Differences between Forged Steel Valves and Cast Steel Valves

Which is better, forged steel valves or cast steel valves?

Cast steel valves are made of steel used for casting. They are a type of cast alloy. Cast steel is categorized into three types: cast carbon steel, cast low-alloy steel, and cast specialty steel. Cast steel refers to a type of steel casting produced by the casting process. Cast steel is primarily used to manufacture parts with complex shapes that are difficult to forge or machine, yet require high strength and ductility.
Forged steel refers to various forgings and forgings produced by the forging process. Forged steel parts are of higher quality than cast steel parts and can withstand high impact forces. They also have higher ductility, toughness, and other mechanical properties than cast steel parts. Therefore, forged steel parts should be used for all important machine parts.

Differences between Forged Steel Valves and Cast Steel Valves:

Forged steel valves are of higher quality than cast steel valves and can withstand high impact forces. They also have higher ductility, toughness, and other mechanical properties than cast steel parts. However, their nominal diameter is smaller, generally below DN50. The pressure rating of cast valves is relatively low. The commonly used nominal pressures are PN16, PN25, PN40, 150LB-900LB. Forged steel valve ratings: PN100, PN160, PN320, 1500LB-3500LB, etc. Cast steel is mainly used to manufacture parts with complex shapes that are difficult to forge or cut and require high strength and plasticity. Casting is liquid molding, while forging is a plastic deformation process. Forging can improve the internal structure of the workpiece, improve mechanical properties, and achieve uniform grains. Important and demanding workpieces must be forged. Casting will cause segregation and defects. Of course, casting has its advantages. Forging complex workpieces is difficult to open the mold, so casting has been adopted.

Introduction to forged valves (forged steel valves):

1. Forging can be divided into the following types according to the forming method:
(1) Closed-mode forging (die forging). It can be divided into die forging, rotary forging, cold heading, extrusion, etc. The metal blank is placed in a forging die with a certain shape and deformed under pressure to obtain a forging. According to the deformation temperature, it is divided into cold forging (forging temperature is room temperature), warm forging (forging temperature is lower than the recrystallization temperature of the blank metal), and hot forging (forging temperature is higher than the recrystallization temperature).
(2) Open forging (free forging). There are two methods: manual forging and mechanical forging. The metal blank is placed between the upper and lower anvils (iron) and the impact force or pressure is used to deform the metal blank to obtain the required forging.

2. Forging is one of the two major components of forging. Important parts in machinery with high loads and severe working conditions are mostly forged. Simpler shapes can be made of rolled welded parts, except for profiles and plates. Forging can eliminate weld holes and cast porosity in metal materials.

3. Correct selection of forging ratio is very important to improving product quality and reducing costs. Forging materials are mainly carbon steel, stainless steel and alloy steel. The forging ratio refers to the ratio of the cross-sectional area of the metal before deformation to the cross-sectional area after deformation. The original state of the material includes ingots, bars, liquid metal and metal powder.

4. The mechanical properties of forgings are generally better than those of castings of the same material. Forging is a processing method that uses a forging machine to apply pressure to the metal blank to cause the metal blank to undergo plastic deformation to obtain a certain shape and size with good mechanical properties.

Detailed introduction to cast valves (cast steel valves):

1. There are many types of casting, which are divided into ordinary sand casting and special casting according to the molding method:
(1) Ordinary sand casting, including dry sand mold, wet sand mold and chemical hardening sand mold.
(2) Special casting, which is divided into two categories according to the casting material: special casting of ore and special casting of metal materials; Special casting with metal as the casting material, including: pressure casting, metal mold casting, low-pressure casting, continuous casting, centrifugal casting, etc. Special casting with natural mineral sand and gravel as the casting material, including: full mold casting, investment casting, shell casting in foundry workshop, clay casting, negative pressure casting, ceramic casting, etc.

2. Casting is a metal heat treatment process. Casting production has good comprehensive mechanical properties, wide adaptability, and low blank cost. For parts with more complex shapes, especially those with complex internal structures, the economic efficiency of casting production can be more apparent.

