KR100611201B1 - High speed steel compound roll for hot strip milling having excellent roughness-resistance - Google Patents

Abstract

In the hot rolling centrifugal casting high speed oral composite roll comprising the outer layer and the center, C, Si, Mn, Ni, Cr, Mo, W, V, P, S and the rest contain iron (Fe) and unavoidable impurities. The contents of C, Cr, Mo, and V satisfy the following formula (1), and -0.05 ≦ C- (0.2V + 0.06Cr + 0.063Mo) ≦ 0.1 .... (1), and the content of Ti is A centrifugal cast high speed coated oral composite roll for hot rolling comprising an outer layer portion made of an alloy satisfying formula (2) and 0.1 wt% ≤ Ti ≤ 0.2 wt% ... (2).

Moreover, it is related with the manufacturing method of the centrifugal casting high speed hole oral composite roll for hot rolling which has the outer layer part containing content of Ti as mentioned above.

In addition, the present invention is a C, Si, Mn, Ni, Cr, Mo, W, V, P, S and the rest of iron (Fe) and in the hot rolled centrifugal casting high speed steel composite roll consisting of the outer layer and the center portion Containing inevitable impurities, and the contents of C, Cr, Mo, and V satisfy the following formula (1), and -0.05 ≦ C- (0.2V + 0.06Cr + 0.063Mo) ≦ 0.1 .... (1), Furthermore, B of content which satisfy | fills following formula (3) is included, (DELTA) T (TL-TS) = 0.1B + 188 <220 .... (3), In said formula (3), B content unit Is ppm, TL is liquidus temperature, TS is solidus temperature, and provides a centrifugal casting high speed oral composite roll for hot rolling.

Hot rolled HSS roll outer layer part of the present invention improves the thermal crack resistance, uniformly disperse high hardness MC carbide to solve the surface roughness problem, exhibits excellent performance in the thick roll rolling operation roll mill To prevent accidents and improve productivity.

Hot Rolled, Centrifugal Casting High Speed Oral Composite Roll

Description

High speed steel compound roll for hot strip milling having excellent roughness-resistance}

1 is a 100-fold and 400-fold micrograph showing the microstructure of the alloy metal of the sample No. 1 of Example 1.

2 is a 100-fold and 400-fold micrograph showing the microstructure of the alloy metal of the sample No. 4 of Comparative Example 1.

3 is a 100-fold and 400-fold micrograph showing the microstructure of the alloy metal of the sample No. 7 of Example 2.

4 is a 100-fold and 400-fold micrograph showing the microstructure of the alloy metal of the No. 10 sample of Comparative Example 2.

The work roll of the hot strip mill is a hot rolled mill made of spherical graphite iron in the center to secure toughness after the outer layer is injected with excellent wear resistance by centrifugal casting. Composite rolls. The outer layer is called Ni-Grain roll if it is composed of M3C carbide, the outer layer is made of high Cr cast iron, and the outer layer is made of high speed tool steel (High) Speed Steel, hereinafter referred to as HSS Roll) Roll.

With the recent high load and high hot load hot rolling operations, the rolls for hot rolling have a strong demand for wear resistance and thermal crack resistance. Hi-Cr cast iron rolls having a Cr content of about 18% have been used as a hot rolled roll to date, but recently, centrifugally cast HSS rolls having excellent wear resistance have been developed, which are about 4-5 times higher than Hi-Cr cast iron rolls. Because of its excellent wear resistance, the application is expanding rapidly. However, such HSS rolls have a problem of excellent wear resistance but poor thermal cracking resistance.

As a method of improving the heat cracking resistance of the HSS roll, the content of B was limited to 300 ppm or less in Korean Patent 1996-0004412. The patent describes that when B is added in excess of 300 ppm, network carbides are produced, and B is concentrated in the network carbides, thereby making the carbides vulnerable. Therefore, due to the heat load generated during rolling, fine cracks are formed in the weak network type carbide, and as the amount of rolling increases, the crack progresses due to the increase of the heat load, and the network carbide drops, resulting in a rough surface of the roll. In addition, the crack formed once is advanced to the inside due to the continuous heat load occurs a rolling accident such as spalling.

