Automobile steel decarburization control method

Abstract

The invention discloses an automobile steel decarburization control method which comprises the following steps: 1) rolling an automobile steel blank to form a 180 mm * 180 mm section, and directly rolling the blank with the 180 mm * 180 mm section without peeling; (2) a blank with the section being 180 mm * 180 mm is used for producing an automobile steel product with the diameter phi being 23 mm to 34 mm; (3) a heat accumulating type heating furnace is adopted for heating, a preheating section, a first heating section, a second heating section, a third heating section and a soaking section are included, the total heating time is controlled to be within 200 min, and the total heating heat preservation time is within 160 min; and (4) the air-fuel ratio of the rolled blank in each section is set to be 2.0-2.1, and the depth of a decarburized layer is reduced. By adopting the reducing atmosphere, the actual heating process time is shortened to heat and control the depth of the decarburized layer.

Description

Technical Field

[0001] The invention relates to the field of automobile steel, and in particular to a method for controlling decarburization of automobile steel. Background Art

[0002] The drive shaft is an important component for transmitting power in the automobile transmission system. Its function is to transmit the power of the engine to the wheels together with the gearbox and drive axle, so that the car can generate driving force. Therefore, under high load conditions, there are high requirements for the raw material structure, decarburization layer, non-metallic inclusions and other indicators.

[0003] The decarburized layer is not allowed to exist on the transmission shaft, otherwise it will directly affect the hardenability of the surface of the transmission shaft during heat treatment, thus ultimately affecting the service life of the transmission shaft. The decarburized layer of steel mainly depends on the control of the billet heating process, and special coating protection technology can also be used (requiring an additional cost of 35 yuan / ton).

[0004] Generally, after processing the raw materials, the transmission shaft manufacturing enterprises will turn the surface of the materials to eliminate the decarburized layer and surface defects. The turning depth is 1.0-1.3mm. The decarburized layer produced by the conventional production process can be completely turned away. However, due to fierce market competition, in order to reduce the loss of materials due to turning, customers with strong processing capabilities can generally control the turning amount to 0.6-0.7mm to ensure roundness. Therefore, the decarburized layer of the raw materials needs to be controlled within 0.3mm, and the raw materials need to be normalized. According to the current process control technology, the decarburized layer of hot-rolled round steel needs to be controlled within 0.6%D, or even within 0.5%D.

[0005] Generally, in order to ensure the mechanical properties of the raw materials of the transmission shaft, large square billets are rolled into small square billets, and then heated and rolled to produce hot-rolled round steel, which is used as the raw material of the shaft after normalizing. The original production process has shortcomings: 1- After the large square billet is rolled, there will be a certain decarburization layer on the surface of the billet, which is generally about 1.0 mm. After heating and rolling again, the decarburization layer generally reaches 1% D, which cannot meet customer needs. 2- In order to ensure that the finished round steel meets customer needs, the billet needs to be peeled. 3- Because the heating furnace is designed for bearing steel production, the length of the heating furnace is relatively long, which increases the heating time in the furnace and affects the control of the decarburization layer of the second fire material. 4- In order to ensure the depth of the decarburization layer of the finished material, peeling is required, which increases the manufacturing cost.

[0006] Therefore, it is necessary to develop new decarburization control methods for automotive steel to overcome the above problems. Summary of the invention

[0007] Purpose of the invention: In view of the shortcomings and defects of the prior art, the present invention provides a method for controlling decarburization of automobile steel, which adopts a reducing atmosphere to shorten the actual heating process time for heating and controlling the depth of the decarburization layer; on the one hand, it solves the problem that the second-fire material is heated for a long time in a longer heating furnace and it is difficult to control the depth of the decarburization layer; on the other hand, it cancels the peeling process of the rolled billet, and meets the requirement of the decarburization layer depth not exceeding 0.5%D at a low cost, while ensuring that the turning amount of the shaft processing enterprise is controlled at 0.6-0.7mm during turning, further reducing the processing cost of customers.

[0008] Technical solution: A method for controlling decarburization of automobile steel according to the present invention is characterized in that it comprises the following steps:

[0009] 1) The automobile steel billet is rolled into a 180 mm × 180 mm section, and the 180 mm × 180 mm section billet is directly rolled without peeling;

[0010] 2) Billets with a cross section of 180 mm × 180 mm are used to produce automotive steel products with a diameter of φ23 mm to 34 mm;

[0011] 3) A regenerative heating furnace is used for heating, including a preheating section, a heating section, a heating section, a heating section and a soaking section. The total heating time is controlled within 200 minutes, and the total heating and heat preservation time is within 160 minutes;

[0012] 4) The air-fuel ratio of the rolling mill in each section is set at 2.0-2.1 to reduce the depth of the decarburization layer.

