting method such as centrifugal casting.

Furthermore, the method of diffusion bonding using solid materials is not practical for relatively large objects such as rolling rolls because the manufacturing equipment is extremely expensive.

Under the above circumstances, attention has been focused on the so-called casting overlay method of manufacturing composite rolls by welding and solidifying the molten metal of the outer layer material around a pre-formed steel shaft material made of cast steel or forged steel. Composite rolls using various combinations of outer layer materials and shaft materials have been proposed.

For example, JP-A No. 60-180608 discloses a composite roll in which the outer layer and the core material are metallurgically bonded, and the outer layer has a weight ratio of C.2.0 to 3.5% and Sl.05 to 1.5%. %, Mn
- o, 4-1.5%, Cr8-25%, Mo: 0.
Constructed of high chromium cast iron consisting of N1 of 5~3°0%, V: 10% or less, and 1.5% or less, with a core material of
The outer layer is made of cast steel or forged steel with a tensile strength of 5 kg/aua2 or more and an elongation of 1.0% or more, and the outer layer is made of metallurgical material by pouring the molten metal of the outer layer components around the outer periphery of a core material prepared in advance. The strength of the joint between the outer layer and the core material is at least stronger than the weaker of the outer layer material and the core material, and the hardness of the outer layer is 70 on the Soyoer hardness scale.
The above discloses a composite roll for hot rolling that has excellent seizure resistance and roughening resistance, and is characterized by a hardness reduction up to 100 mm below the surface and a Nocore hardness of 3 or less.

Furthermore, JP-A No. 60-180609 discloses a composite roll having an outer layer made of high chromium cast iron, a core material made of cast steel, and a surface hardness of 90 or more, and the outer layer is made of a pre-prepared core material. It is formed by a method of metallurgically bonding by pouring /S hot water as an outer layer component onto the outer periphery of the outer layer, and the composition of the high chromium cast iron of the outer layer is C2.5 to 3.5% by weight, Si0.
5-1.5%, MnO, 4-1.596, Ni0.5-
3.0%, Cr 8-25%, Mo 1.0-5.0%, the remainder substantially consists of Fe, the strength and elongation of the core material are each 55 kg / 1) 1 m 2 or more, 1.0% uh
The present invention discloses a high chromium cast iron roll for cold rolling, characterized in that the joint strength at the boundary between the outer layer and the core material is at least greater than the strength of the weaker of the outer layer material and the core material.

However, since the outer layer of these rolling composite rolls is made of high chromium cast iron, although they have good wear resistance, they are not necessarily sufficient to meet the requirements that have become higher and higher in recent years.

In addition, Special Publication No. 51-24969 contains carbon of 0.2 to 0.6
Contains 2% by weight of nickel and 2ffi amount% or less of nickel, 2~
6% by weight chromium, 1-6% by weight molybdenum, 1-6
5-12% by weight of vanadium, 3-10% by weight of niobium, and niobium combined therewith in an iron-based matrix containing at least one element selected from tungsten and up to 10% by weight of Fhardt. Discloses an ultra-wear-resistant steel characterized by crystallized carbides formed by bonding with carbon in an amount required for It is stated that this super wear-resistant steel can be used for rolling rolls, etc., or there is no disclosure that it is used for composite rolls.

In view of the above, the applicant first proposed a weight ratio of 1.5 to 3.5.
% C10, 3-3.0% Si, 0.3-1.5% Mn, 2-7% C'', MO up to 9%, W up to 120%, 3-15% V and the balance A wear-resistant composite roll consisting of an outer layer made of an iron-based alloy consisting essentially of Fe, and a steel shaft metallically bonded to the outer layer, wherein the outer layer has a surface hardness of 70 or more, and the shaft has a Noyoer hardness of 70 or more. Tensile strength and elongation of 55kg/trm 2 or more and 1.
We have proposed a wear-resistant composite roll characterized in that the bonding strength at the boundary between the outer layer and the shaft or the weaker one of the outer layer and the shaft is greater than or equal to 0% (PCT
/JP88100304).

