In last part we know that tungsten carbide tools with (Ti,W)N coating film have superior critical scratch load to high speed cutting hardened steel in mass production. Here in this part we explain the superior quality of (Ti,W,Si)N coating film.

Moreover, the titanium/tungsten-based-coated tungsten carbide tool was evaluated through machining of low-carbon steel AISI 5120H, and showed greatly improved performance. However, the hardness of the (Ti,W)N coating film was lower than that of the (Ti,Al)N coating film. So, a (Ti,W,Si)N coating film, which is a titanium/tungsten/silicon-based   coating film, has been developed.

This titanium/tungsten/silicon-based coating film exhibits both superior critical scratch load and hardness compared with TiN/(Ti,Al)N coating film. In cutting AISI 5120H, the wear progress of the (Ti,W,Si)N-coated cemented tungsten carbide tool is slower than that of the TiN- and (Ti, Al)N-coated tools. Therefore, titanium/tungsten/silicon coating is an effective tool material because it has good wear resistance.

(To be continued. This article is divided into several parts. Here is part 4. For part 3 please refer to http://news.chinatungsten.com/en/tungsten-information/80791-ti-10485; for part 5, please refer to )

In last part we know that tungsten carbide end mills with (Ti,W,Si)N and (Ti,W,Si,Al)N coating films will be tested to determine the best materials for cutting hardened steel. Here in this part we give the results to be reached in this article.

The following results were obtained:

(1) In milling hardened steel at a cutting speed of 3.33 m/s, the tool wear width of the (Ti,W)N/(Ti,W,Si,Al)N-coated tungsten carbide end mill was smaller than that of the (Ti,W)N/(Ti,W,Si)N-coated one. And, compared with the commercial (Ti,Al)N, the tool wear width of the (Ti,W)N/(Ti,W,Si,Al)N-coated tool was smaller than that of the (Ti,Al)N-coated tool.

(2) The tool wear of the (Ti,W)N/(Ti,W,Si,Al)N-coated tool increased with an increase in cutting  speed.

(3) The cemented carbide with (Ti,W)N/(Ti,W,Si,Al)N coating film was an effective tool material for high-speed cutting below a cutting speed of 3.33 m/s.

(To be continued. This article is divided into several parts. Here is part 2. For part 1 please refer to http://news.chinatungsten.com/en/tungsten-information/80788-ti-10483; for part 3, please refer to http://news.chinatungsten.com/en/tungsten-information/80791-ti-10485)

In last part we know that tungsten carbide end mills with (Ti,W,Si,Al)N coating film have the least tool wear at speed of below 3.33 m/s in cutting hardened steel. Here in this part we explain the superior quality of (Ti,W)N coating film.

1. Introduction

Hardened steels used for dies or molds are widely cut as a substitute for grinding. Polycrystalline cubic boron nitride (cBN) compact tools are used for cutting hardened steels, due to their higher hardness and higher thermal conductivity. However, in milling, major tool failure of cBN readily occurs by fracture because cBN has poor fracture toughness. Coated cemented tungsten carbide is an effective tool material for milling hardened steels because it has good fracture toughness and wear resistance. The physical vapor deposition (PVD) method is a widely used coating technology because of its lower treatment temperature, namely 470 K -870 K.

Recently, it has become possible to cut hardened steels with (Ti,Al)N-coated tungsten carbide cutting tools. However, as machine parts are often cut at higher cutting speeds for mass production, tool materials must have excellent fracture toughness and wear resistance. A titanium/tungsten-based coating film, namely (Ti,W)N coating film, has been developed. Titanium/tungsten-based coating film exhibits a superior critical scratch load.

(To be continued. This article is divided into several parts. Here is part 3. For part 2 please refer to http://news.chinatungsten.com/en/tungsten-information/80790-ti-10484; for part 4, please refer to http://news.chinatungsten.com/en/tungsten-information/80792-ti-10486)

Ammonium paratungstate (or APT) is a white crystalline salt of ammonium and tungsten, with the chemical formula (NH₄)₁₀(H₂W₁₂O₄₂)·4H₂O.

Ammonium paratungstate is produced by separating tungsten from its ore. Once the ammonium paratungstate is prepared, it is heated to its decomposition temperature, 600 °C. Left over is WO₃, tungsten(VI) oxide. From there, the oxide is heated in an atmosphere of hydrogen, reducing the tungsten to elemental powder, leaving behind water vapor. From there, the tungsten powder can be fused into any number of things, from wire to bars to other shapes.

A process is disclosed for producing ammonium paratungstate which involves adding hexamethylenetetramine to a first solution of ammonium tungstate, adjusting the pH to about 2 with an acid to form a precipitate which contains the major portion of the tungsten and the hexamethylenetetramine and separating the precipitate from the resulting mother liquor. The tungsten hexamethylenetetramine precipitate is then dissolved in aqueous ammonia to form a second ammonium tungstate solution which is then heated at from about 90℃ to about 100℃ to form a precipitate essentially all of which is ammonium paratungstate and a mother liquor which contains essentially all of the hexamethylenetetramine. The ammonium paratungstate precipitate is then separated from the mother liquor.