CN114196806A - Spheroidizing annealing process for reducing hardness of 20CrMnTiH steel - Google Patents
Spheroidizing annealing process for reducing hardness of 20CrMnTiH steel Download PDFInfo
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- CN114196806A CN114196806A CN202111444352.2A CN202111444352A CN114196806A CN 114196806 A CN114196806 A CN 114196806A CN 202111444352 A CN202111444352 A CN 202111444352A CN 114196806 A CN114196806 A CN 114196806A
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/32—Soft annealing, e.g. spheroidising
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
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Abstract
The invention belongs to the technical field of metallurgical engineering, and particularly relates to a spheroidizing annealing process for reducing the hardness of 20CrMnTiH steel. The spheroidizing annealing process comprises the following steps: firstly, heating steel to 780-800 ℃, and then preserving heat for 8-10 hours; then keeping the temperature of the steel constant within the temperature range of 700-720 ℃ for 6-8 hours; cooling the steel to 450 ℃ after isothermal treatment; finally, the temperature of the steel is reduced to be below 100 ℃, and the steel is discharged and collected. The process is used for annealing in a roller-hearth non-oxidation annealing furnace, can effectively reduce the hardness of the 20CrMnTiH steel, is continuous in production, and has the characteristics of high production efficiency and low cost, and the steel has good hardness uniformity and less iron scale.
Description
Technical Field
The invention belongs to the technical field of metallurgical engineering, and particularly relates to a spheroidizing annealing process for reducing the hardness of 20CrMnTiH steel.
Background
The 20CrMnTiH steel is gear steel with a wide application range, the process for machining the gear is generally a cold extrusion forming process at present, and the 20CrMnTiH steel is required to have low hardness, if the hardness is high, cold extrusion forming is influenced, and defects such as fracture, crack and the like are easy to occur, so that production is influenced. The cold extrusion forming process requires that the Brinell hardness of the 20CrMnTiH steel is less than or equal to 140HB, and the steel has the characteristics of better hardness uniformity, uniform internal structure and shallow thickness of a decarburized layer on the surface of the steel.
The components of the 20CrMnTiH steel are basically fixed, and annealing becomes an effective means for reducing the hardness of the steel. If the stress relief annealing is adopted, the hardness index of less than or equal to 140HB cannot be met; if the full annealing is adopted, the banded structure of the gear steel is deteriorated, and the use performance of the gear is further influenced; therefore, only spheroidizing annealing can be adopted, and a spheroidized structure which is easy to shape and process is obtained.
The conventional spheroidizing annealing process of the 20CrMnTiH is realized by a pit annealing furnace or a trolley type annealing furnace at present, and the single steel loading is large; the temperature rise and the temperature reduction speed in the annealing process are slow; the steel has uneven temperature and long period; poor uniformity of hardness index. Therefore, a reasonably designed annealing process is needed to effectively reduce the hardness of the 20CrMnTiH steel.
Disclosure of Invention
The invention aims to provide a spheroidizing annealing process for reducing the hardness of 20CrMnTiH steel aiming at the defects, the process carries out annealing in a roller-hearth non-oxidation annealing furnace, can effectively reduce the hardness of the 20CrMnTiH steel, is continuous in production, and has the characteristics of high production efficiency and low cost, and the steel has good hardness uniformity and less iron scale.
The technical scheme of the invention is as follows: a spheroidizing annealing process for reducing the hardness of 20CrMnTiH steel comprises the following steps: firstly, putting steel into a roller-hearth non-oxidation annealing furnace, heating to 780-800 ℃, and then preserving heat for 8-10 hours; then keeping the temperature of the steel constant within the temperature range of 700-720 ℃ for 6-8 hours; cooling the steel to 450 ℃ at a cooling speed of less than 35 ℃/h after isothermal operation; and finally, entering a rapid cooling area of an annealing furnace, cooling the steel to be below 100 ℃ after rapid cooling, discharging and collecting. The spheroidizing annealing process mainly aims at reducing the resistance of cold extrusion deformation of 20CrMnTiH steel and reducing the probability of cold extrusion cracking, and the mechanism is that spheroidized tissues are favorable for sliding during cold extrusion deformation, so that the spheroidizing annealing process is suitable for a cold extrusion process with larger deformation. Because the spherical pearlite and a small amount of spheroidized carbide of the spheroidized structure reduce the sliding resistance, the residual stress after forming is much smaller than that of the flaky pearlite, and the overlarge deformation and cracking caused by subsequent heat treatment can be eliminated. The spheroidizing annealing process of the 20CrMnTiH carries out incomplete austenitizing and heat preservation for a period of time within the temperature range of 780-800 ℃, and converts the pearlite structure of the 20CrMnTiH steel into an incomplete austenitizing structure and an insoluble carbide structure; and then isothermal treatment is carried out for a period of time at 700-720 ℃, and a carbide tissue is taken as a nucleus to form spherical pearlite, so that the hardness of 20CrMnTiH is reduced, and the shaping of the material is improved.
