JPS5935983B2 - Steel for rolls in continuous casting equipment - Google Patents

Description

Detailed Description of the Invention The present invention has significantly higher thermal fatigue resistance and high temperature wear resistance than CA-15 steel used for high-temperature slab rolls (support, guide, pinch rolls) used in continuous casting equipment. This invention relates to steel for rolls with improved properties.

Steel for rolls in continuous casting equipment is constantly subjected to heating effects due to contact with high-temperature slabs, and at the same time is also subjected to cooling effects from cooling water. Since roll wear due to oxidation is significant, there is a demand for a roll steel that can replace the above CA-15 steel.

In order to meet the above demands, the present inventors conducted metallurgical alloy design and practical tests, and found that the long-life roll steel shown below has excellent properties such as thermal fatigue resistance, high-temperature wear resistance, and high-temperature oxidation resistance. All results were satisfactory.

That is, the present invention has the following characteristics: (1) C: 0.05 to 0.20, Si: 0.1 to 1.
5゜Mn: 0.1-1.5%, Ni: 0.2
~3.0%, Cr: 7.0~12.0, Mo
: 0.1-2.0%, V2 0.1-1.0%, Nb
:0.03 to 1.0 ratio, steel for rolls in continuous casting equipment, with the remainder substantially consisting of Fe.

(2) C: 0.05-0.20, Si: 0.1-1.
5%, Mn: 0.1-1.5%, Ni: 0.
2-3.0%, Cr: 7.0-12.0%,
Mo: 0.1-2.0%, V: 0.1-1.0%
, Nb: 0.03 to 1.0, and Ti: 0
．． 05-0.50%, Zr:0. O1~0.30%, T
A steel for rolls of continuous casting equipment, containing one or more of the following: a: 0.01 to 0.50%, B: 0.01% or less, with the remainder substantially consisting of Fe.

It is.

The first feature is that by adding Nb, grains are made finer, and by balancing the alloy composition, the formation of 8-ferrite is suppressed, and thermal fatigue resistance is significantly improved.

The second feature is that, in order to ensure high-temperature wear resistance, it contains an alloy component that exhibits a secondary hardening effect and an alloy component that exhibits an effect of improving high-temperature oxidation resistance.

Next, the reason for numerically limiting the alloy composition of the steel of the present invention will be explained.

C: 0.05-0.20% In order to ensure strength and suppress the formation of 8-ferrite, it is necessary to add at least 0.05% or more.

However, if it is contained in a large amount, the toughness decreases, so 0.2
It was set as 0% or less.

Si: 0.1-1.5% Contains at least 0.1% or more to ensure high-temperature oxidation resistance and as a deoxidizing element during melting and refining, but if it is included in a large amount, it tends to impair thermal fatigue resistance. 1.5%
It was determined as follows.

Mn: 0.1-1.5.

The content should be at least 0.1% for deoxidation during melting and refining, but if it is included in a large amount, residual austenite will be generated and the hardness will be reduced, and the toughness will also be reduced, causing roll breakage. It was determined as follows.

Ni: 0.2 to 3.0 Coefficient: 7 to 12% Since coexistence with Cr has the effect of improving thermal fatigue resistance and high temperature wear resistance, it should be contained at least 0.2% or more, but it should not be contained in large amounts. 3. If this happens, the tendency for residual austenite to form during quenching will increase.
It has been set as 0 or below.

Cr: 7. O~12.0% In order to ensure thermal fatigue resistance, high-temperature wear resistance, high-temperature strength, etc., it is necessary to contain at least 7% or more.

In addition, in continuous casting rolls with 11% and 7% Cr, heat cracks occur early in the latter, but Nbs Tiy V,
It has been found that the addition of Ta and Zr significantly reduces the propagation speed of heat cracks, resulting in a longer life than CA-15 steel.

However, if a large amount of Cr is contained, the tendency to generate 8-ferrite during quenching increases, so the content is set at 12% or less.

Mo size 0. i~2.0. % It is necessary to contain at least 0.1% or more in order to exhibit a secondary hardening effect in the high-temperature tempering state and to ensure high-temperature wear resistance.

However, if it is contained in a large amount, the tendency to form 8-ferrite during quenching increases, so it was set to be less than 2.0.

It should be noted that W in an amount almost twice as much can be substituted because it exhibits the same effect as Mo.

v: o, i ~ 1.0% It has a softening resistance effect in the high temperature tempered state, and when coexisting with Mo, it is effective for ensuring high temperature strength and high temperature toughness and ductility, and it is necessary to contain at least 0.1% or more. It is.

However, even if the content exceeds 1.0%, the above-mentioned effects are not significantly increased, and 8-ferrite is more likely to be produced.

From this point of view, V: 0.1-1゛, 0% was determined.

Nb: 0.03-1.0% Nb is the most important element in the steel of the present invention and has the effect of significantly improving the thermal fatigue resistance, which is an essential property, so it is necessary to contain it at least 0.03%. be.

However, this effect tends to be saturated when the content reaches 1.0, which is not preferable because the austenitization temperature increases and the tendency for high-temperature embrittlement increases.

