CN109881097B

CN109881097B - Production process of high-performance tool and die flat steel

Info

Publication number: CN109881097B
Application number: CN201910197362.7A
Authority: CN
Inventors: 余佑祥; 黄生权; 崔建强; 苏雄杰; 唐政良; 王洪祥; 鲁友名
Original assignee: SICHUAN FENG YUAN MACHINERY MANUFACTURING Co
Current assignee: SICHUAN FENG YUAN MACHINERY MANUFACTURING Co
Priority date: 2019-03-15
Filing date: 2019-03-15
Publication date: 2020-05-19
Anticipated expiration: 2039-03-15
Also published as: CN109881097A

Abstract

The invention discloses a high-performance tool and die flat steel which comprises the following components in percentage by weight: c: 0.35% -0.40%, Si: 0.70% -1.0%, Mn: 0.30% -0.60%, P: less than or equal to 0.010 percent, S: less than or equal to 0.005 percent, Cr: 5.20% -5.70%, Ni: 0.40-0.60%, Mo: 1.30% -1.50%, V: 0.90% -1.20%, Cu: less than or equal to 0.10 percent, As + Sn + Pb + Sb + Bi less than or equal to 0.010 percent, and the balance of Fe and inevitable impurity elements. The tool and die flat steel produced by the invention has high yield, high internal purity, less impurities, uniform tissue, high mechanical properties, energy conservation and cost reduction.

Description

Production process of high-performance tool and die flat steel

Technical Field

The invention belongs to the field of alloy steel processing, and particularly relates to a production process of high-performance tool and die flat steel.

Background

Die steel is a steel grade used for manufacturing dies such as cold stamping dies, hot forging dies, die casting dies and the like. The properties of which are mainly influenced by the material and the heat treatment. The requirements on the purity, the cracks and the mechanical properties of steel are very high, and the requirements on harmful impurities such As P, S, H, O, N, As, Sn and the like are strictly controlled. At present, in a common production process, a plurality of components are required to be used, so that the proportion of each component is difficult to control. The performance and parameters of the die steel after being processed and formed often cannot meet practical requirements, and the problems of low yield and the like are caused. In the prior art, the problems are difficult to effectively solve.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a production process of high-performance tool and die flat steel, which aims at overcoming the defects of the prior art, has high yield, saves energy, reduces cost and has good product quality.

The technical scheme adopted by the invention is as follows: a production process of high-performance tool and die flat steel comprises the following steps:

a. feeding scrap steel and pig iron into an electric arc furnace, heating to more than or equal to 1580 ℃ after melting, ensuring that the decarburization quantity is more than or equal to 0.20% in the oxidation period, the decarburization speed is 0.01%/min-0.03%/min, and the C content is more than or equal to 0.10% when discharging;

b. feeding molten steel into an LF furnace, adjusting furnace slag, adding C powder, Fe-Si powder and Si-Ca powder for reduction, finely adjusting the components when the temperature is more than or equal to 1580 ℃, keeping the time in the furnace for more than or equal to 20min after the furnace slag turns white, and discharging the molten steel after the components are qualified and the temperature reaches 1670-1690 ℃;

c. pouring 70-80% of slag, sending the molten steel into a VD furnace, keeping the vacuum for more than or equal to 20min, discharging the molten steel out of the furnace after the soft blowing time is more than or equal to 8min, and discharging the molten steel out of the furnace at the temperature of 1585-1600 ℃;

d. sending molten steel into a continuous casting machine, carrying out whole-process protective casting, discharging drainage sand from an accident station of a molten steel ladle before casting, sleeving a ladle protection pipe, opening Ar gas protection, controlling Ar gas pressure to be 0.2KPa-0.25KPa, opening Ar gas protection in a tundish, controlling Ar gas flow to be 20L/min-40L/min, ensuring that the temperature of a casting blank is controlled to be 890-910 ℃ when the casting blank passes through a withdrawal and straightening machine, carrying out steam fog cooling in the casting blank process, controlling the pressure of a gas pipeline for fog cooling to be 0.8MPa, controlling the pressure of each section of inlet to be 0.2MPa-0.3MPa, controlling the pressure of a secondary cooling water pipeline to be 0.8MPa-0.9MPa, controlling the pressure of each section of inlet to be 0.7MPa-0.8MPa, and controlling the temperature of the casting;

