Production method of bainite cold forging steel wire rod

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...

AI Technical Summary

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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