JPS62207581A - Life extending method for roll receiving high thermal stress - Google Patents

Abstract

PURPOSE:To improve the equipment operation rate, etc. by performing a buildup welding with the heat resistant, corrosion resistant and wear resistant metal material containing the prescribed wt% Cr on the surface of a roll shell, then by forming a remelt zone in the prescribed width by melting with the specified heat input quantity. CONSTITUTION:The surface of a shell part 1 is formed in a flat cylindrical face after performing the buildup welding of the heat resistant, corrosion resistant and wear resistant metal material of a martensite group, etc. containing 11-19% Cr on the surface of the shell part 1 of a roll. The remelt zone 2 in 2-10mm width is then formed in serial state with the small heat input of 600-1,500 Joule/cm without using any filler rod by TIG welding method, etc. for the surface thereof. A crack is caused along the direction of the remelt zone 2 in short time after using the roll, but the thermal stress is released, so the generation of a big crack in the other direction can be prevented. In this way, the roll life is extended and the improvement in the equipment operation rate and reduction in the equipment cost are enabled.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is applicable to continuous caster rolls, slab conveying rollers, blooming plant table rollers, etc. This invention relates to a method for extending the life of rolls that are subjected to high heat loads, uneven heat, and impact forces.

(Prior Art) This type of roll receives a high heat load on the side in contact with the high-temperature slab or billet, and is cooled on the opposite side by internal cooling water and external forced cooling.

Therefore, thermal stress due to repeated heating and cooling acts on the roll surface, causing thermal fatigue cracks to occur. Then, bending loads due to the molten steel static pressure of the molten steel slab of the continuous cast slab, the weight of the slab, etc. act, and there is a risk that cracks will propagate internally and lead to roll breakage.

Conventional techniques for improving crack resistance and crack propagation resistance include (1) rolls using a material with excellent crack propagation resistance for the roll core material and a material with excellent crack resistance for the surface;
(iυ sleeve structure roll, (Co., Ltd.) wave-shaped overlay welding roll, (Roll) roll that is made to undergo quenching embrittlement using a laser to induce microcracks, etc. are known.

(Problems to be solved by the invention) Even with the rolls equipped with the above-mentioned conventional technology, heating,
Thermal fatigue cracks due to repeated cooling cannot be sufficiently prevented, and cracks often occur on the surface within 0.5 to 5 months after use, rendering the product unusable.

In particular, continuous casting rolls have a problem in that the rolls break after about a month of use, forcing casting to be stopped midway.

It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide an effective method for preventing roll breakage and reducing crack depth as the roll is subjected to high heat loads.

(Means and actions to solve the problem) In a roll whose body surface has a uniform structure, thermal fatigue cracks occur in a uniform direction due to repeated heating and cooling, but under other conditions, In other words, it was found that the main cause of roll breakage was the development of cracks in a direction perpendicular to the longitudinal direction of the roll due to the static pressure of the molten steel in the slab and the bending load due to the weight of the slab. .

The present invention was made based on this knowledge with the intention of guiding and regulating the direction in which thermal stress cracks occur and propagate in a direction other than the direction perpendicular to the longitudinal direction that causes roll breakage.

That is, in the method of extending the life of a roll subjected to high thermal stress according to the present invention, the body surface of the roll is
It is formed into a flat cylindrical surface with approximately the finished diameter using a heat-resistant, corrosion-resistant, and wear-resistant metal material such as martensitic, martensitic-ferrite, or martensitic-austenitic material containing thichrome, and then 600 to 15,000 units per unit. It is characterized by forming a remelt zone having a width of 2 to 10113 mm by welding the heat input at the mouth in a row in either a direction parallel to or crossing the roll axis.

Hereinafter, the method of the present invention will be specifically explained with reference to the accompanying drawings.

FIG. 1 shows a roll implementing the method of the invention.

At least the surface portion of the body (1) of this roll is 11 to 19
% Or-containing martensitic, martensitic-ferrite, or martensitic-austenitic heat-resistant, corrosion-resistant, wear-resistant metal materials, finish the body surface, or flat cylindrical surface with a small finishing allowance. Form.

Then, weld the surface with a small heat input of 600 to 15,000 joules/α without using a filler rod using the '1' IG welding method, etc., and remelt the welded part to
Ten remelt zones (2) are formed in a row.

The welding direction of the remelt zones (2), which leaves a non-welded raw material part (3) between the remelt zones, is a lattice pattern of intersecting spirals that are inclined in two directions in the same row, but the welding direction is perpendicular to the longitudinal direction of the roll. A direction other than that, for example, a direction parallel to the axis, a spiral inclined in one direction, or a combination of these may be used.

By doing this, the silimelt zone (2) will have a coarse dendrite structure with coarse crystal grains, and will have a brittle structure.
Hot cracking occurs depending on the welding conditions. In normal welding, such embrittlement and cracking are considered welding defects. In the present invention, cracks occur along the direction of the remelt zone and within the remelt zone within a short time after use of the implementation roll, and the thermal stress is released by this crack, so no cracks occur in other directions, and initially It is possible to induce cracks in an intended pattern in a direction where fc roll breakage is less likely to occur.

