WO2021057218A1 - Continuously cast gcr15 bearing steel wire rod carbide network control method - Google Patents

Abstract

A continuously cast GCr15 bearing steel wire rod carbide network control method. The control method performs design optimization of chemical components of GCr15; before being put into use, a steel billet is evaluated and graded according to a superheating temperature and a macrostructure, feed specifications are clarified according to a billet grading, and special control of a heating process is performed, wherein a high-temperature time period having a furnace temperature ≥1150°C is appropriately extended and a rolling starting temperature is appropriately raised for a downgraded billet, and efforts are made to ease billet segregation under long high-temperature diffusion conditions; a coil air cooling process is improved, a coil in the air cooling process is adjusted according to a specified size, rapid cooling from a laying temperature to 700°C or below is performed, and the coil is kept at approximately 630-700°C for a set period of time before entering a cover again, thereby implementing effective carbide network control.

Description

A kind of continuous casting GCr15 bearing steel wire rod carbide network control method Technical field

The invention relates to a method for controlling the uniformity of wire rod carbides, in particular to a continuous casting GCr15 bearing steel wire rod carbide network control method.

Background technique

High-carbon chromium continuous casting bearing steel wire rod GCr15 is mainly used to make various bearing balls, rollers and rings. It has extremely strict requirements on the uniformity of carbides, especially the presence of network carbides, which will increase the brittleness of steel. Reduce the fatigue life of the bearing. In the production process of bearing steel wire rod, how to reduce the level of network carbide of rolling material has always been the subject of our continuous research.

Bearing steel wire rod carbide network control generally adopts low-temperature final rolling + rapid cooling after rolling, but the problem of cementite precipitation along the grain boundary has not been fundamentally solved, especially on the core of the continuous casting bearing steel wire rod and the segregation zone. The net has always existed.

Summary of the invention

Objective of the invention: In order to overcome the defects of the prior art, the present invention provides a continuous casting GCr15 bearing steel wire rod carbide network control method, which realizes the effective control of the carbide network and meets the requirements of bearing steel users .

Technical Solution: The method of the present invention for continuous casting GCr15 bearing steel wire rod carbide network control method includes:

(1) The content of C, Cr, Mn in the element composition is controlled according to the middle and lower limits of the standard content, and the other elements are controlled according to the standard content;

(2) According to the degree of superheat and low power, the continuous casting billets are divided into class I billets, class II billets and class III billets, and class I billets, class II billets, and class III billets are sequentially downgraded;

(3) According to the rating of the continuous casting billet, determine the size of the material that can be fed, the heating time of the furnace temperature ≥1150℃, and the temperature range of the start-up rolling; Class I billets are used for specifications ≤22mm, Class II billets are used for specifications ≤15mm, and Class III Billets are put into use for sizes ≤7mm; the heating time for high temperature section of Ⅱ and Ⅲ billets is 15 minutes longer than that of class Ⅰ billets, and the opening temperature is 10 degrees higher than that of class Ⅰ billets;

(4) Control the cooling temperature of the coil on the air-cooled line. When the rolling temperature and the spinning temperature are the same, adjust the speed of a section of the roller table, the number of openings of the heat preservation cover, and the number of fans according to the feeding specifications. In order to ensure that the coil is rapidly cooled to below 700°C within 10 seconds from the spinning temperature, and the coil is maintained at 630-700°C for 10-15 seconds before being put into the cover, the coil will return to the highest temperature in the cover. Over 700℃;

(5) Standardize the sampling of finished wire rods: samples are taken from 6 different wire rods for the initial inspection of each rolling number, of which 3 rods are sampled from the head of the spinning, 3 rods are sampled from the tail of the spinning, and only one wire rod is taken from each wire rod. The support sample is used for carbide network inspection.

Wherein, the mass percentage contents of C, Cr, and Mn in the element composition are respectively controlled as C: 0.95-1.01%, Cr: 1.42-1.58%, and Mn: 0.26-0.38%. To optimize the design of the chemical composition of the steel wire rod.

Further, the mass percentage contents of C, Cr, and Mn in the element composition are respectively controlled to be C: 0.97-0.98%, Cr: 1.44-1.45%, and Mn: 0.31-0.33%.

