CN112893490A

CN112893490A - Rolling and cooling method of spring flat steel

Info

Publication number: CN112893490A
Application number: CN202110095196.7A
Authority: CN
Inventors: 王年通; 张强; 王猛; 周益波; 孙志强; 曹锋
Original assignee: Jiangyin Xingcheng Special Steel Works Co Ltd
Current assignee: Jiangyin Xingcheng Special Steel Works Co Ltd
Priority date: 2021-01-25
Filing date: 2021-01-25
Publication date: 2021-06-04
Anticipated expiration: 2041-01-25
Also published as: CN112893490B

Abstract

The invention relates to a rolling and cooling method of a spring flat steel, which comprises the following steps that A, the surface of a steel billet is peeled with a single side of more than or equal to 2 mm; b, heating each section before rolling: the soaking section is 1000-1050 ℃, the heating section II is 980-1030 ℃, the heating section I is 900-; feeding the steel billets in a step-by-step mode in the step-by-step heating furnace, wherein the heating time is reduced by 50% compared with full-load feeding, and the total heating time is less than or equal to 95 min; adjusting the air-coal ratio in the furnace to ensure that the residual oxygen ratio in the furnace is less than or equal to 2 percent; c, measuring a CCT curve of the spring flat steel, carrying out a simulation test on a cooling field to obtain a corresponding cooling speed, and then determining a cooling control parameter: the included angle between the heat-insulating cover of the cooling bed and the horizontal line is 30-40 degrees, when the stepping rhythm of the cooling bed is matched with the tapping rhythm of the heating furnace, the cooling speed of a product on the cooling bed is ensured to be less than or equal to 1.1 ℃/s, the hardness of the product is enabled to be less than or equal to 340HB, and meanwhile, stress cracking is avoided.

Description

Rolling and cooling method of spring flat steel

Technical Field

The invention relates to a method for rolling and cooling spring flat steel.

Background

Along with the development of light weight, high performance and high speed of railways of automobiles, a large growing space is brought to the requirements of high-grade and high-strength spring steel, particularly under the urging of light weight of automobiles, higher requirements are provided for the fatigue life of the high-strength spring flat steel, efficient production needs to be realized by users, the limitation regulation is made on the hardness of the high-strength spring flat steel, and rapid shearing blanking can be realized.

The use characteristics of the high-strength spring flat steel material are combined, and the following difficulties mainly exist in combination with the current production route:

1. the original surface of the blank is decarburized deeply, the surface has defects generated in partial smelting and cooling processes, the defects cannot be eliminated after rolling, meanwhile, the decarburization on the surface is deep, the technical requirements of users are difficult to meet, and during product testing, a fatigue source is formed at the decarburized part with the deep surface to cause fracture and failure;

2. in order to ensure the rapid rolling and the reduction of production energy consumption, full-load steel feeding is carried out in a heating furnace, meanwhile, the heating temperature is set to be high, the oxidizing atmosphere in the furnace is also above 5 percent, the integral heating system has great influence on the structure and surface decarburization of a product, and the guarantee of the fatigue life of the product is not facilitated;

3. after rolling, cooling is matched with the rhythm of the front heating furnace, and for the production of the high-strength spring steel, the speed of the product out of the heat-insulating cover is relatively high, the cooling speed is more than 2 ℃/s, the integral hardness of the material reaches more than 390HB, and meanwhile, through internal ultrasonic flaw detection, 45% of internal crack defects exist, so that the stable and efficient production in batches cannot be met.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a method for rolling and cooling the spring flat steel aiming at the prior art, improve the production process of the existing high-strength spring flat steel, reduce the depth of a decarburized layer of a material, improve the tissue defect and reduce the integral hardness of the material, and thus the high-strength spring flat steel can be produced stably and efficiently in batches.

The inventor of the application makes an improvement in the aspects of the specification of blank quality, the specificity and the accuracy of a heating system, the strict control of a cooling curve after rolling and the like.

