Production method of bainite cold forging steel wire rod
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A production method and technology of cold heading steel, applied in the field of steel rolling, can solve problems such as long spheroidization time, uneven cementite distribution, uneven cooling, etc., and achieve the effect of simplifying annealing and shortening annealing time
Active Publication Date: 2018-12-18
HUNAN VALIN XIANGTAN IRON & STEEL CO LTD
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Problems solved by technology
Due to the fast cooling rate and uneven cooling of the conventionally rolled Cr-Mo cold heading steel, polygonal ferrite, pearlite, bainite and martensite appear in the microstructure of the steel at the same time, and the hardness is high. It is suitable for direct drawing, and it is suitable for the production of refined wires by one-ball-one-drawing or two-ball-two-drawing process. However, due to the coarser grains and uneven distribution of cementite, the spheroidizing time is generally longer
The wire rod rolled by low temperature rolling + slow cooling process can avoid the formation of bainite and martensite, and the hardness is low, but because the original structure is ferrite + pearlite, the dissolution of cementite is slow and the nodularization time also longer
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Embodiment 1
[0027] Embodiment 1: Production method of Φ6.5mm SCM435 steel
[0028] The chemical composition of the steel is shown in Table 1. Process steps include:
[0029] (1) The 150mm×150mm continuous casting slab is inspected and ground and heated to 1020-1060°C. After 30 passes of continuous rolling, the wire rod with a diameter of 6.5mm is obtained. The temperature of the incoming wire rod reducing and sizing unit is controlled at 800-1000 830°C range;
[0030] (2) After rolling, the water tank is rapidly cooled to 750-780°C for silk spinning, and it runs at a speed of 0.36-0.73m / s on the loose-coil cooling conveyor line, and passes through ferrite phase transformation at an average cooling speed of 5°C / s. After the interval (675-515°C), it enters the heat preservation cover and cools slowly to about 420°C, and then rolls are collected.
[0031] (3) Put the wire rod into the annealing furnace, heat it to 770°C for 2 hours, cool it to 720°C at a cooling rate of 20°C / h, and then c...
Embodiment 2
[0032] Embodiment 2: the production method of Φ9.0mmSCM435 steel
[0033] The chemical composition of the steel is shown in Table 1. Process steps include:
[0034] (1) The 150mm×150mm continuous casting slab is inspected and ground, heated to 1020-1060°C, and the wire rod with a diameter of 9.0mm is obtained through 28 continuous rolling passes, and the temperature of the incoming wire rod reducing and sizing unit is controlled at 785-1 815°C range;
[0035] (2) After rolling, the water tank is rapidly cooled to 750-770 ℃ for silk spinning, and the coil cooling conveyor line runs at a speed of 0.41-0.85m / s, and the average cooling rate of 5 ℃ / s passes through ferrite phase transformation After the interval (675-515°C), it enters the heat preservation cover and slowly cools down to about 440°C, and then rolls are collected.
[0036] (3) Put the wire rod into the annealing furnace, heat it to 770°C for 2 hours, cool it to 720°C at a cooling rate of 20°C / h, and then cool it t...
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Abstract
The invention discloses a production method of a bainite cold forging steel wire rod. The production method comprises the following production process flows of molten iron pretreatment, converter smelting, CAS (composition adjustments by sealed argon) refining, LF (ladle furnace) refining, continuous casting, casting blank grinding, controlled rolling and controlled cooling, finished product inspection and warehousing. The steel comprises the following chemical components in weight percentage: 0.33 to 0.38 percent of C, 0.15 to 0.35 percent of Si, 0.60 to 0.90 percent of Mn, not greater than 0.030 percent of P, not greater than 0.030 percent of S, 0.90 to 1.20 percent of Cr, not greater than 0.25 percent of Ni, 0.15 to 0.30 percent of Mo and the balance Fe and few impurities. The bainite cold forging steel wire rod produced by the production method disclosed by the invention is a Cr-Mo series alloy cold forging steel wire rod which can be shortened in annealing time, and the Cr-Mo series alloy cold forging steel wire rod mainly includes an SCM435 wire rod. Through thermal simulation and laboratory investigation, the phase change law of Cr-Mo series alloy cold forging steel is mastered; through controlled rolling and controlled cooling, a hot rolled wire rod forms massive bainite, little ferrite and few martensitic structures, so that structural preparation is provided for shortening the annealing time of the wire rod.
Description
technical field [0001] The invention belongs to the technical field of steel rolling, and relates to a production method of bainitic cold-heading wire rod steel which is easy to be annealed. Background technique [0002] Martensite or bainite structure can be tempered at medium temperature to obtain tempered troostite structure, while high temperature tempering can obtain tempered sorbite structure, further increase the tempering temperature to slightly lower than A1, and the ferrite grains will be possible It becomes larger equiaxed grains, fine and dispersed carbides are continuously aggregated and coarsened, and larger granular carbides are obtained, and finally it becomes spherical pearlite structure. [0003] In order to ensure cold heading performance, generally low and medium carbon alloy cold heading steels require the structure before cold heading to be spheroidized. [0004] At present, a large number of 10.9 and 12.9 high-strength fasteners use Cr-Mo series alloy...
Claims
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