The hardness of brass l63 after annealing. Annealing, hardening and heat treatment of brass

Copper annealing. Copper is also subjected to heat treatment. In this case, copper can be made either softer or harder. However, unlike steel, copper is hardened by slow cooling in air, and copper acquires softness by rapid cooling in water. If a copper wire or tube is heated red-hot (600°) over a fire and then quickly immersed in water, the copper will become very soft. After giving the desired shape, the product can again be heated on fire to 400 ° C and allowed to cool in air. The wire or tube will then become solid.

If it is necessary to bend the tube, it is tightly filled with sand to avoid flattening and cracking.

Annealing brass improves its ductility. After annealing, brass becomes soft, easily bent, knocked out and well drawn. For annealing, it is heated to 500°C and allowed to cool in air at room temperature.

Blueing and "blueing" of steel.

Blueing. After burnishing, steel parts become black or dark blue in various shades, they retain a metallic sheen, and a resistant oxide film forms on their surface; protecting parts from corrosion. Before bluing, the product is carefully ground and polished. Its surface is degreased by washing in alkalis, after which the product is heated to 60-70 ° C. Then it is placed in an oven and heated to 320-325 ° C. An even color of the surface of the product is obtained only with its uniform heating. The product treated in this way is quickly wiped with a cloth dipped in hemp oil. After lubrication, the product is again slightly warmed up and wiped dry.

"Blue" steel. Steel parts can be given a beautiful blue color. For this, two solutions are made: 140 g of hyposulfite per 1 liter of water and 35 g of lead acetate (“lead sugar”) also per 1 liter of water. Before use, the solutions are mixed and heated to a boil. Products are pre-cleaned, polished to a shine, after which they are immersed in a boiling liquid and held until the desired color is obtained. Then the part is washed in hot water and dried, after which it is lightly wiped with a cloth moistened with castor or pure machine oil. Parts treated in this way are less susceptible to corrosion.

BRASS

Brasses are the most common copper-based alloys. A summary list of standard brass according to GOST 15527 and their foreign analogues is given in Table. 1.

The state diagram of the alloy of the copper-zinc system is shown in fig. 1

And changes in the temperature of evaporation, melting and casting of copper-zinc alloys depending on the zinc content - in fig. 2.

Change in the modulus of normal elasticity of copper-zinc alloys depending on the zinc content - fig. 3.

The main parameters of the intermetallic phases of the alloys of the system Cu-Zn are given in table. 2.

During the transition from the disordered β-phase to the ordered β '-phase in the specified temperature range, there is a decrease in the coefficient of mutual diffusion and the growth rate of the phase. The activation energy of mutual diffusion in the β'-phase increases, and in the β-phase it decreases with increasing zinc concentration, while itabout 1.5 times more in the β'-phase than in the β-phase. Partial diffusion coefficients of atoms Zn twice as many as Cu atoms in the disordered β-phase and almost coincide with the ordered β'-phase.

Practical applications are simple brass having a phase composition α, α + β, β and β + γ .

The chemical composition of pressure-treated brasses according to domestic ones is given in App. 1.

SIMPLE BRASS

Simple brass, depending on the phase composition, are divided into two types: single-phase α (up to 33% Zn ) and two-phase α + β (over 33% Zn).

In single-phase brasses, in which the zinc content is close to the saturation limit, small amounts of the β-phase are sometimes present as a result of slow diffusion processes. However, inclusions of the /3-phase, observed in very small amounts, do not have a noticeable effect on the properties α -brass. Thus, although these brasses have a two-phase structure, it is advisable to classify them as single-phase brasses in terms of their physical, mechanical and technological properties.

Forming of plain brasses

single phase (A)brass during hot deformation is very sensitive to the content of impurities, especially fusible ( Bi, Pb ). Bismuth in the alloy can segregate along the boundaries, so even a monoatomic layer of it can cause red brittleness in single-phase brasses with a high zinc content. Machinability α - hot brass with increasing zinc content deteriorates. When cold, single-phase brasses work well.

Two-phaseα + β -brasses are processed in a hot state better than single-phase ones due to the presence of high ductility at elevated temperatures β -phases and are less sensitive to impurities. However, they are sensitive to temperature and speed cooling regimes. For this reason, a heterogeneous structure is often observed in hot-pressed semi-finished products. For example, the front end of a bar (strip or pipe) has a predominantly fine needle-like structure and high mechanical properties, while at the rear end of the bar, as a result of chilling, the structure is granular and has reduced mechanical properties.

In a cold state, two-phase brasses are processed worse than single-phase ones. Their plasticity in the cold state depends on the structure. If α -phase is located on the main background of crystals β -phases in the form of thin needles, the workability of two-phase brasses in the cold state improves.

