KR950008691B1 - Making method of wear resistant steel plate - Google Patents

Abstract

heating a steel slab including (by wt.) 0.18-0.4% C, less than 0.3% Si, 0.4-1.6% Mn, less than 0.02% P, 0.4-0.8% Cr, 0.1-0.3% Mo, 0.01-0.03% Ti, 0.005-0.002% B, 0.02-0.05% Al, less than 0.01% N, balance Fe and inevitable impurities to 1150-1300 deg.C; hot rolling at finish temperature of less than 900 deg.C with total reduction of more than 30%; quenching to room temperature for less than 120 secs. with cooling rate of more than 7 deg.C/sec.; and tempering at 200-350 deg.C.

Description

Method of manufacturing wear resistant steel sheet

1: Graph showing the change of hardness value according to finishing rolling temperature and rolling reduction

The present invention relates to a method for producing a wear-resistant steel sheet that can be applied to various industrial machinery such as civil engineering, construction, and mining, and more particularly, to a method for manufacturing a wear-resistant steel sheet using low alloy high tensile steel as a starting material. It is about.

Industrial machinery used in various industries such as civil engineering, construction, and mining causes members to come in contact with soil, sand and ore to be worn by contact with them. The number of years of use depends on the degree of wear.

Therefore, these members are required to have excellent post-wear resistance, and generally, wear resistance is known to be excellent with a higher hardness value.

As a method of manufacturing a wear resistant steel sheet, a method of manufacturing a high alloy high tensile steel and a low alloy high tensile steel as a starting material is known.In the case of manufacturing a wear resistant steel sheet using a high alloy high tensile steel as a starting material, an expensive alloy element is used. In addition to containing a large amount, there is a problem that the manufacturing cost is increased because the tempering temperature is high.

On the other hand, when the wear-resistant steel sheet is manufactured from low alloy high tensile steel as a starting material, since the addition amount of alloying elements is small, it is not only economical but also maintains wear resistance by securing a predetermined hardness value, and also has excellent workability and weldability. Alloy high tensile strength steel is receiving strong light.

As a method of manufacturing a wear resistant steel sheet using low alloy high tensile steel as a starting material, the steel sleeve produced by the ingot or continuous casting method is heated in a heating furnace, hot rolled to a predetermined size and cooled in air, A so-called reheat heat treatment method known to be produced by reheating in a heat treatment furnace to be quenched and then tempered is known.

When the wear-resistant steel sheet is manufactured by the reheating heat treatment method, since the reheating process is absolutely necessary, a process is added and thus there is an uneconomical disadvantage.

Recently, various steels, such as direct immersion method HT 60, HT 80, petroleum transport pipes and low-temperature steels, which are directly quenched and then tempered after hot rolling of steel slabs in an appropriate method, have been put to practical use.

In the case of manufacturing the wear-resistant steel sheet by the direct immersion method, not only the reduction of the heat source unit by omission of the reheating immersion process, the improvement of the accompanying productivity, the reduction of the alloy element by the improvement of the hardenability, and the proper control of various factors during hot rolling Mechanical improvement by means of having an advantage.

At present, wear-resistant steel is produced by dividing into several grades, and the hardness value is required as a criterion for classifying the grade, and Brinell hardness value (HB) is a kind of wear-resistant steel sheet that uses low-alloy high tensile steel as a starting material. Are currently being produced worldwide, 280, 320, 360, 400 and 500.

The present invention relates to a method for producing a wear-resistant steel sheet corresponding to 400 and 500 of the wear-resistant steel sheet.

