JPS60141832A - Production of hot rolled round steel having excellent wear resistance - Google Patents

Abstract

PURPOSE:To obtain inexpensively a round steel for a rod mill, etc. having excellent wear resistance by subjecting a steel contg. C and Mn at a specific rate to hot rolling and quick cooling then to hardening and tempering by making use of the heat remaining in the round steel. CONSTITUTION:A steel consisting of 0.80-1.00wt% C, 0.4-1.8% Mn, <=0.5% Si, <=0.5% Cr, <=0.5% Ni, <=0.5% Mo and the balance Fe and inevitable impurities is rolled by hot rolling at >=800 deg.C. The surface of such round steel material is forcibly cooled to decrease the surface temp. thereof to <=200 deg.C. The steel material is then allowed to cool to restore the surface temp. up to >=400 deg.C by the heat remaining in the steel material. Tempered martensite structure is formed in the surface layer part and ferrite-pearlite structure is formed in the central part by the above-mentioned method, by which the wear resistance of the hot rolled round bar is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing round steel for rod mills used for crushing iron ore, copper ore, and the like.

(Prior art) What are round bars for rod mills? Dozens of round bars are placed inside a rod mill IO as shown in Figure 1 (a), and materials to be crushed such as ore are charged into the rod mill itself while it rotates. As the rod mill rotates, as shown in Figure 1 (b), the falling rod 1 uses the energy to crush the object to be crushed, such as ore.
Refers to steel materials with a length of ~150+m. Rod mills 10 like this are used in large quantities in mines that crush ores such as iron ore and copper ore, and the important properties of round steel for rod mills are wear resistance and cut resistance. . Regarding wear resistance, in order to reduce the number of wear types per unit weight of ore, round steel for rod mills with better wear resistance has been sought. Regarding breakage resistance, breakage occurs during the collision between rods 1 and 1 in the rod mill, and when breakage occurs, broken rod-shaped fragments are placed on the belt conveyor 2 that carries out the ore to be crushed at the bottom of the rod mill. This could cause the belt conveyor to break and cause equipment failure.

Regarding the wear resistance of round steel for rod mills, it is generally known that the higher the surface hardness, the better the wear resistance, as shown in FIG. For this reason, in order to increase wear resistance, it is important to increase hardness.In order to increase hardness, round steel obtained by hot rolling is heat treated, In order to further increase the hardness, methods have been used to add hardening-enhancing elements (for example, elements such as Cr*NirMo).

The method of heat treatment is a method of quenching and tempering the round steel obtained by hot rolling.With this method, in order to obtain the appropriate hardness and toughness, the round steel is heated twice, namely quenching and tempering. However, in this manufacturing method, the work cost of heat treatment is required in addition to the heat cost, and it is expensive in terms of cost. A: Reducing the manufacturing cost of round steel for rod mills has long been an issue. In addition, in order to further increase the surface hardness after heat treatment in consideration of wear resistance, Cr.

A method of adding elements that improve the hardenability of steel materials, such as Mo + N1, is also used, but when improving the hardenability of steel materials with only these elements, the cost of these elements used in large quantities is This was more expensive and more inconvenient.

(Objective of the Invention) The present invention has been made in view of the above-mentioned disadvantages. Instead of separately heat-treating the steel material obtained by production hot rolling, the sensible heat after hot rolling of the round steel is treated. After forced cooling, the heat remaining inside the round steel is used to quench and temper it. This is a much cheaper heat treatment method than the conventional method, and improves wear resistance. It is possible to increase the hardness without using alloying elements.

(Structure and operation of the invention) The principle of the invention is shown in FIGS. 3 and 4. Figure 4 shows a hot rolling line for round steel. Round steel is generally produced by heating a rectangular cross-section copper material called a billet in a heating furnace 3 to about 1000 to 1200°C, and then hot rolling it in a rolling mill 4. The finishing temperature after hot rolling is measured with a thermometer 7.

After the rolling is completed at a temperature equal to or higher than the Ar5 transformation point in the region of the austenitic structure of the steel material, forced cooling is performed in the cooling trough 5. These temperature histories are shown in FIG. It is important to complete the rolling by controlling the temperature to be above the Ar5 transformation point and as much as possible just above the Ar5 transformation point. The reason for this is that by completing the processing just above the Ar3 transformation point, the subsequent growth of crystal grains is suppressed and the crystal grains can be made finer. This refinement is expected to improve the breakage resistance required for Shirorad steel bars. Therefore, the Ar of the steel of the present invention
3 The transformation point temperature is 700°C to 800°C, and it is necessary to control the finishing temperature to just above 800°C.