On the other hand, there is another explanation for the effect of the addition of B, in Japanese Patent Publication No. 10-8212, when 100-7000 ppm of B is added to the HSS roll, the shape of the MC-type carbide is changed into spherical shape, which causes the friction of the roll. It has been described that the coefficient is reduced and at the same time improves the wear resistance, and this description is contrary to the contents in the above-mentioned Korean Patent 1996-0004412. In addition, Japanese Patent Laid-Open No. 5-31508 discloses that 0.01-2% of Ti and Zr than B can both suppress the segregation of carbides and refine the carbides, thereby improving wear resistance, crack resistance and toughness. This is an aspect of improving and minimizing the shape of the MC carbide rather than removing the network carbide described above, and does not discuss the complete removal of the network type M2C carbide.

In general, in order to improve wear resistance, it is preferable to uniformly fix MC carbide having high hardness on the substrate. However, when the roll is manufactured by the centrifugal casting method, the solidification speed is slow at the final solidified portion, which causes the carbide to coarsen or locally segregate easily. In particular, primary austenite is crystallized during solidification of HSS, and MC and austenite are additionally determined by a process reaction, and M2C carbide is crystallized from the remaining liquid phase. Therefore, if the M2C carbide is crystallized into the network at the final solidification part according to the solidification rate and alloy composition, thermal cracking resistance is inhibited.

Therefore, in the present invention, as well as excellent wear resistance, at the same time to form a network M2C carbide that directly affects the thermal cracking resistance in a form that is not connected in the final solidification, or having a fine and uniform microstructure without M2C itself We want to provide a roll.

From the above point of view, intensive investigation of the effect of trace elements on the network carbide formation in the centrifugal cast HSS composite roll for hot rolling, and the heat resistance without M2C carbide at all compared to the conventional HSS roll by adding a certain amount of Ti It was confirmed that a new HSS roll having excellent cracking property can be produced.

In addition, in the case of containing a certain amount of B, it was found that by reducing the coagulation section, M2C carbide can be formed in the final coagulation section in an independent form instead of a network form to provide an HSS roll having improved heat cracking resistance.

According to the present invention, in the centrifugal casting high speed coating oral composite roll for hot rolling, which consists of an outer layer part and a center part,

0.1 to 3.0 wt% C, 0.3 to 2.0 wt% Si, 0.3 to 1.5 wt% Mn, 0.1 to 3 wt% Ni, 2.0 to 10 wt% Cr, 2.0 to 8.0 wt% Mo, 2.0 to 20 weight percent W, 2.0-8.0 weight percent V, less than 0.1 weight percent P, less than 0.06 weight percent S and the rest as iron (Fe) and unavoidable impurities,

Content of said C, Cr, Mo, V satisfy | fills following formula (1),

-0.05 ≤ C- (0.2V + 0.06Cr + 0.063Mo) ≤ 0.1 .... (1)

The content of Ti is represented by the following formula (2),

0.1% by weight ≤Ti ≤0.2% by weight .... (2)

It provides a hot rolled centrifugal casting high-speed coating oral composite roll comprising an outer layer made of an alloy satisfying.

In addition, according to the present invention, in the hot rolling centrifugal casting high-speed coating oral composite roll consisting of the outer layer portion and the center portion,

The alloy forming the outer layer portion is 0.1 to 3.0% by weight of C, 0.3 to 2.0% by weight of Si, 0.3 to 1.5% by weight of Mn, 0.1 to 3% by weight of Ni, 2.0 to 10% by weight of Cr, 2.0 to 8.0 Wt% Mo, 2.0-20 wt% W, 2.0-8.0 wt% V, less than 0.1 wt% P, less than 0.06 wt% S and the rest as iron (Fe) and unavoidable impurities,

Content of said C, Cr, Mo, V satisfy | fills following formula (1),

-0.05 ≤ C- (0.2V + 0.06Cr + 0.063Mo) ≤ 0.1 .... (1)

Furthermore, it contains B of content which satisfy | fills following formula (3),

ΔT (TL-TS) = 0.1 B +188 ≤ 220 .... (3)

In the above formula (3), the B content unit is ppm, TL is the liquidus temperature, TS is a solid-state temperature, provides a centrifugal casting high speed oral composite roll for hot rolling.

