CN115679227A - High-strength toughened bolt and heat treatment process thereof - Google Patents
High-strength toughened bolt and heat treatment process thereof Download PDFInfo
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Abstract
The invention discloses a high-strength strengthening and toughening bolt and a heat treatment process thereof, and the process comprises the following steps: s1, pre-induction normalizing of a bolt; s2, placing the bolt in a continuous mesh belt quenching furnace, wherein the quenching temperature is 820-900 ℃, the time in the furnace is 50-60min, and the cooling medium is inorganic aqueous solution; s3, placing the bolt in a continuous mesh belt tempering furnace, wherein the tempering temperature is 500-550 ℃, the time in the furnace is 90-120min, and the cooling medium is water; s4, placing the bolt in a well type tempering furnace, heating to 500-550 ℃ from room temperature, keeping the temperature for 75-105min, and taking air as a cooling medium. After the heat treatment of the invention, the tensile strength of the bolt obtained by the invention can reach 1350MPa and impact absorption power KV at-20 DEG C 2 The performance of the bolt reaches more than 100J, the performance of the bolt is far superior to 10.9 or 12.9 grade in the standard, and no fatigue fracture failure occurs in use.
Description
Technical Field
The invention relates to the technical field of bolts, in particular to a high-strength strengthening and toughening bolt and a heat treatment process thereof.
Background
The high-strength bolt is applied to important connecting fasteners of mining machines and shield machines, the thread specification is M36-M60mm, the tensile strength can reach 1350MPa, and no proper reference standard and technical conditions exist in China at present. The bolt applies axial pre-tightening tensile load in installation, bears transverse shearing alternating load in work or bending load compounded by the transverse shearing alternating load, and is easy to generate fatigue fracture at a thread part or a transition part of the thread and a rod to cause early failure, thereby bringing huge potential safety hazards to underground continuous operation mining machines and shield tunneling machines, having high maintenance cost and seriously influencing the construction progress.
How to improve the high strength of the bolt and simultaneously have the obdurability in the aspects of material alloying and heat treatment process, and overcome the fatigue fracture of the bolt becomes a technical problem to be solved by technical personnel in the field. The patent (202010314474.9) discloses a heat treatment method for a delayed fracture-resistant high-strength bolt, which is a heat treatment process method that the material is 42CrMoA, the temperature is slowly raised through steps, then the temperature is rapidly raised to austenitize, and then the temperature is quenched and reduced twice. The method can effectively refine crystal grains and improve the impact toughness of the bolt, but the technology adopts double-liquid cooling, has strict requirements on cooling speed, is not easy to control and has high production difficulty.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a high-strength strengthening and toughening bolt and a heat treatment process thereof, and aims to solve the problem of early fatigue fracture of the high-strength bolt for the existing mining machine and the shield machine. The invention greatly improves the performance of the high-strength bolt applied to the important connecting fastener driven by the mining machine and the shield machine main through the innovation of material selection and heat treatment process, effectively solves the problems of poor hardenability and deformation cracking of the large-diameter bolt in quenching, and simultaneously ensures that the bolt has high toughness under high strength through a grain refining means.
The technical scheme adopted by the invention for solving the technical problems is as follows: a high-strength strengthening-toughening bolt is made of medium-carbon multi-element alloy structural steel and comprises the following chemical components in percentage by mass: c:0.26 to 0.36%, si:0.17 to 0.37%, mn:0.50 to 0.80%, P: less than or equal to 0.015%, S: less than or equal to 0.015 percent, cr:1.3 to 2.2%, ni:1.3 to 2.2%, mo:0.15 to 0.50%, al: 0.015-0.030%, and the balance of Fe and impurities.
The invention also provides a heat treatment process of the high-strength strengthening and toughening bolt, which comprises the following steps:
step one, pre-induction normalizing of the bolt:
secondly, placing the bolts in a continuous mesh belt quenching furnace, wherein the quenching temperature is 820-900 ℃, the time in the furnace is 50-60min, and the cooling medium is inorganic aqueous solution;
thirdly, placing the bolts in a continuous mesh belt tempering furnace, wherein the tempering temperature is 500-550 ℃, the time in the furnace is 90-120min, and the cooling medium is water;
fourthly, placing the bolt in a well-type tempering furnace, heating the bolt from room temperature to 500-550 ℃, keeping the temperature for 75-105min, and taking air as a cooling medium;
and step five, finishing the heat treatment to obtain a semi-finished product before thread rolling.
