JP2002348638A - Roll for continuous casting and for hot rolling superior in hot abrasion resistance and thermal cracking resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a roll for continuous casting and for hot rolling superior in hot abrasion resistance and thermal cracking resistance. SOLUTION: The roll for continuous casting and for hot rolling has a built-up surface layer superior in hot abrasion resistance and thermal cracking resistance, which includes, by mass %, 0.5-0.8% C, 0.2-3.0% Si, 0.3-3.0% Mn, 9.0-17.0% Cr, 2.0-6.4% Nb, and the balance Fe with unavoidable impurities, and satisfies such a relationship that Nb/C is 4.0-8.0. The built-up surface layer is resistant to hot abrasion and hot impact, and contributes to durability of various rolls such as for continuous casting and for hot-rolling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a build-up roll for continuous casting and hot rolling which is used at a high temperature and is repeatedly heated and cooled, and in particular, is excellent in hot abrasion resistance and which is repeatedly heated and cooled. The present invention relates to a continuous casting and hot rolling roll having a built-up surface layer having excellent heat crack resistance.

[0002]

2. Description of the Related Art A slab pinch roll, a guide roll and the like of a continuous casting facility in an ironworks are subject to severe or excessive heat cycling due to a contact load with a high temperature slab for a long period of time, as well as static or dynamic slab. Subject to large bending stress and hot wear due to pressure. Further, it is generally used under severe conditions in which heating and cooling are repeatedly performed by heating with a slab and cooling with cooling water.

[0003] Therefore, it is known that a so-called heat crack occurs on the roll surface in addition to abrasion. This is the same in the case of hot rolling.

As a measure against the above-mentioned problems, in order to improve these characteristics, a roll having a build-up surface layer on the roll surface is disclosed in Japanese Patent Application Laid-Open No. 56-152945, "Abrasion-resistant hot roll". No. 10-156500, "Overlay roll for heat-resistant crack-resistant continuous casting" and the like were proposed.

However, the load condition of the continuous casting roll has become more severe due to the recent increase in the production efficiency and the continuous casting ratio for improving the slab yield, and the above-mentioned proposed overlay roll has advantages and disadvantages. Improvements have been requested. The same applies to hot rolls, and load conditions are severe in order to improve rolling efficiency.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to develop a build-up roll which is more excellent in hot abrasion resistance and hardly causes a heat crack, in view of the above situation. That is, on the surface of the roll substrate having high toughness,
An object of the present invention is to provide a build-up roll having an excellent hot abrasion resistance and a heat-crack-resistant welded layer formed to improve the roll life.

[0007]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have conducted intensive studies and as a result, in the Cr-Fe based heat-resistant alloy overlay material, the C content has been reduced and the Nb / N The inventors have found that maintaining C within a certain range is extremely effective, and have completed the present invention.

The present invention has been made based on the above-mentioned findings.
3.0%, Mn: 0.3-3.0%, Cr: 9.0-1
7.0%, Nb: 2.0 to 6.4%, the balance being F
e and unavoidable impurities, and Nb / C is 4.0.
A roll for continuous casting and hot rolling excellent in hot abrasion resistance and heat crack resistance characterized by forming a build-up surface layer satisfying the relationship of ~ 8.0.

[0009] The present invention also relates to the present invention,
A continuity excellent in hot wear resistance and heat crack resistance as described above wherein a build-up surface layer containing at least one of 4.0% or less, W: 4.0% or less, and V: 2.0% or less is formed. Rolls for casting and hot rolling are also included in the gist.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention, its operation and effects will be described. The present invention proposes to improve the roll life by forming a weld layer having excellent hot abrasion resistance and heat crack resistance on the surface of a roll substrate having high toughness. In order to increase the toughness of the build-up roll, the composition range of the alloy component forming the build-up surface layer was defined based on the technical basis described below.

