Effects of elemental Sn on the properties and inclusions of the free-cutting steel

A new environment-friendly free-cutting steel alloyed with elemental Sn （Y20Sn） was developed to meet the requirements of machinability and mechanical properties according to GB/T8731--1988. The machinability of the steel is enhanced by the segregation of elemental Sn at grain boundaries. The effect of Sn segregation on intergranular brittle fracture at normal cutting temperature from 250℃ to 400℃ is confirmed. The formation mechanism of main inclusions MnS is influenced by the presence of Sn and the attachment of Sn around MnS itself as a surfactant, and this mechanism also explains the improvement in machinability and mechanical properties of the steel. In the steel, the relevant inclusions are mainly spherical or axiolitic, and are uniformly distributed in small volume. Such inclusions improve the machinability of the steel and do not impair the mechanical properties as well. Experimental results demonstrate that the appropriate content of Sn in the steel is 0.03wt% to 0.08wt%, and the remaining composition is close to that of standard Y20 steel.

Influence of cold deformation on microstructure,mechanical properties,and corrosion resistance of high-sulfur free-cutting 316LS stainless steel

In this study,the influence of plastic deformation produced by cold rolling at reduction ratios ranging from 10% to 80% on the microstructure,mechanical properties,and pitting corrosion behavior of high-sulfur freecutting 316 LS austenitic stainless steel was investigated. The results indicate that slipping is the predominant effect and that sulfide inclusions extend along the rolling direction during the cold deformation of 316 LS. The strong austenite stability of 316 LS results in the formation of only a small quantity of deformation-induced martensite. The experimental results reveal that the strength,hardness,and yield ratio increased with increases in the reduction ratio,mainly due to work hardening,whereas the elongation decreased drastically,due to the combined effect of the work hardening and brittleness caused by the numerous sulfide inclusions. Electrochemically active sites on the surface of316 LS increased with an increased reduction ratio,which caused an increased current fluctuation in the passive zone. This also caused the breakdown potential（ E_b） near the pitting zone to exhibit a gradual increase in the zigzag current shift to the left on the polarization curves. The E_b of 316 LS decreased with increases in the reduction ratio,mainly due to the extended sulfide inclusions,the increased dislocation density,and the deformation-induced martensite content.

Analysis on composition and inclusions of ballpoint pen tip steel

Ballpoint pen tip steel, a super free-cutting stainless steel, exhibits excellent corrosion resistance and good machining properties. In this study, inductively coupled plasma spectroscopy, metallographic microscopy, and scanning electron microscopy were used to determine the elemental contents in five ballpoint pen tips and their components, morphologies, and inclusion distributions. The results showed that the steels were all S–Pb–Te super free-cutting ferritic stainless steel. The free-cutting phases in the steels were mainly Mn S, Pb, and small amounts of Pb Te. Mn S inclusions were in the form of chain distributions, and the aspect ratio of each size inclusion in the chain was small. The stress concentration effect could substantially reduce the cutting force when the material was machined. Some of the Pb was distributed evenly in the steel matrix as fine particles（1–2 μm）, and the rest of the Pb was distributed at the middle or at both ends of the Mn S inclusions. The Pb plays a role in lubrication and melting embrittlement, which substantially increases the cutting performance. Pb Te was also usually distributed in the middle and at both ends of the Mn S inclusions, and Te could convert the sulfides into spindles, thereby improving the cutting performance of the steel.

Superior machinability of steel enhanced with BN and MnS particles

The strategy that replacing part of MnS with BN was proposed in order to decrease the sulfur content in sulfur based free-cutting steel. The effects of BN and MnS inclusions on the microstructure and machinability of the steel were systematically investigated. The results show that most of the BN and MnS inclusions exist individually in the steel and only a small amount of them are in a composite state form- ing either isolated particles or clusters of particles. In the case of multi-phased steel, the theoretical calculation predicts that the volume of large BN particles should be 0.7 times of the volume of large MnS particles. The machinability of this type of BN and MnS alloy steel over a wide range of cutting speeds ranging from a low speed appropriate for drilling to a high speed appropriate for turning is confirmed as being equal to or superior to that of an MnS reference steel, even though the sulfur content in the composite steel is only half that of the MnS steel. The aptitude for cutting effect of 240 ppm nitrogen and 115 ppm boron in the composite steel is demonstrated to be equivalent or even better than 1000 ppm sulfur in MnS free-cutting steel.

