What is a transverse crack

What is a transverse crack
The crack is characterized by being perpendicular to the axis. For the unhardened die, there is a large tensile stress peak at the transition part between the hardened zone and unhardened zone. Large tensile stress peaks are easily formed when large dies are rapidly cooled. As the axial stress formed is greater than the tangential stress, transverse cracks are generated. Transverse segregation of S, P, Sb, Bi, Pb, Sn, As and other low melting point harmful impurities in the forging module or transverse microcracks exist in the module, and transverse cracks are formed after quenching.

Preventive measures:
(1) The module shall be forged reasonably. The ratio of raw material length to diameter, that is, the forging ratio is 2-3. The double cross forging is used between the forging. After five upsetting and five drawing, the multi fire forging makes the carbides and impurities in the steel fine, small and evenly distributed in the steel matrix. The forging fiber structure has no directional distribution around the cavity, greatly improving the module's transverse mechanical properties, reducing and eliminating stress sources;
(2) Select the ideal cooling rate and cooling medium: fast cooling above the Ms point of the steel is greater than the critical quenching cooling rate of the steel. The stress generated by the undercooled austenite in the steel is thermal stress, the surface layer is compressive stress, and the inner layer is tensile stress, which offset each other, effectively preventing the formation of thermal stress cracks. Slow cooling between Ms Mf of the steel can greatly reduce the organizational stress when forming quenched martensite. When the sum of thermal stress and corresponding stress in steel is positive (tensile stress), it is easy to quench crack, and when it is negative, it is not easy to quench crack. Make full use of thermal stress, reduce phase transformation stress, and control the total stress to be negative, which can effectively avoid transverse quenching cracks. CL-1 organic quenchant is an ideal quenchant, which can reduce and avoid the distortion of quenching die and control the reasonable distribution of hardening layer. By adjusting the proportion of CL-1 quenchant with different concentrations, different cooling rates can be obtained, and the required hardened layer distribution can be obtained to meet the needs of different die steels.