The effect of zinc content in brass on the temperature range of hot working by pressure is shown in fig. 4.

In brass, in the temperature range of 200–600°C, depending on the phase composition and zinc content, a zone of reduced plasticity is observed.

During cold rolling, drawing and deep stamping of brass, regardless of their phase composition, a structure with a grain size of no more than 0.05 mm is preferable.

The total degree of cold deformation of simple brass is determined by a certain limit, above which the ductility drops sharply. This limit of permissible total cold deformation, which decreases with increasing zinc content, is set for each brand of brass.

If we take the highest hot ductility in the homogeneous region β -phase, and at room temperature in the region α -phase beyond 100%, then the machinability of brass by pressure can be quantified ( table. 3).

Such assessments of the machinability of metals and alloys by pressure and other technological characteristics are often used in foreign practice.

Heat Treatment of Plain Brass. The main types of heat treatment of simple brass are recrystallization annealing and stress relief annealing. The process of recrystallization of brasses is determined by the zinc content and phase composition.

Recrystallization start temperature α -brass decreases with increasing zinc content. Recrystallization α -phase in strongly deformed two-phase brass begins at 300°C. Under these conditions, the β-phase remains unchanged and its recrystallization begins at a higher temperature. Therefore, when choosing the annealing temperature to obtain the optimal structure, it is necessary to take into account this feature of two-phase brasses.

The grain sizes of single-phase brasses are determined according to the standards of microstructures (GOST 5362).

During annealing of brass semi-finished products in an air or oxidizing atmosphere, spots are formed on their surface - oxidation products that are difficult to remove during etching. Reducing the oxygen partial pressure (vacuum annealing) prevents staining, but causes a risk of dezincification. Therefore, it is recommended to carry out annealing at a minimum temperature and in a protective atmosphere. Under production conditions, it is most difficult to avoid stains in brasses containing 37-40% zinc.

Machinability of simple brass by cutting. Machinability of brass cutting (turning, milling, planing, grinding) depends on the phase composition of brass. When machining single-phase brass, the chips are long. Two-phase ( A + β ) brass are processed better than single-phase α -brass. With an increase in the content of /3-phase, the chips become more brittle and short. The quantitative assessment of the machinability by cutting simple brass is determined by comparison with brass LS63-3, the machinability of which is taken as 100%. single phase α -brasses are perfectly polished, two-phase ones are somewhat worse. Machinability and polishability of brasses are given in table. 4.

Soldering and welding of simple l brass. Plain brasses are very easily connected with soft solders. Before soldering with soft solder, the surface is cleaned either by grinding or pickling in acid. As a solder, it is preferable to use alloys containing 60% tin. The content of antimony in the solder due to its strong affinity for zinc should be no more than 0.25-0.5%. Soft soldering is preferably performed with chloride fluxes.

single phaseα -brasses are also easily connected by hard soldering, including silver, two-phase A + β - somewhat worse.

Copper-phosphorus solders are self-fluxing, therefore brass soldering with these solders is carried out without fluxes. When soldering with other hard solders, appropriate fluxes must be used.

The lead content in hard solders is limited to 0.5%.

Quantification of the solderability of simple brasses,%: single-phaseα -brass (soft solders) - 100%, single-phaseα -brass (hard solders) - 100%, two-phaseα+ β -brass (soft solders) - 100%, two-phaseα+ β -brass (hard solders) - 75%.

Weldability of simple brasses is somewhat worse than solderability. General quantitative assessment of the weldability of brasses -75% compared to oxygen-free copper taken as 100%. The following types of welding are used to join brass: arc welding with a carbon electrode, arc welding with a consumable electrode, arc welding with a tungsten (non-consumable) electrode in a protective (inert gas) environment, arc welding with a consumable electrode in an inert gas environment, oxy-acetylene, electric contact (spot , roller, butt).

Brass with 20% content Zn poorly amenable to electric contact welding, lighter - brass with 40% Zn . The high zinc content in duplex brass makes arc welding difficult due to zinc evaporation. Therefore, filler materials used in arc welding should contain a relatively small amount of zinc. Brasses containing more than 0.5% Pb are usually difficult to weld. To improve the wettability of the metal during the welding process, preheating to a temperature of 260 ° C is necessary, especially for brass with a high copper content. Carbon electrode welding of brass containing 15-30%, Zn , best done with filler rods (wire) made of Cu alloy + 3% Si . For single-pass welds, copper rods (wire) alloyed with a small amount of tin can be used; for multi-pass welds it is better to use alloy rods Cu + 3% Si.

