Knowledge of metal materials

Metal materials are the most important engineering materials, including metals and metal-based alloys. Metals and their alloys are divided into two parts in industry:

(1) ferrous materials-iron and iron-based alloys (steel, cast iron and iron alloys).

(2) Non-ferrous materials-all metals except ferrous metals and their alloys.

Nonferrous metals can be divided into light metals, fusible metals, refractory metals, precious metals, rare earth metals and alkaline earth metals according to their properties and characteristics.

(2) Non-metallic materials

Non-metallic materials include refractory materials, refractory insulation materials, corrosion-resistant (acid) non-metallic materials and ceramic materials.

(1) Refractory refractory refers to a material that can withstand the action at high temperature and is not easy to be damaged. Commonly used refractory materials are refractory masonry materials, refractory cement and refractory concrete.

(2) Fire-resistant thermal insulation materials. Fire-resistant insulation materials are also called heat-resistant insulation materials. Commonly used thermal insulation materials include diatomite, frog stone, glass fiber (also known as slag wool), asbestos and its products.

(3) Corrosion-resistant (acid) nonmetallic materials. Corrosion-resistant (acid-resistant) nonmetallic materials are mainly composed of metal oxides, silicon oxides and silicates. In some cases, they are ideal substitutes for stainless steel and corrosion-resistant alloys. Commonly used nonmetallic corrosion-resistant materials include cast stone, graphite, acid-resistant cement, natural acid-resistant stone, glass and so on.

(4) ceramic materials.

(2) Non-metallic materials

Non-metallic materials include refractory materials, refractory insulation materials, corrosion-resistant (acid) non-metallic materials and ceramic materials.

(1) Refractory refractory refers to a material that can withstand the action at high temperature and is not easy to be damaged. Commonly used refractory materials are refractory masonry materials, refractory cement and refractory concrete.

(2) Fire-resistant thermal insulation materials. Fire-resistant insulation materials are also called heat-resistant insulation materials. Commonly used thermal insulation materials include diatomite, frog stone, glass fiber (also known as slag wool), asbestos and its products.

(3) Corrosion-resistant (acid) nonmetallic materials. Corrosion-resistant (acid-resistant) nonmetallic materials are mainly composed of metal oxides, silicon oxides and silicates. In some cases, they are ideal substitutes for stainless steel and corrosion-resistant alloys. Commonly used nonmetallic corrosion-resistant materials include cast stone, graphite, acid-resistant cement, natural acid-resistant stone, glass and so on.

(4) ceramic materials.

Second, the performance and characteristics of commonly used engineering materials

(1) metal material

1, ferrous metal

Alloys with carbon content less than 2. 1 1% by weight is called steel, and the alloy with carbon content greater than 2. 1 1% by weight is called pig iron.

Classification of (1) steel and its alloys

The mechanical properties of steel depend on its composition and metallographic structure. The content of carbon in steel has a decisive influence on the properties of steel.

In engineering, the more general classification is:

L) Classification by chemical composition. It can be divided into carbon steel, low alloy steel and alloy steel.

2) according to the main quality grade classification:

① Ordinary carbon steel, high-quality carbon steel and special carbon steel;

② Ordinary low alloy steel, high quality low alloy steel and special low alloy steel;

③ Ordinary alloy steel, high-quality alloy steel and special alloy steel.

(2) Representation of steel grade. According to the national standard "Brand Representation of Steel Products", the brand of steel products in China is represented by the combination of Chinese phonetic alphabet, chemical symbols and Arabic numerals, namely:

L) The chemical elements in the brand are expressed by international chemical elements.

2) The product name, use, characteristics and technological methods are usually represented by the first letter representing the Chinese phonetic alphabet of the product.

3) The content (%) of main chemical elements in steel is expressed in Arabic numerals.

The brand of alloy structural steel shall be compiled according to the following rules. Numbers represent the average value of carbon content. Alloy structural steel and spring steel are expressed by two digits as a few ten thousandths of the average carbon content, and stainless acid-resistant steel and heat-resistant steel are expressed as one thousandth of the carbon content. Average carbon content < 0. 1% (indicated by "0"); The average carbon content is less than 0.03%, expressed by "00" =. When the average carbon content of alloy tool steel is > 1.00%, the carbon content is not standardized, otherwise it is expressed as one thousandth. High-speed tool steel and bearing steel are not marked with carbon content, and bearing steel is marked with symbol "C". If the average alloy content is less than 1.5%, only the element symbol is marked in the brand, but the content is not marked.

