Machinability of medium carbon tin- bearing free cutting steel

Tin- bearing free cutting steel is environmentally friendly material. The test steel of 100mm in diameter with Sn of 0. 16 mass% by smelting in industrial frequency induction furnace and hot forging was prepared. Machinability experiments of the test steel using a stepless speed regulation lathe(C6140) was conducted. Besides, the distribution of tin, sulfur and manganese in the tested steel using secondary ion mass spectrometer was analyzed. The research results show that the coefficient of relative machinability of the test steel is 1. 75, the style of cutting chip mainly is C- shaped, in addition to this, there is a small amount of helical chip. Therefore, the test steel has excellent machinability, and it can meet the requirements of high speed machining. It is considered that grain boundary embrittlement caused by segregation of tin at ferrite grain boundaries, liquid metal embrittlement and lubrication action caused by low melting point of tin, are main reasons of the improvement of machinability.     

BN型易切削钢中夹杂物的控制及对切削性能的影响

汽车曲轴用钢42CrMo要求在不影响力学性能的前提下,具有较好的切削性。传统的钢种无法满足使用需求,通过在钢中添加B、N元素,并对钢中夹杂物进行控制,以满足性能要求。首先通过坩埚熔炼实验得到不同B、N含量的试样;其次利用FactSage软件计算出理想条件下不同B、N含量的钢液中各种夹杂物的析出量及析出温度;然后通过对试样设置不同的冷却方式和定向凝固实验,得到钢中BN夹杂物的形貌、尺寸及分布的影响因素;最后,通过切削实验研究了夹杂物对切削性能的影响因素,最终得到理想切削性能的BN型易切削钢。结果表明,尺寸较小而密度较大的BN夹杂物对钢的切削性能的改善作用更好。切削性较好的试样,其切削性能已达到与硫系易切削钢Y1215同等水平。     

Application of Thermodynamic Model for Inclusion Control in Steelmaking to Improve the Machinability of Low Carbon Free Cutting Steels

Oxide inclusions formed during steelmaking processes influence the machinability of steel products. At moderate and high cutting speeds, the tool life is dominated by chemical wear. However this wear can be suppressed by engineering exogenous and indigenous glassy oxide inclusions in steel. The present work demonstrates a method to engineer glassy oxide inclusions in a low carbon free cutting steel applying a new thermodynamic model for deoxidation control of steel based on slag‐melt as well as melt‐oxide inclusion equilibration. The model is used online in an industrial production line for the controlled production of glassy inclusions. These inclusions are shown to improve machinability by lubricating the tool‐chip interface during machining of the steel at high cutting speeds. Using an inclusion engineered work piece, the crater wear of an uncoated P10 tool is significantly improved and the tool life is tripled at cutting speeds in the range between 200 and 400 m/min. The industrial results show that thermodynamic modelling is a powerful tool to produce free cutting steels with consistently good machinability behaviour.     

Y45S20易切削钢的工艺优化

在Y45S20易切削钢试制过程中对硫含量、脱氧工艺、钢水温度、连浇温度及速度等关键工艺作了调整和改进，特别是在连铸大批量生产中对各工艺要点的控制以及对各主要成分的分期控制，使Y45S20易切削钢具有合理的成分分布，较好的力学性能和优异的切削性能。     

Active wear and failure mechanisms of TiN-Coated high speed steel and tin-coated cemented carbide tools when machining powder metallurgically made stainless steels

In this study, active wear and failure mechanisms of both TiN-coated high speed steel and TiN-coated cemented carbide tools when machining stainless steels made by powder metallurgy in low and high cutting speed ranges, respectively, have been investigated. Abrasive wear mechanisms, fatigue-induced failure, and adhesive and diffusion wear mechanisms mainly affected the tool life of TiN-coated high speed steel tools at cutting speeds below 35 m/min, between 35 and 45 m/min, and over 45 m/min, respectively. Additionally, fatigue-induced failure was active at cutting speeds over 45 m/min in the low cutting speed range when machining powder metallurgically made duplex stainless steel 2205 and austenitic stainless steel 316L. In the high cutting speed range, from 100 to 250 m/min, fatigue-induced failure together with diffusion wear mechanism, affected the tool life of TiN-coated cemented carbide tools when machining both 316L and 2205 stainless steels. It was noticed that the tool life of TiN-coated high speed steel tools used in the low cutting speed range when machining 2205 steel was longer than that when machining 316L steel, whereas the tool life of TiN-coated cemented carbide tools used in the high cutting speed range when machining 316L steel was longer than that when machining 2205 steel. formerly with the Laboratory of Engineering Materials, Helsinki University of Technology     

