36 Types of Thermomechanical Treatment Process

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The deformation heat treatment process is also known as “thermo-mechanical processing”.

In the machinery manufacturing process, the pressure processing (roll, forging, rolling) and heat treatment process can be effectively combined to play a dual role of both lineal and heat treatment reinforcement to obtain the comprehensive mechanical properties that a single reinforcement method can not achieve.

This composite strengthening process is called thermomechanical treatment.

Thermomechanical Treatment Process

In addition to obtaining excellent mechanical properties, thermomechanical treatment can also eliminate the heat treatment of high-temperature heating again, thus saving a lot of energy, heating equipment and workshop area, reducing the material oxidation decarburization, distortion and other heat treatment defects.

Therefore, the thermomechanical treatment process has both excellent strengthening effect and great economic benefits.

The following 36 examples of thermomechanical treatment methods are listed for reference.

1. 16 cases of hot-forging quenching process

(1) Boring cutter quenching after forging

Boring machine with boring cutter body diameter 4mm, head diameter 6mm, total length 40mm, is quenched immediately after forging, and tempered in a timely manner, increasing the cutting life by more than 30% compared with conventional treatment.

(2)  Lathe tool quenching after forging

A self-use M2 steel turning tool from domestic machine tool electrical factory production of, is quenched oil immediately after forging, and tempered at 550℃, which has more than 1 times than that of market lathe tool.

The self-use 9341 steel 12-square turning tool of Jialong company, is oil-cooled after free forging, which has a relatively long service life.

(3) hot-forging quenching of crusher hammer

Hot-forging quenching of 355mm x 98mm x 33mm crusher hammer with 65Mn steel :

The initial forging temperature is 1050℃, and the final forging temperature is 840~860℃.

After the final forging, it should stay in the air for 2~3s, quench into flowing tap water, temper at 180~200℃, and the surface 10mm inward hardness can reach 50~55HRC.

The service life is increased by more than 50% compared with conventional heat treatment.

(4) Hot-forging quenching of socket wrenches

40Cr steel socket wrench from domestic hardware tool factory, uses forging quenching instead of original salt bath quenching, which is not only energy-saving and environmental friendly, but also of has high quality.

(5) Hot-forging quenching of chisel

55MnSi steel chisel is forging in 2500N air hammer and special die, the high temperature deformation temperature is 920-950 ℃, the deformation variable is about 75%, the final forging temperature is about 900 ℃.

Within 30s after deformation (depending on the fire color of the workpiece surface), it should be quickly water quenched and oil cooled, then tempered at 220-270 ℃.

After thermomechanical treatment, the chisel has high hardness, good toughness, which greatly improves service life.

(6) Hot-forging quenching of thread ring gauge

The 230mm x 120m CrMn steel blank with a mass of about 40kg is forged into 90mm x 90mm x 600mm square bars, then blanking is done according to the ring gauge size.

The blank will be heated to 1050 ~ 1150 ℃, with proper insulation, it is rapid upsetting-extrusion formed in the high temperature deformation area.

The variation of the shape is 35% ~ 40%, final forging temperature is 920 ~ 900 ℃.

Then, it is immediately cooled into 40 ~ 70 ℃ oil foe 40 ~ 60s.

After oil air cooling for about 100 ℃, it is tempered in time.

The surface hardness of the ring gauge is ≥62HRC.

(7) Hot-forging quenching of 45 steel sprockets

The initial forging temperature is 1070 ~ 1150 ℃, the final forging temperature is 850 ℃, the deformation variable is 35% ~ 75%, tempering temperature is 200 ~ 350 ℃.

Compared with the salt bath fire box furnace heating quenching, strength increased by about 30%, wear resistance increased by 26% ~ 30%.

(8) Hot-forging quenching of GCr15 steel bearing

Deformation temperature is 930~970℃, deformation variable is 30%, with oil cooling, tempering temperature is 150~180℃.

Compared with the conventional heat treatment, the strength is increased by nearly 20% and the contact fatigue life is increased by 23%.

(9) Hot-forging quenching of 40Cr steel diesel engine linkage

Initial forging temperature is 1150 ~ 1180 ℃ with tread forging, deformation time is 13 ~ 17 s, the deformation variable is about 40%.

Immediately trimming is on a 2150N crank press, then it conducts quenching immediately after straightening (the temperature of the workpiece at this time is 900~950℃), and finally tempering at 650℃.

