CN116179942A - A kind of 20MnCrS5 steel and its preparation method and application - Google Patents

Abstract

The invention discloses a 20MnCrS5 steel, which belongs to the technical field of preparation of large-scale gear steel. The present invention is composed of the following chemical elements in weight percentage: C: 0.17%-0.22%, Si: 0.15%-0.40%, Mn: 1.10%-1.30%, P≤0.035%, S: 0.035%-0.045%, Cr: 1.00% to 1.30%, Alt: 0.020% to 0.060%, and the balance is iron and unavoidable impurities. The needle of the present invention can improve the cooling condition of the steel ingot by adopting the mold casting process, so that the temperature gradient and cooling intensity of the ingot are weaker than the continuous casting process when the ingot is solidified, avoiding the dendrite overlap of the solidification structure, reducing element segregation, and improving the Density of steel.

Description

A kind of 20MnCrS5 steel and its preparation method and application

technical field

The invention belongs to the technical field of preparation of large-scale gear steel, and in particular relates to a 20MnC rS5 steel and its preparation method and application.

Background technique

20MnCr5 is an alloy structural steel, carburized steel, with high strength and toughness, and good hardenability. 20MnCrS5 is an improved steel grade of 20MnCr5. 20MnCrS5 belongs to alloy structural steel, carburizing steel, and can also be used as quenched and tempered steel. Good hardenability, small heat treatment deformation, good wear resistance, good low temperature toughness, good cutting performance, can be used as carburized parts, large specifications and sections, and high load quenching and tempering parts, such as large wind power gears, Shafts, worms, sleeves, friction wheels, etc.

As mentioned above, 20MnCrS5 can be used as steel parts with large specifications and cross-sections, such as large wind power gears, etc., which requires 20MnCrS5 original steel to have large specifications and parameters related to solidification, such as steel compactness, segregation, porosity and Shrinkage cavities must meet the requirements of use, but the current 20MnCrS5 produced by continuous casting technology cannot fully meet this requirement, especially for large-scale steel products with specifications above φ180mm. The reason is that continuous casting is equivalent to the solidification of a steel ingot with a particularly large height and width ratio. Since the casting slab is forced to cool by strong water spray during solidification, the temperature gradient and cooling intensity during solidification are higher than those of the steel ingot under slow cooling conditions. It is much larger, so the columnar crystals are more developed, especially in the later stage of solidification of the billet, due to the overlapping of columnar dendrites, the lack of equiaxed dendrites or the reduction in volume forms the solidification and crystallization of small steel ingots, and it is easy to form solidification bridges. The lower part has central shrinkage cavity and porosity formation, which aggravates the segregation of elements, resulting in brittleness and fracture of the billet during hot working. In addition, the solidification section of the continuous casting slab is generally small, and it is preferentially solidified from the side first, and a liquid phase gap as deep as tens of meters may be formed inside, which is likely to cause defects such as central shrinkage cavity due to insufficient filling of molten steel. It can be seen that the solidification characteristics of the continuous casting slab determine that it will inevitably produce internal defects such as center segregation and shrinkage cavity.

Due to the continuous production of 20MnCrS5 produced by the continuous casting process, continuous casting requires certain castability for its production. However, since 20MnCrS5 belongs to sulfur-containing steel, sulfur exists in the form of sulfide inclusions in the steel. If the material increases, nodules will accumulate at the continuous casting nozzle and block the nozzle, resulting in poor castability. "Hebei Metallurgy" introduced in the published document "Process Practice of Improving the Castability of Low-Silicon 20MnCrS5 Molten Steel" that 20MnCrS5 reacts with oxygen and sulfur with a high content in molten steel during smelting to form more CaS inclusions, which makes the purity of molten steel worse , a large number of inclusions are formed in the process of smelting and continuous casting, and the inclusions with high melting point accumulate in the nozzle to block the nozzle during the continuous casting process, making the castability of molten steel worse. Although the process has been improved, the number of continuous casting furnaces is also low .

Contents of the invention

In view of the above disadvantages, the present invention provides a 20MnCrS5 steel and its preparation method and application, which avoids the dendrite overlap of the solidification structure, reduces element segregation, and improves the compactness of the steel.

The first aspect of the present invention protects a 20MnCrS5 steel, which is composed of the following chemical elements in weight percentage: C: 0.17%-0.22%, Si: 0.15%-0.40%, Mn: 1.10%-1.30%, P≤0.035% , S: 0.035% to 0.045%, Cr: 1.00% to 1.30%, Alt: 0.020% to 0.060%, and the balance is iron and unavoidable impurities.

