We often hear customers talking about the excellent performance of H13 steel, but do we really know what H13 steel represents?In fact, H13 belongs to the hot work tool steel in the three major tool steel classifications in the United States, and is classified as a medium carbon high chromium series hot work tool steel.
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Comparison of medium carbon and high chromium series hot work tool steel
GradeCSiMnPSCrMoVWCo H100.35-0.450.80-1.250.2-0.7'0.03'0.033.0-3.752.0-3.00.25-0.75-- H110.33-0.430.80-1.250.2-0.6'0.03'0.034.75-5.51.1-1.60.3-0.6-- H120.30-0.400.80-1.250.2-0.6'0.03'0.034.75-5.51.25-1.750.2-0.51.0-1.7- H130.32-0.450.80-1.250.2-0.6'0.03'0.034.75-5.51.1-1.750.8-1.2-- H140.35-0.450.80-1.250.2-0.6'0.03'0.034.75-5.5--4.0-5.25- H190.32-0.450.15-0.500.2-0.5'0.03'0.034.0-4.750.3-0.551.75-2.23.75-4.54.0-4.5For DIN 1. steel,it belongs to the German standard DIN .As a steel grade against H13, it must belong to the hot work tool steel series. It is named 1. according to the German DIN numerical steel number system,which is expressed as hot work tool steel. In addition, 1. corresponds to X40CrMoV5-1 under the DIN naming system.
The Main Characteristics of H13 Steel
This group of steel products H10 to H19 contains chromium, with tungsten, molybdenum, vanadium and cobalt additions in some cases.
The carbon of this group is considered to be rather low, about 0.35-0.40 percent, thus promoting toughness at a normal working strength between 400 and 600 HV, along with the relatively low total alloy content.
The large chromium in these units, combined with low carbon, guarantees a depth of hardening and therefore the air can be hardened in parts of up to 30 cm to fully work hard.
The higher tungsten and molybdenum levels of steels H10 and H14 increase the hardness of the red and heat, but reduce toughness possibly a bit.
Applications
The following are the application of the chromium hot-work steels:
Molybdenum, chromium and vanadium, along with tungsten and different percentages of Carbon are the main alloying elements in this group.
Like high-speed steels the grades of molybdenum in hot working steels have nearly the same characteristics and use as tungsten. Compared to the former group, the main benefit of these steels is excellent resistance to heat
More care is needed in thermal treatment in order to prevent decarburization along with all high molybdenum steels.
Applications
The following are the application of the hot molybdenum steels
Carbon, tungsten, chromium and sometimes vanadium are the primary alloying elements of these steels.
Compared with straight chromium steels, the high alloy content increases resistance to high temperatures softening, but the steels in this category are volatile. The normal toughness of work is between 450 and 600HV.
The large content of tungsten makes the group in contrast to the steels in the hot work chromium unit unsuitable for water cooling.
If we look at this group of steels, the composition of the steels resembles high speed steels, and Type H26 is in fact a high speed steel low carbon version of T1.
Applications
The following are the application of the Tungsten hot work steels:
Is H13 an alloy steel?
First of all, H13 steel is definitely alloy steel, and the total alloy content is between 5% and 10%. Therefore, strictly speaking, we can define H13 steel as a medium alloy hot work tool steel.
How hard is H13 steel?
When H13 steel is delivered in annealed condition,the ideal structure is composed of spherical pearlite and a small amount of granular carbide,its hardness is usually less than 235HBW.
Metallographic structure of H13 annealed steel
After quenching and tempering, the performance of H13 steel will be greatly improved, and its hardness can usually be maintained above 52HRC.
What is the strength of H13 steel?
As a hot work tool steel, under the harsh working conditions of high temperature and high pressure for a long time, it is easy to cause material failure. Therefore, the performance of H13 steel is a very severe test.
In practical production, H13 steel must be able to serve safely for a long time under such working conditions, therefore, it must have extremely excellent strength.
According to experience, the tensile strength of H13 steel should be greater than MPa at room temperature.
At the same time, at high temperature (below 600°C), H13 steel should have the ability to resist mechanical load, that is, the yield strength to maintain the shape and the strength and toughness to avoid breaking. Production experience shows that at working temperature, the yield strength of H13 steel should not be lower than MPa.
Can H13 steel be nitrided?
In order to ensure the service life of the H13 steel mold, surface nitriding treatment is the most commonly used strengthening method.After two nitriding treatments, the thickness of the nitriding layer of H13 steel can reach more than 200um, and its surface hardness can reach HV.
Why H13 steel usually needs to be tempered more than 2 times?
The H13 steel after quenching has high hardness (55-58HRC), but its toughness is not ideal.According to experience, H13 steel will form a lot of internal stress after quenching. If it is not eliminated in time, the stress will be released during use and the material will eventually crack.
Therefore, H13 steel must be tempered after quenching, and in order to achieve the best performance, the number of tempering should be 2-3 times.
It should be pointed out that secondary hardening will occur when H13 steel is tempered at 425°C~520°C, accompanied by the second type of temper brittleness, which will significantly reduce the impact toughness.
If the second tempering is adopted, the second tempering temperature should be about 10°C lower than the first tempering temperature, and the holding time should be shortened by 20%~25%, which can be used to reduce temper brittleness.
Why H13 steel can only be used at temperatures below 600°C?
The final heat treatment structure of H13 steel after tempering is tempered sorbite + a small amount of granular carbide.
When the tempering temperature is lower than 600', its structure still maintains martensitic lath. However, once the tempering temperature is higher than 650°C, the martensite form will gradually disappear and transform into tempered martensite, which will cause serious deterioration of the thermal strength of H13 steel.
Therefore, H13 steel is a medium temperature (<600°C) hot work tool steel with excellent performance.
H13 Steel VS H11 Steel
After the previous introduction, we clearly know that both H13 steel and H11 steel belong to medium carbon high chromium hot work tool steel.It can be clearly seen from the table below that the main difference in their chemical composition lies in the V element content, that is, the V in H11 steel is 0.5% lower than that in H13 steel.
GradeCSiMnPSCrMoV H110.33-0.430.80-1.250.2-0.6'0.03'0.034.75-5.51.1-1.60.3-0.6 H130.32-0.450.80-1.250.2-0.6'0.03'0.034.75-5.51.1-1.750.8-1.2We can consider H13 steel as an improved version of H11 steel. The increase of V content in H13 steel can significantly improve the hardness, wear resistance and tempering stability.
In addition, from the analysis of the chemical composition and the use status of the mold factory, generally speaking, the service life of H13 steel is longer than that of H11 steel for the same product.
H13 steel is the most widely used and most representative air-cooled hardening hot work die steel, which has both strong and tough mechanical properties and good cold and thermal fatigue properties.
H13 steel is mainly used in hot extrusion dies with a working temperature below 600°C, and the material must go through a series of manufacturing processes to achieve its application purpose, so that it can work stably for a long time in the harsh environment of hot extrusion.The figure below shows the general production process of H13 tool steel.Next, we will briefly talk about the process points that we think need to be focused on.
Ingot Melting
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At present, there are two commonly used smelting methods for H13 steel, namely electric furnace smelting + electroslag remelting (EF+ESR) and electric furnace smelting + vacuum refining outside the furnace (EF+LF+VD).
Due to different smelting methods, compared with electroslag steel, H13 electric furnace steel has poor compactness and low purity. Especially in the annealed condition, H13 electric furnace steel has serious band segregation and uneven structure.
Relatively speaking, the cost of H13 electric furnace smelting is low, but a large number of production practices have proved that the H13 steel produced by electric furnace smelting has low transverse toughness and cannot meet the application standards.
Based on the smelting of electric furnace steel, H13 electroslag steel is subjected to secondary smelting in vacuum, which further improves the purity of the steel, further reduces the gas content, and further improves the physical and chemical properties.Therefore, electroslag smelting plays an important role in controlling the cleanliness and uniformity of H13 steel, and it can be used as an important process link in the production of high-quality H13 steel.
Heat Treatment
H13 steel must undergo a heat treatment process to strengthen its performance, so that it can work stably for a long time in the harsh environment of high temperature and high pressure. Generally speaking, the heat treatment process of H13 tool steel includes: Annealing, Quenching, and Tempering.
H13 steel can be considered as hypereutectoid steel, and conventional annealing process can be used, that is, complete annealing or isothermal spheroidizing annealing.
1.H13 steel complete annealing process: 850°C ~900°C x3h~4h heat preservation, cooling to below 500°C with the furnace, and then finally air cooling after being out of the furnace.
2.H13 steel isothermal spheroidizing annealing process: 845°C ~900°C x2h~4h/furnace cooling +700°C ~740°C x3h~4h/furnace cooling, <40°C /h cooling rate, '500°C out of the furnace and finally air cooling.
H13 steel Isothermal Spheroidizing Annealing Diagram
3.For H13 steel molds with high quality requirements, in order to prevent white spots, dehydrogenation annealing should be arranged
4.For H13 molds with complex shapes,stress relief annealing should be performed after rough machining: 600°C~650°Cx2h/furnace cooling.
5.After the heat treatment of the H13 steel mold, if the mold cavity is formed by grinding, EDM and wire cutting, a layer of quenched martensite white layer with a thickness of about 10m~30um will be formed on the surface of the mold.
Due to the large internal stress in the white layer and the brittleness of the quenched martensite itself, it is easy to produce microcracks and grinding cracks on the surface during grinding.Therefore, after grinding, it is best to perform stress relief annealing at a temperature lower than 50°C below the tempering temperature to eliminate grinding stress.
Quenching is the most important heat treatment process for H13 steel. During the quenching process, the austenite at high temperature is quenched into martensite, which greatly improves the hardness and strength of the mold and ensures the service life of the mold.
There are two main types of quenching equipment, vacuum heating and quenching, and atmosphere protection electric furnace heating and quenching. The commonly used media for quenching mainly include oil, water, salt bath furnace and vacuum air quenching.
H13 steel is generally preheated in two stages when heating and austenitizing. Usually, the first stage preheating temperature is selected at about 650°C, and the second stage is selected at about 850°C. The purpose of segmental preheating of H13 steel is to make the internal and external temperature of the material fully uniform, to avoid the stress caused by the temperature gradient formed in the mold cavity by too fast heating, which will cause the distortion of the mold, and to effectively promote the homogenization of austenite.
The austenitization temperature of H13 steel is °C to °C. In this process, the core and surface of the mold should be kept as consistent as possible. The actual quenching temperature needs to be determined according to the working conditions and structural shape of the mold. , manufacturing process and performance requirements.
Therefore, in order to obtain the highest red hardness, the upper limit of austenitization temperature can be used for molds that have high requirements for fracture toughness, thermal fatigue resistance and thermal wear resistance, and that require electrical machining after quenching. For molds that require small distortion, fine grains, and high impact toughness, in order to obtain the best toughness and prevent cracking, the lower limit of austenitization temperature should be used.
The optimization of the holding time for quenching heating should ensure the completion of the transformation of the structure and obtain the required degree of solid solution of the alloying elements. If the holding time is too short, the red hardness and tempering resistance of H13 steel will be reduced.
Known for their unique hardness, tool steels are used in the manufacture of cutting tools such as knives and drills, as well as in hot extrusion, stamping and plastic molds.
Although the selection of tool steel seems to be very simple, this process requires trade-offs, which must be comprehensively considered from the characteristics of tool steel, process performance, production cost and specific applications.
Scientifically correct and reasonable selection of tool steel is the basis for ensuring the best performance, service life, safety and economy of the product. Selecting the best tool steel grade will depend on a variety of factors as follows.
Hardness directly reflects the material's resistance to deformation. The hardness of tool steel is usually expressed by Rockwell hardness HRC.The application hardness of most tool steel is 60 to 62 HRC, and some will be as high as 66 HRC or above. The final application hardness depends on the steel grade.
Tool steels that undergo plastic deformation in service show insufficient hardness.For example, permanent bending of the blade in use, swelling of the end face of the punch and collapse of the surface of the die all indicate insufficient hardness.Since the deformation resistance of steel is directly related to hardness (independent of steel type). Therefore, the correct way to solve the deformation is to increase the hardness, or reduce the working load. At this time, changing the steel grade will not work unless the new steel grade can achieve higher hardness.
When the difference in hardness value is not large, the change in hardness generally has little effect on the wear life of tool steel. Different tool steels usually have the same hardness in use, but their wear life often varies greatly.
The toughness of tool steel is a kind of resistance that characterizes its resistance to fracture under the action of impact force or other stress.
Most tool steels are notch sensitive. Therefore, any small gap in the material will cause it to break under lower impact force.Therefore, in addition to the inherent characteristics of the material, notches, grooves, geometric changes and other small changes on the workpiece will reduce the impact resistance of the corresponding part.
In production, the loss caused by wear failure is usually less than the loss caused by ductile failure (fracture), because fracture failure is often unpredictable, usually interrupts production, and even brings catastrophic losses.Wear failure is generally gradual and it can often be corrected. Toughness failure is due to insufficient toughness of the material itself, or other reasons, such as heat treatment, lubrication method, or other working conditions.The toughness value can characterize the steel's resistance to fracture but not its service life.
Wear resistance refers to the ability of a material to resist mechanical wear. The objects in contact with the material are workpieces, other tools and objects adhered to their surfaces (scale, metal shavings, etc.). Wear resistance is determined by the hardness of the steel and its chemical composition.
