18Ni Steel

1. What Steel is 07Cy18Ni11Nb?

07Cr18Ni11Nb belongs to the national standard austenitic heat-resistant steel, the executive standard: GB/T 20878-2007.

07Cr18Ni11Nb belongs to high carbon niobium-containing Cr-Ni austenitic stainless steel, due to the stabilization element Nb, its intergranular corrosion resistance and polysulfuric acid intergranular stress corrosion resistance are good, in acid, alkali, salt, and other corrosive media, its corrosion resistance is similar to 18-8 austenitic stainless steel containing Ti.

Therefore, it is widely used in boiler, power generation, petroleum, chemical industry, synthetic fiber, food, paper, and other industries. Heat exchangers for large boiler superheater tubes, reheater tubes, steam pipes, and petrochemical industries.

2. Is 18Ni300 stainless steel?

18Ni300 is a maraging steel

2.1 Chemical Composition

2.2 Mechanical Performance

Solution temperature 815-830℃

Aging temperature 4805℃

Hardness after aging HRC53-54

Tensile strength 2060

Yield strength 2010

Elongation after fracture 12

Section shrinkage 60.

2.3 Maraging Steel with Tensile Strength above 5000MPa?

18Ni(200), 18Ni(250), 18Ni(300), 18Ni(350) these maraging steels seem to have a tensile strength of less than 5000Mpa.

3. 350Ni18

350Ni18 Carbon-free (or micro-carbon) martensite as a matrix, aging can produce intermetallic compound precipitation hardening ultra-high strength steel. Unlike traditional high-strength steel, it is strengthened by the dispersion of intermetallic compounds instead of carbon. This gives it some unique properties: high toughness, low hardening index, good formability, simple heat treatment process, almost no deformation during aging, and very good weldability. Therefore, maraging steel has been widely used in departments requiring such characteristics.

3.1 Types

There are three types of this steel, the yield strength is 1350MPa, 1650MPa, and 1950MPa, the impurity content of this kind of steel is very low, and needs to be a primary or secondary vacuum smelting. It contains 0.003%B, 0.002%Zr, and 0.005%Ca to remove impurities and help improve thermoplastic processing properties.

3.2 Treatment Process

The heat treatment process includes 850℃ ~ 870℃ solution treatment, air cooling or water quenching, and then aging at 480℃ for 3h. In addition to Co, the added alloying elements reduce the Ms point but can keep the Mf point above room temperature, so that after solidification and quenching can be completely converted to martensite. The precipitation hardening phase is mainly caused by small flakes, and Mo is the main element of aging hardening.

Different strengths can be obtained by adjusting aging temperature and time. The aging temperature is too high (600℃), due to the low point of the steel, it will cause the formation of austenite, which is highly alloyed, so that the Ms point is reduced to below room temperature, and is stable to remain. If high strength is required, the original low-carbon martensite can be processed with cold plastic deformation of 50% shape variable before aging.

At high tensile strength, this steel still has excellent impact toughness, and has the effect of strengthening the notch, and the ratio of the notch strength to the tensile strength is between 1.35 and 1.65. 50% cold deformation processing before aging can increase the above nominal strength to 1700 MPa, 2000 MPa, and 2100MPa.

3.3 Development

18NI350 aging steel Maraging steel with industrial application value was first developed by International Nickel Corporation (INCO) in the early 1960s. From 1961 to 1962, B0.F0.Decker et al. added different contents of cobalt, molybdenum, and titanium to iron-nickel martensitic alloys and obtained 18Ni(200), 18Ni(250), and 18Ni(300) sheets of steel with yield strengths of 1400, 1700, and 1900MPa respectively through age hardening. First, 18Ni(200) and 18Ni(250) were applied to the rocket engine housing. The emergence of this type of steel immediately aroused the great attention of metallurgical workers in various countries.

The middle and late 1960s was the golden age of research and development of maraging steel. During this period, the International Nickel Company and the Vanadium Alloy Steel Company (Vasco) developed 18Ni(350) with a yield strength of 2400MPa.

Researchers have also done a lot of work on the processing technology, various properties, and strengthening and toughening mechanisms of martensitic aged steels, while also exploring the so-called 400 and 500-grade martensitic aged steels with yield strengths up to 2800 and 3500MPa.

However, these two grades of steel have not been applied in practice because of their low toughness and too complex production process. During this period, maraging steel also had a certain market in the field of tooling. At the same time, the former Soviet Union the Federal Republic of Germany, and other countries have also begun the research of maraging steel.

In the 1970s, Japan carried out systematic and in-depth research on maraging steel due to the development of uranium enrichment centrifuges.

Since the 1980s, due to the rising price of cobalt, the development of cobalt-free maraging steel has made great progress. For example, the United States T-250 (18Ni – 3Mo – 10.4Ti – 0.1A1), Japan’s 14Ni – 3Cr – 3Mo – 10.5Ti alloy, South Korea’s W250 (18Ni – 40.5w – 10.4Ti – 0.1A1) and the former Soviet Union’s H161-6M6(16Ni – 6V – 6Mo) have been successively Come out. These steels not only reduce the production cost by 20% to 30% but also the performance is very close to the corresponding strength level of cobalt-containing maraging steel.

4. Introduction to 18Ni250

18Ni250 maraging steel is a kind of age-hardening plastic die steel, the carbon content of steel is low, and the alloys that play a role in age-hardening are Ti, Al, Co, and Mo. The impurities have a great influence on the properties of martensitic age-hardening steel, and the effect on the higher yield strength steel is more obvious. This requires the steel to be vacuum smelted to reduce impurities, segregation, and air content in the ingot to ensure that the steel has better toughness and fatigue resistance.

4.1 18Ni250 Chemical Composition

4.1 18Ni250 Mechanical Properties

Solution temperature: 815-830℃

Aging temperature: 4805℃

Hardness after aging: HRC50-52

Tensile strength: 1850

Yield strength: 1800

Elongation after breaking: 10-12

Section shrinkage: 48-58