Roll for hot rolling process and method for manufacturing same

Abstract

[PROBLEM] The invention provides a roll for hot rolling process having various types of more excellent durability performances than conventional rolls, and provides also a method for manufacturing the same. [SOLUTION] A cladding layer 4 is formed on an outer circumference portion of a roll for hot rolling process 1, where the cladding layer 4 comprises: 0.5 to 0.7% by mass of C, 2.8 to 4.0% by mass of Si, 0.9 to 1.1% by mass of Cu, 1.4 to 1.6% by mass of Mn, 2.7 to 3.3% by mass of Ni, 13.5 to 14.5% by mass of Cr, 0.8 to 1.1% by mass of Mo, 0.9 to 1.1% by mass of Co, and 0.2 to 0.4% by mass of Nb, with a balance being Fe and inevitable impurities, and has a thickness of 5 mm or more.

Claims

1. A roll for hot rolling process used in rolling equipment for hot-rolled steel, comprising: at least one of a solid shaft and a sleeve forming a body of the roll; and a cladding layer on an outer circumference portion of the solid shaft or sleeve, wherein the cladding layer comprises: 0.5 to 0.7% by mass of C, 2.8 to 4.0% by mass of Si, 0.9 to 1.1% by mass of Cu, 1.4 to 1.6% by mass of Mn, 2.7 to 3.3% by mass of Ni, 13.5 to 14.5% by mass of Cr, 0.8 to 1.1% by mass of Mo, 0.9 to 1.1% by mass of Co, and 0.2 to 0.4% by mass of Nb, with a balance being Fe and inevitable impurities, and has a thickness of 5 mm or more, wherein in the cladding layer, a high temperature hardness at 500° C. is HS 50 or more, wherein the outer circumference portion of the solid shaft or sleeve forming a body of the roll has the cladding layer formed by a continuous pouring process for cladding, wherein the solid shaft or the sleeve formed with the cladding layer is quenched by a forced air cooling after being subject to a solution treatment at 1000° C. for seven hours, and is further subject to an aging treatment at 400 to 600° C. for seven hours while annealing heat treatment is not performed after the continuous pouring process, and wherein corrosion mass loss of the cladding layer is 0.0065 mg/mm.sup.2 or less in a 48-hour corrosion resistance test defined in Japanese Industrial Standard Z2371 (JIS Z2371).

2. A roll for hot rolling process used in rolling equipment for hot-rolled steel, comprising: at least one of a solid shaft and a sleeve forming a body of the roll; and a cladding layer on an outer circumference portion of the solid shaft or sleeve, wherein the cladding layer comprises: 0.7 to 0.9% by mass of C, 3.0 to 4.5% by mass of Si, 0.9 to 2.0% by mass of Cu, 1.4 to 1.6% by mass of Mn, 2.7 to 3.3% by mass of Ni, 13.5 to 14.5% by mass of Cr, 1.8 to 4% by mass of Mo, 0.9 to 3.0% by mass of Co, and 0.4 to 1.5% by mass of Nb, with a balance being Fe and inevitable impurities, and has a thickness of 5 mm or more, wherein in the cladding layer, a high temperature hardness at 500° C. is HS 50 or more, wherein the outer circumference portion of the solid shaft or sleeve forming a body of the roll has the cladding layer formed by a continuous pouring process for cladding, wherein the solid shaft or the sleeve formed with the cladding layer is quenched by a forced air cooling after being subject to a solution treatment at 1000° C. for seven hours, and is further subject to an aging treatment at 400 to 600° C. for seven hours while annealing heat treatment is not performed after the continuous pouring process, and wherein corrosion mass loss of the cladding layer is 0.0065 mg/mm.sup.2 or less in a 48-hour corrosion resistance test defined in Japanese Industrial Standard Z2371 (JIS Z2371).

3. The roll for hot rolling process according to claim 1, wherein a sleeve made of carbon steel has the cladding layer on the outer circumference portion, and the sleeve is fitted onto an outside of a roll shaft to form a body.