The technical scheme adopted by the invention for solving the problems is as follows: a method for rolling and cooling spring flat steel comprises

A, the quality of an original blank is stably ensured, the quality of the blank with steel-making component design and internal quality meeting the requirements of users is subjected to quality regulation, the control stability of each subsequent rolling link is ensured, the essential gauge specification mainly requires that the surface of the blank has no defects such as decarburization and original cracks and slag holes in steel making, the unilateral surface peeling is carried out on the supply of the blank to be larger than or equal to 2mm, in addition, the surface is rechecked before entering a furnace, unqualified blanks are removed, and the quality of the blanks entering the furnace is ensured to be qualified.

B, heating system before billet rolling of the spring flat steel:

(B-1) the heating temperature parameters of each section are as follows: the soaking section is 1000-1050 ℃, the heating section II is 980-1030 ℃, the heating section I is 900-.

(B-2) heating rate: continuous production of billets, and in the step-by-step heating furnace, in order to reduce surface decarburization to the maximum extent, the billets are fed in a manner of one empty step, the heating time is reduced by 50% compared with full-load feeding, and the total heating time is less than or equal to 95 minutes.

(B-3) heating atmosphere: the ratio of the coal gas and the oxygen in the furnace is adjusted to ensure that the residual oxygen ratio in the furnace is less than or equal to 2 percent, and the decarburization tendency of the surface is also reduced.

The above heating system can make the crystal grain of the rolled spring flat steel finer and the decarburization shallower, and ensure the fatigue life of the high-strength spring flat steel.

C, cooling system of the spring flat steel after rolling forming: according to the method, the CCT curve of the spring flat steel is determined, the corresponding cooling speed is obtained through a cooling field simulation test, then a cooling control parameter is determined, the cooling control parameter is the included angle between the heat-preservation cover cap of the cooling bed and the horizontal line, the included angle is 30-40 degrees, when the stepping rhythm of the cooling bed is matched with the tapping rhythm of the heating furnace, the cooling speed of a product on the cooling bed is guaranteed to be less than or equal to 1.1 ℃/s, the hardness of the spring flat steel is further less than or equal to 340HB, and meanwhile, stress cracking cannot be formed inside the spring flat steel at the cooling speed.

Compared with the prior art, the invention has the advantages that: the integral decarburization depth of the spring flat steel obtained by the method is below 0.05mm, the grain size after rolling reaches above 8 grades, and the hardness of the spring flat steel is controlled to be less than or equal to 340HB under the working condition of continuous production.

Drawings

FIG. 1 is a CCT curve of a spring flat steel rolled product designed by the invention, which guides production cooling to control the hardness and internal quality of the product;

FIG. 2 is a view showing decarburization inspection of a product rolled by the present invention, with an overall decarburization depth of about 0.05 mm;

FIG. 3 shows the grain size structure of the rolled product designed and rolled by the present invention.

Detailed Description

The present invention is described in further detail below with reference to examples, which are intended to be illustrative and not to be construed as limiting the invention.

The production process of the flat spring steel of the embodiment relates to: smelting molten steel, continuously casting to obtain a continuous casting billet, slowly cooling the continuous casting billet, peeling the continuous casting billet, heating in a furnace, hot rolling and controlled cooling. The steel type of the spring flat steel is not limited to high-strength spring flat steel such as 52CrMoV4 and FAS 3550. In the embodiment, the temperature of the AC3 of the spring flat steel is 790 ℃, the temperature of the AC1 of the spring flat steel is 743 ℃, the spring flat steel can be used as the typical phase transition temperature of the spring flat steel, and the spring flat steel has wide application reliability and great reference significance.

In order to obtain a shallower decarburized layer and smaller hardness of the high-strength flat spring steel and ensure the quality stability of a produced product, the production process of the flat spring steel is improved as follows.