The second aspect of the present invention protects a preparation method of 20MnCrS5 steel, comprising the following steps: electric furnace smelting, LF furnace refining, VD furnace refining, die casting, heating and rolling;

The molding includes pouring a first inert gas to protect the pouring before pouring, and the first inert gas is preferably argon. Set the amount of molten steel for drainage ≥ 100kg; control the time from lifting the ladle out of the VD furnace to pouring ≤ 10min, and control the superheat at 25°C-35°C; when pouring, the nozzle of the ladle is 150-200mm higher than the funnel brick.

Further, the electric furnace smelting includes controlling the carbon at the end point of tapping to be 0.05%≤C≤0.13%, the phosphorus at the end point to be at P≤0.020%, and the tapping temperature of the electric furnace to be controlled at 1640°C to 1680°C.

Further, the refining of the LF furnace includes a white slag time ≥ 25min, a second inert gas, the second inert gas is preferably argon, the pressure is 0.2MPa-0.4MPa, and the temperature of the LF outlet bag is controlled at 1665°C-1695°C. ℃.

Further, the VD furnace refining includes feeding high-calcium wire, vacuum treatment, the vacuum degree of the vacuum treatment is ≤100Pa, the vacuum treatment time is ≥15min, breaking the vacuum, feeding the sulfur wire, static blowing the third Inert gas, the third inert gas is preferably argon, the static blowing time of the third inert gas is 15min to 35min, the static blowing pressure is 0.1Mpa to 0.3Mpa, and the temperature of the VD furnace bag is 1579°C to 1611°C .

Further, the heating includes heating with a soaking furnace, keeping the temperature at 200°C for 0.5h, then raising the temperature to 1200°C-1220°C in 3h-3.5h, and finally keeping it at 1200°C-1220°C for 1.5h-2h to ensure that the casting The billet temperature is uniform and through-firing.

Further, the rolling includes a starting rolling temperature of 1100°C to 1200°C, a final rolling temperature of 850°C to 1000°C, a rolling specification range of φ180mm to φ250mm, and the steel is slowly cooled in a heat preservation pit after rolling, and the pit entry temperature is ≥550°C , pit temperature ≤ 200 ℃, slow cooling time ≥ 24h.

The third aspect of the present invention protects the application of the above-mentioned 20MnCrS5 steel in gears.

In order to achieve the above object, the present invention adopts the following technical solutions to realize:

Beneficial effect:

(1) The present invention aims at the deficiencies of the existing continuous casting process of 20MnCrS5 in terms of compactness, segregation, porosity and shrinkage cavity of the steel, by adopting the die casting process, the cooling conditions of the steel ingot can be improved, and the temperature gradient when the ingot is solidified And the cooling strength is weaker than the continuous casting process, which avoids the overlapping of solidified structure dendrites, reduces element segregation, and improves the compactness of steel.

(2) In the prior art, 20MnCrS5 has the characteristics of nozzle blockage in the continuous casting process itself, and 20MnCrS5 is a sulfur-containing steel. Sulfur exists in the form of sulfide inclusions in the steel, and it is easier to accumulate nodules at the continuous casting nozzle and block the nozzle. , resulting in poor castability, which ultimately affects the quality of the steel. However, the mold casting process is different from the continuous casting process and requires multiple furnaces to pour continuously, which can effectively avoid product fluctuations caused by continuous casting due to broken pouring.

(3) The 20MnCrS5 of the present invention has a specification range of φ180mm to φ250mm, general porosity ≤ 0.5 grade, center porosity ≤ 1.0 grade, ingot type segregation ≤ 0.5 grade, ultrasonic flaw detection ≥ A grade, grain size ≥ 7 grade, all better than Continuous casting materials of the same specification.

Description of drawings

Fig. 1 is a low magnification inspection sample diagram of Example 1 of the present invention.

Fig. 2 is a low magnification inspection sample diagram of Comparative Example 1 of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

The 20MnCrS5 in this application is to add sulfur element on the basis of 20MnCr5 to increase the cutting performance of steel. Sulfur exists in the form of sulfide in steel. Excellent cutting performance, good machinability can make the surface finish of the product good, easy to break chips during cutting, so that the processing tool is less stressed and consumes less energy, and the tool life is long.

The 20MnCrS5 of the present invention is composed of the following chemical elements in weight percent: C: 0.17% to 0.22%, Si: 0.15% to 0.40%, Mn: 1.10% to 1.30%, P≤0.035%, S: 0.035% to 0.045% %, Cr: 1.00% to 1.30%, Alt: 0.020% to 0.060%, and the balance is iron and unavoidable impurities.

