H13, the national brand comparison is as follows。
1.china:4Cr5MoSiV1,
2.America:h13
3.Japanese:skd11.
chemical component:
C:0.32-0.45,Si:0.80-1.20,Mn:0.20-0.50,Cr:4.75-5.50,Mo:1.10-1.75,V:0.80-1.20,P.S≦0.030.
Conventional heat treatment process of H13 steel.
The structure of H13 steel after forging is banded and usually contains coarse primary carbide, and there is a large internal stress in the structure of parts after forging, which has an adverse effect on the subsequent die processing, service and service life. In order to improve the microstructure and comprehensive properties of H13 steel, proper heat treatment should be carried out after forging to improve the comprehensive properties of the die.
The conventional heat treatment process of H13 steel mainly includes preliminary heat treatment, quenching and tempering
The preparation heat treatment process of H13 steel is mainly annealing or normalizing, with one preheating and multiple preheating. The preparation heat treatment process and preheating times mainly depend on the size of the steel and the complexity of the mold, such as stress relief annealing + nodulization annealing, normalizing + nodulization annealing, double stage nodulization annealing, etc. The main purpose is: (1) to improve the ribbon structure of the steel after forging, eliminate the network carbide, and prepare the organization for the nodulization structure and subsequent heat treatment; ② Avoid the faster heating speed that causes the temperature difference between the inside and outside of the steel to be too large, resulting in greater internal stress, which causes serious deformation or leads to subsequent quenching cracks.
The carbon content of H13 steel is 0.35% ~ 0.45%, containing about 8% of alloying elements, resulting in the alloy eutectoid point shifting left, belongs to hypereutectoid steel. Before quenching, in order to eliminate the network carbide, hypereutectoid steel is often spheroidized annealing near its Ac1 temperature, or incomplete annealing between Ac1 and Ac3 temperatures. H13 steel pre-heat treatment annealing temperature is generally selected 600 ~ 650 ℃, spheroidizing annealing temperature 800 ~ 850 ℃. The lower preheating temperature in the first stage can effectively remove the stress caused by the early processing of the workpiece, prevent the serious distortion of the workpiece caused by subsequent heating, and then cause cracking; It can also speed up the heating speed of phase change recrystallization of the workpiece, shorten the time for the internal and external temperature uniformity of the thick large workpiece, and make the austenite grain distribution more uniform and fine on the large section, thus improving the overall post-thermal performance. However, too high temperature may lead to grain growth or carbide agglomeration spheroidization during subsequent tempering, thus increasing the brittleness of the workpiece. In the second stage, the higher preheating temperature can precipitate a large number of carbides and spheroidize in sections, and the dispersion degree of fine carbides is higher in this process, and the thermal stress and grain growth caused by too high temperature can be avoided.
The results of "forging + normalizing + spheroidizing annealing" and "forging + spheroidizing annealing" on H13 steel show that the normalizing and spheroidizing annealing after forging can improve the morphology and distribution of carbide precipitation in austenite, and then affect the mechanical properties.
After conventional annealing (840 ~ 890) ℃×(2 ~ 4) h and isothermal spheroidizing annealing (840 ~ 890) ℃×(2 ~ 4) h, H13 steel forgings are cooled to 710 ~ 740 ℃ for 3 ~ 4 h, and then cooled to 500 ℃ for air cooling, and then the test block is quenched and tempered twice. The results show that: After isothermal spheroidizing annealing, spherical pearlite and dispersed granular carbide structure can be obtained inside H13 steel, and the re-preheating after spheroidizing annealing can also improve the degree of carbide dispersion, providing the core for the transformation of microstructure after quenching.
