CN103962385B - A kind of rolling mill practice of refinement SCM435 steel austenite crystal - Google Patents

Abstract

The invention belongs to metallurgical technology field, in particular to a kind of rolling mill practice of refinement SCM435 steel austenite crystal, carry out according to following steps: the steel billet after continuous casting is carried out cogging, rolling, weave silk, on roller-way cooling line, be incubated about 400 ~ 450 DEG C collection volumes subsequently always, obtain SCM435 steel stocking.The present invention is controlled by cogging and the control of rolling heating-up temperature and time, steel rolling temperature and roller repairing controls, and improves stocking autstenitic grain size, crystal grain thinning, avoids the growth of abnormal grain, meanwhile, make austenite grain size more even.Refinement of the present invention SCM435 steel austenite crystal, makes it roll rear autstenitic grain size and to reach or close to 11.5 μm, autstenitic grain size controls >=9.5 grades.

Description

A kind of rolling mill practice of refinement SCM435 steel austenite crystal

Technical field

The present invention relates to a kind of steel rolling process, particularly a kind of rolling mill practice of refinement SCM435 steel austenite crystal, belongs to metallurgical technology field.

Background technology

12.9 grades of high-end engine bolt steels such as domestic passenger car, high-end commercial car, aircraft, steamer, train rely on external import always, and the high-level bolting steel of this key position is mainly based on cold-forging steels such as SCM435, SCM440.In car running process, engine cylinder cover and connecting-rod bolts are subject to the effect of high-frequency alternating load, and therefore this steel requires very harsh to its internal performance, and belonging to the part that in automotive safety part, class is the highest, is the Typical Representative of high-end cold-heading product.

Because the performance of austenite grain size to steel has tremendous influence, the refinement of crystal grain not only can improve intensity and plasticity, improve the delayed fracture resistance etc. of steel to a certain extent, and fining austenite grains contributes to improving the even of tissue and degree of refinement, and huge to the martensite size impact after quenching, therefore austenite should be tried one's best refinement and homogenising.And the size of original austenite grains and uniformity coefficient determine primarily of rolling mill practice.

At present about austenite crystal field, study the more display for austenite crystal and detection technique, as CN101368889B patent, disclose a kind of method showing high-strength vessel slab original austenite crystal grain; CN101413786B patent, discloses a kind of method that high temperature laser microscope measures austenite grain size.CN101788419B patent, discloses a kind of method showing X70 and above intensity rank pipe line steel original austenite grains; CN102735704A patent, discloses a kind of method measuring CSP strand austenite grain size; CN101349621 patent, discloses a kind of method of clearly displaying low carbon low alloy steel austenite crystal; CN101187606 patent, discloses a kind of etching pit method showing GCr15 original austenite grains border.

In addition, about fining austenite grains field, disclose the production technology of some steel grades such as heat treatment and X70, as CN101481780B patent, disclose by heat treatment, a kind of ultrahigh-intensity high-toughness easy-to-weld superfine austenite crystal steel and manufacture method thereof; CN103394509A patent, discloses a kind of plate milling method of refinement X70 austenite crystal.

Also there is no the control technology aspect of the rolling mill practice of refinement SCM435 steel austenite crystal there is not disclosed research report at present, and the rolling mill practice of refinement SCM435 steel austenite crystal is the key technology for SCM435 product made from steel Quality advance, therefore studying a kind of rolling mill practice of refinement SCM435 steel austenite crystal, is the current technical issues that need to address.

Summary of the invention

Technical problem to be solved by this invention is to provide a kind of control method of rolling mill practice of refinement SCM435 steel austenite crystal.