e. putting the cast blank after casting molding into a heating furnace, wherein the temperature of the cast blank when the cast blank is put into the heating furnace is 680-750 ℃, heating the heating furnace to 1050-1100 ℃ in a weak oxidation atmosphere environment to heat the cast blank, and the time of the cast blank in the heating furnace is less than or equal to 2.5 h;

f. rolling the casting blank into flat steel by a fifth generation Morgan rolling mill, wherein in the rolling process, the initial rolling temperature is 1050-1100 ℃, the final rolling temperature is 850-880 ℃, and the rolling speed of each 3m long casting blank is 1-1.5 min;

g. annealing the rolled steel by adopting an online continuous type stack cooling annealing process, wherein the Brinell hardness of the annealed flat steel is less than or equal to 220N/mm 2;

h. blanking and forming the annealed steel according to requirements;

i. carrying out quenching and tempering treatment after the product is formed, heating to 760-770 ℃, keeping the temperature for 25min, heating to 980-990 ℃, keeping the temperature for 15min, quenching, cooling the quenching for 5min in an oil cooling mode, then cooling the quenching to 300 ℃, tempering at 570-580 ℃ by air cooling, and obtaining the high-performance tool and die flat steel, wherein the obtained high-performance tool and die flat steel comprises the following components in percentage by weight: c: 0.35% -0.40%, Si: 0.70% -1.0%, Mn: 0.30% -0.60%, P: less than or equal to 0.010 percent, S: less than or equal to 0.005 percent, Cr: 5.20% -5.70%, Ni: 0.40-0.60%, Mo: 1.30% -1.50%, V: 0.90% -1.20%, Cu: less than or equal to 0.10 percent, As + Sn + Pb + Sb + Bi less than or equal to 0.010 percent, and the balance of Fe and inevitable impurity elements.

In one embodiment, in the step a, the content of P is less than or equal to 0.004 percent during tapping; the tapping temperature is more than or equal to 1650 ℃.

In one embodiment, in the step a, 4Kg/t-5Kg/t of Si-Al-Ca alloy is added for pre-deoxidation when the electric arc furnace is discharged, and 25Kg of H-Cr alloy, 8Kg of Fe-Si alloy and 18Kg of Mo-Fe alloy are added into each ton of molten steel at the same time.

In one embodiment, during tapping, the added Si-Al-Ca alloy contains 35-45% of Si, 6-10% of aluminum and 10-15% of calcium.

In one embodiment, in the step b, 3m/t-5m/t of Ca-Si alloy wires are added before the LF furnace is discharged.

In one embodiment, in the step c, before the molten steel enters the VD furnace, slag turning operation is carried out, 70% -80% of slag is poured, and after the VD furnace is opened, a covering agent is added to the periphery of the surface of the steel ladle.

In one embodiment, in step c, the VD furnace takes a gas sample for inspection, wherein H is less than or equal to 1.2PPm, O is less than or equal to 12PPm, and N is less than or equal to 40 PPm.

In one embodiment, the container for receiving the molten steel is a steel ladle between the step a and the step d, the molten steel poured from the steel ladle is received by a tundish, the waiting time of the molten steel in the steel ladle is less than or equal to 10min, the baking temperature of the tundish before casting is more than or equal to 900 ℃, the liquid level height of the tundish within 1min-1.5min is ensured to reach 400mm after casting is started, when the liquid level of the molten steel in the tundish reaches 200mm-300mm, 20 kg/ladle of special covering agent for the molten steel 4 bags-6 bags are added, in the casting process, the liquid level of the tundish is controlled between 500mm-600mm until the molten steel in the large ladle is completely poured, the lowest liquid level of the tundish is more than or equal to 350mm during continuous casting, the superheat degree is controlled between 25 ℃ and 35 ℃ when casting is started, and the superheat degree.