2.2 Quenching
2.2.1 Conventional quenching process
Through the solid solution of various alloying elements, the quenched structure contains a large number of quenched martensite and residual austenite, which can significantly improve the toughness and wear resistance of H13 steel, so H13 steel generally needs to be quenched. The solution holding time is generally determined by the size of H13 steel and the complexity of the mold, usually 0.25 ~ 0.45 min/mm. The solution temperature is generally 1000-1100 ℃, which is mainly determined by the melting point of the inner phase of the matrix. Studies have shown that when the temperature exceeds 1100 ℃, the higher temperature provides enough growth activation energy for the tissue, and the austenite grains will be obviously coarsened, and even overburning. The quenching temperature is generally selected from 1000 to 1080 ℃. When the quenching temperature is high, the content of carbon and alloying elements in martensite increases, the susaturated carbon atoms dissolve in the martensite in the interstitial form, resulting in strong lattice distortion, resulting in increased distortion energy, carbon atoms and dislocation entanglement, which plays a significant role in strengthening the solid solution of martensite, and the hardness is higher after quenching. In addition, when the quenching temperature is higher, the content of residual austenite in the quenched structure increases, and the residual austenite is distributed among the lath martensite to prevent crack propagation and improve the impact toughness. Therefore, in order to obtain a higher red hardness after heating, the quenching temperature is generally selected as the upper limit temperature; In order to obtain better toughness, the lower limit temperature is used during quenching.
The H13 steel was preheated at 650 ℃ and 850 ℃ for 30 min, and austenitic holding at 1020 ~ 1080 ℃ for 5 ~ 7 min, and then oil quenching. The results showed that the hardness of H13 steel increased first and then decreased with the increase of quenching temperature, and the hardness reached the highest at 1050 ℃, reaching 53 HRC. After preheating at 550 ℃ and 800 ℃, H13 steel was quenched at 1030 ℃, 1070 ℃ and 1100 ℃ respectively. After holding, oil cooling and tempering at 600 ℃ were performed. The results showed that the thermal fatigue performance of H13 steel at room temperature and high temperature could be improved after quenching temperature was increased.
2.2.2 Fractional quenching process
In order to reduce the stress of the quenched structure, H13 steel is often quenched in stages, that is, the steel is first quenched in a salt bath above Ms temperature, and the steel is removed after maintaining the temperature of the quenched liquid for a period of time, and then cooled in the air. Fractional quenching can obtain a certain quenching cooling rate, retain the alloy structure with high solid solubility in the matrix, and prevent excessive precipitation of intergranular carbide. In addition, it reduces the quenching stress caused by the inconsistency between the cold and hot shrinkage of the steel inside and outside when the steel is cooled directly to room temperature, and the internal and external surfaces of the workpiece can be martensitic transformation at the same time, and reduce the amount of lower bainite generation, reduce the rapid shrinkage of the mold shape size, and prevent deformation and cracking after quenching.
At present, in addition to ordinary salt bath furnaces, vacuum furnaces are also widely used in the quenching cooling process. Vacuum furnace quenching refers to the whole quenching process in the vacuum furnace, the quenching medium (such as high purity nitrogen) into the vacuum furnace, by controlling the flow rate and temperature of the gas to control the cooling speed, high thermal efficiency, both can achieve rapid heating and cooling, but also can achieve slow heating to reduce the internal stress of the workpiece, temperature control is strict and accurate. After quenching, the workpiece surface has no defects such as oxidation, decarburization and hydrogen embrittlement. And the degree of automation is high, and it is widely used.
In addition, flow particle furnaces are also used for quenching and cooling in production. That is, heat is generated by combustible gas in specific equipment, and heat exchange and heat transfer are accelerated by the continuous movement of the flowing particles such as corundum sand, quartz sand and silicon carbide sand, so as to complete the cooling process of the workpiece. The whole process of furnace temperature control, heating speed, environmental pollution is small, the workpiece will not occur decarbonization, oxidation and other phenomena, can achieve continuous quenching, quenching can also be directly carried out mold blue treatment.