4. A method for manufacturing a roll for hot rolling process used in rolling equipment for hot-rolled steel, the roll including a cladding layer on an outer circumference portion, wherein the cladding layer comprises: 0.5 to 0.7% by mass of C, 2.8 to 4.0% by mass of Si, 0.9 to 1.1% by mass of Cu, 1.4 to 1.6% by mass of Mn, 2.7 to 3.3% by mass of Ni, 13.5 to 14.5% by mass of Cr, 0.8 to 1.1% by mass of Mo, 0.9 to 1.1% by mass of Co, and 0.2 to 0.4% by mass of Nb, with a balance being Fe and inevitable impurities, and has a thickness of 5 mm or more, and wherein in the cladding layer, a high temperature hardness at 500° C. is HS 50 or more, comprising the steps of: using a solid shaft or a sleeve forming a body as a core material and forming the cladding layer on an outer circumference portion thereof by a continuous pouring process for cladding; and quenching the solid shaft or the sleeve formed with the cladding layer by a forced air cooling after subjecting the solid shaft or the sleeve formed with the cladding layer to a solution treatment at 1000° C. for seven hours, and further subjecting the solid shaft or the sleeve formed with the cladding layer to an aging treatment at 400 to 600° C. for seven hours while annealing heat treatment is not performed after the continuous pouring process, wherein corrosion mass loss of the cladding layer is 0.0065 mg/mm.sup.2 or less in a 48-hour corrosion resistance test defined in Japanese Industrial Standard Z2371 (JIS Z2371).

5. The method for manufacturing the roll for hot rolling process according to claim 4, wherein after the sleeve formed with the cladding layer is subject to the solution treatment, the quenching, and the aging treatment, the sleeve is fitted onto an outside of a roll shaft to form a body.

6. A method for manufacturing a roll for hot rolling process used in rolling equipment for hot-rolled steel, the roll including a cladding layer on an outer circumference portion, wherein the cladding layer comprises: 0.7 to 0.9% by mass of C, 3.0 to 4.5% by mass of Si, 0.9 to 2.0% by mass of Cu, 1.4 to 1.6% by mass of Mn, 2.7 to 3.3% by mass of Ni, 13.5 to 14.5% by mass of Cr, 1.8 to 4% by mass of Mo, 0.9 to 3.0% by mass of Co, and 0.4 to 1.5% by mass of Nb, with a balance being Fe and inevitable impurities, and has a thickness of 5 mm or more, and wherein in the cladding layer, a high temperature hardness at 500° C. is HS 50 or more, comprising the steps of: using a solid shaft or a sleeve forming a body as a core material and forming the cladding layer on an outer circumference portion thereof by a continuous pouring process for cladding; and quenching the solid shaft or the sleeve formed with the cladding layer by a forced air cooling after subjecting the solid shaft or the sleeve formed with the cladding layer to a solution treatment at 1000° C. for seven hours, and further subjecting the solid shaft or the sleeve formed with the cladding layer to an aging treatment at 400 to 600° C. for seven hours while annealing heat treatment is not performed after the continuous pouring process, wherein corrosion mass loss of the cladding layer is 0.0065 mg/mm.sup.2 or less in a 48-hour corrosion resistance test defined in Japanese Industrial Standard Z2371 (JIS Z2371).

7. The method for manufacturing the roll for hot rolling process according to claim 6, wherein after the sleeve formed with the cladding layer is subject to the solution treatment, the quenching, and the aging treatment, the sleeve is fitted onto an outside of a roll shaft to form a body.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a longitudinal sectional view illustrating a roll for hot rolling process 1, where in particular, a roll to be used as a pinch roll of rolling equipment and the like is illustrated.

(2) FIG. 2 is a schematic view illustrating an arrangement of various types of rolls for hot rolling process in rolling equipment of a hot-rolled steel sheet A.

(3) FIG. 3 is an explanatory diagram illustrating a continuous pouring process for cladding that is a part of a manufacturing process of the roll for hot rolling process.

(4) FIG. 4 is a graph showing a high temperature hardness of Examples 1 to 4 and Comparative Example 1, for a cladding layer provided on the roll for hot rolling process.

