Hot-rolling anneal-free coil rod production method for 8.8 grade high-strength cold forging steel

Abstract

The invention provides a method which uses hot-finished non-anneal rod to produce 8.8-grade high-strength cold heading steel. The invention still utilizes general ultra-liner rolling device in the process of rolling medium carbon cold heading steel and utilizes general temperature of 950-1050Deg. C in the rough, middle and pre-finished rolling steps. The finished rolling step utilizes heat engine rolling process which is characterized in that the rolled piece is recovered via water cooling and long channel after the pre-finished rolling, and it is fed into finished-rolling machine when the temperature is reduced to the low-temperature area of 730-830Deg. C, and the steel is transformed at dual-phase (ª†+ª‡) region with large transformation valve; the accumulated draft can reach 35-82%; then the rolled piece is quickly water cooled to 800-620Deg. C to be kept temperature for 600-2400 second and natural cooled to room temperature. The invention can reduce the proportion of pearlite via increasing the proportion of ferrite, to spheroidize a part of pearlite and reduce the strength and rigidity and improve the ductility of material, therefore it can realize the purpose of beating bolt without anneal before cold heading.

Description

technical field [0001] The invention belongs to a steel wire rolling method, in particular to an improved hot rolling method for medium-carbon cold heading steel wire. Background technique [0002] Existing bolt fasteners, especially fasteners below M24, are widely formed by cold heading. The use of fasteners is different, and the shape of the bolt head is also different. No matter the simple or complex bolt head, in the process of cold heading, the deformation degree of the bolt head is very large, and the material to be cold heading is required to have good Excellent plastic deformation performance; the carbon equivalent commonly used by fastener enterprises is 0.35% ~ 0.55% high-quality carbon steel or alloy steel wire rod, through spheroidizing annealing, the material is softened, and then changed into cold heading process material after pickling and drawing , and then feed into a multi-station cold heading machine for cold heading and rolling to form bolts, and then un...

AI Technical Summary

Problems solved by technology

The use of fasteners is different, and the shape of the bolt head is also different. No matter the simple or complex bolt head, in the process of cold heading, the deformation degree of the bolt head is very large, and the material to be cold heading is required to have good Excellent plastic deformation performance; the carbon equivalent commonly used by fastener enterprises is 0.35% ~ 0.55% high-quality carbon steel or alloy steel wire rod, through spheroidizing annealing, the material is softened, and then changed into cold heading process material after pickling and drawing , and then feed into a multi-station cold heading machine for cold heading and rolling to form bolts, and then undergo quenching and tempering heat treatment to make 8.8-grade high-strength bolts; the traditional spheroidizing annealing process consumes a lot of energy and causes metal loss , pollute the environment, and increase the chance of surface decarburization of steel wires, affecting the quality and stability of bolts; Chinese invention patent: Patent No. 99115353.7, the spheroidizing annealing process of high-speed and large-deformation hot-rolled cold heading steel carbide; although the traditional spheroidizing The annealing process has been improved to shorten the annealing time, but offline spheroidizing annealing is still required. At present, the domestic demand for medium-carbon steel for grade 8.8 fasteners is 1.2-1.5 million tons, and millions of tons of steel products need to be produced every year. Fastener manufacturing plants perform spheroidizing annealing or annealing heat treatment, which consumes a lot of energy

Images