3. Casting is the basic process of modern machinery manufacturing industry. It is to melt metal into liquid and pour it into the casting mold. After cooling and solidification, the casting is taken out and cleaned to obtain a casting (blank or part) with predetermined size, shape and mechanical properties.

4. The casting process usually includes:
(1) Preparation of casting mold (the mold used to turn liquid metal into solid casting. The quality of the casting mold directly affects the quality of the casting). Casting molds can be divided into disposable molds, multiple-use molds and permanent molds according to the number of times they are used. Casting molds can be divided into metal molds, sand molds, clay molds, ceramic molds, graphite molds, etc. according to the material.
(2) Melting and pouring of casting metal. Casting metals mainly include cast iron, carbon steel and stainless steel.
(3) Treatment and inspection of castings. Casting treatment includes removing foreign matter and cores from the casting surface, treating protrusions (grinding burrs, cutting off pouring nozzles and treating seams, etc.), heat treatment, shaping, rough processing and rust prevention of castings, etc.

5. Disadvantages of the casting production method. Casting will produce noise, harmful gases and dust, etc., which pollute the environment. In addition, it requires a lot of materials (such as molding materials, metals, fuels, wood, etc.) and equipment (such as core making machines, metallurgical furnaces, molding machines, sand mixers, shot blasting machines, etc.).

6. Cast steel is divided into three categories: cast carbon steel, cast low alloy steel and cast special steel.
(1) Cast carbon steel. Cast steel with carbon as the main alloying element and containing a small amount of other elements. Cast low carbon steel contains less than 0.2% carbon, cast medium carbon steel contains 0.2% to 0.5% carbon, and cast high carbon steel contains more than 0.5% carbon. As the carbon content increases, the strength and hardness of cast carbon steel increase. Cast carbon steel has high strength, plasticity and toughness, and is low in cost. It is used in heavy machinery to manufacture parts that bear heavy loads, such as rolling mill frames and hydraulic press bases; and in railway vehicles to manufacture parts that bear large forces and impacts, such as rockers, side frames, wheels and couplers.
(2) Cast low alloy steel. Cast steel containing alloying elements such as manganese, chromium and copper. The total amount of alloying elements is generally less than 5%, has great impact toughness, and can obtain better mechanical properties through heat treatment. Cast low alloy steel has better performance than carbon steel, can reduce the weight of parts and increase service life.
(3) Cast special steel. Alloy cast steels refined to meet special needs are of various types and usually contain one or more high-amount alloying elements to obtain certain special properties. For example, high manganese steel containing 11% to 14% manganese can withstand impact wear and is mostly used for wear-resistant parts of mining machinery and engineering machinery; various stainless steels with chromium or chromium-nickel as the main alloying elements are used for parts working under corrosive conditions or high temperatures above 650°C, such as chemical valve bodies, pumps, containers or turbine housings of large-capacity power stations.

Valve casting process:

1. Casting: It is a process of melting metal into a liquid that meets certain requirements and pouring it into a casting mold. After cooling, solidification and cleaning, a casting (part or blank) with a predetermined shape, size and performance is obtained. It is the basic process of the modern machinery manufacturing industry.

2. Casting produces low-cost blanks, making it particularly economical for parts with complex shapes, especially those with complex internal cavities. It also offers wide adaptability and excellent overall mechanical properties.

3. However, casting requires a large number of materials (such as metal, wood, fuel, molding materials, etc.) and equipment (such as metallurgical furnaces, sand mixers, molding machines, core making machines, sand shakers, shot blasting machines, and cast iron plates), and generates dust, harmful gases, and noise, polluting the environment.