A New Pb-free Machinable Austenitic Stainless Steel

 In the present paper, the machinability tests were conducted by using various processing parameters on a CA6164 lathe with a dynamometer. The metallurgical properties, machinability and mechanical properties of the developed alloy were compared with those of an austenite stainless steel 1Cr-18Ni-9Ti. The results have shown that the machinability of the austenitic stainless steels with free-cutting additives is much better than that of 1Cr-18Ni-9Ti. This is attributed to the present of machinable additives. The inclusions might be composed of MnS. Sulfur and copper addition contributes to the improvement of the machinability of austenitic stainless steel. Bismuth is an important factor to improve the machinability of austenitic stainless steel, and it has a distinct advantage over lead. The mechanical properties of the free cutting austenitic stainless steel are similar to that of 1Cr-18Ni-9Ti. A new Pb-free austenitic stainless steel with high machinability as well as satisfactory mechanical properties has been developed.     

Characterization of Free Cutting Phase in Free Cutting Stainless Steel Containing High Copper

 The machinability of 4Cr13 steel was improved obviously by adding Cu and S. The effect of copper addition on the machinability of 4Cr13 was similar to that of sulphur addition. By means of SEM, EBSD, and HREM, the distribution and size of the free cutting phase in the steel 4Cr13Cu were studied. The results showed that the free cutting phase was copper rich phase. The copper rich phases dispersed in the steel and were determined to have about 10 nm in diameter. The content of copper in the copper rich phase was over 70%.     

铜改善高铬钢机械加工性能的机理

添加铜、硫可以明显提高高铬钢的机械加工性能,且铜、硫对高铬钢的机械加工性能的作用类似.通过高分辨透镜(HREM)和扫描电镜(SEM)对含铜高铬钢中的易切削相进行分析.研究发现,含铜高铬钢中的易切削相是大小为10 nm左右的石墨-铜复合相,该相均匀弥散地分布于含铜高铬钢基体中,该相中76.07％的原子是石墨碳,其余则为铜原子.在机械加工时,石墨-铜复合相的固体润滑膜能够附着在刀具的切削刃上,从而避免了含铜高铬钢与切削刃的直接接触,从而减少了切削刃的磨损,改善了高铬钢的切削性能.     

Effect of Sulfur and Zirconium on the Machinability and Mechanical Properties of AISI 1045 Steels

The effects of small increases of sulfur and addition of zirconium in conjunction with sulfur on the machinability and mechanical properties of laboratory-produced AISI 1045 steels have been investigated. Machinability was measured in terms of cutting energy per unit volume of metal machined. With increasing sulfur, there is a linear increase in sulfide volume fraction and improvement in machinability. Ductility parameters such as tensile reduction in area and impact shelf energy, however, significantly decrease with sulfur, particularly in the transverse direction. Addition of zirconium causes formation of manganese-zirconium sulfides and increased globularity. Although further improvement in machinability by zirconium addition is not evident, there is a significant improvement in transverse impact properties by zirconium addition for steels containing high sulfur. The study suggests that an optimum combination of higher sulfur for improved machinability and zironium for better impact properties yields a steel with acceptable machining and ductility criteria.     

Grain size of high-speed tool steels

Influence of the carbide population on austenite formation during hardening of high speed tool steels has been investigated. It was established that austenite grain size varies directly with the mean primary carbide size or interparticle spacing. The type of annealing treatment—temper annealing or transformation annealing—given prior to hardening has an additional effect on the subsequent austenite grain size. This effect is related to the characteristics of the secondary carbide population. Austenite grain refinement was found to significantly improve the performance of high speed steel tools operating under intermittent cutting conditions. The observed tool wear during intermittent cutting is explained in terms of a combination of mild wear and “microspalling” mechanism at the cutting edge.     

