CN109112398B

CN109112398B - Chromium-containing alloy bar and preparation method thereof

Info

Publication number: CN109112398B
Application number: CN201810998633.4A
Authority: CN
Inventors: 韩常海; 鲁晓静
Original assignee: Chengde Jianlong Special Steel Co Ltd
Current assignee: Chengde Jianlong Special Steel Co Ltd
Priority date: 2018-08-29
Filing date: 2018-08-29
Publication date: 2020-10-30
Anticipated expiration: 2038-08-29
Also published as: CN109112398A

Abstract

The invention relates to a chromium-containing alloy bar and a preparation method thereof, wherein Al and N are added in the process of smelting 40Cr steel to obtain the chromium-containing alloy bar containing 0.020-0.030 wt% of Al and 0.007-0.010 wt% of N. The invention solves the problem of large grain size of the alloy bar in the low rolling ratio process of 40Cr steel by adjusting the chemical components without changing the existing equipment and process, obviously improves the grain size of the steel by utilizing the cooperation of Al and N, and realizes the fine grain strengthening effect. The grain size can be improved by 1.5-2.0 grade compared with the existing 40Cr steel under the same rolling condition, the problem of higher grain size caused by insufficient capacity of the existing equipment is solved, the equipment investment is reduced, and the method has good economic benefit and application prospect.

Description

Chromium-containing alloy bar and preparation method thereof

Technical Field

The invention relates to the technical field of metallurgy, in particular to a chromium-containing alloy bar and a preparation method thereof.

Background

Chromium is an important alloy element added in the metallurgical process and is a main alloy element of stainless steel acid-resistant steel and heat-resistant steel. It can increase the hardenability of steel and has the function of secondary hardening, and can raise the hardness and wear resistance of carbon steel without making the steel brittle. When the chromium content exceeds 12%, the steel can have good high-temperature oxidation resistance and oxidation corrosion resistance, and the heat strength of the steel is also increased. The chromium can improve the wear resistance, hardness and red hardness of the tool steel and has good tempering stability. In electrothermal alloys, chromium can improve the oxidation resistance, electrical resistance, and strength of the alloy.

The 40Cr steel is medium-carbon quenched and tempered steel, and normalizing can promote tissue spheroidization and improve the cutting performance of a blank with the hardness of less than 160 HBS. The steel is tempered at the temperature of 550-570 ℃, and the steel has the best comprehensive mechanical property. The hardenability of the steel is higher than 45 steel, and the steel is suitable for surface hardening treatment such as high-frequency quenching, flame quenching and the like. After quenching and tempering, the material is used for manufacturing mechanical parts bearing medium load and medium speed work, such as a steering knuckle and a rear half shaft of an automobile, and a gear, a shaft, a worm, a spline shaft, a center sleeve and the like on a machine tool; after quenching and medium temperature tempering, the steel is used for manufacturing parts bearing high load, impact and medium speed work, such as gears, main shafts, oil pump rotors, sliding blocks, lantern rings and the like; after quenching and low-temperature tempering, the material is used for manufacturing parts which bear heavy load, have low impact and wear resistance and have the solid thickness of less than 25mm on the section, such as a worm, a main shaft, a lantern ring and the like; after quenching and tempering and high-frequency surface quenching, the alloy is used for manufacturing parts with high surface hardness and wear resistance without large impact. In addition, the steel is suitable for manufacturing various transmission parts subjected to carbonitriding treatment, such as gears and shafts with large diameters and good low-temperature toughness.

The current production process of 40Cr steel mainly comprises the following steps: converter-refining-continuous casting-rolling and other procedures. In the production process, a small rolling ratio is often adopted, and the rolling temperature needs to be increased when the rolling ratio is small, so that the grain size of the bar in a hot rolling state is large, and the product quality is reduced. For example, the Chengdan adopts 200 x 200mm²The 40Cr steel bar with the specification of phi 100 or above is rolled by a square billet, the rolling ratio is only 5.0, the finishing temperature is as high as 1000 ℃, and crystal grains are coarse.