锻造齿轮用钢20MnCrS5HH开发生产实践

山东寿光巨能特钢设计开发了保淬透性结构钢20MnCrS5HH钢种。通过工艺优化改善,精准成分设计、调整,经过炼钢、轧钢工艺进一步优化,该钢种经过渗碳热处理后,强度、韧性较高且淬透性好,具有良好的切削加工性能,综合力学性能优异,完全满足了客户订单的需求。客户经调质处理后,加工成大截面零部件或采用渗碳后加工成小齿轮,达到了工件设计性能的最佳值。

Application of tellurium in free-cutting steels

Te is widely used in iron and steel industry. After adding a certain amount of Te in the steel, many physical and chemical properties can be improved. As a free-cutting element, a small amount of Te can significantly improve the machinability of steel. The existing form of Te in the steel, the modification law of MnS inclusion by Te and the influence rule and mechanism of Te on the machinability of steel are summarized and expounded in detail, providing a reference for further study and development of Te-containing free-cutting steels.

Effects of sulfur addition methods and Ca-Si treatment on the microstructure and properties of 30MnVS

The effects of sulfur addition methods and Ca-Si treatment on the microstructure and properties of free-cutting non-quenched and tempered steel 30MnVS were investigated by using optical microscopy, SEM and tensile test methods. The results show that sulfur addition methods influence the morphology of sulfides and the properties of 30MnVS slightly. Ca-Si treatment is beneficial for the formation of complex sulfides which normally have oxide cores, therefore, improving the distribution of sulfides in the tested steel and enhancing its toughness. The two methods, pyrite addition during LF process and S wire feeding during VD process, slightly influence the morphology and distribution of sulfides and the properties of 30MnVS; Ca addition not only promotes the nucleation of sulfides on the cores of calcium aluminate inclusions, but also creates modification effect on MnS, reducing the relative plasticity and hot deformability of sulfides during hot rolling process, thereby reducing the length/width value of sulfides and improving their distribution, and significantly enhancing its mechanical properties, in particular, the impact toughness increased by 30%.

Effect of Free-cutting Additives on Machining Characteristics of Austenitic Stainless Steels

The machinability tests were conducted by using a YD-21 dynamometer on a CA6161A lathe.The experiments were conducted to determine the effect of free-cutting additives on machining characteristics of austenitic stainless steels.The conventional austenitic stainless steel 1Cr18Ni9Ti（steel A） and the free cutting austenitic stainless steel（steel B） were prepared.The results have shown that machinable inclusions were composed of MnS and CuO,and they might be also Ti4C2S2.The presence of Bi in the inclusion was detected by the atom map and electro-probe microanalysis（EPMA）,which might be one of the most important factors to improve the machinability of austenitic stainless steels.The cutting forces for steel B were lower than those of steel A at various cutting speeds;the abrasion depth of the flank of the tool for steel B was less than that of the steel A under the same cutting conditions.The machinability of austenitic stainless steel was visibly improved by adding free-cutting additives,such as S,Cu and Bi.Ultimate tensile,yield strength,and total elongation values of the free cutting austenitic stainless steel were improved due to the addition of these free-cutting additives.