In the present invention, the C content is 0.1% by mass%.
The reason for setting the content to 5 to less than 0.8% is disclosed in Japanese Patent Application Laid-Open No.
By making the C content lower than that of the invention of No. 52945, "Abrasion resistant hot roll", the toughness of the build-up welded layer is increased and the heat-resistant cracking property is improved, which is caused by cracking under the present severe use conditions. This is because accidents such as roll breakage can be prevented.

However, since the wear resistance during hot work is slightly reduced, when forming a build-up layer by welding, the precipitation state of carbides is adjusted by controlling the welding heat cycle to solve this problem. are doing. It has been found that by further reducing the C, the heat crack resistance is greatly improved.
If the content is less than 0.5%, the abrasion resistance during hot operation is reduced, which is not preferable. Therefore, the C content in the above range was selected.

[0013] Si is added as a deoxidizing component,
If it is less than 0.2%, the effect is extremely small, and if it exceeds 3.0%, the weldability is deteriorated, and particularly in the overlay welding, the occurrence of hot cracks becomes remarkable, so the above range is adopted.

Mn is also added as a deoxidizing component like Si, but if it is less than 0.3%, the effect is insufficient and the toughness of the deposited metal is low. Further, it is added to make the metal structure of the build-up welded layer mainly martensite or a mixed structure of martensite and austenite. If the content exceeds 3.0%, the austenite structure is excessively generated, so The upper limit was set to 3.0%.

[0015] Cr is added as a structure controlling component. C
Combines with chromium carbide to improve hot wear resistance. However, when the amount is small, the formation of martensite and chromium carbide is small, and when the amount is excessive, the structure becomes δ ferrite and sufficient wear resistance cannot be obtained. Therefore, Mn and Cr
The metal structure is controlled and adjusted to a structure mainly containing martensite and chromium carbide by the amount of addition of
9.0-17.0% was selected as an appropriate amount range.

Nb is the most important component in the present invention, and has a remarkable effect on improving heat crack resistance. If the addition is less than 2.0%, the effect is small. On the other hand, if it exceeds 6.4%, a large amount of niobium carbide is formed to increase the amount of intergranular precipitates, which is not preferable, and hot cracks are likely to occur, so the upper limit was made 6.4%.

Nb suppresses grain boundary precipitation of chromium carbide,
Since it is finely dispersed as niobium carbide in the metal structure,
It effectively acts to prevent coarsening of crystal grains, improve toughness, abrasion resistance and hot cracking resistance. Therefore, it is necessary to control the Nb addition amount by the C content, and Nb / C
It was confirmed that the ratio in the range of 4.0 to 8.0 was appropriate. In particular, when this value exceeds 8.0, C is fixed unnecessarily as a carbide, so that the amount of martensite in the metal structure tends to decrease. Therefore, it was selected in the above range.

Mo, W and V to which one or more are added
Is effective in improving the hot abrasion resistance of the build-up layer, increases the curability, and partially forms carbide to disperse in the tissue. However, when a large amount is added, the matrix becomes embrittled, so that Mo and W are each 4.0% or less, and V is 2.0% or less.
%.

In the case of welding, the build-up layer composed of the above components can be build-up welded on the surface of the roll base by covering arc welding, submerged arc welding, or the like. However, since the generated metal structure changes due to the welding heat cycle and the subsequent heat treatment, it is natural that the composition of these components is selected so as to have a predetermined structure ratio.

Since the formation and dispersion state of the carbides is also changed by the post heat treatment after the welding, the predetermined hardness level and the metal structure can be obtained by controlling the annealing temperature and the holding time for removing the residual stress of the overlay roll. Needless to say, The post heat treatment temperature after this welding is 500 to 650 ° C. and 1
It is appropriate to hold for about 5 hours and cool slowly.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described, but the present invention is not limited thereto. A hot abrasion resistance test which determines the durability of the roll and a thermal shock test for evaluating the heat crack resistance were performed. As the wear resistance test material, a flux cored wire using the various welding materials shown in Tables 1 and 2 was manufactured, and the base material was manufactured by a submerged arc welding method.
5 mm thick S25C (C: 0.25%, Si: 0.23
%, Mn: 0.75%, Fe: bal. ) On which 6 layers of 5 mm thick overlay welding were performed, and after the welding, annealing was performed at 550 ° C. for 3 hours. And each test sample was cut out from these. The welding conditions are as shown in Table 1, and the chemical components after welding (analysis samples were taken from the sixth layer) are as shown in Table 3.