In addition, the present invention, the step of dissolving a chemical component constituting the outer layer material in an induction furnace, injecting the dissolved component into a rotating mold, and then using a centrifugal force to close the molten metal to the outside of the mold to produce the outer layer to solidify In the manufacturing method of the hot-rolling centrifugal casting high-speed coating oral composite roll comprising the outer layer portion and the central portion comprising the step, in order to adjust the Ti content in the alloy constituting the outer layer portion in the step of solidifying the outer layer portion in contact with the molten metal. , By treating the molten metal with Al to remove oxygen, and then further removing the remaining oxygen and nitrogen by treating with a small amount of Ti, manufacturing a centrifugal casting high speed oral composite roll for hot rolling. Provide a method.

Looking at the coagulation section according to the B content, as shown in Equation (3), the coagulation section increases as the B content increases. This means that the longer the solidification section, the higher the concentration of C in the liquid phase that remains unsolidified, and the lower the concentration of V, resulting in the formation of M2C eutectic carbide in the final solidification zone. It suggests that they are connected to each other. Therefore, in order to minimize segregation, the composition ratio of each element must be constant as shown in Equation (1) so that the initial austenite and austenite + MC process reactions from the alloy design occupy most of the solidification. In addition, among the elements not included in Equation (1), B should be added at 200 ppm or less, especially since it broadens the solidification section.

Next, the outer layer part composition which comprises the working surface of the composite roll for hot rolling which concerns on this invention is demonstrated.

Elements other than the following are iron (Fe) and unavoidable impurities.

(1) C (carbon)

Carbon is an element necessary to form carbide to increase the wear resistance of the outer layer portion, but the crack resistance of the outer layer portion decreases as the carbon content increases. Carbon content is preferably 1.0 to 3.0% by weight, more preferably in the range of 1.2 to 2.5% by weight. If the carbon content is less than 1.0% by weight, there is no sufficient carbon employment at the base, and thus, it is impossible to obtain a sufficient known hardness, and the amount of carbide precipitated is low and wear resistance is low. On the other hand, when the content exceeds 3.0% by weight, an excessive amount of carbides are formed to soften the matrix and reduce crack resistance.

(2) Si

Silicon is an element necessary as an oxygen scavenger (deoxidizer) and is an element necessary to protect the fluidity of a molten metal. It also reduces the cost of the outer layer by effectively employing M6C carbide instead of expensive elements such as W and Mo. As for content of Si, 0.3-2.0 weight% is preferable, More preferably, it is 0.3-1.5 weight%. If the content of Si is less than 0.3% by weight, there is no deoxidation effect. If the content of Si is more than 2.0% by weight, the mechanical properties deteriorate, and the transformation point temperature of α-Fe to β-Fe is increased, making it difficult to form γ, thereby making it difficult to obtain hardness. do.

(3) Mn

Mn acts as a deoxidation aid of Si and acts as an element for forming a compound containing S into MnS, thereby removing the adverse effects of S. As for content of Mn, 0.3-1.5 weight% is preferable, More preferably, it is 0.3-1.2 weight%. When the amount of Mn exceeds 1.5% by weight, sufficient hardness can not be stably exhibited by being formed in the outer layer portion where the residual austenite phase is formed. On the other hand, when the amount of Mn is less than 0.3% by weight, sufficient oxygen removing function cannot be exhibited. In addition, when Mn is contained in an amount of 2.0% by weight or more, it segregates at grain boundaries and lowers toughness.

(4) Ni

Ni is effective in improving the hardenability of the alloy by stabilizing the austenite phase in the case of large rolls which cannot be hardened by rapid heating. The addition content of Ni is preferably 3% by weight or less, more preferably 0.1 to 1.5% by weight. When Ni is excessively added, the retained austenite phase increases in the outer layer portion, resulting in cracking and poor roughness.

(5) Cr

Cr serves to improve the hardenability of the alloy and generate hard M7C3 carbides. The preferred amount of Cr is 2.0 to 10.0% by weight, more preferably in the range of 3.0 to 8.0% by weight. When the Cr content is less than 2.0% by weight, sufficient hardenability cannot be obtained. On the other hand, when the Cr content is more than 10% by weight, an excessive amount of Cr carbide (M7C3) is formed so that the volume of the hard VC carbide becomes too small. Since M7C3 is softer than MC and M2C, chromium carbide will reduce the wear resistance of the outer layer portion.