锰硫比对1215MS易切削钢力学和切削性能的影响

通过理论计算、扫描电子显微镜、三维腐刻技术、拉伸试验和切削试验等方法,探究了锰硫比对1215MS易切削钢中硫化物析出特性,及其对钢的力学性能和切削性能的影响。结果表明:钢中硫化物的吉布斯自由能随着锰硫比的减小而降低,其形核率和尺寸则增大;相比锰硫比较高的试样,锰硫比较低的试样中MnS夹杂物数量更多、尺寸更大,尤其是细系MnS;长条状MnS夹杂物会导致钢材力学性能的各向异性,锰硫比较低的试样中MnS的长宽比较大,导致其强度低于锰硫比较高的试样;低锰硫比和高锰硫比试样的断裂方式分别为准解理断裂和韧性断裂;低锰硫比试样相比高锰硫比试样具有更好的表面光洁度和切削性能。

硫易切削钢中夹杂物形态的影响因素

硫易切削钢是当今使用最广泛的易切削钢种,钢中硫化物的形态影响钢的切削性能。介绍了改变钢中硫化物形态的不同工艺手段,例如可以改变钢中氧含量、添加稀土、改变锰硫比等因素来控制钢中夹杂物的形态。

低碳高硫易切削钢基体显微组织对切削性能的影响

研究180 mm×240 mm方坯轧制后不同显微组织对低碳高硫易切削钢切削性能的影响,控制合适的显微组织以提高低碳高硫易切削钢的切削性能。低碳高硫易切削钢显微组织由铁素体、珠光体和硫化物组成,但铁素体和珠光体所占比例直接影响材料的切削性能,调整碳含量是改变两种组织比例的有效手段。试验通过调整1215钢不同的碳含量,并对碳含量不同的材料分别进行切削试验,分析显微组织差别对切削性能的影响。结果表明:钢中珠光体体积分数15%~20%时,切削性能最佳,此时钢中C质量分数为0.12%。

含硫易切削钢夹杂物改性分析

针对含硫易切削钢F45MnVS,分别在实验室、工业生产条件下,检测分析了冶炼工艺Ca处理、CaMg复合处理对钢中夹杂物及性能的影响。结果表明,与Ca处理钢相比,CaMg复合处理钢中含有氧化物核心的硫化物的比例相对提高了35%左右,纺锤状硫化物的比例相对提高了76.99%,横向冲击性能提高了13.13%。

钙硫系易切削齿轮钢夹杂物研究及应用

某公司采用130 t EAF-LF-RH-CC工艺路线冶炼钙硫系易切削齿轮钢817M40QT(出口德国),通过控制钢水纯净度、夹杂物形态组成、精准钙处理、精炼渣系控制、连铸防卷渣防氧化控制,实现由连铸替代模铸,并具备钙硫系易切削齿轮钢连浇8炉以上能力,且钢中的夹杂物水平能控制在:A类(细系/粗系):1.5/1.5;B类(细系/粗系):0.5/0.5;C类(细系/粗系):0/0;D类(细系/粗系):1.0/0.5,满足高纯净度要求。

中碳钙硫易切削钢夹杂物形态控制

在实验室进行了1kg坩埚实验,研究了中碳高硫结构钢钙处理前后夹杂物的形态、尺寸及组成.结果表明:钢钙处理后获得了可以改善钢切削性的纺锤形夹杂物,夹杂物的平均纺锤形率为68.11%,并且随钢中[Ca]/[S]增加夹杂物纺锤形化趋势增加;钙处理后小于2.5μm的夹杂物占夹杂物总量的76.05%,夹杂物细小、弥散分布于钢基体中;夹杂物类型以钙铝酸盐芯硫化物外壳的复合夹杂物、(Mn,Ca)S形式的硫化物为主,有少量的铝酸钙与CaS的复合夹杂物;含钙硫的45钢铸态钢锭比普通45钢铸态钢锭切削性能有所改善.

