Commonly used steel castings
There are many classification methods for steel castings, which are often classified by chemical composition and scope of use:
1.By chemical composition: carbon steel, medium, and low alloy steel, and high alloy steel
A. Carbon Steel: Iron-carbon alloy, which also contains a certain amount of manganese and silicon. The manganese content is generally below 1.0%. Sulfur and phosphorus are harmful elements and should be contained as little as possible, and other elements as residual elements, such as Cr, Mo, and Ni, should be reduced as much as possible.
B. Medium and low alloy steel: In addition to carbon elements, to obtain the required performance, a certain amount of alloying elements, such as Cr, Mo, Ni, and other general alloying elements, are consciously added, and the total amount of general alloying elements do not exceed 8%, and the carbon content is mostly in the Below 0.3%.
C. High alloy steel: high alloying element content, such as stainless steel containing more than 12% Cr, and some stainless steel containing CrNi content as high as 50% or more, usually stainless steel, heat-resistant steel, wear-resistant steel.
2. Classification by use
A. Steel for general construction machinery: It is characterized by better comprehensive mechanical properties and process properties (machining, welding, etc.)
B. Construction steel: It is characterized by good plasticity and welding function.
C. Steel for pressure vessels: such as valves, pumps, and pipe fittings
Features: good plasticity and toughness, certain mechanical properties; good craftsmanship
Performance, especially high solderability, is divided into high temperature and low temperature.
D. Steel for high temperature and low temperature
E. Stainless steel: used in corrosive conditions.
3. About the grades of steel castings
A. There are many grades of steel castings;
B. There are various ways to express the grades of steel castings, expressed by chemical elements, expressed by mechanical properties (strength grade), expressed by letters, expressed by numerical codes, or expressed by a mixture of alphanumerics and chemical components.
C. For each grade, it is necessary to find out what standard of which country it belongs to, and what kind of steel it belongs to.
Grades of carbon steel castings
1. Most countries in the world generally do not specify chemical composition except for phosphorus, and usually use mechanical properties (strength grade) to indicate the grade.
A. China’s grades: GB/T11352-1989 stipulates five grades, such: ZG 200-400
ZG: means cast steel
200: Indicates yield strength grade, unit: MPa (megapascal)
400: Indicates the tensile strength grade, unit: MPa (megapascal)
Yield strength: The strength of the material that begins to produce permanent (plastic) deformation under stress, but does not break;
Tensile strength: the strength of the material when it breaks under stress
MPa—1×106Pa, Pa—1N/㎡
1MPa=1×106Pa=1×106N/㎡=1N/m㎡
Newtons and kilograms
Newton: a unit of force
kg: mass unit
On Earth: 1 kg force = 9.81 Newtons
B. International Standard Grade (International Standard ISO)
Use strength grades to indicate grades, such as 200-400 for yield strength grades and tensile strength grades respectively.
200-400W means weldable carbon steel
C. There are 7 grades in ASTMA27/A27M, the carbon steel casting standard for general engineering in the United States, which are represented by groups and strength grades, such as Grade U-60-30
D. There are 3 grades in the British carbon steel casting standard BS3100 for general purpose: A1-A3
E. The German standard DIN1681 for carbon steel castings for general purposes uses GS to indicate carbon steel or low alloy steel and uses strength grades and numbers to indicate grades.
F. Japanese standard JIS5101 uses SC to indicate carbon steel, followed by numbers to indicate strength grades.
2. High-strength cast steel for general engineering and structure is carbon steel and low-alloy steel is strengthened by heat treatment.
A. The international standard ISO9477 uses numbers to indicate the strength level
B. American standard ASTM A148/A148M expresses grades with strength
C. China’s high-strength cast steel and low-alloy steel are classified into one category, which is expressed by carbon content and alloying element content in JB/T6402 and GB/T14408, such as ZG35 CrMo
ZG: cast steel, 35: means carbon content unit 0.01%; Cr content, about 1%; Mo content: 0.2%-0.3%
International medium and low alloy steel
- Pressure-resistant steel castings in the United States, used for steel grades in ASTM A487/A487M
Group and grade representation, are widely used in wellhead valves.
Steel grades in ASTM A389/A389M are indicated by letters and numbers and are characterized by containing vanadium, which is used in steam turbine products.
- German low alloy steel high strength alloy steel, such as GS24Mn6
GS: carbon steel or low alloy steel; Mn: alloying element Mn;
6: Indicates the content of manganese, the number is 4 times the percentage of manganese.
Professional steel
Steel for valve:
A. Fusion weldable carbon steel castings for high-temperature ASTM A216/A216M, WC, WCB, WCC
The valve is the most widely used, with carbon content below 0.3% and Mn content below 1.00%, with good comprehensive mechanical properties and good welding performance.
B. Alloy steel and stainless steel ASTM A217/A217M for high-temperature pressure vessels, with
WC1, WC6, WC9, C12, C5, CA15, etc., low carbon content, Cr, Mo, and Ni, good mechanical properties at high temperature, poor welding performance than WCB, widely used in pressure vessels above 420 ℃ on the valve.
C. Alloy and stainless steel for low-temperature pressure vessel ASTM A352/A352M have LCB, LC3, etc.
Low carbon content, Ni, Mo, some grades contain Cr, good low temperature (below -46 ℃) toughness, widely used in low-temperature valves.
D. Austenitic, austenitic-ferritic stainless steel for pressure vessels
ASTM A351/A351M, ASTMA890/A890M, low carbon content, high Cr, Ni, and some high Mo, wear and corrosion resistance, good mechanical properties, grades are CF3, CF8, CF3M, CF8M, CD4MCn, 4A, 6A, etc., the above grades are commonly used internationally.
In addition, there are many chemical compositions in European standard EN10213, and the performance is the same or similar to the above.
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