In order to solve the above problems, manufacturers generally choose to perform subsequent treatment on the obtained 40Cr bar, for example, CN104630421A discloses a heating process for refining 40Cr steel austenite grains. The method adopts rapid heating means such as electric contact heating or induction heating and heating processes of austenite region graded cooling and short-time heat preservation, and can effectively refine austenite grains to ASTM10-15 grade. However, this method adds a heat treatment step, and is disadvantageous in terms of energy consumption and production cost control.

In addition, steel rolling equipment is improved, and a rolling and cooling control process is carried out, so that the grain size of the alloy bar can be effectively improved. However, the rolling temperature of the last pass is generally 900-. Therefore, the development of a method for solving the problem of coarse grain size of alloy bars in the low rolling ratio process of 40Cr steel at low cost is a problem which needs to be solved urgently by steel enterprises.

Disclosure of Invention

In view of the problems in the prior art, the invention provides the chromium-containing alloy bar and the preparation method thereof, the problem of large grain size of the alloy bar in the low rolling ratio process of 40Cr steel is solved by utilizing chemical component adjustment, and the chromium-containing alloy bar has good economic benefit and application prospect.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a chromium-containing alloy bar, which comprises the following components in percentage by mass: c: 0.37-0.44%, Si: 0.17-0.37%, Mn: 0.50-0.80%, Cr: 0.80-1.10%, Al: 0.020-0.030%, N: 0.007 to 0.010 percent of Mo, less than or equal to 0.10 percent of Cu, less than or equal to 0.02 percent of Ni, less than or equal to 0.30 percent of Ni, and the balance of Fe.

Nitrogen is a strong austenite forming element which can promote austenite formation in ferrite, and can reduce the tendency of grain coarsening due to the presence of the gamma phase. The nitride has a much greater tendency to form than carbide, and the composition segregation index can be reduced significantly during low temperature condensation. The aluminum in the steel can play a role in refining crystal grains and fixing nitrogen in the steel, the aluminum and the nitrogen form aluminum nitride, fine aluminum nitride grain boundary precipitates can prevent grain boundaries from moving, and the fine precipitates are taken as nucleation particles to prevent grain size from growing up, so that the effect of fine grain strengthening is achieved.

According to the invention, Al and N are added into 40Cr steel, the aluminum content in the steel is controlled to be 0.020-0.030%, the nitrogen content in the steel is controlled to be 0.0070-0.010%, the aluminum-nitrogen ratio is strictly limited, the synergistic effect of the aluminum and the nitrogen is utilized, the fine grain strengthening effect is realized to the maximum extent, the grain size of steel is improved, and the chromium-containing alloy bar with good grain size is obtained.

According to the invention, within the above composition range, the mass ratio of Al to N in the chromium-containing alloy bar is not less than 2.5, for the invention, when the mass ratio of Al to N is not less than 2.5, Al and N realize the strongest coordination effect, the grain size of the alloy can be greatly improved, and when the mass ratio of Al to N is less than 2.5, the grain strengthening effect is weakened, the grain size is not improved enough, and the requirement of low rolling ratio is difficult to meet.

According to the invention, the chromium-containing alloy bar contains 0.020-0.030% of Al, for example 0.020%, 0.021%, 0.022%, 0.023%, 0.024%, 0.025%, 0.026%, 0.027%, 0.028%, 0.029% or 0.030% by mass percentage, and the specific values between the above values are limited to space and are not exhaustive for the sake of brevity.

For the invention, when the Al content in the chromium-containing alloy bar is too low, the grain size of the alloy is improved limitedly, and the requirement of low rolling ratio is difficult to meet; when the Al content is too high, the fluidity of the molten steel is obviously reduced, alloy crystal grains are coarsened, and the mechanical property and the wear resistance are correspondingly reduced.

According to the invention, the chromium-containing alloy rod contains N0.007-0.010% by mass, which may be, for example, 0.007%, 0.0075%, 0.008%, 0.0085%, 0.009%, 0.0095% or 0.010%, and the specific values therebetween are not exhaustive for reasons of space and simplicity.

