Hot Steel Research Articles

Tool life improvement for stamping dies in the coining process

ABSTRACT High temperature and high-speed pressing in minting operations lead to the failure of coin-stamping dies. As a result, new coining tools were required more frequently leading to lower operational productivity and higher production costs. This research has examined the effects of materials and surface coating selections on the tool life of the stamping dies in the coining process. The aim of this research was to explore the possibility of extending the tool life of stamping dies. The three kinds of materials under study were alloy tool steel, cold working tool steel, and hot working tool steel. Additionally, Titanium Nitride (TiN) and Chromium Nitride (CrN) surface coating materials using the Physical Vapour Deposition (PVD) process were investigated. The experiment results revealed that the hot working steel yielded the highest tool life of up to 1,300,000 coins, followed by cold working steel at 900,000 coins, and alloy tool steel at 600,000 coins. The CrN PVD coating provided up to more than 400,000 coins compared to TiN PVD coating on hot working tool steel.

An innovative strategy against oxide spallation of hot formed steels

Hot forming is a prominent technique to produce lightweight automotive steels. However, the generation of a weakly adhering oxide scale during hot forming and the subsequent post-processing of the scale pose a great threat to the shape precision of the product. Here, we propose a cost-effective solution to the spallation issue by incorporating minor silicate-molybdate additives into the rinse following pickling. The pre-deposited film serves as an effective barrier against high-temperature oxidation. Our innovative strategy enables the formation of an oxide scale that sticks to the substrate and paint layer, potentially eliminating the necessity for scale removal in industrial settings.

Tribological behaviour of DIN 1.2740 hot working tool steel during mandrel mill stretching process

This study evaluates the tribological properties of DIN 1.2740 hot tool steel against Super Cr13 martensitic stainless steel at 700°C. The results show that the coefficient of friction (COF) ranged from 0.15 to 0.63, indicating moderate frictional interaction. The wear rate of DIN 1.2740 was observed to be low, suggesting good resistance to wear at high temperatures. The complex surface oxide layer that formed on the pin’s top surface, significantly reducing the COF and acting as a solid lubricant at elevated temperatures. The oxide layer was also fragile and unable to withstand the high sliding velocities and high loads. The steel exhibited a high surface roughness when subjected to increasing normal loads and increasing sliding velocities.

The effect of cryogenic treatment on a high Co bearing DIN 1.2888 steel used as die in hot forging process

Abstract Hot work steels used as dies in metal forming processes must endure harsh conditions, typically achieved through a martensitic structure. However, retained austenite can persist after martensitic transformation, negatively impacting mechanical properties. Cryogenic treatment (CT) refines martensite, reduces retained austenite, and increases fine carbide density, thus enhancing performance. DIN 1.2888, a hot work tool steel with high cobalt content (~10%) and low carbon content (~0.2%), is less studied concerning the effects of CT. The objective of this study was to investigate how cryogenic treatment affects the mechanical and microstructural properties of DIN 1.2888 steel. Samples underwent conventional heat treatment (HT) and CT at -100, -140, and -180°C for 6 hours, followed by double tempering. Various analytical methods, including X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and Vickers Microhardness tests, were used to examine the samples. Wear mechanisms were evaluated through pin-on-disc tests under different loads, and impact toughness was measured both at room temperature and the working temperature of dies (350°C). Results indicated that lowering the cryogenic treatment temperature resulted in a slight increase in hardness values from 507HV for the heat-treated sample to 529HV for the sample treated at -180°C. Additionally, the impact toughness improved significantly, with values rising from 12.35J for the heat-treated sample to 23.44J at 350°C for the cryogenically treated sample at -180°C. Wear rates also decreased by approximately 50%, particularly at higher cryogenic treatment temperatures. The improvement in wear resistance was attributed to finer carbide precipitation and a more homogeneous distribution of carbides. These findings suggest that deep cryogenic treatment has a positive effect on DIN 1.2888 steel by decreasing retained austenite and increasing fine carbide density, leading to enhanced mechanical properties and extending the lifespan of the steel in die applications.