[0013] Wherein, the automobile steel includes the following components in weight percentage: C: 0.51% to 0.54%, Si: 0.20% to 0.35%, Mn: 0.90% to 1.10%, Cr: 0.12% to 0.20%, Al: 0.015% to 0.040%, Mo: 0.010% to 0.012%, P≤0.03%, S≤0.03%, and the rest are Fe and unavoidable impurities.

[0014] Wherein, in the preheating process in step 3), the temperature of the steel billet is maintained at 600°C to 720°C by closing some burners.

[0015] Wherein, in the heating process in step 3), the temperature of the steel billet is kept at 850°C to 900°C by closing some burners.

[0016] Wherein, in the second heating process in step 3), the temperature of the steel billet is heated to 900°C to 980°C by reducing the amount of coal gas.

[0017] Wherein, in the three-stage heating process in step 3), the steel billet is heated to 950°C to 1020°C.

[0018] Wherein, in the soaking section process in step 3), the steel billet is heated to 980°C to 1030°C.

[0019] Wherein, the cross-section of the automobile steel billet in step 1) is 320 mm×480 mm.

[0020] Among them, in the step 1), the cross-section of the automobile steel billet is 250mm×300mm, and an empty step operation is required, and the first 25 billets are loaded with one empty step.

[0021] Among them, in the step 1), the cross-section of the automobile steel billet is 220mm×220mm, and an empty step operation is required, and the first 25 billets are loaded with 2 billets and 1 empty step.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The 180mm×180mm cross-section rolling stock of the present invention does not need to be peeled to eliminate the decarburized layer of the rolling stock, saving manufacturing costs and improving production efficiency. The finished round steel does not need to be peeled, reducing production costs and shortening delivery cycles. The shaft processing enterprise can reduce the total turning amount to 0.6-0.7mm, reducing material loss, thereby reducing production costs.

[0023] The present invention can control the heating process to ensure that the decarburization layer of automobile steel is controlled within 0.5%D after reheating when the decarburization layer of the billet is 0.6mm, thereby avoiding billet peeling and finished round steel peeling, saving production costs of 300 yuan / ton. Calculated based on an annual production volume of 10,000 tons, the production cost can be reduced by 3 million yuan / year. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below in conjunction with specific implementation methods.

[0025] Embodiment 1:

[0026] The automotive steel decarburization control method of this embodiment comprises the following steps:

[0027] 1) The automobile steel billet is rolled to form a 180mm×180mm section, and the 180mm×180mm section billet is directly rolled without peeling; the automobile steel includes the following components in weight percentage: C: 0.51%~0.54%, Si: 0.20%~0.35%, Mn: 0.90%~1.10%, Cr: 0.12%~0.20%, Al: 0.015%~0.040%, Mo: 0.010%~0.012%, P≤0.03%, S≤0.03%, and the rest are Fe and inevitable impurities.

[0028] 2) The cross-section of the billet is 180mm×180mm, and the diameter of the steel product for automobiles is φ33.8mm.

[0029] 3) A regenerative heating furnace is used for heating, including preheating section, heating section 1, heating section 2, heating section 3 and soaking section. In the preheating section, the temperature of the steel billet is kept at 630℃~710℃ by closing some burners; in the heating section 1, the temperature of the steel billet is kept at 865℃~880℃ by closing some burners; in the heating section 2, the temperature of the steel billet is heated to 923℃~945℃ by reducing the amount of coal gas; in the heating section 3, the steel billet is heated to 972℃~998℃; in the soaking section, the steel billet is heated to 1009℃~1021℃. The total heating time is controlled at 134min.

[0030] 4) The air-fuel ratio of the rolling mill in each section is set at 2.0-2.1, reducing the depth of the decarburized layer to 0.12 mm.

[0031] Embodiment 2:

[0032] The automotive steel decarburization control method of this embodiment comprises the following steps:

[0033] 1) The automobile steel billet is rolled to form a 180mm×180mm section, and the 180mm×180mm section billet is directly rolled without peeling; the automobile steel includes the following components in weight percentage: C: 0.51%~0.54%, Si: 0.20%~0.35%, Mn: 0.90%~1.10%, Cr: 0.12%~0.20%, Al: 0.015%~0.040%, Mo: 0.010%~0.012%, P≤0.03%, S≤0.03%, and the rest are Fe and inevitable impurities.