This wear-resistant composite roll is manufactured by the so-called continuous casting overlay method, and has good wear resistance and the shaft material has good mechanical strength. However, it has been found that there is a risk that cracks may form on the roll surface, especially when abnormal rolling called chocking, squeezing, or doubling occurs, especially in hot rolling. In addition, jamming is an accident in which the rolls stop in the case of over-throwing, and squeezing is an accident that occurs when the leading edge of the steel plate being rolled rolls up in the longitudinal direction and enters between the rolls. Doubling is an accident where the tip or tail of the steel plate curls up in the lateral direction and ends up between the rolls. In either case, once the roll is cranked, the roll surface must be ground to remove any cracks. For this reason, there has been a strong desire to improve crack resistance in order to extend roll life.

Therefore, the object of the present invention is to provide an abrasion-resistant material that is composed of an outer layer material that has excellent abrasion resistance and crack resistance, and a shaft material made of strong steel thread, and that the outer layer and the shaft are metallically joined. ,
An object of the present invention is to provide a composite roll with excellent crack resistance and a method for manufacturing the same.

[Means to solve the problem]

The wear-resistant composite roll of the present invention with excellent crack resistance is
C of 0.5 to 1.5% by weight, Si of 2.0% or less,
Mn of 1.5% or less, Cr of 2.0 to 7.0%,
Consisting of an iron-based alloy containing V of 0.596 or more and less than 3.0%, Mo of 9% or less and W of 20% or less (however, 2Mo+W = 4 to 20%), and the remainder substantially consisting of Fe and inevitable impurities. A wear-resistant composite roll with excellent crack resistance consisting of an outer layer and a shaft made of cast steel or forged steel metallically bonded to the outer layer, the outer layer being bonded to the shaft by a continuous cast overlay method. It is characterized by the presence of

Further, the method of the present invention for manufacturing the abrasion-resistant composite roll with excellent crack resistance includes a combination mold comprising a refractory frame surrounded by an induction heating coil and a cooling mold coaxially installed under the frame. The steel shaft material is loosely fitted coaxially into the space provided inside the mold, and the molten metal of the iron-based alloy is injected into the gap formed between the shaft and the mold, and the surface of the molten metal is fluxed. At the same time, the molten metal is heated and stirred within a temperature range from the primary crystallization temperature to 100°C higher than that, and the shaft is moved downward coaxially with the mold to cool the molten metal. By bringing it into contact with the mold, solidifying it, and welding it to the shaft,
The outer layer is formed continuously around the shaft.

[Examples and effects]

The wear-resistant composite roll of the present invention with excellent crack resistance is
It consists of an outer layer made of an iron-based alloy and a steel shaft metallically bonded to the outer layer. Further, the above iron-based alloy has a weight ratio of 0.5 to 1
．． 5% C12, 0% Si or less, 1° or less 5% Mn
, 2.0-7.0% Cr, 0.5% or more and less than 3°0% V, 9% or less Mo, and 2096 or less W (however, 2
(Mo+W=4 to 20%), and the remainder substantially consists of Fe and unavoidable impurities.

C is necessary for forming carbides to improve wear resistance, and as its amount increases, crack resistance decreases.

Therefore, it is necessary that the content be within the range of 0.5 to 1.5%. If the amount is less than 0.5%, the amount of crystallized carbide is too small and the wear resistance is not sufficient. On the other hand, C or 1.5
%, C becomes excessive in the balance with V, Mo, W, etc. that form hard carbides, and M, , C, and Mi
Because carbides such as C crystallize, the roughness of the skin decreases.

Si is a necessary element as a deoxidizing agent, and also has a growth effect in replacing expensive elements such as W and Mo by dissolving them in LC carbide and saving 2. However, if it exceeds 2.0%, embrittlement tends to occur, so the content should be 2.0% by weight or less. In addition,
If the amount is less than 0.3%, it is not preferable because there is no deoxidizing effect and casting defects are likely to occur in cast iron materials.

Mn has a deoxidizing effect as well as an effect of fixing S, which is an impurity, as MnS. However, if it exceeds 1.5%, retained austenite tends to occur and sufficient hardness cannot be stably maintained. Incidentally, if the amount is less than 0.3%, deoxidizing properties are poor and this is not preferable.

If the content of Cr is less than 2%, the hardenability is poor, and if it exceeds 7%, chromium-based carbides become excessive, which is disadvantageous. That is, Cr-based carbide, for example M2. C, has lower hardness than MC1M2C and reduces wear resistance.