组织形态对718塑料模具钢切削性能的影响

通过热处理制备出具有回火马氏体组织、下贝氏体组织以及粒状贝氏体组织的718钢,利用光学显微镜、扫描电子显微镜、X射线衍射仪、万能拉伸实验机比较其显微组织及力学性能。同时借助高速铣削实验及光学轮廓仪,研究力学性能以及组织结构对切削性能的影响。结果表明,当切削速度低于145 m·min?1时,贝氏体组织类型比回火马氏体组织更易切削,切削贝氏体组织比切削回火马氏体组织的刀具使用寿命高30%～40%。当切削速度高于165 m·min?1时,马氏体组织发生了加工软化现象,刀具使用寿命提高,切削性能上升。粒状贝氏体组织加工表面因为严重的刀具黏附而出现背脊纹路,马氏体组织具有最佳的切削表面粗糙度。综合考虑之下,三种组织的综合切削性能从高到低排序为:下贝氏体组织、马氏体组织、粒状贝氏体组织,采用300 ℃等温淬火工艺可以有效提升718塑料模具钢的综合切削性能。      

粉末冶金烧结钢的加工性

通过烧结和在铣床上切削加工的实验，研究了添加硫化锰和氟化钙的烧结钢的加工性。结果显示，添加不同的改善切削加工性的第二相颗粒后的粉末烧结制品，其切屑形态有很大差异。添加硫化锰或氟化钙，其切屑变小，利于从孔中排出。在雾化前加入硫化锰的烧结制品，其加工性最好，1个d9．5mm的高速钢钻头可在其中钻凿532个总深13．51m的孔而毋需更换。硫化锰和氟化钙在混料过程中会发生团聚现象，降低了切削加工性。改善硫化锰和氟化钙的分布，将会改善切削加工性。     

Properties of through hardening bearing steels produced by BOF blowing metallurgy and by electric arc furnace with ladle metallurgy

Melting in EAF and BOF-TBM and different methods of aluminium deoxidation in the subsequent ladle treatment result in a similar degree of cleanness. With respect to micro-inclusions the air melted ingot and continuous cast steels achieve nearly the same level as remelted steels. Considering macro-inclusions there still remains a decisive difference: remelted steel is sure to be free from macro-inclusions, whereas some occasionally occur in air melted steel. The random test and metallographic evaluation systems do not allow uniform classification of the various steel groups. None of the applied methods can determine definite inclusion contents. The number and sizes of the evaluated types of inclusions only can define the statistical probability of their occurrence in a larger lot of heats. Up to now they cannot be related to the fatigue behaviour of the steels. Therefore, further investigation is necessary to reveal the effect of critical sizes and chemistry of the various inclusions on the fatigue behaviour. First tests reveal that the machinability seems to be governed by the carbide grain sizes more than by the sulphur contents in the investigated range of 0.003-0.015%. The comparison of test results in terms of cleanness and segregation shows that continuous casting should allow the same application as ingot casting.     

Experimental and Analytical Based Investigations on Machinability of High-Chrome White Cast Iron Using CBN Tools

High-chrome white cast iron (HCWCI) is one of the hardest metals used in the process and mining industries faces tough challenge in metal cutting. Focusing on this issue, influence of cutting parameters (e.g., cutting speed, depth of cut, feed rate) on machinability characteristics (e.g., cutting forces, surface roughness, material removal rate, machining power) of HCWCI has been investigated by experimentally and analytically using cubic boron nitride (CBN) cutting tools. Experimentation is carried out in conjunction with the Taguchi techniques and the influence of each cutting parameter of the process has been analyzed by analytical tools; analysis of variance, regression technique and artificial neural networks (ANNs). The study reveals depth of cut has the highest contribution on the cutting forces, and cutting speed on surface roughness and machining power. The confirmation test identifies both regression and ANN techniques are the most effective tools to evaluate machinability characteristics of HCWCI. Further, the CBN cutting tool exhibits excellent performance in machining of HCWCI.     

铜、硫元素对4Cr13不锈钢切削性能及耐腐蚀性能的影响

 利用车削试验研究了铜、硫元素对4Cr13不锈钢切削性能的影响,并用浸泡试验和极化曲线研究了铜、硫元素对4Cr13钢耐腐蚀性能的影响。研究结果表明：铜、硫元素均能提高4Cr13钢的切削性能,含铜4Cr13钢的切削性能达到了含硫4Cr13钢的切削水平。另外,铜元素还可提高4Cr13钢的耐腐蚀性能,而硫却致使4Cr13钢的耐腐蚀性能下降。     

Machinability of the high-strength corrosion-resistant high-ductility austenitic steel 06Kh22AG15N8M2F

