Influence of different plasma nitriding treatments on the wear and crack behavior of forging tools evaluated by Rockwell indentation and scratch tests

Forging tools are often showing short lifetimes compared to cold forming tools e.g. for sheet metal forming. This is based on the process conditions where high local surface temperatures are alternating with chilling conditions due to the spray cooling with water based cooling lubricants. The resulting thermal shock is provoking fatigue of the tool material in the near surface regions. Crack initiation and crack growth due to thermal shock exposure then causes chipping of the tool steel material in the surface regions. These are starting points for extensive wear.Hardness and wear resistance of tool surfaces at elevated temperatures can be dramatically enhanced with nitriding pretreatments. This has become state-of-the-art for hot forming tool steels in many forging applications. With inappropriate adjustments of the nitriding parameters a decrease of the ductility can occur and will reduce the crack resistance of the tool surface especially under thermal shock conditions.The hot working steel DIN-1.2367 (X38CrMoV5) is currently one of the most often used chromium-molybdenum tool steels in the field of forging. Exemplary for this material is the influence of the nitriding parameters like temperature, nitrogen supply and plasma parameters on the nitriding depth, the maximum hardness and the crack sensitivity will be discussed.Nitrided samples will be investigated with methods developed for the adhesion measurement of hard coatings. It could be shown that this is also appropriate for a qualification of the crack sensitivity of tools. Comparative application tests in the production of automotive components show the influence on the wear behavior and lifetime of forging tools in an industrial environment.     

Chip formation and tool wear in turning of aluminum-alloyed UHC-steels

Aluminum-alloyed ultra-high-carbon steels (UHC-steels) display outstanding mechanical properties combined with a reduced density compared to conventional steels. Consequently, these steels show high potential for industrial applications. A widespread use of UHC-steels containing aluminum depends strongly on efficient machining processes. Since material processing has been restricted to laboratory scale until recently, only few empirical values exist on machining. This paper is focused on the chip formation and tool wear in external turning of aluminum-alloyed UHC-steels. The mechanical loads on the tool are presented and compared to C70MnVS4, which is commonly used for powertrain components. Furthermore, recommendations for optimized cutting tools are given. The results indicate that adhesive wear and chipping are the predominant tool wear mechanisms due to high cutting temperatures and the distinct microstructure of the investigated UHC-steel.     

Solid particle erosion behaviour of 13Cr–4Ni and 21Cr–4Ni–N steels

The 13Cr–4Ni martensitic stainless steel (termed as 13/4 steel and popularly known as CA6NM steel) is currently being used for fabrication of under water parts in hydroelectric projects. There are, however, several maintenance problems associated with the use of this steel. A 21Cr–4Ni–N nitronic steel (termed as 21-4-N steel) has been developed as an alternative with the specific aim of overcoming these problems. A comparative study has been made on the erosion behaviour of as cast 13/4, and as cast and hot rolled 21-4-N steels by means of solid particle impingement using gas jet. It is observed that the hot rolled 21-4-N nitronic steel possesses excellent resistance to erosion followed by as cast 21-4-N and 13/4 steels. The austenitic matrix of the hot rolled 21-4-N steel possesses high hardness coupled with ductility, high tensile toughness and work hardening ability, which result in higher erosion resistance. The erosion damages are in agreement with studies of eroded surfaces on scanning electron microscope (SEM).     

用高氮钢制造复杂高强度零件(英文)

High performance components, e.g., fasteners, nowadays are usually made out of cold forged and heat treated steels like steel 1.5525 (20MnB4). To overcome the problems of heat treatment, e.g., low surface quality, new workpiece materials for cold forging should be found to achieve the needlessness of heat treatment after cold forging. One possible material is given by high nitrogen steels like steel 1.3815 (X8CrMnN19-19). Due to the high strain hardening of these materials the process and tool design for an industrial batch process are challenging and should be conducted by FE-simulation. The numerical results show that, high strength tool materials, like PM-steels or cemented carbides, in most cases, are inevitable. Additionally to the selection of suitable tool materials, the tool layout should be developed further to achieve a high loadability of the tools. The FE-models, used for process and tool design, are validated with respect to the materials’ flow and occurring forming force to assure a proper design process. Also the comparison of strength of components made out of steel 1.5525 in quenched and tempered conditions and steel 1.3815 in strain hardened condition is done. The results show that the component made of steel 1.3815 has a significantly higher strength than the component made of steel 1.5525. This shows that by the use of high nitrogen steels a high performance component can be manufactured by cold forging.     