Single stage salt bath quenching, double stage salt bath quenching, vacuum fractional quenching and fluidized bed quenching were carried out on H13 steel dies of large, medium and small sizes. The hardness and structure of test blocks under different quenching methods were analyzed. The test results showed that: The first stage cooling and holding time of double-stage quenching should be long enough to ensure that the mold surface and center temperature are uniform, and the organizational transformation will not occur during the constant temperature process, so the first stage cooling and holding time can be appropriately extended to minimize the volume of Baines in the steel, and it is recommended that the first stage cooling temperature of H13 steel is about 520 ° C, and the second stage cooling temperature is about 200 ° C.
2.3 Tempering
After quenching, there is generally a large internal stress inside the steel, which needs to be tempered appropriately. Tempering can reduce the internal stress of the structure as much as possible, make it tend to balance, and avoid the large change of the mold size caused by the subsequent change of the structure; It can also continue to transform the residual austenite in the steel into martensitic structure, without reducing the hardness while ensuring the toughness.
The tempering process of H13 steel generally selects 500 ~ 650 ℃ high temperature tempering. At this temperature, the secondary hardening of H13 steel generally occurs, and when the residual austenite is transformed into martensite, the fine carbide particles are precipated in the tempered martensite to produce secondary hardening, the hardness of the workpiece is re-increased to the level of quenching, and the residual stress of the steel is reduced.
The H13 steel after forging was nodulated and annealed at 860 ℃, quenched and held at 1030 ℃ for 30 minutes after oil cooling, and tempered and held at 590 ℃ for 2 hours after oil cooling. The types of carbides in tempered H13 steel were analyzed and thermodynamic calculations were made, and the size and quantity of carbides in different parts were calculated. The results showed that: In tempered H13 steel, V-rich MC carbide, Mo-rich M2C carbide (<200 nm) and Cr-rich M23C6 carbide (>200 nm) are mainly precipitated, of which the first two are mainly precipitated at 1/2R, and the surface is the least.
Since the residual austenite has not been completely transformed after a single tempering, in order to further improve the performance of the material, secondary tempering is often carried out, or even multiple tempering, so that more small dispersed strengthening phases are precipitation in the tissue to improve its overall performance.
Other heat treatment techniques
Nitriding treatment and nitrocarburizing can significantly improve the fatigue strength, wear resistance and corrosion resistance of H13 die steel, and have the advantages of fast nitriding speed and good nitriding layer properties. It is widely used in production and is often used after the completion of mold processing.
After double-stage preheating +1030 ℃ quenching +600 ℃ tempering for H13 die steel, and then 580 ℃× 4.5h gas nitride carburizing, oil cooling, the thickness of nitride carburizing layer is about 0.20mm, and the mold surface hardness is above 900 HV. Gas nitrogen carburizing is equivalent to a tempering after mold quenching and processing, and the mold life is more than 2 times that of conventional heat treatment.
quenched H13 steel at 1050 ℃ +560 ~ 600 ℃ twice tempering treatment, and then carried out 540 ~ 570 ℃×12 h ion nitriding, the surface penetration layer thickness of 0.24mm, the white layer of about 10 μm, the hardness of about 67 HRC, the mold surface wear resistance and life have been improved.
High comprehensive properties of H13 steel can be obtained by stage preparation heat treatment, stage cooling after quenching and multiple tempering.
With the rapid development of society and the continuous innovation of scientific and technological manufacturing level, the demand for H13 steel performance improvement is also increasing. How to play the performance of H13 steel more efficiently and improve its heat treatment level to meet the growing needs will be the direction of continued research by scholars. In the traditional process, the more safe and efficient, higher level of automation, and less environmental pollution of heat treatment strengthening methods will be more widely concerned and studied.
Sichuan province liao fondle special steel trade co., LTD and can provide you with various grades of steel, heat treatment 1.2344.1.2343, 4140 and CrMoA4, 4130,1.7225 1.2767.1.2316, 12 l14, M2. M35, M42, T1.