Compared with the prior art, the invention has the positive effects that:
the invention pre-normalizes the workpiece, has short induction heating time, effectively refines crystal grains, eliminates stress and simultaneously makes organization preparation for quenching. The workpiece is placed in a continuous mesh belt quenching furnace, the temperature is equalized at 820 ℃, the temperature is quickly raised to 900 ℃, the homogenization of austenite of the material can be promoted, the temperature is lowered to 820 ℃, the growth of austenite grains is effectively avoided, and the quenching stress is reduced.
The invention adopts inorganic aqueous solution, the cooling characteristic at 400-600 ℃ is close to that of water, the stability of austenite structure is ensured, the cooling characteristic at 300 ℃ is close to that of oil, and the stress in the quenching process is reduced. The quenching process improves the hardenability of the bolt, solves the problem of imperceptibility of the center of the large-diameter workpiece, and avoids the phenomena of deformation and cracking.
The invention adopts secondary tempering, is beneficial to Mo and other elements in the matrix to form MC type carbide, and is dispersed and precipitated in large quantity and uniformly distributed in the matrix, thereby preventing the strength of the material from being further reduced and simultaneously improving the impact toughness of the material.
At present, the high-strength bolt applied to mining machines and shield machines in China has no clear reference standard and technical conditions, and the tensile strength of the bolt obtained by the invention can reach 1350MPa and the impact absorption power KV at the temperature of-20 ℃ after the heat treatment by referring to the contents of the fastener mechanical property standard GB/T3098.1 2 The performance of the bolt is far superior to 10.9 or 12.9 grade in the standard, and no fatigue fracture failure occurs in use.
Detailed Description
The bolt material is medium-carbon multi-element alloy structural steel, and comprises the following chemical components in percentage by mass: c:0.26 to 0.36%, si:0.17 to 0.37%, mn:0.50 to 0.80%, P: less than or equal to 0.015%, S: less than or equal to 0.015 percent, cr:1.3 to 2.2%, ni:1.3 to 2.2%, mo:0.15 to 0.50%, al:0.015 to 0.030 percent, and the balance of Fe and inevitable impurities. Further, when the tensile strength of the bolt is more than or equal to 1300MPa, the content of each element C:0.26 to 0.31%, cr:1.8 to 2.2%, ni:1.8 to 2.2%, mo:0.30 to 0.50 percent; when the tensile strength of the bolt is 1150-1300 MPa, the content of each element C:0.31 to 0.36%, cr:1.3 to 1.8%, ni:1.3 to 1.8%, mo:0.15 to 0.30 percent. Compared with the common high-strength bolt made of 42CrMoA or 40CrNiMo, the high-strength bolt disclosed by the invention has the advantages that the content of C element is reduced on the material selection, the multi-element alloying of Cr, ni, mo and AL elements is added, the dislocation strengthening effect is improved by refining crystal grains, the tempering temperature is increased as far as possible under the condition of ensuring high strength, and the strengthening and toughening are realized.
The heat treatment process comprises the following steps:
s1, pre-induction normalizing of bolts:
the bolt is heated by ultrasonic frequency induction, and is cooled by air after the temperature of the bolt reaches 1050 ℃;
s2, placing the bolt in a continuous mesh belt quenching furnace, wherein the quenching temperature is 820-900 ℃, the time in the furnace is 50-60min, and the cooling medium is an inorganic aqueous solution, wherein:
(1) The set temperature of the continuous mesh belt quenching furnace 1-6 is 820-820-860-900-820 ℃ respectively.
(2) The baume degree of the inorganic aqueous solution is 10-13 ℃, and the temperature is controlled at 20-40 ℃;
s3, placing the bolt in a continuous mesh belt tempering furnace, wherein the tempering temperature is 500-550 ℃, the time in the furnace is 90-120min, and the cooling medium is water, wherein: setting temperatures of 1-6 areas of the continuous mesh belt tempering furnace are the same;
s4, placing the bolt in a well type tempering furnace, heating to 500-550 ℃ from room temperature, keeping the temperature for 75-105min, and taking air as a cooling medium; wherein: the bolt is vertically placed in a well type tempering furnace after being straightened and machined, and is protected by methanol atmosphere.
