熱分析在球鐵和灰鐵鑄件中的應用

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

史江濤，李 明，Luca De Lissandri

南京譜德儀器科技有限公司（技術中心）

介紹

Introduction

鑄鐵凝固是一種復雜的化學- - 物理過程 ； 受到 很多因素 的影響， 這些因素由于技術或者成本上的原因鑄造廠不能總是控制和進行調整 。

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，由于原材料占鑄造成本的近 40 ％，鑄造廠更注重評估每種不同類型的成本和效益。

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.

與通常認識相反，簡單地控制合金的化學成分遠遠不夠，因為還必須監測其成核狀態和不同的凝固階段。

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.

讓我們假設您正在一個“理想”的鑄造廠工作，在那里您可以購買最好的生鐵和鋼，其中含有鑄鐵凝固的理想成分，大批量生產以避免需要停產換模具，流體鑄造，恒定的澆注重量等。即使在您理想的鑄造廠中，該過程也永遠不會完全受到控制，因為還有其他 變化因素 ，例如周末停，系統故障以及鑄造開始和結束之間的溫差。

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.

這就是為什么鑄件有時會有缺陷的原因，盡管 表面上 是用 生產合格鑄件 相同的鐵 水 澆注。

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

在這種情況下，您可以嘗試通過一 個費時、 昂貴的調查步驟來追溯問題的原因，這些分

析在查明原因時并不總是成功的。

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 ，鑄鐵凝固熱分析是 一個 幫助鑄造廠的非常有用的工具。

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

熱分析的使用

Using thermal analysis

熱分析工具能夠讓技術人員以合理的方式仔細檢查鑄鐵凝固的趨勢，從下游工藝（ 例如 從澆注）一直到熔化開始。然后對各個 工藝 步驟進行 調整 ，直到達到正常。這就像在你家附近流動的溪流 看到了 顏色 變化 ，分析樣品并發現它含有污染物。解決方案就是一直順著河 流，一直到問題的根源。

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.

使用熱分析在鑄造廠中也可以進行相同的操作，通過檢查澆注爐或澆包中的鐵 水， 然后追溯到 整個工藝過程，直到 熔 煉 爐 。

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.

你會遇到什么情況？

What scenarios might you encounter?

沿著水流的路上，你可能會看到一個污染水源的工廠，或者靠近水源的一個水壩讓水停滯變得渾濁。

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.

在鑄造廠中，事情要復雜一些。您可能會發現：

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

? 過高 或太低的殘留 鎂 ；

? 熔爐中硫含量過 高 或過少 ；

? 過高的溫度 、 金屬 爐料或周末停產 造成的成核不足 ；

? 過量或缺乏 孕育；

? 鐵碳圖中的定位不正確 ；

? 過度的石墨膨脹 ； 要么太弱，要么太早 ；

? 亞穩系 凝固，形成滲碳體和D-E 型石墨 ；

? 高 的 收縮和 縮松傾向 。

? ? 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.

顯然，借助熱分析和光譜儀解決這些問題只需要良好的技術知識和豐富的經驗。

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

對于河流的情況，您可以致電技術人員凈化水并修復泄漏。同樣，鑄造廠可以依靠專業供應商安裝最先進的熱分析軟件，對系統進行正 確校準，并要求專業技術人員提供支持，以解釋冷卻曲線并 得到 必要 改進措施建議。

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.

這需要根據產品類型、工藝類型和鑄造工藝流程進行初始軟件校準，并按類別、鑄件類型、工藝類型等區分合金。

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

為此，FASSMET 和 南京譜德儀器科技有限公司 合作提供TCAST 熱分析軟件，并保證校準程序，解釋結果和分析生產所需的 技術支持（圖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).

冶金中的熱分析

Thermal analysis in metallurgy

TCAST 軟件從樹脂砂制成的樣杯中接收來自K 型熱電偶的數據（圖2 和圖3 ）。

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

只需將少于400 克的鐵 水倒入這些樣杯 中，TCAST 就可以計算和分析冷卻曲線及其在凝固過程中的一階導數（約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).

冷卻曲線是溫度與時間的關系，從液相開始，在凝固開始之前，即從TLiquidus 溫度[TLiq] 開始，如果僅測量共晶轉變，在凝固完成時在1000 °C 結束，或者如果分 析共析轉變就在650°C （圖1. 冷卻曲線，溫度[Y 軸] 對時間[X 軸] ）。

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]).