The present invention is to provide a method for producing a wear-resistant steel sheet having excellent workability and weldability by maintaining a good wear resistance by securing a predetermined hardness while applying a direct immersion method using a low alloy high-tensile steel as a starting material, The purpose is.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention is, by weight%, C: 0.18-0.4%, Si: 0.3% or less, Mn: 0.4-1.6%, P; 0.02% or less, Cr: 0.4-0.8%, Mo: 0.1-0.3%, Ti: 0.01-0.03%, B: 0.0005-0.002%, Al: 0.02-0.05%, N: 0.01% or less, balance Fe and other unavoidable After heating the steel slab composed of impurities to a temperature range of 1150-1300 ° C., hot rolling was performed at a finish rolling temperature of 900 ° C. or lower and a total reduction ratio of 30% or higher at a temperature of 900 ° C. or lower, and then 120. It relates to a method of manufacturing a wear-resistant steel sheet by quenching at an average cooling rate of 7 ℃ / sec or more from seconds to room temperature and then tempering at a temperature range of 200-350 ℃.

Hereinafter, the reason for limitations, such as the said steel component and manufacturing conditions, is demonstrated.

In general, the C is a component that influences the hardness value of the steel when the steel is manufactured by quenching, and in order to secure HB 400 or more as in the present invention, 0.18% or more is required, and when 0.4% or more, the weldability is deteriorated. Therefore, the content of C is preferably limited to 0.18-0.4%.

The Si is an alloying element that performs deoxidation and reinforcement, but in the present invention, since deoxidation is secured by Al and reinforcement by C, the content of Si is 0.3% or less, which does not occur in a conventional steelmaking process. It is preferable to set to.

In addition, Mn is an alloying element having a large effect on the quenching property as in C, but when the amount is too large, the carbon equivalent becomes high to impair weldability, and when the amount is too small, the content of Mn is 0.4-. It is preferable to limit to 1.6%.

In addition, since P is an alloying element that impairs toughness, it is better to add as little as possible, but wear-resistant steel is not a steel requiring very good toughness, and in addition, since the load in the steelmaking process for realizing extremely low P increases, Usually, the P content of the steel is preferably limited to 0.02% or less.

In addition, the chromium is an alloying element that improves the hardenability similarly to C and Mn, and if the content is 0.4% or less, the additive effect is not effective, and if the chromium is 0.8% or more, the weldability is impaired. It is preferable.

In addition, Mo is an alloying element having a great effect on the quenching resistance and tempering resistance. If the content is 0.1% or less, the addition effect is not exerted. Therefore, Mo should be added at least 0.1%. It is preferable to limit it to% or less.

In addition, since B is greatly used for the hardenability of the steel even by the addition of a very small amount, steel produced by quenching heat treatment is widely used, but there is one limitation condition.

That is, employment B must be secured because it is effective in improving hardenability.

By the way, since B has affinity with N especially, solid solution B can be ensured by adding Ti larger than affinity with N.

In view of the above, in the present invention, the amount of N is determined to be 0.01% or less, which is an amount contained in a conventional steelmaking process, and accordingly, the content of Ti is preferably limited to 0.01-0.03% in consideration of the stoichiometric ratio with N. Do.

In addition, when the content of B is 0.0005% or less, the hardenability-improving effect is not exhibited, and when the content of B is greater than 0.002%, coarse B carbides are produced, and thus the hardenability is impaired, so it is preferable to limit the content to 0.0005-0.002%. Do.

Al is an almost essential alloy element in the steelmaking process in the element carbonate, but also serves to refine the crystal grains by partially fixing N in the steel, but when the content is less than 0.02%, there is no addition effect, 0.05% In the above case, since toughness is impaired by solid solution Al, the Al content is preferably limited to 0.02-0.05%.

In the present invention, the slab of the steel having the chemical composition as described above is heated to 1150-1300 ° C., which is a general heating range, and then subjected to hot rolling. When the rolling is finished at 900 ° C. or more, recrystallization is softened, so that the finish rolling temperature It is preferable to set the temperature at 900 ° C. or lower, which is not recrystallized.

Similar to the finish rolling temperature, the overall reduction ratio in the unrefined zone is an important factor of the present invention. Rolling in the non-recrystallized zone increases the dislocation density of the steel and also increases the strength by miniaturizing the underlying structure. If it is 30% or less, since there is little effect, it is preferable to set the total reduction rate in a non-recrystallization zone to 30% or more.