In one embodiment, the steel ladle needs to be smelted by mixed special refining slag, and the main components of the slag are as follows: waste runner brick particles: fluorite powder 7: 2: 1 by weight ratio.

The invention has the beneficial effects that:

1. compared with the traditional process, the process adopts an electric arc furnace, an LF furnace and a VD furnace for smelting, the whole continuous casting process is protected for pouring, and program-controlled cooling is carried out for casting blank forming, a five-generation Morgan rolling mill is adopted for precisely controlled rolling forming, online continuous stacking cooling is carried out, the yield is improved by 10% -15%, energy (natural gas) is saved by 30M 3/ton-50M 3/ton, the process cost is reduced by 1000 yuan/ton-3000 yuan/ton, the product quality is good, the casting blank is better rated at low power, the product grade of inclusions A, B, C, D, Ds is all less than or equal to one grade, and the flaw detection qualification rate of the product is more than or equal to 99.8.

2. After rolling, an on-line continuous heap cooling annealing process is adopted, the Brinell hardness of the traditional similar steel flat steel is reduced to be less than or equal to 235N/mm2 and less than or equal to 220N/mm2, and the steel flat steel has the advantages of reduced hardness, easy processing, high yield and low cost.

3. The grain size after tempering is 10 grade, the yield strength is more than or equal to 1700MPa, the tensile strength is more than or equal to 2100MPa, the tensile strength is more than 150MPa higher than that of similar materials, and the V-shaped impact energy is more than or equal to 30J.

Drawings

FIG. 1 is a graph of grain size enlarged by 500 times after corrosion of sodium hydroxide solution and hydrogen peroxide;

FIG. 2 is a graph showing the grain size of a saturated picric acid solution after etching with an activator at 500 times magnification.

Detailed Description

The present invention will be described in further detail with reference to specific examples.

firstly, feeding scrap steel and pig iron into an electric arc furnace, heating to more than or equal to 1580 ℃ after melting, ensuring that the decarburization quantity is more than or equal to 0.20% in the oxidation period, the decarburization speed is 0.01%/min-0.03%/min, and the C content is more than or equal to 0.10% when discharging;

step two, adjusting slag after the molten steel is sent into an LF furnace, adding C powder, Fe-Si powder and Si-Ca powder for reduction, finely adjusting the components when the temperature is more than or equal to 1580 ℃, keeping the time in the furnace for more than or equal to 20min after the slag turns white, and discharging the molten steel after the components are qualified and the temperature reaches 1670-1690 ℃;

step three, pouring 70-80% of slag, sending the molten steel into a VD furnace, keeping the vacuum for more than or equal to 20min, discharging the molten steel out of the furnace after the soft blowing time is more than or equal to 8min, and discharging the molten steel out of the furnace at the temperature of 1585-1600 ℃;

step four, sending the molten steel into a continuous casting machine, carrying out whole-process protective casting, discharging drainage sand from an accident station of a molten steel ladle before casting, sleeving a ladle protection tube, opening Ar gas protection, controlling the Ar gas pressure to be 0.2KPa-0.25KPa, opening Ar gas protection in a tundish, controlling the Ar gas flow to be 20L/min-40L/min, ensuring that the temperature of a casting blank is controlled to be 890-910 ℃ when the casting blank passes through a withdrawal and straightening machine, carrying out steam fog cooling in the casting blank process, controlling the pressure of a gas pipeline for aerial fog cooling to be 0.8MPa, controlling the inlet pressure of each section to be 0.2MPa-0.3MPa, controlling the pressure of a secondary cooling water pipeline to be 0.8-0.9 MPa, controlling the inlet pressure of each section to be 0.7MPa-0.8MPa, and controlling the casting blank temperature;

putting the cast blank after casting into a heating furnace, wherein the temperature of the cast blank when the cast blank is put into the heating furnace is 680-750 ℃, heating the heating furnace to 1050-1100 ℃ in a weak oxidation atmosphere environment to heat the cast blank, and the time of the cast blank in the heating furnace is less than or equal to 2.5 h;

