阅读说明：本技术 一种免退火中碳合金冷镦钢的生产方法 (Production method of annealing-free medium carbon alloy cold heading steel ) 是由 陈立 蒋凌枫 肖冬 杨俊� 周国子 罗卫国 杨瑞文 余刚 杨伟 于 2020-03-31 设计创作，主要内容包括：一种免退火中碳合金冷镦钢的生产方法,钢的化学组成质量百分比为C=0.38-0.39,Si=0.12-0.15,Mn=0.62-0.65,Cr=0.92-0.95,P≤0.015,S≤0.010,其余为Fe和不可避免的杂质；包括以下步骤：(1)连铸：对结晶器电磁搅拌和末端电磁搅拌进行调整,并调整连铸二冷比水量,防止局部成分偏析导致材上出现异常组织；(2)精轧：利用减定径机组设备,采用低温轧制,降低终轧温度,进减定径机组温度按800～850℃控制；(3)精确控制成品尺寸,减少拉拔量降低精线硬度；(4)控制冷却：LCC风冷线,采用延迟缓冷模式,吐丝温度750℃～830℃,LCC风冷线辊道速度0.1m/s,LCC风冷线保温罩开前1～3个,其余全关；LCC风冷线冷却风机全关；盘条集卷后在保温区域停留30min。(A production method of annealing-free medium carbon alloy cold heading steel comprises the following steps of (1) continuously casting, namely adjusting electromagnetic stirring of a crystallizer and electromagnetic stirring of the tail end, adjusting the secondary cooling specific water amount of continuous casting, and preventing abnormal structures from appearing on a material due to local component segregation, (2) finely rolling, namely using a reducing sizing mill group for equipment, adopting low-temperature rolling to reduce the finish rolling temperature, controlling the temperature of the reducing sizing mill group at 800-850 ℃, 3) accurately controlling the size of a finished product, reducing the drawing amount, reducing the hardness of a fine line, (4) controlling the cooling, namely L CC air cooling line, adopting a delayed slow cooling mode, enabling the spinning temperature to be 750-830 ℃, L CC line roller speed to be 0.1m/S, L CC line hardness to be reduced, keeping the temperature of a coil for 3 min, keeping the coil warm, keeping the coil for 30min, and keeping the coil temperature of a coil cold collection fan to be 30-3 CC air cooling coils before the annealing.)

1. The production method of the annealing-free medium carbon alloy cold heading steel is characterized by comprising the following steps of: the chemical composition mass percentage of the steel is C =0.38-0.39, Si =0.12-0.15, Mn =0.62-0.65, Cr =0.92-0.95, P is less than or equal to 0.015, S is less than or equal to 0.010, and the balance is Fe and inevitable impurities; the method comprises the following steps:

(1) continuous casting: adjusting electromagnetic stirring of a crystallizer and electromagnetic stirring of the tail end, and adjusting the secondary cooling specific water amount of continuous casting to prevent abnormal structures from appearing on the material due to local component segregation;

(2) finish rolling: reducing the final rolling temperature by using the reducing sizing mill set equipment and adopting low-temperature rolling, and controlling the temperature of the reducing sizing mill set according to 800-850 ℃;

(3) the size of a finished product is accurately controlled, the drawing amount is reduced, and the fine wire hardness is reduced; the out-of-roundness of the finished product is controlled according to C-level precision, and the difference between the nominal diameter of the wire rod and the minimum diameter of the wire rod is not more than 0.15 mm; the size of the finished product is strictly matched with the fine wire specification, and the drawing amount is not more than 0.5 mm;

(4) and (3) controlling cooling, namely L CC air cooling lines, adopting a delayed slow cooling mode, controlling the spinning temperature to be 750-830 ℃, the roller speed of the L CC air cooling line to be 0.1m/s, controlling the rest to be fully closed before 1-3 heat-preserving covers of the L CC air cooling lines are opened, controlling the L CC air cooling line cooling fan to be fully closed, and keeping the wire rod in a heat-preserving area for 30min after the wire rod is collected.

Technical Field

The invention belongs to the technical field of metallurgy, and relates to a method for producing annealing-free medium carbon alloy cold forging steel M L40 Cr.

Background

The medium carbon alloy cold heading steel M L Cr is used for producing fasteners of 10.9 grade, and has wide application and large use amount, the prior fastener industry uses M L Cr to produce fasteners of 10.9 grade, and the spheroidizing annealing treatment is carried out on raw materials, so the spheroidizing annealing treatment has the advantages of large equipment investment, long production period, high production cost, high environmental protection pressure, and the problems of surface decarburization, surface recarburization, poor spheroidizing grade low plasticity and the like easily caused when the spheroidizing annealing process is not controlled properly, thereby causing the quality defect of product cracking in the cold heading forming process.