Evaluation of layer adhered on PCBN tools during turning of AISI D2 steel

Polycrystalline cubic boron nitride (PCBN) tools have high abrasion resistance and are thus suitable for application in the machining of steels with a high volume fraction of primary carbides in their microstructure. These tools are usually applied in the machining of steels with hardness above 45–50 HRC and in the case of application to steels with hardness below 45 HRC, the formation of an adhered layer on the rake face of the tools often occurs. This paper reports a study on the impact of the layer adhered on PCBN tools during the turning of AISI D2 steel, with 35 and 50 HRC. The microhardness and microstructure of the adhered material were determined, as well as the tool wear based on volumetric wear parameters. The layer adhered on the PCBN tool rake face has the same chemical elements as the machined steel alloy. Its microstructure is oriented in the direction of the chip flow and the primary carbides were fragmented. For the sample with 35 HRC the amount of material adhered (W_AM) on the rake face of the PCBN tool was approximately 360% higher than the steel with 50 HRC. The material layer adhered on the PCBN tool rake surface in the case of the 35 HRC steel acts as an edge (assuming the cutting function), while for the 50 HRC steel, the adhered layer intensifies the adhesion wear mechanism through spalling on the tool rake face. The results obtained provide important information for the selection of materials and grades for the development of new cutting tools.     

The influence of the microstructure of hardened tool steel workpiece on the wear of PCBN cutting tools

Due to the recent developments of advanced cutting tool materials in the superbarasive family, such as cubic boron nitride (CBN) tools, the interest in cutting hardened steels has increased significantly. High flexibility and ability to manufacture complex workpiece geometry in one set up is the main advantage of hard turning compared to grinding. The focus of this study is to investigate the performance and wear behavior of CBN tools in finish, dry turning of four different hardened steels, treated to the same hardness R_c = 54. The following four materials were machined: X155CrMoV 12 cold work steel (AISI D2), X38CrMoV5 (AISI H11) hot work steel, 35NiCrMo16 hot work steel and 100Cr6 bearing steel (AISI 52100). A large variation in tool wear rate was observed in the machining of these steels. The tool flank grooves have been correlated to the microstructure of these steels, namely the presence of various carbides. The chip study reveals that there is presence of different amounts of white layers in machining these steels.     

Performance evaluation of cryogenically treated tungsten carbide tools in turning

This paper describes a study on the effects of cryogenic treatment of tungsten carbide. Cryogenic treatment has been acknowledged by some as a means of extending the tool life of many cutting tool materials, but little is known about the mechanism behind it. Thus far, detailed studies pertaining to cryogenic treatment have been conducted only on tool steels. However, tungsten carbide cutting tools are now in common use. The main aim of this study is to analyze the differences in tool performance between cryogenically treated and untreated tool inserts during orthogonal turning of steel. This will aid in the quest for optimal cutting conditions for the turning of steel using these inserts, and will also enhance the understanding of the mechanism behind the cryogenic treatment of tungsten carbide, and the changes in its properties after cryogenic treatment. In the process of ascertaining these findings, it was shown in this study that under certain conditions, cryogenic treatment can be detrimental to tool life and performance. It was also shown that cryogenically treated tools perform better while performing intermittent cutting operations.     