Brass containing more than 30% Zn , can be welded with a carbon electrode with brass filler rods (wire) Cu + 40% Zn or Cu + 3% Si . To improve the quality of welding, it is necessary to preheat the metal to a temperature of 210°C. As consumable electrodes, wire or rods made of tin-phosphor bronze or aluminum bronze are used.

Arc welding of brass with a tungsten electrode in an inert gas environment is complicated by the release of zinc oxide vapors, which suppress the action of the arc. Therefore, welding should be carried out at high speeds.

Oxy-acetylene welding gives good results. For welding brass with a content of 15-30% Zn it is necessary to use alloy filler rods (wire) Cu + 1.5% Si. Ifoperating conditions of finished products do not cause local corrosion (dezincification), you can use brass with 40% Zn (L60). For welding brass containing more than 30% Zn alloy is used as filler material Cu + 3% Si.

Influence of impurities on the properties of simple brasses. Impurities do not have a significant effect on the mechanical, physical (with the exception of iron, which, at a content of > 3.0%, changes the magnetic properties of brasses) and chemical properties of simple brasses, but significantly affect their technological characteristics. During hot working, single-phase brasses are especially sensitive to fusible impurities.

The quality of products obtained from brass by deep forging depends on the purity of the alloy, therefore, in simple brass intended for deep forging, the content of impurities should be minimal.

Influence of impurities on the quality of semi-finished brass products:

aluminum worsens the quality of the casting, causing foaming in the castings; bismuth causes hot brittleness of brasses, especially single-phase ones; iron hinders the recrystallization process;

siliconimproves soldering and welding processes, increases corrosion resistance; nickel raises the temperature at which recrystallization begins;

leadcauses hot brittleness of brasses, especially single-phase, containing zinc in the range of 30-33%;

antimonynegatively affects the machinability of brass by pressure. Antimony microadditives (<0,1 %) к двухфазным латуням частично локализуют коррозию, связанную с обесцинкованием;

arsenicdegrades the ductility of brasses as a result of the separation of brittle phases at a concentration above its solubility limit: in brasses in the solid state (> 0.1%). Small amounts of arsenic supplements (< 0,04%) предохраняют латуни от коррозионного растрески­вания и обесцинкования при контакте с морской водой;

phosphorus refines the structure in the cast state and prevents cracking when heated, accelerates the growth of grains during recrystallization; reduces corrosion associated with dezincification; not recommended as a deoxidizer for copper-zinc alloys;

tinlowers the ductility of brasses and can cause cracking when heated if the iron content is > 0.05%.

Brass Modification carried out by introducing into the melt:

additives of elements that form refractory compounds, which, if structurally consistent, will serve as centers of crystallization;

surface-active metals, which, concentrating on the faces of nascent crystals, slow down their growth.

As modifiers in brass, elements such as iron, nickel, manganese, tin, yttrium, calcium, boron, and mischmetal are used.

Corrosion properties of brasses. Brass has satisfactory resistance to industrial, marine and rural atmospheres. They fade in the air. Corrosive effect on brass containing >15% zinc, exert carbon dioxide and halogens.

Brass containing <15% Zn , in their corrosion resistance are close to industrial purity copper.

Under the influence of oxidizing acids, brass corrodes intensively. The limiting concentration of nitric acid, at which no noticeable corrosion is observed, is 0.1% (by weight). Sulfuric acid acts less aggressively on brass, however, in the presence of oxidizing salts K 2 SG 2 ABOUT 7 And Fe 2 (S0 4) 3the corrosion rate increases by 200-250 times. Of the non-oxidizing acids, hydrochloric acid has the strongest corrosive effect.

Corrosion resistance of brasses in relation to most acids that do not have an oxidizing ability is satisfactory. Brass is also resistant to dilute hot and cold alkaline solutions (with the exception of ammonia solutions) and cold concentrated neutral salt solutions. Brass is inert to river and salt water. Upon contact with river water containing a small amount of sulfuric acid, and in sea water, simple brasses noticeably corrode. The corrosion rate depends on the temperature, concentration, degree of contamination and the speed of the flow around the metal surface. In relation to the soil, brass has good corrosion resistance, and is neutral to food products. The corrosion rate of brass in soil ranges from 0.0005 mm/year (in loamy soil with pH 5.7) to 0.075 mm/year (in ash soil with pH 7,6).

Dry gases - fluorine, bromine, chlorine, hydrogen chloride, hydrogen fluoride, carbon dioxide, oxides of carbon and nitrogen at a temperature of 20 ° C and below have practically no effect on brass, however, in the presence of moisture, the effect of halogens on brass increases sharply; sulfur dioxide causes corrosion of brass at its concentration in the air - 1% and air humidity > 70%; hydrogen sulfide significantly affects brass under all conditions, however, brass containing Zn > 30% more resistant than brass with low zinc content.

