φ40×100mm的40Cr钢试样经淬火后得到沿断面呈W形分布的硬度梯度曲线。本文对在20%Aqua-Quench251介质中淬冷的试样运用变温马氏体形成的动力学方程进行计算得到心部马氏体量的增多,可相应认为其M_a点提高32℃(△M_a=M_(a心)-M_(s1/2R)=32℃),并根据已发表的试验数据,推算出心部受到约220MPa的残余拉应力。试样心部在淬火过程中受到的应力由压应力变化成拉应力,从而影响珠光体或贝氏体转变和马氏体转变的进行,这十分恰当地解释了自三十年代至今一直悬而未决的问题。 The 40Cr steel sample of φ 40 × 100mm was hardened to obtain the hardness gradient profile along the W-shaped distribution along the section. In this paper, the amount of martensite in the heart is calculated by using the kinetic equation of martensite formation quenched in 20% Aqua-Quench251 medium, and the M_a point of the quenched specimen can be increased by 32 ℃ (△ M_a = M_ (a heart) -M_ (s1 / 2R) = 32 ° C), and according to the published test data, it is estimated that the heart is subjected to a residual tensile stress of about 220 MPa. The stress applied to the heart of the test specimen during quenching changes from compressive to tensile stress, thereby affecting the pearlite or bainite transformation and the martensitic transformation. This is a very appropriate explanation of what has been pending since the 1930s problem.