And S5, finishing the heat treatment to obtain a semi-finished product before thread rolling.
In order to make the technical solutions and advantages of the present application clearer, the present invention is further explained below with reference to specific embodiments.
Example one
A high-strength bolt for a mining machine comprises the following chemical components: 0.31%, si:0.28%, mn:0.57%, P:0.011%, S:0.007%, cr:2.06%, ni:2.15%, mo:0.36%, al:0.021 percent. The heat treatment process comprises the following steps:
s1, pre-induction normalizing of the bolt.
Specifically, the workpiece is heated by ultrasonic frequency induction, and is cooled by air after the temperature reaches 1050 ℃.
S2, placing the workpiece in a continuous mesh belt quenching furnace for quenching treatment.
Specifically, the temperature of the 1-6 area of the continuous mesh belt quenching furnace is set to be 820-820-860-900-820-820 ℃, the furnace is charged at room temperature, and the time in the furnace is 50min; the cooling medium is inorganic aqueous solution with Baume degree of 11.5 deg.C, and the temperature is controlled at 20-40 deg.C.
S3, placing the workpiece in a continuous mesh belt tempering furnace for tempering treatment.
Specifically, the temperature is set to be 500 ℃ in a 1-6 area of a continuous mesh belt tempering furnace, and the time in the furnace is 90min; the cooling medium is water, and the water temperature is controlled at 20-50 ℃.
And S4, placing the workpiece in a well type tempering furnace for secondary tempering treatment.
Specifically, the workpiece is vertically placed in a well type tempering furnace after being straightened and machined, the temperature is raised to 500 ℃ from room temperature, and the heat preservation time is 75min; discharging and air cooling; preferably, the secondary tempering is protected by a methanol atmosphere.
And S5, finishing the heat treatment to obtain a semi-finished product before thread rolling.
The bolt after the heat treatment has the tensile strength of 1350MPa, the elongation of 15 percent, the reduction of area of 57 percent and the impact absorption power KV at the temperature of minus 20 DEG C 2 The bolt strength reaches 85J, the strength grade of the bolt is far superior to 12.9 grades in GB/T3098.1, and no fatigue fracture failure occurs in use.
Example two
A high-strength bolt for a shield machine comprises the following chemical components of 0.33% of C, si:0.33%, mn:0.66%, P:0.012%, S:0.009%, cr:1.47%, ni:1.45%, mo:0.18%, al:0.020%. The heat treatment process comprises the following steps:
s1, pre-induction normalizing of the bolt.
The specific workpiece is heated by ultrasonic frequency induction, and is cooled by air after the temperature reaches 1050 ℃.
S2, placing the workpiece in a continuous mesh belt quenching furnace for quenching treatment.
Specifically, the set temperature of the 1-6 areas of the continuous mesh belt quenching furnace is 820-820-860-900-820-820 ℃, the furnace is charged at room temperature, and the time in the furnace is 60min; the cooling medium is inorganic aqueous solution with Baume degree of 10.5 deg.C, and the temperature is controlled at 20-40 deg.C.
S3, placing the workpiece in a continuous mesh belt tempering furnace for tempering treatment.
Specifically, the temperature of a 1-6 area of a continuous mesh belt tempering furnace is set to be 550 ℃, and the time in the furnace is 120min; the cooling medium is water, and the water temperature is controlled at 20-50 ℃;
and S4, placing the workpiece in a well type tempering furnace for secondary tempering treatment.
Specifically, the workpiece is vertically placed in a well type tempering furnace after being straightened and machined, the temperature is raised to 550 ℃ from room temperature, and the heat preservation time is 105min; discharging and air cooling; preferably, the secondary tempering is protected by a methanol atmosphere.
And S5, finishing the heat treatment to obtain a semi-finished product before thread rolling.
The bolt after the heat treatment has the tensile strength of 1198MPa, the elongation of 17 percent, the reduction of area of 60 percent and the impact absorption power KV of-20 DEG C 2 The bolt strength grade is far superior to 10.9 grade in GB/T3098.1, and no fatigue fracture failure occurs in use.
