KR100262440B1 - Cr-mo alloy steel and the manufacturing method of low-temperature bolt-nut - Google Patents

Abstract

PURPOSE: A process for preparing Cr-Mo steel and Cr-Mo-B steel used for round steel by suppressing impurities exerting a bad influence on fatigue strength and performing vacuum degassing for a long time is provided, thereby producing steel for low temperature bolt and nut having improved low temperature impact characteristics. CONSTITUTION: The titled steel comprises C: 0.40 to 0.44wt.%, Si: 0.15 to 0.35wt.%, Mn: 0.75 to 0.90wt.%, P: 0.030wt.%, S: 0.030wt.%, Cu: 0.30wt.%, Ni: 0.20 to 0.25wt.%, Cr: 0.80 to 1.10wt.%, Mo: 0.20 to 0.25wt.%, Al: 0.037 to 0.020wt.%, N2: 100ppm or less and the balance of Fe and inevitable impurities. The steel is prepared by the process consisting of: preparing steel; hot-rolling at 1,050±25deg.C at finish rolling temperature of 925±25deg.C; oil-quenching after quenching heat treatment at 830 to 880deg.C; and air- or water-quenching after tempering heat treatment at 640 to 690deg.C.

Description

[Name of invention]

Cr-Mo (-B) steel for low temperature ball nut and its manufacturing method

Detailed description of the invention

[Purpose of invention]

[Technical field to which the invention belongs and the prior art in that field]

The present invention relates to Cr-Mo steel for low temperature ball nut, Cr-Mo-B steel, and a method for manufacturing the same, and more particularly, to use as a round steel for low temperature ball nut with improved low temperature toughness in a material use environment. It relates to Cr-Mo steels, Cr-Mo-B steels and a method of manufacturing the same.

Conventional low-temperature ball-nut Cr-Mo steel has a problem such that it is broken when used in a low temperature environment due to insufficient impact toughness in a low temperature use environment.

[Technical problem to be achieved]

The present invention provides a low-temperature ball-nut Cr-Mo steel, Cr-Mo-B steel, and a method of manufacturing the same to improve the low-temperature toughness greatly in the use environment of the material to solve the conventional problems, extremely excellent low-temperature impact energy value It aims to do it.

[Configuration and Function of Invention]

The present invention is to achieve the above object, the Cr-Mo steel for low temperature ball-nut is C: 0.40 to 0.44%, Si: 0.15 to 0.35%, Mn: 0.75 to 0.90%, P: 0.030% S: 0.030% or less, Cu: 0.30% or less, Ni: 0.20 to 0.25%, Cr: 0.80 to 1.10%, Mo: 0.20 to 0.25%, Al: 0.007 to 0.020%, N2: 100 ppm or less, and The rest is characterized in that the low temperature impact energy consisting of Fe and impurities inevitably contained in the steelmaking process is 27 J (-101 ° C) or more.

Another Cr-Mo-B steel for low temperature ball and nut of the present invention is C: 0.40 to 0.44%, Si: 0.15 to 0.35%, Mn: 0.75 to 0.90%, P: 0.030% or less, S: 0.030 % Or less, Cu: 0.30% or less, Ni: 0.20 to 0.25%, Cr: 0.80 to 1.10%, Mo: 0.20 to 0.25%, Al: 0.007 to 0.020%, N2: 100 ppm or less, B: 0.0005 to 0.0030% The rest is characterized by a low temperature impact energy of 27 J (-101 ° C.) or more, which is composed of Fe and impurities inevitably contained in the steelmaking process.

The method for producing the low-temperature ball-nut Cr-Mo steel (or low-temperature ball-nut Cr-Mo-B steel) having a low temperature impact energy of 27 J (-101 ° C) or higher is C: 0.40 to 0.44 by weight. %, Si: 0.15 to 0.35%, Mn: 0.75 to 0.90%, P: 0.030% or less, S: 0.030% or less, Cu: 0.30% or less, Ni: 0.20 to 0.25%, Cr: 0.80 to 1.10%, Mo: 0.20 to 0.25%, Al: 0.007 to 0.020%, N2: 100 ppm or less (or B: 0.0005 to 0.0030%), and the remainder is Cr-Mo (-or consisting of Fe and impurities inevitably contained in the steelmaking process. B) manufacturing the steel; Performing a long vacuum degassing process on the steel; And hot rolling with a rolling heating temperature of 1050 ± 25 ° C. and a finish rolling temperature of 925 ± 25 ° C. The reason for limiting the additive component in the low-temperature ball nut nut material of the present invention is as follows.

