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热分析在球铁和灰铁铸件中的应用
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热分析在球铁和灰铁铸件中的应用

The use of thermal analysis in the production of ductile and grey iron castings

史江涛,李 明,Luca De Lissandri

南京谱德仪器科技有限公司(技术中心)

介绍

Introduction

铸铁凝固是一种复杂的化学- - 物理过程 受到 很多因素 的影响, 这些因素由于技术或者成本上的原因铸造厂不能总是控制和进行调整

Cast-iron solidification is a complex chemical-physical process; influenced by a high number of variables that foundrymen cannot always control and adjust at will, for technical and also for cost reasons.

例如,由于原材料占铸造成本的近 40 %,铸造厂更注重评估每种不同类型的成本和效益。

For example, as raw materials account for almost 40% of casting costs, foundries take great care to assess the costs and benefits of each different type.

与通常认识相反,简单地控制合金的化学成分远远不够,因为还必须监测其成核状态和不同的凝固阶段。

Contrary to common belief, simply controlling the chemical composition of the alloy is far from sufficient because its nucleation state and various solidification phases must also be monitored.

让我们假设您正在一个“理想”的铸造厂工作,在那里您可以购买最好的生铁和钢,其中含有铸铁凝固的理想成分,大批量生产以避免需要停产换模具,流体铸造,恒定的浇注重量等。即使在您理想的铸造厂中,该过程也永远不会完全受到控制,因为还有其他 变化因素 ,例如周末停,系统故障以及铸造开始和结束之间的温差。

Let’s assume for a moment that you are working in an ‘ideal’ foundry, where you can purchase the best pig iron and steel containing the ideal elements for cast-iron solidification, with long series production to avoid stops to change patterns, fluid casting, constant mould weight, etc. Even in your ideal foundry the process will never be entirely under control because there are other variables, such as weekend stops, system faults, and temperature differences between the beginning and end of casting.

这就是为什么铸件有时会有缺陷的原因,尽管 表面上 是用 生产合格铸件 相同的铁 浇注。

This is why castings are sometimes defective despite having been apparently poured with the same iron that produced satisfactory pieces.

在这种情况下,您可以尝试通过一 个费时、 昂贵的调查步骤来追溯问题的原因,这些分

析在查明原因时并不总是成功的。

In situations like this you can attempt to trace back the cause of the problem through a long, costly series ofinvestigatory steps, which are not always successful in pinpointing the reason.

另外 ,铸铁凝固热分析是 一个 帮助铸造厂的非常有用的工具。

Alternatively, cast iron solidification thermal analysis is a very useful tool for aiding the foundryman.

热分析的使用

Using thermal analysis

热分析工具能够让技术人员以合理的方式仔细检查铸铁凝固的趋势,从下游工艺( 例如 从浇注)一直到熔化开始。然后对各个 工艺 步骤进行 调整 ,直到达到正常。这就像在你家附近流动的溪流 看到了 颜色 变化 ,分析样品并发现它含有污染物。解决方案就是一直顺着河 流,一直到问题的根源。

The most modern thermal analysis tools allow technicians to scrutinise the trends of cast iron solidification in a logical manner working back from the downstream process (i.e. from the pouring) all the way up to the start of melting.Changes are then made to the various process steps until normality is achieved. This is like seeing a stream flowing near your house change colour, analysing a sample and discovering that it contains pollutants. The solution is to follow the stream, all the way to the source.

使用热分析在铸造厂中也可以进行相同的操作,通过检查浇注炉或浇包中的铁 水, 然后追溯到 整个工艺过程,直到

The same can be done in a foundry using thermal analysis by checking the iron in the pouring furnace or pouring ladle and then tracing the entire process back to the melting furnaces.

你会遇到什么情况?

What scenarios might you encounter?

沿着水流的路上,你可能会看到一个污染水源的工厂,或者靠近水源的一个水坝让水停滞变得浑浊。

Working your way back up the stream, you may see a factory which is polluting the water, or a dam near the source that makes the water stagnate turning it murky.

