On 2018-08-08 14:48:54
Solution to the tempering problem
Advantages of 100℃ hot water tempering
Low temperature tempering often use 180℃ to 200℃ or so tempering, using oil to cook tempering. If the use of 100℃ hot water to stop tempering, there will be a lot of advantages, including :(1) 100℃ tempering can add the onset of grinding; (2) tempering at 100℃ can slightly increase the hardness of the workpiece and improve the wear resistance; (3) the time when hot water tempering at 100℃ can cause cracks caused by rapid heating; (4) when the cryogenic disposal is stopped, the probability of occurrence of cryogenic cracks in the workpiece is reduced, which has a buffering effect on the residual vosfield body and adds strong and toughness data; (5) the workpiece appearance will not produce oil coke, appearance hardness is slightly low, suitable for grinding machine grinding processing, also will not produce oil boiling hot dry burning scene.
Low temperature tempering for secondary hardening
For the eastern and western steel, the residual stress and the residual vosfield have bad effects on the steel. In terms of SKD11, the steel hardness obtained by tempering at 530℃ is slightly lower than that obtained by tempering at 200℃, but the heat resistance is better, it will not produce aging deformation, and can improve the heat resistance of steel, but also can prevent the processing deformation of discharge machining, there are many benefits.
Why does the embrittlement scene occur when tempering treatment stops at about 300℃?
Department steel in about 270℃ to 300℃ when the tempering treatment, will be residual vosfield body analysis, and the crystallization of carbide on the limit, resulting in tempering brittleness. When the secondary hardening of the steel is heated to 500℃~600℃, it will cause the analysis. At 300℃, it will not cause the analysis of the residual vosfield body, so there is no scene of 300℃ embrittlement.
Tempering fracture produced by tempering
When tempered steel materials are treated with tempering, the cracks caused by rapid cooling, rapid heating or structural change are called tempering cracks. Rare high speed steel, SKD11 die steel and other tempered hardened steel in low temperature tempering after rapid cooling will also occur. Such steel quenching in the first time to produce the first MaTian medium, quenching tempering on produce second MaTian repose of disorder (residual austenitic disorder into MaTian medium), and cracks. Therefore, in order to prevent tempering cracks, the tempering temperature should be used to cool slowly, and the operation of quenching and tempering should also stop the delay of tempering and quenching.
Tempering produces tempering brittleness
Can be divided into 300℃ brittleness and tempering cold brittleness two. The so-called 300℃ brittleness refers to the department of steel at about 270℃ to 300℃ when the tempering disposal, will be residual vosfield body analysis, and the crystallization of carbide on the limit, resulting in tempering brittleness. The so-called tempering creep and cooling brittleness refers to the brittleness presented when the tempering temperature (500℃~600℃) is tempering, ni-cr steel is quite obvious. Tempering creep and cold brittleness, can be stopped by rapid tempering temperature, according to a variety of results, the machine structure of alloy steel, since the tempering temperature to implement air cooling, at the cooling rate of more than 10℃/min, will not produce tempering creep and cold brittleness.
High frequency quenching is rare
There are three rare defects in high frequency quenching treatment: quenching crack, soft spot and peeling. High frequency wave quenching avoids the overheating scene of the department area caused by uneven heating, such as the workpiece acute Angle, keyway parts, holes around the location are very easy to cause overheating, and lead to the attack of quenching cracks, the above situation can be by adding copper to reduce the quenching crack attack. Other high cycle quenching workpiece in the quenching process is not average, will cause the workpiece appearance hardness is low defects, called soft point, this scene is due to high cycle quenching temperature is not average, water hole block or hole size and the number of improper. The third kind of loss is the appearance of peeling scene, the secondary reason is the section of the hardness of the change in the amount of large or too shallow hardening layer, so commonly used preheating to deepen the hardening layer, can effectively stop peeling scene.
Why can't stainless steel be tempered between 500℃ and 650℃?
Big department of stainless steel after solution treatment, if in the long time the temperature between 475 ℃ to 500 ℃, will produce stiffness increasing, the scene of a brittle surged this the 475 ℃ embrittlement, there are many secondary causes, everything on the phase analysis, grain boundary precipitation of chromium carbides and Fe - Cr compounds, such as the real temperature toughness, and corrosion resistance is poor, ordinary stainless steel heat treatment should stop often trouble holding temperature on the temperature field. In addition, if the temperature is held for a long time between 600℃ and 700℃, s phase will be precipitated. This s phase is fe-cr intermetallic compound, which is not only hard and brittle in texture, but also a small amount of chromium outside the steel will be exhausted, so that the corrosion resistance and toughness of stainless steel are low.
Why the temper deformation?
Will produce deformation of tempering secondary reason for quenching tempering of the residual force or structural change incur, i.e. by tempering the tensile stress alleviation and expansion, and alleviation of compressive stress, everything early tempering e carbide precipitation will be how much inflation, xue Ming carbon knot tie ning process will be a small amount of inflation, residual voss Tian Tie disorder into martensitic iron swells, residual voss Tian Tie disorders become ductile iron will swell, cause deformation of the workpiece after tempering. Methods to stop include :(1) the implementation of pressure tempering treatment; (2) add residual stress by heat bath or atmosphere quenching; (3) main points for machining correction and (4) main points for reserving deformation amount.
Tempered and hardened varieties
(1) embrittlement between 270℃ and 350℃ : also known as low temperature tempering hardenability, mostly occurs in carbon steel and low alloy steel.
(2) 400℃~550℃ embrittlement: usually the structure of alloy steel in this temperature category is easy to produce embrittlement scene.
(3) embrittlement at 475℃ : it refers to the embrittlement of ferric stainless steel with a content of more than 13% of fertilizer grains. When tempering treatment is conducted between 400℃ and 550℃, the embrittlement scene caused by the addition of stiffness is particularly obvious at about 475℃.