The technical scheme that the present invention solves its technical problem is:

A rolling mill practice for refinement SCM435 steel austenite crystal, it is characterized in that, its processing step is:

(1) steel billet after continuous casting is carried out cogging, in cogging process, heating-up temperature is 1080 ~ 1120 DEG C, and the heat time is 3 ~ 4h;

(2) rolling heating-up temperature is 1080 ~ 1100 DEG C, and the heat time is 1.5 ~ 2h;

(3) in the operation of rolling, start rolling temperature is 1050 ~ 1080 DEG C, and finishing temperature is 820 ~ 850 DEG C, and laying temperature is 780 ~ 820 DEG C;

(4) be quickly cooled to 750 ~ 700 DEG C with the cooldown rate of 5 ~ 15 DEG C/s after billet rolling, on roller-way cooling line, slow cooling always, to about 400 ~ 450 DEG C collection volumes, obtains SCM435 steel stocking subsequently.

Select scheme as one of the present invention, the roller table speed of roller-way cooling line controls at 0.4 ~ 0.5m/s.

Wherein, for cogging place, its principle be by improve cogging place heating-up temperature and the heat time makes the element of formation dendritic segregation, residual carbon compound spreads evenly to a certain extent, reach austenite homogenising, avoid the too high or heat time long abnormal growth causing crystal grain of heating-up temperature simultaneously.

Wherein, for the heating and temperature control of rolling process, its principle makes austenite homogenising by heating-up temperature and heat time, avoid that heating-up temperature is too high or the heat time is long simultaneously, cause the abnormal growth of crystal grain, and reserve part remains precipitate, be conducive to the refinement of austenite crystal.

For wire rod rolling place, its principle is the quick cooling by controlling after start rolling temperature, finishing temperature and laying temperature, control austenite grain size and grow up, avoid the appearance of abnormal grain, for guaranteeing the uniformity that lap-joint and non-overlapping place temperature reduce, roller table speed is controlled at 0.4 ~ 0.5m/s.

With the display of austenite crystal compared with detection technique, control device, method and research object are all different; With come compared with fining austenite grains by heat treatment, control device, method and control objectives are also different; The content of simultaneously the present invention research is SCM435 steel, not yet has this steel grade by the patent of thin rolling mill practice fining austenite grains and relevant report.

The present invention has following advantages and effect: (1) is controlled by cogging place temperature and time, reaches austenite homogenising, avoids the abnormal growth of crystal grain simultaneously.(2) by the heating and temperature control of rolling process, avoid the abnormal growth of crystal grain, and reserve part remains precipitate, be conducive to the refinement of austenite crystal.(3) controlled by the temperature and time of the operation of rolling, fining austenite grains as much as possible, avoid the appearance of abnormal grain simultaneously, homogenising austenite crystal; (4) controlling by rolling rear temperature and time, avoiding growing up of austenite crystal, equally effectively avoiding growing up of abnormal grain; (5) to be intended to make as much as possible lap-joint and non-overlapping place temperature to reduce degree relatively uniform in the control of roller table speed.

By above Comprehensive Control, basic refinement, homogenising SCM435 steel original austenite grains, make its austenite grain size reach or close to 11.5 μm, autstenitic grain size controls >=9.5 grades.As shown in Figure 1, Figure 2, Figure 3 shows, Fig. 1 is the austenite crystal before technology is implemented in actual contrast; Fig. 2 is that in heating, rolling, cooling procedure, temperature and time controlled not at that time, and will occur indivedual abnormal super large crystal grain after rolling, in figure, red arrow indication is abnormal grain; Fig. 3 is the austenite crystal after technology is implemented, and can find out the obvious refinement of crystal grain, homogenising.

Accompanying drawing explanation

Fig. 1 is austenite crystal figure after prior art SCM435 steel rolling;

Fig. 2 is for controlling not austenite crystal figure (indivedual abnormal grain) after SCM435 steel rolling at that time;

Fig. 3 is austenite crystal figure after SCM435 steel rolling of the present invention;

Fig. 4 is austenite crystal after rolling in the embodiment of the present invention 1;

Fig. 5 is austenite crystal after rolling in the embodiment of the present invention 2.