In the classification of steel, high-quality steel is classified according to ().

A. chemical composition B. use C. smelting quality D. smelting method

Answer: c

(3) Properties and characteristics of steels and their alloys commonly used in engineering.

L) carbon structural steel.

Carbon structural steel has simple production process, good process performance (such as weldability and pressure workability), necessary toughness, good plasticity, low price and easy supply, and is generally used after hot rolling. It has been widely used in bridges, buildings and ships. Some mechanical parts that are not very important and have low requirements for toughness are also widely used.

2) Low alloy high strength structural steel. Low-alloy high-strength structural steel has higher toughness than carbon structural steel, and has good weldability, cold and hot pressure workability and corrosion resistance. Some steel grades also have low ductile-brittle transition temperatures.

3) Alloy structural steel. Alloy structural steel is widely used to manufacture various important mechanical parts and components that require high toughness. Quenched parts with complex shapes or large cross-sectional dimensions or requiring high toughness are generally alloy structural steel.

4) Stainless steel and acid-resistant steel. Widely used in chemical industry, petroleum, food machinery and national defense industry.

According to the metallographic structure of stainless steel in use, it can be divided into five types: ferrite, martensite, austenite, ferrite plus austenite and precipitation hardening stainless steel. The characteristics of various stainless steels are briefly described as follows:

① Ferritic stainless steel. Chromium is the main alloying element in ferritic stainless steel. High chromium steel has good high temperature oxidation resistance and good corrosion resistance in oxidizing acid solution such as nitric acid solution, so it is widely used in nitric acid and nitrogen fertilizer industries. The disadvantages of high chromium ferritic stainless steel are high notch sensitivity and ductile-brittle transition temperature, and the steel is also sensitive to intergranular corrosion after heating.

② Martensite stainless steel. Chromium is the main alloying element in steel. It is usually used in weakly corrosive media, such as seawater, fresh water and steam, with a temperature less than or equal to 580℃, and is usually used as a manufacturing material for parts and tools with great stress. Because of its poor weldability, this steel is generally not used as a weldment.

③ Austenitic stainless steel. The main alloying elements in steel are chromium and nickel. This steel has high toughness, low ductile-brittle transition temperature, good corrosion resistance and high temperature strength, good oxidation resistance and good pressure working and welding properties.

④ Ferrite-austenitic stainless steel.

⑤ Precipitation hardening stainless steel. This kind of steel is mainly used to manufacture containers and structural parts that require high strength and corrosion resistance, and can also be used as high-temperature parts, such as steam turbine parts.

5) Cast steel. Cast steel has good strength, plasticity and toughness, and can be cast into steel castings of various shapes, sizes and qualities.

(4) Classification and name of cast iron. Most of the boxes, shells, racks, supports and parts with little stress are made of cast iron. Some important parts with little impact, such as the crankshaft of small diesel engine, are mostly made of ductile iron. The reason is that cast iron is cheap, excellent in cutting performance and casting performance, which is conducive to saving materials and reducing processing hours, and has the necessary strength and some excellent properties, such as high wear resistance, shock absorption and low notch sensitivity.

1) classification of cast iron.

According to the shape characteristics of graphite, cast iron can be divided into three categories: gray cast iron (graphite flake), ductile cast iron (graphite ball) and malleable cast iron (graphite ball).

According to whether the composition of cast iron contains alloying elements, it can be divided into general cast iron and alloy cast iron. General cast iron can be divided into ordinary cast iron and metamorphic (inoculation) cast iron.

2) Representation method of cast iron brand:

① Use the first capital letter of Chinese Pinyin corresponding to various cast irons as the cast iron code. When the code letters of two cast irons are the same, lowercase letters can be added after uppercase letters.

② The symbols of conventional elements C. Si, Mn, S, P are generally not marked in the brand, and only when they have special functions are their element symbols and contents marked.

③ A set of numbers after the code in the brand indicates the tensile strength value (such as grey cast iron HT 100). When there are two sets of numbers, the first set of numbers indicates the tensile strength value, and the second set of numbers indicates the elongation value (such as ductile iron QT400- 18), and the two sets of numbers are separated by a "-".

