Mold repair is a viable strategy for saving energy and reducing CO 2 emissions. Papers in the literature show that repairing a limited damaged area of the mold instead of producing a new one is becoming increasingly attractive, especially considering the latest European and international regulations introduced with the green deal. In this paper, the authors are pleased to present some preliminary results related to the repair of AISI H13 tool steel molds by Laser-Directed Energy Deposition. Steel blocks (20 x 55 x 100 mm3), previously tempered at 435±10 HV, were machined to reproduce the material removal of the damaged part of the mold. Subsequently, the region was repaired by L-DED using commercial H13 powder. The process parameters were optimized to obtain a defect-free welded area. Since the microstructure of the deposited tool steel consists of hard (730±10 HV) and brittle (7 J Charpy impact toughness) martensite, a series of post-process heat treatments were performed at different temperatures to restore a hardness compatible with that of the base steel. However, this goal was only partially achieved due to the different tempering behavior of L-DED-deposited and bulk H13 steel. In particular, the tempering temperature had to be limited to avoid softening of the base steel. In the best case, double tempering at 620 °C resulted in a toughness recovery of up to 42 J. Thermal fatigue tests showed better resistance to crack propagation after tempering, as evidenced by the shallower penetration depth compared to the as-built material.

This study investigates the heat treatment response and microstructure evolution of high-carbon steels for additive manufacturing. Moreover, the role of nitrogen as an interstitial alloying element is addressed. Stainless steel 440C, cold-work D2, hot-work H13, and T15 high-speed tool steel overspray powders from spray forming were investigated. The thermal behavior of these materials was examined using a thermal analyzer that combines calorimetry and thermogravimetry. Additionally, interstitial alloying with nitrogen was performed in-situ to understand its influence on thermal behavior. The (near-)equilibrium nitrogen solubility in 440C and D2 in contact with flowing N 2 gas was recorded as a function of temperature through the interval 1200 to 800 °C. The microstructure of the steel powders was characterized by light optical microscopy and X-ray diffraction. The potential of nitrogen alloying and the importance of optimized heat treatment protocols are emphasized with respect to high-carbon steels in additive manufacturing applications.

Additive manufacturing is increasingly used in a variety of applications. Directed Energy Deposition (DED) technology using powder feedstock enables the production of materials in combinations that would be very problematic using conventional technologies. DED is a technological process where the fed material is melted directly at the desired location using a laser beam. The research described here deals with the additive manufacturing and subsequent induction heat treatment of a functional deposited layer of M2 high-speed steel. Induction treatment has the advantage that only the functional layer of the component can be heat treated without affecting the base material. It is therefore possible to heat treat a combination of completely different materials with different properties without degrading the base material. Hardness values reached 950 HV (68 HRC) both after additive manufacturing and after additive manufacturing and induction treatment. Induction heat treatment of the deposited M2 layer ensured removal of traces of the original melt pools produced by the additive manufacturing. Investigation of the microstructure and mechanical properties of M2 tool steel after induction heat treatment produced by DED highlights its potential for high performance tooling and machining applications. The main objective of this research is to improve the final properties and tool life of forming tools when the tool is made of less expensive low-alloy steel and its functional layer is made of M2 high speed steel using additive manufacturing technology.

Selective laser melting (SLM) is an additive manufacturing technique that can be used to make the near-net-shape metal parts. M2 is a high-speed steel widely used in cutting tools, which is due to its high hardness of this steel. Conventionally, the hardening heat treatment process, including quenching and tempering, is conducted to achieve the high hardness for M2 wrought parts. It was debated if the hardening is needed for additively manufactured M2 parts. In the present work, the M2 steel part is fabricated by SLM. It is found that the hardness of as-fabricated M2 SLM parts is much lower than the hardened M2 wrought parts. The characterization was conducted including X-ray diffraction (XRD), optical microscopy, Scanning Electron Microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) to investigate the microstructure evolution of as-fabricated, quenched, and tempered M2 SLM part. The M2 wrought part was heat-treated simultaneously with the SLM part for comparison. It was found the hardness of M2 SLM part after heat treatment is increased and comparable to the wrought part. Both quenched and tempered M2 SLM and wrought parts have the same microstructure, while the size of the carbides in the wrought part is larger than that in the SLM part.

This paper presents the results of a study on a new coating method for alloy steel. The coatings were synthesized on the surface of H21 die steel through a combination of thermal-chemical treatment (TCT) and electron beam processing (EBP). A paste containing boron and aluminum was applied to the test samples which were then heated to accelerate the diffusion process. After 2 h at 950 °C, the diffusion layers were found to be 120 μm thick, and after 2 h at 1050 °C, they were 580 μm thick. The subsequent EBP led to a complete transformation of the primary diffusion layer and an increase in thickness to 1.6 mm. XRD analysis showed significant differences in composition before and after EBP and the presence of tungsten and iron borides. It was also found that the distribution of microhardness and composition over the layer thickness had a more favorable profile after EBP.

