Study On Heat Treatment And High-temperature Oxidation Resistance Of Aluminum-Containing High Boron High Speed Steel

The addition of boron to high speed steel partially replaces the expensive metal elements to obtain high boron high speed steel materials,which are characterized by low cost,easy processing,and good wear resistance.In industrial production,they can partially replace high-chromium cast iron and traditional High-speed steel and other materials.In this paper,six groups of high boron high speed steels with different compositions were designed to deeply study the microstructure and properties of as-cast and heat-treated structure and high-temperature oxidation resistance.Firstly,the microstructure and properties of high boron high speed steel after casting and heat treatment were studied by means of metallographic microscope,scanning electron microscope,energy spectrum analysis,X-ray diffraction analysis and Rockwell hardness tester.The results show that:1)high casting-state Boron high-speed steel is composed of pearlite or martensite and eutectic boron carbide.When the aluminum content is constant,with the increase of boron content,M₂?B,C?changes from reticulate to massive and chrysanthemum reticulate.On the substrate;after quenching,M₂?B,C?breaks through the network,and the formation of fine particles,hardness reaches 60HRC or more;when the boron content is unchanged,the aluminum content gradually increases,will promote the increase of ferrite matrix,making the quenching After the hardness decreased significantly;when the aluminum content is 1.0wt.%,the boron content is in the range of 1.0².0wt.%,and the quenching temperature is 1050°C,the alloy with high hardness and good toughness can be obtained.2)The tempering structure of the alloy is composed of martensite and eutectic boron carbide.When the tempering temperature is lower than 500°C,the tempering structure is not significantly different from the quenched structure,and the boron carbide is slightly reduced.When the tempering temperature exceeds 500°C,the eutectic phase recovers the network structure,the isotropic trend of the matrix grains is more obvious,and the grain size of the grains becomes gradually uniform.When the tempering temperature is 550°C,the eutectic structure further increases.When the tempering temperature reaches 600°C,the tempering temperature is too high,causing the tissue to grow significantly and coarsen.Secondly,with the aid of the M-200 ring block wear tester,the wear test was performed on the heat treated specimens under the above test conditions.The results showed that when the quenching temperature was 1050°C,the 2#sample at the tempering temperature of 500°C had the smallest amount of wear and was the best wear-resistant.Finally,high temperature cyclic oxidation tests of high boron high speed steels with different compositions were carried out.The test results showed that:1)After the high boron steels with different B contents were oxidized cyclically at 650°C/250h and 800°C/250h,the oxidation gain curves all conformed to the parabola Regularity,but the increase of oxidation temperature,will further promote the high temperature oxidation reaction,the surface oxide film of each sample did not appear obvious peeling.The addition of element B improves the high temperature oxidation resistance of high boron high speed steel.The 3.0 wt.%B high boron high speed steel has the thinnest oxide film and exhibits the best oxidation resistance.B oxidizes to form B₂O₃ and is mainly concentrated at the interface of the oxide film/substrate.It flows through the oxide film at high temperature to fill in defects,and it is easy to form B₂O₃-SiO₂ borosilicate with SiO₂,and the more B content,the more favorable the formation of B₂O₃.The B₂O₃-rich B₂O₃-SiO₂ borosilicate oxide layer is more conducive to its spread in the oxide film,which can significantly improve the high boron high-speed steel oxidation resistance.2)After high boron high speed steels with different Al contents are oxidized at 650°C/250h and 800°C/250h,the oxidation growth curves conform to the parabolic law.The increase of oxidation temperature will further promote the occurrence of high temperature oxidation reactions.6#aluminum-free high boron steel oxide film thickness is the thickest,and there is cracking and spalling phenomenon.With the increase of Al content,the phenomenon of cracking and spalling of the oxide film gradually disappeared.The addition of Al element improves the high temperature oxidation resistance of high boron high speed steel.The 5#high boron steel oxide film containing Al 2.0 wt.%has the thinnest and shows the best oxidation resistance.Al oxide forms Al₂O₃,and the Al₂O₃ oxide layer has a dense structure,which can effectively inhibit the diffusion of ions.At the same time as a typical n-type ingrowth oxide film Al₂O₃,can be closely combined with p-type outgrowth Cr₂O₃ oxide film.The more Al content,the more favorable the combination of two oxide films,which can significantly improve the high boron steel high speed steel oxidation resistance.