3) Properties and characteristics of cast iron commonly used in engineering:

① Gray cast iron. The matrix can be ferrite, pearlite or ferrite plus pearlite, which is equivalent to the structure of steel.

② Ductile iron. The comprehensive mechanical properties of ductile iron are close to those of steel.

Ductile iron can replace steel to make some important parts, such as crankshaft, connecting rod and camshaft.

③ Vermicular graphite cast iron. The strength of vermicular graphite cast iron is close to that of nodular cast iron, and it has certain toughness and high wear resistance. At the same time, it has good castability and thermal conductivity of gray cast iron.

Vermicular graphite cast iron is mainly used to produce cylinder heads, cylinder liners, ingot molds and hydraulic valves.

④ Malleable cast iron. Malleable cast iron can partially replace carbon steel.

⑤ Wear-resistant cast iron. Wear-resistant cast iron is cast iron that works under abrasive wear conditions and should have high and uniform hardness.

⑥ Heat resistant cast iron. Heat-resistant cast iron is a kind of casting that works at high temperature, such as the bottom of heat treatment furnace, heat exchanger, tank clamp, conveyor chain and so on.

⑦ Corrosion resistant cast iron. Corrosion-resistant cast iron is mainly used in chemical components, such as valves, pipelines, pumps, containers and so on.

2. Nonferrous metals

L) aluminum and its alloys.

Industrial pure aluminum can be used to make wires, cables, utensils and alloys. Aluminum alloy can be used to manufacture machine parts and components that bear heavy loads.

① Rustproof aluminum alloy (LF). It is mainly used for weldments, containers, pipes or parts and products under moderate load, and can also be used as rivets.

② Hard aluminum alloy (LY). Low alloy hard aluminum has good plasticity and low strength. Mainly used for making rivets, often called rivet hard aluminum; The strength and plasticity of standard hard aluminum alloy are at a medium level. Mainly used for rolling products, forging products, stamping parts, propeller blades and large rivets and other important parts; High alloy hard aluminum alloy contains many elements, with high strength and hardness, and poor plasticity and deformability. Used to manufacture important parts such as pins and shafts.

③ superhard aluminum alloy (LC).

This alloy has poor corrosion resistance and softens quickly at high temperature. It is mostly used to manufacture important parts with large stress, such as aircraft girders and landing gears.

④ Forging aluminum alloy (LD). This alloy is mainly used for heavy-duty forgings and die forgings.

2) Copper and its alloys. Copper alloy has high strength and plasticity, high elastic limit and fatigue limit, good corrosion resistance, alkali resistance, excellent friction reduction and wear resistance.

General copper alloys are divided into three categories: brass, bronze and white copper.

① brass (h). Copper alloy with zinc as the main alloying element is called brass.

2 bronze (q). Bronze originally refers to copper-tin alloy, but the copper-based alloy containing aluminum, silicon, lead and manganese is used to be called bronze in industry.

3) Nickel and its alloys. Nickel and nickel alloy are ideal metal materials in various harsh corrosive environments such as chemistry, petroleum, nonferrous metal smelting, high temperature, high pressure, high concentration or mixed with impurities.

4) Titanium and its alloys. Titanium has high melting point, low thermal expansion coefficient, poor thermal conductivity, low strength and good plasticity. Titanium has excellent corrosion resistance and heat resistance, and its oxidation resistance is better than that of most austenitic stainless steels, but it can still maintain high strength at higher temperatures.

Titanium has excellent corrosion resistance at room temperature. It is very stable in the atmosphere, seawater, nitric acid and alkali solution, but it can be quickly dissolved in hydrofluoric acid of any concentration.

5) Lead and its alloys.

Lead is stable in the atmosphere, fresh water and seawater, but it has good corrosion resistance to sulfuric acid, phosphoric acid, sulfurous acid, chromic acid and hydrofluoric acid. Lead is not resistant to nitric acid corrosion and unstable in hydrochloric acid.

6) Magnesium and its alloys. Magnesium alloy is an important structural material in aviation industry, which can bear large impact and vibration loads and has good machinability and polishing performance. Its disadvantages are poor corrosion resistance, high notch sensitivity and complicated casting process.