When forced cooling is performed in a cooling trough, the temperature of the surface layer is rapidly cooled, but the temperature of the center of the round steel is cooled more slowly than the surface layer. The steel surface temperature at the exit side of the cooling trough is 200
It needs to be below ℃.

The reason for this is that steel generally differs depending on the steel type. (5) υ martensitic transformation occurs by cooling to Ms (martensitic transformation starting temperature) @ degrees within a certain limit time. MSS temperature 2 for c = ' o, s ~ 1.0 chi
It's about 00. Therefore, in order to obtain a martensitic structure, it is necessary that at least Table 1- is below 200°C.

When the forced cooling in the cooling trough is completed in a short time, the temperature distribution inside the round steel is high inside and low on the surface.Here, heat transfer from inside the round steel occurs, resulting in a forced quenched layer on the surface of the round steel. On the contrary, during slow cooling on the cooling bed after the cooling trough, it will be heated. The recuperation temperature that the surface of the steel reaches is preferably 400°C or higher. The reason for this is that steel is generally hard and brittle in its quenched structure. Therefore, in order to use it in places where breakage resistance is required, such as rod steel, it is necessary to temper it.

For steel with C=0.8 to 1.0%, if the tempering temperature is too low, the steel will become brittle at 250°C and there will be a problem in breakage resistance, so to avoid this effect, the reheating temperature is preferably 400°C or higher.

(6) A tempered martensitic structure is obtained on the red side of the round steel, and a ferrite pearlite structure similar to that normally obtained is obtained on the inner diameter side.

In general, tempered martensitic structures have not only high hardness but also moderate toughness and extremely high wear resistance.

In addition, the ferrite structure in the center has low hardness and lacks wear resistance, but it ensures toughness against breakage of the rod, and as a round steel for rod mills, it can ensure both wear resistance and cutability at the same time. bawl. In particular, rod rods for rod mills generally use only the surface layer from a certain diameter to a certain diameter. It is usually not used often. When the method of the present invention is applied, only the surface layer can be made hard, which is extremely convenient. =X shows an example of the components of the present invention.

Generally, round steel for rod mills is 5AE1080~SA.
Carbon steel near eutectoid steel of about E 1095 has a high carbon content, high hardness after rolling, and is inexpensive, so it is often used as round steel for rod mills.

The method of the present invention also basically satisfies SAE 1080 to 5AE109.
Based on steel equivalent to No. 5, with hardenability improving elements cr lN
i, MO, etc. are added within a range that does not increase the cost.

Concerning St, if it is included in a large amount, the steel material becomes brittle and the number of inclusions increases in proportion to the amount of S1.

Table 2 shows selected examples using the force component system of Table 1 and examples using the force component system of Pouch 1 for comparison of the method according to the present invention and the conventional method.

(Table 1) (9) (10) The hardness distribution in the diametrical direction of the steel equivalent to 5AE1095 produced by the method of the present invention is shown in FIG. 5 (a). In the method of the present invention, the hardness at the center of the round steel is about 310 (Hv), while the hardness near the surface reaches its maximum, about 370 (Hv). This same charge, same component SAE 10
The same diagram also shows the hardness distribution in the diametrical direction of the steel equivalent to 95. The hardness distribution is uniform and gentle in the diametrical direction, and the average hardness is about 300 (Hv).

In the method of the present invention, the maximum hardness appears approximately 10 m from the surface layer, and the hardness decreases toward the center, and the tS distribution becomes approximately uniform and gentle at the 20 m surface layer. Also, the reason why the hardness is uneven at the center in both the method of the present invention and the conventional method is thought to be because components in the steel such as carbon are concentrated due to center segregation of the steel material.

Generally, round steel for rod mills has an initial diameter of 20 to 30 mm.
When about 50% of the fruit wears out, it is removed and discarded. It is said that the breakability and breakability deteriorate, and especially the breakability is such that breakage in a rod mill is likely to lead to equipment accidents, but the method of the present invention can be applied to round steel with a diameter of about 100s+A where the hardness is almost 30mm. %, and the inner part of the steel material has soft and sticky properties, so the part that wears and wears out has a high hardness, while the steel part in the center that does not wear out has soft properties. .

Incidentally, in the steel of the present invention in Figure 5 (a), the structure from the surface layer up to the maximum hardness is tempered martensite, the structure from the point where the hardness is constant above the maximum hardness is bainite, and from the point where the hardness distribution is gentle to the center. has a ferrite pearlite steel structure. For this reason, the coating layer of the round steel for rods made using ITO has an ideal structure that has both the wear-resistant structure of heat-restored martensite and the toughness of the ferrite-pearlite structure inside. .

