Reference for Production Process of Isothermal Quenched Ductile Iron in the United States

There are some differences in mechanical properties between isothermal quenched ductile iron in the United States and isothermal ductile iron in China. For example, isothermal ductile iron in China starts with mechanical properties of 900 megapascals, while in the United States it starts with 750 megapascals. In addition, there are also unique aspects in terms of production process details, melting, and heat treatment. Let's take a look at these places that are different from our domestic ones and see if there are any areas we can learn from. The standard grades of isothermal quenched ductile iron in the United States are mainly based on ASTM A897, and the common ones are as follows:

ASTM A897 Grade 110/70/11 Mechanical properties: Tensile strength ≥ 758MPa, yield strength ≥ 483MPa, elongation ≥ 11%. Scope of application: Suitable for general mechanical parts that require a balance between strength and toughness, such as small gears, shaft sleeves, etc. ASTM A897 Grade 130/90/09 Mechanical properties: Tensile strength ≥ 896MPa, yield strength ≥ 621MPa, elongation ≥ 9%. Scope of application: It can be used to manufacture parts that can withstand moderate loads and certain impacts, such as steering knuckles, suspension arms, etc. of automobiles.

ASTM A897 Grade 150/110/07 Mechanical properties: Tensile strength ≥ 1034MPa, yield strength ≥ 758MPa, elongation ≥ 7%. Scope of application: Commonly used for manufacturing parts that require high strength and wear resistance, such as crusher hammers, liners, etc. in mining machinery. ASTM A897 Grade 175/125/04 Mechanical properties: Tensile strength ≥ 1207MPa, yield strength ≥ 862MPa, elongation ≥ 4%. Scope of application: Suitable for manufacturing high-strength and high hardness parts, such as rollers and molds for large rolling mills. ASTM A897 Grade 200/155/02 Mechanical properties: Tensile strength ≥ 1379MPa, yield strength ≥ 1069MPa, elongation ≥ 2%. Scope of application: It can be used to manufacture special parts with extremely high strength requirements and relatively low toughness requirements, such as certain key components in the aerospace field.

ASTM A897 Grade 230/185/01 Mechanical properties: Tensile strength ≥ 1586MPa, yield strength ≥ 1276MPa, elongation ≥ 1%. Scope of application: Generally used for manufacturing ultra high strength wear-resistant and impact resistant parts, such as certain important components in military equipment. In addition, there are standard grades such as Grade 1-6. What are the differences in chemical composition of isothermal ductile iron between China and the United States? In the American ASTM A897 standard, the typical chemical composition of isothermal quenched ductile iron such as Grade 2 and Grade 5 is 3.7% carbon, 2.5% silicon, 0.28% manganese, ≤ 0.80% copper, 0.00% -0.25% molybdenum, ≤ 2.0% nickel, and 93% iron. The chemical composition of Chinese QT1050-6 and other grades of isothermal quenched ductile iron is generally 3.5% -3.9% carbon, 2.2% -2.6% silicon, 0.2% -0.4% manganese,<0.04% phosphorus,<0.02% sulfur, 0.03% -0.05% magnesium, 0.3% -0.5% copper, 0.15% -0.25% molybdenum, and 0.02% -0.05% rare earth. Comparison shows that the carbon content of the main element is relatively fixed at around 3.7% in some American standards, while the carbon content of different grades in China varies between 3.5% and 3.9%, and can be adjusted more finely according to specific grades and performance requirements. Silicon content: Generally around 2.5% in the United States and 2.2% -2.6% in China, which is relatively more flexible. The manganese content of alloy elements: Generally, it is 0.28% in the United States, while in China, the content is mostly between 0.2% and 0.4%, with the United States being relatively more stable. Copper content: The United States stipulates a copper content of ≤ 0.80%, while China generally ranges between 0.3% -0.5% or 0.4% -0.6%, with a relatively clearer range of content in China. Molybdenum content: 0.00% -0.25% in the United States and approximately 0.15% -0.25% in China. China has relatively more specific control over molybdenum content. Nickel content: The United States allows nickel content to be ≤ 2.0%, while China does not explicitly specify nickel content in common chemical composition standards for isothermal quenched ductile iron. Magnesium content of spheroidizing element: China generally controls the magnesium content at 0.03% -0.05%, while the US standard does not clearly specify the range of this key spheroidizing element content. Rare earth content: China has clearly stipulated that the rare earth content is between 0.02% and 0.05%, while the United States has not mentioned it.

What are the differences in heat treatment processes for isothermal ductile iron between China and the United States?

Austenitization stage temperature: In China, ductile iron is generally heated to 850-950 ℃. In the United States, when producing ductile iron such as 120-90-2, the quenching heating temperature is 860-900 ℃, the complete austenitization normalizing temperature is 880-930 ℃, and the incomplete austenitization normalizing temperature is 820-860 ℃.

Insulation time: China usually maintains insulation for 1-2 hours, while the United States determines insulation for about 1 hour every 25mm wall thickness based on the wall thickness and size of the casting.

Cooling rate during quenching stage: China emphasizes rapid cooling to a temperature range that prevents the formation of pearlite in castings and is higher than the temperature at which martensite begins to form, usually between 250-380 ℃, but does not mention specific cooling rate values. When quenching in the United States, castings are quickly cooled in quenching media such as oil or molten salt to obtain martensitic structure. Quenching medium: Salt bath is commonly used as a quenching medium in China, such as using a nitrate formula of 55% potassium nitrate and 45% sodium nitrite. The United States uses quenching media such as oil or molten salt.

Isothermal treatment stage isothermal temperature: In China, isothermal quenching is generally carried out between 250-380 ℃. In the United States, when producing ductile iron such as 120-90-2 for tempering, the tempering temperature is usually between 250-350 ℃. For castings that require high comprehensive performance, a tempering temperature of 500-600 ℃ can also be used.

Isothermal time: China maintains this temperature for 1.5-3.5 hours, while the tempering and insulation time in the United States is generally 1-3 hours.

Cooling stage in China: usually air-cooled to room temperature. The cooling method after tempering in the United States is usually air cooling or furnace cooling.