Simulation of the Evolution of Phase Composition and Austenite Grain Size upon Multi-Pass Hot Deformationof Low-Alloy Steels

The paper presents a model for predicting the structural characteristics and phase composition of low-alloy steels upon hot rolling in the multi-pass deformation mode. The model considers recovery, dynamic, primary, dynamic and static recrystallization of grains, and the normal grain growth, as well as nucleation (including accelerated nucleation during deformation), growth or dissolution, and coarsening of carbonitride particles. The comparison between the calculated results and the experimental data available in the publications shows a satisfactory agreement.

Evolution mechanism of Mo-rich, B2-NiAl, and Cu-rich particles under aging and its influence on strength and elongation in a maraging hot work steel SDH88

A novel maraging hot work steel, SDH88, is developed to achieve a balance between ultimate tensile strength (UTS), yield strength (YS), and elongation by combining nanometer-scale precipitates of B2-NiAl, Cu-rich, and M2C carbide. The peak-aging sample demonstrates a YS of ∼1281.8 MPa, a UTS of ∼1665.9 MPa, and an elongation (EL) of ∼17.5 % at room temperature. The microstructure and precipitation changes from peak aging (8h) to over-aging (48h) were examined using different techniques. Under peak aging condition, the precipitates consist of four nanoparticles: 9R-Cu, B2-NiAl, Cu-NiAl, and M2C carbides. However, at over-aging condition, the type of particles changes and consist of B2-NiAl, M6C, Laves phases and FCC-Cu. This study systematically investigates the precipitation evolution of Mo-rich, B2-NiAl, and Cu-rich particles from peak-aging to over-aging conditions. The high YS at peak aging condition is attributed to high precipitation strengthening of ∼553.3 MPa and dislocation strengthening of about 430.8 MPa. The number densities of NiAl (<3.8 nm) particles are more than that of Cu particles which indicates that the NiAl nanoparticles are the dominant strengthening phase. Finally, this work clearly demonstrates that the new alloy composition design allows the application of aging steels in die casting steels with great advantages and potential for obtaining balanced mechanical properties through the systematic study of the aging process and mechanism of precipitation evolution. Proposing a new approach for designing hot work die steel without quenching treatment during mold processing.

Tailored Casting and Hot Rolling Temperatures for the Preparation of Hot Stamping Steel Thin Strip

Tailored Casting and Hot Rolling Temperatures for the Preparation of Hot Stamping Steel Thin Strip

Analysis of Rolling Force and Friction in Hot Steel Rolling with Water‐Based Nanolubrication

Analysis of Rolling Force and Friction in Hot Steel Rolling with Water‐Based Nanolubrication

Spotting ignition of plastic foam by a fast-moving hot metal particle

Spotting ignition involves dynamic interaction between fuel bed and hot particles, but the scientific understanding of the ignition by a fast-moving hot particle is still limited. Herein, a hot steel particle with various horizontal velocities, temperatures, and sizes is shot to ignite vertically oriented low-density expandable polystyrene foam. A high-speed particle can directly get embedded into the foam to achieve flash-point, fire-point, or no ignition, while a low-speed particle bounces away from the foam without ignition. Results show that for a particle of 1150 °C, its minimum velocity for embedding is 12.00 m/s. Such a critical velocity for hot-particle embedded or ignition slightly decreases as particle temperature increases. Minimum ignition temperature of these high-speed particles is 200 °C higher than that of near-static or with a low free-fall velocity, due to the shorter residence time and insufficient to produce a flammable mixture. Moreover, when the particle is neither too slow to bounce away nor too fast to get embedded, it will be partially embedded on the sample surface to burnout the fuel, posing the biggest fire hazard. It deepens our knowledge of the complex interaction between hot moving particles and insulation foam to reduce spotting fire risk for building façade.