在铸造厂中,事情要复杂一些。您可能会发现:

Matters are a little more complicated in a foundry. You may discover:

过高 或太低的残留

熔炉中硫含量过 或过少

过高的温度 金属 炉料或周末停产 造成的成核不足

过量或缺乏 孕育;

铁碳图中的定位不正确

过度的石墨膨胀 要么太弱,要么太早

亚稳系 凝固,形成渗碳体和D-E 型石墨

收缩和 缩松倾向

excessive or lack of residual magnesium;

either too much or too little sulphur in melting furnaces;

lack of nucleation caused by excessively high temperatures, metallic charge or weekend stops;

excessive or lack of inoculation;

incorrect positioning in the iron-carbon diagram

excessive graphitic expansion; either too weak or too early;

metastable system solidification with formation of Cementite and D-E type graphite;

high shrinkage and porosity tendency.

显然,借助热分析和光谱仪解决这些问题只需要良好的技术知识和丰富的经验。

Obviously, intervening in these areas with the aid of thermal analysis and a spectrometer only requires good technical knowledge and lots of experience.

对于河流的情况,您可以致电技术人员净化水并修复泄漏。同样,铸造厂可以依靠专业供应商安装最先进的热分析软件,对系统进行正 确校准,并要求专业技术人员提供支持,以解释冷却曲线并 得到 必要 改进措施建议。

In the case of the stream, you can call technical personnel to purify the water and repair the leak. Similarly,foundrymen can rely on expert suppliers to install state-of-the-art thermal analysis software, have the system correctly calibrated and ask for support by expert technical personnel for interpreting cooling curves and receiving indications for the necessary adjustments.

这需要根据产品类型、工艺类型和铸造工艺流程进行初始软件校准,并按类别、铸件类型、工艺类型等区分合金。

This requires initial software calibration according to production type, process type and foundry layout, and differentiating alloys by category, casting type, process type, etc.

为此,FASSMET 南京谱德仪器科技有限公司 合作提供TCAST 热分析软件,并保证校准程序,解释结果和分析生产所需的 技术支持(图1 )。

For this purpose, FASSMET and PUDEKJ have partnered up to supply TCAST thermal analysis software and guarantee the technical support needed to calibrate the program, interpret results and analyses production in general(Figure 1).

 

冶金中的热分析

Thermal analysis in metallurgy

TCAST 软件从树脂砂制成的样杯中接收来自K 型热电偶的数据(图2 和图3 )。

The TCAST software receives data from K-type thermocouples in sampling cups made of bonded sand (Figures 2 and3).

只需将少于400 克的铁 水倒入这些样杯 中,TCAST 就可以计算和分析冷却曲线及其在凝固过程中的一阶导数(约250 秒)。

Simply pouring less than 400g of iron into these cups allows TCAST to calculate and analyse the cooling curve and its first derivative during the solidification process (approx. 250 seconds).

冷却曲线是温度与时间的关系,从液相开始,在凝固开始之前,即从TLiquidus 温度[TLiq] 开始,如果仅测量共晶转变,在凝固完成时在1000 °C 结束,或者如果分 析共析转变就在650°C (图1. 冷却曲线,温度[Y ] 对时间[X ] )。

A cooling curve is the measurement of temperature versus time, starting from the liquid phase, before solidification begins, i.e. starting from the TLiquidus temperature [TLiq] and ending at 1000°C when solidification is complete ifmeasuring the eutectic transformation only, or at 650°C if analyzing the eutectoid transformation as well (Figure 1.Cooling curve, temperature [Y-axis] versus time [X-axis]).

一阶导数表示冷却速度随时间的变化;这对于 析出和相变 的几何计算至关重要。冷却速度根据每相 析出所产生 的凝固潜热而变化。例 如,在亚共晶铁的情况下,“ 析出 ”的第一相是 初生 奥氏体,其 产生的 潜热并因此减慢冷却。当所有的初生奥氏体“ 析出 ”时,冷却再次加速,直至下一次 析出 (共晶),再次减速。

The first derivative shows the speed of cooling as a function of time; this is essential for the geometric calculation of the points of precipitation and transformation. The speed of cooling varies according to the latent heat of solidification emitted with the precipitation of each phase. For example, in the case of hypoeutectic iron, the first phase toprecipitate” is primary austenite, which emits latent heat and thus slows down cooling. When all the primary austenite has “precipitated”, cooling picks up speed again until the next precipitation (eutectic), when it slows downagain.