step six, rolling the casting blank into flat steel by a fifth generation Morgan rolling mill, wherein in the rolling process, the initial rolling temperature is 1050-1100 ℃, the final rolling temperature is 850-880 ℃, and the rolling speed of the casting blank with the length of 3 meters per mill is 1-1.5 min;

seventhly, annealing the rolled steel by adopting an online continuous type stack cooling annealing process, wherein the Brinell hardness of the annealed flat steel is less than or equal to 220N/mm 2;

step eight, blanking and forming the annealed steel according to requirements;

ninth, quenching and tempering are carried out after the product is formed, the temperature is raised to 760-770 ℃, the temperature is kept for 25min, the temperature is raised to 980-990 ℃, the temperature is kept for 15min, quenching is carried out, oil cooling is adopted for cooling for 5min, then air cooling is carried out to 300 ℃, tempering temperature is 570-580 ℃, the high-performance tool and die flat steel is obtained, and the obtained high-performance tool and die flat steel is composed of the following components in percentage by weight: c: 0.35% -0.40%, Si: 0.70% -1.0%, Mn: 0.30% -0.60%, P: less than or equal to 0.010 percent, S: less than or equal to 0.005 percent, Cr: 5.20% -5.70%, Ni: 0.40-0.60%, Mo: 1.30% -1.50%, V: 0.90% -1.20%, Cu: less than or equal to 0.10 percent, As + Sn + Pb + Sb + Bi less than or equal to 0.010 percent, and the balance of Fe and inevitable impurity elements.

In the embodiment, in the first step, the content of P is less than or equal to 0.004 percent during tapping; the tapping temperature is more than or equal to 1650 ℃.

In the first step of the present embodiment, 4Kg/t-5Kg/t of Si-Al-Ca alloy is added for pre-deoxidation during tapping of the electric arc furnace, and 25Kg of H-Cr alloy, 8Kg of Fe-Si alloy and 18Kg of Mo-Fe alloy are added per ton of molten steel.

In the embodiment, when the alloy is discharged, the Si content of the added Si-Al-Ca alloy is 35-45%, the aluminum content is 6-10% and the calcium content is 10-15%.

In the second step, 3m/t-5m/t of Ca-Si alloy wire is added before the LF is discharged.

In the third step, before the molten steel enters the VD furnace, slag turning operation is carried out, 70% -80% of slag is poured out, and after the VD furnace is opened, covering agent is added to the periphery of the surface of the steel ladle.

In the third step of the present embodiment, a VD furnace samples gas for inspection, where H is less than or equal to 1.2PPm, O is less than or equal to 12PPm, and N is less than or equal to 40 PPm.

In the embodiment, the container for receiving the molten steel is a steel ladle between the first step and the fourth step, the molten steel cast by the steel ladle is received by a tundish, the waiting time of the molten steel in the steel ladle is less than or equal to 10min, the baking temperature of the tundish before casting is more than or equal to 900 ℃, the liquid level height of the tundish within 1min-1.5min is ensured to reach 400mm after casting is started, when the liquid level of the molten steel in the tundish reaches 200mm-300mm, 20 kg/ladle of special covering agent for the molten steel 4 bags-6 bags are added, in the casting process, the liquid level of the tundish is controlled between 500mm-600mm until the molten steel in the ladle is completely cast, the lowest liquid level of the tundish is more than or equal to 350mm during continuous casting, the superheat degree is controlled between 25 ℃ and 35 ℃ when casting is started, and the superheat degree.

In the embodiment, the steel ladle needs to be smelted by mixed special refining slag, and the main components of the slag are as follows: waste runner brick particles: fluorite powder 7: 2: 1 by weight ratio.