(2) is an essential element for forming MC-based carbides that are effective in improving wear resistance. By adding in a range of 0.5% or more and less than 3.0%, wear resistance can be improved while preventing carbide segregation. In addition, by making the hardness of the outer layer material uniform, the surface of the rolled product can be finished neatly. However, if it is less than 0.5%, these effects cannot be obtained, and on the other hand, if it is more than 3.0%, the MC carbide becomes coarse and segregates easily, resulting in poor machinability.

It can also cause rough skin.

Mo and W combine with C to crystallize M, C, M2C type carbides.The presence of these M, C, M2C type carbides may also have the effect of improving wear resistance, but it is mainly due to secondary tempering hardening. Improves heat resistance and heat resistance.

At this time, if Mo and W exceed 9% and 20%, respectively, the amount of carbides becomes too large and becomes brittle. The preferred addition amounts of Mo and W are 2 to 7% and 2 to 16%, respectively. Also, it has an effect equivalent to twice the amount of Mo as W.
In order to fully obtain the above effect, the amount of 2Mo+W must be 4
Is it necessary to contain more than %?

However, if it is contained in excess, the toughness will decrease significantly, so
The content of Mo and W is suitably 4 to 20% as 2Mo+W amount.

In addition to the above elements, the iron-based alloy for outer layer material of the present invention contains N1, Co
It can be included singly or in combination.

Ni has the effect of improving hardenability. Therefore, it can be added in an amount of 2% or less. However, if the amount exceeds this amount, retained austenite increases and problems such as cracking and rough skin during rolling occur, so the content can be limited to a maximum of 2%.

Co is a useful element in terms of temper softening resistance and secondary hardening, but if it exceeds 12%, the toughness decreases.

In addition, one or more of Ta, 7r, H[, and T1, which form MC-based carbides, may be added as appropriate for the purpose of improving wear resistance.

In addition, by adding a very small amount of B, hardenability is improved,
It can also prevent a decrease in toughness. However, if added in excess, the toughness decreases, so it is necessary to limit the amount to 500 ppm or less.

In addition to the above elements, the iron-based alloy consists essentially of iron excluding impurities. The main impurities are P and S, or P
is 0.1% or less to prevent embrittlement, and S is 0.1% or less to prevent embrittlement.
It may be less than 0.06%.

The shaft of the composite roll of the present invention is made of steel, and may be either cast steel or forged steel. Its tensile strength must be 55 kg/In12 or more, and its elongation must be I, 0% or more.

This is because when used as a rolling roll, a large rolling blade is required and the roll must be able to withstand the bending force applied to both ends of the shaft to correct deflection during rolling. Further, the shaft must be firmly bonded to the outer layer made of the above-mentioned iron-based alloy. For this purpose, the bonding strength at the boundary between the two must be equal to or higher than the mechanical strength of the weaker of the outer layer and the shaft.

In order to form the outer layer on the outer periphery of the steel shaft with high bonding strength, the following method is used.

The manufacturing method is basically a method as shown in PCT/JP88100304, in which a high frequency coil is used to continuously form an outer layer around steel.

FIG. 1 shows an example of an apparatus that can be used to carry out the method of the invention. This device has a combination mold IO consisting of a funnel-shaped refractory frame 1 having a circumferential wall with a tapered part and a parallel part, and a cooling mold 4 coaxially installed below the refractory frame 1.

An annular induction heating coil 2 is arranged in the refractory frame l so as to surround the outer periphery of the refractory frame l, and an annular buffer type coil having an inner hole having the same diameter as the lower part of the refractory frame 1 coaxially at the lower part thereof. 3
Or is provided. Also, the cooling type 4 below is the buffer type 3.
It has approximately the same inner diameter and is coaxial. Cooling water is continuously introduced into the mold from the population I4 of cooling mold 4, and the exit +
It is discharged from 4'.

The roll shaft 5 is placed inside the combination mold 10 having the above configuration.
Set. A closing member (not shown) having an outer diameter approximately the same as the outer diameter of the injection outer layer is fixed at the lower end of the shaft 5 or at a position appropriately separated from the lower end as necessary, and furthermore, the lower part of the closing member is fixed to the lower end of the shaft 5 or at a position appropriately separated from the lower end. Attach to a mechanism (not shown). Molten metal 7 is poured into the space between the shaft 5 and the refractory frame 1, and the surface of the molten metal is covered with molten flux 6 so as not to come into contact with air. Then, the molten metal 7 is heated and stirred using a heating coil 2 to prevent it from solidifying.

