How to judge the self tempering temperature of induction heat treatment?

It seems that the discussion is getting more and more interesting. I would like to add a few points: 1. The definition of self-tempering.

As the name suggests, self-tempering is to use the waste heat of the parts after quenching to achieve the purpose of tempering. The main problem is whether this tempering can be sufficient. 2. On the application of actual self-tempering.

Some are in order to prevent crackable parts from cracking after quenching, so the liquid temperature (stop spraying temperature) is controlled relatively high, and the high waste heat is used to eliminate large stress in time. Some are in order to save a process, reduce production costs and improve efficiency, which often needs to confirm whether the self-tempering is sufficient. The way to confirm is generally to look at the residual temperature of the workpiece after quenching, and also to look at the metallographic structure.

In order to reduce the tempering process in a furnace for the purpose of process requirements quenching process control is very high, that is, the quenching process deterioration must be small and controlled, some domestic manufacturers and some advanced equipment can fully meet such requirements, but most production sites are unable to meet such requirements. Zhao Gong's second automobile should have some equipment that can meet this requirement, but there are still many that cannot meet this requirement. 3. The application of self-tempering is affected by the advanced and controllable degree of the process equipment system, the actual quenching conditions of its own parts, and the technical level of technical personnel.

In short, there is only one principle, if you can ensure that the waste heat is used to achieve sufficient tempering of the workpiece, self-tempering is very beneficial and promising. At present, the application of induction hardening and self-tempering is mainly concentrated in the production site of large-scale modern equipment for some automobile and motorcycle parts.

It depends on whether you are back in high temperature or low temperature. Then look at the color of the workpiece after tempering.

If it is tempered at low and medium temperatures, it can be judged according to the surface color of the workpiece.

Is it a direct tempering on the machine? If so, it is recommended that you use a thermometer.

Induction heating, quenching, and tempering have temperature requirements, and different tempering processes obtain different tempering structures.

1.Low-temperature tempering structure: Induction heating tempering temperature is 250-400, quenched martensite decomposes into a complex mixed structure composed of fine carbide precipitation and ferrite, this mixed structure maintains the shape of plate lattice martensite, called tempered martensite.

Tempered martensitic has the characteristics of high hardness, high strength and low toughness.

2.Medium temperature tempering: When the tempering temperature of induction heating is 400-600, the ferrite grains begin to grow, and the fine cementite begins to accumulate and grow, and the two still maintain the shape of the lath martensitus.

A hybrid structure consisting of two phases is called tempered tostenite, and tempered tostenite steels show high elastic limits, yield limits, and good toughness.

3.High-temperature tempering structure: the induction heating tempering temperature is 600-750, the carbon content of ferrite increases, reaches the equilibrium composition and begins to change from flake to equiaxed grains, and the flake cementite grows into large grains.

This complex phase structure consisting of equiaxed grained ferrite** policy coarse carburizing is called tempered sostenite. Tempered sotenitic steel shows excellent comprehensive properties, which not only has a certain strength and hardness, but also has good plasticity and toughness.

In short, different tempering processes obtain different tempering structures, and different tempering structures have different characteristics. Low-temperature tempered structure is suitable for high-carbon tool steels; Medium-temperature tempered structure is suitable for spring steel; The high-temperature tempered structure is suitable for carbon structural steel.

A type of tempering brittleness appears at 200 350 degrees and is irreversible.

Type II tempered brittleness appears at 400 650 degrees.

Heat treatment refers to a metal thermal processing process in which materials are heated, kept warm and cooled by means of heating, heat preservation and cooling to obtain the expected structure and properties.

1.Normalizing: Heating the steel or steel parts to an appropriate temperature above the critical point AC3 or ACM for a certain period of time and then cooling in the air to obtain the thermal treatment of the pearlite structure.

Annealing: A heat treatment process in which the sub-eutectic steel workpiece is heated to 20-40 degrees above AC3, kept warm for a period of time, and then slowly cooled with the furnace (or buried in sand or lime cooled) to below 500 degrees and cooled in air.

3.Solution heat treatment: The alloy is heated to a constant temperature in the high-temperature single-phase zone, so that the excess phase is fully dissolved into the solid solution, and then quickly cooled to obtain the heat treatment process of supersaturated solid solution.

4.Aging: The phenomenon that the properties of the alloy change with time when it is placed at room temperature or slightly higher than room temperature after solution heat treatment or cold plastic deformation.

5.Solution treatment: fully dissolve various phases in the alloy, strengthen the solid solution and improve toughness and corrosion resistance, eliminate stress and soften, so as to continue processing and molding.