(6) Mo

Mo is necessary to obtain high temperature strength and tempering hardness. The content of Mo is preferably in the range of 2.0 to 8.0% by weight, more preferably in the range of 2.0 to 7.0% by weight. If it exceeds 8% by weight, the amount of hard VC carbide decreases as the amount of M2C or M6C carbide increases, which is undesirable. That is, a part of Cr and Mo is distributed in the matrix structure to increase the hardenability and at the same time have a function of precipitation hardening at high temperature. However, when the amount of Mo exceeds 9% by weight, M6C and M2C carbides in metal are increased in balance with C, V, and Mo, thereby reducing toughness and resistance to surface roughness.

(7) W

W is an element necessary to maintain high temperature strength. In addition, it is dissolved in VC carbides to increase the specific gravity to reduce the gravity segregation of VC carbides. As for content of W, 2.0-20.0 weight% is preferable, More preferably, it is 2.0-12.0 weight%. If the amount of W exceeds 20.0% by weight, M6C carbide increases in the metal structure, resulting in poor toughness and roughening resistance. W also has the disadvantage of making carbides coarse.

(8) V

V is an essential element necessary to form MC carbide for increasing the wear resistance of the outer layer portion. The preferred amount of V is 2.0 to 8.0% by weight, more preferably 3.0 to 6.0% by weight. If the amount of V is less than 2.0% by weight, a sufficient effect cannot be obtained. On the other hand, if the amount of V is more than 8.0% by weight, the amount of carbide is increased because the VC carbide is extracted as a primary, resulting in deterioration of rough resistance. do. In addition, since the specific gravity of the VC carbide is much smaller than that of the molten metal, the distribution is biased on the inner surface of the outer layer, thereby producing a heterogeneous material. In addition, the melt is severely oxidized to increase the viscosity of the melt, making it difficult to dissolve the alloy in the atmosphere.

(9) P and S

The unavoidable impurities of high alloy cast steel or cast iron are P and S. The outer layer should be less than 0.1% by weight and less than 0.06% by weight in order to prevent fragility.

(10) B

B, which is an important trace element of the present invention, increases the coagulation section (difference between liquidus and solidus temperature) when it exceeds 320 ppm to promote the production of networked carbide at the site of final solidification. In addition, it occurs during rolling at the interface between the network carbide and the matrix to form fine cracks due to the thermal load, and promotes wear-out of the crystal grains at the site, which causes extreme wear and roughness of the outer layer by crack propagation. . However, if the content of B is below 320 ppm, M2C carbide is formed in the final solidification part, but it does not have a network form, and essentially no crack occurs along the carbide.

(11) Al and Ti

Al and Ti are the most important trace additive elements in the present invention. Al forms an oxide in the molten metal to lower the oxygen content in the molten metal, thereby improving the product integrity and inhibiting the oxidation of Ti. Ti reacts with carbon in the molten metal to form TiC, and the resultant carbide acts as VC crystal nuclei to have an effect of miniaturizing the coagulation structure. Therefore, Al is added for the purpose of deoxidation (oxygen removal), and Ti is added to improve heat cracking resistance due to miniaturization of the cast structure. In addition, since TiC is important for dispersion and crystallization of VC carbide, Al should be added in a range of 0.02 to 0.1% by weight and Ti in a range of 0.1 to 1.0% by weight. On the other hand, when Ti is added, MC carbide becomes fine by TiC, and the precipitation of network carbide which becomes the path of crack propagation is suppressed.

(12) Ca and Mg

Mg and Ca, which have the same effect as Al, are strong deoxidation or desulfurization elements, forming oxides of MgO or CaO, and completely removing excess oxygen to help Ti become TiC without oxidation. Therefore, Mg and Ca are effective when the total amount is more than 0.005% by weight, but when it exceeds 0.1% by weight, the effect is saturated and the reaction with the molten metal is high.

The present invention is explained in more detail through the following examples and comparative examples.