On the other hand, it should be directly immersed within 120 seconds after the end of hot rolling, and the average cooling rate at this time is preferably 7 ℃ / sec or more, the reason is that if the 7 ℃ / sec or less soft phase such as ferrite This is because the strength value is lowered rather than generated.

After the direct soaking as described above is subjected to a tempering treatment in the temperature range of 200-350 ℃.

In the state where only direct quenching is performed, tempering treatment should be performed at 200 ℃ or higher because there is a problem such as plate deformation or cracking during welding, and when tempering at temperature of 350 ℃ or higher, the tempering is sharply lowered. It is preferable to limit temperature to 200-350 degreeC.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

The ingot formed as shown in Table 1 was heated to 1250 ℃, and then hot rolled to prepare a hot rolled steel sheet.

At this time, hot rolling was a finish rolling temperature of 800 ℃, and a total reduction rate of less than 900 ℃ to 35%.

The hot rolled hot rolled steel sheet as described above was directly immersed at an average cooling rate of 10 ℃ / sec, and then tempered at a temperature of 200-350 ℃ as shown in Table 2 to prepare a specimen, each specimen Mechanical properties, that is, tensile properties, room temperature shock absorption energy, and Brinell hardness values were measured, and the results are shown in Table 2 below.

In addition, for comparison, the specimens were prepared by the reheating method, and the mechanical properties of each specimen were measured and shown in Table 2 below.

At this time, the quenching temperature at the time of reheating was set to 930 degreeC which is a temperature normally applied.

TABLE 1

TABLE 2a

TABLE 2b

As shown in Table 2, it can be seen that the inventive material (1-11) prepared according to the present invention (direct immersion method) is superior in strength and hardness values compared to the comparative example (ai) prepared by the reheat immersion method. .

Example 2

A hot rolled steel sheet was prepared by heating the ingot formed as in steel type 4 shown in Example 1 to 1250 ° C. and then hot rolling.

At this time, as shown in Table 3 below, the hot rolling was performed at a hot finish rolling temperature of 750-1000 ° C., and the reduction ratio at each hot finish rolling temperature was changed to 10-50%.

The hot rolled hot rolled steel sheet as described above was directly quenched at an average cooling rate of 10 ° C./sec, and then tempered at 200 ° C. to prepare respective specimens, and the hardness values of each specimen were measured. It is shown in Table 3, and is shown in figure 1 and shown.

TABLE 3

As shown in Table 3 and FIG. 1, when the hot finish rolling temperature is 920 ° C., the hardness value decreases as the reduction ratio increases, and when the temperature is 1000 ° C., there is almost no change.

On the other hand, when the hot finish rolling temperature is 750 ℃ and 800 ℃ almost no increase in hardness value up to 20% reduction, it can be seen that the hardness value is significantly increased when more than 35%.

This means that the hot finish rolling temperature should be 900 ° C. or lower, and the total reduction ratio in the uncrystallized zone should be 30% or higher.

Claims (1)

By weight%, C: 0.18-0.4%, Si: 0.3% or less, Mn: 0.4-1.6%, P: 0.02% or less, Cr: 0.4-0.8%, Mo: 0.1-0.3%, Ti: 0.01-0.03% , B: 0.0005-0.002%, Al: 0.02-0.05%, N: 0.01% or less, after heating the steel slab composed of the balance Fe and other unavoidable impurities in the temperature range of 1150-1300 ℃, After hot rolling with the total reduction ratio at 900 ℃ or less and the temperature of 900 ℃ or less and 30% or more, and then quenching at an average cooling rate of 7 ℃ / sec or more from 120 seconds to room temperature, and then 200 Method for producing a wear-resistant steel sheet, characterized in that tempering treatment in the temperature range of -350 ℃.