一階導數表示冷卻速度隨時間的變化；這對于 析出和相變 的幾何計算至關重要。冷卻速度根據每相 析出所產生 的凝固潛熱而變化。例 如，在亞共晶鐵的情況下，“ 析出 ”的第一相是 初生 奧氏體，其 產生的 潛熱并因此減慢冷卻。當所有的初生奧氏體“ 析出 ”時，冷卻再次加速，直至下一次 析出 （共晶），再次減速。

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 to“precipitate” 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

圖4 - 主界面圖：冷卻曲線和一階導數

主要參數是：

The main parameters are:

T °Liquidus [TLiq] ：與曲線上的第一個點重合，表示凝固開始的溫度。  該值隨碳當量（CEQ ）而變化，取決于下表所示的 鑄 鐵的類型（數值為近似值）：

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):

T °[TEStart] ：當共晶凝固開始時，與TLiquidus 之后的一階導數的最小點一致。

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

TLiquidus.

T °[TEMin] 最 低 共晶溫度：它與一階導數和零軸之間的交點重合。  該值與滲碳體的形成間接成比例，如下圖所示（值為近似 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)

圖5 - TEMin（y軸）與滲碳體（x軸）的關系

該參數高度依賴于 鑄 鐵的成核程度 以及孕育 。

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

T °[TEMax] 最 高 共晶溫度：它是曲線 上的最大值。它與一階導數和零軸之間的第二交點重合。該值由凝固期間的相的 結晶 潛熱產生。它特別與石墨 析出 和膨脹有關。

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] ： 鑄 鐵完全凝固的溫度。它與一階導數的最小點重合。

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

TCAST 處理上述參數以獲得：

TCAST processes the above parameters to obtain:

初生奧氏體[PrAust] ：初生奧氏體的百分比。這在球墨鑄鐵中是不希望的，因為它與宏觀收縮的形成成正比，特別是在小型鑄件中。

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.

初 生 石墨[PrGraph] ：初生 石墨的百分比。這在球墨鑄鐵中是不希望的，因為它的存在導致形成大的結節和石墨浮選，特別是在大型鑄件中。

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.

奧氏體的共晶 析出[CellAust] ：該參數與共晶 析出 的效率有關，以秒為單位測量。因此，高值是理想的，因為它們保證鑄件沒有孔隙或微收縮。但是，超過最大標準值會帶來 產生 石墨 漂浮 的風險。 理想的參數值 ：

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:

Recalescence [Rec] :( TeMax - TeMin ）。  它涉及在石墨膨脹過程中 鑄 鐵 的膨脹。  理想 的參數值 是：

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

較高的值可能導致鑄造變形并因此形成 縮松 。

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

[KCond] ：是導數的角度，表示從半固態到固態的速度。 數 值越低， 基體中的收縮 越少。該參數對于找到精確的TSolidus [TSol] 點至關重要，該點與凝固完成時間一致。 理想的參數值是 ：

[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:

缺陷

Defects

冷卻曲線及其一階導數不易讀取，但TCAST 軟件 幫助鑄造工程師 解釋結果并在易于閱讀的彩色表盤上顯

示這些結果。彩色表盤有三個顏色區域。紅色刻度盤中的彩色值表示存在高缺陷風險，黃色刻度盤中的彩色值表示存在中等缺陷風險，而綠色區域中的彩色值表示缺陷風險較低。

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.

當然，初始軟件校準是必要的，可以在安裝后的前幾天完成。

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

其他顏色的刻度盤表明 鑄 鐵 的各種 趨向 ，包括 石墨膨脹 、 石墨 漂浮、球化率、 縮 孔 和 縮松、 滲碳體形成 、反白口、 鐵碳圖中的實際位置 ，球墨鑄鐵 的有用信息，如 石墨球數 ， 球化率 和最終質量指數。

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.

只需幾個小時的使用后就可以確定改善區域。

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

在采集階段，當工作站通過TCP / IP 技術遠程連接時，可以實時查看 處理后的數據和結果（FoundryIntranet ） 。 此機制用于提供交互式Web 界面，通過使用任何連 網 的設備 如個人電腦、智能電視、平板電腦和智能手機 遠程監控詳細信息。

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.

作者介紹：

史江濤：南京譜德儀器科技總經理，高級工程師，2004年從事于分析儀器，專注于爐前鑄鐵熱分析

李  明：工學碩士，畢業于武漢理工大學，高級工程師，主要從事于鑄造技術工作

Luca De Lissandri：意大利FASSMET技術總工