The production process of the 20MnCrS5 is: electric furnace smelting→LF furnace refining→VD furnace refining→die casting→heating→rolling, which specifically includes the following steps:

(1) electric furnace smelting

Electric furnace smelting adopts eccentric bottom tapping electric furnace, adopts oxygen oxidation, foams slag throughout the process, decarburization amount ≥ 0.25%, carbon at the end of tapping is controlled at 0.05% ≤ C ≤ 0.13%, phosphorus at the end is controlled at P ≤ 0.020%, and steel is tapped in the electric furnace The temperature is controlled at 1640 ℃ ~ 1680 ℃, and aluminum-iron alloy is added during the tapping process (composition: Al: 43 ~ 48%, C<0.05%, Si<1.0%, P<0.08%, S<0.05, the balance is Fe) 2.5～3.5kg/t as pre-deoxidizer, 0.8～1.0kg/t of calcium carbide is added when tapping 1/4 of the steel, and medium carbon ferromanganese (composition: Mn: 75～82%, C≤2.0%, Si≤1.5 %, P≤0.20%, S≤0.03%, the balance is Fe) and low-carbon ferrochrome (composition: Cr: 60-70%, C≤0.25%, Si≤1.5%, P≤0.03%, S≤0.025 %, the balance is Fe) alloying, the addition of medium-carbon ferromanganese is 11.5-12.5kg/t, the addition of low-carbon ferrochrome is 13.0-14.5kg/t, the slag is added with lime 8.0-10.0kg/t, fluorite 2.0 ~3.0kg/t. Add the alloy and calcium carbide first, and then add the slag.

(2) LF furnace refining

The LF furnace adopts diffusion deoxidation to produce white slag. The amount of deoxidizer aluminum powder added is 1.0-1.3kg/t, lime 14.0-16.0kg/t and alumina balls 5.0-6.0kg/t are added to the slag material, and the white slag time is ≥25min. High carbon ferromanganese (composition: Mn: 65～72%, C≤7.0%, Si≤2.5%, P≤0.25%, S≤0.03%, the balance is Fe) 3.0～4.0kg/t and low carbon ferrochrome (Composition: Cr: 60～70%, C≤0.25%, Si≤1.5%, P≤0.03%, S≤0.025%, the balance is Fe) 4.0～5.0kg/t to adjust the composition of molten steel, blowing argon at the bottom of the ladle Stir to facilitate the uniform composition and removal of non-metallic inclusions. The argon pressure is controlled at 0.2MPa-0.4MPa, and the aluminum wire is fed at 2.0-2.5m/t for fine adjustment of the composition and temperature of the molten steel. The temperature of the LF out of the furnace is controlled at 1665 ℃～1695℃.

(3) VD furnace refining

Calcium treatment is performed before vacuuming the VD furnace, feeding high calcium wire 2.4~3.2m/t, then vacuum treatment, vacuum degree ≤100Pa, holding time under vacuum ≥15min, feeding sulfur wire 2.5~2.5~ according to sulfur composition after vacuum breaking 3.5m/t, followed by static blowing of argon for 15min to 35min, the argon pressure maintained at 0.1Mpa to 0.3Mpa, subject to slight movement of the slag surface and no exposure of molten steel, it is strictly forbidden to add alloys after degassing. The temperature drop value during vacuum refining should be considered to ensure that the temperature before degassing is appropriate, and it is not allowed to blow argon to cool down after vacuum refining. The temperature of the VD furnace bag is controlled at 1579 ° C ~ 1611 ° C.

(4) Mold casting

Die-cast ingot dimensions are shown in Table 1.

Table 1 Die casting ingot size

The time from lifting the ladle from VD to pouring should be ≤10min, and the superheat should be controlled at 25°C to 35°C. When pouring, the ladle nozzle should be 150-200mm higher than the funnel brick. Administer argon gas in time before opening the injection to do argon protection pouring, and the amount of molten steel to be drained is ≥100kg. To strengthen the cap opening filling operation, the trickle filling method or stamping filling method can be used according to the steel type and the specific conditions of pouring. When pouring with light-weight heat-insulating lining board and composite mold slag, each plate is cast to 2/3 of the riser and starts to add riser thermal insulation agent. The thermal insulation agent is carbon powder, and the addition amount is 1.5kg/t～2.0kg/t. After pouring, the funnel brick should be pried off immediately to prevent the middle injection pipe from being unable to be removed after cooling.

(5) heating

Use soaking furnace for heating, adopt cold charging process, hold at 200°C for 0.5h, then take 3h~3.5h to heat up to 1200°C~1220°C, and finally keep at 1200°C~1220°C for 1.5h~2h to ensure the temperature of the billet Evenly and thoroughly cooked.

(6) Rolling

The rolling adopts φ1150mm preliminary rolling mill and continuous rolling unit, the starting rolling temperature is 1100℃～1200℃, the final rolling temperature is 850℃～1000℃, the rolling specification range is φ180mm～φ250mm, and the steel is slowly cooled in the heat preservation pit after rolling. 550°C, exit temperature ≤ 200°C, slow cooling time ≥ 24h.

The following are specific examples.

