Effect of nickel and boron on properties on 40kh steel

1. The replacement of nickel by boron in construction steels for the purpose of ensuring hardenability is inadvisable when the nickel content is 0.5–1%. 2. The negative effect of boron on the austenite grain growth wanes as the nickel content in the steel is raised above 2%. 3. Nickel and nickel plus boron do not affect strength. The impact toughness of steel containing nickel or, particularly, nickel plus boron declines as the nickel content is increased during tempering at 400–600°. 4. Steels alloyed with nickel reduce the toughness margin at HRC 30 (tempering at 550°) and increase it at HRC 25 (tempering at 605°). This is evidently because nickel in the presence of chromium intersifies the tendency of the steel toward reversible temper brittleness, which appears during tempering at 500–600°.