(1) hardness is the main technical indexes of steel mold, mold to maintain its shape and size change in the role of high stress, must have a sufficiently high hardness. At room temperature the general hardness of about HRC60 in the cold die steel, hot die steel according to the working conditions and general requirements remain in the range of HRC40~55. For the same grade, in a certain range of hardness, hardness and deformation resistance is proportional; but with the same hardness and different steel composition and microstructure, the plastic deformation resistance may have obvious difference.
(2) die redhardness under the condition of high temperature working heat required to maintain its structure and performance is stable, so as to maintain a sufficiently high hardness, this performance is called red hardness. Low carbon tool steel, alloy tool steel can usually maintain this performance in the temperature range of 180~250 DEG C, Cr Mo hot die steel generally maintain this performance in the temperature range 550~600 DEG c.. The chemical composition and heat treatment process of steel redhardness depends mainly on steel.
(3) the compressive yield strength and compressive strength bending strength of mould is often affected by the high pressure and the effects of bending in the use process, so the requirements of mold material should have certain compressive strength and flexural strength. In many cases, the compressive test and the actual working conditions of bending test conditions close to the mold (such as die steel deformation resistance, the measured compressive yield strength and punch work has shown consistent). Another advantage of bending test is a variable absolute value, can sensitively reflect the differences between different grades and in different heat treatment and microstructure deformation resistance.
In the work process, mould under impact load, in order to reduce in the process of using the broken blade in the form of damage, collapse, die steel has certain toughness requirements.
The chemical composition, mould steel, grain size, purity, quantity, carbides and inclusions such as morphology, size and distribution, bring great impact and heat treatment system and heat treatment of die steel after the microstructure factors on toughness of steel. Especially the purity and thermal processing of steel deformation influence on the transverse toughness is more obvious. The toughness of the steel, strength and wear resistance are often contradictory. Therefore, to a reasonable selection of the chemical composition of steel and reasonable refining, heat processing and heat treatment process, so that the mold material wear resistance, strength and toughness to achieve the best match.
The impact toughness characteristics of materials in a table in the process of impact specimen total energy absorption in the whole process of fracture. But many of the tools is fatigue fracture under different working conditions, therefore, can not fully reflect the impact toughness of the conventional fracture properties of die steel. Small energy multiimpact fracture work or life times of fracture and fatigue life test technology is being used.
Hot die steel under service conditions in addition to the periodic change of the load bearing and also by high temperature and periodic thermal shock effect, therefore, the thermal mechanical fatigue fracture resistance of mould steel materials for thermal evaluation should pay attention to. Thermo mechanical fatigue is a kind of comprehensive performance indicators, including mechanical properties, thermal fatigue crack propagation rate of fatigue and fracture toughness of three aspects.
The thermal fatigue property of reflecting material before thermal fatigue crack initiation life, high thermal fatigue resistance materials, thermal cycling times more adorable heat fatigue crack; mechanical fatigue crack growth rate reflects the material after the thermal fatigue crack initiation, crack in forging pressure to internal expansion, expand the amount of each stress cycle the fracture toughness of materials; reflect on the crack existing lose steady expansion force. Fracture toughness of materials, such as to the occurrence of crack instability expansion, must have a high enough at the crack tip stress intensity factor, that is must have larger crack length. In the premise of constant force, a fatigue crack has existed in a mold, if the fracture toughness of die material is higher, then the crack must be extended deeper, can occur instability expansion.
That is to say, the thermal fatigue performance determines that part of life of fatigue crack was adorable; and the crack propagation rate and the fracture toughness can be determined when the crack initiation occurred after subcritical extension that part of life. Therefore, if you want to get high hot die life, mold material should have high resistance to thermal fatigue crack, low growth rate and high fracture toughness.
Kunshan cold die steel The thermal fatigue performance index can use thermal cycling number adorable thermal fatigue cracking, fatigue cracks can also be used by some after thermal cycling after the number and average length or depth to measure.