JPS6112985B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to slab guide rolls for continuous casters, such as roller apron rolls or pinch rolls, for continuous steel casters used in corrosive environments. Conventional slab guide rolls for continuous casting machines have, for example, C 0.20% or less, Si 0.2 to 0.4%, and Mn 0.4 to 0.7.
%, Ni 0.4~0.7%, Cr 0.5~1.0%, Mo 0.20~
Low carbon low alloy steel containing 0.35% and V 0.1~0.2% is heat treated and tempered to a hardness of approximately Hs40° or less. It functions to guide this onto the table in the vertical direction or while gradually changing direction from the vertical direction to the horizontal direction. A slab guide roll for a continuous casting machine is constantly water-cooled during casting operations, but its surface is rapidly heated as it comes into contact with the slab each time it rotates, and then rapidly cooled by cooling water. That is, each point on the working surface of the roll is repeatedly heated and cooled at the same cycle as the roll rotation. The instantaneous maximum temperature on the roll surface is approximately 500 to 600℃, and the minimum temperature is approximately 100℃.
℃, but by repeating this process, the surface hardness of the roll gradually decreases, and the wear resistance further deteriorates. Moreover, repeated heating and cooling causes heat cracks due to thermal fatigue, and the roll surface is worn and deformed due to the frictional force between the scale existing therein and the slab roll. Furthermore, if heat cracks develop, the skin will become rough due to chipping of the surface tissue. On the other hand, in a roller apron, when the wear and roughness of any one roll reaches its limit, all the rolls are removed and replaced with new rolls. These rolls are replaced approximately once every two months, but since a recutting amount of approximately 2 mm is required, including a 1.2 to 1.5 mm turning amount and wear amount to remove heat cracks, productivity is reduced. In order to increase this, there is a demand for an improvement in the width of the reclassification interval. Originally, the effective diameter of slab guide rolls for continuous casting machines is extremely small compared to the barrel diameter, at most a few millimeters or less, and re-cutting is rarely performed, so the amount of wear and its variation will affect the life of the roll. Significantly affected. Therefore, in order to extend the service life, it is extremely important to improve the wear resistance and heat crack resistance of the material. On the other hand, the cooling water used in a continuous casting plant must be as non-corrosive as possible. This is because the corrosive cooling water corrodes the surface of the roll, further shortening the life of the roll. However, depending on the factory, there may be cases where it is unavoidable to use highly corrosive cooling water. For example, this may occur when seawater is mixed into the cooling water source. In this case, the roll material must not only have excellent abrasion resistance and heat crack resistance, but also excellent corrosion resistance, but the rolls conventionally used in continuous casting machines cannot meet these requirements. It cannot withstand harsh conditions. The present invention greatly improves the lack of abrasion resistance and heat crack resistance, which are the drawbacks of conventional rolls as described above, and furthermore, the present invention provides a continuous roll that exhibits sufficient corrosion resistance even against cooling water mixed with seawater. This product was developed for the purpose of providing a slab guide roll for a casting machine, and consists of the following three components. (1) A composite roll or composite sleeve in which the outer shell layer is welded onto the body surface of a strong core member. The core member is a shaft core part in which the roll shaft part and the core part of the body part are integrated, and is made of cast steel or cold steel having a chemical composition and hardness as illustrated in Table 1 below.