The requirements for evaluation and classification are: the superheat of the type I billet is 15-25℃, low power: center porosity ≤2.0, shrinkage cavity ≤0.5, center segregation ≤2.0; the superheat of the type II billet is 25～35 ℃, low power: center porosity ≤ 2.5, shrinkage cavity ≤ 1.0, center segregation ≤ 2.5; the superheat of the type III billet ≤ 15 ℃ or ≥ 35 ℃, low power: center porosity ≥ 3.0, shrinkage cavity ≤ 1.5, center Segregation is ≥3.0; and any one of the low power of type I billet and type II billet exceeds the upper limit, the rating of the continuous casting billet will be downgraded.

The charging specification of the type I billet is 5.0-22.0mm, the furnace temperature is ≥1150℃, the heating time in the high temperature section is ≥55min, and the rolling temperature is 1110-1140°C; the charging specification of the type II billet is 5.0-15.0mm, and the furnace temperature Heating time for high temperature section ≥1150℃≥70min, start rolling temperature 1120-1150℃; the feeding specification of the type III billet is 5.0-7.0mm, furnace temperature ≥1150℃, heating time for high temperature section≥70min, start rolling temperature 1120-1150 ℃.

When the feeding specification is 15.5-22.0mm, the speed of a section of the roller table is 41-50rpm, the protective cover is turned on 1-12#, the fan is turned on 8-10, and the temperature of the inlet cover is 630-680℃; when the feeding specification is 7.5-15.0 When mm, the speed of the first roller table is 51-60rpm, the protective cover is opened 1-10#, the fans are turned on 5-7, and the temperature of the cover is 640-690℃; when the feeding specification is 5.0-7.0mm, the speed of the first roller table It is 61-70rpm, the protective cover is open 1-8#, the fan is turned on 2-4 sets, and the temperature of the cover is 650-700℃.

The specific sampling inspection standards are as follows:

In the initial inspection, when the carbide network of the 6 samples meets the requirements, it is judged as qualified.

In the initial inspection, if one of the 6 samples is unqualified, 2 wire rods are randomly drawn from the remaining coils of the rolling number; if the unqualified sample is the head, then 2 heads are taken. If the qualified sample is the tail, then take 2 tails; if the two re-inspected samples are both qualified, it is judged as qualified, otherwise it is judged as unqualified.

During the initial inspection, if 2 of the 6 samples are unqualified, 4 wire rods will be randomly drawn from the remaining coils of the rolling number; if the unqualified sample is a head, 2 heads shall be taken for each , If the unqualified sample is the tail, then 2 tails shall be taken for each tube; if the 4 samples in the re-inspection are all qualified, it is judged as qualified, otherwise it is judged as unqualified.

In the initial inspection, if 3 of the 6 samples are unqualified, it will be directly judged as unqualified and no re-sampling will be required.

Beneficial effects: This control method optimizes the design of the chemical composition of GCr15; evaluates and classifies the billet according to the degree of superheat and low power before putting it into use, clarifies the feeding specifications according to the billet classification, and performs special control on the heating process, and the downgrading of the billet is appropriate Extend the furnace temperature ≥1150℃ for the high temperature period, while appropriately increasing the rolling temperature, work hard to alleviate the segregation of the cast slab under the condition of long-term high temperature diffusion; improve the coil air cooling process, and the coil is cooled in the air cooling process according to the specifications. Adjust, from the spinning temperature to quickly cool to below 700℃ within 10 seconds, and the coil will be maintained at 630-700℃ for 10-15 seconds and then put into the cover. The highest temperature of the coil in the cover will not exceed 700. ℃; Realize the effective control of carbide network.

detailed description

A continuous casting GCr15 bearing steel wire rod carbide network control method. The method first designs and optimizes the chemical composition of GCr15, evaluates and classifies billets according to superheat and low power, and performs special control on feeding specifications and heating processes. The coil air-cooling process is improved to realize the effective control of the carbide network. Specific requirements are as follows:

(1) Chemical composition: carbon, chromium, and manganese are controlled by the lower limit of the point composition, and the other components are controlled normally. Among them, the control of carbon, chromium and manganese in terms of mass percentage is carbon 0.98±0.03%, chromium 1.5±0.08%, and manganese 0.32±0.06.

