35-punch steel normalizing material for deep drawing and production method of 35-punch steel normalizing material

Abstract

The invention discloses a 35 punching steel normalizing material for deep drawing and a production method thereof, and the 35 punching steel normalizing material comprises the following chemical components in percentage by mass: 0.33-0.39% of C, 0.17-0.37% of Si, 0.50-0.80% of Mn, less than or equal to 0.025% of P, less than or equal to 0.020% of S, less than or equal to 0.25% of Cr, less than or equal to 0.25% of Ni, less than or equal to 0.20% of Cu and the balance of Fe and inevitable impurities. A continuous casting and continuous rolling production process is adopted, a normalizing treatment mode is adopted for heat treatment, and the mechanical property in a delivery state is equivalent to that of traditional 35 steel after normalizing, quenching and high-temperature tempering.

Description

Technical Field

[0001] The invention relates to a steel grade and a manufacturing method thereof, in particular to a normalizing material for deep drawing steel and a production method thereof. Background Art

[0002] 35 steel, as a high-quality carbon structural steel, has high yield strength and tensile strength, and can meet various high-strength, high-rigidity and high-stability application requirements. It has good plastic deformation ability, is easy to process and form, and can adapt to various complex mechanical processing and manufacturing processes. It has good toughness, is not easy to become brittle, and can adapt to various harsh environmental conditions and impact loads. The welding performance is acceptable and can meet general welding needs. It is widely used in the manufacture of crankshafts, rotating shafts, axle pins, levers, connecting rods, beams, sleeves, rims, washers, screws, nuts, fuse bodies and other parts. Traditional 35 steel is delivered after rolling. After receiving the goods, users often need to undergo a heat treatment process of normalizing, quenching and high-temperature tempering. This process not only increases costs, but also makes the production process cumbersome. Summary of the invention

[0003] In order to overcome the shortcomings of the prior art, the present invention provides a 35 steel normalized material for deep drawing and a production method thereof, which adopts a continuous casting + continuous rolling production process, and a normalizing treatment method for heat treatment, so that various indicators can meet the standard requirements. Compared with traditional 35 steel, 35 steel is delivered in a normalized state, and the mechanical properties in the delivery state are equivalent to those of traditional 35 steel after normalizing, quenching and high-temperature tempering. The present invention eliminates the need for users to undergo subsequent quenching and tempering heat treatment, thereby effectively reducing costs and simplifying the production process.

[0004] The present invention adopts the following technical solution:

[0005] A 35 punching steel normalizing material for deep drawing. The chemical composition of the steel, measured by mass percentage, includes: C: 0.33-0.39%, Si: 0.17-0.37%, Mn: 0.50-0.80%, P: ≤0.025%, S: ≤0.020%, Cr: ≤0.25%, Ni: ≤0.25%, Cu: ≤0.20%, and the rest is Fe and unavoidable impurities.

[0006] Furthermore, the tensile strength of the 35 steel normalizing material for deep drawing is ≥530MPa, the yield strength is ≥315MPa, the elongation after fracture is ≥20%, the shrinkage after fracture is ≥45%, and the impact toughness is ≥60J.

[0007] The production method of the above-mentioned 35 steel normalizing material for deep drawing comprises: electric furnace smelting → LF furnace refining → RH furnace refining → continuous casting → heating → rolling → normalizing; specifically comprises the following steps:

[0008] (1) Electric furnace smelting

[0009] Electric furnace smelting uses all scrap steel as raw materials, and decarbonizes, dephosphorizes, and adjusts the temperature by means of oxygen supply, slag making, and electricity. The tapping temperature is 1600-1630℃, the chemical composition C is controlled to be 0.05%-0.10%, P≤0.010%, and the residual elements meet the requirements. Before tapping, argon is blown from the bottom of the ladle to ensure the effect of argon blowing from the bottom of the ladle during the tapping process. The argon flow rate is adjusted to 500-750L / min during tapping, and the argon flow rate is adjusted to ≤150L / min after tapping. The argon gas is turned off before the ladle is hoisted. It is strictly forbidden to blow too much bottom gas to expose the molten steel surface.

[0010] (2) LF furnace refining

[0011] The LF furnace is used for white slag smelting, the white slag time is ≥15min, argon is blown from the bottom of the ladle for stirring, the argon flow rate is 100~200NL / min, and the LF furnace ladle temperature is controlled at 1618℃~1658℃.

[0012] (3) RH furnace refining

[0013] The vacuum degree is kept below 100Pa for ≥10min. Composition adjustment is not allowed after vacuum. RH tapping temperature is 1563℃~1598℃.

