Adding nickel to steel can indeed improve the strength and toughness of steel, but the appropriate nickel content depends on the specific type of steel, its purpose and production conditions.
Generally speaking, the appropriate nickel content ranges from 0.5% to 5%.
This range is not absolute, because different steels have different requirements for nickel.
Analysis of nickel content to improve strength and toughness
1. Effect of nickel on strength:
- Nickel can strengthen ferrite and refine pearlite in steel, thereby improving the strength of steel.
According to statistics, every 1% increase in nickel can increase the strength of steel by about 29.4Pa (Note: the unit here may be a typo of MPa or Pa. It is usually more common to express strength in MPa, but it is given here according to the original information).
- As the nickel content increases, the yield strength of steel increases faster than the tensile strength, so the strength ratio of nickel-containing steel may be higher than that of ordinary carbon steel.
2. Effect of nickel on toughness:
- While nickel improves the strength of steel, it has relatively little damage to the toughness, plasticity and other processing properties of steel. This means that while increasing strength, good toughness can be maintained.
- For low carbon steel that does not require quenching and tempering and is used in the rolled, normalized or annealed state, a certain amount of nickel can increase the strength of the steel without significantly reducing its toughness.
Choice of nickel content
- Low carbon steel: For this type of steel, an appropriate amount of nickel can increase the strength without significantly reducing toughness. The specific nickel content needs to be determined according to the specific use and production conditions of the steel.
- Medium carbon steel: Nickel can reduce the pearlite transformation temperature, make the pearlite finer, and reduce the carbon content of the eutectoid point, thereby increasing the amount of pearlite and improving the strength of the steel.
If the strength of the steel is the same, the carbon content of nickel-containing steel can be appropriately reduced, thereby improving the toughness and plasticity of the steel.
- Stainless steel and special steel: In stainless steel and some special steels, a higher nickel content is required to improve its corrosion resistance, heat resistance and strength.
For example, steel containing 3.5% nickel can be used at -100°C, while steel containing 9% nickel can work at -196°C.
Precautions
- Too high a nickel content may increase the brittleness of the steel, thereby reducing its toughness. Therefore, when designing alloys, it is necessary to comprehensively consider strength, toughness and other performance requirements to determine the optimal nickel content.
- The price of nickel is relatively high, and too high a nickel content will increase production costs. Therefore, in practical applications, it is necessary to weigh the relationship between performance improvement and cost increase.
In summary, the specific content of nickel added to steel should be determined according to the type, purpose and production conditions of the steel to ensure that good toughness and other properties are maintained while improving strength.