The process produces the die steel, has high requirements on the purity, cracks and mechanical properties of the steel, and strictly controls harmful impurity elements such As P, S, H, O, N, As, Sn and the like. The boiling degassing work in the oxidation period is required to be carried out, the raw materials are clean and dry, and the cleanness of the molten steel is ensured; secondary gettering is to be prevented during casting. The melting point is about 1490 ℃; according to the relation curve of the carbon content in the steel and the hardness of the quenched steel, the quenching hardness of the steel is about 55 HRC. In the case of tool steels, a portion of the carbon in the steel enters the matrix of the steel to cause solid solution strengthening, and another portion of the carbon will combine with carbide-forming elements in the alloying elements to form alloyed carbides. For the tool and die steel, the alloy carbide is required to be dispersed and precipitated on a quenched martensite matrix during tempering to generate a secondary hardening phenomenon besides a small amount of residue. Thereby the properties of the tool and die steel are determined by the structures of the uniformly distributed residual alloy carbon compound and the tempered martensite. It can be seen that the C content in the steel cannot be too low, and that an increase in the carbon content in the steel will increase the strength of the steel, and in the case of tool and die steels, will increase the high temperature strength, hot hardness and wear resistance, but will result in a decrease in toughness. The carbon content of the steel is reduced as much as possible on the premise of keeping the strength, and when the tensile strength of the steel reaches more than 1550MPa, the carbon content is preferably 0.3-0.4%. The process adopts a continuous casting mode to process the casting blank. Compared with the traditional die casting, the continuous casting mode can reduce the segregation of steel and improve the uniformity of the steel through the technologies of electromagnetic stirring, low-temperature casting and the like; secondary oxidation is reduced. Improving the surface decarburization of the steel; the structure and the performance of the steel are stable and uniform; the yield and the production efficiency are improved; the oxygen content is reduced and the chemical composition of the steel is effectively controlled by matching with the external refining technology.

The low-power rating and the high-power rating of the casting blank of the tool and die flat steel produced by the process are higher than the industrial standard.

The casting blank low power rating standard is as follows: the central shrinkage cavity is 0 grade, the central porosity is 0.5 grade, the intermediate crack is 0 grade, the central crack is 0 grade, and the subcutaneous crack is 0.5 grade.

High power rating criteria are as in table 1:

table 1 high power rating defect qualification level standard high power rating:

the process has certain differences with the standard process in each component and component ratio, which are specifically shown in table 2:

TABLE 2 Components and component ratios of the present Process and Standard Process

In the process, the process parameters of the continuous casting machine in the casting process are shown in the table 3:

TABLE 3 technological parameter chart of two-stream casting machine

In the process, the parameters of the secondary cooling water distribution curve of each specification of the continuous casting machine are as shown in table 4:

TABLE 4 Secondary cooling distribution curve parameters of each specification of continuous casting machine

In the process, the tundish is built by MgCr bricks, the upper section of the nozzle is made of Zn material, the immersed long nozzle is made of aluminum-carbon-zirconium, and the stopper rod is made of aluminum-carbon-zirconium, so that the pollution of refractory material erosion to molten steel in the casting process is reduced. Before casting, impurities around the water gap of the tundish are cleaned, and the water gap is ensured to be smooth. When the stopper rod is used for casting steel, whether the stopper rod is displaced in the baking process is checked, and if the stopper rod cannot block a water gap due to displacement, casting can be started only after correction. Before casting, the ladle drainage sand is discharged at an accident station, a ladle protection tube is sleeved on the ladle drainage sand, Ar gas protection is conducted, the Ar gas pressure is controlled to be 0.2KPa-0.25KPa, the protection tube is inserted into molten steel, the phenomenon that gas is slightly turned over can be seen, the Ar gas protection is conducted in the tundish, secondary oxidation in the tundish is prevented, and the Ar gas flow is controlled to be 20-40L/min. When the liquid level of the tundish molten steel reaches 400mm, closing a ladle nozzle, and carrying out tundish temperature measurement; the liquid level of the tundish is controlled between 500mm and 600mm during casting, in order to ensure normal casting, the opening of a water gap is adjusted back and forth to control the liquid level of the tundish steel between 500mm and 600mm until the ladle steel is completely cast, and the lowest liquid level of the tundish is more than or equal to 350mm during continuous casting. The temperature measurement is carried out between the control areas of the molten steel of the 1 flow and the 2 flow, the insertion depth is more than or equal to 200, the temperature of the molten steel of the tundish is measured according to the time interval of three times of 3min after casting, half of casting and the last stage of casting (5 min before the end), the first furnace of the tundish is increased once 5min after casting, and the temperature measurement can be increased for 1-2 times according to specific conditions. The tundish temperature and the steel drawing speed are well matched. According to weighing of a steel ladle balance, an operator needs to close a ladle slide plate in time when molten steel is poured quickly, and slag is prevented from entering a tundish. When the pouring of the tundish is completed, the height of the residual water is more than or equal to 150 mm.

