Pre-hardened Mold Steel Research Articles

EFFECTS OF A Cu ADDITION ON THE CORROSION RESISTANCE OF LOW-ALLOY PRE-HARDENED PLASTIC MOLD STEEL

The influence of Cu on the corrosion performance of low-alloy Cu-bearing pre-hardened plastic mold steel was investigated and compared with non-Cu-bearing mold steel using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), salt-spray tests and electrochemical impedance spectroscopy (EIS). The results reveal that the formed rust layer is composed of α-FeOOH, β-FeOOH, γ-FeOOH, Fe3O4 and large amounts of amorphous compounds. The corrosion product in the early stages of corrosion is loose and porous but becomes denser and more tightly bound to the steel matrix in the later stages, and the corrosion rate of Cu-bearing steel decreases with the increasing corrosion time. With a further Cu addition, the free-corrosion potential of Cu-bearing steel increases and, consequently, the electrochemical impedance, the capacitive single semicircular arc on the impedance spectra and the charge transfer resistance are also significantly enhanced. Therefore, Cu effectively enhances the corrosion resistance of pre-hardened mold steel, prolonging its service life and ensuring a high quality and shape fidelity of molded plastic products.

Effects of Rare Earth elements on microstructure evolution and mechanical properties of 718H pre-hardened mold steel

718H Pre-hardened mold steels with different Rare Earth (RE) contents were prepared to investigate the influence of RE on microstructure evolution and mechanical properties through a series of experiments and theoretical analysis. The results indicated that the toal oxygen (T.O) content decreased from 15 ppm to 6 ppm with 0.022 wt% RE addition, which is attributed to the active chemical properties of RE elements. For test steels, RE additions of 0.012 wt% and 0.022 wt% were significantly effective for refining inclusions by eliminating 11.5% large-sized inclusions with diameter exceeding 10 μm compared with that of 0RE steel. RE addition contributed to modify irregular MnS and Al2O3 inclusions into ellipsoidal RE-inclusions (RE2O3, RES, RE2O2S and REAlO3). The purification of molten steel and the modification of inclusions by RE treatment have significant effects on improvement of the fatigue crack growth tests (FCG) inhibition ability and impact energy as well as the isotropy. However, excessive addition of RE elements (0.07 wt%) seriously reduced the impact energy, ultimate tensile strength and FCG inhibition ability due to rapidly increase of the volume fraction of large-sized inclusions. In addition to the inclusions formed by RE treatment, trace solid solution RE atoms improve the stability of undercooled austenite, resulting in the transformation region of bainite and perlite of 0.07RE steel shifting to the bottom right and prolonging the incubation period compared with that of 0RE steel.

Effect of vanadium micro-alloying on the microstructure evolution and mechanical properties of 718H pre-hardened mold steel

The effects of different contents of vanadium (V) (0.1, 0.2, and 0.3 wt%) on the microstructure evolution and mechanical properties of 718H steel were investigated. The precipitate was characterized by means of atom probe tomography (APT) and bright-field transmission electron microscopy (TEM). The increase in V content has great benefits for strength, but has an adverse effect on impact toughness. The strength increase can be attributed to the influence of V addition on dislocation density, misorientation gradient, and fine scale MC precipitates. Precipitation strengthening mainly contributes to the V-added steel by analyzing various strengthening mechanisms. However, fine scale MC precipitates can pin dislocation leading to a decrease in its mobility. A large number of immovable dislocations will increase the dislocation accumulation, internal stress and brittle cracking, resulting in a gradual decrease in impact toughness with the V addition. In addition, compared with V-free steel, the dissolved V content in austenite decreases the grain boundary energy and inhibits the diffusion of the C atoms, ultimately reducing the transformation range of pearlite (P).

The Effect of Processing on The Surface and Subsurface Characteristic of Plastic Injection Mold Steel

AISI P20 is prehardened mold steel that is commonly used to manufacture plastic injection molding. The surface characteristics of molds play crucial role to control plastic injected molds parts. Besides, the characteristic of molds is mainly influenced by machining process, the manufacturing process to produce molds. This study presents the extensive experimental work focusing on the machining processing conditions on the surface characteristics of Plastic Injection mold steels. The input parameters are cutting speeds, feed rates and cutting inserts’ geometry (wiper and non-wiper). The measured output parameters are subsurface hardness of machined parts and phase transformation induced from cutting process. Experimental results show that wiper insert significantly helps to improve surface quality of components. Besides, microhardness measurement shows that thermal softening occurs resulting from machining of this alloy. XRD data illustrates peak broadening and increased intensity with machined samples.