Role of oxidation in thermal fatigue damage mechanisms and life of X38CrMoV5 (AISI H11) hot work tool steel

Hot work tools steels, which are submitted to severe solicitations in service, are often damaged by thermal fatigue and corrosion. Interrupted Thermal Fatigue experiments were performed on X38CrMoV5 tool steel between 100 and 650 °C, in air and reduced oxygen partial pressure atmospheres after primary or secondary vacuum. A thermal and thermo-mechanical analysis by finite element method was carried out to estimate the strains and stresses undergone by the axisymmetric disc-shaped specimen during thermal cycling. The morphology, structure and phase composition of the oxide layer were analysed using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. It was shown that the thickness, homogeneity, structure, and compacity of the oxide multilayer formed on the specimen changed depending on test atmosphere. In air, crack initiation and propagation were strongly assisted by oxidation, leading to reduced fatigue life compared to inert atmospheres. Steel softening was highlighted in sub-surface, whatever the test atmosphere.

Continuous cooling transformation behavior of V microalloyed hot-bent X80 pipeline steel

Abstract Continuous cooling transformation (CCT) behavior of a vanadium-microalloyed hot bent pipeline steel was studied by using Gleeble 3800 thermal simulation machine, and the hot-rolling technique of the tested steel was designed. Acicular ferrite and granular bainite can be observed with the cooling speeds ranging from 1~ 40 °C/s. Higher cooling speed leads to grain refinement. The yield strength is 570 MPa. The ultimate tensile strength (UTS) is 757 MPa. The fracture elongation is 22.50 %. The low temperature toughness at -40 °C is 325 J. The tested steel has both high strength and good low temperature toughness, and meets the mechanical performance requirement of API Spec 5L specification for X80 pipeline steel.

In-Situ Observation Combined with Numerical Simulation of the Solidification and Subsequent Cooling Process for Hot Stamping Steel

In-Situ Observation Combined with Numerical Simulation of the Solidification and Subsequent Cooling Process for Hot Stamping Steel

Nanoindentation Creep Behavior of Additively Manufactured H13 Steel by Utilizing Selective Laser Melting Technology.

Nowadays, H13 hot work steel is a commonly used hot work die material in the industry; however, its creep behavior for additively manufactured H13 steel parts has not been widely investigated. This research paper examines the impact of volumetric energy density (VED), a critical parameter in additive manufacturing (AM), and the effect of post heat-treatment nitrification on the creep behavior of H13 hot work tool steel, which is constructed through selective laser melting (SLM), which is a powder bed fusion process according to ISO/ASTM 52900:2021. The study utilizes nanoindentation tests to investigate the creep response and the associated parameters such as the steady-state creep strain rate. Measurements and observations taken during the holding phase offer a valuable understanding of the behavior of the studied material. The findings of this study highlight a substantial influence of both VED and nitrification on several factors including hardness, modulus of elasticity, indentation depth, and creep displacement. Interestingly, the creep strain rate appears to be largely unaltered by these parameters. The study concludes with the observation that the creep stress exponent (n) shows a decreasing trend with an increase in VED and the application of nitrification treatment.

Jet impingement quenching of a hot steel plate using a surfactant added CuO nanofluid

The mechanical properties of the steel are significantly impacted by the cooling rate. In the steel industry, cooling rates on the run-out table customizes the microstructure of the steel plate, which enhances plate strength. In this research, the AISI 304 steel plate underwent cooling from a starting surface temperature of 900 °C. The effect on the jet cooling of a steel plate has been investigated using surfactant-added CuO nanofluid and methanol-added CuO nanofluid. It was found that using surfactant-added CuO nanofluid and methanol-added CuO nanofluid as a coolant, the cooling rate increased by 32.09 % and 38.66 %, respectively, in contrast to pure water.