Example 1

The material having the outer layer chemical composition shown in Sample No. 1 and No. 2 of Table 1 was dissolved in an induction furnace to obtain a melt, and injected into a rotating mold having an inner diameter of 665 mm and a length of 1422 mm, and then using a centrifugal force. The molten metal was brought into close contact with the outer side of the outer layer to solidify in the form of a cylinder having a thickness of about 50-70 mm.

On the other hand, in order to manufacture the HSS outer layer consisting of MC carbide formula (2) must be satisfied. However, even if Ti is added in the same amount, it is difficult to obtain a Ti component having a desired content because it shows a large deviation in Ti recovery. The term Ti recovery refers to the ratio of Ti residual content in the actual product to the theoretical Ti residual content in the product according to the Ti input. Therefore, the input amount is fixed. If Ti forms an oxide, the residual content decreases and the recovery rate decreases.

In addition, when a larger amount of Ti is added for the Ti component as a final target, oxidation of the molten metal and a decrease in fluidity occur, thereby causing a problem in injecting the Ti component. Therefore, in the present invention, in order to minimize the above-described Ti recovery variation, the molten metal is first deoxidized with Al to remove oxygen, followed by a small amount of Ti to remove the remaining oxygen, and further, formation of TiN. After nitrogen was removed by the addition of Ti in order to meet the final target component (target content 0.1-0.15%), a constant Ti recovery rate (63% by weight) was obtained as in samples No.1 and No.2. The final content of Ti in the alloy was obtained at 0.11% by weight and 0.10% by weight, respectively.

Comparative Example 1

Dissolved in an induction furnace using the outer layer chemical components shown in Tables 1 to 6 of Table 1, injected into a rotating mold having an inner diameter of 665 mm and a length of 1422 mm, and then contacting the molten metal to the outside of the mold using centrifugal force. The outer layer was solidified in the form of a cylinder having a thickness of about 50-70 mm. In Comparative Example 1, unlike Example 1, the molten metal was deoxidized with Al, or subsequently, an outer layer was manufactured without a process of treating with a small amount of Ti. In this case, the Ti recovery was in the range of 18% to 41%, and thus the Ti content of the final metal was in the range of 0.03 to 0.08% by weight.

Example 2

Regarding the removal of the network carbide of the final solidification part, in order to examine the effect of B addition, as shown in Nos. 7 and 8 of Table 1, an HSS including an outer layer part containing a B content satisfying Equation (3) The roll was made. The production method was prepared in the same manner as described in Example 1.

Comparative Example 2

In order to examine the effect of the addition of B in relation to the removal of the network carbide of the final solidification part, the rolls in which the content of B in the chemical composition shown in Nos. 9 and 10 in Table 1 are outside the range of Equation (3). An HSS roll including an outer layer was prepared. The production method was prepared in the same manner as described in Example 1.

Observational Results of Outer Layer Microstructure of HSS Roll

(1) Comparison of carbide composition ratio

As a result of observing the microstructure of the outer layer of the HSS roll manufactured by the method described in Example 1, as shown in the micrograph of FIG. 1, the content of Ti was satisfied and the Ti content was 0.1 wt% or more and 0.2 wt%. It was confirmed that the alloy of No. 1 in the range of% or less was composed of MC carbide of 95% by weight or more.

On the other hand, when the microstructure of the outer layer of the HSS roll manufactured by the method described in Comparative Example 1 was observed under a microscope, as shown in the photograph of FIG. 2, the content of Ti, which does not satisfy the formula (2), was For alloys less than 0.10% by weight, more than 5% by weight of M2C eutectic carbides were observed in the final solidification zone.

In addition, when compared with the conventional rolls based on the application criteria of Table 2, the dispersion of MC carbide compared to the HSS rolls in which the microstructure of the HSS rolls satisfying Formulas (1) and (2) did not satisfy the above two conditions It can be seen that there is a clear difference in degrees and segregation degree.

(2) M2C process carbide shape

As a result of observing the alloy microstructure of No. 7 of Example 2 in which the conditions of Formulas (1) and (3) were satisfied from FIG. 3, no network carbides were observed in the final solidification part, and the obtained M2C carbides themselves. It was confirmed that the needles did not aggregate together.