Dilatometry test systems are commonly used for characterizing the transformation behavior in steels and induction heating is commonly the heating source. In these systems, the steel test article is assumed to have a uniform temperature throughout the sample. This is a good assumption for slow heating rates with small samples, however, for induction hardening cycles this may or may not be accurate. Using computer models, it is possible to predict the temperature dynamics of the sample, both radially and axially, during the thermal processing cycle (heating and cooling). O1 tool steel was utilized to characterize and model heating and cooling temperature gradients. Specimens instrumented with multiple thermocouples were induction heated and gas quenched. The test data and geometry were evaluated with 1- D and 2-D models to characterize transient temperature gradients. The goal of the modeling is to better characterize temperature corrections required when rapid heating and cooling processes are used to determine transformation behavior in induction hardenable steels.

Thermal fatigue is a dominant mechanism that causes premature failure in components exposed to high temperature. In order to extend the useful life of tools for hot work, studies have been conducted trying to understand the mechanisms involving thermal fatigue. Thus, different types of materials combined with different parameters of thermal and surface treatments have been investigated using thermal fatigue tests. This review addresses the main aspects of thermal fatigue as well as the main alternatives used to increase the resistance of the material to this type of failure.

M-42 is Molybdenum-series high speed steel used as a cutting tool material because of its hot hardness and toughness properties. With the better hot hardness and wear resistance, M-42 is one of the most widely used tool materials for cutting tools. These Molybdenum steels are heat treated conventionally in four steps viz., preheating, austenitizing, quenching along with two stages of tempering. The main step in heat treatment, austenitizing is done with the aid of salt bath furnace by heating the tool steel to the austenitizing temperature (1260°C) with three stages of preheating. This method is often a time consuming process with most of the time and energy utilized for the achievement of the required temperature. This study deals with the rapid heat treatment of the aforementioned M-42 steel samples by the action of microwaves from a hybrid microwave furnace. The quenching is done as of in a conventional method using a neutral salt bath maintained at a temperature of 550 °C. Comparison between the rapidly heat treated specimen and the conventionally heat treated specimen With similar dimensions is carried out. The tempering processes for both the specimens were carried out conventionally. Mechanical properties such as hardness, microstructure, etc., are compared between the conventional and the rapid heat treated specimens. Scanning electron microscopy was also taken to study the grain refinement of the microwave heat treated steel specimen at a higher magnification. The comparison between the properties and the microstructure revealed minute changes in mechanical properties of the rapid heat treated specimen and also resulted in the marked drop of the heating time and the energy saving thereby reducing the costs incurred for the heat treatment process.

In the recent years, there has been a remarkable increase in the use of deep cryogenic treatment (DCT) for enhancing performance of tool steels. It is a supplementary treatment where components are treated below subzero temperatures for several cryo-soaking hours. This paper focuses on to study the effect of deep cryogenic treatment and cryo-soaking time on microstructural and mechanical properties of AISI H-13 tool steel. Deep cryogenic treatment at different cryo-soaking time (16-48 hours) were applied and tool steel performance was analyzed by using mechanical, fatigue and wear testings. The microstructural evolutions during DCT were evaluated by using scanning electron microscope (SEM). It was observed that microstructural modifications like increase in carbide density, fine and uniform martensitic structure during DCT had significantly improved properties which were influenced by cryo-soaking time.

A study was conducted on a set of H13 steels to enhance their performance as matrices and pins. The steels were austenitized in a high-pressure vacuum furnace at 1015 °C for 180 minutes, followed by nitrogen quenching in a high vacuum (2 bar). Two tempering treatments were applied: one at 540 °C and another at 580 °C, each for 180 minutes, with subsequent nitrogen cooling to room temperature. The nitrocarburizing process was carried out in a liquid bath salt furnace at 580 °C for varying durations of 45, 60, 90, 120, 150, and 180 minutes to assess the impact of treatment time on the quality of the nitrocarburizing layer. Post quenching and tempering, the steels exhibited hardness values ranging from 550 to 570 HV. After nitrocarburizing, the surface hardness increased to between 740 and 810 HV, with a nitrocarburizing layer thickness of less than 14 μm. The microstructural evolution of the compound layer was analyzed using scanning electron microscopy and X-ray diffraction. The characterization revealed a continuous nitrocarburizing ε-Fe 2–3 (C,N) layer. Specimens treated for 45 to 60 minutes demonstrated superior wear performance compared to those treated for 90 to 180 minutes.