(10) Precooling quenching after forging of 45Mn2 steel ball

When using 45Mn2 steel diameter 70 ~ 100mm steel balls, the initial forging temperature is about 1200 ℃, the final forging temperature should be controlled in 1000 ~ 1050 ℃.

According to the steel ball specifications to choose different pre-cooling time after water quenching, 150 ~ 180 ℃ tempering steel ball surface hardness is ≥ 57 HRC, the depth of the hardened layer of ≥50HRC is greater than 20mm, which meets the use of large specification steel ball requirements.

(11) Immediate quenching  of 65 Mn steel ploughshare roll forging

Intermediate frequency induction heating is in 1100 ~ 1200 ℃, from the beginning of deforming with roll forging to about 20 s before quenching, the deformation of different parts of the ploughshare is 56% ~ 83%, quenching heat density after deformation is 1.30 ~ 1.35g/cm3 CaCl2 aqueous solution.

After quenching, it is tempered at 460~480℃×3h, and the hardness is 40~45HRC.

Compared with the conventional heat treatment process of plowshare, the number of heating times from 4 to 5 times reduced to two times, production efficiency increased by about 4 times, product quality all reach first-class product requirements, economic benefits are very significant.

(12) Hot-forging quenching of steering knuckle

For the 40Cr steel steering knuckle with a diameter of 60mm, it is forged after heating at 1150~1200℃, the final forging temperature is 900~850℃, which conducts oil cooling, and is tempered at 600℃×2h.

The use of forging waste heat quenching, not only saves energy and reduce costs, but also significantly improves the organizational structure and material force performance, especially the improvement of impact toughness is more significant for automotive safety.

(13) Cr12MoV steel precision plastic hot press die forging and hot quenching

The overall size of the die is 70mm×20mm×10mm.

There are 20 small holes with diameters of 1.5mm, 2.5mm and 3mm on the 20mm width plane, requiring heat treatment of the hole spacing tolerance of ± 0.006mm, flatness <0.01mm and hardness 56 ~ 60HRC.

Due to the serious segregation of eutectic carbides in Cr12MoV steel, there is a certain degree of fracture after billet rolling.

However, it is still distributed in strips along the rolling direction, and the core is distributed in mesh, block and piles, which become stress concentration and crack sources, leading to material anisotropy and increasing heat treatment distortion.

The use of forging heat deformation is better to solve the above problems.

The specific process is as follows:

The initial forging temperature is 1050~1160℃, the final forging temperature is 850~950℃.

It conduces oil-cooling when it is hot and twice tempering at 780℃ for 3h.

Metallographic structure after final heat treatment:

Martensite +  lower bainite + dispersion carbide powder + small amounts of residual austenite.

The specific volume is close to that of the thermal-tempered sorbite.

To achieve micro-deformation, it does not need straightening after heat treatment.

Distortion all meet the technical requirements, with a hardness of 58 ~ 60HRC and qualified rate of 99.99%.

According to the above heat-treated process, the die has high heat resistance, thermal hardness and wear resistance, and long service life.

There are many examples of quenching with forging waste heat and high temperature tempering, such as hexagonal drawing dies, deep drawing dies and cold punching dies etc., so it does not mention them all.

(14) Hot-forging quenching of miscellaneous metal ware and tool

Miscellaneous metal ware and tool such as wrenches, screwdrivers, pliers, and scissors were the first to be hardened by the residual heat of forging, which might be the first prototype of thermomechanical treatment.

It heats the parts of the tool to be quenched in a coke furnace, and observes the fire color, that is, line forging.

Some need a few fires to hit the established size, the last fire forging after forming do not need air-cooling.

According to the material, the appropriate coolant should be selected, and then put on the side of the furnace or tempered with its own residual heat.

A special tempering furnace is rarely used.

(15) Hot-forging quenching of woodworking tool

After free forging, planers, axes and chisels in woodworking tools are generally quenched with residual heat, which saves electricity and time, and has high production efficiency.

(16) Immediate quenching  of agricultural equipment

Now in some market towns in the countryside, coke ovens are still used.

Agricultural machinery quenched by forging residual heat includes sickles, shovel, shovel, raking targets, crusher hammers, as well as kitchen spoons, spatulas and kitchen knives etc.

