CN116603857A - Production method for reducing residual stress of alloy steel bar - Google Patents

Abstract

The invention relates to a production method for reducing residual stress of alloy steel bars, belonging to the technical field of steel rolling in the metallurgical industry. The technical proposal is as follows: the control is performed according to the following requirements: (1) heating: tapping temperature is 1240-1260 ℃; (2) cogging mill rolling: the final rolling temperature of the intermediate billet is 1050-1070 ℃; and (3) rolling by a continuous rolling mill unit: the initial rolling temperature of the continuous rolling unit is 980-1020 ℃, the final rolling temperature is more than 950 ℃, and the elongation coefficient is 1.13-1.23; (4) import and export guide of a finished product rolling mill: the hole type guide is adopted, namely the inlet and outlet guide of the finished product rolling mill is provided with a hole type matched with the rolled piece. (5) The rolled material is put into a slow cooling pit at the temperature of 400-600 ℃ for 48-72 h, and the pit outlet temperature is less than 200 ℃. The beneficial effects of the invention are as follows: residual stress after straightening is effectively reduced, and internal tissues of the bar are improved.

Description

A Production Method for Reducing Residual Stress of Alloy Steel Bars

technical field

The invention relates to a production method for reducing the residual stress of alloy steel rods, and belongs to the technical field of steel rolling in the metallurgical industry.

Background technique

The production process of bars: walking heating furnace → billet rolling machine → hydraulic shearing head → continuous rolling mill rolling → metal sawing → cooling bed cooling → off-line pit cooling → finishing (chamfering, straightening Straightening, grinding, flaw detection, etc.) → hand in to the warehouse.

After the bar is straightened, due to the inhomogeneity of deformation on the section surface during the straightening process, there is residual stress after straightening, the core is tensile stress, and the surface is compressive stress. Certain special steel types have stricter requirements for flaw detection. After straightening, there is residual tensile stress in the core of the bar and compressive stress on the surface. The tensile stress in the core will cause the growth of core defects during the aging process. Defects may exceed the standard during inspection. For example: the head bending rate of φ200mm~φ300 alloy steel bars produced by φ600mm continuous casting slabs reaches 18.4%, which cannot meet the delivery conditions and needs to be delivered after straightening. The cost of straightening steel per ton is 83.5 yuan, resulting in bar The production cost increases, and after the bar is slowly cooled, manual chamfering and spread inspection are required. If the bending rate exceeds the standard, it needs to be straightened, which increases the turnover times of the blank and prolongs the delivery cycle.

Contents of the invention

The purpose of the present invention is to provide a production method for reducing the residual stress of alloy steel rods, effectively reduce the residual stress after straightening, improve the internal structure of the rods, and solve the problems existing in the background technology.

Technical scheme of the present invention is:

A production method for reducing the residual stress of alloy steel bars, comprising heating, billet mill rolling, tandem mill rolling, cooling bed cooling, pit cooling and finishing, controlled according to the following requirements:

(1) Heating: the furnace temperature is 1240~1260°C;

(2) Billet rolling: the final rolling temperature of the intermediate billet is 1050~1070°C;

(3) Rolling by continuous rolling mill: the starting rolling temperature of the continuous rolling mill is 980°C~1020°C, the final rolling temperature is >950°C, and the elongation coefficient is 1.13~1.23;

(4) The entrance and exit guides of the finished rolling mill: the pass guides are used, and the pass guides are the entrance and exit guides of the finished rolling mills, which have a pass that matches the rolled piece.

(5) The temperature of the rolled material entering the slow cooling pit is 400~600°C, the slow cooling time is 48h~72h, and the temperature out of the pit is <200°C.

The pass shape of the inlet guide of the finished rolling mill is an ellipse that matches the rolled piece, and the pass shape of the exit guide of the finished rolling mill is circular, and its inner cavity size: bar diameter + 20mm ± 5mm.

When the diameter of the bar is 200~230mm, the length of the exit guide of the finished rolling mill shall not be less than 650mm; when the diameter of the bar is 240~300mm, the length of the exit guide of the finished rolling mill shall not be less than 1000mm.

The heating: the continuous casting slab heating time is 6h~15h;

Rolling by the tandem rolling mill: the elongation coefficient ranges of the last two rolling mills are 1.13~1.2 and 1.13~1.19 respectively.

Before rolling by the billet opening machine, it is necessary to dephosphorize the continuous casting billet with high-pressure water, and the descaling pressure is 250-310 Bar.

The rolling of the blanking machine is 9-11 passes of reciprocating rolling, and the rolling passes of continuous rolling are 4-6 passes.

