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.     

Improved Machinability in Hard Milling and Strategies for Steel Development

The synergetic advantage of tailoring alloyed steels to improve their machinability in the hardened (30 ∼55HRC) state is the focus here. Results from milling tests and systematic study of steel microstructure and tool wear mechanisms using high resolution microscopy (FEG-SEM) and EDS clearly indicates that traditional machinability improvement treatments are not always adequate here. In high alloyed hot working steels, suitable primary carbides distribution could be better than inclusion modification. In low alloyed steels secondary carbide density appears to be critical and correlates well with machinability. The study also points to strategies for steel development and their efficient hard milling.     

Resistance to Oxidation at Elevated Temperatures of a Number of Alloy Steels

Abstract

A wide range of steels, extending from a plain carbon steel to high chromium-nickel, austenitic types and some nickel-based alloys, have been subjected to a cyclic oxidation test in natural gas combustion products at various temperatures. Resistance to oxidation can be expressed in terms of a breakdown temperature which provides a convenient parameter by means of which the behaviour of steels and alloys may be compared. On this basis, the beneficial effects of additions of chromium of up to 30% are confirmed, as are additions of silicon and/or aluminium to chromium steels. Cobalt, copper, molybdenum, vanadium, tungsten, niobium, titanium and nitrogen have comparatively little effect. Manganese appears to be detrimental when added to chromium steels and carbon can be in some circumstances. Nickel can enhance oxidation resistance in some circumstances but is detrimental in others. The presence of sulphur in free-machining, stainless steels appears to counteract the effect of a higher-thannormal manganese content.     

预硬型塑料模具钢718的切削性能和夹杂物研究

对预硬型塑料模具钢ASSAB718和国产的GC718的切削加工性能进行了对比性研究，并结合Thermo-Calc软件对钢中非金属夹杂物进行了分析。结果表明，由于钢中夹杂物的影响，ASSAB718钢的切削加工性能优于GC718钢；运用Thermo-Calc软件可实现对钢中夹杂物的预测。     

Effect of the pearlite structure of structural steel on its machinability

Factors affecting the machinability of automatic steels containing sulfur and lead, namely, the microstructure of the pearlite and the content of sulfur and lead additive, are investigated. It is shown that satisfactory machinability of lightly loaded parts can be provided under certain cutting conditions by producing an optimum morphology for the pearlite in the steel and increasing the sulfur concentration without adding lead. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 29–31, January, 1997.     

The effect of thermal cycles and welding technology on the structure and mechanical properties of joints made in HCM12 and HCM12A steels

Abstract

Previously developed and practically employed low-carbon low-alloy high-strength steels for welded structures are broadly classified into: 1) steels containing few alloying elements and manufactured with an as-hot-rolled or normalised structure (such as eg SM steels); 2) thermomechanically processed steels with a reduced content of alloying elements (such as eg TMCP steels); 3) steels strengthened by addition of alloying elements and conditioning treatment (eg high-strength low-carbon low-alloy steels such as HT780 steel). Previously used 800 MPa class steels for welded structures, while manufactured by the technique noted in (3), face problems such as weldability, cost, recyclability, etc. To overcome these problems, research has been increasingly focused on the development of 800 MPa class high-strength steels for welded structures with mild steel-equivalent contents of alloying elements.^1–3 The basic concept underlying high strengthening involves the ferrite grains being ultra-refined to a grain size of less than 1 ìm in accordance with the Hall–Petch rule.^4–8     

锡对提高材料切削性能作用的研究

高切削性能的易切削钢含有铅,然而铅及其氧化物有毒,使其应用受到限制.作者开发了用锡代铅的易切削钢,该新产品对环境无危害.研究结果表明,锡提高钢切削性能的原理主要是其在铁素体晶界、硫化锰界面处的偏聚,以及锡的熔融金属脆性.     

Study on the machinability of resulfurized composite free-cutting steels

The machinability of S, S-Ca, S-RE, and S-RE-Ca system resulfurized composite free-cutting steels were investigated, where RE is rare earths, mostly cerium. The experimental results showed that in the low cutting speed range (≤35 m/min), the S-RE system free-cutting steel had better machinability than the others and that the S-RE-Ca system free-cutting steel exhibited the best machinability at high cutting speeds. A protective layer capable of preventing diffusion wear was formed on the rake face of a P30 tool when S-RE-Ca system free-cutting steel was machined in the cutting speed range of 120 to 160 m/min.     

Effect of lead on the properties of structural steel

Conclusions The effect of lead on the fatigue strength of structural steels and their susceptibility to embrittlement during heating is due to the difference in the coefficient of thermal expansion of lead particles and iron with heating of lead-containing steels and to the mosaic stresses resulting from this, which induce fracture and prefracture, and also the influence of liquid lead as a surface-active substance with regard to the steel. These characteristics of the behavior of lead particles in steel in the cutting zone at high strain rates are accompanied by an increase of temperature and promote better machinability of the steel in comparison with the steel without lead. On the basis of the results we do not recommend lead-containing steel for parts subject to fatigue and having high strength _b<1200–1400MPa) or for parts heated to 200–500° in the course of operation.Scientific-Research Institute of Metallurgy, Chelyabinsk. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 6–8, November, 1980.     