Fluorinated organic compounds, such as freon, have practically no effect on brass.

In wet saturated steam at high speeds (about 1000 m 3 / c ) pitting corrosion is observed; therefore, brass is not used for superheated steam.

Corrosion resistance of brasses in various environments is given in table. 5.

In mine waters, especially in the presence of Fe 2 (SO 4 ) 3 brass corrodes heavily. The fluoride salts present in the water have a weak effect on brass, the chloride salts have a stronger effect, and the iodine salts have a very strong effect.

Brass, in addition to general corrosion, is also subject to special types of corrosion: zinc coating and "seasonal" cracking.

Dezincification is a special form of corrosion in which a solid solution of zinc in copper dissolves and copper is electrochemically deposited at cathode sites. Zinc corrosion products can be removed or retained in the form of an oxide film. The solution in which brass is subjected to dezincification usually contains more zinc than copper.

As a result of dezincification, brass becomes porous, reddish spots appear on the surface, and mechanical properties deteriorate. Dezincification is observed when brass comes into contact with electrically conductive media (acidic and alkaline solutions) and manifests itself in two forms: continuous and local. The dezincification process intensifies with an increase in the zinc content, as well as with an increase in temperature and aeration. Single phase brass containing >15% Zn , undergo dezincification in acidic solutions (nitrates, sulfates, chlorides, ammonium salts and cyanides). In two-phase brass, the dezincification process is markedly enhanced and can occur even in aqueous media. The most vulnerable isβ-phase.

Small additions of arsenic, phosphorus and antimony partially localize corrosion associated with dezincification. Arsenic and antimony protect against dezincification mainlyα -phase.

"Seasonal" or intergranular cracking is observed in brass as a result of exposure to corrosive agents in the presence of tensile stresses. Corrosive agents include: vapors or solutions of ammonia, condensates with sulfurous gases, wet sulfuric anhydride, solutions of mercury salts, various amines, components of pickling solutions, wet carbon dioxide. If the atmosphere contains traces of ammonia, wet carbon dioxide, sulfur dioxide, and other corrosive agents, then "seasonal" cracking occurs with temperature fluctuations, as a result of which condensation of corrosive agents occurs on the surface of the parts.

Brass containing up to 7% zinc is not very sensitive to "seasonal" cracking. In brass containing 10 to 20% zinc, intergranular cracking is not observed if the internal tensile stresses do not exceed 60 MPa. Zn , undergo stress corrosion cracking only in the cold-deformed state in an aqueous solution of ammonia. The most prone to stress corrosion cracking are single-phase brasses with a zinc concentration close to the saturation limit, and two-phase brasses. They are resistant to "seasonal" cracking only in the presence of tensile stresses.< 10 МПа.

The susceptibility to corrosion cracking of copper-zinc alloys in ammonia vapor is shown in fig. 5.

To prevent corrosion cracking of brass, it is necessary to apply low-temperature annealing and protect them from oxidation during storage. To relieve internal stresses, pre-recrystallization annealing is performed.

To protect brass from oxidation, it is recommended to passivate them in the following media: a slightly acidic aqueous solution containing about 6% chromic anhydride and 0.2% sulfuric acid; aqueous solution containing 5 % chromic and 2% chrome alum.

Brass is also protected with corrosion inhibitors such as benzotriazole or toluenetriazole. Benzotriazole forms a film on the surface (< 5 нм), которая предохраняет латуни от коррозии в водных средах, различных атмосферах и других агентах. Коррозионные ингибиторы могут быть введены в состав лаков и защитной оберточной бумаги.

In the case of electrochemical corrosion, brass, in contact with various metals and alloys, manifests itself in two ways: in some cases, the anode, in others, the cathode ( tab. 6 ).

When brass comes in contact with silver, nickel, cupronickel, copper, aluminum bronze, tin and lead, electrochemical corrosion does not occur.

Brass oxidizes when heated. The rate of oxidation of brass increases exponentially with increasing temperature, doubling approximately every 360K. At temperatures above 770K, evaporation of zinc is most intense if its concentration in the alloys exceeds 20 %.

The change in some of the physical and mechanical properties of brass depending on the zinc content is shown in fig. 6-9.

Typical physical, mechanical and technological properties of brass are given in P ril. 2, 3, 4.

Special pressure treated brass

Special or multi-component brasses are copper-zinc alloys of complex compositions in which the main alloying elements are aluminum, iron, manganese, nickel, manganese, nickel, silicon, tin and lead. These elements, as a rule, are introduced into brass in such quantities that they are completely dissolved inα andβ phases. In addition to these elements, small additions of arsenic, antimony and other elements are introduced into brass.