[Table] The core member and the outer shell layer may be welded together, for example, by the following method. (a) A method of performing submerged arc welding on the shell surface of a core member having the components shown in Table 1 using a welding core having the composition to become the outer shell layer material described later. (b) A method of welding the outer shell layer material and the core member by centrifugal casting. That is, while rotating a mold with a cylindrical or roll-shaped inner shape, first the molten metal for the outer shell layer material is cast, then the inner surface of the molten metal is coated with flux, the solidification of the outer shell material progresses, and the flux While a certain amount of unsolidified molten metal remains below, the molten metal for the core member is poured and the two are welded together. (c) A method of welding the molten metal of the outer shell layer material to the surface of the solid core member. That is, a core member (cylindrical) is placed concentrically inside a mold with a cylindrical inner surface and preheated, and then the molten metal that is to become the outer shell layer is rotated in the cylindrical space between this and the mold. Pour the mixture while heating it and gradually cool it down. (2) The material of the outer shell layer is martensitic precipitation hardening stainless steel consisting of the following chemical components.
That is, C 0.01-0.25%, Si 0.15-2.0%, Mn 0.2
~2.0%, Ni 3.0~6.0%, Cr 12.0~20.0%,
Cu 2.0 to 5.0%, Mo 0.1 to 1.5%, and the remainder is substantially Fe.Although the above-mentioned steel in the present invention is somewhat similar to SUS630 steel, the substance range is adjusted to meet the purpose of the present invention. The above steel is SUS630 steel with C, Cr, Cu, and some other elements expanded in the range, 0.1 to 1.5% Mo added, and Nb+Ta omitted. , which has the purposes and effects described below. The above steel is a martensitic precipitation hardening stainless steel that has a maximum precipitation hardening hardness around 470°C, and the optimum heat treatment conditions vary slightly depending on the composition, but as shown in Figure 1,
By aging at ℃, a high hot hardness of Hs 40 to 50℃ and hot wear resistance suitable for the purpose of the present invention can be obtained. The toughness (first
(Fig. 1, Charpy impact value) is improved, and sufficient crack resistance can be obtained. Figure 1 shows 400~
Corrosion rates obtained from roll samples of the present invention aged at various temperatures between 650°C (concentration 0.08%,
(by NaCl solution with temperature 70℃ and pH 7.1-8.2)
Table ² shows the relationship between aging temperature and precipitation hardness Hs, precipitation hardening hardness Hs, Charpy impact value Kg·m/cm ² and aging temperature. In the figure, (1) is corrosion rate, (2) is precipitation hardening hardness,
(3) is the Shalpy impact value.

[Table] In addition, the steel of the outer shell material in the present invention exhibits high corrosion resistance as described below, even though it contains considerably higher C% than SUS630 steel. Figure 2 is a comparative diagram of the corrosion resistance of various materials shown in Table 3 below, in which A and B are steels with components that belong to the present invention, and A and B are steels with components that belong to the invention (1). - This is an example of an outer shell layer welded to a core member by the method of (c). Further, C is a conventional low alloy steel roll material, and D is 13Cr stainless steel. The data in Figure 2 are all concentrations.
These results were obtained by repeatedly immersing and taking out the sample in a NaCl solution with a concentration of 0.08%, a temperature of 70°C, and a pH of 7.1 to 8.2.The outer shell materials of the rolls of the present invention all have excellent corrosion resistance, and are superior to conventional ones. It shows 150 to 200 times more corrosion resistance than roll steel. or,
Even when compared to 13Cr stainless steel, which has a reputation for corrosion resistance, it can be seen that it shows a marked advantage in corrosion resistance.