Example:

The present invention sets 3 embodiments, and the chemical composition of embodiment 1-3 is shown in Table 2.

The chemical composition wt% of table 2 embodiment of the present invention

The electric furnace smelting process of Examples 1-3 is shown in Table 3.

The electric furnace smelting process of the embodiment of the present invention of table 3

The LF furnace refining process of Examples 1-3 is shown in Table 4.

Table 4 Electric furnace smelting and LF refining process of the embodiment of the present invention

The VD furnace refining process of Examples 1-3 is shown in Table 5.

The VD furnace refining process of the embodiment of the present invention of table 5

The molding process of Examples 1-3 is shown in Table 6.

Table 6 The molding process of the embodiment of the present invention

The heating and rolling process of Examples 1-3 are shown in Table 7.

The heating and rolling process of table 7 embodiment of the present invention

Comparative example:

As a comparison, the composition system of the comparative example is the same as that of the present invention, the smelting adopts converter+LF furnace+RH vacuum treatment, which is a conventional process, and the casting adopts a 350mm×470mm rectangular billet continuous casting process, and the heating and rolling and process are the same as those of the present invention. The rolling specification of Example 1 is φ180mm, and the rolling specification of Comparative Example 1 is also φ180mm. See Table 8 for the low magnification, ultrasonic flaw detection, end and grain size of the embodiment of the present invention and the comparative example. Embodiment 1 and comparative example 1 low magnification test sample as shown in Figure 1 and Figure 2, all can find out from index and comparison picture, the product quality of the present invention is better than conventional craft product.

Low magnification, ultrasonic flaw detection and grain size of the embodiment of the present invention and comparative examples of table 8

The above disclosures are only preferred embodiments of the present invention, and certainly cannot limit the scope of rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope of the present invention.

Claims (8)

1. A 20MnCrS5 steel, characterized in that it consists of the following chemical elements in weight percent: C: 0.17% to 0.22%, Si: 0.15% to 0.40%, Mn: 1.10% to 1.30%, P≤0.035% , S: 0.035% to 0.045%, Cr: 1.00% to 1.30%, Alt: 0.020% to 0.060%, and the balance is iron and unavoidable impurities. 2. a preparation method of 20MnCrS5 steel according to claim 1, is characterized in that, comprises the steps: electric furnace smelting, LF furnace refining, VD furnace refining, mold casting, heating and rolling; The mold casting includes introducing the first inert gas for protective pouring before pouring, setting the amount of molten steel for drainage to be ≥ 100kg; controlling the time from hoisting the ladle out of the VD furnace to the start of pouring to be ≤ 10min, and controlling the superheat at 25°C to 35°C; When pouring, the ladle nozzle is 150-200mm higher than the funnel brick. 3. The preparation method of 20MnCrS5 steel according to claim 2, characterized in that, the electric furnace smelting includes controlling the carbon at the end point of tapping at 0.05%≤C≤0.13%, controlling the phosphorus at the end point at P≤0.020%, and tapping the steel in the electric furnace The temperature is controlled at 1640°C to 1680°C. 4. The preparation method of 20MnCrS5 steel according to claim 2, characterized in that, the LF furnace refining includes white slag time ≥ 25min, the pressure of the second inert gas is 0.2MPa～0.4MPa, and the temperature of the LF furnace bag is controlled at 1665℃～1695℃. 5. The preparation method of 20MnCrS5 steel according to claim 2, characterized in that, said VD furnace refining comprises feeding high-calcium wire, vacuum treatment, the vacuum degree of said vacuum treatment≤100Pa, the time of said vacuum treatment ≥15min, break the vacuum, feed the sulfur wire, and blow the third inert gas statically. The static blowing time of the third inert gas is 15min~35min, the static blowing pressure is 0.1Mpa~0.3Mpa, and the temperature of the VD furnace hanging bag is 1579 ℃～1611℃. 6. The method for preparing 20MnCrS5 steel according to claim 2, characterized in that the heating includes heating in a soaking furnace, keeping the temperature at 200°C for 0.5h, and then raising the temperature to 1200°C-1220°C in 3h-3.5h , and finally keep it at 1200℃～1220℃ for 1.5h～2h to ensure uniform temperature and thorough firing of the slab. 7. The method for preparing 20MnCrS5 steel according to claim 2, characterized in that the rolling includes a starting rolling temperature of 1100°C to 1200°C, a final rolling temperature of 850°C to 1000°C, and a rolling specification range of φ180mm to φ250mm, After rolling, the steel is slowly cooled in the heat preservation pit, the temperature of entering the pit is ≥550°C, the temperature of exiting the pit is ≤200°C, and the slow cooling time is ≥24h. 8. The application of the 20MnCrS5 steel as claimed in claim 1 or the 20MnCrS5 steel prepared by any preparation method as claimed in claims 2 to 8 in gears.

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