Since the invention of the vacuum furnace in the 1950s and up until the 1970s, its primary use was for annealing aerospace components. In the 1980s, vacuum equipment began to be used for heat treating tools and dies. By the 1990s, the need for faster quenching of high-alloy steels led to the development of vacuum furnaces capable of quenching at pressures up to 20 bar. Prior to this, only certain hot-work steels and a few tool steels with small cross-sections could be satisfactorily hardened in vacuum furnaces. Today, it is understood that simply increasing quenching pressure does not necessarily yield optimal results. Modern vacuum furnace technology allows for the precise design of the entire quench curve to maximize material performance while minimizing distortion. Continuous advancements and new concepts, such as multi-directional cooling systems, separate quenching chambers, and integrated cryo-cooling systems, have led to oxidation-free and low-distortion vacuum heat treatment for a wide range of parts and materials. This paper demonstrates how modern vacuum furnace designs and processes can improve quenching and cooling. It includes proven heat treatment results and examples from the international tool and die industry, which has been utilizing this technology over the past 25 years.

Usually bainitic microstructures exhibit good toughness and austempering is typically the preferred heat treatment when toughness is the primary requirement of the component. Several reports have shown such characteristics when compared to tempered martensite. High carbon steel may exhibit brittle characteristics but it is a good steel with respect to mechanical properties and wear resistance. The objective of this study was to compare the impact properties of AISI O1, a high carbon tool steel as VND in Brazil. This was done by comparing Charpy impact strength under different heat treatment cycles. Tempered martensite and bainite was obtained at 350°C after holding at temperature for 20, 40, and 60 minutes. Since hardness influences impact behavior, comparative studies were performed at the same surface hardness level. Results show a low absorbed energy for the austempered samples which for this temperature is independent of the holding time.

The use of high hardness surface layers can extend the life of components such as molds and dies by increasing their wear resistance. However, corrosion and oxidation resistance are also important to improve the durability of the components, especially for those that work under more demanding environments. In this work, samples of AISI H13 tool steel for hot work were borided by the pack cementation process, producing uniform and high hardness layers (1400-1800 HV). Afterwards the samples were subjected to a quasi-isothermal oxidation testing at 550 °C, the same working temperature of H13 steel in aluminum extrusion dies. Throughout the test, the mass gain of the untreated substrate, used for comparison, was 100%, while the borided sample treated at 900 °C for 2 hours had mass gain of 83% and the sample treated at 1000 °C for 4 hours presented a mass gain of 43%. The oxidation coefficients of the borided samples were similar, indicating similar oxidation kinetics but different from the untreated substrate.

Austempering, which produces a bainitic microstructure, is widely recognized as the preferred heat treatment when toughness is the primary requirement for a component. The literature contains numerous studies comparing the mechanical properties of tempered martensite with bainite of equivalent hardness. The majority of these findings demonstrate superior properties in bainitic microstructures. Bainite exists in two forms: upper bainite, which forms during isothermal transformation at higher temperatures (typically around 500 °C), and lower bainite, which develops at lower temperatures (approximately 350 °C, depending on the specific alloy steel). Lower bainite exhibits hardness values similar to tempered martensite and is preferred in applications where elastic characteristics are desired.

This article examines heat treatment processes for molds, dies, and tools fabricated from H11 and H13 steel and comprehensively analyzes valid standards based on NADCA, FORD, and GM requirements, highlighting the critical differences between these specifications. The research showcases a modern single-chamber vacuum furnace with a dynamic cooling system operating at high gas pressures of 15/25 bar, detailing its advanced performance capabilities and achieved cooling rates. The furnace's integrated dynamic cooling system enables programmable gas inflow direction changes and isothermal quenching, while an integrated simulator allows real-time prediction and tracking of the cooling process. Demonstrating the complexity of tool heat treatment, the study illustrates how advanced technologies such as vacuum nitriding and carburizing can be comprehensively executed in a single vacuum furnace cycle.

Die life is an important ingredient in cost of forgings, particularly in hot forgings. A number of surface hardening techniques are used to improve the die wear life. Surface hardening mainly constitutes surface preparation and its treatment to obtain desired properties. In this investigation gaseous ferritic nitrocarburizing was carried out on the DIN 1.2714(55NiCrMov7) steel that is used to manufacture dies for crankshafts and axle beams. The compound layer (White layer), diffuse layer, and core structure were identified using optical microscope. The effect of surface treatment (sand blasting) and process parameters like nitrogen and carbon activities on the formation of different layers during nitrocarburizing are reported and discussed in the paper. The wear rate with respect to sliding distance, sliding velocity and normal load are reported along with the analysis of wear mechanisms.