The influence of alloying elements is manifested in two ways: phase properties change (Aand/3) and their relative amounts, i.e. boundary of phase transformations.

To determine the boundaries of phase transformations in the system or the "apparent" ("fictitious") copper content when adding an alloying element, an empirical equation is used:

A ’ = A *100/(100+ X *(K e-1)),

Where A'- apparent (fictitious) content of copper, % (by weight); A -actual copper content, % (by weight); X- the content of the third component, % (by weight); Ke- Guinier coefficient characterizing the influence of the alloying element on the phase composition (at K e> 1, the number ofβ'-phase).

Meaning Kefor various elements: for Ni K uh from -1.2 to -1.4, for co K e=-1, for Mn K e=0.5, for Fe K e=0.9, for Pb K e=1, for Sn K e=2, for Al K e=6, for Si K e from 10 to 12.

Lead brass

Lead brass - copper-zinc alloys alloyed with lead. System State Diagram Cu-Zn-Pb featured on rice. 10.

The solubility of lead in alloys in the solid state is negligible. In two-phase copper-zinc alloys (containing Zn 40%) lead solubility at 750°С inβ -phase a little more than 0.2%; Lead is practically insoluble at room temperature. In two-phase brass (in equilibrium), lead is located insideα Andβ -phases and partially at the boundaries of these phases. Lead, when released along the boundaries of phases or grains, significantly worsens the deformability of brass in the hot state.

Lead in alloys A + β performs a dual role: on the one hand, it is used as a phase that promotes chip breaking, on the other - as a lubricant that reduces the coefficient of friction during cutting. The effectiveness of lead additives is determined by its amount and the structure of the alloy, the size and nature of the distribution of lead particles, grain size a -phase, quantity and distributionβ-phases.

By improving machinability, lead significantly reduces the impact strength of brasses, impairs machinability by pressure, soldering and welding, polishability, and complicates the galvanic surface treatment of products.

The strength characteristics of lead brass decrease more intensively with increasing temperature compared to simple brass. The tensile strength of brasses containing about 2% lead at a temperature of 600°C is 10 MPa, at a temperature of 800°C - practically equal to zero.

Depending on the processing of finished deformed semi-finished products, lead brass is classified into three main types: for cold working by pressure, for hot stamping, for processing on automatic lathes.

Structure lead visty la tuney. processed by cold pressure state, consists ofα -phase and lead, the content of which should be within such limits as to ensure high machinability. These alloys include brass grades LS74-3, LS64-2, JIC 63-3 and LS63-2.

Lead e lat un and hot-pressurized condition and intended for hot forging and stamping - two-phase (α +β). The zinc content in brass should be such that the transformation α + β cleanβ -phase occurred completely and at a relatively low temperature.

Estimated content β -phase is about 20%. The lead content is from 1 to 3%. These brasses include lead brass grades LS60-1, LS59-1 and LS59-3. Lead e no lat. used for machining on automatic lathes and in microtechnology (i.e. for the manufacture of parts that are very small in size, on the order of 1 mm) - two-phase, with a high lead content; LS63-3 (low/3-phase) and LS58-3 (high β -phases).

Brass used in microtechnology is subject to special requirements for the uniformity of the chemical composition, tolerances for the main components and microstructure (size and distribution of lead particles, quantity and distribution β -phases, grain size α -phases). The homogeneity of the chemical composition (homogeneity of the alloy) must be ensured in small areas.

The boundaries of the optimization of the microstructure of lead brass for "micro-details" are determined by the content β -phases from 10 to 30%, grain size α -phase - from 10 to 50 microns with an average lead particle diameter of 1-5 microns.

Processing of lead brass. Oxides of various elements impair the machinability of lead brass, therefore, when they are melted and cast, careful control over their content is necessary. Of the impurity elements, iron has the most negative effect on machinability, so its content is subject to special restrictions. Casting is carried out in two ways: in molds and semi-continuous (continuous) method. To achieve stability of the chemical composition, it is preferable to cast lead brass in a continuous (semi-continuous) way.

Lead does not affect the temperature and the crystallization process of copper-zinc alloys, it solidifies at 326°C and, in the case of precipitation along grain (phase) boundaries, worsens the hot deformability of two-phase alloys.

The composition areas of standard hot and cold processed lead brass are shown in fig. eleven.

When hot stamping lead brass containing 56-60% Cu (LS59-1), the tendency to cracking is determined mainly by the deformation temperature. The optimal temperature range at which cracks do not form is quite narrow and is in the temperature range that makes up the lines on the state diagram Cu-Zn , delimiting the two-phase α + β Andsingle-phaseβ - areas.

