Transverse Crack of Quenching Crack on Press Brake Tooling

The so-called transverse crack on the press brake tooling means that the crack feature is perpendicular to the axial direction. In the unhardened mold, there is a large tensile stress peak in the transition part between the hardened area and the unhardened area. When the large mold is rapidly cooled, a large tensile stress peak is easily formed. The axial stress formed is greater than the tangential stress, resulting in lateral crack. The lateral segregation of low melting point harmful impurities such as S, P, Sb, Bi, Pb, Sn, As in the forging module or the module has lateral microcracks, which expand to form lateral cracks after quenching.

Usually the preventive measures mainly include:

1. The module should be forged reasonably. The ratio of the length to the diameter of the raw material, that is, the forging ratio, is preferably between 2 and 3. Between forgings, the double-cross deformation is forged in the direction of forging. Impurities are fine, small and evenly distributed in the steel matrix, and the forged fiber structure is distributed in no direction around the cavity, which greatly improves the transverse mechanical properties of the module and reduces and eliminates stress sources;

2. Select the ideal cooling rate and cooling medium: fast cooling above the Ms point of the steel, greater than the critical quenching cooling rate of the steel, the stress generated by the supercooled austenite in the steel is thermal stress, the surface layer is compressive stress, and the inner layer is The tensile stress cancels each other out, effectively prevents the formation of thermal stress cracks, and cools slowly between the Ms-Mf of the steel, which greatly reduces the structural stress during the formation of quenched martensite. When the sum of the thermal stress and the corresponding stress in the steel is positive (tensile stress), it is easy to be quenched and cracked, and when it is negative, it is not easy to be quenched and cracked. Make full use of thermal stress, reduce phase transformation stress, and control the sum of stress to be negative, which can effectively avoid the occurrence of transverse quenching cracks. CL-1 organic quenching medium is an ideal quenching agent, at the same time, it can reduce and avoid the distortion of the quenching and bending machine mold, and can also control the reasonable distribution of the hardened layer. Adjusting the ratio of different concentrations of CL-1 quenching agent can obtain different cooling rates, obtain the required distribution of hardened layers, and meet the needs of different mold steels.