A novel large cross-section quenching and tempering mold steel matching excellent strength–hardness–toughness properties

According to the synergistic effect of multiple elements, a novel large cross-section pre–hardened mold steel is designed with higher strength and hardness as well as toughness (HSTPM steel) compared with industrial high–end 718H steel during the normal tempering temperature range (530–650 °C). The achievements on the strength and hardness of HSTPM steel are attributed to the effects of 0.5 wt% molybdenum (Mo) and 0.1 wt% vanadium (V) additions on the matrix structure, including misorientation gradient, dislocation density, and nano–sized precipitates. The main strengthening precipitate (V, Mo)C was finely characterized by high angle annular dark field–scanning transmission electron microscope (HADDF–STEM) analysis. In addition, it was found that rare earth (RE) additions of 0.015 wt% in HSTPM steel highly effective in refining inclusions for changing the morphologies of strip MnS and Al2O3 to tiny spherical RE2O2S, and the number of coarse inclusions (diameter exceeding 5 µm) is significantly decreased in the same statistical volume (4.69 × 108 μm3) by three–dimensional X–ray microtomography statistical technique. The purification of molten steel and modification of inclusions by RE treatment are responsible for the improvement of impact toughness. Simultaneously, the lower carbon (C) content in HSTPM steel (high–end 718 H, 0.34 wt%; HSTPM, 0.23 wt%) also plays a large role in improving impact toughness. Finally, the synergistic effect of multiple elements delayed and eventually reduced the transformation range in pearlite compared with that in 718H steel.

Improvement of Strength-Toughness-Hardness Balance in Large Cross-Section 718H Pre-Hardened Mold Steel

The strength-toughness combination and hardness uniformity in large cross-section 718H pre-hardened mold steel from a 20 ton ingot were investigated with three different heat treatments for industrial applications. The different microstructures, including tempered martensite, lower bainite, and retained austenite, were obtained at equivalent hardness. The microstructures were characterized by using metallographic observations, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and electron back-scattered diffraction (EBSD). The mechanical properties were compared by tensile, Charpy U-notch impact and hardness uniformity tests at room temperature. The results showed that the test steels after normalizing-quenching-tempering (N-QT) possessed the best strength-toughness combination and hardness uniformity compared with the conventional quenched-tempered (QT) steel. In addition, the test steel after austempering-tempering (A-T) demonstrated the worse hardness uniformity and lower yield strength while possessing relatively higher elongation (17%) compared with the samples after N-QT (14.5%) treatments. The better ductility of A-T steel mainly depended on the amount and morphology of retained austenite and thermal/deformation-induced twined martensite. This work elucidates the mechanisms of microstructure evolution during heat treatments and will highly improve the strength-toughness-hardness trade-off in large cross-section steels.

Microstructure evolution and mechanical properties in 718H pre-hardened mold steel during tempering

The effects of tempering temperature on the microstructure and mechanical properties of 718H pre-hardened mold steel were investigated. After normalizing and quenching treatments, seven specimens were tempered at a temperature in the range of 500–650°C for two hours. After heat treatments, the tempered microstructures were characterized by X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy. In addition, the phase identification and microchemistry of tempered carbides were performed by the physicochemical phase analysis method; then the precipitation sequence of tempered carbides was examined in detail by transmission electron microscopy and selected area electron diffraction patterns. Results indicate that the yield strength, ultimate tensile strength, and the hardness decrease; in contrast, impact energy increases with the increase in tempering temperature. The influence of tempering temperature on mechanical properties of 718H steel is attributed to the precipitation of tempered carbides, the recovery of the martensite lath, the dislocation density, and the grain structure. Furthermore, a more accurate study of the micromechanics was performed through the fatigue crack growth test. And a correlation between microstructure and mechanical properties was established by electron back-scattered diffraction. Finally, the fracture surface of the impact specimen was analyzed by SEM and energy-dispersive X-ray spectroscopy. According to the change in microstructure and mechanical properties as a function of tempering temperature, the optimal tempering temperature has been determined in the range of 530–560°C.