[0014] (4) Continuous casting

[0015] A 6-machine 6-strand arc continuous casting machine is used to continuously cast steel billets.

[0016] (5) Heating

[0017] It is heated by a walking beam heating furnace and adopts a cold charging process. The temperature of heating section 1 is 940-960°C, the temperature of heating section 2 is 1060-1170°C, the temperature of the soaking section is 1060-1170°C, the total heating time is 120-360min, and the furnace outlet temperature is 1050±30°C.

[0018] (6) Rolling

[0019] The starting rolling temperature is 860℃~1050℃, the final rolling temperature is 850℃~950℃, the steel is pile cooled after rolling, the stacking temperature is ≥300℃, and the stacking cooling time is ≥8h.

[0020] (7) Normalizing

[0021] The steel is heated to 850°C to 870°C at a heating rate of ≤75°C / h for normalizing, kept at this temperature for 5h to 8h, and then air-cooled to room temperature after being taken out of the furnace. Figure 1 .

[0022] Furthermore, in step (1), during the electric furnace smelting process, the reference amount of each slag material added is: 2700-3500kg of lime in the furnace, preferably 3200-3220kg, 1500-2000kg of magnesite, preferably 1600-1850kg; the ladle baking temperature requirement is: the ladle bottom temperature ≥700°C, preferably 720-750°C.

[0023] Furthermore, in step (4), a 6-machine 6-strand arc continuous casting machine is used to continuously cast the steel billet.

[0024] Furthermore, in step (4), the shape of the continuous casting billet is 210×210 mm.

[0025] Furthermore, in step (4), when the ladle is poured, a special tool is used to collect the flowing sand. The remaining steel volume of the ladle is ≥3 tons. The ladle is cast under argon protection with a long nozzle, and the argon pressure is 0.01MPa to 0.02MPa. The middle ladle is baked for ≥3 hours, the temperature is >1100℃; the immersion nozzle temperature is >500℃, and the pulling speed is 0.95 to 1.1m / min. The continuous casting billet is kept warm for ≥24h, and the exit temperature is guaranteed to be ≤200℃.

[0026] Furthermore, in step (6), dephosphorization is performed before rolling the continuous casting slab, and the dephosphorization pressure is ≥24 MPa.

[0027] Furthermore, in step (6), the rolling is carried out using a φ1150mm primary rolling mill and a continuous rolling mill group.

[0028] Furthermore, in step (7), the steel is taken into the furnace and divided into small bundles and arranged in layers. The number of steel bars in a single bundle is less than or equal to 30. A tie rope is added every 500 to 600 mm between each bundle. The interval between bundles is more than 200 mm. Iron pads are placed between layers to ensure that the steel bars are flat and firm.

[0029] Furthermore, the specification of 35 punching steel normalizing material for deep drawing is 30 to 80 mm.

[0030] Beneficial effects of the present invention:

[0031] The invention provides a 35 punching steel normalized material for deep drawing and a production method thereof. Compared with traditional 35 steel, the 35 punching steel is delivered in a normalized state, and the mechanical properties in the delivered state are equivalent to those of traditional 35 steel after normalizing, quenching and high-temperature tempering, with a tensile strength of ≥530MPa, a yield strength of ≥315MPa, an elongation after fracture of ≥20%, a shrinkage after fracture of ≥45%, and an impact toughness of ≥60J. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 : Heat treatment process curve.

[0033] Figure 2 : Normalizing material placement method. DETAILED DESCRIPTION

[0034] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0035] Examples 1-5

[0036] A 35 steel normalizing material for deep drawing. The specific chemical compositions of Examples 1-5 are shown in Table 1.

[0037] Table 1 Chemical composition of the present invention (wt%)

[0038] Example C Si Mn P S Cr Ni Cu 1 0.37 0.24 0.59 0.017 0.003 0.1 0.04 0.04 2 0.36 0.21 0.58 0.015 0.002 0.1 0.04 0.04 3 0.37 0.23 0.54 0.019 0.011 0.09 0.05 0.09 4 0.37 0.23 0.58 0.014 0.005 0.1 0.04 0.05 5 0.36 0.22 0.57 0.015 0.007 0.1 0.03 0.04

[0039] The production method of the above-mentioned 35 punching steel normalizing material for deep drawing comprises the following steps:

[0040] (1) Electric furnace smelting

[0041] Electric furnace smelting uses all scrap steel as raw materials, and decarbonizes, dephosphorizes, and adjusts the temperature by means of oxygen supply, slag making, and electricity. The reference amount of slag added to each furnace during the electric furnace smelting process: 3200-3220kg of lime in the furnace, 1835-1850kg of magnesite; ladle baking temperature requirements: ladle bottom temperature 740-750℃. Steel tapping temperature 1615-1620℃, chemical composition C: 0.072-0.075%, P: 0.004-0.007% and residual elements meet the requirements before steel tapping. Before steel tapping, argon is blown from the bottom of the ladle to ensure the effect of argon blowing from the bottom of the ladle during the steel tapping process. The argon flow rate is adjusted to 620L / min during steel tapping, and the argon flow rate is adjusted to 120L / min after steel tapping. The argon gas is turned off before the ladle is hoisted. It is strictly forbidden to cause the steel liquid surface to be exposed due to excessive bottom blowing.

[0042] (2) LF furnace refining

[0043] The LF furnace is used for white slag smelting, with a white slag time of 16 to 18 minutes. Argon is blown from the bottom of the ladle for stirring, and the argon flow rate is 170NL / min. The LF furnace ladle temperature is controlled at 1635 to 1642°C.

[0044] (3) RH furnace refining

[0045] The vacuum degree is kept below 100Pa for 13 to 15 minutes. No composition adjustment is allowed after vacuum. RH tapping temperature is 1562 to 1574℃.

[0046] (4) Continuous casting

[0047] The continuous casting uses a 6-machine 6-stream arc continuous casting machine to continuously cast steel billets with a billet shape of 210×210mm. When the ladle is poured, a special tool is used to connect the drain sand. The ladle capacity is 120 tons, and the remaining steel volume is 5 tons. The ladle is cast with argon protection under the long water nozzle, and the argon pressure is 0.015MPa. The middle ladle is baked for 3 hours, the temperature is 1105~1120℃; the immersion water nozzle temperature is 500~510℃, and the pulling speed is 0.96m / min. The continuous casting billet is kept warm for 24h, and the temperature out of the pit is 160~180℃.

[0048] (5) Heating

[0049] A walking beam heating furnace was used for heating, and a cold charging process was adopted. The specific heating processes of Examples 1-5 are shown in Table 2.

[0050] Table 2 Heating process of the embodiment of the present invention

[0051] Example Heating 1 stage temperature / ℃ Heating 2-stage temperature / ℃ Soaking section temperature / ℃ Oven temperature / ℃ Total heating time / min 1 948 1064 1065 1056 245 2 953 1063 1064 1054 235 3 953 1063 1063 1055 245 4 946 1066 1066 1054 245 5 952 1062 1063 1058 245

[0052] (6) Rolling

[0053] Dephosphorization is performed before rolling the continuous casting billet, and the dephosphorization pressure is 25-28 MPa. The rolling adopts a φ1150mm primary rolling mill and a continuous rolling mill group, and the steel is pile-cooled after rolling. The specific rolling process of Examples 1-5 is shown in Table 3.

[0054] Table 3 Rolling process of the embodiment of the present invention

[0055] Example Rolling temperature / ℃ Final rolling temperature / ℃ Specification / mm Cooling after rolling 1 976 875 34 Pile cooling, stacking temperature 312℃, stack cooling time 8.5h 2 972 864 34 Pile cooling, stack temperature 321℃, stack cooling time 8.5h 3 972 876 43 Pile cooling, stack temperature 316℃, stack cooling time 8.5h 4 974 872 43 Pile cooling, stack temperature 318℃, stack cooling time 8.5h 5 976 869 43 Pile cooling, stack temperature 316℃, stack cooling time 8.5h

[0056] (7) Normalizing

[0057] The steel is heated to 850℃~870℃ at a heating rate of ≤75℃ / h, kept warm for 6h, and air-cooled to room temperature after being taken out of the furnace. The steel is unpacked into small bundles and arranged in layers. There are 25 steel bars in a single bundle. A rope is added every 500mm between each bundle. The interval between bundles is 200mm. Iron pads are placed between layers to make the steel flat and firm. The specific normalizing process of Examples 1-5 is shown in Table 4; the mechanical properties of the corresponding examples are shown in Table 5. Example 1 Normalizing material placement method is as follows Figure 2 shown.