DESCRIPTION OF EMBODIMENTS

(5) FIG. 1 illustrates a structure of a roll for hot rolling process 1, which is an example of the invention. In the roll 1 illustrated in the figure, a hollow sleeve 3 is attached on the outside of the roll shaft 2 by shrink fitting, and the cladding layer 4 is integrated as one with the outer circumference portion of the sleeve 3. The body 5 that is a portion contacting the hot-rolled steel sheet is formed by fitting the sleeve 3 having the cladding layer 4 onto the roll shaft 2. The roll shaft 2 and the sleeve 3 are fixed by a welding portion 6 at one end.

(6) The body 5 of the roll 1 is used in a high temperature corrosive environment where cooling water and the like came in contact while the body 5 slides and collides with a hot-rolled steel sheet. Therefore, the cladding layer 4 (with a thickness of 5 mm or more, preferably, 10 mm or more) made of high-alloy steel is provided on the outside of the sleeve 3 made of low-carbon steel (for example, JIS-SS400) to enhance the mechanical strength, the corrosion resistance, and the like of the outer circumference portion.

(7) FIG. 2 illustrates an arrangement diagram of various types of rolls for hot rolling process 12 to 15 including the roll having the same structure as that of the roll 1 of FIG. 1. In the rolling equipment of a hot-rolled steel sheet A, a plurality of rolls for hot rolling process including a run-out table roll (conveyance roll) 12, a pinch roll 13, a winding mandrel 14, a wrapper roll 14, and the like are arranged, for example, on a downstream side of a finishing rolling mill 11 as illustrated. Any of the rolls is used while being affected by a high mechanical load in a high temperature corrosive environment.

(8) The roll 1 of FIG. 1 is configured to be used as the pinch roll 13 or the wrapper roll 14 in the arrangement of FIG. 2; however, the roll 1 can be used as another roll for hot rolling process. Further, for any of the rolls for hot rolling process, the structure of the roll is not limited to the structure of FIG. 1. For example, even if a roll, in which a roll shaft is integrated as one with the body not including the sleeve and a cladding layer is formed on the body, can be used as the roll for hot rolling process.

(9) In the roll 1 of FIG. 1, the cladding layer 4 on the outer circumference portion of the sleeve 3 is formed by a continuous pouring process for cladding, which is schematically illustrated in FIG. 3. That is, the above-described sleeve made of low-carbon steel (reference numeral 3 in FIG. 1) is concentric-vertically inserted in the inner portion of a hollow combined mold 21 as the core material 23 and the core material 23 is continuously lowered while the molten metal 22 is poured into an annular gap portion outside of the core material 23. Thus, the cladding layer 24 (that is, the cladding layer 4 of FIG. 1) is formed by depositing and solidifying the molten metal 22 described above onto the outer circumference of the core material 23 (that is, the sleeve 3 of FIG. 1).

(10) Even if the roll has a different structure from that of FIG. 1, it is preferable that the rolls for hot rolling process 12 to 15 and the like illustrated in FIG. 2 is formed similarly by the continuous pouring process for cladding as shown in FIG. 3. If the roll does not have the sleeve, the body of the roll shaft is used as the solid core material 23, and the cladding layer 24 can be formed on the outer circumference of the core material 23.

(11) After forming the cladding layer 24 on the outer circumference of the hollow or solid core material 23, the cladding layer 4 and the like are appropriately heat treated and the surface and the like are machine-finished. In the roll 1 in which the hollow sleeve 3 is used as in the example of FIG. 1, the sleeve 3 which have been subject to the heat treatment and the machine-finish is fitted onto the roll shaft 2.

(12) The inventers prepared, for steel to be adopted in the cladding layer 4 of FIG. 1, a steel sample of a chemical component shown in the following Table 1 (where in any sample, the balance is Fe and inevitable impurities), and carried out various tests for the durability performance. In Table 1, the test sample of Comparative Example 1 is a material conventionally employed as the cladding layer for a wrapper roll and the like, and those of Examples 1 to 4 are materials for the cladding layer newly developed this time.

