Конструкциялық материалдар және термоөңдеу Конструкционные материалы и термообработка Constructional materials and heat treatment Учебное пособие для специальности: 5В071200– «Машиностроение»

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Repeated pressing is used for production of difficult form details. Repeated 
pressing provides given sizes and demanded form of a product when the first 
pressing forms preparation with approximate sizes and simpler form. 
The mechanical engineering is the main consumer of powder details. To the 
share of machine-building details falls to 80% of all volume of made 
constructional powder details. 
For production of details we use the restored and sprayed powders of 
carbonaceous and low-alloyed steel. If necessary we apply cementation, training 
by heating by the currents of high frequency (CHF) or volume hardening, 
processing by steam to increase of corrosion resistance and in addition wear 
resistance. 
Nomenclature of powder details. 
Now in cars we apply the following powder details: pulleys of camshafts for 
toothed belt transfers, naves and cones of synchronizers conducting gear wheels 
of the oil pump, a cover of bearings case of cranked shaft, details of 
management knot with strengthening, sleeves of cylinders, national teams of 
camshafts, various types of yokes and saddles of valves. Possibilities of 
production from powder materials of door loops, forks and sliding couplings of 
transmission are investigated. 
Corrosion-resistant alloys. 
At operation in corrosion environments, metal alloys are exposed to 
spontaneous destruction (corrosion) that is explained by their high electric 
conductance and chemical activity. 
Corrosion of metals is a spontaneous destruction of metal materials owing to 
chemical or its electrochemical interaction with environment. 
Depending on conditions in which corrosion process proceeds, we distinguish 
atmospheric, soil, sea, acid and alkaline corrosion. According to nature of 
destruction we distinguish uniform and local corrosion. For different types of 
local corrosion we use the following concepts. 
Contact corrosion is the strengthened corrosion destruction of more 
electronegative metal in contact with more electropositive. 
Intercrystalline corrosion is fragile corrosion destruction on borders of the 
crystals, resulting structural transformations during the processing and 
operation. 
Dot corrosion is a local type of corrosion destruction in electrochemical non-
uniform corrosion environment. 
Corrosion endurance is corrosion destruction under the influence of cyclic 
loadings and electrochemical influence of the environment. 
Corrosion-resistant is steel in which process of corrosion develops slowly. 

222 
Traditional methods of corrosion protection - drawing on external surfaces of 
sheetings details (enamel, paint and varnish, oxidic) - don't give satisfactory 
firmness at operation of products in active environments (damp atmosphere in 
combination with high temperature of operation, acid or alkaline environment). 
High-alloyed steel with the content of chrome not less than 13% that provides 
formation of protective film on a metal surface are corrosion-resistant. 
Corrosion-resistant steel. 
Depending on structure which is formed after high-temperature heating and 
cooling on air, we distinguish martensitic, martensitic-ferritic, austenitic and 
austenitic-martensitic steel. 
Now industrial ways of an alloying of liquid steel by nitrogen are developed 
that led to creation of a new perspective class of corrosion-resistant high-
nitrogenous steel, differing high mechanical durability. 
Austenitic steel (brands 12X18H9, 12X18H10T, 08H18N12B-chromium-
nickel, 10H14AG15, 10H14G14N4T-chrome-manganese) - are the most 
universal in steel use. They possess high plasticity and viscosity, satisfactory 
foundry properties and satisfactory weldability. 
To the shortcomings of these steel we possible to consider: 
-low values of a fluidity limit and bad workability cutting. 
- susceptibility to corrosion cracking and dot corrosion. 
Austenitic ferritic steels (brands 08X22H6T, 08X21H6M5T) have an optimum 
complex of mechanical properties. They are stronger than austenitic steel by 1,5-
2 times. Products from these steel can be operated at temperatures not above 
350ºС. 
Austenitic-martensitic steel (brands 07X16H6, 09Х15Н9Ю, have high 
durability and high impact strength. 
Ferritic steels (brands 08Х13, 12X17T, 15X25T) aren't strengthened by heat 
treatment. After annealing, the steel have moderate durability (250-300 MPa) 
and plasticity. The main lack of these steel is sharp embrittlement after heating 
from above 1000ºС that complicates its welding. 
Martensitic steel (brand 20Х13, 30Х13, 20X17H2) possess good strength 
properties, are well processed by cutting, are recommended for use in slightly 
aggressive environments (fresh water, diluted solutions of acids and salts). 
Heat-resistant alloys. 
Heat resistance - is ability of an alloy to resist to corrosive attack of the high-
temperature gas environment. 
At low temperatures (20-25ºС) on a surface of metal appears -9 
protective oxidic film 3-10 nanometers thick (1nm=10 m). The crystal lattice of 
oxide is similar to a crystal lattice of metal. 

223 
When heating, thickness of oxide increases, and the crystal lattice comes 
nearer to a lattice of compact oxide. Thus both lack of ions of metal and oxygen 
of lattice knots, and surplus of ions between the knots occupied with ions of 
oxygen, is possible. It accelerates diffusive processes in an oxidic film and 
worsens its protective properties. 
The metal alloying elements with bigger activity to oxygen, than the main 
metal, leads to accumulation of ions of alloying metals in an oxidic layer, to 
reduction of deficiency of a crystal lattice of oxide and increase of protective 
properties of an oxidic film. 
Pure metals have various thermal stability. 
Magnesium has bad thermal stability that is connected with emergence of a 
friable oxidic film. Niobium, tantalum, molybdenum, tungsten have a dense 
oxidic film, but when heating to 550ºС the film cracks, and oxide of 
molybdenum evaporates. 
For the titanium and zirconium big solubility of oxygen is characteristic when 
heating. Oxides of these metals lose oxygen and at a temperature 700-800ºС 
oxide becomes friable and the speed of oxidation increases. 
Copper, nickel, cobalt and iron possess satisfactory thermal stability. When 
heating to 700-800ºС deficiency of a lattice of oxides increases and the speed of 
oxidation increases. 
Aluminum, chrome, beryllium possess good thermal stability as have small 
chemical affinity to oxygen. 
Heat resistance of steel increase an alloying by chrome (to 30%), silicon (to 
2%) and aluminum (to 5%). Brands heat-resistant steel are 08X17T, 15X28, 
20X23H18. 
The basic alloying element is chrome as the alloyed oxides of iron are replaced 
with chrome oxides. The content of silicon and aluminum in steel is limited as 
these elements lead to embrittlement and deterioration of plasticity of an alloy. 
This shortcoming can be excluded at the expense of superficial alloying. 
Heat resistance of brass and bronze is higher than the heat resistance of pure 
copper. The majority of alloying elements in copper alloys possess big chemical 
affinity to oxygen, than copper. When heating alloying elements form own 
oxides possessing the best protective properties. The copper alloys alloyed by 
aluminum and beryllium show the greatest heat resistance. 
Titanium alloys absorb oxygen therefore on their surface it isn't formed 
protective oxides. It is possible to increase the heat resistance of alloys only in 
case of application of heat-resistant coverings. 

224 
Table-10. Indicators of constructional powder materials 
Loading 
efficiency 
detail 
Density 
of 
the material 
Bubbly 
material 
Strength, % 
Plasticity of 
uncrumbly 
materials % 
Strength 
of 
powder steel 
кg/м
3
Little loading 
1 
25-16 
30-45 
25-35 
6000-6600 
Approximate 
loading 
2 
15-10 
45-65 
35-65 
6700-7100 
Average 
loading 
3 
9-2 
65-95 
60-90 
7200-7700 
Hard loading 
4 
2 
95-100 
90-100 
7700

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