1. According to test data of a sample at the early stage and inspection of a fracture, decarburization is adopted mainly influencing fatigue life in rolling, the quality condition of an original blank is firstly confirmed aiming at decarburization, the depth of a decarburization layer on the whole surface is found to be about 1mm, meanwhile, a small amount of slag holes and other defects exist on the surface, the blank of the high-strength spring flat steel is determined to be processed, a blank peeler is used for peeling a single side of more than 2mm to ensure zero decarburization and zero defect on the surface, and the blank with high surface quality is provided; secondly, the particularity and the accuracy of a heating system are reformed and controlled, and the heating system of the high-strength spring flat steel is changed into that: the heating temperature parameters of each section are as follows: the soaking section is 1000-1050 ℃, the heating section II is 980-1030 ℃, the heating section I is 900-; heating speed: the method is a stepping heating furnace, and in order to reduce surface decarburization to the maximum extent, steel is fed in a one-by-one vacant-step mode, the heating time is reduced by 50% compared with the conventional mode, and the total heating time is less than or equal to 95 minutes; thirdly, the heating atmosphere is adjusted by the ratio of the coal gas and the oxygen in the furnace, so that the residual oxygen ratio in the furnace is less than or equal to 2 percent, and the decarburization tendency of the surface is also reduced. The above heating system can make the crystal grain of the rolled spring flat steel finer and the decarburization shallower, and ensure the fatigue life of the high-strength spring flat steel.

2. The test after the early-stage sample production finds that the hardness is 390HB, the shearing and blanking can not be carried out, meanwhile, 45% of internal cracking defect exists in the sample through the internal ultrasonic test of a hand, the sample is sawed and sent, the batch stable production is realized for solving the problem, the cooling curve after the rolling is strictly controlled, the corresponding cooling speed is obtained through the field simulation test through the measurement of the CCT curve of the steel type, as shown in the table 1, the sample is solidified into accurate control parameters, the cooling bed is mainly covered to be 30-40 degrees with the horizontal line, the stepping rhythm is matched with the tapping rhythm of a heating furnace, the cooling speed of the product on a cooling bed is ensured to be less than or equal to 1.1 ℃/s, the hardness of the product is ensured to be less than or equal to 340HB, and meanwhile, the stress cracking cannot be formed in the interior below.

TABLE 1

Cooling Rate/. degree.C/s	hardness/HRC	hardness/HB
			0.1	23	243
0.2	23.5	245
			0.5	27.5	267
1	34.5	323
			2	41.5	385
3	49	451
			5	55.5
10	61
			20	61
30	62

In conclusion, the standard of the blank and the technological innovation of heating and cooling are applied to the production technology of the whole flow to ensure all indexes of the rolled product, and the stable and efficient production is realized.

Claims

1. A rolling and cooling method of spring flat steel is characterized in that: comprises that

A, peeling the surface of a billet before rolling, wherein the single edge of the peeled billet surface is more than or equal to 2mm, so that the billet surface has no decarburization and the defects of steel-making original cracks and slag holes;

b, heating system before billet rolling of the spring flat steel:

(B-1) the heating temperature parameters of each section are as follows: the soaking section is 1000-1050 ℃, the heating section II is 980-1030 ℃, the heating section I is 900-;

(B-2) heating rate: continuously producing steel billets, feeding the steel billets in a step-by-step heating furnace in a manner of one empty step by step, reducing the heating time by 50 percent compared with full-load feeding, and ensuring that the total heating time is less than or equal to 95 minutes;

(B-3) heating atmosphere: adjusting the ratio of coal gas and oxygen in the furnace to ensure that the ratio of residual oxygen in the furnace is less than or equal to 2 percent;

c, cooling system of the spring flat steel after rolling forming: according to the method, the CCT curve of the spring flat steel is determined, the corresponding cooling speed is obtained through a cooling field simulation test, then a cooling control parameter is determined, the cooling control parameter is the included angle between the heat-preservation cover cap of the cooling bed and the horizontal line, the included angle is 30-40 degrees, when the stepping rhythm of the cooling bed is matched with the tapping rhythm of the heating furnace, the cooling speed of a product on the cooling bed is guaranteed to be less than or equal to 1.1 ℃/s, the hardness of the spring flat steel is enabled to be less than or equal to 340HB, and meanwhile stress cracking is avoided.

2. The method of claim 1, wherein: and the peeled billet is rechecked before being put into a furnace and heated before being rolled, so that the quality of the billet put into the furnace is qualified.

3. The method of claim 1, wherein: the whole decarburization depth of the spring flat steel obtained by the method is below 0.05 mm.

4. The method of claim 1, wherein: the grain size of the spring flat steel obtained by the method after rolling reaches more than 8 grades.