A Novel Design to Enhance the Tribological Properties of High‐Cr Hot Work Die Steel via Trace TiC Ceramic Nanoparticles

Excellent wear properties can improve the service performance and service life of high‐Cr hot work die steels. Herein, an innovative method is proposed to introduce TiC nanoparticles into the matrix of high‐Cr hot work die steels, and the effects of TiC nanoparticles on the microstructure and wear resistance of high‐Cr hot work die steels are investigated. In isothermal spheroidizing and quenching and tempering heat treatments, the TiC nanoparticles refine the granular pearlite, tempered martensite, and precipitates, which are attributed to the improved nucleation rates by increasing the number of heterogeneous cores. In sliding wear tests, the nanoparticle‐reinforced high‐Cr hot work die steels show higher wear resistance under the temperatures of 20 and 400 °C. The better wear properties of high‐Cr hot work die steels are because the substrates are strengthened and toughened, the dislocations are hindered, the mating areas are partially separated, and external loads are withstood by nanoparticles. This work shows new prospects for the development of high‐Cr hot work die steels with excellent wear performance.

Full-Process Numerical Simulation of Flow, Heat Transfer and Solidification for Hot Stamping Steel Manufactured via Thin Slab Continuous Casting Process

Full-Process Numerical Simulation of Flow, Heat Transfer and Solidification for Hot Stamping Steel Manufactured via Thin Slab Continuous Casting Process

EXPERIMENTAL INVESTIGATION ON ONE-WAY ABRASIVE FLOW MACHINING ON HOT WORK STEEL

Abrasive flow machining (AFM) is a process where a semi-solid abrasive-laden media is forced to flow through the internal passages of a workpiece under pressure. In high-resolution work, increased accuracy and faster smooth surface polishing work with the developed motorized AFM prototype. This research presents the effect of the clearance of specimen tools for surface roughness (Ra) of SKD 61 (AISI H13) hot work steel related to AFM. This research experimented with half-spherical specimens. AFM experiments are performed to identify the improved surface roughness when applied to the polishing specimens. Specimens were prepared by being turned, hardened, and polished with sandpaper from number P180 to P1200 and measured with an original value of Ra compared with the final value of Ra at the end of the process. The experimental prototype uses a unidirectional motor drive system different from previously developed machines. The process parameters are as follows: a pressure (p) of 1, 2, and 3 bar, cycle time (t) of 10, 15, and 20 min., an abrasive particle size (Al2O3) of 5.0 μm in Silicon Oil (50 % concentration by weight), hardness of specimens 45±2 HRC, etc. The experimental results show that under these conditions, the average surface roughness of specimens was decreased from an original value of Ra 0.057 to 0.042 μm. The greatest response surface (RSM) was obtained at a pressure of 3 bar and a time of 20 minutes. The result allows for better precision control and further development in industrial applications.

Non-destructive evaluation of subsurface corrosion on hot steel angle sections embedded in concrete and its repair by cement slurry and nitozinc coating

Non-destructive evaluation of subsurface corrosion on hot steel angle sections embedded in concrete and its repair by cement slurry and nitozinc coating

Mechanical and tribological properties of Ti1-xZrxB2 coatings deposited by magnetron sputtering on hot work steel

Low fracture toughness is a common problem encountered by many researchers in the application of pure TiB2 coatings. To improve their properties, a convenient and useful method is the use of doping, so this study proposes the deposition of TiB2 enriched with Zr on a steel substrate. The objective of the research was to investigate the impact of Zr addition to TiB2 coatings on both their mechanical and tribological properties. Four coatings with varying compositions (pure TiB2; TiB2 doped with 3, 6, and 10 at.% Zr) were deposited using magnetron sputtering from TiB2 and Zr targets. The coating structures were analyzed by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Nanoindentation, scratch test, and ball-on-disk test were used to determine the mechanical and tribological properties. In most cases, only two factors have a significant impact on the mechanical and tribological properties of the Zr-doped coating. Firstly, a change in the preferred orientation of the coating from (102)(111) to (100) results in increased hardness and wear resistance. Secondly, a reduction in crystallite and column size enhances ductility and fracture toughness by impeding or altering the direction of crack propagation. Based on the study, one can conclude that the optimal Ti1-xZrxB2 properties were obtained for 6 at.% Zr content.

Design of PSO controller for real-time non-reversible operation of PMBLDC motor drive system in hot steel rough rolling applications

Design of PSO controller for real-time non-reversible operation of PMBLDC motor drive system in hot steel rough rolling applications