Ti, Zr, Ta: Like Nb, in addition to its grain refining effect, it is useful for improving tempering softening resistance and secondary hardenability, and can increase toughness and high-temperature strength, so each should be 0.05% or more, 0
．． By containing 0.01% or more, 0.01% or more, thermal fatigue resistance and high temperature strength are further improved.

However, containing a large amount increases the austenitizing temperature and increases the tendency for high-temperature embrittlement.
0.30, 0.50 or less.

B: 0.01 or less B is added alone to the first invention steel, or Tis
When B is added in combination with Zry Ta,
Furthermore, it is possible to strengthen grain boundaries and has the effect of reducing the propagation speed of heat cracks, so it is contained in a range of 0.01% or less.

Next, the features of the steel for rolls of the present invention will be explained in detail using examples.

Example 1 For comparison with the steel for rolls of the present invention having the composition shown in Table 1 in an experimental melting furnace, CA-15 steel (C-1), which has conventionally been used for this type of application, and its A low Cr Ni-Cr-Mo-V steel was also produced.

C-L S-1, S-2 and S-4 test materials in Table 1 were quenched (950°C x 1.5hr A, C) and tempered (650°
CX2hrA,C) treatment was performed, and high temperature tensile strength was measured.

The results are shown in FIG.

As can be seen from the figure, the steels of the present invention (S-1, S-2, S
-4) is superior to the conventional steel (C-x), especially the second invention steel (S-4) containing Ta and Zr.
It is clear that -4) has excellent high temperature strength.

Next, the parallel part (
D: 10 $mm) using a test piece with a hole a of 1 mm in diameter and 2 mm in depth, using a high-frequency heating fatigue testing machine under the thermal cycle shown in Figure 3 (heating and cooling rate = 10°C/5ec). We investigated the propagation characteristics of heat cracks, which are used as an index for evaluating thermal fatigue resistance.

The results are shown in FIG. According to this, as long as the number of repetitions of thermal cycles is small, there is no significant difference between each sample material.

However, as the number of repetitions exceeds 300, the crack length of the conventional steel grows rapidly, but the crack length of the steel of the present invention containing Nb grows very slowly.

This means that even though heat cracks occur due to heat cycling in the rolls of continuous casting equipment, the growth rate of cracks is slow and the life of the rolls is long.

Example 2 The steel for rolls of the present invention having the composition shown in Table 2 and the conventional steel for brazing were melted in an experimental melting furnace, then cast in a horizontal continuous casting pipe manufacturing device, heat-treated, and cast. Diameter 450noX
We prototyped a roll with an inner diameter of 33'Omm and a length of 2300 mm.
A practical test was conducted as a pinch roll for continuous casting equipment for 10 months, and the depth and number of cracks were investigated.

The results are shown in FIG. As is clear from the figure, the conventional steel (C-3) had many large cracks, but the steel of the present invention (S-5) had shallow cracks.

It was confirmed that continuous casting rolls with a large number of cracks but with shallow cracks and with a slow crack propagation speed have a long life.

Furthermore, in order to confirm the high-temperature wear resistance as a characteristic required for continuous casting rolls, among the above test steels, conventional steel C-3 and inventive steel S-1, S-5 to 6 were tested. A wear test piece with the shape shown in the figure (D: 30f, DI:
22/, D2: 16. W: 11, Wl: 3) were sampled, and the specific wear amount was measured under the test conditions shown in Table 3.

The results are shown in FIG.

As shown in the figure, the specific wear amount of the steel of the present invention is significantly smaller than that of the conventional steel.

In other words, it is clearly seen that the high-temperature wear resistance is excellent.

As mentioned above, compared to CA-15 steel, which has conventionally been used as a steel for continuous casting rolls, the steel of the present invention contains appropriate amounts of niobium and vanadium to significantly improve thermal fatigue resistance. The results are significant.

[Brief explanation of drawings]

Figure 1 is a diagram of the high-temperature tensile strength curve of the sample material, Figure 2 is a schematic diagram of a heat fatigue test piece, Figure 3 is a diagram showing the thermal cycle of the heat fatigue test, and Figure 4 is the heat fatigue resistance of the sample material. FIG. 5 is a diagram showing the distribution of surface oxidation on the practical test material, FIG. 6 is a diagram showing a high-temperature wear resistance test piece, and FIG. 7 is a high-temperature wear resistance curve diagram.

Claims (1)

[Claims] IC: 0.05 to 0.20, Si: O, i to 1.
5%, Mn: 0.1-1.5%, Ni: 0.
2-3.0%, Cr near, 0-12.0%, Mo
: 0.1-2.0%, V: 0.1-1.0%, N
b: 0.03 to 1.0 ratio, steel for rolls in continuous casting equipment, with the remainder being substantially Fe. 2C: 0.05-0.20%, Si: O, 1-1.5%
, Mn: 0.1-1.5%, Ni: 0.2
~3.0%, Cr near, 0~12.0%, Mo:
0.1-2.0 ratio, V: 0.1-1.0 ratio, Nb: 0
In addition to the basic component consisting of 103 to 1.0%, Ti
: 0.05-0.50%, Zr: 0.01-0
．． 30%, Ta: 0.01-0.50%, B: 0.
Copper for rolls in continuous casting equipment containing 0.01% or less of one or more of the above, with the remainder substantially consisting of Fe.