For the invention, when the content of N in the chromium-containing alloy bar is too low, the chromium-containing alloy bar is difficult to form coordination with Al, and the grain size of the alloy is also improved to a limited extent; when the content of N is too high, the plasticity, particularly the toughness of the steel material is remarkably reduced, the weldability is deteriorated, and the cold brittleness is increased.

In a second aspect, the present invention provides a method for preparing the chromium-containing alloy bar material according to the first aspect, wherein the method comprises: al and N are added in the process of smelting 40Cr steel to obtain the chromium-containing alloy bar containing 0.020-0.030 wt% of Al and 0.007-0.010 wt% of N.

According to the invention, the method comprises the following specific operations: adding an aluminum-containing raw material in the smelting process of a converter with the smelting grade of 40Cr steel, and controlling the alloy to contain 0.030-0.040 wt% of Al when the converter is finished; nitrogen is added in the LF refining process, and the alloy contains 0.007 to 0.010 weight percent of N and 0.020 to 0.030 percent of Al when the refining end point is controlled.

The smelting process of the chromium-containing alloy bar comprises the following steps: converter smelting, LF furnace refining, continuous casting and rolling.

According to the present invention, the aluminum-containing raw material may be an aluminum block or an alloy of aluminum and other elements, and the present invention is not particularly limited thereto.

According to the invention, the nitrogen increasing operation is as follows: and (4) feeding a MnN wire before LF smelting is finished.

As a preferable technical scheme, the preparation method of the chromium-containing alloy bar material can be as follows: adding an aluminum-containing raw material in the smelting process of a converter with the grade of 40Cr steel, and controlling the alloy to contain 0.030-0.040 wt% of Al when the converter is finished; and (2) feeding a MnN wire for increasing nitrogen before LF smelting is finished, controlling the alloy to contain 0.007-0.010 wt% of N and 0.020-0.030% of Al at the refining end point, and continuously casting and rolling to obtain the chromium-containing alloy bar.

Compared with the prior art, the invention has at least the following beneficial effects:

(1) according to the invention, aluminum and nitrogen are added into 40Cr steel, the content of aluminum is controlled to be 0.020-0.030%, the content of nitrogen is controlled to be 0.0070-0.010%, and the grain size of steel is improved by utilizing the cooperation effect of the two elements, so that the fine grain strengthening effect is realized.

(2) The invention solves the problem of large grain size of the alloy bar in the low rolling ratio process of 40Cr steel by utilizing chemical component adjustment without changing the existing equipment and process, the grain size can be improved by 1.5-2.0 grade compared with the existing 40Cr steel under the same rolling condition, the problem of high grain size caused by insufficient capacity of the existing equipment is solved, the equipment investment is reduced, and the invention has good economic benefit and application prospect.

Detailed Description

For the purpose of facilitating an understanding of the present invention, the present invention will now be described by way of examples. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

Example 1

This example produces chromium-containing alloy bars according to the following method:

component control (mass fraction): c: 0.37-0.44%, Si: 0.17-0.37%, Mn: 0.50-0.80%, Cr: 0.80-1.10%, Al: 0.020-0.030%, N: 0.007 to 0.010 percent of Mo, less than or equal to 0.10 percent of Cu, less than or equal to 0.02 percent of Ni, less than or equal to 0.30 percent of Ni, and the balance of Fe.

The raw material selection, the component control and the adding process of each component are the same as the method for smelting the 40Cr steel.

The total loading of the converter is controlled to be 75 tons, the molten iron ratio is more than or equal to 85 percent, and the balance is high-quality scrap steel. Tapping end point component C: 0.08-0.15%, P is less than or equal to 0.016%, tapping temperature T: 1640 ℃; 150kg of aluminum blocks, 500kg of lime and 240kg of refining slag are added in the tapping process, manganese-silicon alloy, silicon-iron alloy and high-carbon ferrochrome are added in the tapping process for alloying after the furnace, and the slag falling of the converter is reduced by adopting a sliding plate slag stopping technology in the tapping process. Target value of Mn when the converter leaves the station: 0.60 percent; al: 0.030-0.040%.