2. 2 cases of forging normalization

forging normalization

(1) Normalizing treatment of 3Cr3Mo3W2V steel hot forging die to eliminate chain carbide

The steel is easy to appear chain-like carbide after slow cooling after forging, leading to die brittle fracture, cracking or thermal cracking failure.

Using normal heat can dissolve M6C.

In the air cooling speed > 15 ℃ / min, more than the formation of chain carbide critical cooling speed, can eliminate the chain carbide and annealing in spheroid annealing to obtain particles of uniform fine distribution of carbide.

The recommended normalizing temperature is 1130 ℃, the modified forging normalizing impact toughness value is from 26J/cm2 to 23J/cm2, service life is from the original 1500 pieces to up 2000 pieces.

(2) 20CrMn steel forging hot normalizing

High temperature deformation normalizing means that the workpiece is directly placed in the air to cool after the final forging at about 850°C, which not only improves the strength, but also greatly improves the impact toughness, wear resistance and fatigue resistance of the steel, and reduces the brittle transition temperature of steel.

The outer dimensions of the 20CrMnTi steel forging blank are 80mm×80mm×40mm.

After forging, it is air-cooled and the cooling speed is controlled, which greatly improves the mechanical properties and facilitates cutting.

Some domestic machinery companies, 20CrMnTi steel automotive gears, use forging waste heat for normalizing.

Producing 1t gear can save more than 300kW·h of electricity.

3. 2 cases of forging thermal annealing

forging thermal annealing

(1) Rapid spheroid annealing of HSS forgings

Some domestic units immediately put the high-speed steel into Ac1-(20~30)℃ for 2~3h after stopping forging, the furnace is cooled to 550℃, and the furnace is air-cooled, which simplifies the process, shortens the production cycle, and saves electricity of 70% to 90%, reduces production costs, improves working conditions, improves the quality of forgings, and facilitates mechanized operations.

For high-speed steel workpieces processed by rolling, die forging and isothermal processing, it is not necessary to follow the conventional annealing process, which can refer to this example.

(2) 8Cr2WMnMoVS (referred to as 8Cr2S) system of precision cold die forging annealing residual heat

The die dimension is 250mm×200mm×42mm, the starting forging temperature is 1150~1100℃, the final forging temperature is 900~850℃.

Annealing process: 800~820℃×4~6h furnace cooled to 500℃ with air cooling.

4. 5 cases of residual heat quenching of rolls, rolling and extrusion

(1) Set rolling quenching of mechanical blade

Some of the rotary and planing knives used in the wood processing industry are formed by the flanging method.

The blade is made of an alloy tool steel such as 5Cr8W2MoVSi, the body (or back) of the blade is 45 steel Q235A steel, heated to the forging temperature of the blade steel, and the blade steel and body are welded together in a rolling mill.

It belongs to a solid phase welding method, which is rolled to a specified size, controlled the final rolling temperature, and quenched and cooled in a timely manner.

The blade manufactured by this method saves time and electricity and has good quality, high hardness and long life.

(2) Rolling hot quenching of M2 steel lathe tool

Rolling hot quenching is a heat treatment process that uses the residual heat of various profiles after rolling to quench them.

Its strengthening effect is the same as forging hot quenching.

M2 steel 1220 ℃ rolling (250 rolling mill, 50r/min) into the size of the specified is direct quenched, hardness can reach 65HRC above, lathe tool cutting life are higher than the salt bath quenching.

(3) Rolling hot quenching of 45 steel machine woodworking twist drill

The author has successfully implemented thermomechanical treatment with machine-use twist drills from a domestic tool company.

Through the high-frequency heating device, four-roller hot rolling is conducted.

Austenitizing temperature is 950 ~ 1000 ℃, deformation temperature is 880 ~ 950 ℃, deformation variable is about 30%, quenching agent for the cycle is two nitrate aqueous solution, water temperature is <70 ℃, after quenching hardness is ≥ 54 HRC, hardness is ≥ 50 HRC after 240 ~ 260 ℃ × 1h tempering, which meets the technical requirements and more than 95% meet the deformation requirements.

(4) Rolling hot quenching of reinforced bar

20MnSi steel reinforced bar needs hot-rolled supply, performance requirements of tensile strength is ≥ 510MPa, flexural strength is ≥ 335MPa, elongation is ≥ 16%.

60mm × 60mm billet is rolled into a 16mm diameter reinforced bar.