Korrosionsbeständigkeit von CrNi-Stahlguß (Typ 18/9 bzw. 18/13) mit erhöhtem Siliciumgehalt in konzentrierten Salpetersäurelösungen

Corrosion resistance of chromium nickel cast steel (types 18/9 and 18/13) within increased silicon content in concentrated nitric acid solutions The corrosion resistance of CrNi cast steel, types 18/9 and 18/13, with different carbon (0.035-0.12%) and silicon (appr. 4%) contents was investigated in nitric acid (27-96%) eventually containing Cr⁶⁺ ions between 25 and 100°C. In this connection mechanical properties and structure of the above cast steels were determined, too. It has been found that in the case of 80% nitric acid solutions and of nitric acid solutions of higher or lower concentrations but containing Cr⁶⁺ ions the cast steel must have a silicon content of appr. 4% together with a carbon content as low as possible. The results of the laboratory tests have been confirmed unter industrial conditions.     

Effect of boron concentration on the corrosion resistance of cast B‐bearing steel in molten zinc

The microstructures, mechanical properties and corrosion resistance in molten zinc of five kinds of cast B‐bearing steels containing X wt% B ‐ 0.8 wt% Si ‐ 1.0 wt% Mn ‐ (1.0～2.0) wt% Cr ‐ (0.3～0.5) wt% C (X = 0.50, 1.00, 1.50, 2.00, 2.50) were studied. The effects of boron concentration on microstructure and mechanical properties of cast B‐bearing steels have been investigated by optical microscopy (OM), X‐ray diffraction (XRD) analysis, hardness and impact tester. The evaluation of corrosion resistance in molten zinc of cast B‐bearing steel is calculated from the slopes of mass loss versus dipping time and surface area of sample at 480 °C. The results showed that boride volume fraction and hardness increased and the impact toughness of cast B‐bearing steel decreased with the increase in boron concentration. The corrosion rate of cast B‐bearing steels decreased and corrosion resistance in molten zinc increased with the increase in boron concentration. Moreover, the corrosion rate of cast B‐bearing steels decreased with the increase in temperature of molten zinc.     

Wear behavior of Al2O3/Ti(C,N)/SiC new ceramic tool material when machining tool steel and cast iron

Design, fabrication and application of ceramic cutting tools are one of the important research topics in the field of metal cutting and advanced ceramic materials. In the present study, wear resistance of an advanced Al₂O₃/Ti(C,N)/SiC multiphase composite ceramic tool material have been studied when dry machining hardened tool steel and cast iron under different cutting conditions. Microstructures of the worn materials were observed with scanning electronic microscope to help analyze wear mechanisms. It is shown that when machining hardened tool steel at low speed wear mode of the kind of ceramic tool material is mainly flank wear with slight crater wear. The adhesion between tool and work piece is relatively weak. With the increase of cutting speed, cutting temperature increases consequently. As a result, the adhesion is intensified both in the crater area and flank face. The ceramic tool material has good wear resistance when machining grey cast iron with uniform flank wear. Wear mechanism is mainly abrasive wear at low cutting speed, while adhesion is intensified in the wear area at high cutting speed. Wear modes are dominantly rake face wear and flank wear in this case.     

高强度焊接铸钢性能的研究

分析对比了国外焊接结构铸钢的化学成分和力学性能，以碳、锰元素为主配制了适宜碳当量的焊接铸钢。采用特定的冶金方法，严格控制铸钢硫、磷杂质含量，对铸件施以强韧化处理，从而得到了高强度、高塑性、高韧性、高可焊性和表面质量的铸钢件。该类铸件已成功地应用于大跨度、大面积钢结构屋面。     

Direct laser deposition of Cu alloy on forming tool surfaces—Process window and mechanical properties

Direct laser deposition offers a widespread spectrum of applications. Creating functional surfaces for forming tools is one of them where inexpensive material for the main tool body is complemented layer by layer with a second material to tune the desired properties and shape. Investigations on coating mild tool steel with copper alloy have been carried out to outline the chances and challenges in this cost effective way of producing forming tools for processing stainless steels, e.g. 1.4301. This paper reports on experimental investigations showing the influence of the absolute angle of the tool surface and the relative angle between surface and laser beam/powder nozzle on the process window and the mechanical properties that can be obtained.     