The rapid cooling speed in the rapid cooling area in the spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel is 40-70 ℃/h.
In the spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel, the hardness of the 20CrMnTiH steel is reduced to be below 140HB after spheroidizing annealing.
In the spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel, the steel is kept at the temperature of 780-800 ℃ for 8 hours.
In the spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel, the temperature of the steel is kept constant for 8 hours at the temperature of 700-720 ℃.
The rapid cooling in the spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel adopts air cooling.
20CrMnTiH steel produced by the spheroidizing annealing process.
The invention has the beneficial effects that: the spheroidizing annealing process realizes the continuous annealing heat treatment production of the 20CrMnTiH steel and has the characteristics of high production efficiency, low cost, uniform hardness and less iron scale. Aiming at the characteristics of the 20CrMnTiH steel, the invention innovatively designs reasonable heat preservation temperature, heat preservation time, temperature drop speed and temperature before quick cooling, can effectively reduce the hardness of the 20CrMnTiH steel, meets the requirement that the Brinell hardness of the annealed 20CrMnTiH steel is reduced to be below 140HB, and meets the requirement of a cold extrusion molding process on the 20CrMnTiH steel.
The spheroidization effect is closely related to austenitizing time and isothermal time, so that the spheroidization annealing process designed by the invention controls the incomplete austenitizing time to be 8-10 h and the isothermal time to be 6-8 h, and has high spheroidization rate and low hardness. According to the JB/T5074-2007 standard, the structure of the annealed 20CrMnTiH steel meets the spheroidized body grade of more than or equal to 3.0 grade.
Drawings
FIG. 1 is a photograph of a hardness test of 20CrMnTiH steel, which has been subjected to the spheroidizing annealing process described in example 1.
FIG. 2 is a photograph of a hardness test of 20CrMnTiH steel, which has been subjected to the spheroidizing annealing process described in example 2.
FIG. 3 is a photograph of a hardness test of 20CrMnTiH steel, which has been subjected to the spheroidizing annealing process described in example 3.
FIG. 4 is a photograph of a hardness test of 20CrMnTiH steel, which has been subjected to the spheroidizing annealing process described in example 4.
FIG. 5 is a curve of the 20CrMnTiH annealing process of the present invention.
FIG. 6 is a metallographic structure drawing (500 times) of a steel material subjected to spheroidizing annealing described in example 1.
FIG. 7 is a metallographic structure drawing (500 times) of a steel material subjected to spheroidizing annealing described in example 2.
FIG. 8 is a metallographic structure drawing (500 times) of a steel material subjected to spheroidizing annealing described in example 3.
Detailed Description
The present invention will be described in further detail with reference to examples.
Example 1
The spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel comprises the following steps of: firstly, putting steel into a roller-hearth non-oxidation annealing furnace, heating to 780 ℃, and then preserving heat for 8 hours; then keeping the temperature of the steel constant for 8 hours at 700 ℃; cooling the steel to 450 ℃ at a cooling speed of less than 35 ℃/h after isothermal operation; and finally, entering a rapid cooling area of an annealing furnace, rapidly cooling at a cooling speed of 40-70 ℃/h, reducing the temperature of the steel to be below 100 ℃, discharging and collecting.
And (3) after sampling, using a Brinell hardness tester for hardness test, wherein the diameter of a pressure point is 5.09-5.15 mm, and looking up a table to obtain that the hardness is 134-137 HB.
Example 2
The spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel comprises the following steps of: firstly, putting steel into a roller-hearth non-oxidation annealing furnace, heating to 800 ℃, and then preserving heat for 8 hours; then keeping the temperature of the steel constant for 8 hours at 700 ℃; cooling the steel to 450 ℃ at a cooling speed of less than 35 ℃/h after isothermal operation; and finally, entering a rapid cooling area of an annealing furnace, rapidly cooling at a cooling speed of 40-70 ℃/h, reducing the temperature of the steel to be below 100 ℃, discharging and collecting.
