Metal materials and process properties

Metal materials are usually classified into ferrous metals, non-ferrous metals, and specialty metallic materials.

(1) Ferrous metals, also known as steel materials, include industrial pure iron containing more than 90% of iron, 2% to 4% of carbon containing carbon, carbon steel containing less than 2% carbon, and structural steel and stainless steel for various purposes. Heat resistant steel, high temperature alloy, stainless steel, precision alloy, etc. The broad ferrous metals also include chromium, manganese and their alloys.

(2) Non-ferrous metals refer to all metals and their alloys other than iron, chromium and manganese. They are usually classified into light metals, heavy metals, precious metals, semi-metals, rare metals and rare earth metals. Non-ferrous alloys generally have higher strength and hardness than pure metals, and have large electrical resistance and low temperature coefficient of resistance.

(3) Special metal materials include structural metal materials and functional metal materials for different purposes. Among them are amorphous metal materials obtained by rapid condensation process, as well as quasi-crystal, microcrystalline, nanocrystalline metal materials, etc.; and special functional alloys such as stealth, hydrogen, superconductivity, shape memory, wear resistance, vibration damping and the like. And metal matrix composite materials.

Generally divided into two categories of process performance and performance. The so-called process performance refers to the performance of metal materials under the specified cold and hot processing conditions during the manufacturing process. The technical performance of metal materials determines its adaptability to processing during the manufacturing process. Due to different processing conditions, the required process properties are different, such as casting properties, weldability, forgeability, heat treatment properties, machinability, etc.

1, welding performance

Refers to the ability of the welded metal to obtain high quality welds under normal welding process conditions. For carbon steel and low alloy steel, the welding performance is mainly related to the chemical composition of the metal material, wherein the carbon has the greatest influence, and the higher the carbon content, the worse the weldability. For example, low carbon steel has good welding performance, and high carbon steel and cast iron have poor welding performance.

2, forging performance

The ease with which a metal material is formed by a forging process is called forging performance. Its merits and demerits depend on the plasticity and deformation resistance of the metal material. When the metal with good plasticity is deformed, it is not easy to crack; the metal with low deformation resistance is labor-saving when forging, and the tool and the mold are not easy to wear. For example, carbon steel has better forging performance under heating, and cast iron cannot be forged.

3, cutting performance

It refers to the difficulty of metal cutting. It is generally considered that the metal material is more easily cut when it has a suitable hardness (170 to 230 HBS) and sufficient brittleness. Therefore, gray cast iron has better cutting performance than steel, and general carbon steel has better cutting performance than high alloy steel. Changing the chemical composition of steel and performing proper heat treatment is an important way to improve the cutting performance of steel.

4, heat treatment performance

The heat treatment performance of metal materials is evaluated according to their hardenability, hardenability, grain growth tendency, temper brittleness tendency, etc.

5, casting performance

The ability of a metal material to obtain a good casting using a casting method is called casting performance. Its pros and cons are manifested in the following three aspects:

(1) Fluidity Fluidity is the ability of a cast metal to flow itself or to fill a mold during casting. It is mainly affected by metal chemical composition and casting temperature. Metallic liquids with good fluidity can cast castings with complete shapes, precise dimensions and clear outlines.

(2) Shrinkage It refers to the phenomenon that the volume and size of the molten metal are reduced during the entire cooling process in the mold, which is called shrinkage. The shrinkage of the casting not only affects the size, but also causes defects such as shrinkage, porosity, internal stress, deformation and cracking of the casting. Therefore, the metal used for casting has a smaller shrinkage ratio.

(3) Segregation is a phenomenon in which the chemical composition of the liquid metal is not uniform after solidification. When the segregation is severe, the mechanical properties of various parts of the casting can be greatly different, which reduces the quality of the casting.