 

Figure 4 - Graphs of the main page: cooling curve and first derivative

4 - 主界面图:冷却曲线和一阶导数

 

主要参数是:

The main parameters are:

T °Liquidus [TLiq] :与曲线上的第一个点重合,表示凝固开始的温度。  该值随碳当量(CEQ )而变化,取决于下表所示的 铁的类型(数值为近似值):

T° Liquidus [TLiq]: coincides with the first inflexion point on the curve and indicates the temperature at which solidification begins. This value varies with the Carbon Equivalent (CEQ) and depends on the type of iron produced as shown in the table below (values are approximate):

 

GG20HT200

1160 – 1180

GG25HT250

1175 – 1210

GG30HT300

1190 1230

GGG(球墨铸铁)

 

 

1140 – 1155

 

T °[TEStart] :当共晶凝固开始时,与TLiquidus 之后的一阶导数的最小点一致。

T° [TEStart]: when eutectic solidification starts, coincides with the minimum point on the first derivative after

TLiquidus.

T °[TEMin] 共晶温度:它与一阶导数和零轴之间的交点重合。  该值与渗碳体的形成间接成比例,如下图所示(值为近似 值):

T° [TEMin] minimum eutectic temperature: it coincides with the point of intersection between the first derivative and the zero axis. This value is indirectly proportional to the formation of Cementite, as shown in the graph below(values are approximate):

 

Figure 5 – Relationship TEMin (y-axis) versus Cementite (x-axis)

5 - TEMiny轴)与渗碳体(x轴)的关系

 

该参数高度依赖于 铁的成核程度 以及孕育

This parameter is highly dependent upon the degree of nucleation of the iron and thus inoculation.

T °[TEMax] 共晶温度:它是曲线 上的最大值。它与一阶导数和零轴之间的第二交点重合。该值由凝固期间的相的 结晶 潜热产生。它特别与石墨 析出 和膨胀有关。

T° [TEMax] maximum eutectic temperature: It is the maximum on the curve. It coincides with the second point of intersection between the first derivative and the zero axis. This value is generated by the latent heat of the phases during solidification. It is specifically linked to graphite precipitation and expansion.

T °Solidus [TSol] 铁完全凝固的温度。它与一阶导数的最小点重合。

T° Solidus [TSol]: temperature at which the iron has completely solidified. It coincides with the minimum point on the first derivative.

TCAST 处理上述参数以获得:

TCAST processes the above parameters to obtain:

初生奥氏体[PrAust] :初生奥氏体的百分比。这在球墨铸铁中是不希望的,因为它与宏观收缩的形成成正比,特别是在小型铸件中。

Primary Austenite [PrAust]: the percentage of primary austenite. This is undesirable in ductile iron as it is directly proportional to the formation of macro-shrinkage, especially in small castings.

石墨[PrGraph] :初生 石墨的百分比。这在球墨铸铁中是不希望的,因为它的存在导致形成大的结节和石墨浮选,特别是在大型铸件中。

Primary Graphite [PrGraph]: the percentage of primary graphite. This is undesirable in ductile iron as its presence results in the formation of large nodules and graphite flotation, especially in large castings.

奥氏体的共晶 析出[CellAust] :该参数与共晶 析出 的效率有关,以秒为单位测量。因此,高值是理想的,因为它们保证铸件没有孔隙或微收缩。但是,超过最大标准值会带来 产生 石墨 漂浮 的风险。 理想的参数值

Eutectic precipitation of austenite [CellAust]: this parameter relates to the efficiency of eutectic precipitation,measured in seconds. High values are therefore ideal, as they guarantee castings with no porosity or microshrinkage.However, exceeding the maximum standard value carries the risk of creating the conditions for graphite flotation.Ideal values:

 

 

 

Grey Iron灰铸铁

 

 

 