[0058] Table 4 Normalizing process of the embodiment of the present invention

[0059]

[0060] Table 5 Mechanical properties of the embodiments of the present invention

[0061]

Claims

1. A 35 steel normalizing material for deep drawing, characterized in that: The chemical composition of the steel, calculated by mass percentage, includes: C: 0.33-0.39%, Si: 0.17-0.37%, Mn: 0.50-0.80%, P: ≤0.025%, S: ≤0.020%, Cr: ≤0.25%, Ni: ≤0.25%, Cu: ≤0.20%, and the rest are Fe and unavoidable impurities.

2. The 35 steel normalizing material for deep drawing according to claim 1 is characterized in that: The tensile strength of the 35 punching steel normalizing material for deep drawing is ≥530MPa, the yield strength is ≥315MPa, the elongation after fracture is ≥20%, the shrinkage after fracture is ≥45%, and the impact toughness is ≥60J.

3. The method for producing the 35 steel normalizing material for deep drawing according to claim 1, characterized in that: The steps include: (1) Electric furnace smelting Electric furnace smelting uses all scrap steel as raw material, the tapping temperature is 1600-1630℃, the chemical composition C is controlled to be 0.05%-0.10%, P≤0.010% and the residual elements meet the requirements before tapping. Before tapping, argon is blown from the bottom of the ladle. The argon flow rate is adjusted to 500-750L / min during tapping. After tapping, the argon flow rate is adjusted to ≤150L / min or less. The argon is turned off before hanging the ladle. (2) LF furnace refining The LF furnace is used for white slag smelting, the white slag time is ≥15min, argon is blown from the bottom of the ladle for stirring, the argon flow rate is 100~200NL / min, and the LF furnace hanging ladle temperature is controlled at 1618℃~1658℃; (3) RH furnace refining Vacuum degree below 100Pa, holding time ≥10min; RH tapping temperature 1563℃~1598℃; (4) Continuous casting The continuous casting machine is used to continuously cast the steel billet; (5) Heating The walking beam heating furnace is used for heating, and the cold charging process is adopted. The temperature of the heating section 1 is 940-960°C, the temperature of the heating section 2 is 1060-1170°C, the temperature of the soaking section is 1065°C, the total heating time is 120-360min, and the furnace discharge temperature is 1020-1080°C. (6) Rolling The starting rolling temperature is 860℃~1050℃, the final rolling temperature is 850℃~950℃, the steel is pile-cooled after rolling, the stacking temperature is ≥300℃, and the stacking cooling time is ≥8h; (7) Normalizing The steel is heated to 860℃±10℃ at a heating rate of ≤75℃ / h for normalizing, kept warm for 5h~8h, and air-cooled to room temperature after being taken out of the furnace.

4. The method for producing 35 steel normalizing material for deep drawing according to claim 3, characterized in that: In step (1), during the electric furnace smelting process, the amount of slag added to each furnace is: 2700-3500kg of lime and 1500-2000kg of magnesite in the furnace; the ladle baking temperature requirement is: the ladle bottom temperature is ≥700°C.

5. The method for producing 35 steel normalizing material for deep drawing according to claim 3, characterized in that: In step (4), an arc-shaped continuous casting machine is used to continuously cast the steel billet.

6. The method for producing 35 steel normalizing material for deep drawing according to claim 3, characterized in that: In step (4), when the ladle is poured, the flowing sand is connected; the remaining steel amount of the ladle is ≥3 tons; the ladle is cast under argon protection with a long water nozzle and an argon pressure of 0.01MPa to 0.02MPa; the middle ladle is baked for ≥3 hours at a temperature of >1100°C; the immersion water nozzle temperature is >500°C and the pulling speed is 0.95 to 1.1m / min; the continuous casting billet is kept warm for ≥24h and the exit temperature is ensured to be ≤200°C.

7. The method for producing 35 steel normalizing material for deep drawing according to claim 3, characterized in that: In step (6), dephosphorization is performed before rolling the continuous casting slab, and the dephosphorization pressure is ≥24 MPa.

8. The method for producing 35 steel normalizing material for deep drawing according to claim 3, characterized in that: In step (6), the rolling is carried out using a primary rolling mill and a continuous rolling mill group.

9. The method for producing 35 steel normalizing material for deep drawing according to claim 3, characterized in that: In step (7), the steel is unbundled and placed in layers after entering the furnace. The number of steel bars in a single bundle is less than or equal to 30. A tie rope is added to each bundle every 500 to 600 mm. The interval between bundles is more than 200 mm, and iron pads are placed between layers.

10. The method for producing 35 steel normalizing material for deep drawing according to claim 3, characterized in that: The specifications of 35 punching steel normalizing materials for deep drawing are 30~80mm.

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