The role of boron in steel

It isn’t related to neutron absorption. Adding a minimum of 0.0007% boron already can increase the hardness of the steel, if adding boron exceeds 0.005%, the hardness increase is not big. Adding 0.002-0.003% boron in low carbon boron is equivalent to 0.7% Cr, 0.5% Mo or 1% Ni to the hardness of steel. Compared with C, Mn, Si, Al and other elements in the content of these elements in steel is only a few percent of the content, that is to say the content is very low, so the boron cannot increase the gloss.

Effect of boron in the steel mold: in order to improve the hardenability of the steel, generally adding a little boron powder (0.0003%~0.005%). aincrease the high temperature strength of steel, strengthening the role of grain boundaries. The mechanism of boron improve hardenability have been proposed many theories, in which a more consistent understanding is: due to boron delayed nucleation of ferrite (but does not affect the thermodynamic properties of austenitic or ferritic matrix, that boron can reduce the nucleation rate of ferrite, but does not affect its growth rate of pearlite and martensite formation velocity) to improve the permeability of mold steel quenching."

According to metal powder supplier, boron is a rich resource, low price. Added boron in steel can significantly save nickel, chromium, molybdenum and other expensive alloy elements, there is considerable economic benefits. The main advantages of boron steel is cheap, to ensure the steel has the required hardenability and mechanical properties, at the same time, steel’s heat, cold processing properties is better. The main drawback is the hardenability fluctuations larger than not containing boron steel. The main effect of boron in the steel is to increase the hardenability of steel, thus saving the rare and precious metal, such as nickel, chromium, molybdenum etc. It can replace 1.6% Ni 0.3% Cr or 0.2% Mo, use boron instead molybdenum should pay attention that because of molybdenum can prevent or reduce the temper brittleness, and boron is slightly can promote the tendency of temper brittleness, so you can't use boron instead of molybdenum completely.

Adding boron in the steel, because of increasing the hardenability can make thick 20mm above steel’s properties of quenched and tempered have greatly improved, therefore, can use 40B steel and 40MnB steel instead of 40Cr steel, use 20Mn2TiB steel instead of 20CrMnTi steel. General require complete quenching, usually the spring section is small, the boron steel favorable. Effect of volatility on boron high silicon spring steel is larger, inconvenient for using. Boron and nitrogen and oxygen have a strong affinity, add 0.007% boron in steel while boiling, can eliminate the aging phenomenon of steel.

While boron steel heat treatment temperature is higher than 900 , boron carbide in steel are mostly dissolved, cooling speed has a great influence on the precipitation of boron carbide, cooling more slowly, the more intergranular precipitates numbers, leading to grain boundary precipitates grew into massive (such as cooling after hot rolling when stacking). The heat treatment after quenching and tempering, before the hot processing temperature and cooling speed distribution and impact the performance impact of boron in steel after quenching and tempering treatment. Through 1180  heat treating, quenching and tempering at 450 ~ 550 tempering temperature range, effect on the impact properties and boron tempering temperature is not obvious.

Source:http://www.mhcmp.com