And (3) after sampling, using a Brinell hardness tester for hardness test, wherein the diameter of a pressure point is 5.11-5.23 mm, and looking up a table to obtain the hardness of 129-136 HB.
Example 3
The spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel comprises the following steps of: firstly, putting steel into a roller-hearth non-oxidation annealing furnace, heating to 780 ℃, and then preserving heat for 10 hours; then keeping the temperature of the steel constant for 6 hours at 700 ℃; cooling the steel to 450 ℃ at a cooling speed of less than 35 ℃/h after isothermal operation; and finally, entering a rapid cooling area of an annealing furnace, rapidly cooling at a cooling speed of 40-70 ℃/h, reducing the temperature of the steel to be below 100 ℃, discharging and collecting.
And (3) after sampling, using a Brinell hardness tester for hardness test, wherein the diameter of a pressing point is 5.18-5.20 mm, and looking up a table to obtain the hardness between 131 HB and 132 HB.
Example 4
The spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel comprises the following steps of: firstly, putting steel into a roller-hearth non-oxidation annealing furnace, heating to 780 ℃, and then preserving heat for 8 hours; then the steel is isothermal for 8 hours at 720 ℃; cooling the steel to 450 ℃ at a cooling speed of less than 35 ℃/h after isothermal operation; and finally, entering a rapid cooling area of an annealing furnace, rapidly cooling at a cooling speed of 40-70 ℃/h, reducing the temperature of the steel to be below 100 ℃, discharging and collecting.
And (3) after sampling, using a Brinell hardness tester for hardness test, wherein the diameter of a pressure point is 5.15-5.18 mm, and looking up a table to obtain that the hardness is 132-134 HB.
Claims (7)
1. A spheroidizing annealing process for reducing the hardness of 20CrMnTiH steel is characterized by comprising the following steps: firstly, putting steel into a roller-hearth non-oxidation annealing furnace, heating to 780-800 ℃, and then preserving heat for 8-10 hours; then keeping the temperature of the steel constant within the temperature range of 700-720 ℃ for 6-8 hours; cooling the steel to 450 ℃ at a cooling speed of less than 35 ℃/h after isothermal operation; and finally, entering a rapid cooling area of an annealing furnace, cooling the steel to be below 100 ℃ after rapid cooling, discharging and collecting.
2. The spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel according to claim 1, wherein the rapid cooling speed in the rapid cooling area is 40-70 ℃/h.
3. The spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel according to claim 1, wherein the hardness of the 20CrMnTiH steel is reduced to below 140HB after spheroidizing annealing.
4. The spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel according to claim 1, wherein the steel is subjected to heat preservation for 8 hours at a temperature range of 780-800 ℃.
5. The spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel according to claim 1, wherein the steel material is isothermal for 8 hours at a temperature ranging from 700 ℃ to 720 ℃.
6. The spheroidizing annealing process for reducing the hardness of the 20CrMnTiH steel according to claim 1, wherein the rapid cooling adopts air cooling.
7. 20CrMnTiH steel produced by the spheroidizing annealing process according to any one of claims 1 to 6.
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| CN202111444352.2A CN114196806A (en) | 2021-11-30 | 2021-11-30 | Spheroidizing annealing process for reducing hardness of 20CrMnTiH steel |
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| CN202111444352.2A CN114196806A (en) | 2021-11-30 | 2021-11-30 | Spheroidizing annealing process for reducing hardness of 20CrMnTiH steel |
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102005870A (en) * | 2010-12-16 | 2011-04-06 | 镇江中虎弹簧有限公司 | Rotor manufacture process |
| CN104646975A (en) * | 2015-02-13 | 2015-05-27 | 湖南中联重科车桥有限公司 | Wheel rim speed reducer gear ring and manufacturing method thereof |
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- 2021-11-30 CN CN202111444352.2A patent/CN114196806A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102005870A (en) * | 2010-12-16 | 2011-04-06 | 镇江中虎弹簧有限公司 | Rotor manufacture process |
| CN104646975A (en) * | 2015-02-13 | 2015-05-27 | 湖南中联重科车桥有限公司 | Wheel rim speed reducer gear ring and manufacturing method thereof |
Non-Patent Citations (1)
| Title |
|---|
| 马火金 等: "精锻齿坯在辊底式保护气氛连续炉中的球化退火", 热处理, vol. 25, no. 6, pages 78 - 80 * |
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