冷激型低合金球墨鑄鐵之耐磨耗性探討

Abstract

本研究的主要目的在固定合金成分之情形下(2.5%Ni-1.0%Cr-0.5Mo-0.4Mn)，探討 C與Si含量、接種處理(二次接種)及冷卻速率等對於低合金球墨鑄鐵之顯微組織(石墨形態、雪明碳鐵含量、基地組織)、硬度及耐磨耗性之影響。 在碳當量相同之條件下(CE≅4.1%)，Si含量較高者(1.2%至1.7%)，其球墨數目較多、雪明碳鐵含量較低、且變韌鐵含量亦較少，又，施以二次接種會增加球墨數目，並稍微減少雪明碳鐵量。在Si含量相同之條件下(Si≅1.5%)，C含量較高者(3.4%至3.8%)，其球墨數目較多、雪明碳鐵含量較低、變韌鐵含量稍高，又，施以二次接種會增大鑄件表面與鑄件內部之變韌鐵/波來鐵比例的差異。此外，針對凝固冷卻速率之影響，冷激鐵放置處之鑄件表面，不僅其球墨數目最高、尺寸小，且雪明碳鐵量亦最高，硬度值亦最高。 由Pin-On-Disk耐磨測試之結果顯示(對磨材料為Al2O3)，冷激鐵放置處其磨耗量反較未放置冷激鐵處高，進一步對顯微組織(球墨數目、雪明碳鐵含量、基地組織)進行多元線性迴歸分析後，得知磨耗量與球墨數目成正比，而與變韌鐵量成反比；另一方面，往復式磨耗之結果顯示放置冷激鐵對磨耗量較無明顯影響(對磨材料為S45C)；由以上兩種磨耗測試結果可知，欲得到較佳耐磨耗性其球墨數目需適中且變韌鐵量較高。在合金C、Si成分方面，Si含量較低者其耐磨耗性有明顯提升之效果，C含量之影響較不顯著。

The primary purpose of this research is study the effects of C and Si contents, solidification cooling rate (with and without chilling), and late inoculation on microstructure, hardness and wear resistance of ductile cast irons under fixed alloy compositions of 2.5%Ni-1.0%Cr-0.5%Mo-0.4%Mn. The experimental results show that, at a fixed CE of about 4.13%, increasing Si content (from 1.15% to 1.68%) increases graphite nodule count, but reduces both carbide and bainite contents. In addition, the employment of late inoculation (0.1% Fe-Si inoculant) increases nodule count, while slightly reduces carbide content. On the other hand, at a fixed Si content of some 1.46%, increasing C content (from 3.44% to 3.81%) increases both graphite nodule count and bainite content, but reduces carbide content. Late inoculation promotes bainite formation. Furthermore, when the alloy solidification cooling rate was increased by chilling, the microstructure exhibits increased graphite nodular count and carbide content, and also the carbides formed are more refined. As a result, the hardness is higher with a higher solidification cooling rate. Regarding the pin-on-disc tests (Al2O3 as dics material), the results show that the chilled specimens exhibit higher wear loss compared with non-chilled specimens. By means of multiple linear regression analysis, wear loss is functions of nodule count and bainite content, with the nodule count being a positive effect, while the bainite content a negative effect. However, a reversed results on wear loss were obtained for pin-on-flat tests (S45C as stationary counter material). In summary, alloys with moderate nodule count and with a merely bainitic matrix can attain the best wear resistance. In addition, the wear resistance is affected more by varying Si content than by C content.