(2) Continuous casting slabs are evaluated and classified according to the principles of Table 1 according to the superheat and low power:

Table 1 Continuous casting billet classification principle

Blank classification	Overheating	Low times (one of which exceeds the upper limit and the rating will be reduced)
Class Ⅰ billet	15-25℃	Center porosity≤2.0, shrinkage cavity≤0.5, center segregation≤2.0
Class Ⅱ billet	25-35℃	Center porosity≤2.5, shrinkage cavity≤1.0, center segregation≤2.5
Class Ⅲ billet	≤15℃ or ≥35℃	Center porosity≥3.0, shrinkage cavity≤1.5, center segregation≥3.0

(3) Continuous casting steel billets are determined according to the rating to determine the size of the material that can be fed, the furnace temperature ≥ 1150 ℃ high temperature section heating time and the opening temperature range. Class I billets can be used in all production specifications, and Class II billets can only be used in specifications ≤ 15mm. Class III billets can only be used in sizes ≤ 7mm. In order to ensure the effective diffusion of segregation of continuous casting billets, the high temperature period of class II billets and class III billets must be extended by 15 minutes, and the rolling temperature should be increased by 10 degrees. See Table 2 for details:

Table 2 Feeding specifications, heating time in high temperature section, and start rolling temperature parameters

Blank classification	Put into use specifications	Furnace temperature ≥1150℃ time	Rolling temperature
Class Ⅰ billet	5.0-22.0mm	≥55min	1110-1140°C
Class Ⅱ billet	5.0-15.0mm	≥70min	1120-1150°C
Class Ⅲ billet	5.0-7.0mm	≥70min	1120-1150°C

(4) Control the cooling temperature of the coil on the air-cooled line. Under the condition that the rolling temperature and the spinning temperature are basically the same, adjust the speed of a section of the roller table, the number of openings of the heat preservation cover, and the number of fans according to the feeding specifications. , To ensure that the coil is rapidly cooled to below 700°C within 10 seconds from the spinning temperature, and the coil is maintained at 630-700°C for 10-15 seconds and then enters the cover. The coil returns to the highest temperature in the cover. Not more than 700℃; specific requirements are shown in Table 3:

Table 3 Control parameters of coils of various feeding specifications on the air-cooled line

Production specifications	Speed of a section of roller table	Cover opening quantity	Number of fans on	Into the cover temperature
15.5-22.0mm	41-50rpm	1-12#	8-10 units	630-680℃
7.5-15.0mm	51-60rpm	1-10#	5-7 sets	640-690℃
5.0-7.0mm	61-70rpm	1-8#	2-4 sets	650-700℃

(5) Sampling specifications for finished wire rods: samples are taken from 6 different wire rods for each rolling number, of which 3 wires are sampled from the head of the spinning wire, 3 wires are sampled from the tail of the spinning wire, and only one sample is taken from each wire rod , 6 samples of carbide network do not exceed GB/T 18254-2016 Appendix A No. 7 rating chart judged as qualified. In the initial inspection, one sample is unqualified, and then two coils are randomly drawn from the remaining coils of the rolling number. If the unqualified sample is the head, two tails are taken, and if the unqualified sample is the tail, two tails are taken, and re-inspection If the two samples are qualified, it will be judged as qualified, otherwise it will be judged as unqualified. In the initial inspection, 2 samples are unqualified, and 4 coils are randomly selected from the remaining coils of the rolling number. If the unqualified sample is the head, two heads are added, and if the unqualified sample is the tail, two tails are added. The 4 re-inspected samples are all qualified and judged as qualified, otherwise they are judged as unqualified. In the initial inspection, 3 samples were unqualified and directly judged as unqualified, and re-samples are not allowed.

Example 1: A furnace number of 19704977 in a factory. Its chemical element composition contains 0.97% carbon, 1.45% chromium, and 0.33% manganese. The remaining components are under normal control. The furnace number has a superheat of 23°C, a center porosity of 1.5, a shrinkage cavity of 0.5, and a center segregation of 1.5. It is rated as Class I billet. The feeding specification is 22.0mm, the furnace temperature is ≥1150℃, the time is 58min, and the rolling temperature is 1110°C. The speed of a section of the roller table is 45rpm, the cover is open 1-12#, the fan is open 10, and the temperature of the cover is 680 degrees. There are a total of 45 steels for this heat number. Samples are taken from the qualified products of the first 3 steels and the last 3 steels. The first 3 steels are taken from the head and the third steels are used for the tail. The carbide network of the 6 samples does not exceed the 7th rating of GB/T 18254-2016 Appendix A Figure, comprehensively judged as qualified.