We usually intuitively believe that the wear resistance of high hardness tool steel is better than that of low hardness. However, at the same hardness, different steel grades have different wear resistance. For example, O1, A2, D2 and M2, even though their hardness is 60HRC, their wear resistance is not all equally excellent.
Facts have shown that under some working conditions, the wear resistance of low-hardness high-alloy tool steel is better than that of high-hardness low-alloy tool steel. Therefore, for wear resistance, the influence of other factors other than hardness must be considered, such as carbides, heat treatment processes, etc.
The above three factors,hardness and toughness can be regarded as the function of 'enough is enough'. That is to say, as long as the performance of tool steel in this area is to prevent its failure in this area, it is enough, and it is not necessary to further improve these properties. However, wear resistance can be considered as a 'never enough' function, that is, improving the wear resistance of the tool will increase its life. In order to increase tool life, the wear resistance of tool steel should be improved endlessly. Therefore, as long as other properties are not damaged, it is always beneficial for tool steel to improve wear resistance.
There are many types of tool steels available, depending on their composition, the temperature range at which they are forged or rolled, and the type of hardening they undergo.
For details, please refer to the article on this website: what is tool steel?
Here, this article takes cold work tool steel as an example. Cold working tool steel is mainly used for blanking and shearing, cold forming, cold extrusion, cold forging and powder press forming.According to the classification of cold work tool steel, it can be divided into three types, of which O1, A2, and D2 are their typical representatives. They all have good hardness, wear resistance and deformation resistance at room temperature.
O1 is an oil-hardening steel with high hardness and good machinability. This grade of tool steel is primarily used for items such as cutting tools and drills, as well as cutlery.
A2 is a commonly used air-hardening steel with a moderate amount of alloying material (chromium). It has good machinability and a balance of wear resistance and toughness. It is commonly used in blanking forming punches, trimming dies and injection molds.
D2 steels can be oil hardened or air hardened and contain higher percentages of carbon and chromium than O1 and A2 steels.It has high wear resistance, good toughness and low deformation after heat treatment. The higher carbon and chromium content in D2 steel makes it ideal for applications requiring longer tool life.
Other tool steel grades contain higher percentages of different types of alloys, such as HSS M2, which can be selected for high-volume production. Various hot-worked steels can maintain sharp cutting edges at higher temperatures up to °C.
When choosing a tool steel, we must consider the machinability of the material. Tool steel will eventually be applied to products, and products will involve machining, including not only rough machining before heat treatment, but also final finishing after heat treatment. Therefore, the difficulty of machining performance often determines the cost and quality of the product.
In general, the chemical composition of a tool steel is important, the higher the alloy composition, the more difficult it is to machine. As the carbon content increases, the machinability of the metal decreases.
The formed structure of the steel is also very important to the metal machinability. Different constructions include: forged, cast, extruded, rolled and machined. Generally, forgings and castings have very difficult surfaces.
More importantly, hardness is an important factor affecting metal processing performance. The general rule is that the harder the steel, the harder it is to machine. For tool steel, the conventional hardness is about 60HRC, which is even more unfavorable for processing.
Before selecting a tool steel grade, it is important to consider which tool steel is most likely to fail in this application by examining failed tools. For example, some tools fail due to abrasive wear, where the material being cut wears away the surface of the tool, although this type of failure occurs slowly and predictably. Tools that wear out to failure require tool steels with higher wear resistance.
Other types of failure are more catastrophic, such as cracking, chipping or plastic deformation. For tools that have broken or cracked, the toughness or impact resistance of the tool steel should be reinforced(note that impact resistance can be reduced by nicks, undercuts, and sharp corner radii, which are common in tools and dies). For tools that deform under pressure, hardness should be increased.
But keep in mind that the properties of tool steels are not directly related to each other. For example, you may need to sacrifice toughness for higher wear resistance.This is why it is so important to understand the properties of the different tool steels, as well as other factors such as the geometry of the die, the material being machined, and the manufacturing history of the tool itself.
The final issue to consider when choosing a tool steel type is cost, and it is a factor that has to be considered. Roughly speaking, the overall production cost includes material cost, heat treatment cost, machining cost, assembly and packaging transportation cost.
In fact, when choosing tool steel, you cannot blindly choose high-grade materials, but you should comprehensively consider the impact of materials on product functions and costs to achieve the best results.If the tooling proves to be of poor quality and fails prematurely, the choice of material may not reduce the overall cost of production. At this point a cost-benefit analysis should be performed to ensure that the tool steel material selected will provide the desired properties.
In the end, we should also consider comprehensively according to the stress, temperature, corrosion resistance and other conditions of the product, rather than simply pursuing a certain performance index.