Production method for reducing decarburized layer of low-carbon alloy carburizing steel cold drawing rod

Abstract

The invention discloses a production method for reducing a decarburized layer of a low-carbon alloy carburizing steel cold drawing rod, which comprises the following steps of: performing blank finishing treatment, blank spraying treatment, blank heating treatment, coil rolling treatment, coil annealing treatment, coil cold drawing treatment, cold drawing rod softening annealing treatment and the like, so that the decarburized layer of the low-carbon alloy carburizing steel cold drawing rod can be controlled to be less than or equal to 0.05 mm; and the structure is controlled to be a spheroidized structure, the performance is uniform, and the quality requirements of high-end users are met.

Description

Technical Field

[0001] The present invention relates to a production process for cold-drawn bars of low-carbon carburizing steel, and more specifically to a production method for reducing the decarburized layer of cold-drawn bars of low-carbon alloy carburizing steel. Background Art

[0002] Low-carbon alloy carburizing steel refers to low-carbon alloy structural steel used after carburizing heat treatment, which has the properties of hard outside and tough inside, and is used for wear-resistant parts that bear impacts, such as transmission gears in automobiles and tractors, camshafts and piston pins in internal combustion engines, etc.

[0003] The composition of low-carbon alloy carburizing steel is: C: 0.15 - 0.20 wt%, Si: 0.15 - 0.40 wt%, Mn: 0.40 - 0.60 wt%, P: ≤0.020 wt%, S: 0.015 - 0.025 wt%, Cr: 1.95 - 2.10 wt%, Ni: 1.90 - 2.00 wt%, Al: 0.015 - 0.030 wt%, and the rest is refined material of Fe and inevitable impurities, and it is made into a steel product for easy cutting through rolling and cold processing.

[0004] The cold-drawn bar of low-carbon alloy carburizing steel refers to: a product of alloy carburizing steel produced by using the cold-drawing process technology for coiled bars, with a specification of Φ14mm - 20mm round.

[0005] However, the appearance of a decarburized layer on the surface of the current cold-drawn bars of low-carbon alloy carburizing steel will affect the uniformity of the subsequent carburized layer, and further reduce the fatigue life of the parts.

[0006] Therefore, it is necessary to specifically develop a method for reducing the thickness of the decarburized layer of cold-drawn bars of low-carbon carburizing steel. By reducing the thickness of the decarburized layer of the cold-drawn bars, the uniformity of the carburized layer of the parts can be improved.

[0007] A method for controlling the decarburized layer depth of cold-heading steel wire rods for high-strength fasteners with the patent application number CN202411017344.3 controls the decarburized layer depth by removing water vapor, heating, and controlled rolling and controlled cooling. This patent does not involve cold-drawn bars, and the method used mainly still obtains wire rods without full decarburization and with a total decarburized layer depth less than 0.6%D in the front stage of the whole process during the wire rod production process, which is difficult to meet high-end requirements.

[0008] A production method for controlling the decarburized layer depth of tool steel wire rods with the patent application number CN202210570628.X controls decarburization through finish rolling and controlled cooling. This patent does not involve cold-drawn bars, and the surface decarburized layer depth of the tool steel hot-rolled wire rods produced by this patent is ≤1.0D%, which is difficult to meet high-end requirements. Summary of the Invention

[0009] The object of the present invention is to provide a production method for reducing the decarburized layer of cold-drawn bars made of low-carbon alloy carburizing steel. By using this method to produce cold-drawn bars, the depth of the decarburized layer can be controlled within 0.05 mm, the structure is spheroidized structure, and the performance is stable, so as to meet the high-end requirements of automotive parts in the market.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions.

[0011] A production method for reducing the decarburized layer of cold-drawn bars made of low-carbon alloy carburizing steel, comprising the following steps:

[0012] A. Blanking finishing treatment, completely peeling the surface of the blank and polishing it to achieve a smooth transition;

[0013] B. Blanking spraying treatment, evenly spraying a medium-high temperature metal decarburization inhibitor on the periphery of the blank to prevent decarburization during the heating process;

[0014] C. Blanking heating treatment, successively: preheating section ≤ 800 °C, heating section I 950 - 1000 °C, heating section II 1000 °C - 1100 °C, soaking section 1050 °C - 1150 °C;

[0015] D. Coiling rolling treatment, successively: starting rolling temperature 1000 - 1050 °C, final rolling temperature 760 - 810 °C, slow cooling;

[0016] E. Coiling annealing treatment, successively: entering the furnace at 600 - 700 °C and holding for 60 - 90 min, heating to 760 - 790 °C at a rate of 50 - 100 °C / h, holding for 6 h, cooling with the furnace to 700 - 720 °C, holding for 4 h, and then cooling to 660 - 630 °C and discharging from the furnace, blowing N 2 for protection, dew point ≤ -30 °C;

[0017] F. Coiling cold drawing treatment, directly cold-drawing the coiled material into a straight bar, and controlling the single-pass cold deformation amount in the range of 20 - 35%;

[0018] G. Softening annealing treatment of cold-drawn bars, controlling the annealing temperature at 630 - 680 °C, holding for 8 - 12 h, blowing N 2 for protection, dew point ≤ -30 °C;

[0019] The blank used is a square blank, all four sides of which are peeled, and then the four corners are polished to achieve a smooth transition, and the R angle is 25°.