The electrifying time of an LF refining primary electrode is more than or equal to 10 minutes, 100kg of lime, 0-30kg of magnesium balls, 0-50kg of fluorite particles, 20-40kg of aluminum particles and 20-40kg of silicon carbide are added into the materials, and aluminum is supplemented once according to the refining period. The electrifying time of the secondary electrode is more than or equal to 10 minutes, and 0-100kg of lime and 20-40kg of silicon carbide are added into the materials. 30-50kg of silicon carbide is added into the materials in the rest time, 1.9m/t before LF smelting is finished is fed into a MnN wire, the nitrogen is increased by 40PPM, and the manganese is increased by 0.05%. The total LF refining time is more than or equal to 38min, and the white slag retention time is more than or equal to 15 min. Feeding a silicon-calcium line 40-60 m/furnace for calcium treatment after refining is finished, wherein the LF off-station target value is as follows: al: 0.020-0.030%, N: 0.007-0.010%.

The continuous casting speed is 1.35m/min, the tundish superheat degree is 20-30 ℃, and the crystallizer is electromagnetically stirred: 300A/3Hz, end electromagnetic stirring: 50A/10 Hz. The ladle nozzle and the long nozzle are protected by argon, and the tundish nozzle adopts an integral nozzle to reduce secondary oxidation of molten steel. The crystallizer casting powder is F02 special casting powder, and the liquid level of the steel in the crystallizer is stable and controllable in the casting process.

The continuous casting billet is transported to a heating furnace through a feeding system, the heating furnace is in a stepping heat accumulation type, blast furnace gas is used as fuel, and the temperature of a preheating section of hot charging 40Cr steel is as follows: 900-: 1160-1210 ℃, temperature of the soaking section: 1170-1200 ℃, heating time: 90-150min, rolling temperature: 1060 +/-10 ℃. The heated steel billet is dephosphorized by high pressure water to remove the iron scale on the surface of the steel billet, and enters a rolling unit through a roller way, a Danieli short stress line rolling mill is adopted as a rolling mill, 6 stands are horizontally and vertically distributed alternately, the steel billet is rolled into a phi 100mm specification by 6 passes, and the final rolling temperature is 1000 plus material 1020 ℃.

The chromium-containing alloy bar prepared by the method mainly comprises the following components: c: 0.40 percent of Si, 0.25 percent of Mn, 0.70 percent of Al, 0.025 percent of Cr, 0.95 percent of N and 7.5 to 8.0 grade of grain size.

Example 2

Compared with the embodiment 1, the addition amount of the aluminum blocks in the converter smelting process and the addition amount of the nitrogen in the LF refining process are controlled, so that the Al content in the finally prepared chromium-containing alloy bar is 0.020%, the N content is 0.007%, and other procedures and condition control are completely the same as those in the embodiment 1.

The results show that the bars obtained in this example have a grain size of grade 7.5 to 8.0.

Example 3

Compared with the example 1, the addition amount of the aluminum blocks in the converter smelting process and the addition amount of the nitrogen in the LF refining process are controlled so that the Al content in the finally prepared chromium-containing alloy bar is 0.030 percent and the N content is 0.090 percent, and other procedures and condition control are completely the same as those in the example 1.

Example 4

Compared with the example 1, the addition amount of the aluminum blocks in the converter smelting process and the addition amount of the nitrogen in the LF refining process are controlled so that the Al content in the finally prepared chromium-containing alloy bar is 0.022%, the N content is 0.010%, namely Al/N is 2.2, and other procedures and conditions are completely the same as those in the example 1.

The results show that the bars obtained in this example have a grain size of grade 7.0 to 7.5.