On the contrary, as a result of observing the microstructure of the alloy of Sample No. 10 of Comparative Example 2 in which the content of B did not satisfy the condition of Formula (3), it was confirmed that a large amount of carbide network existed as shown in FIG. Could.

division Sample number Alloy element component (wt%) Deoxidizer Ti recovery C Si Mn Ni Cr Mo V B Ti Al Ti Example 1 No.1 1.76 0.78 0.32 0.53 4.14 5.21 5.86 - 0.11 0 0 63% No.2 1.80 0.73 0.30 0.65 4.40 5.24 5.80 - 0.10 0 0 63% Comparative Example 1 No.3 1.77 0.70 0.33 0.50 4.27 5.30 5.71 - 0.06 X X 34% No.4 1.75 0.68 0.44 0.55 4.33 5.42 5.90 - 0.08 X X 41% No.5 1.78 0.75 0.28 0.53 4.33 5.22 5.91 - 0.03 X X 18% No.6 1.82 0.80 0.38 0.56 4.36 5.26 5.79 - 0.07 X X 25% Example 2 No.7 1.75 0.72 0.30 0.50 4.37 5.22 5.76 0.010 - 0 X No.8 1.76 0.74 0.34 0.55 4.47 5.21 5.81 0.020 - 0 X Comparative Example 2 No.9 1.78 0.74 0.31 0.54 4.36 5.65 5.92 0.110 - X X No.10 1.79 0.74 0.43 0.61 4.38 5.55 5.94 0.095 - X X

division sample Application Carbide composition ratio M2C eutectic carbide shape (One) (2) (3) MC M2C network couch Example 1 No.1 0.01 0.11 - 95% 5% - - Comparative Example 1 No.4 -0.03 0.08 - 95% or less More than 5% O O Example 2 No.7 0.01 - 199 80% 20% X O Comparative Example 2 No.10 -0.01 - 283 60% 40% O O

The HSS roll outer layer part for hot rolling of the present invention may improve thermal cracking resistance and uniformly disperse high hardness MC carbide to solve the surface roughness problem. In addition, it exhibits excellent performance in the roll for thick plate rolling and contributes to preventing accidents and improving productivity in rolling mills.

Claims (3)

In the hot rolling centrifugal casting high speed oral composite roll comprising the outer layer and the central portion, 0.1 to 3.0 wt% C, 0.3 to 2.0 wt% Si, 0.3 to 1.5 wt% Mn, 0.1 to 3 wt% Ni, 2.0 to 10 wt% Cr, 2.0 to 8.0 wt% Mo, 2.0 to 20 weight percent W, 2.0-8.0 weight percent V, less than 0.1 weight percent P, less than 0.06 weight percent S and the rest as iron (Fe) and unavoidable impurities, Content of said C, Cr, Mo, V satisfy | fills following formula (1), -0.05 ≤ C- (0.2V + 0.06Cr + 0.063Mo) ≤ 0.1 .... (1) The content of Ti is represented by the following formula (2), 0.1% by weight ≤Ti ≤0.2% by weight .... (2) Satisfactory, high-speed centrifugal cast oral composite roll for hot rolling comprising an outer layer portion made of an alloy containing more than 95% MC carbide. In the hot rolling centrifugal casting high speed oral composite roll comprising the outer layer and the central portion, The alloy forming the outer layer portion is 0.1 to 3.0% by weight of C, 0.3 to 2.0% by weight of Si, 0.3 to 1.5% by weight of Mn, 0.1 to 3% by weight of Ni, 2.0 to 10% by weight of Cr, 2.0 to 8.0 Wt% Mo, 2.0-20 wt% W, 2.0-8.0 wt% V, less than 0.1 wt% P, less than 0.06 wt% S and the remainder as iron (Fe) and unavoidable impurities, Content of said C, Cr, Mo, V satisfy | fills following formula (1), -0.05 ≤ C- (0.2V + 0.06Cr + 0.063Mo) ≤ 0.1 .... (1) Furthermore, it contains B of content which satisfy | fills following formula (3), ΔT (TL-TS) = 0.1 B +188 ≤ 220 .... (3) In the formula (3), the B content unit is ppm, TL is the liquidus temperature, TS is the solidus temperature, hot-rolling centrifugal casting high speed oral composite roll. delete

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