The beneficial effects of the present invention are:

1) The heating process is optimized, the furnace temperature is increased, and the deformation resistance is reduced;

2) The continuous rolling process is optimized, the elongation coefficient of the finished rolling mill is reduced, and the rolling bending rate can be reduced;

3) Straightening on the cooling bed and slow cooling in the slow cooling pit can effectively reduce the cooling rate, reduce the cross-sectional temperature difference of the bar, and then reduce the thermal stress and structural stress, which can effectively reduce the residual stress;

4) Changing the shape of the guides at the entrance and exit of the finished rolling mill can guide the rolled piece and also play the role of online "hot straightening". After the bar is slowly cooled, it does not need to be straightened, which can reduce the loss of resulting residual stress.

Description of drawings

Figure 1 is the front view of the entrance pass guide of the finished rolling mill;

Fig. 2 is a side view of the entrance pass guide of the finished rolling mill;

Fig. 3 is the front view of the exit pass guide of the finished rolling mill;

Fig. 4 is a top view of the outlet pass guide of the finished rolling mill;

Fig. 5 is a side view of the exit pass guide of the finished rolling mill;

In the figure: L is the length of the exit pass guide of the finished rolling mill.

Implementation

Below in conjunction with accompanying drawing, the present invention will be further described by examples.

Referring to accompanying drawings 1-5, a production method for reducing the residual stress of alloy steel bars, including heating, billet mill rolling, continuous rolling mill rolling, cooling bed cooling, pit cooling and finishing, is controlled according to the following requirements :

(1) Heating: the furnace temperature is 1240~1260°C;

(2) Billet rolling: the final rolling temperature of the intermediate billet is 1050~1070°C;

(3) Rolling by continuous rolling mill: the starting rolling temperature of the continuous rolling mill is 980°C~1020°C, the final rolling temperature is >950°C, and the elongation coefficient is 1.13~1.23;

(4) The entrance and exit guides of the finished rolling mill: the pass guides are used, and the pass guides are the entrance and exit guides of the finished rolling mills, which have a pass that matches the rolled piece.

(5) The temperature of the rolled material entering the slow cooling pit is 400~600°C, the slow cooling time is 48h~72h, and the temperature out of the pit is <200°C.

The pass shape of the inlet guide of the finished rolling mill is an ellipse that matches the rolled piece, and the pass shape of the exit guide of the finished rolling mill is circular, and its inner cavity size: bar diameter + 20mm ± 5mm.

When the diameter of the bar is 200~230mm, the length of the exit guide of the finished rolling mill shall not be less than 650mm; when the diameter of the bar is 240~300mm, the length of the exit guide of the finished rolling mill shall not be less than 1000mm.

The heating: the continuous casting slab heating time is 6h~15h;

Rolling by the tandem rolling mill: the elongation coefficient ranges of the last two rolling mills are 1.13~1.2 and 1.13~1.19 respectively.

Before rolling by the billet opening machine, it is necessary to dephosphorize the continuous casting billet with high-pressure water, and the descaling pressure is 250-310 Bar.

The rolling of the blanking machine is 9-11 passes of reciprocating rolling, and the rolling passes of continuous rolling are 4-6 passes.

Example 1

Taking rolling φ200mm as an example, the steps are as follows:

The first step: continuous casting slab heating

The cold-charged or hot-charged continuous casting slab is heated in a walking heating furnace for a heating time of 6h~15h, and the temperature of the heated continuous casting slab is 1240~1260℃;

Step 2: After high-pressure water descaling, the descaling pressure is 250~310Bar, and the oxide scale on the surface is removed.

The third step: billet rolling

The surface temperature of the continuous casting slab after high-pressure water dephosphorization is 1150~1170°C, after 11 passes of reciprocating rolling, the final rolling temperature of the intermediate billet is 1050~1070°C, conveyed by roller table, hydraulic shearing head, and then Delivered to the continuous rolling mill for rolling. The rolling schedule of the blanking machine is as follows:

Step 4: Continuous rolling mill

The starting rolling temperature of the continuous rolling unit is 980°C~1020°C, the final rolling temperature is >950°C, the continuous rolling pass is 6 passes, and the elongation coefficient is 1.13~1.23, of which the elongation coefficient of K1 hole is 1.18, and the elongation coefficient of K2 hole 1.176;

The optimized entrance and exit pass guides are used. The entrance and exit guides of the finished rolling mill are all pass guides. The entrance guides play a better guiding role and reduce the impact of the rolled piece on the guide wheel. The exit holes Type guides can play the role of "hot straightening" to increase the straightness of the bar. The wear-resistant iron of the import pass guide is shown in Figure 1 and 2, and the export pass guide is shown in Figure 3, 4 and 5. The diameter of the inner cavity of the pass is 220mm, and the length of the guide is 650mm.

the fifth step:

The sawn bar is cooled and straightened on the cooling bed with straightening function, the temperature of the rolled material entering the slow cooling pit is 400~600°C, the slow cooling time is 48h, and the temperature out of the pit is <200°C.

Step 6: After leaving the pit, manual spread inspection, chamfering, and bending degree measurement, etc., if the bending exceeds the standard, perform pressure straightening or multi-roller straightening. The bending rate of the head made by rolling is reduced from 11.1% to 2.6%, and most bars no longer need to be straightened, which can effectively reduce the residual stress caused by the uneven deformation during the straightening process, and reduce the straightening cost .

