Microstructure and Mechanical Properties of Nodular Cast Iron Produced by Melted Metal Die Forging Process

The microstructure and mechanical properties of nodular cast iron produced by the melted metal die forging process （MMDF for short） were experimentally researched.The main obtained results are ： the nodular cast iron produced by this process can be machined as easy as traditional one only if holding at the remained temperature for 4 h ; its strength and plasticity are obviously higher than those of traditional ones ; the graphite size arrived at grade 8 , and the graphite spheroidizing arrived at grade 1 or 2 , but a streamline molded distribution of the graphite slightly appeared.Both of the strength and plasticity increased with the pressure when the pressure holding time was larger than its critical value.A new way to produce high properties nodular cast iron was provided.

Preparation of Ni60-WC Coating by Plasma Spraying, Plasma Re-melting and Plasma Spray Welding on Surface of Hot Forging Die

In order to produce the hear-resistant inner layer of hot-forging die, the plasma spraying and plasma re-melting and plasma spray welding were adopted. Substrate material was W6Mo5Cr4V2, including 10%, 20%, 30% tungsten carbide （WC） ceramic powder used as coating material to obtain different Nickel-based WC alloys coating. Micro-structure and micro-hardness analysis of the coating layer are conducted, as well as thermophysical properties for the coating layer were measured. The experimental results show that the coating prepared with 70%Ni60, 30%WC powder has the best properties with plasma spray welding, in which the micro-hardness can achieve 900HV, meanwhile it can improve the thermal property of hot-forging die dramatically.

STUDY ON DESIGN TECHNIQUES OF A LONG LIFE HOT FORGING DIE WITH MULTI-MATERIALS

A new design technique for the long life hot forging die has been proposed. By finite element analysis, the reason .for the failure of hot forging die was analyzed and it was concluded that thermal stress is the main reason for the failure of hot forging die. Based on this conclusion, the whole hot forging die was divided into the substrate part and the heat-resistant part according to the thermal stress distribution. Moreover, the heat-resistant part was further subdivided into more zones and the material of each zone was reasonably selected to ensure that the hot forging die can work in an elastic state. When compared with the existing techniques, this design can greatly increase the service life because the use of multi-materials can alleviate the thermal stress in hot forging die.

Ni60-SiC Coating Prepared by Plasma Spraying, Plasma Re-melting and Plasma Spray Welding on Surface of Hot Forging Die

In order to produce the hear-resistant inner layer of hot-forging die, plasma spraying and plasma re-melting and plasma spray welding were adopted. Substrate material was W6Mo5Cr4V2, including 10%, 20%, 30% SiC ceramic powder used as coating material to obtain different Ni-based SiC alloys coating. Micro-structure and micro-hardness analysis of the coating layer were followed, as well as thermophysical properties for the coating layer were measured. The experimental results show that the coating prepared with 70% Ni60, 30% SiC powder has best properties with plasma spray welding, in which the micro-hardness can achieve 1100 HV, meanwhile can improve the thermal property of hot-forging die dramatically.

Carbide Coating Preparation of Hot Forging Die by Plasma Processing

To meet the performance requirements of hot forging die heat resistant layer, the Ni60-SiC coating, Ni60-Cr3C2 coating, and Ni60-WC coating were prepared using W6Mo5Cr4V2 as substrate material with 30%SiC, 10%Cr3C2, 30%WC powder by means of plasma spraying and plasma spray re-melting and plasma spray welding, respectively. Microstructure of each carbide coating was analyzed, micro-hardness was tested, and mainly thermal parameters of coating were detected. The experimental results show that using plasma spray welding, the performance of 70%Ni60/30%SiC powder is the best, and its micro-hardness can achieved 1100HV, showing good thermal-physical property.

Fatigue Behavior of Cemented Carbide Die in Cold Forging of Steel

The fatigue behavior of cemented carbide die under service load in the multistage cold forging of steel was investigated. It was found that the fatigue cracks do not initiate at the stress concentration position and the crack initiation position can be classified to three types. The crack initiation position can be predicted by FEM only when the plastic deformation of the die is considered.

Effects of Lanthanum on Mechanical Properties of 5CrNiMo Forging Die Steel

The alteration of the strength, hardness and impact ductility of 5CrNiMo steel using three different additions of RE La element is studied in this paper. The mechanical properties of 5CrNiMo steel with RE La additions are be compared with that of the 5CrNiMo steel on the same heat-treatment condition without RE La element addition. The results show that the strength, hardness and impact ductility of 5CrNiMo steel will be improved obviously when the content of RE La element is proper, and as the content of RE La element is 0.033%(mass fraction), the 5CrNiMo steel has the best mechanical properties.