Fig. 6 is austenite crystal after rolling in the embodiment of the present invention 3.

Detailed description of the invention

A rolling mill practice for refinement SCM435 steel austenite crystal, its processing step is:

(1) steel billet after continuous casting is carried out cogging, in cogging process, heating-up temperature is 1080 ~ 1120 DEG C, and the heat time is 3 ~ 4h;

(2) rolling heating-up temperature is 1080 ~ 1100 DEG C, and the heat time is 1.5 ~ 2h;

(3) in the operation of rolling, start rolling temperature is 1050 ~ 1080 DEG C, and finishing temperature is 820 ~ 850 DEG C, and laying temperature is 780 ~ 820 DEG C;

(4) be quickly cooled to 750 ~ 700 DEG C with the cooldown rate of 5 ~ 15 DEG C/s after billet rolling, on roller-way cooling line, slow cooling always, to about 400 ~ 450 DEG C collection volumes, obtains SCM435 steel stocking subsequently.

The roller table speed of roller-way cooling line controls at 0.4 ~ 0.5m/s.

Below in conjunction with embodiment, the present invention will be further described.

The metallographic microscope taking metallograph in the embodiment of the present invention is that AxioImager.M2m (Zeiss, Germany company) is just putting full-automatic material microscope (Beijing Pu Ruisaisi Instrument Ltd. agency).

Embodiment 1

Certain steel mill adopts 325mm × 280mm bloom continuous casting-cogging-wire rod rolling technological process to produce high-strength bolt Φ 12mm wire rod, the steel grade trade mark and composition as shown in table 1.

Table 1SCM435 steel grade main chemical compositions mass percent

C	Si	Mn	P	S	Cr	Mo
							0.35	0.2	0.65	0.013	0.007	0.95	0.2

(1) steel billet after continuous casting is carried out cogging, in cogging process, heating-up temperature is 1120 DEG C, and the heat time is 3h;

(2) be rolled by the steel billet after cogging, rolling heating-up temperature is 1080 DEG C, and the heat time is 1.5h;

(3) in the operation of rolling, start rolling temperature is 1050 DEG C, and finishing temperature is 820 DEG C, and laying temperature is 780 DEG C;

(4) be quickly cooled to 750 DEG C with the cooldown rate of 5 DEG C/s after billet rolling, on roller-way cooling line, be incubated about 400 DEG C collection volumes subsequently, roller table speed is 0.4m/s, obtains SCM435 steel stocking always.The roller-way cooling setpoint of this factory Φ 12mm specification is as shown in table 2, and the blower fan place of opening stay-warm case is opened, and blower fan closedown place stay-warm case is closed.

850 DEG C of insulation 1h, quenching post-etching, obtains austenite crystal (as shown in Figure 4), by the detection method of up-to-date GB GBT6394-2002, average grain size is 11.9 μm, and grain size number is 10 grades, contrast known with Fig. 1, Fig. 2, austenite crystal refinement homogenising more.

By above Comprehensive Control, refinement original austenite grains, simultaneously homogenising austenite crystal, avoids the growth of abnormal grain.

Table 2 roller-way cooling setpoint

Specification	1# blower fan	2# blower fan	3# blower fan	After 4# blower fan
					Φ12	100%	100%	Close	Close

Embodiment 2

Certain steel mill adopts 325mm × 280mm bloom continuous casting-cogging-wire rod rolling technological process to produce high-strength bolt Φ 10mm wire rod, the steel grade trade mark and composition as shown in table 1.