Example 2

Taking rolling φ300mm as an example, the steps are as follows:

The first step: continuous casting slab heating

The cold-charged or hot-charged continuous casting slab is heated in a walking heating furnace for a heating time of 6h~15h, and the temperature of the heated continuous casting slab is 1240~1260℃;

Step 2: After high-pressure water descaling, the descaling pressure is 250~310Bar, and the oxide scale on the surface is removed;

The third step: billet rolling

The surface temperature of the continuous casting slab after dephosphorization by high-pressure water is 1150~1170°C, after 9 passes of reciprocating rolling, the final rolling temperature of the intermediate billet is 1050~1070°C, conveyed by roller table, hydraulic shearing head, and then Delivered to the continuous rolling mill for rolling. The rolling schedule of the blanking machine is as follows:

Step 4: Continuous rolling mill

The starting rolling temperature of the continuous rolling unit is 980°C~1020°C, the finishing temperature is >950°C, the continuous rolling passes are 4 passes, and the elongation coefficient is 1.13~1.23, of which the elongation coefficient of K1 hole is 1.14, and the elongation coefficient of K2 hole 1.13.

The optimized entrance and exit pass guides are used. The entrance and exit guides of the finished rolling mill are all pass guides. The entrance guides play a better guiding role and reduce the impact of the rolled piece on the guide wheel. The exit holes Type guides can play the role of "hot straightening" to increase the straightness of the bar. The inlet pass guides are shown in Figures 1 and 2, and the exit pass guides are shown in Figures 3, 4 and 5. The diameter of the inner cavity of the pass is 325mm, and the length of the guides is 1049mm.

the fifth step:

The sawn bar is cooled and straightened on the cooling bed with straightening function. The temperature of the rolled material entering the slow cooling pit is 400~600°C, the slow cooling time is 72h, and the temperature out of the pit is <200°C.

Step 6: After leaving the pit, manual spread inspection, chamfering, and bending degree measurement, etc., if the bending exceeds the standard, perform pressure straightening or multi-roller straightening. The bending rate of the head produced by rolling is reduced from 23.4% to 1.8%, and most bars no longer need to be straightened, which can effectively reduce the residual stress caused by the uneven deformation during the straightening process, and reduce the straightening cost .

Claims (7)

1. The production method for reducing the residual stress of the alloy steel bar comprises heating, rolling by a cogging mill, rolling by a continuous rolling unit, cooling by a cooling bed, pit cooling and finishing, and is characterized in that: the control is performed according to the following requirements:

(1) Heating: tapping temperature is 1240-1260 ℃;

(2) Rolling by a cogging mill: the final rolling temperature of the intermediate billet is 1050-1070 ℃;

(3) Rolling by a continuous rolling unit: the initial rolling temperature of the continuous rolling unit is 980-1020 ℃, the final rolling temperature is more than 950 ℃, and the elongation coefficient is 1.13-1.23;

(4) Import and export guide of finished product rolling mill: adopting a hole type guide, wherein the hole type guide is that an inlet guide and an outlet guide of a finished product rolling mill are provided with holes matched with rolled pieces;

(5) The rolled material is put into a slow cooling pit at the temperature of 400-600 ℃ for 48-72 h, and the pit outlet temperature is less than 200 ℃.

2. The production method for reducing residual stress of alloy steel bar according to claim 1, wherein: the hole pattern of the inlet guide of the finished product rolling mill is elliptic matched with the rolled piece, the hole pattern of the outlet guide of the finished product rolling mill is circular, and the size of the inner cavity of the hole pattern is as follows: the diameter of the bar is +20mm+/-5 mm.

3. The production method for reducing residual stress of alloy steel bar according to claim 2, wherein: when the diameter of the bar is 200-230 mm, the length of the outlet guide of the finished product rolling mill is not less than 650mm, and when the diameter of the bar is 240-300 mm, the length of the outlet guide of the finished product rolling mill is not less than 1000mm.

4. The production method for reducing residual stress of alloy steel bar according to claim 1, wherein: the heating: and the heating time of the continuous casting blank is 6-15 h.

5. The production method for reducing residual stress of alloy steel bar according to claim 1, wherein: rolling by the continuous rolling unit: the extension coefficient ranges of the last two rolling mills are 1.13-1.2 and 1.13-1.19 respectively.

6. The production method for reducing residual stress of alloy steel bar according to claim 1, wherein: before the cogging mill rolls, high-pressure water dephosphorization is needed to be carried out on the continuous casting billet, and the descaling pressure is 250-310 Bar.

7. The production method for reducing residual stress of alloy steel bar according to claim 1, wherein: the cogging mill is used for rolling in a reciprocating mode with 9-11 passes, and the continuous rolling passes are 4-6 passes.