Evaluation of machinability in turning of microalloyed and quenched-tempered steels: Tool wear,statistical analysis,chip morphology

The machinability of microalloyed steel (30MnVS6) and quenched-tempered (QT) steels (AISI 1045 and AISI 5140), at different cutting condition, is presented in the paper. An experimental investigation was conducted to determine the effects of cutting speed, feed rate, hardness, and workpiece material on the flank wear land and tool life of coated cemented carbide inserts in the hard turning process. It was tried that for any test condition the hardness of these steels became almost identical by using appropriate heat-treatment processes. The statistical analysis was used for evaluation of different factors on cutting forces. Chips characteristics and chip/tool contact length were also investigated. The different sections (shear plane, microcrack, thickness and edge) of the chip were examined by scanning electron microscope (SEM). Shear planes and microcracks of the chips in microalloyed steel show that the chips of microalloyed steel are regular and discontinuous. Crater wear of the tools was studied by using video microscope in turning process. The results showed that the tool life and machinability of the microalloyed steel is better than the QT steels at identical cutting condition.     

Drilling of X2CrNi 19 11 stainless steel with hiped NiTi coating

This study investigated suitability of TiN and TiCN-coated cemented carbide tools in the machining of conventionally produced stainless steel with HIPed (Hot Isostatic Pressed) NiTi coating. Near-equiatomic nickel–titanium alloy (NiTi) has many attractive material properties, such as pseudo-elasticity and shape memory effects, which result into beneficial engineering properties, e.g. as cavitation resistant coatings in addition to its well-known shape memory properties. Stainless steels are often considered to be poorly machinable materials; materials with high elasticity are also difficult to machine. In drilling stainless steel with a pseudo-elastic coating material, machinability difficulties are caused by the high strength and work hardening rate of steel and the pseudo-elastic properties of the coating material. The machinability was studied by analyzing cemented carbide drills and chips. The interface between stainless steel and NiTi coating was examined with SEM (scanning electron microscopy) and EDS (energy dispersive spectroscopy) analysis. The effect of feed rate on chip formation and tool wear was analyzed. The cutting tests indicated that cutting speeds of 50 m/min, a feed rate of 0.1–0.2 mm/rev, and solid carbide drills can be applied, from a machinability standpoint. A HIPed pseudo-elastic coating decreases machinability. When effective cutting speeds and feed rates were utilized, optimal tool life was achieved without a decrease in coating properties.     

The effect of machinability on thermal fields in orthogonal cutting of AISI 4140 steel

The micro-scale temperature fields in the cutting of two AISI 4140 steels with different machinability ratings were measured. A custom infrared microscope was constructed; each pixel was calibrated separately to reduce measurement uncertainty. Orthogonal cutting experiments were performed on a high speed machining center with surface speeds up to 500 m min⁻¹ and uncut chip thicknesses ranging from 0.1 mm to 0.3 mm. The results indicate that in certain critical regions of the thermal field, improved machinability correlates with significant reductions in temperature that exceed measurement uncertainties. Such micro-scale temperature measurements will help to design materials with further improved machinability.     

Dissimilar friction welding of induction surface-hardened steels and thermochemically treated steels

Results on friction welding of surface-hardened steels are analyzed based on experiments using induction-hardened steels as pivotal component, joined with quench-hardened steels and steels thermochemically treated by carburization and nitriding, respectively. Higher axial pressure needs to be applied, in order to fully expunge the hardened layers from the joining plane. A smooth surface for the burr, without cracks, can be obtained for adequate welding parameters and the burr can be subsequently removed without major risks, immediately after the friction welding process ends. For joining an induction hardened C55 steel with a quenched hardened C55 steel, the maximal friction pressure has to be limited to about 200 N/mm², in order to avoid materials separations in the centre of the joint. High axial pressures lead to good mechanical characteristic for friction welding an induction-hardened 34CrNiMo6 steel with a carburized 16MnCr5 steel. Friction welding of an induction-hardened C55 steel with a C45 nitrided steel showed that an increase of the friction upset distance to 6 mm favours the complete expulsion of the nitride debris, with positive effects on the quality and mechanical properties of the joint.     

The effect of oxygen in resulfurized steels—Part II

Part I of this two-part paper, which appeared in the June issue, covered the effects of deoxidation with silicon, boron, aluminum, or carbon (under vacuum) on the machinability and microstructure of low-carbon resulfurized steels containing nominally 0.1%C-1.0%Mn-0.25%S. Deoxidation reduced machinability and it was concluded that the removal of oxygen was directly responsible. Deoxidation was found to suppress the formation of large random sulfide inclusions so that sufficiently strong deoxidation, such as with aluminum, caused the steel to solidify with a characteristic eutectic structure in which the inter dendritic sulfide inclusions were comparatively small. Consequently, the inclusions in the rolled steel were small and machinability was reduced.     