Claims (10)
1. A high-strength strengthening and toughening bolt is characterized in that: the material is medium-carbon multi-component alloy structural steel, and comprises the following chemical components in percentage by mass: c:0.26 to 0.36%, si:0.17 to 0.37%, mn:0.50 to 0.80%, P: less than or equal to 0.015 percent, S: less than or equal to 0.015 percent, cr:1.3 to 2.2%, ni:1.3 to 2.2%, mo:0.15 to 0.50%, al:0.015 to 0.030 percent, and the balance of Fe and impurities.
2. The high-strength toughened bolt as claimed in claim 1, wherein: when the tensile strength of the bolt is more than or equal to 1300MPa, the contents of all elements are as follows: c:0.26 to 0.31%, cr:1.8 to 2.2%, ni:1.8 to 2.2%, mo:0.30 to 0.50 percent.
3. The high strength, tough bolt according to claim 1, wherein: when the tensile strength of the bolt is 1150-1300 MPa, the contents of the elements are as follows: c:0.31 to 0.36%, cr:1.3 to 1.8%, ni:1.3 to 1.8%, mo:0.15 to 0.30 percent.
4. A heat treatment process of a high-strength strengthening and toughening bolt is characterized in that: the method comprises the following steps:
step one, pre-induction normalizing of a bolt:
secondly, placing the bolt in a continuous mesh belt quenching furnace, wherein the quenching temperature is 820-900 ℃, the time in the furnace is 50-60min, and the cooling medium is an inorganic aqueous solution;
thirdly, placing the bolt in a continuous mesh belt tempering furnace, wherein the tempering temperature is 500-550 ℃, the time in the furnace is 90-120min, and the cooling medium is water;
fourthly, placing the bolt in a well-type tempering furnace, heating the bolt from room temperature to 500-550 ℃, keeping the temperature for 75-105min, and taking air as a cooling medium;
and step five, finishing the heat treatment to obtain a semi-finished product before thread rolling.
5. The heat treatment process for the high-strength toughened bolt according to claim 4, wherein: the method for pre-induction normalizing comprises the following steps: and (3) performing ultrasonic frequency induction heating on the bolt to enable the temperature of the bolt to reach 1050 ℃, and then performing air cooling.
6. The heat treatment process of the high-strength toughened bolt according to claim 4, wherein: setting the temperatures of the areas 1 to 6 of the continuous mesh belt quenching furnace in the step two as follows: 820 deg.C, 860 deg.C, 900 deg.C, 820 deg.C.
7. The heat treatment process of the high-strength toughened bolt according to claim 4, wherein: in the second step, the Baume degree of the inorganic aqueous solution is 10-13 ℃, and the temperature is controlled to be 20-40 ℃.
8. The heat treatment process of the high-strength toughened bolt according to claim 4, wherein: and step three, setting the same temperature in the areas 1-6 of the continuous mesh belt tempering furnace.
9. The heat treatment process of the high-strength toughened bolt according to claim 4, wherein: and in the fourth step, the bolt is straightened and machined and then vertically placed in a well type tempering furnace.
10. The heat treatment process of the high-strength toughened bolt according to claim 4, wherein: and step four, adopting a methanol atmosphere for protection in the well type tempering furnace.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN202211377421.7A CN115679227A (en) | 2022-11-04 | 2022-11-04 | High-strength toughened bolt and heat treatment process thereof |
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| CN202211377421.7A CN115679227A (en) | 2022-11-04 | 2022-11-04 | High-strength toughened bolt and heat treatment process thereof |
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| CN115679227A true CN115679227A (en) | 2023-02-03 |
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| CN114941104A (en) * | 2022-05-09 | 2022-08-26 | 河南中原特钢装备制造有限公司 | Ultrahigh-strength 30CrNi2MoV forging drilling tool material and heat treatment process |
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2022
- 2022-11-04 CN CN202211377421.7A patent/CN115679227A/en active Pending
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| CN114941104A (en) * | 2022-05-09 | 2022-08-26 | 河南中原特钢装备制造有限公司 | Ultrahigh-strength 30CrNi2MoV forging drilling tool material and heat treatment process |
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