The molten metal 7 flows in the direction shown by arrow A in the figure and causes stirring movement. Next, the closing member fixed to the shaft 5 is sequentially lowered together with the shaft member. In conjunction with the descent of the shaft material and closing member, the molten metal 7 also descends, and the molten metal #17 falls on the buffer mold 3 and water-cooled mold 4 surface.
Coagulation begins. During this solidification, the shaft and the outer layer are completely metallically bonded. The surface of the molten metal in the pool will either drop as the shaft member and closing member descend, or new molten metal will be injected as appropriate to maintain the liquid level at a certain level. Then, the outer layer 8 is formed by sequentially repeating the lowering and pouring to solidify the molten metal from below.

The composite roll obtained in this way is further quenched,
A desired outer layer hardness is obtained by performing heat treatment such as tempering.

The surface hardness of the outer layer of the obtained composite roll was Shore hardness 7.
0 or more, the tensile strength of the shaft is 55 kg / 82 or more, and the elongation is 1.0% or more.Since the outer layer and the shaft are joined metallically, the bonding strength at the boundary is the same as that of the outer layer and the shaft. The strength is greater than that of the weaker one.

The present invention will be further explained in detail by the following examples.

Example 1 Molten metal for the outer layer having the composition shown in Table 1 was prepared in order of diameter 80 and height 80.
A small roll material for a rolling wear test was cast by pouring into a 002 mm sand mold. This material is heat treated at 1050~1) 50℃ and tempered at 500~550℃, and then the outer diameter is 60mm, the inner diameter is 35mm, and the length is 40mm.
A sleeve-shaped test roll was prepared.

The hardness of the outer layer surface of each test roll was measured using a Shore hardness meter, and the results are shown in Table 2. Next, a rolling wear test was conducted on this test roll. As shown in FIG. 2, the rolling wear test machine includes a rolling mill 21, an upper roll 22 and a lower roll 23 incorporated in the rolling mill 21, a heating furnace 24 for preheating the rolled material S, and a heating furnace 24 for cooling the rolled material S. It consists of a cooling water tank 25, a winder 26 that applies constant tension during rolling, and a tension controller 27 that adjusts the tension. The test conditions were as follows.

Rolled material: SUS 304, thickness: 1 city, width: 15 Rolling distance: 800 m Rolling temperature: 900°C Reduction rate: 25% Rolling speed: 150 m/min Roll cooling: Water Wear on the surface of the cooling test roll The depth was measured using a stylus type surface roughness meter (SURFCOM). Table 2 shows the results of determining the average wear depth by averaging the wear depth of each roll over the rolling width.

Comparative Example 1.2 High chromium cast iron (Comparative Example 1) and PCT as conventional materials
A test roll was produced in the same manner as in Example 1 using the roll outer layer material (Comparative Example 2) described in /JP88100304. However, heat treatment was applied to suit these materials. A wear test was conducted in the same manner as in Example 1, and the measured values of the wear depth are shown in Table 2. The hardness measurement results are also shown in Table 2.

Table 2 Example 2 Using the molten metal for the outer layer having the composition shown in Table 3 and the shaft having the diameter and material shown in Table 4, and using the apparatus shown in FIG. was manufactured. The preheating temperature of the shaft and the temperature of the molten metal for the outer layer are as shown in Table 4, respectively. The surface of the molten metal was sealed with molten flux to prevent it from coming into contact with air. The dimensions of the composite roll thus obtained are shown in Table 3. Each composite roll was subjected to heat treatment of quenching from 1080°C and tempering at 550°C.

Table 4 shows the results of measuring the hardness of the outer layer surface using a Shore hardness meter.

In addition, an ultrasonic inspection of the inside of the composite roll of sample No. 1 was conducted. As a result, no defects such as cavities were found in the outer layer or the boundary between the outer layer and the shaft material, and the outer layer and the shaft material were welded together soundly. Thereafter, the surface of the body was polished and corroded, and the metallographic structure was observed. As a result, a tempered martensite base with fine secondary carbides distributed, network-like M, C carbides, LC carbides, and fine M
C carbide was observed.