Machinability of BN free-machining steel in turning

In the past few years, extensive researches have been done to improve the machinability of work materials in order to increase productivity and reduce the effect on the environment. To satisfy these demands, various free-machining steels have been researched and developed. One of them is BN free-machining steel that contains hexagonal boron nitride (h-BN). However, the machinability was not stable. In this study, machining tests were carried out to clarify the machinability of steels and appropriate chemical composition of work material and tool material to achieve high efficient machining. Tested work materials were plane carbon steel JIS S45C and BN free-machining steels. The JIS S45C was used as the standard. The tool wear in turning BN free-machining steel was smaller than that in turning standard steel. In case of turning BN1 with P30 at 200, 300 m/min, the wear progress rate of flank wear and crater depth were about half as much as that in turning standard steel. BN free-machining steel showed slightly lower cutting temperature and smaller cutting force in comparison with standard steel at the tested cutting speeds. Al and N were detected as a layer at the tool wear region of P grade carbide tools after turning BN free-machining steel at high cutting speed. It is thought that one of the main reasons of outstanding machinability of BN free-machining steel is that the deposited layer containing Al and N acts as diffusion barrier at the tool–chip interface. In turning larger Al content BN-added steel with higher Ti content cutting tools, a larger wear reduction was observed. Therefore, it is said that not only added BN but also appropriate Al is necessary in work material.     

Composition,microstructure and mechanical properties of boron containing multilayer coatings for hot forming tools

The tribological conditions of hot forming processes are much different from those at room temperature. Thus classical wear-resistant coating like CrN, CrAlN, TiAlN in most cases are not sufficient for hot forming tools in industrial applications.Additionally the use of lubricants is limited, thermal shock conditions and the increase of sticking work piece material are leading to severe wear.This paper presents examples for ternary boron based Ti–B–N gradient coatings in specific multilayer designs obtained through plasma enhanced chemical vapor deposition. After a thorough characterization of the chemical composition by Auger electron spectroscopy, the microstructure by X-ray diffraction and the mechanical properties by microindentation and small-angle cross section nanoindentation, the coatings were applied onto hot forming tools made from DIN 1.2367 tool steel. The coated tools were tested in hot forging of AISI 1043 raw parts in an automatic press and have been compared in terms of adhesion and wear resistance. In this study an optimum design has been found which significantly reduces sticking of work piece material and wear. This allows an efficient production without interruptions for a reworking of the tools and enables to increase the process reliability paired with a longer tool life.     

Three-body Impact Corrosion-Abrasion: Studying for Low Carbon High Alloy Liner in Ore Grinder

The impact-corrosion-abrasion resistance of the low carbon high alloy steel, which can be used for mill lining under impact-corrosion-abrasion condition, are tested in laboratory by means of a new kind of experimental facility. The industrial trial run in the same condition has also been completed. The results show that the new alloy containing 0.2 wt.% carbon, 9 wt.% chromium, and 2 wt.% nickel is consisted of lath martensite entirely, and is more than two times superior to Mn13 cast steel in impact-corrosion-abrasion resistance. Spelling is the leading wear mechanism in impact-corrosion-abrasion condition for this alloy, which is lighter than that of high manganese steels because of its better hardness-toughness match.     

Properties and rational use of low-alloy high-speed steels

Conclusions Of the investigated low-alloy high-speed steels 11R3AM3F2 steel is closest to R6M5 steel in service characteristics and then R2M5 and 11M5F.However, 11R3AM3F2 steel has poorer grindability than R6M5 steel and therefore its use in place of more highly alloyed steels is technically and economically desirable only for tools of simple form not requiring large amounts of grinding (saws for metal, cutters, etc.).R2M5 steel may be a replacement for R6M5 steel for various tools in machining of comparatively easily machinable materials (low-alloy and carbon steels, gray iron, aluminum and copper base nonferrous metals, etc.).11M5F steel, with its basic properties at the level of R2M5 steel, is characterized by a high tendency toward decarburization, oxidation, and mixed grain size in heat treatment, which requires high-quality hot working and heat treatment of the billets and tools for rational use of it.ÉK41 and ÉK42 steels are significantly inferior to the above steels in all production characteristics and may not be considered as fully equivalent replacements for R6M5 steel. Narrow areas of use in which the reduction in life of the tool will not be significant may possibly be found for them. However, even such a use of these steels does not lead to economy in material and financial resources since it significantly complicates operation of the tool services.In contrast to ÉK41 and ÉK42 steels, 11M5FYuS steel is promising together with R2M5 steel.Ukrainian Scientific-Research Institute for Special Steel. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 51–55, May, 1988.     