Improved uniformity of hardness by continuous low temperature bainitic transformation in prehardened mold steel with large section

Expanding automobile industry energized the demand for large section plastic mold steel, large (465mm × 1325mm × length) pre-hardened mold (PHM) steel was trial-produced by quenching the forged slab at temperature between start (Ms) and finish (Mf) temperature of martensite, followed by tempering, according to the thermal expansion experiments and finite element modeling (FEM) of cooling rate from core to surface. Continuous low temperature bainitic transformation in PHM steel created high volume fractions of refined bainitic-ferrite laths, filmy retained austenite and dispersed carbides. Uniformity of microstructure and hardness, and the impact toughness of the PHM steel were remarkably superior to the one produced by conventional quenching & tempering (QT) process.

A comparative study on the dry sliding wear behaviour of nitrocarburised, gas nitrided, fluidised-bed nitrided, and plasma nitrided plastic mould steel

Plastic injection moulds suffer wear due to the relative movements of the mould parts and the polymeric material flow which is often reinforced by hard abrasive fibres or whiskers. Several studies were performed on the wear behaviour of diverse nitrided surfaces; however, comparative studies are needed. The present study aims to compare the dry sliding wear behaviour of nitrocarburised, gas-nitrided, fluidised-bed nitrided, and plasma-nitrided Impax Supreme (equivalent to AISI P20) pre-hardened plastic mould steel. The wear tests were performed against AISI 4140 pins under 100 N normal loads, with the total stroke length of 10 mm, the frequency of 1.5 Hz, and the total sliding distance of 400 m. After tests, worn surfaces and wear debris were microstructurally and chemically characterised and the wear rates were calculated. Results suggested that all samples presented mainly combination of adhesive and abrasive wear during the run-in period of sliding (severe wear), and mainly oxidative wear during the steady-state of (mild wear). Although no significant difference was observed between the treated samples, plasma-nitrided samples presented the lowest wear rate as mean values.

The Influence of Heat Treatment on the Microstructure and Machinability of a Prehardened Mold Steel

The machinability performance of a modified AISI P20 steel, heat treated to have the same hardness but three different microstructures, lower bainite, tempered martensite, and primary spheroidized carbides in a tempered martensite matrix, was studied. The microstructures were characterized using light optical and scanning electron microscopy and X-ray diffraction, and mechanical properties were compared by means of tensile and Charpy V-notch impact tests. The influence of microstructure and the resultant mechanical properties on machinability was studied in the context of single tooth end milling operation. The results showed that the material containing primary spheroidized carbides exhibited a superior machinability at the expense of a marginal loss of tensile strength and impact toughness, with comparable yield strength to that of the material containing tempered martensite. By contrast, the material with bainitic mi- crostructure showed the lowest yield strength and the poorest machinability performance while having the highest uniform elongation.

Effects of Cutting Speed on the Wear Properties of TiAlN PVD Coated Tool for Cutting P20 Mold Steel

High-speed cutting is an important method for improving the efficiency and quality of machining mold steel, but the wear of tool is one of the key factors restricting the improvement of cutting speed, which brings higher requirement for the material of tools. At present, most of the research is about high-speed cutting for high hardness mold steel, while only a limited research work on the pre-hardened plastic mold steel with hardness between 30 HRC and 42HRC, such as P20 mold steel. To explore the effects of cutting speed on the wear properties of TiAlN PVD coated tool for cutting P20 mold steel, the experiments in different cutting speeds were carried out under dry condition. Wear characterization of the rake and the flank surfaces were investigated by using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). It was revealed that at the low speed (160m/min), adhesion (built-up edge) followed by delamination was found to be the cause of wear damage; at the high speed (320m/min), the dominant wear mechanisms were oxidation wear and diffusion wear, followed by adhesive wear and melt wear; as the cutting speed increased, the proportion of oxidation wear and diffusion wear was gradually increased.

CLC 1.2316S

Abstract CLC 1.2316S is a prehardened mold steel with improved corrosion resistance. Sulfur is added for machinability. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming and heat treating. Filing Code: SS-1177. Producer or source: Industeel USA, LLC.

CLC 1.2316

Abstract CLC 1.2316 is a prehardened mold steel with improved corrosion resistance. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming and heat treating. Filing Code: SS-1176. Producer or source: Industeel USA, LLC.

Study on Machinability of Pre-Hardened Plastic Mould Steel

The relationship between machinability and microstructure of plastic mould steel is still not clear enough, despite the application of plastic mould steel is more and more wide. In this study, two typical plastic mould steels, namely, 718 (DIN 1.2738) and SDP1 steel with the same hardness are chosen to investigate turning force, tool wear and milling force by experimental test. Combining with the turning and milling test, discussions about cutting force and the relationship between machinability and microstructure are made. And it’s found that the micro-uniformity has a great effect on the machinability of plastic mould steel.