(1) steel billet after continuous casting is carried out cogging, in cogging process, heating-up temperature is 1080 DEG C, and the heat time is 4h;

(2) be rolled by the steel billet after cogging, rolling heating-up temperature is 1100 DEG C, and the heat time is 2h;

(3) in the operation of rolling, start rolling temperature is 1080 DEG C, and finishing temperature is 850 DEG C, and laying temperature is 820 DEG C;

(4) be quickly cooled to 700 DEG C with the cooldown rate of 5 DEG C/s after billet rolling, on roller-way cooling line, be incubated about 450 DEG C collection volumes subsequently, roller table speed is 0.5m/s, obtains SCM435 steel stocking always.The roller-way cooling setpoint of this factory Φ 12mm specification is as shown in table 3, and the blower fan place of opening stay-warm case is opened, and blower fan closedown place stay-warm case is closed.

Table 3 roller-way cooling setpoint

Specification	1# blower fan	2# blower fan	3# blower fan	After 4# blower fan
					Φ12	100%	100%	50%	Close

850 DEG C of insulation 1h, quenching post-etching, obtains austenite crystal (as shown in Figure 5), by the detection method of up-to-date GB GBT6394-2002, average grain size is 12.8 μm, and grain size number is 9.5 grades, contrast known with Fig. 1, Fig. 2, austenite crystal refinement homogenising more.By above Comprehensive Control, refinement original austenite grains, simultaneously homogenising austenite crystal, avoids the growth of abnormal grain.

Embodiment 3

Certain steel mill adopts 325mm × 280mm bloom continuous casting-cogging-wire rod rolling technological process to produce high-strength bolt Φ 8mm wire rod, the steel grade trade mark and composition as shown in table 1.

(1) steel billet after continuous casting is carried out cogging, in cogging process, heating-up temperature is 1100 DEG C, and the heat time is 3h;

(2) be rolled by the steel billet after cogging, rolling heating-up temperature is 1080 DEG C, and the heat time is 1.5h;

(3) in the operation of rolling, start rolling temperature is 1080 DEG C, and finishing temperature is 850 DEG C, and laying temperature is 820 DEG C;

(4) be quickly cooled to 700 DEG C with the cooldown rate of 15 DEG C/s after billet rolling, on roller-way cooling line, be incubated about 350 DEG C collection volumes subsequently, roller table speed is 0.4m/s, obtains SCM435 steel stocking always.The roller-way cooling setpoint of this factory Φ 8mm specification is as shown in table 4, and the blower fan place of opening stay-warm case is opened, and blower fan closedown place stay-warm case is closed.

Table 4 roller-way cooling setpoint

Specification	1# blower fan	2# blower fan	3# blower fan	After 4# blower fan
					Φ8	100%	100%	Close	Close

850 DEG C of insulation 1h, quenching post-etching, obtains austenite crystal (as shown in Figure 6), by the detection method of up-to-date GB GBT6394-2002, average grain size is 11.2 μm, and grain size number is 10 grades, contrast known with Fig. 1, Fig. 2, austenite crystal refinement homogenising more in Fig. 6.By above Comprehensive Control, refinement original austenite grains, simultaneously homogenising austenite crystal, avoids the growth of abnormal grain.

Claims (2)

1. a rolling mill practice for refinement SCM435 steel austenite crystal, is characterized in that, its processing step is:

(1) steel billet after continuous casting is carried out cogging, in cogging process, heating-up temperature is 1080 ~ 1120 DEG C, and the heat time is 3 ~ 4h;

(2) rolling heating-up temperature is 1080 ~ 1100 DEG C, and the heat time is 1.5 ~ 2h;

(3) in the operation of rolling, start rolling temperature is 1050 ~ 1080 DEG C, and finishing temperature is 820 ~ 850 DEG C, and laying temperature is 780 ~ 820 DEG C;

(4) be quickly cooled to 750 ~ 700 DEG C with the cooldown rate of 5 ~ 15 DEG C/s after billet rolling, on roller-way cooling line, slow cooling always, to about 400 ~ 450 DEG C collection volumes, obtains SCM435 steel stocking subsequently.

2. the rolling mill practice of refinement SCM435 steel austenite crystal according to claim 1, is characterized in that, the roller table speed of roller-way cooling line controls at 0.4 ~ 0.5m/s.