[0020] In step C, a walking beam reheating furnace is used for heating, and the entire heating time is 2 h - 3.5 h.

[0021] The slow cooling adopts slow cooling with a heat preservation cover, and the temperature when leaving the heat preservation cover is controlled at ≤ 550 °C.

[0022] The production method for reducing the decarburized layer of cold-drawn bars made of low-carbon alloy carburizing steel can control the decarburized layer of the cold-drawn bars made of low-carbon carburizing steel to be ≤0.05 mm by adopting blank finishing treatment, blank spraying treatment, blank heating treatment, coil rolling treatment, coil annealing treatment, coil cold drawing treatment, soft annealing treatment of cold-drawn bars, etc., and the structure is controlled to be spheroidized structure, with relatively uniform properties, meeting the quality requirements of high-end users. Specific embodiments

[0023] The production method for reducing the decarburized layer of cold-drawn bars made of low-carbon alloy carburizing steel, wherein the cold-drawn bars made of low-carbon alloy carburizing steel are characterized in that:

[0024] (1) The supply state is in the form of cold-drawn bars.

[0025] (2) Its main performance requirements: the decarburized layer ≤0.05 mm (0.4%D), and the structure is spheroidized structure.

[0026] (3) Surface quality: There are no defects on the surface of the steel.

[0027] The specific production method is as follows:

[0028] A. Blank finishing treatment: Use square blanks to first peel all four sides, and then polish the four corners to achieve smooth transition, with the R angle being about 25 degrees, so as to achieve basically no decarburization of the blanks.

[0029] B. Blank spraying treatment: Automatically and evenly spray a medium-high temperature metal decarburization prevention isolation agent (BTF002-B, purchased externally) around the blanks at the furnace door to prevent decarburization during the heating process. The main substances of this medium-high temperature metal decarburization prevention isolation agent include: water, silicon oxide, potassium oxide, aluminum oxide, magnesium oxide, chromium oxide, calcium oxide, etc., and the proportion of water is 40-60%.

[0030] C. Blank heating treatment: It is designed in sequence as follows: the preheating section ≤800 °C, the heating section I 950-1000 °C, the heating section II 1000 °C - 1100 °C, the soaking section 1050 °C - 1150 °C. The heating furnace adopts a walking beam heating furnace, and the entire heating time is 2h-3.5h.

[0031] D. Coil rolling treatment: It is designed in sequence as follows: the starting rolling temperature is 1000-1050 °C, the final rolling temperature is 760-810 °C, slow cooling with a heat preservation cover, and the temperature out of the heat preservation cover is controlled to be ≤550 °C.

[0032] E. Coil annealing treatment: It is designed in sequence as follows: enter the furnace at 600-700 °C and keep warm for 60-90 min, heat up to 760-790 °C at 50-100 °C / h and keep warm for 6 h, cool with the furnace to 700-720 °C, keep warm for 4 h, and then cool to 660-630 °C and take out of the furnace. N is blown throughout the furnace. 2Protection, dew point ≤ -30°C;

[0033] F. Coiling and cold drawing treatment: The coiled material is directly cold drawn into a straight bar, and the single-pass cold deformation amount is controlled within the range of 20 - 35% to ensure smooth drawing and no drawing or fracture during the drawing process;

[0034] G. Annealing treatment of cold drawn bar: The annealing temperature is controlled at 630 - 680°C, the holding time is 8 - 12 hours, and the furnace is purged with N 2 Protection, dew point ≤ -30°C.

[0035] Example 1

[0036] Full peeling of 160mm square billet → Automatic spraying of billet → Hot rolling into Φ18mm coiled material, preheating section ≤ 800°C, heating section I 960°C, heating section II 1050°C, soaking section 1100°C, heating time 3h → Final rolling temperature 780°C, slow cooling in the holding hood, temperature out of the holding hood 540°C → Coiled material annealing, entering the furnace at 650°C and holding for 60min, heating to 770°C at 50°C / h and holding for 6h, cooling with the furnace to 710°C, holding for 4h, and then cooling to 650°C and discharging from the furnace. The furnace is purged with N2 for protection, dew point ≤ -30°C → Cold drawing and forming treatment of coiled material into Φ16.4mm bar → Softening annealing treatment of Φ16.4mm bar, annealing temperature controlled at 650°C, holding time 8 hours, the furnace is purged with N2 for protection, dew point ≤ -30°C → Eddy current flaw detection inspection is carried out online, and defective products with surface defects > 0.05mm are automatically sorted out to produce qualified products.