Example 2: The furnace number 19704272 of a factory has a chemical element composition of 0.98% carbon, 1.44% chromium, and 0.31% manganese, and the remaining components are under normal control. The furnace number has a superheat of 28°C, a center porosity of 2.0, a shrinkage cavity of 0.5, and a center segregation of 2.0. It is rated as a type II billet. The feeding specification is 15.0mm, the furnace temperature is ≥1150℃, the time is 72min, and the rolling temperature is 1120°C. The speed of a section of the roller table is 55rpm, the cover is open 1-10#, the fan is open 7 sets, and the temperature of the cover is 690 degrees. There are a total of 40 steels for this heat. Samples are taken from the first 3 and the last 3 qualified products. The first 3 samples are taken from the first and the third is the last. The carbide network of the 6 samples does not exceed the 7th rating of GB/T 18254-2016 Appendix A Figure, comprehensively judged as qualified.

Example 3: A furnace number of 19704286 in a factory has a chemical element composition of 0.98% carbon, 1.44% chromium, and 0.31% manganese, and the remaining components are under normal control. The furnace number has a superheat of 33°C, a center porosity of 2.5, a shrinkage cavity of 1.5, and a center segregation of 2.5, which is rated as a Class III billet. The feeding specification is 7.0mm, the furnace temperature is ≥1150°C, the time is 75min, and the rolling temperature is 1120°C. The speed of one section of the roller table is 65rpm, the cover is opened 1-8#, the fan is opened 4, and the temperature of the cover is 700 degrees. There are a total of 42 steels for this heat number. Samples are taken from the qualified products of the first 3 steels and the last 3 steels. The first 3 steels are taken from the head and the third steels are used for the tail. The carbide network of the 6 samples does not exceed the 7th rating of GB/T 18254-2016 Appendix A Figure, comprehensively judged as qualified.

In addition, multiple sets of test data are also provided to prove the control effect of the present invention. The situation of each embodiment is shown in Table 4 and Table 5.

Table 4 Ratings of Examples 4-10

Table 5 Parameters of Example 4-10

Examples 4-10 are all sampled and tested according to the sampling specification for finished wire rods of the present invention, among which, the first inspection of Examples 4-9 does not exceed the 7th rating chart of Appendix A of GB/T 18254-2016, and the initial inspection of Example 10 If one is not in conformity, the re-sample is qualified and comprehensively judged as qualified.

Using this control method, the control qualification rate on the production line is 100%.

Claims (10)

1. A continuous casting GCr15 bearing steel wire rod carbide network control method is characterized in that it comprises:

   (1) The content of C, Cr, Mn in the element composition is controlled according to the middle and lower limits of the standard content, and the other elements are controlled according to the standard content;

   (2) According to the degree of superheat and low power, the continuous casting billets are divided into class I billets, class II billets and class III billets, and class I billets, class II billets, and class III billets are sequentially downgraded;

   (3) According to the rating of the continuous casting billet, determine the size of the material that can be fed, the heating time of the furnace temperature ≥1150℃, and the temperature range of the start-up rolling; Class I billets are used for specifications ≤22mm, Class II billets are used for specifications ≤15mm, and Class III Billets are put into use for sizes ≤7mm; the heating time for high temperature section of Ⅱ and Ⅲ billets is 15 minutes longer than that of class Ⅰ billets, and the opening temperature is 10 degrees higher than that of class Ⅰ billets;

   (4) Control the cooling temperature of the coil on the air-cooled line. When the rolling temperature and the spinning temperature are the same, adjust the speed of a section of the roller table, the number of openings of the heat preservation cover, and the number of fans according to the feeding specifications. In order to ensure that the coil is rapidly cooled to below 700°C within 10 seconds from the spinning temperature, and the coil is maintained at 630-700°C for 10-15 seconds, then it will enter the cover. The coil will return to the highest temperature in the cover. Over 700℃;