Next, the outer layer of the roll was cut out and macro-etched, and the cross section was observed, and no segregation of carbides was observed.

Comparative Example 3 Using a molten metal with the composition shown below, an outer diameter of 8 was formed by centrifugal casting.
A roll outer layer having a diameter of 0.00 mm, an inner diameter of 600 mm, and a length of 200 mm was manufactured.

(Composition of molten metal for outer layer (wt%)) C: 0.84, Si: 0.34, Mn: 0.38, N
i: o, 10, Cr: 4.08, Mo: 5.19, V
: 1.99, W: 6.05, Fe: remainder.

Next, a molten alloy of ductile cast iron at a temperature of 1600°C was cast into the space within the outer layer of the roll. At that time, the inner surface temperature of the outer layer was maintained at about 950°C.

After manufacturing a composite roll as in step 2, an ultrasonic inspection of the inside of the roll was conducted. As a result, many cavities were observed inside the outer layer, and a healthy tissue could not be obtained.

Example 3 A heat crack resistance test was conducted on the outer layer materials of samples Nos. 1 to 3 in Example 2.

Heat crack resistance test is 30mmφX35m+y+A
A cylindrical test piece of This was done by measuring. As a result, the heat crack depths of outer layer material sample No. 1.2.3 of the present invention were 2.5 mm, 1.9 mm, 1, and 8 m, respectively.
The heat crack depths of Comparative Examples 1 and 2 were 3.8 mm and 3.0 mm, respectively.

From this, it can be seen that the composite roll having the outer layer material of the present invention has excellent heat crack resistance.

〔Effect of the invention〕

As detailed above, the composite roll of the present invention has good mechanical strength as well as excellent wear resistance and crack resistance, so it can be widely used, especially as a roll for hot rolling.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of an apparatus used to carry out the present invention, and FIG. 2 is a schematic diagram showing a rolling abrasion tester used for an abrasion test of the outer layer of a roll.

Claims (6)

[Claims] (1) 0.5 to 1.5% C by weight, 2.0% or less Si, 1.5% or less Mn, 2.0 to 7.0% Cr,
V of 0.5% or more and less than 3.0%, Mo of 9% or less and 2
an outer layer made of an iron-based alloy consisting of 0% or less W (however, 2Mo + W = 4 to 20%), and the remainder substantially consisting of Fe and unavoidable impurities; and a cast steel or forged steel shaft metallically joined to the outer layer. 1. A wear-resistant composite roll having excellent crack resistance, characterized in that the outer layer is joined to the shaft by a continuous casting overlay method. (2) The wear-resistant composite roll according to claim 1, wherein the iron-based alloy further contains Ni in a weight ratio of 2% or less. (3) The wear-resistant composite roll according to claim 1 or 2, wherein the iron-based alloy further contains Co in a weight ratio of 12% or less. (4) In the wear-resistant composite roll according to any one of claims 1 to 3, the content of B in the iron-based alloy is 500 p.
A wear-resistant composite roll characterized in that it is pm or less. (5) In the wear-resistant composite roll according to any one of claims 1 to 4, the content of P in the iron-based alloy is 0.1%.
A wear-resistant composite roll characterized in that the content of S is 0.06% or less. (6) 0.5 to 1.5% C by weight, 2.0% or less Si, 1.5% or less Mn, 2.0 to 7.0% Cr,
V of 0.5% or more and less than 3.0%, Mo of 9% or less and 2
an outer layer made of an iron-based alloy consisting of 0% or less W (however, 2Mo + W = 4 to 20%), and the remainder substantially consisting of Fe and unavoidable impurities; and a cast steel or forged steel shaft metallically joined to the outer layer. In the method of manufacturing a wear-resistant composite roll with excellent crack resistance, the inside of a combination mold consisting of a refractory frame surrounded by an induction heating coil and a cooling mold coaxially installed under the frame. The shaft is loosely fitted coaxially into the provided space, and the molten metal of the iron-based alloy is injected into the gap formed between the shaft and the mold,
The surface of the molten metal is sealed with flux, and the molten metal is heated and stirred within a temperature range from the primary crystallization temperature to 100°C higher than that, and the shaft is moved downward coaxially with the mold to cool the molten metal. By bringing it into contact with the cooling mold to solidify it and welding it to the shaft,
A method characterized in that the outer layer is formed continuously around the axis.