(13) It is noted that, in each test, when an actual machine test described later was carried out, a roll in which the cladding layer was formed by using the continuous pouring process for cladding illustrated in FIG. 3 was manufactured and used. When tests other than the actual machine test were carried out, each test was performed by using a test piece obtained by a metal die mold for testing (inner diameter ϕ 90 mm×length 400 mm) similar in solidifying speed to a case where the roll was manufactured by the continuous pouring process for cladding. The manufactured test piece and the roll for the actual machine test were used after being subjected to a heat treatment in which the solution treatment was performed at 1000° C. for seven hours, which was followed by forced air cooling, and then, the age hardening treatment was carried out at 400 to 600° C. for seven hours. The annealing after the continuous pouring process for cladding was not performed.

(14) TABLE-US-00001 TABLE 1 Sample # C Si Cu Mn Ni Cr Mo Co Nb V Example 1 0.64 2.94 0.96 1.58 2.78 13.8 0.8 1.08 0.36 — Example 2 0.86 4.12 1.02 1.6 3.05 13.9 1.98 0.93 1.01 — Example 3 0.86 4.08 1.04 1.55 3.06 13.8 2.82 0.92 1.01 — Example 4 0.86 4.01 1.01 1.49 2.97 13.5 3.54 0.9  0.96 — Comparative 0.51 2.99 — 0.7 5.79 7.26 1.53 — — 0.23 Example 1

(15) In Example 1 in Table 1, a target value as follows is established for chemical component of the cladding layer 4. That is, the chemical component is: 0.5 to 0.7% by mass of C, 2.8 to 4.5% by mass of Si, 0.9 to 1.1% by mass of Cu, 1.4 to 1.6% by mass of Mn, 2.7 to 3.3% by mass of Ni, 13.5 to 14.5% by mass of Cr, 0.8 to 1.1% by mass of Mo, 0.9 to 1.1% by mass of Co, and 0.2 to 0.4% by mass of Nb (where the balance is Fe and inevitable impurities).

(16) Cr has an effect of enhancing the corrosion resistance and Si has an effect of preventing the seizing, and thus, to appropriately obtain well balanced effects of both, ranges of both content amounts are set as above. When the amount of Si in the range described above is contained, Si provides an effect of improving the corrosion resistance under a condition of high temperature oxidation and high temperature water vapor. The appropriate amount of Mo and Co is included to improve the high temperature property. The appropriate amount of Nb is added for a purpose of suppressing the precipitation of the Cr carbide to the grain boundary and within the grain; preventing reduction of the corrosion resistance and the toughness resulting from reduction of the metal Cr; and suppressing solidification and growth of the crystal grain at the time of the solution treatment to finely granulate the crystal grain. Further, Cu is a precipitant hardening type element, and thus, the appropriate amount described above of Cu is added to improve the strength of the base structure.

(17) In Examples 2 to A of Table 1, a target value as follows is established for chemical component of the cladding layer 4. That is, 0.7 to 0.9% by mass of C, 3.0 to 4.2% by mass of Si, 0.9 to 1.1% by mass of Cu, 1.4 to 1.6% by mass of Mn, 2.7 to 3.3% by mass of Ni, 13.5 to 14.5% by mass of Cr, 1.8 to 4% by mass of Mo, 0.9 to 1.1% by mass of Co, and 0.9 to 1.1% by mass of Nb (where the balance is Fe and inevitable impurities).

(18) Compared to the chemical component of Example 1, amounts of C, Mo, and Nb are increased. The high temperature property of the cladding layer 4 is strengthened when the amount of these components are increased and contained in the above-described range.

(19) Various tests were performed on the test piece manufactured by the method described above (each cladding layer of Example 1 and Comparative Example 1) and the property for the durability performance was investigated. Table 2 shows the results.

(20) The test piece of Example 1 is higher in any of the tensile strength, the durability, the elasticity, the drawing, and the hardness than that of Comparative Example 1, and the same also applies to each property at a high-temperature. In the test piece of Example 1, a linear expansion coefficient is low and the durability is high, and thus, it is estimated that Example 1 has a superior performance in thermal crack resistance. Besides, Example 1 is higher in corrosion resistance, seizing resistance, and high-temperature oxidation property than Comparative Example 1.