The hot rolling Rockwell hardness HRB value of the M L40 Cr wire rod used at present is generally about 95, the hardness of the raw material is higher, and the direct drawing and cold heading forming production is difficult to carry out, the key point of the annealing-free M L40 Cr material is to reduce the hardness of the raw material and the work hardening in the cold working process, the hot rolling Rockwell hardness HRB of the raw material can be less than 90 by narrow component control and the way of improving the structure by using advanced equipment to control rolling and cold control, the dimensional precision is improved, and the drawing amount of a user can be reduced and the work hardening is reduced.

With the rapid development of the fastener industry, the annealing-free medium carbon cold forging steel M L40 Cr has wide prospect and huge market potential, and has important significance for the research on the production technology of the annealing-free medium carbon alloy cold forging steel.

Disclosure of Invention

The invention aims to provide a production method of annealing-free medium carbon alloy cold forging steel M L40 Cr, which is used for developing a medium carbon alloy cold forging steel M L40 Cr wire rod capable of producing 10.9-grade fasteners in an annealing-free manner by combining the existing equipment and process technology according to the influence of material chemical components and production process technology on material hardness, metallographic structure, dimensional accuracy and the like.

The technical scheme of the invention is as follows:

the production method of the annealing-free medium carbon alloy cold heading steel comprises the following steps of enabling the chemical composition of the steel to be C =0.38-0.39, Si =0.12-0.15, Mn =0.62-0.65, Cr =0.92-0.95, P is less than or equal to 0.015, S is less than or equal to 0.010, and the balance of Fe and inevitable impurities; the method comprises the following steps:

(1) continuous casting: adjusting electromagnetic stirring of a crystallizer and electromagnetic stirring of the tail end, and adjusting the secondary cooling specific water amount of continuous casting to prevent abnormal structures from appearing on the material due to local component segregation;

(2) finish rolling: reducing the final rolling temperature by using the reducing sizing mill set equipment and adopting low-temperature rolling, and controlling the temperature of the reducing sizing mill set according to 800-850 ℃;

(3) the size of a finished product is accurately controlled, the drawing amount is reduced, and the fine wire hardness is reduced; the out-of-roundness of the finished product is controlled according to C-level precision, and the difference between the nominal diameter of the wire rod and the minimum diameter of the wire rod is not more than 0.15 mm; the size of the finished product is strictly matched with the fine wire specification, and the drawing amount is not more than 0.5 mm;

(4) and (3) controlling cooling, namely L CC air cooling lines, adopting a delayed slow cooling mode, controlling the spinning temperature to be 750-830 ℃, the roller speed of the L CC air cooling line to be 0.1m/s, controlling the rest to be fully closed before 1-3 heat-preserving covers of the L CC air cooling lines are opened, controlling the L CC air cooling line cooling fan to be fully closed, and keeping the wire rod in a heat-preserving area for 30min after the wire rod is collected.

The annealing-free medium carbon alloy cold forging steel with the hot rolling Rockwell hardness of the wire rod less than 90HRB and the metallographic structure of the wire rod of F + P is obtained by the method.

The method has the advantages that steel components are controlled by accurate components, the influence of component fluctuation on material hardness is reduced, a reducing sizing mill set is adopted for low-temperature rolling, an advanced L CC air cooling line is adopted, a delayed slow cooling mode is used for controlled cooling, the hot rolling Rockwell hardness of the wire rod is smaller than 90HRB, the metallographic structure F + P of the wire rod is achieved, the size of a finished product is accurately controlled, the drawing amount is reduced, the fine line hardness is reduced, and a client does not anneal to perform cold heading production after drawing.

Drawings

FIG. 1 is a hot-rolled metallographic structure of a wire rod according to example 1.

FIG. 2 is a hot-rolled metallographic structure of a wire rod in example 2.

FIG. 3 is a hot-rolled metallographic structure of a wire rod according to example 3.

Detailed Description

The main contents of the present invention, such as the composition control, the continuous casting process control, the heating temperature control range, the optimum rolling method, etc., will be further described with reference to the following examples.

The method is produced according to the process flows of converter, refining, continuous casting, 150-square continuous casting billet inspection, heating, coil rolling, coiling, controlled cooling, finishing and the like, wherein the converter is a 90-ton top-blown converter, the refining is an electric arc ladle refining furnace, the continuous casting is a 150-square four-machine four-flow high-speed continuous casting machine, a rough and medium rolling mill and a pre-finishing rolling mill are short-stress-line mills, the finishing mill is a KOCKS three-roll reducing sizing mill set, and a cooling roller table is an L CC air cooling line.