42CrMo steel is a kind of ultra-high strength steel, which has strong resistance to plastic deformation, less possibility of brittle fracture, higher hardenability and no obvious toughness decline after quenching and tempering. After quenching and tempering, the fatigue limit and impact resistance of 42CrMo steel are improved, It has good low temperature impact toughness.

The characteristics of several main alloying elements and their effects on 42CrMo steel are summarized as follows:

1) Carbon

Carbon can combine with Cr, Mo, V to form carbides. The carbon dissolved in the matrix can harden martensite during quenching.

2) Silicon

Compared with other elements, silicon has the most amount of oxygen, which can be removed from molten steel during metal smelting. The hardenability of the material is deepened in the presence of silicon, nickel and Luo. The strength and heat resistance of the matrix can be improved by dissolving silicon in the matrix without forming carbides.

3) Manganese

The main function of manganese is to remove oxygen and sulfur from molten steel during refining. A part of manganese in molten steel combines with sulfur to form a non-metallic inclusion, manganese sulfide (MNS), which remains in the matrix and reduces the toughness of the material. But sometimes in order to improve the cutting performance of materials, some sulfur elements will be added specially.

4) Chromium

Chromium can be dissolved in the matrix, and the presence of chromium can improve the hardenability of the steel. It can also eliminate tempering softening. The addition of chromium can also improve the toughness and high temperature strength of the steel. Chromium is easy to combine with carbon to form hard carbides. These carbides exist in the matrix of steel and can improve the corrosion resistance of steel.

5) Molybdenum

Molybdenum can be dissolved in the matrix to improve the hardenability, thermal stability and corrosion resistance of steel. The main characteristic of molybdenum is that fine carbide Mo2C will precipitate when the molybdenum dissolved in the matrix is tempered at about 500 ℃, which can make the steel show obvious precipitation hardening effect. Moreover, compared with vanadium, tungsten, chromium, molybdenum has better secondary hardening effect.

The raw material of the test sample is 42CrMo sheet formed by hot rolling. According to the requirements of MTS810 fatigue tensile testing machine fixture and its own research content, the compact tensile test sample was processed. According to astme 647-05, the specific sampling direction is shown in the following figure: