德语
1. Strength performance
(1) Hardness
Hardness is the main technical indicator of mold steel. If the mold wants to keep its shape and size unchanged under the action of high stress, it must have a high enough hardness. The hardness of cold-working mold steel is generally maintained at about HRC60 under room temperature conditions, and the hardness of hot-working mold steel is generally required to be maintained in the range of HRC40~55 according to its working conditions.
For the same steel type, within a certain range of hardness values, the hardness is proportional to the deformation resistance; but the plastic deformation resistance may be significantly different between steel types with the same hardness value and the composition and structure.
(2) Red hardness
Thermal working molds that work in high temperatures require the stability of their structure and properties, thereby maintaining a sufficiently high hardness. This performance is called red hardness.
Carbon tool steel and low alloy tool steel can usually maintain this performance within the temperature range of 180~250℃, while chromium-molybdenum hot-working mold steel generally maintain this performance within the temperature range of 550~600℃. The red hardness of steel mainly depends on the chemical composition of the steel and the heat treatment process.
(3) Compression yield strength and compression bending strength
During use, molds are often subject to high-strength pressure and bending, so the mold material must have a certain compressive strength and bending strength.
In many cases, the conditions for performing the compression test and bending test are close to the actual working conditions of the mold (for example, the measured compressive yield strength of the mold steel is more consistent with the deformation resistance shown when the punch is working).
Another advantage of bending test is that the ** value of the strain value is high, which can more sensitively reflect the differences in deformation resistance between different steel types and under different heat treatment and structure states.
2. Resilience
During the working process, the mold is subjected to impact loads. In order to reduce the damage caused by breakage, cracking, etc. during use, the mold steel is required to have a certain toughness.
The chemical composition, grain size, purity, quantity, morphology, size and distribution of carbides and inclusions, as well as the heat treatment system of mold steel and the metallographic structure obtained after heat treatment, all have a great impact on the toughness of steel. In particular, the impact of the purity of steel and the thermal deformation on its lateral toughness is more obvious.
The toughness, strength and wear resistance of steel are often contradictory. Therefore, it is necessary to reasonably select the chemical composition of steel and adopt reasonable refining, thermal processing and heat treatment processes to achieve the best coordination of the wear resistance, strength and toughness of the mold material.
Impact Toughness Chart Table Characteristics The total energy absorbed by the sample during the entire fracture process during one impact. However, many tools are fatigued and broken under different working conditions, so conventional impact toughness cannot fully reflect the fracture performance of mold steel. Test technologies such as small energy multiple impact fracture work or multiple fracture life and fatigue life are being adopted.
3. Wear resistance
The most important factor that determines the service life of the mold is often the wear resistance of the mold material. The mold bears considerable compressive stress and friction during work, which requires the mold to maintain its dimensional accuracy under strong friction. The wear of the mold is mainly three types: mechanical wear, oxidative wear and melt wear.
In order to improve the wear resistance of mold steel, it is necessary to maintain the high hardness of mold steel, and to ensure that the composition, morphology and distribution of carbides or other hardened phases in the steel are relatively reasonable.
For molds that are in service under heavy-load and high-speed wear conditions, it is required that the surface of the mold steel can form a thin and densely adhered oxide film to maintain lubrication, reduce the melt wear such as sticking and welding between the mold and the workpiece, and reduce the oxidation wear caused by oxidation on the surface of the mold. Therefore, the working conditions of the mold have a great impact on the wear of the steel.
Wear resistance can be measured using simulated test methods to measure the relative wear resistance index as a parameter for characterizing the wear resistance level under different chemical components and tissue states. The lifespan before the specified burr height is presented, reflecting the wear resistance level of various steel types; the test is compared with Cr12MoV steel as the reference.
4. Resistant heat fatigue
In addition to the periodic changes in load under service conditions, thermally-worked mold steel is also affected by high temperature and periodic quenching and rapid heat. Therefore, the breaking resistance of thermally-worked mold steel should be evaluated to pay attention to the thermal mechanical fatigue fracture properties of the material. Thermomechanical fatigue is an indicator of comprehensive performance, which includes three aspects: thermal fatigue performance, mechanical fatigue crack propagation rate and fracture toughness.
Thermal fatigue performance reflects the working life of the material before the initiation of thermal fatigue cracks. Materials with high thermal fatigue resistance have more thermal cycles initiation of thermal fatigue cracks; the mechanical fatigue crack propagation rate reflects the expansion amount of each stress cycle when the material expands to the interior under the action of forging pressure after the initiation of thermal fatigue cracks; the fracture toughness reflects the resistance of the material to instable expansion of existing cracks.
For materials with high fracture toughness, if cracks are to propagate unstablely, they must have a sufficiently high stress intensity factor at the crack tip, that is, they must have a large crack length. Under the premise that the stress is constant, a fatigue crack already exists in a mold. If the fracture toughness value of the mold material is high, the crack must expand deeper before unstable expansion can occur.
In other words, thermal fatigue resistance determines the part of life before fatigue crack initiation; while the crack growth rate and fracture toughness determine the part of life that occurs when subcritical expansion occurs after crack initiation. Therefore, in order to obtain a long service life of a hot work mold, the mold material should have high thermal fatigue resistance, low crack growth rate and high fracture toughness value.
The thermal fatigue resistance index can be measured by the number of thermal cycles that initiate thermal fatigue cracks, or by the number and average depth or length of fatigue cracks that appear after a certain thermal cycle.
5. Bite resistance
The bite resistance is actually the resistance when "cold welding" occurs. This property is important for mold materials.
During the test, the tested tool steel sample is usually subjected to a constant-speed dual friction motion with a material with a tendency to bite (such as austenitic steel) under dry friction conditions, and the load is gradually increased at a certain speed. At this time, the torque also increases accordingly. This load is called "biting critical load". The higher the critical load, the stronger the biting resistance.
Commonly used mold steel material components, what is mold steel made of?
What material is mold steel made of?
Mold steel is a type of steel used to make molds such as cold stamping dies, hot forging dies, and die-casting dies. Molds are the main processing tools for manufacturing parts in industrial sectors such as machinery manufacturing, radio instruments, motors, and electrical appliances.
The quality of the mold directly affects the quality of the pressure processing technology, product accuracy, output and production cost. In addition to reasonable structural design and processing accuracy, the quality and service life of the mold are mainly affected by the mold material and heat treatment.
What materials are there in mold steel?
1. Commonly used mold steels in the domestic market include:
420SS corrosion-resistant plastic mold steel, American AISI and ASTM standard steel grade. Approximate steel grades: Chinese 4Cr13 (GB), German X38C13 (DIN), French Z40C40 (NF), Russian 40X13 (I'OCT).
440C corrosion-resistant plastic mold steel, American AISI and ASTM standard steel grade. Approximate steel grades: China 11Cr17 (GB), Japan SUS440C (JIS), Russia 95X18 (I'OCT).
P20 pre-hardened plastic mold steel, American AISI and ASTM standard steel grade. It has been included in my country's national standard (see GB/T 1299-2000, 3Cr2Mo). The pre-hardened hardness is generally in the range of 30 to 32 HRC, and it is suitable for making large and medium-sized precision plastic molds with complex shapes. Approximate steel grades: China 3Cr2Mo (GB), Germany 1.2330 (W-Nr), France 35 CrMo8 (NF), etc.
2. Japanese plastic mold steel commonly used in the domestic market
G-STAR corrosion-resistant plastic mold steel is a manufacturer's brand of Japan's Datong Special Steel Co., Ltd. This steel can be pre-hardened, with a factory hardness of 33 to 37 HRC. It has good corrosion resistance and machinability, and can be combined with S-STAR steel to form a corrosion-resistant plastic mold.
NAK55/NAK80 mirror plastic mold steel, manufacturer's brand of Japan's Datong Special Steel Co., Ltd. Both steels can be pre-hardened to a hardness of 37 to 43 HRC. NAK55 has good cutting performance, and NAK80 has excellent mirror polishing properties and is used to make high-precision mirror plastic molds.
PXZ pre-hardened plastic mold steel, manufacturer's brand of Japan's Daido Special Steel Co., Ltd. The factory hardness of this steel is 27~34 HRC. This steel has good cutting performance and welding repair performance, and is used to make large corrosion molds and plastic molds such as automobile bumpers, instrument panels, and home appliance casings.
PX4/PX5 mirror plastic mold steel, manufacturer's brand of Japan's Datong Special Steel Co., Ltd. The steel can be pre-hardened to a hardness of 30 to 33 HRC. Both types of steel are modified American P20 and are used to make large mirror plastic molds, automobile taillights, front fender molds, cameras, household appliance casing molds, etc.
S45 C/S50C/S55 C ordinary plastic mold steel. Japanese JIS standard steel grades are respectively similar to my country's high-quality carbon structural steel 45, 50, and 55, and are commonly used in non-important parts of molds, such as formwork frames, etc.
Due to the special requirements of mold steel, the production process of this type of steel requires fine materials, refining and vacuum degassing. The carbon content range of the steel is narrowed and the sulfur and phosphorus content are controlled to be lower. For example, in YB/T 107-1997, the steel grades of carbon plastic mold steel are SM45, SM48, SM50, SM53 and SM55, etc., to distinguish them from high-quality carbon structural steel for general purposes.
S-STAR corrosion-resistant mirror plastic mold steel, manufacturer's brand of Japan's Datong Special Steel Co., Ltd. This steel is a martensitic stainless steel with high corrosion resistance, high mirror polishability, and small heat treatment deformation. It is used to make corrosion-resistant mirror precision plastic molds.
3. German plastic mold steel commonly used in the domestic market
GS-083、GS-083ESR、GS-083VAR、GS-083H、GS-083M、GS-128H、GS-162、GS-312、GS-316、GS-316ESR、GS-316S、GS-318、GS-343EFS、GS-343ESR、GS-3615、GS-379、GS-711、GS-738、GS-767、GS-808VAR、GSW-2083等。
Note: All pictures in the article are reprinted online, and will be deleted if infringed!
