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研究了高碳合金钢A(SAE 52100,1.02%C、0.21%Si、0.35%Mn、1.44%Cr、0.20%Ni,质量分数)的相变,并与另一种钢B(0.53%C、0.27%Si、0.35%Mn、0.66%Cr,质量分数)进行了比较。结果表明,两种钢过冷奥氏体中的碳和铬的含量均随着奥氏体化温度的升高而提高。当加热温度为工业中常用的840℃时,A钢奥氏体中的含碳量远低于相图中表明的数值,仅达到中碳钢的水平。这可能是由于奥氏体中碳和铬的不均匀分布所致。业已证明,用萃取法测定的A钢奥氏体中的含碳量只是奥氏体中的平均含碳量,不能准确反映奥氏体中不同区域的含碳量。因此,碳和合金元素含量相同时,由于A钢奥氏体中碳的不均匀分布改变了TTT图的性质,从而使其比B钢奥氏体更容易发生转变。当采用通常的淬火和低温回火工艺时,与TTT图相比的这些改变促进了在奥氏体的高碳区形成含有先共析渗碳体(Fe3C)的珠光体,而在其低碳区形成含有先析铁素体(α-Fe)的贝氏体。这就是高碳合金钢具有优良综合力学性能的原因。
The phase transformation of high carbon alloy steel A (SAE 52100, 1.02% C, 0.21% Si, 0.35% Mn, 1.44% Cr and 0.20% Ni) 0.27% Si, 0.35% Mn, 0.66% Cr, mass fraction). The results show that the content of carbon and chromium in both superheated austenite increases with the increase of austenitizing temperature. When the heating temperature is 840 ℃ commonly used in the industry, the carbon content of austenite in A steel is much lower than the value indicated in the phase diagram, and only reaches the level of medium carbon steel. This may be due to the uneven distribution of carbon and chromium in austenite. It has been shown that the carbon content of austenite in steel A measured by the extraction method is only the average carbon content in austenite and does not accurately reflect the carbon content in different regions of austenite. Therefore, when the contents of carbon and alloying elements are the same, the variation of the TTT pattern due to the non-uniform distribution of carbon in austenite of A steel makes it easier to change than the austenite of B steel. These changes compared to the TTT plot promote the formation of pearlite containing pro-eutectoid cementite (Fe3C) in the high-carbon region of austenite when using conventional quenching and low-temperature tempering processes, whereas in its low-carbon The zone forms a bainite containing pre-ferrite (α-Fe). This is why high-carbon alloy steel has excellent mechanical properties.