Cooling speed steel high-temperature use of the heated barn have more significant effect on the distribution of boron. When the heating temperature is higher than 900 ℃, basically dissolved boron steel solid solution. When the rapid cooling is affected by the rate of diffusion of boron segregation at grain boundaries only rarely precipitate formed. Boron distributed in the grain boundary and grain of relatively uniform. When the slower speed of the cooling, with decreasing temperature, adsorption of grain boundaries from weak to strong, solid solution to reduce the solubility of boron, causing boride along the grain boundary precipitation.
    As long as proper control of the hot rolling process and heat treatment of steel, to ensure the majority of boron dissolved in solid solution, boron steel can get a good hardenability. It should be noted that, when properly controlled steel smelting N and Ti contents, to prevent precipitation of BN. As boron improve permeability quenching mechanism, there are two views: one boron can reduce the austenite grain boundaries. Since boron easily adsorbed in the austenite grain boundaries, the austenite grain boundaries can be reduced, reducing the ferrite generally favorable position in the nucleation of austenite grain boundaries, increasing the stability of austenite, ferrite and upper bainite incubation period increases, the transition curve to the right. The second is to reduce boron diffusion capacity of carbon from the austenite grain boundaries, when ferrite core, not only require a favorable nucleation sites, but also the diffusion of carbon atoms, boron atoms present in the grain boundaries to prevent the diffusion of carbon atoms therefore delayed the formation of ferrite, pearlite transformation also blocked.
SPV490 plus boron steel by controlling the heat treatment process can effectively improve the hardenability, and good toughness.
SPV490 steel sink in the outer furnace quenching, tempering reasonable combination, get a good performance. By controlling the amount of cooling water after rolling and quenching process of adjustment, plate thickness hardenability will reach more than 60mm.
To Cr, Ni and other elements to improve hardenability, 12mm thick steel plate can be obtained after the air-cooled high-temperature tempering above 690MPa yield strength and good toughness.
Steel boron content should be controlled at 20 × 10-6 or less. Otherwise, it will seriously damage the toughness of the steel and reduce its increase hardenability effect.