The initial rolling temperature is 1100 to 1200°C, the rolling shape variable is about 93%, and the final rolling temperature is 950 to 900°C, which is exactly the temperature of the low-carbon martensite quenching of the steel.

After rolling, cooling water is out within 1 ~ 1.26 s.

550 ~ 600 ℃, it uses its own heat to do self-tempering.

The mechanical properties of the reinforced bar treated by the above rolling quenching and tempering process far exceed the values specified in GB1499, and also exceed the mechanical properties specified in the British BS4449 standard.

(5) Extrusion immediate quenching of 35CrMo steel oil jumper joints

The deformation temperature of extrusion is 1100~1200℃ and the tempering temperature is 570~580℃.

Hardness is 300 ~ 335HBW, mechanical properties of tensile strength is ≥ 1068MPa, flexural strength is ≥ 960MPa, elongation is ≥ 14.5%, which meets the requirements of the Ministry of Standards.

Practice tells us that for large workpieces such as joints for extrusion waste heat quenching, it must carefully select the deformation temperature, the residence time before quenching after deformation, the quenching medium, the cooling time of the workpiece in the quenching medium, the tempering temperature and other process parameters.

5. 4 cases of transformation superplasticity heat treatment

(1) Superplastic thermomechanical treatment of 9SiCr steel

The purpose of 840℃×2h oil cooling and 200℃×2h tempering is to obtain double refinement tissue.

Then superplastic deformation is 800 ℃ , the deformation rate is 2.5 × 10s, tensile deformation variable is 250%, then cooling in oil is conducted after deformation.

After the superplastic deformation test of the steel bending strength and multi-stroke life and hardness indicators, the results show that the flexural strength is 28% higher than the conventional treatment, multi-stroke life increased by 38.6%, hardness is ≥ 60HRC, and conventional quenching is equivalent.

(2) Low-temperature thermomechanical treatment

The bending strength of H11 steel is 1852 MPa and the elongation rate is 12.5% after two tempering cycles at 482°C in conventional quenching.

If conducting the low-temperature deformation quenching and 482 ℃ temperings, 2% deformation aging is performed at about 316°C, and finally tempered at 482°C.

Although this process is a little more complicated, the value of flexural strength of steel rose to 2548MPa with an increase of 37.5%, the elongation remains the original level.

(3) Heat treatment combined high and low deformation

This compound thermomechanical treatment is a process in which high temperature deformation quenching is followed by a small amount of deformation and tempering at a given temperature.

When conducting martensite deformation aging after high-temperature deformation quenching, it can make the steel to obtain much higher strength properties than any other heat treatment.

For example, the mechanical properties 50CrVA by conventional quenching and 200 ℃ tempering are: tensile strength of 2119MPa, flexural strength of 1497MPa and 41.7% shrinkage at section.

The mechanical properties after the high temperature deformation quenching, 200 ℃ tempering, 3% deformation and 200 ℃ tempering are:

The tensile strength of 2597MPa and flexural strength of 2254MPa, that is, a composite thermomechanical heat treatment combining high temperature deformation quenching and martensitic deformation aging, so that the tensile strength, the flexural strength of 50CrVA steel were increased by 22.6% and 50.7%.

(4) Roll straightening of mechanical blade

Mechanical blades such as planing knives and rotary knives with a length of more than 2m produced by Jialong Company are heated and quenched in a protective atmosphere furnace at a temperature of about 500℃.

When the workpiece is cooled to about 200℃, using the principle of phase change superplasticity, it is rolled back and forth on the roller press several times, and the straightness can be adjusted to ≤0.30mm immediately after bending 10-15mm.

This deformation reinforcement not only straightens a well-bent insert, but also causes residual compressive stress of about 5 mm depth on the rolled surface, which helps to increase the tool life.

6. 7 cases of chemical thermomechanical treatment 

(1) Cold deformation carburizing

The process is to carburize after the cold deformation of the workpiece, due to the cold deformation produced a number of structural defects, which can accelerate the carburizing process.

For example, the deformation of 20CrNiMo after the cold heading is 25%, and the gas carburizing at 930~950℃×2h, the depth of the carburizing layer reaches 0.84mm;

If the deformation variable is 50%, the coating can reach 0.88mm, the larger the deformation variable, the deeper the penetration layer.

(2) Cold deformation nitriding

The process is a composite heat treatment process in which the workpiece is nitrided after cold deformation at room temperature.