4. Casting is one of the earliest metal heat processing techniques mastered by humans, with a history of approximately 6,000 years. Bronze frog castings appeared in Mesopotamia as early as 3200 BC. Between the 13th and 10th centuries BC, China reached a peak in bronze casting, achieving a high level of craftsmanship. Examples include the 875-kilogram Simuwu Fangding (Simuwu Square Ding) from the Shang Dynasty, the Zenghouyi Zun Pan (Zenghouyi Zun Pan) from the Warring States Period, and the light-transmitting mirror from the Western Han Dynasty, all of which are representative products of ancient casting. Early casting was heavily influenced by pottery, with most castings being tools and utensils for agricultural production, religion, and daily life, often characterized by a strong artistic quality. In 513 BC, China produced the world's earliest recorded iron casting—the Jin Dynasty tripod (weighing approximately 270 kilograms). Iron casting production began in Europe around the 8th century AD. Following the Industrial Revolution of the 18th century, casting entered a new era of serving large-scale industry. The 20th century saw rapid development in casting, with the development of ductile iron, malleable iron, ultra-low-carbon stainless steel, and cast metal materials such as aluminum-copper, aluminum-silicon, aluminum-magnesium alloys, and titanium- and nickel-based alloys. New processes for inoculating gray cast iron were also invented. Since the 1950s, new processes have emerged, including wet sand high-pressure molding, chemically hardened sand molding and core making, vacuum molding, and other specialized casting processes, including shot blasting.

5. There are many types of casting, which are usually divided into the following categories according to the molding method:
(1) Ordinary sand casting, including wet sand mold, dry sand mold and chemical hardening sand mold.
(2) Special casting, which can be divided into two categories according to the molding material: special casting with natural mineral sand as the main molding material (such as investment casting, clay mold casting, foundry shell casting, negative pressure casting, full mold casting, ceramic mold casting, etc.) and special casting with metal as the main casting material (such as metal mold casting, pressure casting, continuous casting, low pressure casting, centrifugal casting, etc.).

6. The casting process usually includes:
(1) Preparation of the mold (the container that turns liquid metal into solid casting). The mold can be divided into sand mold, metal mold, ceramic mold, clay mold, graphite mold, etc. according to the material used. It can be divided into disposable mold, semi-permanent mold and permanent mold according to the number of times it is used. The quality of the mold preparation is the main factor affecting the quality of the casting;
(2) Melting and pouring of cast metal. Cast metal (cast alloy) mainly includes cast iron, cast steel and cast non-ferrous alloy;
(3) Casting treatment and inspection. Casting treatment includes removing foreign matter from the core and casting surface, cutting off the pouring riser, grinding burrs and seams and other protrusions, as well as heat treatment, shaping, rust prevention and rough processing. Imported pump valve

Valve forging process:

1. Forging: It is a processing method that uses a forging machine to apply pressure to the metal blank to cause it to undergo plastic deformation to obtain forgings with certain mechanical properties, certain shape and size.

2. One of the two major components of forging. Forging can eliminate the looseness of the metal in the casting state and weld the holes. The mechanical properties of forgings are generally better than those of castings made of the same material. For important parts in machinery with high loads and severe working conditions, forgings are mostly used, except for those with simpler shapes that can be made of rolled plates, profiles or welded parts.

3. Forging can be divided into the following types according to the forming method:
(1) Open forging (free forging). The metal is deformed between the upper and lower iron blocks (anvils) by impact force or pressure to obtain the required forgings. There are mainly two types: manual forging and mechanical forging.
(2) Closed forging. The metal billet is compressed and deformed in a forging die with a certain shape to obtain forgings. It can be divided into die forging, cold heading, rotary forging, extrusion, etc. According to the deformation temperature, forging can be divided into hot forging (processing temperature is higher than the recrystallization temperature of the billet metal), warm forging (lower than the recrystallization temperature) and cold forging (room temperature).

4. The materials used for forging are mainly carbon steel and alloy steel of various compositions, followed by aluminum, magnesium, titanium, copper, etc. and their alloys. The raw material state includes bar stock, ingots, metal powder, and liquid metal. The ratio of the metal's cross-sectional area before deformation to its cross-sectional area after deformation is called the forging ratio. Correctly selecting the forging ratio is crucial for improving product quality and reducing costs.