Hot-forging Die Cavity Surface Layer Temperature Gradient Distribution and Determinant

Based on the car front-wheel-hub forging forming process of numerical simulation, the temperature gradient expression of forging model cavity near the surface layer was got ten, which illustrates that the forging temperature gradient is related to forging die materials thermal conductivity, specific heat and impact speed, and the correlation coefficient is 0.97. Under the different thermal conductivity, heat capacity and forging speed, the temperature gradient was compared with each other. The paper obtained the relevant laws, which illustrates the temperature gradient relates to these three parameters in a sequence of thermal conductivity 〉 impact speed〉 specific heat capacity. To reduce thermal stress in the near-surface layer of hot forging cavity, the material with greater thermal conductivity coefficient and specific heat capacity should be used.

The Invalidation Analysis of a Working 5CrMnMo Forging Die and Ways of Precaution

The paper introduced the 5 CrMnMo steel, including the chemical composition, the heat treatment technology, the forging die working condition, and the invalidation form （such as the cavity arris wear, the cavity subsidence, the cold and the heat fatigue crackle）. Then gave some precautions for prolonging the mould life by improving the heat treatment technology.

Simulation-Based Investigation of Crack Formation in Forged MB15 Magnesium Alloy

In the process of riveting an MB15 forging die,cracks were discovered emerging along the longitudinal direction and near the riveting hole.Through fracture analysis,microscopic observation,energy spectrum analysis,metallographic examination,and hardness test,the properties and causes of the cracks are discussed.The results indicate that the cracking type is intergranular brittle cracking,occurring during the forging stage.Furthermore,the recrystallization at the crack site is found to be incomplete,which is attributed to the low deformation temperature.

Microstructure and Thermal Physical Parameters of Ni60-Cr_3C_2 Composite Coating by Laser Cladding

To satisfy performance and long life requirements for hot forging die,Ni60-Cr3C2 composite coatings were prepared on the high-speed steel W6Mo5Cr4V2 using laser cladding technology.Laser clad coatings with different ratios of Ni60：Cr3C2 were investigated by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,energy-dispersive X-ray analysis（EDX） and micro-hardness tester,respectively.Specific heat capacity and thermal conductivity were measured by Laser Thermal Constant Meter.Thermal expansion coefficient and elastic modulus were measured by Dynamic Mechanical Thermal Analyzer and Electro-Hydraulic Servocontrolled Testing System,respectively.The results indicated that Ni60＋50wt% Cr3C2 composite coating had dense and homogeneous structure,as well as a metallurgical bonding with the substrate.With the increase of Cr3C2 content,volume of chromium-containing compounds in the composite coating increased,microhardness increased and microstructure refined.The thermal physical parameters results showed that Ni60＋50wt% Cr3C2 composite coating was overall worse than W6Mo5Cr4V2,but had a higher hot yield strength to alleviate hot fatigue and surface hot wear of hot forging die during hot forging and thus improve the service life of hot forging die.

Mechanism of Cracking Resistance of Hardfacing Specimens of Steel 5CrNiMo Improved by Rare Earth Oxide

The cracking morphology of the hardfacing specimens taken from steel 5CrNiMo was observed. Meanwhile, the residual stress fields were measured and simulated. Based on experiment mentioned above, the improved structure and modified inclusion in hardfacing metal with rare earth （RE） oxide were analyzed. The results show that, the hardfacing crack is initiated from the coarse dendritic crystal grain boundary, inclusions and coarse austenite grain boundary in the HAZ and propagated by the residual stress existing in the center of the hardfacing metal and HAZ. The primary columnar grain structure can be refined by adding RE oxide in the coating of the electrode. The inclusion in the hardfacing metal can be modified as well. Meanwhile, if the martensite transformation temperature is decreased, the largest value of the residual tensile stress in the dangerous region can be reduced.

Numerical Analysis of Unconventional Forging Process of Hollowed Shaft from Ti-6Al-4V Alloy

This paper presents theoretical analysis of unconventional forging process of hollowed shaft from Ti-6Al-4V alloy in a three-slide forging press.This method in comparison with other metal forming methods allows for obtaining of hollowed products.The designed process is verified theoretically by means of numerical simulations based on finite element method with assumption of 3D state of strain.The following factors are considered in the analysis:material flow kinematics,strain distribution,temperature distribution and force of process.On the basis of results,it is stated that the application of designed technology allows for obtaining of a product of assumed quality.A comparison is made between material consumption in analyzed process and material consumption in typical metal forming methods,also in used at present technology of shaft manufacturing by machining only.It is stated that the application of forging in the three-slide forging press allows for a considerable decrease of manufacturing costs due to material savings and decrease of labor consumption of operations at finishing.