Cold deformation nitriding differs from cold deformation carburizing.

Cold deformation slows down nitrogen penetration and reduces the depth of the seepage layer, and the trend of seepage layer thinning becomes more pronounced with increasing deformation.

This phenomenon may be caused by nitrogen atoms on the dislocation of the pinning effect (or dislocation of nitrogen atoms on the trap effect), which hinders the diffusion of nitrogen atoms.

However, the cold deformation nitriding can make the pure iron toughness rise.

Nitriding temperature and holding time depends on the type of steel, for example, 38CrMoAl steel and 20 steel is 650 ℃ and 550 ℃, respectively.

(3) Cold deformation boron infiltration

This is a combined heat treatment process in which the workpiece is deformed at room temperature followed by boron infiltration.

For example, 20 steel workpieces are rolled and deformed in a greenhouse, followed by a 900°C holding period and solid infiltration of boron at different heating rates.

Tests have shown that cold deformation significantly increases the depth of the infiltration layer.

The optimal deformation of the maximum penetration depth varies with the heating rate and the holding time of the boron infiltration.

The reason for this phenomenon is due to the cold deformation of the steel organization to accelerate the steel surface of the boron atomic adsorption process.

(4) Cold deformation of carbon and nitrogen co-infiltration

Cold deformation carbonitriding is a composite heat treatment process in which medium temperature carbonitriding is carried out after room temperature deformation.

The cold treatment before surface treatment has a significant effect on the carbonitriding process of the steel, which increases the C and N content of the surface, as well as the thickness of the penetration layer at the optimum deformation.

For example, when 20CrMnTi steel cold-rolled deformation variable is 15%, the thickness of 860℃×2h and 860℃×4h carbon and nitrogen co-infiltration is 0.65mm and 0.80mm, respectively.

(5) Deformation titanium infiltration

Deformation at room temperature not only affects the diffusion process of interstitial atoms in steel, but also affects the penetration process of substitutional atoms in steel.

For example:

the cold deformation of 16Mn steel for titanium infiltration, examined the effect of cold deformation on the solid infiltration process of titanium.

The test shows that the temperature of titanium infiltration is 900~950℃, and the deformation of 30% is the best.

As the temperature of titanium carburizing increases, the longer the holding time, the thicker the penetration layer.

(6) Forging heat carburizing quenching

The thermomechanical heat treatment process is to heat the workpiece blank to the initial forging temperature to change forging, then put it into the carburizing furnace for carburizing, and then quench it directly.

Forging heat carburizing quenching saves the electrical energy required for heating the workpiece during carburizing, and improves carburizing speed, surface hardness and wear resistance, making it suitable for medium modulus gears, as well as other types of carburized workpieces.

Another form of combined carburizing and thermomechanical treatment is carburizing and forge heat quenching, which involves carburizing followed by hot-die forging and quenching.

The implementation of this process can thicken the effective hardened layer of the workpiece, increase the surface compressive stress, increase the breaking power, and extend the product life.

(7) Nitriding quenching compound heat treatment of 9SiCr steel  circular screwing die

The hardness of 9SiCr steel circular screwing die heat treatment is 62 ~ 65HRC, conventional heat treatment is 860 ~ 880 ℃ with salt bath heating quenching and 150 ~ 180 ℃ tempering, black factory.

In general, in order to improve the tool hardness, wear resistance can be used surface chemical heat treatment.

But the chemical heat treatment process temperature is at least 400 ℃, which is obviously inappropriate for 9SiCr steel tools, and the nitriding quenching can solve this problem.

Nitriding is performed in an LD 60kW ion nitriding furnace, then heated in a 100kW medium temperature salt bath furnace, oil-cooled, cold treated, and finally tempered at 150-180°C.

After testing, the distance from the surface is 0.10~0.80mm, the hardness is >927HV5, and the peak hardness is 974~986HV5.

The hardness at 0.20~0.60mm is ≥857HV5, which improves the anti-tempering property of the hardened area and prolongs the service life of the mater.

7. Conclusion

The thermomechanical treatment process is extremely widely used.

From the perspective of processing objects, it is suitable for almost all metal materials such as various carbon steels, alloy steels, alloy structural steels, and nickel-based alloys.

From the perspective of processing methods, it can combine the two to meet the special requirements for parts and toughness, thereby greatly improving the quality and life of deformed components.

The future of thermomechanical treatment is bright.

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