C (carbon): C is one of the strong alloying elements that adversely affects the notch toughness, such as increasing the hardening hardness, generating carbide to increase the strength, but increasing the impact transition temperature and reducing the fracture energy. Since the required strength cannot be obtained below, and ductility and toughness are reduced at 0.44% or more, the carbon content should be kept as low as possible within the required strength for maximum toughness.

Si (silicon): Si is effective as a deoxidizer and increases the impact resistance by lowering the impact transition temperature and increasing the breakdown energy, increasing the low temperature temper resistance, but deoxidation of steel below 0.15% due to insufficient deoxidation of steel. It is necessary to increase the strength, and 0.35% or more is required to be limited to less than 0.35% because it inhibits toughness.

Mn (manganese): Mn increases the hardenability to increase abrasion resistance and strength, and is effective as a deoxidizer, but below 0.75%, it is difficult to obtain the required strength. It is necessary to limit the range of additive components as much as possible within the required strength since it adversely affects the toughness of the quenched / tempered steel.

P (phosphorus): P forms a banded structure during hot rolling, which makes it easy to damage the uniformity of the structure and cause segregation, promotes temper brittleness, and in particular, lowers the impact resistance, making it difficult to obtain good toughness. It should be limited to less than%.

S (sulfur): S forms a low-melting emulsion and viscously deforms in the rolling direction to reduce toughness and impact value. Since the compound with Fe degrades hot workability, the upper limit is limited to 0.030%.

Cu (copper): Cu is effective in improving toughness but is not satisfactory because of the risk of red brittleness, impairing weldability and inhibiting formability at 0.30% or more. Therefore, it is necessary to limit the upper limit to 0.30% or less.

Ni (nickel): Ni is very useful for increasing the hardenability and especially preventing low temperature brittleness to increase the notch toughness of the steel at low temperatures. Ni is added in an amount of 0.20% or more and 0.25% or less.

Cr (chromium): Cr has an effect of improving toughness by increasing hardenability and temper resistance and easily making stable carbide, and adding 0.80% or more as an element for increasing wear resistance because C absorbs C as stable carbide. Due to the risk of brittleness, the limit was less than 1.10%.

Mo (Molybdenum): Mo is effective for structural steels such as increasing the tempering resistance, increasing hardenability, and increasing grain coarsening temperature by making stable complex carbide with Cr, so that it is 0.20% or more to secure required physical properties. However, when the addition is excessive, the impact transition temperature is increased, so it is limited to 0.25% or less.

Al (aluminum): Al is effective as a strong deoxidizer, inhibits the growth of austenite as a nitride (AIN) forming element, and refines grains. In addition, it is required to be 0.007% or more to improve the toughness, but it is necessary to limit to 0.020% or less because the increase of the transition temperature when excessive addition, the rise of oxide is difficult to reduce the cleanliness of the steel.

B (Boron): B is a quenched / tempered steel, in which 0.0005 to 0.0030% is added as a useful alloy component that can obtain toughness without deteriorating strength.

N (nitrogen): N combines with Al to refine grain size and increase notch toughness of steel, but nitrogen itself adversely affects notch toughness such as increasing impact transition temperature and lowering breaking energy. Therefore, when excessively added, the toughness is generally lowered, and carbonitride is excessively precipitated and the impact transition temperature is increased to impair low temperature toughness. Therefore, it is necessary to limit it to 0.010% or less.

The present invention is to suppress the impurities affecting the fatigue strength to the maximum by the application of the inclusion control technology and the high clean steel control technology, and to perform the vacuum degassing operation for a long time to suppress the gas components that adversely affect the low-temperature toughness to the maximum as described above A steel sheet having a temperature of 1165 ± 25 ° C., which is heated to a temperature of 1165 ± 25 ° C., and heated to a temperature of 1050 ± 25 ° C., which is subjected to small hot rolling to be rolled to a predetermined size, followed by correction. Is done in a way.

The heating temperature for hot processing is adopted in consideration of various conditions such as the material's hot strength and production volume, but excessive increase of the heating temperature reduces the growth inhibition function of the austenitic grain growth of carbonitride, which eventually forms coarse pearlite upon completion of processing. Therefore, in the present invention, the rolling heating temperature is 1050 ± 25 ℃ and the finish rolling temperature is characterized by performing a small hot rolling by selecting an operating temperature range of 925 ± 25 ℃.

