Generally speaking, for low-carbon steels in the rolled, normalized or annealed state that have not been quenched and tempered, a certain nickel content can increase the strength of the steel without significantly reducing its toughness.

Carbon carbon

As the carbon content in steel increases, the yield point and tensile strength increase, but the plasticity and impact properties decrease. When the carbon content exceeds 0.23%, the welding performance of the steel deteriorates. Therefore, the carbon content of low-alloy structural steel used for welding generally does not exceed 0.20%. The high carbon content will also reduce the atmospheric corrosion resistance of the steel, and the high-carbon steel in the open yard is easy to rust; in addition, carbon will increase the cold brittleness and aging sensitivity of the steel.

Chrome Chrome

Chromium can increase the hardenability of steel, and has the effect of secondary hardening, which can increase the hardness and wear resistance of carbon steel without making the steel brittle. When the content exceeds 12%, the steel has good high temperature oxidation resistance and oxidation corrosion resistance, while also increasing the thermal strength of the steel. Chromium is the main alloying element of stainless steel, acid-resistant steel and heat-resistant steel.

Chromium can increase the strength and hardness of carbon steel in the rolled state, and reduce the elongation and section rate. When the chromium content exceeds 15%, the strength and hardness will decrease, and the elongation and reduction of area will increase accordingly. After grinding, chromium-containing steel parts can easily obtain higher surface quality.

The main function of chromium in the quenched and tempered structure is to improve the hardenability, so that the steel has better comprehensive mechanical properties after quenched and tempered. Chromium-containing carbides can also be formed in carburized steel, thereby increasing the surface resistance of the material. Abrasive. Chromium-containing spring steel is not easy to decarburize during heat treatment. Chromium can improve the wear resistance, hardness and red hardness of tool steel, and has good tempering stability. In electric heating alloys, chromium can improve the oxidation resistance, electrical resistance and strength of the alloy.

Nickel Nickel

Nickel strengthens ferrite and refines pearlite in steel. The overall effect is to increase the strength, and the impact on plasticity is not significant.

Generally speaking, for low-carbon steels in the rolled, normalized or annealed state that have not been quenched and tempered, a certain nickel content can increase the strength of the steel without significantly reducing its toughness. According to statistics, every increase of 1% of nickel can increase the strength by about 29.4Pa.

As the nickel content increases, the yield of steel increases faster than the tensile strength, so the proportion of nickel-containing steel can be higher than that of ordinary carbon steel. Although nickel improves the strength of steel, compared with other alloying elements, it does less damage to the toughness, plasticity and performance of other processes.

For medium carbon steel, nickel reduces the pearlite transformation temperature and makes pearlite finer; and because nickel reduces the carbon content of the eutectoid point, it has more pearlite than carbon steel with the same carbon content. The strength of nickel-containing pearlitic ferritic steel is higher than that of carbon steel with the same carbon content. On the contrary, if the strength of the steel is the same, the carbon content of the nickel-containing steel can be appropriately reduced, and the toughness and plasticity of the steel can be improved. Nickel can improve the fatigue resistance of steel and reduce the sensitivity of steel to notches. Nickel reduces the low-temperature brittleness transition temperature of steel, which is of great significance to low-temperature steel. Steel with 3.5% nickel can be used at -100°C, and steel with 9% nickel can be used at -196°C. Nickel does not increase the creep resistance of steel, so it is generally not used as a strengthening element for hot-strength steel.

For iron-nickel alloys with high nickel content, the coefficient of linear expansion changes significantly as the nickel content increases or decreases. Using this feature, it is possible to design and produce precision alloys and bimetal materials with extremely low or certain linear expansion coefficients. In addition, the addition of nickel to steel can not only resist acid, but also alkali, and has corrosion resistance to the atmosphere and salt. Nickel is one of the important elements of stainless and acid-resistant steel.