Comparative example 1

Compared with the embodiment 1, Al and N are not added in the smelting process, and other procedures and condition control are completely the same as the embodiment 1, namely the 40Cr steel bar is directly prepared.

The results show that the 40Cr steel bar obtained in the example has a grain size of 5.0-6.0 grade.

Comparative example 2

Compared with the embodiment 1, the addition amount of the aluminum blocks in the converter smelting process is controlled, so that the Al content in the finally prepared chromium-containing alloy bar is 0.010 percent, namely the aluminum content is insufficient, and other procedures and condition control are completely the same as those in the embodiment 1.

The results show that the bars obtained in this example have a grain size of grade 5.5 to 6.5.

Comparative example 3

Compared with the embodiment 1, the addition amount of the aluminum blocks in the converter smelting process is controlled so that the Al content in the finally prepared chromium-containing alloy bar is 0.050 percent, namely the aluminum content is excessive, and other procedures and condition control are completely the same as those in the embodiment 1.

The results show that the grain size of the bar obtained in the embodiment is 6.0-6.5 grade, the fluidity of the molten steel is obviously reduced in the smelting process, and the mechanical properties of the obtained alloy are also reduced.

Comparative example 4

Compared with the example 1, the nitrogen addition amount in the LF refining process is controlled, so that the N content in the finally prepared chromium-containing alloy bar is 0.003 percent, namely the nitrogen content is too low, and other procedures and conditions are completely the same as those in the example 1.

The results show that the bars obtained in this example have a grain size of grade 6.5 to 7.

Comparative example 5

Compared with the example 1, the nitrogen addition amount in the LF refining process is controlled, so that the N content in the finally prepared chromium-containing alloy bar is 0.015 percent, namely the nitrogen content is too high, and other procedures and condition control are completely the same as those in the example 1.

The results show that the grain size of the bar obtained in the example is 7.5-8.0 grade, but the plasticity and toughness of the steel are obviously reduced, the workability is deteriorated, and the performance requirements of the product are difficult to meet.

The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.

It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Claims

1. The chromium-containing alloy bar is characterized by comprising the following components in percentage by mass: c: 0.37-0.44%, Si: 0.17-0.37%, Mn: 0.50-0.80%, Cr: 0.80-1.10%, Al: 0.020-0.030%, N: 0.007 to 0.010 percent of Mo, less than or equal to 0.10 percent of Cu, less than or equal to 0.02 percent of Ni, and the balance of Fe, wherein the mass ratio of Al to N in the chromium-containing alloy bar is more than or equal to 2.5.

2. The method of making chromium-containing alloy bar of claim 1, wherein the method is: al and N are added in the process of smelting 40Cr steel to obtain the chromium-containing alloy bar containing 0.020-0.030 wt% of Al and 0.007-0.010 wt% of N.

3. The method of making chromium-containing alloy bar of claim 2, wherein the method is: adding an aluminum-containing raw material in the smelting process of a converter with the grade of 40Cr steel, and controlling the alloy to contain 0.030-0.040 wt% of Al when the converter is finished; nitrogen is added in the LF refining process, and the alloy contains 0.007 to 0.010 weight percent of N and 0.020 to 0.030 percent of Al when the refining end point is controlled.

4. The method of claim 2, wherein the chromium-containing alloy bar is prepared by the following smelting steps: converter smelting, LF furnace refining, continuous casting and rolling.

5. The method of preparing chromium-containing alloy bar according to claim 3, wherein the nitrogen increasing is performed by: and (4) feeding a MnN wire before LF smelting is finished.

6. The method of making chromium-containing alloy bar of claim 2, wherein the method is: adding an aluminum-containing raw material in the smelting process of a converter with the grade of 40Cr steel, and controlling the alloy to contain 0.030-0.040 wt% of Al when the converter is finished; and (2) feeding a MnN wire for increasing nitrogen before LF smelting is finished, controlling the alloy to contain 0.007-0.010 wt% of N and 0.020-0.030% of Al at the refining end point, and continuously casting and rolling to obtain the chromium-containing alloy bar.