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Delayed fracture resisting high-strength bolt thermal treatment method

A technology of high-strength bolts and heat treatment methods, applied in heat treatment furnaces, heat treatment equipment, furnace types, etc., can solve problems such as delayed fracture and fatigue fracture, and achieve the effect of long service life

Inactive Publication Date: 2020-07-17
ANHUI CHANGJIANG FASTENERS
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0002] High-strength bolts are the most widely used fasteners in the machinery industry. At present, 40Cr and 42CrMo are usually used to produce high-strength bolts in China, and their strength can reach 1200MPa. However, due to the high notch sensitivity of high-strength bolts, when the tensile strength exceeds When the pressure is 1200MPa, delayed fracture is prone to occur, and delayed fracture and fatigue fracture are likely to occur at the transition between the rod and the head, resulting in early failure
[0003] How to overcome the above defects so as to improve the mechanical strength of bolts, to solve the problem of early failure when the strength is above 1200MPa, has become a technical problem to be solved urgently by workers in the field

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0023] A heat treatment method for delayed fracture resistant high-strength bolts, comprising the steps of:

[0024] S1. Put the workpiece whose raw material is 42CrMoA alloy steel in the normalizing furnace, raise the temperature from room temperature to 500°C, the heating rate is 4°C / min, and keep it for 1 minute; continue to heat up to 1100°C, the heating rate is 8°C / min, keep it warm 50s;

[0025] S2. Place the workpiece after S1 treatment in quenching furnace a, use oil as the cooling liquid, and quickly cool down to 400°C, and the cooling curve in quenching furnace a is T=0.01t 2 +11t+1100, among them, T is temperature, the unit is ℃; t is time, the unit is min;

[0026] Then keep it warm for 40 minutes, then place it in the quenching furnace b, use water as the cooling liquid, and drop it to 240°C at a rate of 12°C / min;

[0027] S3. Place the workpiece after S2 treatment in a tempering furnace, raise the temperature to 650° C. at a rate of 10° C. / min, keep it warm for...

Embodiment 2

[0029] A heat treatment method for delayed fracture resistant high-strength bolts, comprising the steps of:

[0030] S1. Put the workpiece whose raw material is 42CrMoA alloy steel in the normalizing furnace, raise the temperature from room temperature to 550°C, the heating rate is 2°C / min, and keep it for 5 minutes; continue to heat up to 1000°C, the heating rate is 10°C / min, keep it warm 20s;

[0031] S2. Place the workpiece after S1 treatment in quenching furnace a, use oil as the cooling liquid, and quickly cool down to 450°C. The cooling curve in quenching furnace a is T=0.01t 2 +11t+1000, where T is temperature in °C; t is time in min;

[0032] Then keep it warm for 20 minutes, then place it in the quenching furnace b, use water as the cooling liquid, and drop it to 200°C at a rate of 16°C / min;

[0033] S3. Place the workpiece after S2 treatment in a tempering furnace, raise the temperature to 600° C. at a rate of 15° C. / min, keep it warm for 20 minutes, and air cool t...

Embodiment 3

[0035] A heat treatment method for delayed fracture resistant high-strength bolts, comprising the steps of:

[0036] S1. Put the workpiece made of 42CrMoA alloy steel as the raw material in the normalizing furnace, raise the temperature from room temperature to 520°C, the heating rate is 3.5°C / min, and keep warm for 2 minutes; continue to heat up to 1080°C, the heating rate is 8.5°C / min, keep warm 40s;

[0037] S2. Place the workpiece after S1 treatment in quenching furnace a, use oil as the cooling liquid, and quickly cool down to 410°C, and the cooling curve in quenching furnace a is T=0.01t 2 +11t+1080, where T is temperature in °C; t is time in min;

[0038] Then keep it warm for 35 minutes, then place it in the quenching furnace b, use water as the cooling liquid, and drop it to 230°C at a rate of 13°C / min;

[0039] S3. Place the workpiece after S2 treatment in a tempering furnace, raise the temperature to 630° C. at a rate of 12° C. / min, keep it warm for 12 minutes, an...

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Abstract

The invention discloses a delayed fracture resisting high-strength bolt thermal treatment method which comprises the following steps: 1, placing a workpiece in a normalizing furnace, raising the temperature to 500-550 DEG C from the room temperature, and carrying out thermal insulation for 1-5 minutes; 2, continuing raising the temperature to 1000-1100 DEG C, and carrying out thermal insulation for 20-50 seconds; 3, placing the workpiece treated in the step 1 in a quenching furnace a, rapidly reducing the temperature to 400-450 DEG C, and carrying out thermal insulation for 20-40 minutes; 4, then, placing the workpiece treated in the step 1 in a quenching furnace b, rapidly reducing the temperature to 200-240 DEG C; and 5, placing the workpiece treated in the step 2 in a tempering furnace,raising the temperature to 600-650 DEG C, carrying out thermal insulation for 10-20 minutes, and carrying out air cooling to the room temperature. Through the thermal treatment technology, the tensile strength of the obtain high-strength bolt can reach 1340 N / mm2 or above, the percentage elongation after fracture can reach 18%, the impact absorbing energy AKV 2 at minus 40 DEG C can reach 108 J and the strength grade can meet 10.9 or above.

Description

technical field [0001] The invention relates to the technical field of bolts, in particular to a heat treatment method for delayed-fracture-resistant high-strength bolts. Background technique [0002] High-strength bolts are the most widely used fasteners in the machinery industry. At present, 40Cr and 42CrMo are usually used to produce high-strength bolts in China, and their strength can reach 1200MPa. However, due to the high notch sensitivity of high-strength bolts, when the tensile strength exceeds When the pressure is 1200MPa, delayed fracture is prone to occur, and delayed fracture and fatigue fracture are likely to occur at the transition between the rod and the head, resulting in early failure. [0003] How to overcome the above defects so as to improve the mechanical strength of bolts and solve the problem of early failure when the strength is above 1200MPa has become a technical problem to be solved urgently by workers in the field. Contents of the invention [...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C21D1/28C21D1/18C21D1/60C21D9/00
CPCC21D1/18C21D1/28C21D1/60C21D9/0093
Inventor 汪豪豪曾晖陈元杨照军张楠楠
Owner ANHUI CHANGJIANG FASTENERS