6.Aging treatment: heat and keep warm at the temperature of the precipitated phase of the strengthened phase, so that the precipitated precipitation of the strengthened phase can be hardened and the strength can be improved.

7.Quenching: A heat treatment process in which the austenitization of steel is cooled at an appropriate cooling rate, so that the workpiece undergoes martensite and other unstable microstructure transformation in all or a certain range within the cross-section.

50crva spring steel 880 quenched metallographic structure.

8.Tempering: The quenched workpiece is heated to an appropriate temperature below the critical point AC1 for a certain period of time, and then cooled by a method that meets the requirements to obtain the required structure and properties.

Carbon nitriding of steel: Carbonitriding is the process of infiltrating carbon and nitrogen into the surface layer of steel at the same time. Traditionally, carbonitriding, also known as cyanidation, is widely used in medium-temperature gas carbonitriding and low-temperature gas carbonitriding (i.e., gas soft nitriding).

The main purpose of medium-temperature gas carbonitriding is to improve the hardness, wear resistance and fatigue strength of steel. Low-temperature gas carbonitriding is mainly based on nitriding, and its main purpose is to improve the wear resistance and seizure resistance of steel.

10.Quenching and

tempering): It is generally customary to combine quenching and high temperature tempering heat treatment as quenching and tempering treatment. Quenching and tempering treatment is widely used in a variety of important structural parts, especially those connecting rods, bolts, gears and shafts that work under alternating loads.

After quenching and tempering treatment, the tempered sostenite structure was obtained, and the mechanical properties of the tung compound were better than that of the normalized sostenite structure of the same hardness. Its hardness depends on the high temperature tempering temperature and is related to the tempering stability of the steel and the cross-sectional size of the workpiece, generally between HB200 and 350.

11.Brazing: A heat treatment process in which two workpieces are heated and melted together with brazing metal.

Tempering is generally carried out immediately after quenching, and its purpose is to:

a) Eliminate the residual stress generated during the quenching of the workpiece to prevent deformation and cracking;

b) Adjust the hardness, strength, plasticity and toughness of the workpiece to meet the performance requirements;

c) Stabilize the structure and size to ensure accuracy;

d) Improve and enhance processability. Therefore, tempering is the last important step in the process of obtaining the required performance of the workpiece.

According to the tempering temperature range, tempering can be divided into low temperature tempering, medium temperature tempering and high temperature tempering.

1) Low temperature tempering.

Tempering of workpieces up to 250.

The purpose is to maintain the high hardness and wear resistance of the quenched workpiece, reduce the residual stress of quenching and brittle tempering to obtain tempered martensite.

2) Tempering at medium temperature.

The workpiece is tempered between 250 500.

The aim is to obtain a higher elasticity and yield point with proper toughness.

After tempering, tempered tropes are obtained.

3) High temperature tempering.

Tempering of workpieces above 500.

The purpose is to obtain comprehensive mechanical properties with good strength, plasticity and toughness.

After tempering, tempered sostenite is obtained.

If tempered and cooled, the temperature can be baked after the temperature drops to 200, and the oxide layer can be basically ignored at this time. If there are strict requirements for the surface, it is recommended that the flushing shielding gas should be cooled to room temperature with the furnace.

Assabriking (Viking) is a multi-purpose high-alloy oil-cooled, air-cooled hardened steel. It is characterized by a good match between the high hardness and wear resistance required for heavy duty blanking and the molding process.

It can effectively blank and punch materials with a thickness of 25mm, and can also be used for precision blanking, scissor blades, deep drawing, cold forging, cold extrusion dies with complex structures, pipe forming tools, etc.

Its metallurgical composition is: ,, delivery terms: soft (chemical) annealing to 225hbs; Normal use hardness: 52 58hrc.

Its forging temperature is 1090 900 . When forging, it should be slowly heated to 700, and then quickly heated to the forging temperature zone, and then slowly cooled with the furnace after forging, or slowly cooled in sand or vermiculite.

Softening annealing: heating to 880 for a certain period of time, slowly cooling to 650 with the furnace and then air cooling;

Stabilization (relaxation) treatment: 650 2h slow cooling to 500 air cooling, used for stress relief after rough machining or after a certain period of service;

Quenching: 600 700 preheating, austenitization temperature 980 1050 (common temperature 1010), can be oil cooled, can be blown by strong wind, can also be quenched in a hot bath of 200 550.

Nitriding (soft nitriding): 525 nitriding for 20h, layer deep nitriding for 60h, layer depth up to 1000HV; 570 soft nitriding for 2h, surface hardness 900 1000hv.

The steel is also suitable for flame hardening or high-frequency quenching.