末端淬透性

Steel hardenability test by end quenching (Jominy test) 末端淬透性试验（乔米尼试验）

When a steel work-piece is quenched, the area in contact with the water immediately cools, the inner depths of the material however, do not cool quite so rapidly and in work-pieces that are large, the cooling rate may be slow enough to allow the austenite to transform fully into a structure other than martensite or bainite. This results in a work-piece that does not have the same crystal structure throughout its entire cross section. 

Steel with a poor hardenability is risk for gear material manufacturing expecially. The core hardness can not reach the specified value.

The hardenability of a ferrous alloy is measured by a Jominy test: a round metal bar of standard size is quenched on one end with room-temperature water. The cooling rate will be highest at the end being quenched, and will decrease as distance from the end increases. Subsequent to cooling a flat surface is ground on the test piece and the hardenability is then found by measuring the hardness along the bar. The farther away from the quenched end that the hardness extends, the higher the hardenability. This hardness and distance is plotted to a hardenability graph.

当钢件被淬火时，先接触到水的部分会马上冷却，金属内部冷却相对较慢，有可能会导致心部会产生马氏体和贝氏体以外的组织，例如珠光体。这将导致钢件在横截面上的组织不统一，影响材料的整体力学性能和疲劳强度。

对于齿轮的原材料来说，淬透性差的材料会引起渗碳淬火后的齿轮心部硬度达不到要求，可能引起产品报废。

材料的淬透性可以通过Jominy test检测：规定尺寸的圆钢棒，使其一端用常温的水冷却，接触水的一端冷却速度最快，随着距离原理末端，冷却速度降低，之后将钢棒圆周表面磨制出两个平行面测试硬度，在原理末端一定距离的硬度越高，淬透性越好，最后可以用淬透性曲线来形象的表征其特征。

 

增加淬透性曲线三条