40 65 seconds

Ductile Iron球墨铸铁

 

 

 

90 110 seconds

 

 

Recalescence [Rec] :( TeMax - TeMin )。  它涉及在石墨膨胀过程中 的膨胀。  理想 的参数值 是:

Recalescence [Rec]: (TeMax – TeMin). It relates to the dilation of the iron during graphite expansion. Ideal values are:

 

 

 

 

Grey Iron灰铸铁

 

 

 

< 7°C

Ductile Iron球墨铸铁

 

 

 

< 5°C

 

 

较高的值可能导致铸造变形并因此形成 缩松

Higher values could result in casting deformation and the consequent formation of porosity.

[KCond] :是导数的角度,表示从半固态到固态的速度。 值越低, 基体中的收缩 越少。该参数对于找到精确的TSolidus [TSol] 点至关重要,该点与凝固完成时间一致。 理想的参数值是

[KCond]: is the angle of the derivative that indicates the speed of passing from the semi-solid to the solid state. The lower the value, the fewer shrinkage cavities in the matrix. This parameter is essential in order to find the exact TSolidus [TSol] point, which coincides with the completion of solidification. Ideal values are:

 

 

 

Grey Iron灰铸铁

 

 

< 20°

 

 

 

Higher values indicate the

presence of porosity/shrinkage

高值表明出现缩松缩孔

 

 

Ductile Iron球墨

铸铁

 

 

25 – 45°

 

 

 

 

Higher values indicate the risk of

shrinkage, lower values indicate the

formation of degenerated graphite forms(vermicular and/ or lamellar)

高值表明出现缩松缩孔,数值低表明

片状或蠕墨石墨形成

 

 

缺陷

Defects

冷却曲线及其一阶导数不易读取,但TCAST 软件 帮助铸造工程师 解释结果并在易于阅读的彩色表盘上显

示这些结果。彩色表盘有三个颜色区域。红色刻度盘中的彩色值表示存在高缺陷风险,黄色刻度盘中的彩色值表示存在中等缺陷风险,而绿色区域中的彩色值表示缺陷风险较低。

The cooling curve and its first derivative are not easy to read, but the TCAST software helps foundry metallurgists by interpreting the results and displaying these on easy-to-read colored dial. The colored dials feature three color zones.The colored values in the red dials indicate a high risk of defects, those in the yellow dials indicate a medium risk of defects and those in the green zones indicate a low risk of defects.

当然,初始软件校准是必要的,可以在安装后的前几天完成。

Initial software calibration is, of course, necessary and can be completed in the first few days after installation.

其他颜色的刻度盘表明 的各种 趋向 ,包括 石墨膨胀 石墨 漂浮、球化率、 缩松、 渗碳体形成 、反白口、 铁碳图中的实际位置 ,球墨铸铁 的有用信息,如 石墨球数 球化率 和最终质量指数。

The other colored dials indicate the tendency of the iron toward graphite expansion, graphite flotation, nodularity,shrinkage and porosity, cementite formation, inverse chill, actual position in the iron-carbon diagram, useful information for ductile irons such nodule counts, nodularity and final quality index.

只需几个小时的使用后就可以确定改善区域。

Improvement areas can be identified after only a few hours of use.

在采集阶段,当工作站通过TCP / IP 技术远程连接时,可以实时查看 处理后的数据和结果(FoundryIntranet 此机制用于提供交互式Web 界面,通过使用任何连 的设备 如个人电脑、智能电视、平板电脑和智能手机 远程监控详细信息。

During the acquisition phase, the processed data and results can be seen in real time when the working stations are remotely connected via TCP/IP technology (Foundry Intranet) This mechanism is used to provide interactive Web interfaces to monitor elaborations remotely by using any device connected to the networks as PCs, smart TVs, tablets and smartphones.

作者介绍:

史江涛:南京谱德仪器科技总经理,高级工程师,2004年从事于分析仪器,专注于炉前铸铁热分析

  明:工学硕士,毕业于武汉理工大学,高级工程师,主要从事于铸造技术工作

Luca De Lissandri:意大利FASSMET技术总工