(21) TABLE-US-00002 TABLE 2 Material Comparative Example 1 Example 1 General machine strength Tensile strength (Mpa) (500° C.) 859 (899) 950 (997) (accident resistance) 0.2% Resistance (Mpa) (500° C.) (819) 890 Elasticity (%) (500° C.) 0 (0.8) 0.2 (0.22) Drawing (%) (500° C.) 0 (0.2) 1.8 (10) Total evaluation Acceptable Good Wear resistance and Mechanical wear and hardness HS Good: 65 to 75 Very good: 65 to 75 corrosion resistance (300° C., 500° C., 700° C.) (54, 35, 12) (63, 57, 16) Corrosion resistance (48 hrs (mg/mm.sup.2) Good (0.0200) Very good (0.0049) Total evaluation Good Very good Seizing resistance Critical ratio to slip initiation (0.5 mm or more) 40%, Good 60%, Very good Thermal shock resistance Critical temperature for crack initiation 800° C. or more 800° C. or more High temperature oxidation property Increased amount of oxidation (900° C. × 24 hrs) 52.22 g/m.sup.2 .Math. hr 2.18 g/m.sup.2 .Math. hr Heat resistance property Ac1 Transformation point (° C.) 570 670 Coefficient of linear expansion 20 to 100° C. (×100° C.) Acceptable: 13.9 Very good: 11.1 (Thermal crack resistance) Surface roughening resistance Prediction from the high temperature oxidation Good Very good Total evaluation Good Very good

(22) (A particular test among) various types of tests to find out the property shown in Table 2 (is) are carried out in a manner described below.

(23) Corrosion resistance: Based on a salt spray testing method of JIS Z2371, a 48-hour test was performed to measure a corrosion mass loss before and after the test.

(24) Seizing resistance: A slip ratio at a time of seizing (critical ratio to slip initiation, the seizing width of 0.5 mm or more) was investigated by rotating a test piece using a heat seizing and wear testing machine developed by FUJICO Co., Ltd. and pressing a load member onto a surface of the test piece at a predetermined pressure (it was assumed that the SUS would be hot rolled and a stainless steel material was used as a load member).

(25) Thermal shock resistance: The test piece that has been checked in advance for no crack was heated up to a predetermined temperature and then thrown into water after which a heating temperature at which a crack occurred was measured.

(26) High-temperature oxidation property: After being cleaned and dried, the test pieces were maintained at 900° C. for 24 hours in an electric furnace in the atmosphere and then cooled, and then, the increased amount of oxidation of the test piece where the mass of a scale was included was measured.

(27) Further, an actual machine test was performed for a roll having the cladding layer of Example 1 and a roll having the cladding layer of Comparative Example 1. That is, each of the rolls was used as a wrapper roll at an actual hot rolling factory for a predetermined duration (about 100 days). In the wrapper roll of the factory, the stainless steel sheet and the like are wound up at a temperature of over 700° C., and thus, a load applied on the outer circumference portion of the roll is high.

(28) A result of the actual machine test described above indicated that the decreased amount of an outer diameter of the cladding layer of Example 1 by wear and the like (amount decreased per unit time) was 1/3.5 a similarly decreased amount of the cladding layer of Comparative Example 1. In addition, at the end of the above-described test duration, red rust was observed on the surface of the cladding layer of Comparative Example 1; however, red rust was not observed on the cladding layer 4, of Example 1 and a gloss observed before starting the test was maintained over a whole area of the surface.

(29) In addition, the inventors measured a high temperature hardness from a room temperature to 700° C. for all the test pieces including those of Examples 2 to 4. FIG. 4 shows the results.

(30) In all the test pieces of Examples 1 to 4, the hardness at 300° C. and 500° C. (and temperatures in the vicinity thereof) is far greater than the hardness of Comparative Example 1. This would result from an effect caused by a specially added element having a property of maintaining a high-temperature strength in Examples 1 to 4. It is estimated that a high degree of hardness in a high-temperature region provides an advantageous effect on the wear property of the roll in the actual machine usage environment as well as a scratch resistance, a seizing resistance, and the like.

REFERENCE SIGNS LIST

(31) 1 Roll for hot rolling process

(32) 2 Roll shaft

(33) 3 Sleeve

(34) 4 Cladding layer

(35) 5 Body

(36) 13 Pinch roll

(37) 15 Wrapper roll