Use of hypereutectoid high-speed steel 11M5F for the production of cutting and cold-stamping tools in the Avtovaz Joint-Stock Company

The development of low-alloy high-speed steels that reduce the production cost of cutting tools and dies can present practical interest for plants and small enterprises manufacturing tools for their special purposes. The present paper gives the results of an investigation of hypereutectoid low-alloy high-speed steel 11M5F and a widely used steel of grade R6M5. The basic and technological properties of these steels are compared, and the results of industrial tests of cutting, thread-rolling, cold-stamping tools and tools for semihot deformation operating under various conditions are described. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 7–10, May, 1997.     

铸造热锻模具钢的研究与应用

简述了精铸热锻模具国内外应用状况,对铸造模具钢的研究进展进行了研究。铸造热锻模具钢的开发研究对铸造热锻模的应用是至关重要的,铸造热锻模具钢的研究大致分为三个阶段,第一个阶段主要是直接采用商用锻造模具钢;第二阶段,是在原锻造模具钢的基础上采用微合金化,或加入单元素合金化,提高某一方面的性能;第三阶段是以性能要求为基础,结合铸态金属的性能特点及铸造工艺要求,进行全面的合金化设计,该类铸造模具钢更能满足热锻模的要求,具有高的性能和寿命。同时指出了当前精铸模具应用中存在的问题,并提出了建议。     

Evaluation of factors influencing deep cryogenic treatment that affect the properties of tool steels

Deep cryogenic treatment (DCT) of tool steels is used as an additive process to conventional heat treatment and usually involves cooling the material to liquid nitrogen temperature (−196 °C). This kind of treatment has been reported to improve the wear resistance of tools. In this study, the Taguchi method was used to identify the main factors of DCT that influence the mechanical properties and the wear resistance of the powder metallurgically produced cold-work tool steel X153CrVMo12 (AISI D2). Factors investigated were the austenitizing temperature, cooling rate, holding time, heating rate, and tempering temperature. In order to study the significance of these factors and the effect of possible two-factor interactions L₂₇(3¹³), an orthogonal array (OA) was applied to conduct several heat treatments, including a single DCT cycle directly after quenching prior to tempering. The results show that the most significant factors influencing the properties of tool steels are the austenitizing and tempering temperatures. In contrast, the parameters of deep cryogenic treatment exhibit a lower level of significance. Further investigations identified a nearly constant wear rate for holding times of up to 24 h. The wear rate reaches a minimum for a longer holding time of 36 h and increases again with further holding.     

Hard turning in continuous and interrupted cut with PCBN and whisker-reinforced cutting tools

PCBN (polycrystalline cubic boron nitride) is the most widely used material for tools employed in hardened steel turning applications due to its high hardness, wear resistance and thermal stability. However, its high costs severely limit its use. Alumina-based ceramics reinforced with whiskers, an alternative and less expensive material for these tools, has been used successfully in turning interrupted surfaces. The objective of this work is to investigate the conditions under which PCBN and ceramic tools can promote optimal results in the turning of hardened steel with continuous and interrupted surfaces. These tools were used in the radial turning of hardened steel with three types of surfaces: continuous surfaces and surfaces with 4 and 8 interruptions. The results indicated that, in continuous turning, the longest tool life was achieved using PCBN, but similar tool longevity was attained in interrupted turning using both PCBN and ceramic. In terms of roughness, the PCBN tools showed better results for continuous and interrupted surfaces.