CN103736744B - A kind of hot-rolling method controlling low-carbon steel rod bundle tertiary cementite - Google Patents

Abstract

Control a hot-rolling method for low-carbon steel rod bundle tertiary cementite, belong to technical field of steel rolling.Controlling the hot rolling technology method of tertiary cementite in tissue, for improving the drawing limit of wire rod, reducing wire broken rate.Concrete steps are: after weaving silk, the cooldown rate of 900-750 DEG C of temperature range controls at 1.5-2 DEG C/s; Air-cooled line length slow cooling distance controlling is at 85-100m, and roller-way designs 4 sections of falling, and roller speed adopts 13 sections of designs; The cooldown rate of 570-670 DEG C of temperature range controls at 0.2-0.5 DEG C/s; The cooldown rate of 450-570 DEG C of temperature range controls at 0.8-1 DEG C/s.Advantage is, can realize, to the control of low-carbon steel rod bundle tertiary cementite, both ensureing amount of precipitation, controls to separate out size simultaneously, meets the requirement of wire rod deep drawing, be applicable to the variety development in high line workshop, and the key control point of technique is clear and definite, strong operability.

Description

A kind of hot-rolling method controlling low-carbon steel rod bundle tertiary cementite

Technical field

The invention belongs to technical field of steel rolling, in particular, provide a kind of hot-rolling method controlling low-carbon steel rod bundle tertiary cementite.Controlling the hot rolling technology method of tertiary cementite in tissue, for improving the drawing limit of wire rod, reducing wire broken rate.

Background technology

The kind of wire fabrication and quality, be not only decided by itself production Technology and equipment, and more depend on smelting and the rolling technique of wire rod to a great extent.When product development reaches certain level, the raising of wire quality, will more consider deep shaping property and technique.The deformation extent of different product is different, requires it is have light and heavy degree to distinguish to the machining deformation of wire rod.Generally speaking, finished product distortion is more complicated, and hot candied wire diameter is thinner, requires that wire rod structure property is harsh.

For mild steel, in organizational controls, more concern ferrite grain sizes control all the time, pearlite ratio controls, yield strength controls, and for the carbon of wire rod inside, be exist with solid solution state, or be present in wire rod to separate out state, two aspect influence research of existence are not deep enough.

The first, exist to separate out state form, to be exactly major part be all exists with tertiary cementite form, during when tertiary cementite size is larger and with netted being present in matrix, possibly under large effect of stress, brings out the generation of crackle.

Second, exist with solid solution state form, most carbon is solid-solubilized in ferrite matrix, these solid solution carbon atoms are present in the interstitial site of lattice dot matrix, during drawing, meeting and dislocation produce reciprocation, thus produce KESHI gas mass, cause steel wire to harden, there is dynamic time effect, increase the drawing wire broken rate of steel wire.

So the control of tertiary cementite will take into full account the impact of these two aspects, amount of precipitation and the precipitation morphological research of tertiary cementite seem very important.The scholar of Central South University has found the effect that crystal boundary tertiary cementite worsens material deep shaping property in the research of ftractureing to cold-heading mild steel.The control of tertiary cementite in tissue all paid attention to by Ma Gang and Baosteel in low-carbon (LC) al-killed hot-strip production process.Beijing University of Science & Technology sieve sea culture and education is awarded and is analyzed the precipitation form of ultra-low-carbon steel tertiary cementite and precipitation condition, even if find under Quench condition, tertiary cementite still can be separated out.And oversaturated solid solution C in mover iron ferritic, even the theory still can separated out at ambient temperature.Shoudu Iron and Steel Co researcher has carried out network analysis to material deep shaping property especially in the exploitation of long-term Low Carbon Steel Wire Rod, emphasize that the control of strand N is to reduce drawing sclerosis, a large amount of basic research is carried out to structural transformation process simultaneously, analyze mild steel structural transformation characteristic.But for how by refinement height line production technology, realize the optimization to structure property, the form of conservative control tertiary cementite, rarely has relevant report both at home and abroad.

The present invention is on long-term production practices basis, user's deep-processing process fracture of wire problem is conducted in-depth analysis, find the induction Crack Extension phenomenon of bulky grain tertiary cementite, analyze different size, form tertiary cementite to the impact of draw crack expansion process, Binding experiment chamber base research simultaneously, mild steel tertiary cementite amount of precipitation at different temperatures, precipitation form are analyzed, indicates that tertiary cementite the best separates out interval and process for cooling.