[0037] Example 2

[0038] Full peeling of 160mm square billet → Automatic spraying of billet → Hot rolling into Φ19mm coiled material, preheating section ≤ 800°C, heating section I 970°C, heating section II 1060°C, soaking section 1100°C, heating time 3h → Final rolling temperature 770°C, slow cooling in the holding hood, temperature out of the holding hood 520°C → Coiled material annealing, entering the furnace at 650°C and holding for 60min, heating to 770°C at 50°C / h and holding for 6h, cooling with the furnace to 710°C, holding for 4h, and then cooling to 650°C and discharging from the furnace. The furnace is purged with N2 for protection, dew point ≤ -30°C → Cold drawing and forming treatment of coiled material into Φ17.4mm bar → Softening annealing treatment of Φ17.4mm bar, annealing temperature controlled at 650°C, holding time 8 hours, the furnace is purged with N2 for protection, dew point ≤ -30°C → Eddy current flaw detection inspection is carried out online, and defective products with surface defects > 0.05mm are automatically sorted out to produce qualified products.

[0039] Example 3

[0040] 160 mm square billet is fully skinned → the billet is automatically sprayed → hot-rolled into Φ18 mm coil, preheating section ≤800 °C, heating section I 960 °C, heating section II 1070 °C, soaking section 1080 °C, heating time 3 h → final rolling temperature 760 °C, slow cooling with heat preservation cover, temperature out of heat preservation cover 520 °C → coil annealing, furnace temperature 650 °C for heat preservation for 60 min, heating up to 770 °C at 50 °C / h for heat preservation for 6 h, cooling with the furnace to 710 °C, heat preservation for 4 h, then cooling to 650 °C and discharging from the furnace. The furnace is purged with N2 throughout the process, dew point ≤ -30 °C → the coil is cold drawn into Φ16.4 mm bars → Φ16.4 mm bars are softened and annealed, annealing temperature controlled at 650 °C, heat preservation time 8 hours, the furnace is purged with N2 throughout the process, dew point ≤ -30 °C → eddy current flaw detection is carried out online, products with surface defects > 0.05 mm are automatically sorted out, and qualified products are produced.

[0041] Comparative Example 1:

[0042] Compared with Example 1, the difference in Comparative Example 1 is that: the anti-decarburization isolation agent is not coated, and other operations are the same as in Example 1.

[0043] Comparative Example 2:

[0044] Compared with Example 1, the difference in Comparative Example 2 is that: the heating time is 5 h, which is greater than 3.5 h, and other operations are the same as in Example 1.

[0045] Comparative Example 3:

[0046] Compared with Example 1, the difference in Comparative Example 3 is that: the billet is not skinned, and other operations are the same as in Example 1.

[0047] Comparative Example 4:

[0048] Compared with Example 1, the difference in Comparative Example 4 is that: the dew point of coil annealing is -15 °C, and other operations are the same as in Example 1.

[0049] Comparative Example 5:

[0050] Compared with Example 1, the difference in Comparative Example 5 is that: the heat preservation time of cold drawn bar annealing is 14 h, and other operations are the same as in Example 1.

[0051] Properties of the bars after cold drawing:

[0052]

[0053] Those of ordinary skill in the art in this technical field should recognize that the above embodiments are only used to illustrate the present invention, rather than to limit the present invention. As long as within the scope of the substantial spirit of the present invention, changes and modifications to the above-described embodiments will fall within the scope of the claims of the present invention.

Claims

1. The production method for reducing the decarburized layer of the cold-drawn bar of low-carbon alloy carburizing steel according to claim 1, characterized in that: It includes the following steps: A. Finish machining of the blank: Completely peel the surface of the blank and perform grinding to achieve smooth transition; B. Spraying treatment of the blank: Uniformly spray medium- and high-temperature metal decarburization prevention and isolation agent around the blank to prevent decarburization during the heating process; C. Heating treatment of the blank: Sequentially: preheating section ≤800 °C, heating section I 950 - 1000 °C, heating section II 1000 °C - 1100 °C, soaking section 1050 °C - 1150 °C; D. Coiling and rolling treatment: Sequentially: rolling start temperature 1000 - 1050 °C, rolling end temperature 760 - 810 °C, slow cooling; E. Coil annealing treatment, in sequence: heating to the furnace and holding at 600 - 700 °C for 60 - 90 min, heating to 760 - 790 °C at a rate of 50 - 100 °C / h, holding for 6 h, cooling with the furnace to 700 - 720 °C, holding for 4 h, and then cooling to 660 - 630 °C and taking out of the furnace, with N blown throughout the process in the furnace 2 protection, dew point ≤ -30 °C; F. Cold drawing treatment of the coil: Directly cold draw the coil into a straight bar, and the single-pass cold deformation amount control range is between 20 - 35%; G. Soft annealing treatment of cold-drawn bars, the annealing temperature is controlled at 630 - 680 °C, heat preservation for 8 - 12 h, and N is blown throughout the furnace 2 for protection, dew point ≤ -30 °C.

2. The production method according to claim 1, characterized in that: In step A, the blank uses a square blank. All four surfaces of it are peeled, and then the four corners are ground to achieve smooth transition, and the R angle is 25°.

3. The production method according to claim 1, characterized in that: In step C, a walking beam reheating furnace is used for heating, and the entire heating time is 2h - 3.5h.

4. The production method according to claim 1, characterized in that: In step D, the slow cooling uses a heat preservation cover for slow cooling, and the temperature when exiting the heat preservation cover is controlled at ≤550 °C.

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