TiN析出相對中碳Cr-Mo耐磨鋼凝固組織的影響

TiN析出相對中碳Cr-Mo耐磨鋼凝固組織的影響EFFECT OF TiN PRECIPITATES ON SOLIDIFICATION MICROSTRUCTURE OF MEDIUM CARBON Cr-Mo WEAR RESISTANT STEEL

借助熱力學(xué)理論計算, 設(shè)計了固液兩相區(qū)保溫凝固和連續(xù)冷卻凝固實驗, 采用 OM, SEM, EDS 和 EPMA 等方法, 研究了中碳 Cr-Mo耐磨鋼中 TiN 的析出行為及其對凝固組織的影響. 結(jié)果表明, 隨著 Ti, N 含量的增加, TiN 在固液兩相區(qū)的析出溫度逐漸升高. 當(dāng)鋼中 Ti 含量為 0.090%, N 含量為 0.014%時, TiN 直接在液相區(qū)析出. 在液固兩相區(qū)內(nèi)不同溫度保溫并水淬凝固后, TiN 主要分布于凝固組織的粗大枝晶間、枝晶前沿和剩余液相區(qū)域的等軸晶晶界處. 此外, 少量 TiN 分布在粗大枝晶和等軸晶內(nèi). 在連續(xù)冷卻凝固過程中, TiN 析出相的形成溫度是影響凝固組織粗細(xì)的主要因素. 隨著 Ti 含量的增加, TiN 析出相的形成溫度升高, 鋼液實際凝固溫度增高, 凝固區(qū)間增大, 局部凝固時間延長, 凝固組織的二次枝晶臂間距不斷增大; 當(dāng) Ti 含量超過 0.066%后, TiN 析出相的形成溫度與液相線接近或高于液相線, 鋼液實際凝固溫度變化不大, 二次枝晶臂間距趨于穩(wěn)定.

As an important type of wear-resistant material, the low-alloyed medium carbon wear resistant steel has been widely used in mining, power and metallurgical industries due to its low cost and excellent mechanical properties. However, the coarse as-cast microstructure tends to form in large wear resistant castings because of the long solidification time. As a result, spalling wear resulting from the preferential initiation and propagation of cracks along interdendrite will occur during service process, which severely degrades the wear resistance and service life. In this work, Ti is added to improve the mechanical properties of medium carbon Cr-Mo wear resistant steel. The precipitation behavior of TiN in the solidification process and its effect on the solidification microstructure were investigated by thermodynamic calculation, constant temperature solidification experiment at solid-liquid two phase region and continuous cooling solidification experiment by using OM, SEM, EDS and EPMA. The results show that TiN precipitation temperature gradually increases at solid-liquid two phase region with the increase of contents of Ti and N. TiN precipitates directly in the liquid region when Ti and N contents are 0.090% and 0.014%, respectively. Holding at different temperatures of solid-liquid two phase region, a very small amount of TiN precipitates are present within the dendritic arm, and a large number of TiN precipitates are present at the interdendritic positions and frontiers of dendrites. After quenching, in the remaining liquid most of TiN are present at the boundaries of equiaxed grain and a little amount of TiN stay within the equiaxed grain. During the continuous cooling solidification, TiN precipitation temperature is the main factor affecting the refinement of solidification microstructure. With the increase of Ti content, TiN precipitation temperature increases. At the same time, the actual solidification temperature of liquid steel rises, the solidification temperature range broadens and the local solidification time extends, which results in the increase of secondary dendrite arm spacing. When Ti content exceeds 0.066%, TiN precipitation temperature is near or above the liquidus line. The actual solidification temperature of liquid steel remains unchanged. Therefore, the secondary dendrite arm spacing becomes stable.

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