The content of lead, as well as low-melting impurities (bismuth, antimony, and others) does not affect the tendency to cracking during hot stamping of two-phase lead brass (α + β ).

The influence of the chemical composition on the machinability and pressure of lead brass is shown in table. 7.

Leadα -brasses are processed in a cold state, however, under certain conditions, hot pressing is also possible.

The main types of heat treatment of lead brass are full recrystallization annealing and low-temperature annealing to relieve internal stresses.

Leaded brasses are worse than simple brasses, soldered, welded and polished. For joining lead brass, it is not recommended to use oxy-acetylene welding, arc welding in a shielding gas environment and arc welding with a consumable electrode.

Co. corrosion resistance of lead brass . Lead brass has: excellent resistance to pure hydrocarbons, freon, fluorinated hydrocarbon coolants and varnishes; good resistance to industrial, marine, rural atmospheres, alcohols, diesel fuel and dry carbon dioxide; moderate resistance to crude oil and aqueous carbon dioxide; poor resistance to ammonium hydroxide, hydrochloric and sulfuric acids.

Tin yanny la t uni

Tin slightly affects the change in the boundaries of phase transformations, however, it significantly changes the nature β -phases. System State Diagram Cu-Zn-Sn shown on rice. 12.

Duplex tin brasses have high corrosion resistance in many environments. With an increased content of tin in brass, a new phase γ appears. The γ phase is a brittle component that significantly impairs the cold workability of brass. Appearance γ -phases in two-phase brass (a +/3) is observed when the content of tin is over 0,5% (if the tin content exceeds this limit, then during the transformation β a δ-phase is released, enveloping α -phase. The appearance of brittle phases limits the alloying of brass with tin. Tin content over 2% in brass impairs their hot workability. Standard tin brass can be divided into two types: single-phase (α - solid solution) and three-phase ( α + β + γ ).

Aluminum brass

Aluminum brass - copper-zinc alloys, in which the main alloying additive is aluminum.

Aluminum, due to its high Guinier coefficient (Ke = 6) and significant solubility in the solid state, compared with other elements (except silicon), even in small quantities, has a noticeable effect on the properties of brass. Aluminum additives increase the mechanical properties and corrosion resistance of brasses, but somewhat worsen their ductility. The amount of introduced aluminum is limited to the limits above which brittle γ -phase ( rice. 13).

With copper content, % (by weight): 70; > / J 65; 60 limiting aluminum content, % (by weight): 6; 5 and 3, respectively. In pressure-treated brasses, the aluminum content does not exceed 4%, in foundry high-strength brasses 7%.

Alloying of brasses is carried out with aluminum alone or in certain proportions with other elements (iron, nickel, manganese and etc.).

One aluminum, as a rule, is alloyed with single-phase brasses (LA85-0.5, LA77-2). For containment of dezincification and prevention of stress corrosion cracking in contact with sea water in single-phase aluminum brasses containing more than 15% Zn, 0.02-0.04 As (LAMsh77-2-0.05) is introduced.

An excess of arsenic (> 0.062%) impairs the ductility of brasses. Aluminum together with iron (LAZH60-1-1) and nickel (LAN59-3-2) is introduced mainly into two-phase brass.

Iron improves the ductility of lead-containing brasses; when hot, it refines the structure and improves their mechanical properties; Nickel improves corrosion resistance. Iron and nickel somewhat reduce the cold ductility of brass.

Alloying brasses with aluminum, nickel and small additions of manganese and silicon (LANKMts75-2-2.5-0.5-0.5) makes them precipitation hardening and significantly improves mechanical properties, especially elastic characteristics.

Single-phase aluminum brasses are satisfactorily processed by pressure in the hot state and well - in the cold; two-phase - good in a hot state and satisfactorily in a cold one. Machinability varies from 30 to 50% (compared to LS63-3 brass).

Aluminum brass, compared to lead, is worse connected with solders, but welds somewhat better; in terms of polishability, they are close to two-phase simple brasses ( tab l. 8).

Ferrous brasses

Iron additives significantly refine the structure of brass, thereby improving mechanical properties and technological characteristics. However, the "alloys of the system Cu-Zn-Fe rarely applied. Distribution received multicomponent brass.

manganese brass

Alloying brass with manganese significantly increases their corrosion resistance in contact with sea water, chlorides and superheated steam.

System Alloy State Diagram Cu-Zn-Mn shown in fig. 14.