Relationship between machinability index and in-process parameters during orthogonal cutting of steels

Temperature and plastic strain maps were obtained during orthogonal cutting of two steels with different machinability indexes using a high-speed dual-spectrum (visible and infrared) and visible spectrum cameras, respectively. Surface and internal temperature were compared by simultaneous measurements with a thermal camera and thermocouples embedded in the flank face of the cutting tool. A cause–effect relationship between the machinability index and the analyzed in-process variables is determined. This will help with developing a practical tool for the scientific design of different machinability index materials, as well as an alternative method to time-consuming and expensive standardized machinability tests.     

Tool life and machinability models for drilling steels

Four models for drilling steels are developed from an extensive machinability experiment. General purpose HSS drills were used for drilling 0.12% carbon steel. Predictive models were developed for tool life, thrust and torque on the drill, and surface roughness of the holes drilled. The research consisted of a laboratory experiment involving four independent variables; cutting speed ranging from 162 to 330 mm/s (32 to 65 sfpm), feed ranging from 0.0635 to 0.381 mm/rev (0.0025 to 0.015 ipr), drill diameter ranging from 7.54 to 14.68 mm (0.2969 to 0.5781 in.), and steel hardness ranging from 146 to 330 BHN. The experiment was designed as a central composite design with 30 treatment combinations. Tool life varied from 3.98 to 265.5 min. Full second-order models, containing 15 terms, were simplified to reduced models. Model fits ranged from an R-square of about 0.68 to about 0.92.     

Energy-efficient steels for motor laminations

Motors use over 60% of all electricity generated, and their losses exceed 200 × 10⁹ kW.hr/year. A significant part of this loss results from eddy currents and hysteretic processes in the motor laminations. These so- called core losses cost motor users about $3 × 10⁹/year. The metallurgy and economics of using various steels are considered, with emphasis on 5- to 125- hp polyphase induction motors. A lower core loss steel, even though it is more expensive, is economically justified most of the time when the operating costs of motors are considered. Impurities must be minimized, and steels can now be made with the principal impurities being less than 30 ppm. Further reduction of core losses depends on using the best steel processing equipment available, production of a consistently low carbon content so that decarburizing during the final anneal can be eliminated, developing a better understanding of the relation between material properties and performance in motors, and an increased willingness by the motor users to pay more for better motors that are cheaper to own in the long run. Work sponsored by the Electric Power Research Institute, Contract No. RP3070-24.     

Vermeidung der Wasserstoffversprödung vergüteter Stähle bei galvanotechnischen Prozessen durch thermische Legierungsbildung

Avoidance of hydrogen embrittlement of high strength steels during electroplating processes by thermal alloying Low alloyed high strength steels are often electroplated by metal layers protecting against corrosion. For ultra high strength, quenched and tempered steels with yield strengths > 1000 Nmm^?2 embrittlement by hydrogen being envolved during the electrochemical pretreatment as well as metal deposition has to be avoided. More over the corrosion protecting layers should form a diffusion barrier for hydrogen which can be formed during corrosion processes under special circumstances. In this paper two problem solutions including thermal alloying processes will be discussed. Plating the steel substrate with a nickel layer subsequently annealed at a temperature above 800°C in an inert gas atmosphere an austenitic iron-nickel-alloy at the boundary is formed, being a high efficient diffusion barrier for hydrogen. Further zinc plating is improving the corrosion resistance avoiding at the same time pitting corrosion problems. Plating the steel substrate with a copper and a following nickel layer on top and annealing it at the temperature of 800°C a highly corrosion resistant copper-nickel-alloy is formed showing excellent barrier behaviour for hydrogen diffusion. In both cases hydrogen being formed during the plating process itself and penetrating into the base metal does not lead to embrittlement as it is effusing during the annealing procedure.     

2000 MPa grade low alloy,ultrahigh strength multiphase steels

Abstract

The benefit of steels with a combination of high strength and good ductility has attracted generations of researchers to work in this area. The strength of current Chinese structural steels typically falls in the range 400–1000 MPa. Higher strengths are desired to achieve the aims of saving energy and raw materials and protecting the environment, through reducing the weight of steel parts, or of improving safety standards. Thus, there is an urgent need to develop ultrahigh strength steel.     

Isothermal and Step Isothermal Oxidation of Copper-Containing Steels in Air at 980–1220°C

The oxidation and copper enrichment behaviors of several copper-containing mild steels under isothermal and step-isothermal conditions at 980–1220^°C in ambient air, and the effects of nickel additions, are examined. The oxidation kinetics for all steels does not obey the parabolic law because of the formation of blisters in the scale. At 980^°C, decreased parabolic oxidation kinetics is observed, whereas at 1120 and 1220^°C, the oxidation kinetics exhibits an undulating pattern. High nickel content and high oxidation temperature are two prerequisites for the occlusion mechanism to operate during steel oxidation. For the low nickel steel, a planar scale-steel interface develops at all temperatures, and a copper phase is always seen to form and spread along the scale-steel interface. For the high nickel steels, a planar scale-steel interface develops at 980 and 1120^°C, but at 1220^°C, the scale-steel interface becomes rugged and the copper-rich phase is occluded into the scale. Introduction of a 980^°C and/or 1220^°C oxidation step significantly affects the copper enrichment behaviors of all steels normally exhibited at 1120^°C.