The tool often needs to be tougher, stronger, and resistant to wear from the material it is working with. Therefore, materials used for tooling must have as high stiffness and strength as possible, but adequate ductility, in accordance with the conditions of use, except for a few exceptions. Particularly in the case of tools that perform separation, form and shape change, and are difficult to impact or impact, they are required to have the highest hardness cracking resistance which can be achieved with high hardness, good abrasion resistance and high ductility with them.
The most important size when characterizing a mechanistic use feature is the hardness determined by Rockwell or Vickers methods. Hardness can also be measured by back splash when the surface of the surface is not desired to be printed. Knoop hardness measurement method can also be used in very hard and brittle materials. Although the elasticity limit determined by the tensile test, the yield limit or the limit of 0.2, the tensile strength, the elongation at break and the shrinkage values can be taken as the criterion for evaluating the strength and shape changeability of the materials for the tools, As little plastic form change occurs, these are not enough to identify the material. A better evaluation of the mechanical properties can be made by determining the elastic bending strength, the elastic bending strength, and the plastic bending strength, determined by the static bending test. Torsion and impact torsion testing can also be used when the tools are tested in accordance with practical requirements. Although the lifetime of the tool is determined by separating it from the risk of fracture, quantitative determination of ductility and fracture resistance is problematic.
Until today, in most cases, the determination of ductility is made on the basis of the work done up to the crush, in relation to the yield and fracture resistance. Accordingly, qualitatively the levels of ductility can be classified as follows:
Fragile: low stiffness, little plastic deformation work
Ductile soft: low stiffness, high plastic deformation work
Ductile hard: High stiffness, high plastic deformation work
The determination of the ductility state of the high hardness material has been made up to now by pulsed bending and static bending tests on notched and notched specimens. However, new possibilities for characterization of ductility on the basis of fracture toughness, given the fracture mechanics, are also given for ‘relatively fragile tool materials’. Thus, the definition of this material characteristic as a resistance against non-destructive crack expansion can also be linked to wear conditions.
The strength and lifetime of the separating tools are determined by the wear at the contact point between the first planar tool and the material. In addition to mechanical stresses, thermal stresses are also effective in the wear mechanism, since temperatures of up to 1000 ° C may occur during machining. Thus, a decrease in thermal stability and breakage of the cut materials results in coincidental microscopic adhesion erosion and crack formation.
Cutting edge wear, which is seen in the form of rounding of the cutting edges, is found in very unalloyed and low alloy steels. The formation of the wear surface, defined as the width, wear mark “B”, is characterized as free surface wear. Rarely, there is wear on the surface of the chip, which is known as abrasion of the chip surface. This wear form is seen in the form of hollow wear (cratering), especially in tools made from speed steels and hard metals. Alongside the cutting, small flat craters deepen and continue to slide in the direction of the cutting edge form the continuation of the cutting period, which causes rapid destruction and blindness.
In addition to requiring good resistance to abrasive wear, a high strength is also expected in adequate ductility. When hot work tool steels are used for forming at elevated temperatures, they must resist both mechanical and thermal stresses. In addition to good hardness and heat resistance, the oxidation must have enough thermal resistance, expressed in terms of resistance to burning and tackiness to cracking in the hotter end. If the tool is subjected to too many temperature changes in the periodic work flow, such as die casting molds and forging molds, cracks in the combustion may occur. The tool surface, which comes into direct contact with the heated material, suddenly heats up and expands within a very short period of time. Due to the less expansion of the colder layers inside the tool material, compression stresses are formed, and in the subsequent cooling, the tensile stress is generated and is in the opposite state. As a result of the elastic-plastic deformations associated therewith, surface cracks in the form of webs occur (wear with abrasion). Alongside the cracks of combustion, especially in deep-cut tools, the cross-section changes and cracks in the hot cracks penetrate into the inside of the tool. The measure for crack sensitivity, also referred to as shock resistance against heat, is the heat conduction capability and expansion coefficient of the material along with the notch impact resistance and the heat flux limit. Furthermore, it should be borne in mind that for the estimation of team behavior under operating conditions, there are often long-running constraints due to mechanical vibration or temperature effects. In such cases, the material is subjected to continuous vibration resistance or to the determination of the time constant resistance.
For the cutting and measuring tools in the mold, the stability of the measurement is also important. This phenomenon includes both form changes in heat treatment during heat treatment and change in form that can not be prevented by volume change due to form change and conversion events, and form changes that can not be corrected in heat treatment which is not done in accordance with the rule. Dimensional changes can be very complex and depend on the amount of alloy, heat treatment technology and tool form and gauge.
It is of utmost importance that the melting, alloying and heat treatment technology of tool or work steels change within wide boundaries and that very different demands are met. Conventionally, steels can be classified in the following manner:
Unalloyed tool steels
Alloy cold work steels
Hot working steels
High Speed steels
There is no definite boundary between construction and tool steels in terms of chemical composition. For example, a steel containing the same amount of chromium may be used for both the roller bearing (Section 9.6.i) and the cold rolling mill. On the other hand, the case hardening steels described in Section 5.6 are the most important materials for tools used in the processing of high polymers.
In addition to the steels, additionally cast hard alloys, sintered hard metals and oxide ceramics, hard castings, diamonds and synthetic hard materials are used. Non-ferrous metals and alloys are used only in special places. Example: Nickel based hot cutting knife and injection molding die,
Since tool steels are important for almost all processing methods, besides the introduction of materials, their production and machinability are also described below. In addition to the heat treatment information specified in Section 4, additional information is also provided which is important for tool steels.
MOLDING AND FORMING
Tool steels are in principle produced as prime steel and more often in basic arc furnaces. The most important approach for good quality is to use clean scrap containing a small amount of Cr, Ni and Cu. High-quality tool steel production is also becoming widespread in the molting, under vacuum, under electron bombardment multi-chamber furnace (EMO) and under slag melting (ESU). In the EMO method, the improvement of kahenin is achieved by solidification in the crystallizer cooled at low pressure and in the ESU method, which is achieved by refining the reactionable slag dripping from the steel through the process. The structure of UA steel produced in this way is free of voids, no bubbles, no pores and nuclei and shows better chemical homogeneity due to the tendency to precipitate very little. The good core properties obtained in this way are particularly beneficial for large size tools. Another advantage of ultra-fine steels is a significantly reduced amount of gas. Thus, in the EMO method, the amount of oxygen is reduced to about 70% and the amount of nitrogen is reduced to 30 to 50%. The amount of non-metallic bonding is greatly reduced, and the significant improvement in the degree of microscopic haze is ensured. In addition, when vacuum is applied under low pressure, the easily flowable elements, such as Pb, Bi, Sb and As, which reduce hot forming and hot ductility, can also be completely removed from the steel. It is of great importance that the polishing process (production of high polymer materials and cold rolling tools), improved abrasion resistance (increased resistance to abrasion of the hot rolled steel) and increased hot ductility (reduced wear resistance) are of great importance in the manufacturing process. The life span of ultra-moment steel tools is 20 to 100% higher than that of steel produced in the usual manner, depending on tool grade and JSRR conditions.
The determination of the circumferential state of the material with a high hardness has been made up to now, with notched and notched specimens, with pulsed bending and static bending tests. However, new possibilities for characterizing ductility on the basis of fracture toughness Kje (see Section 7.2.3), by inflating fracture mechanics, are also given for relatively fragile tooling materials. Thus, the definition of this material characteristic as resistance to non-destructive crack growth can also be linked to wear conditions.
Further development of the I SiS process has also prevented the appearance of crystal dislocations and has imparted isotropic properties to the steels. The result of the provision of a single-phase structure, rising perpendicular to the direction of rolling, improves fracture toughness and reduces notch sensitivity in multi-axis tension situations. The cold work and hot work tool steels produced according to this method have two to three times higher life.
After the logs are poured, they are processed again by rolling or forging. Care should be taken to ensure that the hot forming temperature is precisely maintained, since cementite webs can form in high-carbon steels and black temperatures can occur at low temperatures.
Materials made from steel casting or precision casting are only preferred, as they may be economical for a large number of manufactured tools. If steel casting is used, the tool’s heat resistance and abrasion resistance are increased, and better isotropy is achieved in mechanical properties.
The strength and lifetime of the separating tools are determined by the wear at the contact point between the first planar tool and the material. In addition to mechanical stresses, thermal stresses are also effective in the wear mechanism, since temperatures of up to 1000 ° C may occur during machining. Thus, a decrease in thermal stability and breakage of the cut materials results in coincidental microscopic adhesion erosion and crack formation. The characteristic wear profiles for the lathe are shown in Figure 154.
Cutting edge wear, which is seen in the form of rounding of the cutting edges, is found in very unalloyed and low alloy steels. The formation of the wear surface, defined as the width, wear mark “B”, is characterized as free surface wear. Rarely, there is wear on the surface of the chip, which is known as abrasion of the chip surface. This wear form is seen in the form of hollow wear (cratering), especially in tools made from speed steels and hard metals. Alongside the cutting, small flat craters deepen and continue to slide in the direction of the cutting edge are formed continuously and this causes rapid destruction and blindness.
As the wear definition size, the depth of the cavity on the free surface and the distance to the cutting edge of the cavity axis (Figure 155) is important. For this to be determined, a chip test is required. For this purpose, a wear characteristic test is carried out in which the wear width B is determined by the cutting speed or the cutting path. Acceptable wear is dependent on the sign width, the material, the choice of the tool and the economic outlook. At the outset, it is possible to optimize the machining ‘shaping’ method by measuring the direct overrun during the operating process.
Effect of alloy elements:
With the addition of alloying elements, the properties of the tool steels can be changed to be multi-ply. Alloying elements either dissolved in the iron core or incorporated for special carbide formation improve different degrees of hardenability, temper strength, hardness, strength, ductility and wear resistance. The specific effect of each of the important alloy elements on tool steel is, in summary:
Carbon: It is possible to reach a hardening depth of 1 to 4 mm in alloy steels by rapid cooling hardening. On the% I carbon, the highest hardness achievable is fixed, but the wear resistance gradually increases with increasing amount of carbur.
Mangan: Conversion increases the hardenability because it reduces the speed, thus it allows to harden in larger sections. However, the grain also becomes rough and causes tempering fragility. There is a tendency for cold hardening to increase wear resistance in impact and compression.
Silicon; It increases the resistance to oxidation, but at the same time, the tendency to decrease carbon (decarburis) increases.
Due to the increase in elasticity limit, silicon alloy steels are used for good spring properties. In Hot Work tool steels, the sticking tendency is reduced by 1% Si.
Chromium: Critical cooling reduces speed and thus increases hardenability. Because special carbides are formed, it increases abrasion resistance, cold tolerance. In tool steels, it is one of the most important alloying elements.
Tungsten: Grain acts as a thinner, reduces sensitivity to overheating, and provides resistance to wear, heat resistance and temper strength. The downside is that it reduces the ability to conduct heat and, in conjunction therewith, increases the tendency for crack formation in heat treatment.
Molybdenum: It inhibits temperability and as a strong carbide builder increases hardness, wear resistance and temper strength.
Vanadium: The result of the formation of difficult-to-dissolve carbides prevents grain growth at high austenite temperatures and increases wear resistance. Therefore, in high vanadium quantities the polishability of the tool deteriorates.
Cobalt: Increases the ability of the carbide forming elements to dissolve ostenite and also improves hot strength, hot hardness, temper strength and heat conduction ability.
Nickel: Improves the hardening depth and reduces the wrinkle. Nickel addition is of particular importance in terms of increasing the ductility of the working tools by impact and impact forces.
In addition to requiring good resistance to abrasive wear, a high strength is also expected in adequate ductility. When hot work tool steels are used for forming at elevated temperatures, they must resist both mechanical and thermal stresses. In addition to good hardness and heat resistance, the oxidation must have enough thermal resistance, expressed in terms of resistance to burning and tackiness to cracking in the hotter end. If the tool is subjected to too many temperature changes in the periodic work flow, such as die casting molds and forging molds, cracks in the combustion may occur. The tool surface, which comes into direct contact with the heated material, suddenly heats up and expands within a very short period of time. Due to the less expansion of the colder layers inside the tool material, compression stresses are formed, and in the subsequent cooling, the tensile stress is generated and is in the opposite state.