In addition, the present invention quenching the tensile strength, cross-sectional shrinkage required for the structural material such as the present invention, quenching / tempering heat treatment to satisfy all mechanical properties such as abrasion resistance and particularly low temperature impact characteristics, to fully cure the core Heat-treat the oil quenched heat treatment at a temperature of 830-880 ° C. and then temper heat-treatment at a temperature of 640-690 ° C. to give toughness to obtain a ball-nut material with improved strength and low temperature toughness. Method.

Hereinafter, embodiments of the present invention will be described in detail.

EXAMPLE

Steels of the components as shown in Table 1 were obtained by the method described above.

TABLE 1

Chemical composition (wt%)

The steel was subjected to vacuum degassing for a long time in order to actively reduce the gas components which adversely affect the low temperature toughness characteristics. After performing the vacuum degassing operation, it was heated to a rolling heating temperature of 1050 ° C. and hot-rolled at a finish heating temperature of 925 ° C. to produce a φ 55 steel bar. In order to impart a predetermined strength to the steel thus produced, it was maintained at 830 to 880 ° C. for 60 minutes to perform an oil quenching heat treatment. Thereafter, tempering heat treatment was performed at 640 to 690 ° C for 120 minutes to give toughness, followed by air cooling or water cooling. After performing the heat treatment as described above, the low temperature impact value was measured at -101 ° C. The measurement results are shown in Table 2.

TABLE 2a

Impact test results (average value after testing at least 3 specimens)

TABLE 2b

[Effects of the Invention]

According to this embodiment, as a result of measuring the low temperature shock absorption energy value, as shown in the above table, it showed an excellent low temperature shock absorption energy value of 27 J (= 2.75 kgfm) or more.

Claims (4)

C: 0.40 to 0.44% by weight, Si: 0.15 to 0.35%, Mn: 0.75 to 0.90%, P: 0.030%, S: 0.030%, Cu: 0.30%, Ni: 0.20 to 0.25%, Cr: 0.80 to 1.10%, Mo: 0.20 to 0.25%, Al: 0.007 to 0.020%, N ₂ : 100 ppm or less, and the rest is 27 J (-101 ° C) of low temperature impact energy consisting of Fe and impurities inevitably contained in the steelmaking process. Cr-Mo steel for low temperature ball nut. C: 0.40 to 0.44% by weight, Si: 0.15 to 0.35%, Mn: 0.75 to 0.90%, P: 0.030%, S: 0.030%, Cu: 0.30%, Ni: 0.20 to 0.25%, Cr: 0.80 to 1.10%, Mo: 0.20 to 0.25%, Al: 0.007 to 0.020%, B: 0.0005 to 0.0030%, N ₂ : 100 ppm or less, and the rest is a low temperature impact energy consisting of Fe and impurities inevitably contained in the steelmaking process Cr-Mo-B steel for low temperature ball nut, characterized by more than 27 J (-101 ℃). C: 0.40 to 0.44% by weight, Si: 0.15 to 0.35%, Mn: 0.75 to 0.90%, P: 0.030%, S: 0.030%, Cu: 0.30%, Ni: 0.20 to 0.25%, Cr: 0.80 to 1.10%, Mo: 0.20% to 0.25%, Al: 0.007% to 0.020%, N ₂ : 100ppm or less, the rest of which comprises a steel material consisting of Fe and impurities inevitably contained in the steelmaking process; Performing vacuum degassing for a long time; Performing hot rolling with a hot heating temperature of 1050 ± 25 ° C. and a finish rolling temperature of 925 ± 25 ° C .; Quenching the oil after quenching at 830 to 880 ° C .; And air cooling or water cooling after tempering heat treatment at 640 to 690 ° C., wherein the low temperature impact energy is 27 J (−101 ° C.) or more. C: 0.40 to 0.44% by weight, Si: 0.15 to 0.35%, Mn: 0.75 to 0.90%, P: 0.030%, S: 0.030%, Cu: 0.30%, Ni: 0.20 to 0.25%, Cr: 0.80 to 1.10%, Mo: 0.20 to 0.25%, Al: 0.007 to 0.020%, B: 0.0005 to 0.0030%, N ₂ : 100 ppm or less, and the rest is made of steel consisting of Fe and impurities inevitably contained in the steelmaking process Doing; Performing vacuum degassing for a long time; Performing hot rolling with a hot heating temperature of 1050 ± 25 ° C. and a finish rolling temperature of 925 ± 25 ° C .; Quenching the oil after quenching at 830 to 880 ° C .; And air cooling or water cooling after tempering heat treatment at 640-690 ° C., wherein the low-temperature impact energy is 27 J (−101 ° C.) or more.