The machinability of the high-nitrogen corrosion-resistant austenitic steel 06Kh22AG15N8M2F during turning is studied. The specific features of the structure of the surface layers in steel workpieces after turning are revealed. The cutting conditions that provide the lowest wear of VK8 alloy cutting tools upon turning are found: the cutting speed is 21–74 m/min, the feed is 0.15–0.60 mm/rev, and the cutting depth is 0.15–0.75 mm. The presence of a large amount of Cr₂N-type chromium nitrides in the structure of the steel annealed at 800°C for 2 h and a high nitrogen content in the austenite of the steel quenched from 1100°C increase the wear of the cutting tools. As to turning of the forged steel, the wear resistance of the cutting tools upon turning of the 06Kh22AG15N8M2F steel is higher than that upon turning of 08Kh18N10T steel, in which deformation martensite forms (in surface layers) during turning.     

CaSRE系超易切削钢的研究开发

在1.5t感应炉中用硅钙合金和稀土金属处理了含硫钢水,开发了一种新型环保易切削钢并进行了切削性能和力性测试,结果表明,钢材切削性能极佳,力学性能达到了国标中相应钢种的标准。借助于扫描电镜和能谱分析技术研究了钢中M n-RE-C a-S系复合夹杂物,切削过程中这种夹杂物在刀具前刀面上形成一层保护膜,减轻了刀具磨损,改善了切削过程。     

磁处理提升高速钢刀具切削性能的机理

利用自制的磁化装置对W6Mo5Cr4V2高速钢刀具进行磁化处理,并利用测量仪器分析对比不同磁化参数下高速钢刀具磨损以及工件加工质量的变化情况,并通过观察高速钢试样表面形貌和设计隔绝氧气切削和普通切削对比试验,探究刀具磁化后切削性能得到提升的机理。试验结果表明:磁化参数对磁化效果影响较大,且W6Mo5Cr4V2高速钢刀具最佳磁处理参数为30V、5 Hz、60s。磁场能促进微小磨屑的表面吸附,进而提高刀具的切削性能,且氧气的存在对工件表面粗糙度有一定的影响。磁化处理对高速钢残余奥氏体转变率的影响不是提高高速钢刀具耐磨性以及工件表面质量的主要原因。     

国内外易切削钢的现状和研究进展

易切削钢比普通碳素钢有较好的切削性能和更好的产品表面光洁度。随着自动化加工工业和汽车工业的发展,易切削钢的使用量不断增加。目前,国外普遍采用电弧炉二次精炼连铸流程生产易切削钢。工业化国家切削钢已形成标准化系列产品,并伴随连铸技术的广泛采用,使易切削钢具有均匀的切削性能。现有易切削钢种为易切削碳钢、渗碳钢、调质钢和不锈钢,并不断将易切削钢扩展到诸如模具钢、高锰钢、耐热钢、高工钢等钢类。在分析国内外易切削钢发展的基础上,讨论了易切削钢生产工艺、钢种的发展方向。     

硫化物改质对20MnCr5齿轮钢夹杂物和切削性能的影响

 齿轮钢广泛应用于汽车、机械等传动系统,易切削化是提高齿轮加工效率、降低制造成本的主要途径之一。提高钢中硫元素含量是改善齿轮钢切削性能的有效方式,然而过多的硫元素在轧制时会形成条带状MnS,增大钢的各向异性,因此需要对硫化物进行改制处理。分别采用Ca处理和Mg处理两种方式对20MnCr5齿轮钢进行硫化物改质,通过对力学性能、组织形态、夹杂物分布以及切削性能等表征,对比分析不同改制方式对材料的影响。结果表明,Ca处理和Mg处理后试验钢的强度和塑性保持一致,而Mg处理试样的晶粒尺寸较小,因而韧性较高。Ca处理试验钢中MnS夹杂物数量较多,长条状夹杂物比例相对较高;而采用Mg处理可以有效降低钢中夹杂物的数量,夹杂物平均尺寸有所增大,同时小长径比夹杂物数量增多,但是复合氧化物型夹杂物的数量也有所增加。在240~280 m/min条件下进行了干切削试验,结果表明两种试验钢均出现前刀面磨损、后刀面磨损和边界磨损,其中Ca处理试样的刀具磨损较为严重,同时在较高切削速度下出现了积屑瘤和崩角现象,而Mg处理试样则具有更长的刀具使用寿命,对切削速度的敏感性也较低。分析可知,Mg处理后钢中存在较多的大尺寸球状硫化物夹杂物,提高了应力集中效应,更有利于改善切削性能,因而改制效果更好。