A study of heat treatment of high‐boron high‐speed steel roll

High‐boron high‐speed steel (HSS) is a cheap roll material. In the paper, the authors research the effect of heat treatment on the microstructure and properties of high‐boron high‐speed steel HSS roll containing 0.54% C, 1.96% B, 3.82% W, 7.06% Mo, 5.23% Cr and 2.62% Al by means of the optical microscopy (OM), the scanning electron microscopy (SEM), X‐ray diffraction (XRD) and hardness test. The results showed that as‐cast structure of boron‐bearing high‐speed steel HSS consisted of martensite, pearlite, M₂(B, C), M₃(B, C) and M₂₃(B, C)₆ type borocarbides. After quenching, the matrix transformed into the lath martensite, and M₃(B, C) dissolved into the matrix. When quenching temperature is lower than 1050°C, the hardness is increased with the increase of quenching temperature under oil cooling, while quenching temperature excels 1100°C, the hardness will decrease with the increase of quenching temperature. Under the condition of salt bath and air cooling, the effect of quenching temperature on the hardness is similar to the above law, but the quenching temperature obtaining the highest hardness is higher than that of oil cooling. The highest hardness is obtained while tempering at 525°C. The hardness of high‐boron high‐speed steel HSS roll is 66.5 HRC, and its impact toughness excels 13.1 J/cm². Using in pre‐finishing stands of high‐speed hot wire‐rod rolling mill, the wear rate of high‐boron HSS rolls is 0.26 mm/one thousand tons steel. However the manufacturing cost of high‐boron HSS rolls is obviously lower than that of powder metallurgy hard alloy rolls, it is only 28% of that of powder metallurgy (PM) hard alloy rolls.     

Effect of tempering temperature on microstructure and properties of aluminium-bearing high boron high speed steel

Heat treatment is of great significance to the performance improvement of high speed steel. Via heat treatment, the microstructure of high speed steel can be improved, thus greatly improving the material performance. The effect of tempering temperature on the microstructure of aluminium-bearing high boron high speed steel (AB-HSS) was investigated by optical microscope (OM), scanning electron microscope (SEM) and x-ray diffraction (XRD). The hardness and wear resistance of the alloy at different tempering temperatures were tested by Rockwell hardness tester, micro-hardness tester and wear tester. The experimental results indicate that the tempering microstructure of aluminium-bearing high boron high speed steel consists of α-Fe, M₂B and a few of M₂₃(C, B)₆. Tempering temperature could greatly affect the wear resistance of materials. With the increase of tempering temperature, the wear resistance of aluminium-bearing high boron high speed steel firstly increase and then decrease. The alloy tempered at 450 °C has the best wear resistance and minimum wear weight loss. This study provides a reference for the formulation of heat treatment process of aluminium-bearing high boron high speed steel.     

Microstructures and high temperature properties of spray formed niobium‐containing M3 high speed steel

The billets of M3 high speed steel (HSS) with or without niobium addition were prepared via spray forming and forging, and the corresponding microstructures, properties were characterized and analysed. Finer and uniformly‐distributed grains without macrosegregation appear in the as‐deposited high speed steel that are different to the as‐cast high speed steel, and the primary austenite grain size can be decreased with 2% niobium addition. Niobium appears in primary MC‐type carbides to form Nb₆C₅ in MN2 high speed steel, whereas it contributes less to the creation of eutectic M₆C‐type carbides. With same treatments to forged MN2 high speed steel and M3 high speed steel, it is found that the peak hardness of these two steels are almost the same, but the temper‐softening resistance of the former is better. With higher high‐temperature hardness of the forged MN2 high speed steel, its temper softening above 600 °C tends to slow down, which is related to the precipitation of the secondary carbides after tempering. A satisfactory solid solubility of Vanadium and Molybdenum can be obtained by Nb substitution, precipitation strengthening induced by larger numbers of nano‐scaled MC and M₂C secondary carbides accounts for the primary role of determining higher hardness of MN2 high speed steel. The results of the wear tests show that the abrasive and adhesive wear resistance of MN2 high speed steel can be improved by the grain refinement, existence of harder niobium‐containing MC carbides, as well as solute strengthening by more solute atoms. The oxidational wear behavior of MN2 high speed steel can be markedly influenced by the presence of the high hardness and stabilization of primary niobium‐containing MC‐type carbides embedded in the matrix tested at 500 °C or increased loads. The primary MC carbides with much finer sizes and uniform distribution induced by the combined effects of niobium addition and atomization/deposition would be greatly responsible for the good friction performance of the forged MN2 high speed steel.     

Fundamental investigation of interfaces in particle reinforced steel sheets processed by thin strip casting

Along the steel industry history, the production of flat‐steel products has technologically evolved towards reducing slab thickness at the output of the continuous casting machine. This development has been related to the incessant requirement of providing a certain steel quality at lower costs. As a result of this procedure, the thin strip casting technology emerged in a commercial scale at the end of the nineties, with all the advantages of a near‐net‐shape manufacturing process. In particularly, the higher energy efficiency and reduced environmental impact turned it as a very promising and attractive technology for the steel industry. With the purpose of obtaining new types of steel sheets, characterized by improved mechanical and tribological properties, reinforced steel strips have been produced by introducing slight modifications to a twin‐roll caster. In this regard, a considerable enhancement of the mechanical properties has been achieved.     

A study of casting high‐boron high‐speed steel roll materials

In this paper, we design and prepare five kinds of high‐boron high‐speed steel roll materials. The microstructure, mechanical property and wear resistance of high‐boron high‐speed steel roll materials were studied by means of optical microscopy (OM), scanning electron microscopy (SEM), X‐ray diffraction (XRD) and hardness measurement, impact test and abrasion test. The results show that as‐cast microstructure of high‐boron high‐speed steel consists of martensite, retained austenite and borocarbide. Hardness of as‐cast high‐boron high‐speed steel excels 64 HRC. In unmodified high‐boron high‐speed steel, eutectic borocarbide is distributed in a network along the grain boundary. With the addition of RE‐Mg‐Ti compound modifier, the networks of borocarbide is broken. The hardness of high‐boron high‐speed steel gradually decreased with the increase of tempering temperature. Under the same conditions, the impact toughness of unmodified high‐boron high‐speed steel roll material is slightly lower than that of modified steel. The wear resistance of modified high‐boron high‐speed steel roll material is greater than that of high‐carbon high‐vanadium high‐speed steel roll.     

Combined vacuum plasma surface treatment for increase of durability of face milling cutters from high‐speed steel

The article deals with the influence of the vacuum plasma surface treatment on the life of the face milling cutter of high‐speed steel R6M5 (analog M2 (USA, AISI/ASTM)). Such processing combines ion nitriding in gas plasma and the deposition of the wear‐resistant TiAlN layer in the metal gas plasma of the vacuum‐arc discharge. Research verifies that the use of vacuum plasma treatment combining the formation of the transition nitrided layer in the gas plasma and the subsequent deposition of TiAlN coating in metal gas plasma created by a vacuum‐arc discharge is an effective way to improve the tool life of high‐speed steel face milling cutters.