It is also extremely effective to add small amounts of elements that increase hardenability, such as Cr, Ni, and Mo. Cr within a range where the cost does not increase significantly, that is, 0.5% or less,
The platform to which Ni and Mo are added is effective because it has the effect of increasing the thickness of the six-layered tempered martensitic structure relative to the added alloying elements.

Figure 5 ←) shows an example of the present invention method for steel equivalent to SAE 1085. It is similar to the steel equivalent to SAE 1095 in Figure 5 (a), but the narrow surface hardness and center hardness are lower due to the smaller amount of C. descend. The structure distribution is almost the same as steel equivalent to SAE 1095, but SAE 1095 is superior in wear resistance, but 8AE 1085 is superior in cut resistance.

FIG. 6 shows the results of a test conducted by charging the round steel for rod mills produced by the method of the present invention into an actual rod mill.

(13) A wear resistance test was conducted by charging a plurality of rod mill round steel bars with a length of 5 m and a diameter of 100 m, both those manufactured illegally with the same charge and those manufactured using the conventional rolling method, into the same rod mill. It is something that This rod mill is used to crush lumpy iron ore. Figure 6 shows a deformed view of the wear dimensions of the round steel for the rod mill as it wears out.The wear is noticeable on both ends, but this is because the iron ore is supplied from the trunnions on both sides of the A2 domill. Figure 6 shows how the chopsticks wear out just like chopsticks used for eating. When compared in Figure 6, the diameter is 100.
Using the conventional method, round steel for rod mills with an initial diameter of mm is 160,000 tons.
On the other hand, with the method of the present invention, the waste diameter is reached after crushing about 190,000 tons of iron ore.

Comparison of the amount of iron ore crushed and the consumable cover of round steel for rod mills
As shown in the figure, the method of the present invention is 20% lower than that of the conventional method.
It can be seen that the life of round steel for rod mills is long. This means that the rod mill, which conventionally used 1000 tons/year, can now produce only 800 tons/year.

(Effects of the Invention) As described above, the round steel for rod mills manufactured by the method of the present invention is obtained by subjecting inexpensive SAE 1080 to 5AE1095 class steel materials to appropriate forced quenching and cooling using the sensible heat immediately after hot rolling. This method obtains a tempered martensitic structure in the central part and a ferritic/relitic structure in the center, but the method of the present invention converts relatively inexpensive steel into a steel material with wear resistance equivalent to hardened and tempered round steel. This is considered to be extremely effective industrially, as it can reduce rod consumption in steel mills that crush iron ore and copper mines that have many rod mills, thereby reducing crushing costs.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of a rod mill, (A) is a side view, (B) is a cross-sectional view, Figure 2 is a diagram showing the relationship between wear resistance measurement value and hardness, and Figure 3 is the principle of the present invention. FIG. 4 is an explanatory diagram of the hot rolling line of Kyugi. FIG. ) is SAE 1085 according to the present invention.
Figure 6 shows the hardness distribution in the diametrical direction of the equivalent steel, Figure 6 shows the test results of the round steel for rod mills according to the present invention charged into a rod mill, and Figure 7 shows the amount of crushed iron ore and the round steel for rod mills. FIG. 3 is a diagram showing a comparison of steel consumable lids. (17) 1st Closed 2nd Break Yasushi (Hv) Request for Amendment of Assignment Procedures (Voluntary) December 25, 1980 Commissioner of the Patent Office Manabu Shiga 1, Indication of Case 1988 Patent Application No. 249841 No. 2, Title of the invention: Method for manufacturing hot rolled round steel with excellent wear resistance 3, Relationship to the amended case Patent applicant: 6-3 Otemachi 2-chome, Chiyoda-ku, Tokyo (665) Nippon Steel Corporation Representative Takeshi 1) Yutaka 4, Agent 2-4-1-6 Marunouchi, Chiyoda-ku, Tokyo 100, Detailed description of the invention and drawing 7 in the specification subject to amendment, Amendment Contents (1) “Steel materials O” in line 3 on page 5 of the specification shall be corrected to “Steel materials O”. (2) Figure 3 is corrected as shown in the attached sheet.

Claims (1)

[Claims] Heavy, C: 0.80 to 1.00%, Mn: 0
．． 4 to 1.8%, and further contains one or more of the following: Sl: 0.5% or less Cr: 0.5% or less Ni: 0.5% or less Mo: 0.5% or less. After hot rolling a steel whose composition consists of Fe and unavoidable impurities at a high finishing temperature of 80OL or more, the surface of the steel material is forcedly cooled to at least 200°C or less, and then released. A method for producing hot-rolled round steel with excellent wear resistance, characterized by reheating the i-plane temperature to 400° C. or higher using heat inside the cold steel material.