Development of Domestic Prehardened Plastic Mould Steel

The classification, properties of the domestic prehardened plastic mould steel are reviewed, the composition design and heat treatment process improvement in the chinese prehardened plastic mould steel are commented, its development direction is pointed out. Quenched and tempered prehardened steel has been developed and upgraded based on foreign steels, while non-quenched and tempered prehardened was invented by ourselves, and has been researching and developing because of its good cost performance ratio.

The Influence of Austenitization Temperature on the Mechanical Properties of a Prehardened Mould Steel

The many practical difficulties and longer lead time with heat treatment of mould steels after machining have led to increased demand for steels in prehardened condition, typically ~ 40HRC. At this hardness the steel possesses an optimal combination of high strength and machinability. The steels used for moulds require a wide range of demanding properties, among which high enough strength and toughness are the primary necessities in order to resist any deformation and dimensional change in mould during use. Uddeholm Impax HH which resembles the modified AISI P20 has been widely used for moulding of plastics and die-casting of low melting temperature metals. The common hardening process for Impax HH is conventional quenching and tempering. Hence, investigating the effect of hardening parameters on the required properties upon this steel grade is beneficial in improving it for better performance as a prehardened mould steel. In the present work, the effect of changes in austenitization temperature and consequently the prior austenite grain and martensite packet sizes on the tensile properties and impact toughness of Uddeholm Impax HH at the hardness of ~40HRC is studied. The results have shown reduction in impact toughness but no considerable change in yield and ultimate tensile strength upon increasing the austenitization temperature.

Machinability evaluation of pre-hardened plastic mould steels

There are multiple demands placed upon plastic mould steels, depending on the application they will have. Among these requirements, machinability has generally a great economic importance in mould steels and in pre-hardened mould steels in particular. The machining cost can exceed more than half of the cost of a mould. Nevertheless, to avoid subsequent heat treatment, distortion and dimensional inaccuracy, there has been the tendency to use even higher hardness in the pre-hardened mould steels, a hardness range of 38-40 HRC instead of 30-32 HRC. In this work, machinability of some of the most popular grades of pre-hardened plastic mould steel at 38-40 HRC is compared in two milling and two drilling operations. The materials have shown very different properties in different machining operations. This, beside the high requirements upon the plastic mould steels, such as polishability, hardness, impact toughness etc. makes it very complicated to improve these types of steels to be superior in all mould applications.

The effect of the martensitic packet size on the machinability of modified AISI P20 prehardened mold steel

The effect of martensitic packet size on the machinability of prehardened mold steel at a hardness of ~40 HRC (typical hardness for prehardened mold steels) was studied in terms of cutting force and tool life. The machinability tests were performed in end milling using coated, cemented carbide tools at three different cutting speeds. The results showed that an increase in the martensite packet size led to higher cutting force and shorter tool life. The increase in cutting force was related to the increase of work hardening. The work material with a coarser martensite packet size showed a higher amount of work hardening that can explain the higher cutting force. The longer tool life in the workpieces with finer structure was correlated to smaller amplitude of the variation in cutting force.

Micro cutting of ferrous materials using diamond tool under ionized coolant with carbon particles

A new coolant for micro cutting of ferrous materials using a diamond tool was proposed. The effects of the new coolant (ion-shot coolant) which consists of ionized coolant and carbon particles on two steel materials, a high carbon chromium steel and a pre-hardened mold steel were investigated. Also mechanism of the ion-shot cutting was discussed by the observation on material structure at the primary shear zone and frictional coefficient between diamond tool and ferrous material. The ion-shot coolant showed great potential for the used of the diamond tool on ferrous material in terms of tool wear and surface quality.

Investigation of the Effects of an Electrolytic Coolant with a Nano Carbon Additive in Diamond Micro Cutting on Ferrous Materials

A special coolant system called ‘Ion-shot coolant system’ which consists of an electrolytic liquid and a nano carbon additive was developed. A series of experimental studies had been conducted to understand the effects of the coolant in micro cutting of two steel materials with different carbon content, a high carbon chromium steel (SUJ-2) and a pre-hardened mold steel (SUS420J-2) using a diamond tool. Significant improvement of the diamond tool wear was observed while cutting ferrous materials. Additional benefits of the ion-shot coolant system were discussed in this paper.