【table】

[Table] (3) Heat-treat the outer shell layer of the composite roll or composite sleeve described in (1) and (2) above, and
Age harden to Hs40~50°. Since the steel used in the present invention is a martensitic precipitation hardening stainless steel, it is first cooled from a solution at around 1050°C to a martensitic + austenite structure as a pre-aging treatment, and then
It is age-hardened at 500-650°C to provide stable hardness of Hs 40-50° and the required toughness. However, in the case of composite materials made by submerged arc welding as shown in (1)-(a) above, the weld metal becomes martensitic during the process of welding the outer shell layer onto the core member, so solution treatment at 1050℃ is required. This has the advantage that processing can be omitted. In this case, 500 to 60 after welding
There is an advantage that waste rolls can be used as core members because only low-temperature treatment is required, and oxidation loss and thermal deformation can be ignored. Furthermore, the above-mentioned age hardening temperature range of 500 to 650°C for the outer shell layer material almost coincides with the range of instantaneous maximum temperature variation at the contact surface between the slab and the roll during continuous casting. The contact surface temperature of the roll changes depending on the installed position, continuous casting speed, cooling conditions, etc., but the maximum value of the contact temperature can be determined by utilizing the coincidence of the temperature ranges of the precipitation hardening temperature and the contact surface temperature. If this temperature is used for aging treatment, a roll with extremely stable hardness can be obtained. This temperature range slightly exceeds the maximum precipitation hardening temperature (approximately 470°C), so this hardness does not reach the maximum hardness of approximately Hs55° that this steel can reach, but as mentioned above, it is Hs40~50, It has a high hardness compared to the Hs of 35 to 40 degrees for rolls, and has an overwhelmingly high content of Cr, Mo, etc., so it has extremely high wear resistance. As mentioned earlier, the steel of the present invention has extremely excellent crack resistance and corrosion resistance within the above aging temperature range, and has a life several times longer than that of conventional rolls. Next, the effects of alloying elements in the present invention and the reason for limiting the content range will be described. C: The lower the C%, the easier it is to become martensite and the better the corrosion resistance. Conversely, the higher the C%, the better the wear resistance. However, if the C content is less than 0.01%, the strength is insufficient and it is not suitable for the purpose of the present invention, and if the C content exceeds 0.25%, corrosion fatigue progresses due to a decrease in corrosion resistance and toughness, resulting in a shortened roll life. Therefore, the content range of C is 0.01 to 0.25%. Si: As a deoxidizing element, a minimum of 0.15% must remain, so the lower limit is 0.15%. However, if it exceeds 2.0%, toughness decreases and heat crack resistance is lost, so the upper limit is set at 2.0%. Mn; Since Mn is added as a desulfurizing agent, it is inevitable that 0.2% or more of Mn remains. However, if it exceeds 2.0%, it will have a negative effect on martensite formation, so the content range of Mn should be 0.2~
2.0%. Ni: Ni improves corrosion resistance and heat crack resistance. However, if it is less than 3.0%, the effect is insufficient from the purpose of the present invention, and if it is less than 6.0%.
If it exceeds this amount, there will be too much retained austenite, making it impossible to obtain sufficient wear resistance. Accordingly
The Ni content range is 3.0 to 6.0%. Cr: Cr significantly increases corrosion resistance and wear resistance, and is also an essential component for martensitic formation and precipitation hardening. However, if it is less than 12%, corrosion resistance is insufficient, and on the other hand, if it exceeds 20%, ferrite increases. This results in loss of wear resistance. Therefore, the Cr content range suitable for the purpose of the present invention is 12.0 to 20.0%.
It is. Cu: Similar to Cr, Cu improves corrosion resistance and also forms a precipitate phase together, contributing to hardness and wear resistance. However, if it is less than 2.0%, precipitation hardening is insufficient, and if it is more than 5.0%, toughness decreases and heat crack resistance is lost. Therefore, Cu should be 2.0 to 5.0%. Mo: Mo increases tempering resistance and improves corrosion resistance. However, if it is less than 0.1%, there is no effect, and if it is more than 1.5%, the effect increases only slightly compared to the increase in the amount added, so the content range is set at 0.1 to 1.5%. Next, examples of the present invention and their usage results will be shown. Example 1 Name Guide roll for continuous casting machine apron Dimensions 300mmφ x 2000mm (body) x 3000mm (total length)

[Table] Manufacturing process Core member casting → Heat treatment x Finishing only the body diameter → Welding the outer shell material to the shell surface by submerged arc welding → Age hardening treatment at 600℃ → Mechanical finishing → Inspection welded copper (outer shell Material) thickness (finishing condition) 6 mm (diameter) Hardness Hs42゜ Usage results Results of continuous use for 7 months Amount of roll diameter wear 0.4 to 0.5 mm Roll surface condition Hardly any heat cracks Uniformity of wear Good modification Amount 0.8mm (wear amount) Example 2 Name Guide roll sleeve for continuous casting machine apron Dimensions 300mmφ (outer diameter) x 200mmφ (inner diameter) x 2000mm
(long)

[Table] Manufacturing process Horizontal centrifugal casting method Casting using the method (1)-(b) above (cylindrical mold internal shape) →
Rapid cooling held at 1050℃ → Aging treatment at 500℃ → Finishing of the outer periphery and inner surface → Shrink fitting of the above sleeve to the core material recycled from waste rolls → Machined finish Thickness of outer shell material (finished state) 6 mm (diameter) ) Hardness Hs49゜ Usage results Results of 8 months of continuous use Roll diameter wear amount 0.2 to 0.3 mm Roll surface condition Hardly any heat cracks Wear uniformity Good modification amount 0.5 mm (wear amount)

[Brief explanation of the drawing]

Figure 1 shows the relationship between the aging treatment temperature and corrosion rate, precipitation hardening hardness, and Shapey impact value of the steel in the present invention, and Figure 2 compares the corrosion resistance of the steel in the present invention and conventionally known steels. It is something.

Claims (1)

[Claims] 1. In a composite roll or composite sleeve formed by welding an outer shell layer to the surface of a strong core member, the outer shell layer contains 0.01 to 0.25% C and 0.15 to 2.0% Si.
%, Mn 0.2~2.0%, Ni 3.0~6.0%, Cr 12.0~
20.0%, Cu 2.0~5.0%, Mo 0.1~1.5%, the remainder is made of martensitic precipitation hardening stainless steel consisting essentially of Fe, and is age hardened to increase its hardness.
Abrasion resistance characterized by Hs40~50°,
A slab guide roll for continuous casting machines with excellent corrosion resistance and heat crack resistance.