The Technic of Metals Heat Treatment - Heating Heat preservation Cool

The Technic of Metals Heat Treatment

The stainless steel heat treatment craft includes the heating, the heat preservation, to cool three processes generally, sometimes only then heats up and cools two processes. These processes link up mutually, cannot interrupt.When metal heating, the work piece exposes in the air, has the oxidation, the decarbonization (i.e. stainless steel tube and iron components surface carbon content to reduce) frequently, this after the heat treatment the components superficial performance has the very disadvantageous influence.

The heating is one of heat treatment important steps. Heat Treatment of Metals's heating means are many, is most early uses the charcoal and the coal takes the heat source, then application liquid and gaseous fuel. The electricity application causes the heating easy to control, and non-environmental pollution. Using these heat sources may the direct heating, may also through the fusing salt or the metal, down to the fluctuation granule carries on the indirect heating.

Therefore the metal usually should in the controllable atmosphere or the protective atmosphere, in the fusing salt neutral vacuum heats up, also the available coating or the packing method carry on the protection heating.

The heating temperature is one of heat treatment craft important technological parameters, the choice and the controlled heating temperature, is guarantees the heat treatment quality the subject matter. The heating temperature along with the metallic material which and the heat treatment goal processes is different and is different, but is generally heats up to the transformation temperature above, obtains the organization which needs. Moreover the transformation requires certain time, when therefore the metal work piece surface meets the requirements the heating temperature, still needs at this temperature maintains certain time, causes the inside and outside temperatures to be consistent, causes the Microstructure to transform completely, this period of time are called the soaking time. When uses the high energy density heating and the superficial heat treatment, the rate of heating is extremely quick, generally does not have the soaking time or the soaking time is very short, but thermochemical treatment's soaking time is often long.

Cooling is also in the heat treatment technological process the essential step, the cooling method is different because of the craft and is different, is mainly the controlled cooling speed. Generally the annealing cooling rate is slowest, the hot cooling rate is quick, the quenching cooling rate is quicker. But also different has the different request because of the aluminum, for example the spatial hard steel may use the hot same cooling rate to carry on hardly.

The Heat Treatment of Metals craft may divide into the overall heat treatment, the superficial heat treatment, the partial heat treatment and the thermochemical treatment roughly and so on. According to the heating medium, the heating temperature and cooling method's difference, each broad heading may differentiate for certain different heat treatment craft. The identical metal uses the different heat treatment craft, may obtain the different organization, thus has the different performance. The steel and iron is in the industry applies the broadest metal, moreover the steel and iron Microstructure is also most complex, therefore steel and iron heat treatment craft great variety.

The overall heat treatment is to the work piece whole heating, then by suitable speed cooling, changes its overall mechanical properties the Heat Treatment of Metals craft. The steel and iron overall heat treatment has the annealing, the normalizing, quenching and the tempering four basic crafts approximately.

The annealing is heats up the work piece to the suitable temperature, uses the different soaking time according to the material and the work piece size, then carries on slow cooling, the goal is enables the metal Underlying tissues to achieve or the close state of equilibrium, obtains the good shop characteristics and the operational performance, or to further quench makes the organization to prepare. The normalizing is heats up the work piece after the suitable temperature cools in the air, the hot effect same annealing is similar, is only the organization which obtains is thinner, commonly used in improvement material cutting value, also sometimes uses to some request not high components takes the final heat treatment.

After quenching is the work piece heating heat preservation, in quenched medium and so on water, oil or other inorganic salt, organic peroxide solution rapid chilling. After the quenching, the steel stock stiffens, but with time-variable crisp. In order to reduce the steel stock brittleness, after will quench the steel stock is being higher than the room temperature is lower than 710℃ some suitable temperature to carry on the long time the heat preservation, carries on cooling again, this craft is called the tempering. The annealing, the normalizing, quenching, the tempering are in the overall heat treatment “four fires”, in which quenching and the tempering relations are close, coordinates the use frequently, indispensable.

“four fires” along with heating temperature and coolant conditions difference, also evolves the different heat treatment craft. In order to obtain certain intensity and toughness, unifies the craft quenching and the high tempering, is called the quenching and tempering. After certain alloy quenching forms the oversaturation solid solution, puts in the room temperature it or under the slightly high suitable temperature maintains the long time, enhances the alloy degree of hardness, the intensity or the electric properties magnetic and so on. Such heat treatment craft is called the aging treatment of metal. Effectively and unify closely the shaping deformation and the heat treatment carry on, cause the work piece to obtain the very good intensity, the tough coordination method to be called the deformation heat treatment; The heat treatment which carries on the negative pressure atmosphere or the vacuum is called the vacuum heat treatment, it not can only cause the work piece not to oxidize, does not decarbonize, after maintaining processing, the work piece surface is bright and clean, enhances the work piece the performance, but may also pass over infiltrates the medicinal preparation to carry on the thermochemical treatment.

The superficial heat treatment only heats up the work piece surface layer, changes its surface layer mechanical properties the Heat Treatment of Metals craft. To only heat up the work piece surface layer not to enable excessively many quantity of heats to spread to the work piece, the use heat source must have the high energy density, namely gives the big heat energy on unit area's work piece, causes the work piece surface layer either can partially short-time or the instant achieves the high temperature. The superficial heat treatment's main method, has the laser heat treatment, the flame hardening and the induction heating heat treatment, the commonly used heat source has flame, the induced current, the laser and the electron beam and so on oxy-acetylene or oxygen propane and so on.

The thermochemical treatment is through the change work piece surface layer chemical composition, the organization and the performance Heat Treatment of Metals craft. The thermochemical treatment and the superficial heat treatment difference was the latter changed the work piece surface layer chemical composition. The thermochemical treatment is places the work piece including the carbon, the nitrogen or other alloying element medium (gas, liquid, solid) heats up, heat preservation long time, thus causes work piece surface layer elements and so on permeating carbon, nitrogen, boron and chromium. After permeating the element, sometimes must carry on other heat treatment craft like quenching and the tempering. Thermochemical treatment's main method has the cementation, azotize, to infiltrate the metal, compound to infiltrate and so on.

The heat treatment is one of the machine parts and in labor die making process important working procedures. , It may guarantee and enhance the work piece roughly each performance, like wear-resisting, anti-corrosive and so on. May also improve the semifinished materials the organization and the stress condition, favors carries on each kind coldly, the hot-working.