[0022]

[0023]

[Table 2]

[0024]

[Table 3]

The hot abrasion resistance test is a pin-on-disk type abrasion test shown in FIG. 1 and is a tester of a system in which a test sample is heated to 350 ° C. by the lower heater 14 during the test. In FIG. 1, reference numeral 11 denotes a build-up layer, and reference numeral 12 denotes a pin (material SKD-
11) and 13 are wear surfaces, and 14 is a heater for heating the sample. The pin has a diameter of 20 mm, is pressed with a load of 5 kg, and slides along a 50 mm diameter circular orbit. The evaluation was made based on the wear depth of the overlay. A thermal shock test was performed to evaluate thermal cracking. Under the same welding conditions as in the wear resistance test, a sample roll (115φ × 1
322L, SNCM220 material), build-up welding having a thickness of 5 mm, and annealing at 550 ° C. for 3 hours. And
The machine was finished to a predetermined size of 120 mmφ. The components of the weld layer of each sample roll material were almost the same as those of the plate material in Table 2.

In this test, the generation of heat cracks and the degree of growth can be compared by the load on the sample roll and the thermal stress of heating and cooling. That is, FIG. 2 shows the outline of the test method. A sample roll 21 is heated to 400 ° C. by a frame 22 while rotating the sample roll, and rapidly cooled to 200 ° C. by a water-cooled header 23 on the opposite side. The load is applied by 24 hydraulic mechanisms. After the specified test time,
The shape of the heat crack on the surface is inspected and the cross section is cut to measure the depth of the heat crack. Table 4 shows the conditions of this test, and Table 5 shows the test results of both.

[0027]

[0028]

[Table 5]

N0.1 to N4 are examples of claim 1 of the present invention. 5 to 9 are examples of claim 2. Others are comparative examples, and it was confirmed that the abrasion resistance was much higher than that of an SNCM forged steel material (corresponding to a solid material without overlay welding). From the test results, the sample material of the present invention has a small amount of wear and a small number of surface cracks due to the thermal shock test.

[0030]

Since the present invention is constructed as described above, the surface build-up layer formed on the roll is resistant to hot abrasion and thermal shock due to slabs and has high durability for continuous casting and hot working. It is most suitable for use as various rolls for rolling, improves productivity and is extremely useful in industry.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory diagram of a hot pin-on-disk wear test of a build-up roll material sample of the present invention.

FIG. 2 is a schematic explanatory view of a flame heating type thermal shock test under a bending stress of a sample of the overlay material of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Overlay welding layer 21 Sample roll 12 Pin (no heating) 22 Frame torch 13 Sliding wear part 23 Water cooling nozzle 14 Heater 24 Load hydraulic mechanism 25 Roll holding stand 26 Motor drive part

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) F16C 13/00 F16C 13/00 EF term (reference) 3J103 AA02 BA15 EA06 FA01 FA09 FA12 FA13 FA14 GA02 GA17 HA04 HA15 HA32 HA52 HA54 4E016 CA08 EA02 FA14

Claims (2)

[Claims] 1. mass%, C: 0.5 to less than 0.8%,
Si: 0.2 to 3.0%, Mn: 0.3 to 3.0%, C
r: 9.0-17.0%, Nb: 2.0-6.4%, the balance being Fe and unavoidable impurities, and N
A roll for continuous casting and hot rolling excellent in hot abrasion resistance and heat crack resistance, wherein a build-up surface layer satisfying a relationship of b / C of 4.0 to 8.0 is formed. 2. Mo: 4.0% or less, W:
2. A continuous casting and hot rolling excellent in hot wear resistance and heat crack resistance according to claim 1, wherein a buildup surface layer containing at least one of 4.0% or less and V: 2.0% or less is formed. For roll.