[0034] 2) The cross-section of the billet is 180mm×180mm, and the diameter of the steel product for automobiles is φ30.8mm.

[0035] 3) A regenerative heating furnace is used for heating, including preheating section, heating section 1, heating section 2, heating section 3 and soaking section. In the preheating section, the temperature of the steel billet is kept at 653℃~707℃ by closing some burners; in the heating section 1, the temperature of the steel billet is kept at 855℃~878℃ by closing some burners; in the heating section 2, the temperature of the steel billet is heated to 936℃~955℃ by reducing the amount of coal gas; in the heating section 3, the steel billet is heated to 982℃~1000℃; in the soaking section, the steel billet is heated to 1000℃~1015℃. The total heating time is controlled at 140min.

[0036] 4) The air-fuel ratio of the rolling mill in each section is set at 2.0-2.1, reducing the depth of the decarburized layer to 0.10 mm.

[0037] Embodiment 3:

[0038] The automotive steel decarburization control method of this embodiment comprises the following steps:

[0039] 1) The automobile steel billet is rolled to form a 180mm×180mm section, and the 180mm×180mm section billet is directly rolled without peeling; the automobile steel includes the following components in weight percentage: C: 0.51%~0.54%, Si: 0.20%~0.35%, Mn: 0.90%~1.10%, Cr: 0.12%~0.20%, Al: 0.015%~0.040%, Mo: 0.010%~0.012%, P≤0.03%, S≤0.03%, and the rest are Fe and inevitable impurities.

[0040] 2) The cross-section of the billet is 180mm×180mm, and the diameter of the automobile steel product is φ30mm.

[0041] 3) A regenerative heating furnace is used for heating, including preheating section, heating section 1, heating section 2, heating section 3 and soaking section. In the preheating section, the temperature of the steel billet is kept at 649℃~705℃ by closing some burners; in the heating section 1, the temperature of the steel billet is kept at 862℃~881℃ by closing some burners; in the heating section 2, the temperature of the steel billet is heated to 935℃~948℃ by reducing the amount of coal gas; in the heating section 3, the steel billet is heated to 978℃~993℃; in the soaking section, the steel billet is heated to 1003℃~1022℃. The total heating time is controlled at 128min.

[0042] 4) The air-fuel ratio of the rolling mill in each section is set at 2.0-2.1, reducing the depth of the decarburized layer to 0.12 mm.

[0043] Embodiment 4:

[0044] The automotive steel decarburization control method of this embodiment comprises the following steps:

[0045] 1) The automobile steel billet is rolled to form a 180mm×180mm section, and the 180mm×180mm section billet is directly rolled without peeling; the automobile steel includes the following components in weight percentage: C: 0.51%~0.54%, Si: 0.20%~0.35%, Mn: 0.90%~1.10%, Cr: 0.12%~0.20%, Al: 0.015%~0.040%, Mo: 0.010%~0.012%, P≤0.03%, S≤0.03%, and the rest are Fe and inevitable impurities.

[0046] 2) The cross-section of the billet is 180mm×180mm, and the diameter of the steel product for automobiles is φ23.7mm.

[0047] 3) A regenerative heating furnace is used for heating, including preheating section, heating section 1, heating section 2, heating section 3 and soaking section. In the preheating section, the temperature of the steel billet is kept at 636℃~694℃ by closing some burners; in the heating section 1, the temperature of the steel billet is kept at 869℃~886℃ by closing some burners; in the heating section 2, the temperature of the steel billet is heated to 928℃~953℃ by reducing the amount of coal gas; in the heating section 3, the steel billet is heated to 988℃~995℃; in the soaking section, the steel billet is heated to 1001℃~1019℃. The total heating time is controlled at 130min.

[0048] 4) The air-fuel ratio of the rolling mill in each section is set at 2.0-2.1, reducing the depth of the decarburized layer to 0.08 mm.

[0049] Embodiment 5:

[0050] The automotive steel decarburization control method of this embodiment comprises the following steps:

[0051] 1) The automobile steel billet is rolled to form a 180mm×180mm section, and the 180mm×180mm section billet is directly rolled without peeling; the automobile steel includes the following components in weight percentage: C: 0.51%~0.54%, Si: 0.20%~0.35%, Mn: 0.90%~1.10%, Cr: 0.12%~0.20%, Al: 0.015%~0.040%, Mo: 0.010%~0.012%, P≤0.03%, S≤0.03%, and the rest are Fe and inevitable impurities.