Manganese additives have little effect on the structure of brasses. However, manganese reduces the stability of the ordered phase lattice β . When the content of Mn > 4.7% (at.) in the alloy, a partially disordered state is observed at a quenching temperature of 520°C.

Manganese has the most favorable effect on the properties and technological characteristics of brass in combination with other alloying elements (aluminum, iron, tin, nickel).

Silicon brasses

Silicon in the solid state is soluble in brass in significant quantities, but its solubility decreases with increasing zinc content. Solid solution region Aunder the influence of silicon and zinc, it shifts sharply towards the copper corner (Fig. 15 ) .

With an increase in the silicon content in the alloy structure Cu-Zn-Si a new phase appears Tohexagonal syngynia, which is plastic at elevated temperatures and, unlike β -phase is polarized. As the temperature decreases (below 545°С), the eutectoid decomposition of the c-phase intoα + γ ".

Silicon brass containing 20% Zn and 4% Si not suitable for pressure treatment due to low plasticity. To obtain deformed semi-finished products, silicon brass containing<4% Si.

Small additives of silicon improve the technological characteristics of brass during casting and hot forming, increase mechanical properties and anti-friction properties.

Nickelbrass

Alloying brasses with nickel increases their mechanical properties and corrosion resistance. Nickel brass is more resistant to dezincification and stress corrosion cracking than other brasses.

As can be seen from the state diagram of the alloy system Cu-Zn-Ni (rice. 16), nickel has a noticeable effect on the structure of brass, expanding the area of ​​solid solution α

When alloying with nickel, some two-phase brasses can be converted into single-phase ones.

Alloying of brass L62 with nickel in an amount of 2-3% (by weight) makes it possible to obtain a single-phase alloy with fine grains, high and uniform mechanical properties and increased corrosion resistance. Due to the addition of nickel in the production of deformed semi-finished products, the occurrence of such a negative phenomenon as a line structure is excluded.

Recommendations for improving the properties of copper-zinc alloys based on foreign experience. The properties of brass, along with the purity of the initial alloy components, the methods and modes of melting and casting, are greatly influenced by the modes of their processing and preparation of the charge.

To reduce the formation of porosity and bubbles in sheets (strips) and strips made of brass grades L70, L68, L63 and L60: avoid contamination of the charge with phosphorus; waste in the form of shavings containing oil, emulsion, etc., be subjected to oxidative roasting before melting; add copper oxide to the melt in the amount of 0.1-1.0 kg per 100 kg of charge; pay special attention to the optimal modes of casting and hot rolling; anneal hot-rolled strips before cold rolling.

To increase the resistance of brasses L68 and L70 to corrosion cracking, it is necessary to pay great attention to the selection of the cold rolling and annealing regime. The total reduction during the last cold rolling should be more than 50%, the optimum annealing temperature is 260-280°C.

To increase the resistance of two-phase brass to dezincification (and this is possible if the proportion β -phase in the structure of the alloy is about 30%), it is necessary to carry out heat treatment in the temperature range of 400-700°C (depending on the composition of the alloy).

To prevent dezincification of L63 brass and obtain a high-quality surface during light annealing (in bell and shaft furnaces), the recrystallization annealing temperature is maintained within 450-470°C. At this temperature, within 1-4 hours, a strip (tape) is obtained with a grain size of 0.035-0.045 mm, a tensile strength of 33-35 kgf/mm 2 and a relative elongation of 50%.

Tempering the metal allows you to make some changes in its structure, making it softer or vice versa hard. When hardening, a lot depends not only on the heating itself, but also on the process and time of cooling. Basically, manufacturers harden steel, making the product more durable, however, copper can also be hardened if the need arises.

Copper tempering - manufacturing process

Copper is hardened using the annealing method. During heat treatment, copper can be made softer or harder, depending on what it will be used for. However, it is important to remember that the way copper is quenched is significantly different from the way steel is quenched.

Hardening of copper occurs during slow cooling in air. If it is necessary to obtain a softer structure, then hardening is carried out by rapidly cooling the metal in water immediately after heating. If you want to get a very soft metal, then you should heat the copper to red (this is about 600 °), and then lower it into water. After the product has gone through the deformation process and acquired the desired shape, it can be heated again to 400 °, and then allowed to cool in the air.

Copper Hardening Plant

Hardening of copper is carried out in special equipment designed for this. There are several types of hardening machines, but induction equipment has become the most popular today. The induction machine is excellent for hardening copper, allowing you to get a high quality product. Thanks to the automated software of the HDTV equipment, it is configured with high accuracy, which indicates the heating time, temperature, as well as the method of cooling the metal.