Summary of the invention

The object of the present invention is to provide a kind of hot-rolling method controlling low-carbon steel rod bundle tertiary cementite, with solving in wire rod deep drawing process because bulky grain cementite particle and crystal boundary separate out the drawing fracture of wire problem that cementite causes, technique directiveness is strong, is applicable to trial-production and exploitation that mild steel kind is carried out in high line workshop.

The technical parameter of processing step of the present invention and control is:

(1) after weaving silk, wire rod controls at 1.5-2 DEG C/s in the cooldown rate of 900-750 DEG C of temperature range.

The running status of the setting relation whole piece air-cooled line of process for cooling after weaving silk, laying temperature is too high, and cooldown rate brings impact can to too slowly the control of wire rod scale on surface, and surface there will be bubbling, affects the surface quality of drawn steel wire.After weaving silk, cooldown rate is too fast, and wire rod can be caused to organize too thin, intensity is too high.

(2) air-cooled line length slow cooling distance controlling is at 85-100m, roller-way design 4 sections of falling, and roller speed adopts 13 sections of designs, and each section of roller speed is:

0.12-0.15-0.15-0.15-0.15-0.15-0.15-0.15-0.15-0.15-0.35-0.35-0.35m/s。

Tertiary cementite organizational controls, key is the control how realizing retarded cooling process, relate to soaking zone length and roller-way speed, but ensure under comparatively strict roller-way running status, the uniformity of wire rod cooling, ensure to collect volume state normally, the transmission speed of each section of roller-way must be set and fall the speed of fragment position, simultaneously too low transmission speed, although ensure that slow cooling time and slow cooling temperature, proposes strict requirement to the heat resistance of roller-way.

The roller-way temperature of second section of falling under the different roller-way initial rate of table 1 and temperature retention time, online wire rod weight

(3) 570-670 DEG C of interval cooldown rate controls at 0.2-0.5 DEG C/s

The cooldown rate in tertiary cementite Precipitation Temperature interval controls to be the key that whole retarded cooling process controls, under different temperatures, the precipitation size of tertiary cementite, form and position all there are differences, under high temperature, grain boundary sites is separated out, under low temperature, ferrite intracrystalline is separated out, and different cooling rate is also different to Precipitation Kinetics process influence.

Tertiary cementite under table 2 different temperatures separates out volume and size

(4) cooldown rate of 450-570 DEG C of temperature range controls at 0.8-1 DEG C/s.

The control in cryogenic temperature interval is the precipitation ensureing intracrystalline tertiary cementite on the one hand, reduces wire rod simultaneously and licks the thermal stress formed in journey, further optimizing tissue performance at collection.

Accompanying drawing explanation

Fig. 1 is the drawing micro-crack that tertiary cementite causes.

The tertiary cementite of conventional production process in Fig. 2 mild steel.

Fig. 3 is the mild steel tertiary cementite form after adopting the present invention.

Detailed description of the invention

Embodiment 1

Be applied in the ultra-low-carbon steel M6 wire rod of Shoudu Iron and Steel Co exploitation specification 6.5mm, concrete steps are:

(1) after weaving silk, the cooldown rate of 900-750 DEG C of temperature range controls at 1.5-2 DEG C/s

(2) air-cooled line length slow cooling distance controlling is at 85-100 rice, roller-way design 4 sections of falling, and roller speed adopts 13 sections of designs, and each section of roller speed is:

0.12-0.15-0.15-0.15-0.15-0.15-0.15-0.15-0.15-0.15-0.35-0.35-0.35m/s

(3) 570-670 DEG C of interval cooldown rate controls at 0.3 DEG C/s

(4) cooldown rate of 450-570 DEG C of temperature range controls at 0.9 DEG C/s

Adopt the percentage by volume 0.7% of tertiary cementite amount of precipitation of the present invention, control at about 0.4 grade, the particle size of simultaneously separating out, at 6-10 μm, does not have the drawing fracture of wire phenomenon found because the hard phase constitution of cementite causes in user's use procedure.

Claims (1)

1. control a hot-rolling method for low-carbon steel rod bundle tertiary cementite, it is characterized in that: the technical parameter of processing step and control is:

(1) after weaving silk, the cooldown rate of 900-750 DEG C of temperature range controls at 1.5-2 DEG C/s;

(2) air-cooled line length slow cooling distance controlling is at 85-100m, roller-way design 4 sections of falling, and roller speed adopts 13 sections of designs, and each section of roller speed is: 0.12-0.15-0.15-0.15-0.15-0.15-0.15-0.15-0.15-0.15-0.35-0 .35-0.35m/s;

(3) cooldown rate of 570-670 DEG C of temperature range controls at 0.2-0.5 DEG C/s;

(4) cooldown rate of 450-570 DEG C of temperature range controls at 0.8-1 DEG C/s.