In the method of the present invention, the roll surface is made of 11 to 19 chromium steel because its martensite-based structure maintains the integrity of the original material other than the 11 melt zone, and the material other than the remelt zone is compatible with the melt zone. This is to avoid cracking as much as possible. If the width of the remelt zone is less than 2 mm, it will not be possible to induce the desired crack generation.If the width of the melt zone exceeds 10 to 1, cracks may also occur in the width direction of the remelt zone. It becomes impossible to induce cracks in the direction. The reason why the heat input for remelt welding is set to 600 to 15,000 joules/cIlt is to form a remelt zone with an appropriate width. Figures 2 (a), (b) <-> and 2) are sketch diagrams of the macrostructure results when a silimelt condition investigation test was conducted using a TIG arc without a filler rod, and the magnification is 3.

The relationship between the heat input and the width of the melt zone for each entered welding condition is shown. In Figure 2 (b), cracks (4) have occurred in the remelt zone. 2) is not preferred because the heat input is 1'6900 joules/cmM, which is outside the range of the present invention, and the surface becomes uneven, requiring surface refinishing.

(Example) Trunk diameter 400+n, trunk length 2200 M after long-term use
After the body of M was overlay welded using 15G band arc welding, heat treated, and finished, the surface of the body was remelted using TIG arc welding without using a filler rod, as shown in Figure 1. The conditions are as follows.

Electrode: diameter 5.2 M, thorium-filled tungsten.

Polarity: Positive polarity of base material positive and electrode negative.

Welding conditions: 400A, 19V, 580PM
, heat input: 7700 Joule/cIR.

Angle between roll axis in remelt direction = 45°Remelt width: 7 degrees.

Rimelt pitch: 404.

Remelt line direction: Cross direction of right-handed and left-handed threads.

Finishing after remelting: Only grinder maintenance required, no machine finishing.

The rolls tested under the above conditions had hair cracks in the remelt zone in the remelt welding direction. When this roll was tried on an actual machine, the hair cracks in the remelt zone developed in the direction of the remelt line, creating a twill pattern.
No major cracks occurred in other parts, and good results were obtained.

The method of the present invention can be implemented with various changes and specifications added to the implementation conditions in addition to the above-mentioned examples. For example, in addition to TIG arc welding, carbon arc welding and plasma arc welding can be used for remelt welding.

Furthermore, it is permissible to add some melt additive to the remelt zone, thereby making it possible to adjust the properties of the remelt zone. In particular, for base rolls with relatively low hardness that contain residual austenite and ferrite, it is effective to take measures to prevent shrinkage cracks and nonmetallic inclusions from accumulating in ghost lines by selecting the form of the remelt zone. In this method, if the remelt metal is formed as a porous bead, it is possible to suppress the propagation of induced cracks. Although remelt welding is often performed with a single electrode, it can be performed with multiple electrodes to increase work efficiency and shorten the work time.

Furthermore, even if the remelting treatment area is limited to the entire length of the body or the high-stress area, such as the middle part of the body length 1/2, an effective anti-breakage effect will be exhibited and the construction burden will be reduced. Further, as shown in the examples, the present invention is applicable not only to new rolls but also to welding repair of rolls worn out due to use.

(Effects of the Invention) As described above, according to the method of the present invention, it is possible to obtain a roll that is highly durable and has a longer service life than the manufacturing method of the prior art for rolls that are subjected to high heat loads. Moreover, there is little increase in material costs, processing labor, and processing equipment burden during implementation, and the cost is lower than that of the conventional technology. As a result of the extended life, the cost of purchasing spare rolls can be reduced, and many positive results can be brought about in the operation of the equipment and equipment using this roll.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional side view of a roll showing one embodiment of the present invention;
Figure 2 (a) is a cross-sectional view of the remelt zone when the heat input is low during remelt welding according to the present invention, and Figure 2 (b) is a cross-sectional view of the remelt zone when the heat input is medium. ) is a sectional view of the remelt zone when the heat input is also large, and FIG. 2) is a sectional view of the remelt zone when the heat input is excessive for comparison. (1) Fist Φ body, (2)...remelt zone, (3) @
・Protoplasm, (4)...Crack.

Claims (1)

[Claims] The surface of the body of the roll is formed into a flat cylindrical surface with approximately the finished diameter using a heat-resistant, corrosion-resistant, and wear-resistant metal material of martensitic, martensitic/ferrite, or martensitic/austenitic materials containing 11 to 19% chromium. And then 6
High thermal stress characterized by welding with a heat input of 00 to 15,000 joules/cm in a row in either direction parallel to or intersecting the roll axis to form a 2 to 10 mm wide glue melt zone. How to extend the lifespan of rolls.