If an enterprise constantly hardens metal products, then it would be best to pay attention to a special set of equipment designed for comfortable fast hardening. The hardening complex ELSIT has all the necessary equipment for high frequency hardening. The set of the hardening complex includes: an induction unit, a hardening machine, a manipulator and a cooling module. If the customer needs to harden products with different shapes, then a set of inductors of various sizes can be included in the package of the hardening complex.

Graaver 04-03-2010 20:17

I'll start from afar.
I have been manufacturing sports medals for more than ten years, but there are questions that I constantly encounter, but I have not found out the final answers to them .. can anyone help? here is one of them..

To increase plasticity, when pressing, the brass billet must be annealed .. and here the fun begins ..
At the moment I use the following recipe for annealing brass L63 (experimentally derived):
Heating in the oven to t=560 C, holding for 1.5-2 hours, cooling in air..

With the same parameters (brand of brass, maintenance mode), the output is a completely different result.

In one case, all "chiki-bunches" .. brass becomes "soft", easily deformed and has an even, mirror-smooth surface (corresponding to the "mirror" of the stamp).
In another version, everything seems to be the same .. "soft" (plastic), only where there should be a "mirror", a light, barely noticeable "cellulite-orange peel" appears .. it seems like a trifle, but horror is not pleasant

The question is..
Maybe someone faced a similar problem, how is it solved?

Interested in - temperature, exposure time during heating and time (method) of cooling ..

Also, is it possible to "cure" brass billets "infected with cellulite" (not the correct MOT)?

With all respect, Andrew.

Ress75 04-03-2010 20:47

In jewelry techniques, there is such a technique: it is called r .. (I don’t remember longer). The meaning is repeated annealing (6 times) of silver, etc. The metal begins to shove from the inside of the product and with each cycle the surface of the product swells locally - such a desert relief comes out with orange peel. In general, it’s beautiful. Further, it naturally faded, etc. Maybe something similar comes out here?

Yuzon 04-03-2010 21:45

Precisely the whole L 63? or maybe LS

Graaver 04-03-2010 22:08

quote: And brass from one party, or different deliveries?
Precisely the whole L 63? or maybe LS

Graaver 04-03-2010 22:19

Maybe someone knows under what conditions (exceeding what parameters) this muck occurs?

sm special 04-03-2010 23:35

Perhaps "google" on a request for brass annealing defects can clarify something ...

Yuzon 05-03-2010 11:53

You can also try:
You don’t need to do a long exposure, according to the process: at t = 600 C, loading, warming up about 1 mm / min. as the temperature leveled off, so cooling in air or through water.
IMHO: With a long exposure in an oxidizing atmosphere, zinc begins to oxidize and "rushes" the surface.
And sometimes sheet distributors are to blame (they can’t stand their own process)

Graaver 05-03-2010 14:41

When experimenting with t = 600 C, I was guaranteed to get "cellulite", although the exposure time was long ..
In the near future there will be an opportunity to experiment again ..
I'll try to reduce the time the blanks are in the oven ..

Nestor74 05-03-2010 16:39

2Graaver
after the holidays I’ll check with my people (the guys work a lot with brass - souvenirs, premium paraphernalia), maybe they’ll tell me something, I’ll unsubscribe if by that time this issue is still relevant.

Yuzon 05-03-2010 16:50

quote: I'll try to reduce the time the blanks are in the oven ..

Boole 05-03-2010 17:28

you can, your 5 kopecks: immediately into the water, without exposure to air

Boole 05-03-2010 17:29

simple rolling of copper alloys is directly opposite to the TO of steels - ductility rises

Graaver 05-03-2010 20:12

quote: after the holidays I’ll check with my people (the guys work a lot with brass - souvenirs, award paraphernalia), maybe they’ll tell me something, I’ll unsubscribe if by that time this issue is still relevant.

quote: load at 600 and transfer the oven to t=560.
Do not ship in a tight pack.

Graaver 12-03-2010 19:52

What happened was the least expected.

The story in a nutshell is...
I ordered two sheets of brass, without checking I gave it to production ..
It turned out that one sheet, as ordered, was brass (L63), and the second was bronze (the brand is unknown, it has a pleasant pink tint) ..
Bronze does not suit me for those. characteristics.

Therefore, the whole party, in order not to disappear idle, moves to a flea market.

Who might need it?

Here is a photo of blanks and a "trial" medal from this material.

Graaver 13-03-2010 09:27

I conducted an experiment with a new batch .. the "minimum required" holding time in the oven + "loose" load + cooling in water ..
The experiment was a success.. "cellulite" is missing!

Many thanks to the one-palatniks "Bul" and "UZON" for good advice !!!

I apologize for being annoying..
Is it possible to "restore" brass after a wrong MOT?

With all respect, Andrew.