As shown in figures 1 and 2, the tool and die flat steel prepared by the invention has high carbon content and chromium content, and the prior austenite grain size corrosion is difficult, so that a plurality of methods are required, and different methods are suitable for steel in different states. The corrosive agent in fig. 1 adopts sodium hydroxide solution + hydrogen peroxide, and the corrosive agent in fig. 2 adopts saturated picric acid solution + active agent.

The above-mentioned embodiments only express the specific embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.

Claims

1. A production process of high-performance tool and die flat steel is characterized by comprising the following steps:

b. feeding molten steel into an LF furnace, adjusting furnace slag, adding C powder, Fe-Si powder and Si-Ca powder for reduction, finely adjusting components when the temperature is more than or equal to 1580 ℃, keeping the time in the furnace for more than or equal to 20min after the furnace slag turns white, and discharging the molten steel after the components are qualified and the temperature reaches 1670-1690 ℃;

h. blanking and forming the annealed steel according to requirements;

2. The production process of the high-performance tool and die flat steel as claimed in claim 1, wherein in the step a, the P content is less than or equal to 0.004% when tapping; the tapping temperature is more than or equal to 1650 ℃.

3. The process for producing a high performance tool and die flat steel as claimed in claim 1, wherein in step a, the electric arc furnace is tapped with Si-Al-Ca alloy at 4Kg/t to 5Kg/t for pre-deoxidation, and simultaneously, H-Cr alloy at 25Kg, Fe-Si alloy at 8Kg and Mo-Fe alloy at 18Kg per ton of molten steel.

4. The process for producing a high performance tool and die flat steel as claimed in claim 3, wherein the Si-Al-Ca alloy added at the time of tapping is 35% to 45% Si, 6% to 10% Al and 10% to 15% Ca.

5. The process for producing high performance tool and die flat steel as claimed in claim 1, wherein in step b, the Ca-Si alloy wire is added at 3m/t-5m/t before discharging from the LF furnace.

6. The process for producing high performance tool and die flat steel according to claim 1, wherein in step c, before the molten steel enters the VD furnace, slag turning operation is performed, 70% -80% of slag is poured off, and after the VD furnace is opened, covering agent is added to the periphery of the surface of the steel ladle.

7. The process for producing high performance tool and die flat steel as claimed in claim 1, wherein in step c, the VD furnace takes gas sample for inspection, wherein H is less than or equal to 1.2PPm, O is less than or equal to 12PPm and N is less than or equal to 40 PPm.

8. The process for producing high performance tool and die flat steel according to claim 1, wherein the vessel for receiving molten steel in steps a to d is a ladle, molten steel poured from the ladle is received by a tundish, the waiting time of molten steel in the ladle is less than or equal to 10min, the baking temperature of the tundish before casting is more than or equal to 900 ℃, the tundish is guaranteed to reach the liquid level of 400mm within 1min to 1.5min after casting is started, when the liquid level of the molten steel in the tundish reaches 200mm-300mm, adding 20 kg/ladle of special covering agent for the molten steel in 4 bags-6 bags, during the casting process, the liquid level of the tundish is controlled between 500mm and 600mm until the ladle molten steel is completely poured, the lowest liquid level of the tundish is more than or equal to 350mm during continuous pouring, the superheat degree is controlled between 25 ℃ and 35 ℃ when the pouring is started, and the superheat degree is controlled between 20 ℃ and 30 ℃ during the pouring process.

9. The production process of the high-performance tool and die flat steel as claimed in claim 8, wherein the steel ladle is required to be smelted by using mixed special refining slag, and the slag mainly comprises the following components: waste runner brick particles: fluorite powder 7: 2: 1 by weight ratio.