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前言 活塞销在发动机中的工况条件十分恶劣,负荷大,润滑条件差,压力分布不均匀等。为了保证其工作可靠,须有严格的配合间隙,良好的摩擦表面质量。一般在发动机工作温度下,活塞销与连杆衬套之间的间隙以及销与销座的间隙最好在（0.0003～0.0005）d范围内,间隙过小导致摩擦面咬死,但过大破坏油膜,产生噪音。为此,活塞销必须有很好的尺寸稳定性。影响尺寸稳定性有三个因素即马氏体的析出、残余奥氏体的转变和内应力。提高尺寸稳定性必须尽可能降低马氏体的正方度,减少残余奥氏体量和降低内应力。在三个因素中残余奥氏体是主导的,要求渗碳淬硬层中的残余奥氏体必须切实消除,以免发动机在运转一段时间后,残余奥氏体逐步变成马氏体,致使晶格变大体积膨胀,活塞销外形尺寸增大。 控制活塞销残余奥氏体量（r_R）的方法:一般有控制含碳量,控制淬火温度,控制冷却速度,控制回火温度和冰冷处理等。但由于活塞销使用的钢种不同,要求的性能不一样,目前,还不能确立一种统一的方法。本文是采用几种不用的热处理工艺来控制活塞销外圆尺寸的变化,进行了如下的工艺试验。
Preface Piston pin in the engine operating conditions are very poor, heavy load, poor lubrication conditions, uneven pressure distribution. In order to ensure its reliable work, there must be strict with the gap, a good surface quality of friction. Generally at engine operating temperature, the clearance between the piston pin and the connecting rod bush and the clearance between the pin and the pin seat are preferably in the range of (0.0003-0.0005) d. The clearance is too small to cause the friction surface to seize, but the excessive destruction Oil film, produce noise. For this reason, the piston pin must have good dimensional stability. Three factors that affect dimensional stability are the precipitation of martensite, the transformation of retained austenite, and internal stresses. Increasing the dimensional stability must reduce the squareness of the martensite as much as possible, reduce the amount of retained austenite and reduce the internal stress. Residual austenite in the three factors is the dominant, require carburizing hardened layer of residual austenite must be effectively eliminated, so that the engine is running for some time, the residual austenite gradually become martensite, resulting in crystal Grid to expand the volume expansion, piston pin shape size increases. Control piston pin retained austenite volume (r_R) method: the general control of carbon content, control the quenching temperature, control the cooling rate, control the tempering temperature and ice-cold treatment. However, due to the different types of steel used in the piston pin, the required performance is not the same, at present, can not establish a unified approach. This article is the use of several different heat treatment process to control the piston pin cylindrical size changes, the following process test.