[0052] 2) The cross-section of the billet is 180mm×180mm, and the diameter of the automobile steel product is φ27mm.

[0053] 3) A regenerative heating furnace is used for heating, including preheating section, heating section 1, heating section 2, heating section 3 and soaking section. In the preheating section, the temperature of the steel billet is kept at 645℃~690℃ by closing some burners; in the heating section 1, the temperature of the steel billet is kept at 875℃~882℃ by closing some burners; in the heating section 2, the temperature of the steel billet is heated to 936℃~949℃ by reducing the amount of coal gas; in the heating section 3, the steel billet is heated to 983℃~997℃; in the soaking section, the steel billet is heated to 998℃~1018℃. The total heating time is controlled at 143min.

[0054] 4) The air-fuel ratio of the rolling mill in each section is set at 2.0-2.1, reducing the depth of the decarburized layer to 0.09 mm.

[0055] Table 1 - Heating temperature table of Examples 1-5

[0056]

[0057] Table 2 - Carbon layer data table for Examples 1-5

[0058]

[0059]

[0060] The 180mm×180mm cross-section rolling stock of the present invention does not need to be peeled to eliminate the decarburized layer of the rolling stock, thereby saving manufacturing costs and improving production efficiency. The finished round steel does not need to be peeled, thereby reducing production costs and shortening delivery cycles. A shaft processing enterprise can reduce the total turning amount to 0.6-0.7mm, reduce material loss, and thus reduce production costs.

[0061] The present invention can control the heating process to ensure that the decarburization layer of automobile steel is controlled within 0.5%D after reheating when the decarburization layer of the billet is 0.6mm, thereby avoiding billet peeling and finished round steel peeling, saving production costs of 300 yuan / ton. Calculated based on an annual production volume of 10,000 tons, the production cost can be reduced by 3 million yuan / year.

Claims

1. A method for controlling decarburization of automobile steel, characterized in that: The steps include: 1) The automobile steel billet is rolled into a 180 mm × 180 mm section, and the 180 mm × 180 mm section billet is directly rolled without peeling; 2) Billets with a cross section of 180 mm × 180 mm are used to produce automotive steel products with a diameter of φ23 mm to 34 mm; 3) A regenerative heating furnace is used for heating, including a preheating section, a heating section, a heating section, a heating section and a soaking section. The total heating time is controlled within 200 minutes, and the total heating and heat preservation time is within 160 minutes; 4) The air-fuel ratio of the rolling mill in each section is set at 2.0-2.1 to reduce the depth of the decarburization layer.

2. The method for controlling decarburization of automobile steel according to claim 1, characterized in that: The automobile steel comprises the following components in weight percentage: C: 0.51%-0.54%, Si: 0.20%-0.35%, Mn: 0.90%-1.10%, Cr: 0.12%-0.20%, Al: 0.015%-0.040%, Mo: 0.010%-0.012%, P≤0.03%, S≤0.03%, and the rest are Fe and inevitable impurities.

3. The method for controlling decarburization of automobile steel according to claim 1, characterized in that: In the preheating process in step 3), the temperature of the steel billet is maintained at 600°C to 720°C by closing some burners.

4. The method for controlling decarburization of automobile steel according to claim 1, characterized in that: In the heating process in step 3), the temperature of the steel billet is kept at 850°C to 900°C by closing some burners.

5. The method for controlling decarburization of automobile steel according to claim 1, characterized in that: In the second heating process in step 3), the temperature of the steel billet is heated to 900°C to 980°C by reducing the amount of coal gas.

6. The method for controlling decarburization of automobile steel according to claim 1, characterized in that: In the three-stage heating process in step 3), the steel billet is heated to 950°C to 1020°C.

7. The method for controlling decarburization of automobile steel according to claim 1, characterized in that: In the soaking section process in step 3), the steel billet is heated to 980°C to 1030°C.

8. The method for controlling decarburization of automobile steel according to claim 1, characterized in that: In the step 1), the cross section of the automobile steel billet is 320 mm×480 mm.

9. The method for controlling decarburization of automobile steel according to claim 1, characterized in that: In the step 1), the cross section of the automobile steel billet is 250 mm×300 mm, and an empty step operation is required, with one empty step for each of the first 25 billets.

10. The method for controlling decarburization of automobile steel according to claim 1, characterized in that: In the step 1), the cross section of the automobile steel billet is 220 mm×220 mm, and an empty step operation is required, and the first 25 billets are loaded with 2 billets and 1 empty step.

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