   (5) Standardize the sampling of finished wire rods: samples are taken from 6 different wire rods for the initial inspection of each rolling number, of which 3 rods are sampled from the spinning head and 3 rods are sampled from the spinning tail. Only 1 wire rod is taken from each wire rod The support sample is used for carbide network inspection.
2. The continuous casting GCr15 bearing steel wire rod carbide network control method according to claim 1, wherein the mass percentage content of C, Cr, Mn in the element composition is controlled to C: 0.95-1.01%, Cr : 1.42-1.58%, Mn: 0.26-0.38%.
3. The continuous casting GCr15 bearing steel wire rod carbide network control method according to claim 2, wherein the mass percentage content of C, Cr, and Mn in the element composition is controlled to C: 0.97-0.98%, Cr : 1.44-1.45%, Mn: 0.31-0.33%.
4. The continuous casting GCr15 bearing steel wire rod carbide network control method according to claim 1, wherein the superheat of the type I billet is 15-25°C, low power: center porosity≤2.0, shrinkage cavity≤ 0.5, center segregation≤2.0; the superheat of the type II billet is 25～35℃, low power: center porosity≤2.5, shrinkage cavity≤1.0, center segregation≤2.5; the superheat of the type III billet≤15℃ Or ≥35℃, low magnification: center porosity ≥3.0, shrinkage cavity ≤1.5, center segregation ≥3.0; and any one of the low magnification of type I billet and type II billet exceeds the upper limit, the rating of the continuous casting billet will be downgraded.
5. The continuous casting GCr15 bearing steel wire rod carbide network control method according to claim 4, characterized in that the charging specification of the type I billet is 5.0-22.0mm, and the furnace temperature is ≥1150℃, and the heating time in the high temperature section is ≥55min , The opening-rolling temperature is 1110-1140°C; the feeding specification of the class II billet is 5.0-15.0mm, the furnace temperature is ≥1150°C, the heating time in the high temperature section is ≥70min, and the opening temperature is 1120-1150°C; the charging of the class III billet The specification is 5.0-7.0mm, the furnace temperature is ≥1150℃, the heating time in the high temperature section is ≥70min, and the rolling temperature is 1120-1150℃.
6. The continuous casting GCr15 bearing steel wire rod carbide network control method according to claim 5, characterized in that, when the feeding specification is 15.5-22.0mm, the speed of a section of the roller table is 41-50rpm, and the protective cover is opened 1-12 #, 8-10 fans are turned on, and the temperature of the cover is 630-680℃; when the feeding specification is 7.5-15.0mm, the speed of a roller table is 51-60rpm, the protective cover is turned on 1-10#, and the fan is turned on 5-7 Stage, the temperature of entering the cover is 640-690℃; when the feeding specification is 5.0-7.0mm, the speed of a roller table is 61-70rpm, the protective cover is turned on 1-8#, the fan is turned on 2-4 sets, and the temperature of the entering cover is 650 -700°C.
7. The carbide network control method of continuous casting GCr15 bearing steel wire rod according to claim 1, characterized in that, in the initial inspection, when the carbide network of 6 samples meets the requirements, it is judged as qualified.
8. The continuous casting GCr15 bearing steel wire rod carbide network control method according to claim 1, characterized in that, during the initial inspection, if one of the 6 samples fails, then the remaining coils from the rolling number Two wire rods are randomly selected from the top; if the unqualified sample is the head, then two heads are taken; if the unqualified sample is the tail, then two tails are taken; if the two re-inspected samples are both qualified, it will be judged as qualified, otherwise Determined as unqualified.
9. The continuous casting GCr15 bearing steel wire rod carbide network control method according to claim 1, characterized in that, during the initial inspection, if 2 of the 6 samples are unqualified, then the remaining coils from the rolling number 4 wire rods are randomly selected from the top; if the unqualified sample is the head, 2 heads shall be taken for each piece; if the unqualified sample is the tail, 2 tails shall be taken for each piece; the 4 reinspected samples are all qualified It is judged as qualified, otherwise it is judged as unqualified.
10. The continuous casting GCr15 bearing steel wire rod carbide network control method according to claim 1, characterized in that, during the initial inspection, if 3 of the 6 samples are unqualified, it is directly judged as unqualified and no longer Resample.