环保石墨易切削钢的组织及性能

石墨易切削钢是顺应易切削无铅、低硫这一发展趋势而产生。具有亚共析成分的钢种其石墨化过程一直较难,因此开发该钢种的关键是促进其石墨化过程。研究表明,通过合理的成分设计和工艺处理,可以在较短的时间内钢中C原子的石墨化。石墨化退火时,C原子除了能在析出相上形成石墨外,还能自发形核及长大形成石墨。经石墨化退火后,试验钢的组织主要由铁素体+石墨+少量渗碳体组成,其中,石墨粒子的尺寸较为细小,分布也较为均匀,渗碳体主要以球状的形式分布铁素体晶粒晶界及晶内。抗拉强度和伸长率分别为595 MPa和33%,表现较高的强度和较好的塑性。

含锡易切削钢的冶炼和性能研究

以锡替代铅 ,用 2 0kg感应炉熔炼了成分 (% )为 :0 2 0～ 0 2 1C ,0 5 6～ 0 6 0Si,0 78～ 0 80Mn ,0 2 8～ 0 2 9S ,0 0 6 6～ 0 0 70P ,0～ 0 0 4 9Sn易切削钢。试验结果表明 ,加锡可以明显改善钢的切削性能 ,经 6 0min切削 ,高速钢刀具后刀面磨损宽度 (Vb)由切削未加Sn钢的 0 6 0mm降到切削加Sn钢的 0 4 5mm。加锡钢的力学性能与含铅易切削钢相当。扫描电镜和能谱对钢中夹杂物和断口分析表明 。

圆珠笔头用新型易切削不锈钢的组织与切削性能

采用中频炉+电渣重熔方法制备了一种新型硫-铅复合铁素体易切削不锈钢,利用光学显微镜、扫描电镜、能谱仪和超精密数控车床对该钢的化学成分、显微组织、夹杂物及切削性能进行了研究。结果表明:试验钢棒材及其成品线材、进口SF20T钢成品线材中易切削相均为MnS、铅及其与碲形成的复合夹杂物,棒材中MnS呈纺锤形,经冷拔后的成品线材中MnS横向呈细小的椭圆形并沿拉拔方向呈断续、串链状分布,比SF20T钢成品线材的横、纵向尺寸均小;试验钢成品线材基体组织为铁素体,晶粒度约为10级,在高速中等进给量下切削性能良好,可兼顾切屑形貌和表面粗糙度的要求。

国内1215系低碳高硫易切削钢的工艺流程和内部质量控制

对国内100 t EAF-LF-CC和80 t、100 t、160 t转炉-LF-CC四条生产线生产的1215系低碳高硫易切削钢(/%:0.05～0.10C、≤0.013Si、1.06～1.33Mn、0.051～0.061P、0.24～0.36S、0.012 0～0.0140[O]、≤0.005A1)进行实物分析。结果表明,国内1215低碳高硫钢成分控制特点为通过适当提高Mn含量控制钢中的Mn/S(3.7～3.9),个别流程通过降低S含量可使Mn/S达4.4;160 t转炉流程在夹杂物控制上优于其余流程(Mn/S=3.8,MnS夹杂面积和长宽比波动较小)。.由于连铸坯元素偏析较小和轧后冷却速度控制得当,80 t转炉流程和160 t转炉流程生产的钢中无明显的带状组织,而100 t电弧炉流程和100 t转炉流程生产的钢中带状组织级别为3～4。

夹杂物对易切削钢性能的影响机理研究

为了研究易切削钢中纳米级夹杂物与其机械性能的关联,对两种典型易切削钢进行性能测试以及利用扫描电镜、透射电镜观察其表面夹杂物的分布、形状和各元素的质量分数.研究中发现样品Ⅱ在夹杂物的分布上更均匀,夹杂物颗粒大小适中,形状多为球状或纺锤状,同时夹杂物MnS对于硬质元素的包裹性能更好,从微观上阐述了两种材料在机械加工性能上的区别,为易切削钢切削加工工艺的制定提供指导.

P20SRE塑料模具钢的热处理及性能

研究了P20SRE易切削塑料模具钢的热处理工艺、组织与性能．试验结果表明，该钢的热处理工艺简单，切削性能优于P20及P20S钢，在预硬至35HRC状态下，能进行各种机加工。